Understanding infrared thermography reading 7 part 1 of 2

Infrared Thermal TestingReading VII Part 1 of 2My ASNT Level III, Pre-Exam Preparatory Self Study Notes 12 June 2015

Charlie Chong/ Fion Zhang

Military Applications








The Magical Book of Infrared Thermography




ASNT Certification GuideNDT Level III / PdM Level IIIIR - Thermal/Infrared Testing Length: 4 hours Questions: 135

1. Principles/Theory• Conduction• Convection• Radiation• The nature of heat and heat flow• Temperature measurement principles• Proper selection of Thermal/Infrared testing

2. Equipment/Materials• Temperature measurement equipment• Heat flux indicators• Performance parameters of non-contact devices


3. Techniques• Contact temperature indicators• Non-contact pyrometers• Infrared line scanners• Thermal/Infrared imaging• Heat flux indicators• Exothermic or endothermic investigations• Friction investigations• Fluid Flow investigations• Thermal resistance (steady state heat flow)• Thermal capacitance investigations

4. Interpretation/Evaluation• Exothermic or endothermic investigation• Friction investigations• Fluid flow investigations• Differences in thermal resistance• Thermal capacitance investigations


5. Procedures• Existing codes and standards• Job procedure development

6. Safety and health• Safety responsibility and authority• Safety for personnel• Safety for client and facilities• Safety for testing equipment

Reference Catalog NumberNDT Handbook, Third Edition: Volume 3, Infrared and Thermal Testing 143Fundamentals of Heat and Mass Transfer 952ASNT Level III Study Guide: Infrared and Thermal Testing 2265


Fion Zhang at Shanghai12th June 2015

http://meilishouxihu.blog.163.com/



Charlie Chong/ Fion Zhang http://greekhouseoffonts.com/



Notation:h = Plank’s constantσ = Stephen-Boltzmann constantα = absorptivityε = emissivityρ = reflectivityτ = transmissivity


Infrared Spectrum


IVONA TTS Capable.

http://www.naturalreaders.com/


Assorted Reading Subject matters approaches


Reading VIIContent Reading One: Thermocouples: The Operating Principle Reading Two: Facilities Instructions, Standards, & Techniques Vol.4~11+2

“Thermal Analysis” Reading Three: Infrared Thermography Guide-R3 Reading Four: Emissivity: Understand the difference between apparent

and actual IR temperatures


Reading: OneThermocouples: The Operating Principle

http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html


■ THERMOCOUPLES: THE OPERATING PRINCIPLE

A thermocouple is a device made by two different wires joined at one end, called junction end or measuring end. The two wires are called thermo elements or legs of the thermocouple: the two thermo elements are distinguished as positive and negative ones. The other end of the thermocouple is called tail end or reference end (Figure 1). The junction end is immersed in the environment whose temperature T2 has to be measured, which can be for instance the temperature of a furnace at about 500°C, while the tail end is held at a different temperature T1, e.g. at ambient temperature.

Figure 1: Schematic drawing of a thermocouple



Because of the temperature difference between junction end and tail end a voltage difference can be measured between the two thermo elements at the tail end: so the thermocouple is a temperature-voltage transducer. The temperature versus voltage relationship is given by:

where Emf is the Electro-Motive Force or Voltage produced by the thermocople at the tail end, T1 and T2 are the temperatures of reference and measuring end respectively, S1,2 is called Seebeck coefficient of the thermocouple and S1 and S2 are the Seebeck coefficient of the two thermoelements; the Seebeck coefficient depends on the material the thermoelement is made of.



Looking at Equation1 it can be noticed that:

1. a null voltage is measured if the two thermoelements are made of the same materials: different materials are needed to make a temperature sensing device,

2. a null voltage is measured if no temperature difference exists between the tail end and the junction end: a temperature difference is needed to operate the thermocouple,

3. the Seebeck coefficient is temperature dependent.

In order to clarify the first point let us consider the following example (Figure 2): when a temperature difference is applied between the two ends of a single Ni wire a voltage drop is developed across the wire itself. The end of the wire at the highest temperature, T2, is called hot end, while the end at the lowest temperature, T1, is called cold end.



Figure 2: Emf produced by a single wire



When a voltmeter, with Cu connection wires, is used to measure the voltage drop across the Ni wire, two junctions need to be made at the hot and cold ends between the Cu wire and the Ni wire; assuming that the voltmeter is at room temperature T1, one of the Cu wires of the voltmeter will experience along it the same temperature drop from T2 to T1 the Ni wire is experiencing. In the attempt to measure the voltage drop on the Ni wire a Ni-Cu thermocouple has been made and so the measured voltage is in reality the voltage drop along the Ni wire plus the voltage drop along the Cu wire.

The Emf along a single thermoelement cannot be measured: the Emfmeasured at the tail end in Figure1 is the sum of the voltage drop along each of the thermoelements. As two thermoelements are needed, the temperature measurement with thermocuoples is a differential measurement.

Note: if the wire in Figure 2 was a Cu wire a null voltage would have been measured at the voltmeter.



The temperature measurement with thermocouples is also a differential measurement because two different temperatures, T1 and T2, are involved. The desired temperature is the one at the junction end, T2. In order to have a useful transducer for measurement, a monotonic Emf versus junction end temperature T2 relationship is needed, so that for each temperature at the junction end a unique voltage is produced at the tail end.

However, from the integral in Equation1 it can be understood that the Emf depends on both T1 and T2: as T1 and T2 can change independently, a monotonic Emf versus T2 relationship cannot be defined if the tail end temperature is not constant. For this reason the tail end is maintained in an ice bath made by crushed ice and water in a Dewar flask: this produces a reference temperature of 0°C. All the voltage versus temperature relationships for thermocouples are referenced to 0°C.

The resulting measuring system required for a thermocople is shown in Figure 3.



Figure 3: A measuring system for thermocouples



In order to measure the voltage at the tail end, two copper wires are connected between the thermoelements and the voltmeter: both the Cu wires experience the same temperature difference and as a result the voltage drops along each of them are equal to each other and cancel out in themeasurement at the voltmeter.

The ice bath is usually replaced in industrial application with an integrated circuit called cold junction compensator: in this case the tail end is at ambient temperature and the temperature fluctuations at the tail end are tolerated; in fact the cold junction compensator produces a voltage equal to the thermocouple voltage between 0°C and ambient temperature, which can be added to the voltage of the thermocouple at the tail end to reproduce the voltage versus temperature relationship of the thermocouple.

A sketch of a thermocouple with cold junction compensation is reported in Figure 4.



Figure 4: An example of Cold Junction Compensation



It should be underlined that the cold junction compensation cannot reproduce exactly the voltage versus temperature relationship of the thermocouple, but can only approximate it: for this reason the cold junction compensation introduces an error in the temperature measurement.

Figure4 shows also the filtering and amplification of the thermocouple. Being the thermocouple voltage a DC signal, removal of AC noise through filtering is beneficial; furthermore the thermocouples produce voltage of few tens of mV and for this reason amplification is required. The small voltage range for some of the most common thermocouples (letter designated thermocouples) is shown in Figure5, where their voltage versus temperature relationship is reported.

Type R, S and B thermocouples use Pt-base thermoelements and they can operate at temperatures up to 1700°C; however they are more expensive and their voltage output is lower than type K and type N thermocouples, which use Ni-base thermoelements. However, Ni base thermocouples can operate at lower temperatures than the Pt-base ones. Table1 reports the approximate compositions for positive and negative thermoelements of the letter designated thermocouples.



Figure 5: Voltage vs Temperature relationship for letter-designated thermocouples



Table 1: Approximate composition for thermoelements of letter-designated thermocouples



All the voltage-temperature relationships of the letter designated thermocouples are monotonic, but not linear. For instance the type N thermocouple voltage output is defined by the following 10 degree polynomials, where t is the temperature in degree Celsius:

The coefficients Ci are reported in Table2.In order to have a linear voltage-temperature relationship the Seebeck coefficient should be constant with temperature (see Equation1); however the Seebeck coefficient is temperature dependent, as shown for instance for type K thermocouple in Figure6. Additional details on the voltage-temperature relationships for letter designated thermocouple can be found at:

http://srdata.nist.gov/its90/main/



Table 2: Type N thermocouple coefficients



Figure 6: Type K Seebeck coefficient versus Temperature



■ Thermocouple BasicsLet's start with T. J. Seebeck, who in 1821 discovered what is now termed the thermoelectric effect. He noted that when two lengths of dissimilar metal wires (such as iron and Constantan) are connected at both ends to form a complete electric circuit, an emf is developed when one junction of the two wires is at adifferent temperature than the other junction. Basically, the developed emf (actually a small millivoltage) is dependent upon two conditions:

(1) the difference in temperature between the hot junction T2 and the cold junctionT1, ΔT. Note that any change in either junction temperature can affect the emf value and ΔV

(2) the metallurgical composition of the two wires. S1, S2, Seebeck coefficient of the two thermoelements


Although a ‘thermocouple’ is often pictured as two wires joined at one end, with the other ends not connected, it is important to remember that it is not a true thermocouple unless the other end is also connected! It is well for theuser to remember this axiom 公理 : 'Where there is a hot junction there is always a cold or reference junction ' (even though it may seem hidden inside an instrument 1,000 feet away from the hot junction). Still in Seebeck's century, two other scientists delved deeper into how the emf is developed in a thermoelectric circuit. Attached to their names are two phenomena theyobserved:

■ The Peltier effect (for Jean Peltier in 1834) and ■ The Thompson effect (for Sir William Thompson a.k.a Lord Kelvin in 1851).


Without getting into the theories involved, we can state that:

“the Peltier effect is the emf resulting solely from the contact of the two dissimilar wires. Its magnitude varies with the temperature at the juncture.”

Similarly,

‘the Thompson effect can be summarized as having to do with emf's produced by a temperature gradient along a metal conductor.”

Since there are two points of contact and two different metals or alloys in any thermocouple, there are two Peltier and two Thompson emfs. The net emf acting in the circuit is the result of all the above named effects.

Read more on Peltier and Thompson effectshttp://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20Word%20-%20Class%206_Temperature%20Measurements%20using%20Thermocouples.pdf


Polarity of the net emf is determined by:

(a) the particular metal or alloy pair that is used (such as iron/ constantan)and (b) the relationship of the temperatures at the two junctions.

The value of the emf can be measured by a potentiometer, connected into the circuit at any point. In summary, the net emf is a function primarily of the temperature difference between the two junctions and the kinds of materials used. If the temperature of the cold junction is maintained constant, or variations in that temperature are compensated for, then the net emf is a function of the hot junction temperature.

(cold junction either at constant known temperature of compensated)

In most installations, it is not practical to maintain the cold junction at aconstant temperature. The usual standard temperature for the junction(referred to as the 'reference junction') is 32 º F (0 ºC). This is the basis forpublished tables of emf versus temperature for the various types ofthermocouples.


The Law of Intermediate Temperaturesprovides a means of relating the emf generated under ordinary conditions to what it should be for the standardized constant temperature (e.g., 32 º F). Referring to Figure 4-1, which shows thermocouples 1 and 2 made of the same two dissimilar metals; this diagram will provide an example of how the law works.


Figure 4-1: Thermocouple Operation

200 400 600 8000

0

2

4

6

8mV

º F

Thermocouple 2

Thermocouple 1

Thermocouple 3


Thermocouple 1 has its cold junction at the standard reference temperature of 32 º F and its hot junction at some arbitrary intermediate reference temperature (in this case, 300 º F). It generates 2.68 mv.

Thermocouple 2 has its cold junction at the intermediate reference point of 300 º F and its hot junction at the temperature being measured (700 º F). It generates 4.00 mv.

The Law of Intermediate Temperatures states the sum of the emfs generated by thermocouples 1 and 2 will equal the emf that would be generated by asingle thermocouple (3, shown dotted) with its cold junction at 32 º F and its hot junction at 700 º F, the measured temperature. That is, it wouldhypothetically read 6.68 mv and represent the 'true' emf according to the thermocouple's emf vs. temperature calibration curve.


Based upon this law, the manufacturer of an infrared thermocouple need onlyprovide some means of substituting for the function of thermocouple 1 toprovide readings referenced to the standard 32 º F cold junction. Manyinstruments accomplish this with a temperature-sensitive resistor whichmeasures the variations in temperature at the cold unction (usually causedby ambient conditions) and automatically develops the proper voltagecorrection.

Another use of this law shows that extension wires having the samethermoelectric characteristics as those of the thermocouple can be introduced into the thermocouple circuit without affecting the net emf of the thermocouple.

In practice, additional metals are usually introduced into the thermocouplecircuit. The measuring instrument, for example, may have junctures that are soldered or welded. Such metals as copper, manganin, lead, tin, and nickel may be introduced.


Would not additional metals like this modify the thermocouple's emf? Not so,according to the Law of Intermediate Metals. It states that the introduction ofadditional metals will have no effect upon the emf generated so long as the junctions of these metals with the two thermocouple wires are at the same temperature.

This effect is illustrated in Figure 4-2, with A and B representing the thermocouple wires. A practical example of this law is found in the basic thermoelectric system shown in Figure 4-3. The instrument can be located at some distance from the point of measurement where the thermocouple is located. Several very basic and practical points are illustrated in this elementary circuit diagram: Quite often the most convenient place to provide the cold junction compensation is in the instrument, remote from the process. With the compensation means located in the instrument, in effect, the thermoelectric circuit is extended from the thermocouple hot junction to the reference (cold) junction in the instrument. The actual thermocouple wires normally terminate relatively near the hot junction.


Conventional couples have what is called a 'terminal head' at which point interconnecting wires, known as 'extension wires' are required as shown. Since these wires are in the thermoelectric circuit, they must essentially match the emf vs. temperature characteristics of the thermocouple.

With the cold junction located inside the instrument, internal extension wires of the proper materials must be used between the instrument terminals and the cold junction.

With this set-up, there are in effect three added thermocouples in the circuit: one in the thermocouple assembly, one in the external extension wire, and in the internal extension wire.

However, according to the Law of Intermediate Temperatures, the actual temperatures at the terminal head and at the instrument terminals is of no consequence: the net effect of the three thermocouples is as if one thermocouple ran from the hot junction to the cold junction.


Figure 4-2: Equivalent Thermocouple Circuits


Figure 4-3: Typical Thermocouple Installation


The Law of Intermediate temperaturesThe law of intermediate temperatures indicates that the electromotive forces are additive for temperature intervals The sum of two electromotive forces, generated by two thermocouples:

E1 with its junctions between T1 and T2 E2 with its junctions between T2 and T3 Eequivalent to emf generated by one thermocouple with its junctions between

T1 and T3

http://www.energy.kth.se/compedu/webcompedu/WebHelp/S3_Measuring_Techniques/B7_Temperature_Measurements/C2_Practical_Thermometers/S3B7C2_files/Intermediate_temperatures.htm


Law of Homogeneous MaterialsA thermoelectric current cannot be sustained in a circuit ofa single homogeneous material by the application of heatalone, regardless of how it might vary in cross section.

Law of Intermediate MaterialsThe algebraic sum of the thermoelectric forces in a circuitcomposed of any number of dissimilar materials is zero if allof the circuit is at a uniform temperature.

Law of Successive or Intermediate TemperaturesIf two dissimilar homogeneous materials produce thermal emf1when the junctions are at T1 and T2 and produce thermal emf2when the junctions are at T2 and T3, the emf generated whenthe junctions are at T1 and T3 will be emf1 + emf 2.

Could somebody talk about intermediate connecting 3rd material?


What is the law of intermediate metals?According to the Thermocouple’s Law of Intermediate Metals, illustrated in the figure, inserting any type of wire into a thermocouple circuit has no effect on the output as long as both ends of that wire are the same temperature, or isothermal.

Consider the circuit in the next figure. Both circuits are quitesimilar but a short length of constantan wire has been inserted just before junction J3 and the junctions are assumed to be held at identical temperatures. Assuming that junctions J3 and J4 are the same temperature, the Thermocouple Law of Intermediate Metals indicates that the circuit in the figure on left is electrically equivalent to the circuit of the figure on right. Consequently, any result taken from the circuit in the figure on left also applies to the circuit illustrated in the figure on right.

http://www.thermibel.be/documents/thermocouples/thermoocuple-law-metals.xml?lang=en


What is the law of intermediate metals?According to the Thermocouple’s Law of Intermediate Metals, illustrated in the figure, inserting any type of wire into a thermocouple circuit has no effect on the output as long as bothends of that wire are the same temperature, or isothermal.

Mtls-A Mtls-B Mtls-A Mtls-B Mtls-C

Isothermal Region


The Law of Intermediate temperaturesThe law of intermediate temperatures indicates that the electromotive forces are additive for temperature intervals The sum of two electromotive forces, generated by two thermocouples:

E1 with its junctions between T1 and T2 E2 with its junctions between T2 and T3 Eeqv Equivalent to emf generated by one thermocouple with its junctions

between T1 and T3

http://www.energy.kth.se/compedu/webcompedu/WebHelp/S3_Measuring_Techniques/B7_Temperature_Measurements/C2_Practical_Thermometers/S3B7C2_files/Intermediate_temperatures.htm


Peltier effectThe Peltier heat is the quantity of heat in addition to the quantity I2R that must be removed from the junction to maintain the junction at a constant temperature. This amount of energy is proportional to the current flowing through the junction; the proportionality constant is the Peltier coefficient πAB , and the heat transfer required to maintain a constant temperature is:

Qπ = πAB∙I

http://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20Word%20-%20Class%206_Temperature%20Measurements%20using%20Thermocouples.pdf

caused by the Peltier effect alone. This behavior was discovered by Jean Charles Athanase Peltier(1785-1845) during experiments with Seebeck’s thermocouple. He observed that passing a current through a thermocouple circuit having two junctions, as in Figure 4, raised the temperature at one junction, while lowering the temperature at the other junction.


Thomson effectConsider the conductor shown in Figure 5, which is subjected to a longitudinal temperature gradient and also subject to a potential difference, such that there is a flow of current and heat in the conductor.

Qσ = σ∙I(T2-T1)

where σ is the Thomson coefficient

http://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20Word%20-%20Class%206_Temperature%20Measurements%20using%20Thermocouples.pdf


End Of Reading One


Reading: Two(abstract)

Facilities Instructions, Standards, & Techniques Vol.4~11+2 “Thermal Analysis”

U.S. Department of the Interior Technical Service Center Bureau of Reclamation Denver, Colorado


1.1 Infrared Thermogram Image QualityImage quality is affected by many factors, as shown in figure 7: Image quality contributors.


1.1.1 Spot Size (IFOV)The thermal analysis equipment will record the temperature of a “spot” in the image and display this temperature. The size of the spot is critical since the temperature recorded is the average of the temperatures of the pixels within the spot. If the spot is too large, the average may “water down” a hot spot pixel, giving the false impression that the temperature is lower (or higher) than the pixel centered on the hot spot. Ideally, the spot size will be as small as possible, but there are practical limits. The spot size is partially determined by how close the device is to the target; and, in some cases, the approach distance must be relatively large for safety or physical obstructions or because the target is in the air. Using a telephoto lens on IR cameras will reduce the spot size of distant targets. Even though these can be expensive, they should be used where quantitative measurement is needed.


When using hand-held radiation thermometers, it is critical to understand and take into account the spot size for your specific equipment. Hand-held radiation thermometers typically have a spot size ratio ranging from 6:1 to 110:1. For comparison, thermal imaging cameras have a spot size ratio ranging from 63:1 to 889:1 with the typical spot size being approximately 250:1. The spot size of a thermal imaging camera can be changed depending on work to be performed by using different lenses.

Figure 8 is an example of how the actual spot size changes based on spot size ratio and the distance from the target. Assuming the employee is 6 feet from the equipment under test, the actual spot size can vary from 0.65 inch to 12 inches. If the actual target size is 0.5 inch, then with a spot size ratio of 110:1, the employee would need to be within 55 inches of the target to only measure the temperature of the target. If the spot size ratio was 12:1, then the employee would need to be within 6 inches of the target to only measure the temperature of the target.


Figure 8. Spot size of hand-held radiation thermometer.


It is important to understand the device’s spot size ratio, sometimes called the distance-to-spot ratio or instantaneous measurement field of view (IFOV), which determines the maximum distance the thermographer can be from the target and still get a good reading.

For example, a spot size ratio of 250 to 1 means that, at 250 inches (about 21 feet), the spot size to be measured must be a minimum of 1 inch (the projected spot will cover 1” by the individual sensing pixel, should the target of interest is smaller than 1”, the reading will be the averaging of the adjacent areas of interest covered by the projected spot?) . If the thermographer cannot get within 21 feet, a telephoto lens should be used. If the spot size or target is less than 1 inch (for example, ½ inch), the device would need to be closer than approximately 10½ feet for accurate temperature readings, or a telephoto lens would be required. For ¼ inch, the device would need to be closer still. The target should be larger than the spot size to ensure accurate data.


The realtionship between IFOVgeo and IFOVmeas

IFOVmeas = 3 x IFOVgeo

Where IFOVgeo = is the theoretical spot size base on angle subtended by the pixel in mRad.IFOVmeas is the practical spot size for correct measurement. The area ofinterest should not be larger than IFOVmeas for meaningful measurement.

(to be verified!)


1.1.2 Distance The physical distance of the IR thermal equipment to the target is one parameter that cannot be corrected after the image is taken and saved. The distance to the target is an important variable in determining apparent temperatures. The distance should be measured or estimated and entered into the camera. Using a laser distance device is an easy way to measure the distances between the thermographer and equipment. Never use a metal tape measure to determine the distance between the thermographer and equipment when working near energized equipment. The discussion above on spot size shows that the correct distance is very important to obtain quality IR images and proper analysis. The distance from the IR thermal equipment to the target needs to be reported on the PM forms. To simplify the process, it is possible to mark the floor in front of the equipment so the thermographer always maintains the same distance from the target, allowing for repeatable measurements.


1.1.3 Field of View and Instantaneous Field of View The definition of field of view depends on the type of instrument used. For a hand-held radiation thermometer, the field of view (or instantaneous field of view [IFOV]) is the target spot size. (as there is only one sensor FOV=IFOV?)

In a scanner, imager, or radiometer, the field of view is the scan angle, picture size, or total field of view. This can be related to a regular 35-millimeter (mm) camera; a 50-mm lens will provide a certain picture size. If the lens size isdoubled to 100 mm (a basic telephoto lens), at the same distance, the overall field of view is reduced, but the items in the picture appear closer and clearer in detail. In IR thermography, the lenses are designated using angular notations. As the lens angle increases, so does the field of view. A “standard”24-degree lens will have a larger field of view than a 12-degree telephoto lens. IFOV relates directly to spatial resolution of the instrument used. IFOV is the smallest area that can be accurately seen at a given instance.

Figure 9 illustrates the field of view and the relation to the instantaneous field of view when using a thermal imaging camera.


Figure 9. Field of view of an IR camera.


1.1.4 Estimating Emissivity εBefore inspection of any component, it is essential that the emissivity of that component be estimated and set in the IR thermal inspection equipment. Otherwise, inaccurate temperatures will be recorded. For qualitative inspections, the starting emissivity may be estimated at 0.9–0.95. It is a good practice for a facility to establish a uniform starting emissivity for consistent results. Hand-held radiation thermometers may or may not allow the user to change the emissivity of the instrument.

If the instrument does not allow the user to change the emissivity, then it will only provide accurate results for objects with the preprogrammed emissivity. Coatings may be added to equipment included in the thermal analysis program that will change the emissivity of the object.


Some cameras and the associated analyzing software programs can adjust emissivity after the image is saved. However, if the emissivity is set prior to imaging, quicker analysis may be made in the field as to the severity of any anomalies found.

Emissivity tables are provided in many publications and also can be found in appendix F. These tables should be used sparingly and with caution.

The best emissivity value for a given target is established in the field using accepted practices for determining the target’s emissivity. See appendix E.


1.1.5 Background Sources Heat energy from sources of radiation other than the target must be estimated and entered into the camera for a more accurate temperature measurement. There are specific procedures for using the camera to determine the background temperature. Once obtained, these values should be inputted into the camera.

(The reflectivity ρ ? or Tamb only? without the ρ, the ambient contributions could not be quantified?)

ρ


1.1.6 Pointing, Aiming, and Ambient Reflections Viewing angles can affect the amount of IR radiation gathered by the thermal analysis instrumentation. The optimum angle of the instrument to the target is 90° (perpendicular) to the plane of the target. Effort should be made to ensure the best possible viewing of the target. The optimum angle cannot always be achieved or maintained. Therefore, the temperature recorded from a target on an angle other than 90° may not be as accurate.

Generally, shiny surfaces do not emit radiation energy efficiently and can be hot while appearing cool in an IR thermographic image or on the readout of the hand-held radiation thermometer. Likewise, direct reflections of sun rays from shiny surfaces into the camera can be misread as hot spots. One method of determining if the spot observed in a camera is an anomaly or is the result of a reflection is to move around the target when possible. Usually, when conducting outdoor inspections, if the “hot” spot goes away or diminishes significantly, then the “hot” spot was probably a reflection. If the hot spot remains, measure it.


Do not rely on this technique for all targets. Targets may be large or shaped so that hot spots on the front side may be completely obscured when viewed from the back side. The technique of moving around then will not accurately locate all anomalies. The thermographer must be aware of unusual conditions that may influence the IR radiation measured by the test instrument. This points out the need for training and experience. It also emphasizes the need to have the thermographer familiar with the workings of the equipment being inspected.


1.1.7 Calibration Have the thermal analysis instrumentation calibrated periodically, according to the manufacturer’s recommendations. This will help ensure the instruments are working properly and recording accurate thermograms and/or temperatures.


2.1.8 Reference Photos It is very helpful when analyzing thermograms to have a visual reference photo taken with a standard camera of the equipment at the same time and point of view as the thermogram. The reference photo will make it easier to identify components that might not be obvious in the thermogram. When using hand-held radiation thermometers, reference photos are critical to identify locations of hot spots. Since hand-held radiation thermometers do not capture data, extensive notes and reference photos are the only way to document the location of temperature data for future reference.


1.2 Methods of Determining or Enhancing the Emittance of a Target

Thermographers calculate or determine the emissivity of different targets in a number of ways. Accurate emissivity values are needed if quantitative temperature measurements are required. If possible, emissivity enhancement coatings can be applied to target areas. Coatings, usually in the form of paint, have known emissivities. These coatings are usually applied to shiny or reflective surfaces to provide a higher known emissivity and to provide accurate temperature measurements. Most of the coatings today have emissivities at or near 0.95. Black electrical tape (3M Scotch 33™) can be used to determine the emissivity of targets. This tape has been measured and is used as a reference by many thermographers. Emissivity of the tape is 0.95. This technique requires the tape to be placed on the target material prior to energizing, loading, or heating the equipment to be monitored. For the following technique to work properly, the measured target or component temperature must be raised 20 degrees Fahrenheit (°F) or higher above ambient temperature. This technique will not work if the target is at ambient temperature.


Place a ½- to 1-inch square of the electrical tape on the target. Measure the background temperature by setting the emissivity to 1.0 in the infrared (IR) camera and pointing the camera away from the target. In most cases, defusing the focus will give an average background temperature. The background temperature also can be measured by using a piece of cardboard with an aluminum foil cover set next to the target. Again, set the camera emissivity to 1.0 and the camera slightly out of focus. Measure the temperature at the center of the cardboard/aluminum foil.

The background temperature should be entered into the camera if the camera being used allows this. The correct distance to the target should be added to the camera settings. The thermographer needs to recognize the spot size and ensure that the target size is adequate and is in focus. (the target should be 3x the instrument spot size) Set the camera to an emissivity of 0.95. Once the target is at temperature, measure the temperature of the taped (or emissivity enhanced) area.


Note the temperature. Move the measuring spot just off of the tape and on to the surface for which emissivity is to be determined. Adjust the emissivity in the camera, until the temperature of this spot matches the temperature measured on the tape. Once the temperatures match, read and record the emissivity. This emissivity now can be used in the future for this particular equipment and perhaps similar equipment.

Other techniques for increasing emissivity of targets include using the geometry of the components. For instance, the intersection where a lug or nut meets the connection surface will form a small cavity that, when viewed in the IR camera, will have an increased emissivity. ( if the depth to width ration is 7, the emissivity could be assume to be 0.98?) All types of cavities will tend to have higher emissivities and should be used whenever possible. Other techniques or formulas for calculating emissivity can be found in numerous publications and are usually included in most training classes.

Cavity radiator——A hole, crack, scratch, or cavity that will have a higheremissivity that the surrounding surface because reflectivity is reduced. Acavity seven times deeper than wide will have an emissivity approaching 0.98.


Thermograms

Figure 1. Transformer bushing with incorrect washer that does not allow correct connection. Connection spot 1 (52.4 degrees Celsius [°C]), is greater than (>) 30 °C hotter than spot 2 (22.2 °C) on similar bushing under same load.


Thermograms

Figure 2. High-side connection from transformer, illustrating a “barber pole” effect where only part of the cable strands carry the current. This qualitative image prompted immediate remedial action.


Thermograms


Thermograms


End Of Reading Two


Reading: ThreeInfrared Thermography Guide-R3Electric Power Research Institute



ABSTRACT This guide is a valuable reference for the development of infrared thermography (IR) capabilities as part of a plant predictive maintenanceprogram. The guide includes IR theory, a summary of IR inspectionapplications, and the technical information necessary to develop an effectivein-house program. The body of the guide is structured for the general user ofIR, and the appendices provide a more in-depth look at this technology for theadvanced user. This third revision of Infrared Thermography Guide containsupdated information on IR equipment technology, IR inspection applications,and training and certification criteria.


INTRODUCTIONMany electric generating stations and utilities have integrated the non-contact, nondestructive capabilities of infrared thermography (IR) for conditionmonitoring and diagnostics in their predictive maintenance program. Thepurpose of this guide is to assist the nuclear industry in its efforts to factor IRinto its predictive maintenance program. This guide provides the theory of IR,a summary of existing and potential applications, and the technicalinformation necessary to develop an effective in-house program. Alsoincluded is a matrix that lists all of the known manufacturers of IR instrumentsfor a broad range of applications.


IR has been used in commercial applications since the early 1970s. In the early 1990s, at the time this guide was first completed, the most frequent applications centered on building energy losses, roof moisture detection, and inspections of major electric equipment. Applications have since expanded to almost all areas of plant predictive maintenance (PdM), product and process control, and nondestructive testing of materials. The wide and growing selection of thermal imagers and viewers available for these applications provides both qualitative and quantitative displays of temperature distribution patterns.


The manufacturers of modern thermal imagers and viewers have kept pace as detector and microprocessor technologies have advanced. Thecapabilities of today.s IR thermal imagers and viewers have yet to be fullyexplored and developed for commercial applications. In addition, computersoftware programs are now available to store, retrieve, analyze and compareinfrared images.

Much of the information presented in the original guide was developed as a result of a demonstration project at a U.S. nuclear utility. In addition to information gathered through this demonstration project, all Nuclear Maintenance Applications Center (NMAC) members were surveyed to provide data on the implementation status of IR technology at their facilities.This latest revision of the guide (Revision 3) was undertaken to correct texterrors, to update the information on IR products vendors, certification, training,and techniques, and to restructure the guide so that it can become a livingdocument, able to be readily updated to reflect technology changes. The bodyof the guide is structured for the general user of IR, and the appendicesprovide an in-depth look at this technology designed for the more advanceduser.


Basic IR ConceptsA target at any temperature above absolute zero will emit infrared radiation in proportion to its temperature. Thermal imagers develop an electronic imageby converting the invisible heat radiation emitted by that target into electricalsignals that can be displayed on a monitor and/or recorded on a variety of electronic storage media. By monitoring these targets with thermal imaging equipment, a visual image of their temperature differentials can be displayed. The variations in intensities of the blacks, grays, and whites (or color variations) provide an indication of the temperature differences. Areas of higher temperatures will appear brighter and the areas at lower temperatures will appear darker (or appear as different colors). The quantity and wavelength distribution of the energy that is radiated depends upon the temperature and spectral characteristics of the material, and on that materials radiation efficiency (emissivity). Thermal imagers convert the invisible heat radiation (thermal detector?) into visible images while spot radiometers convert the heat radiation from a single spot into a number indication on a meter. (the photon detector not addressed?)


The thermographer views the target through an IR instrument, while looking for unexpected or unusual temperature patterns. A qualitative examinationcompares the apparent temperature pattern of one component to that of anidentical or similar component under the same or similar operating conditions.

Temperature differences can be measured quantitatively as well. Theachievement of accurate temperature indications, however, is dependentupon many factors and extreme care must be taken in the selection ofvariables used in temperature calculations. The thermal images obtained canbe stored on memory sticks, PCMCIA cards, computer hard drives, floppydisks, CDs, ZIP disks, or video tape. An advantage of infrared monitoring ortesting is that it can be performed with the equipment in service at normaloperating conditions (that is, it will not interfere with normal plant operations).


CONTENTS1. Thermography overview 2. A compendium of commercial infrared sensing and imaging instrument3. The measurement mission 4. Inspection techniques 5. Examples of infrared applications 6. Basic elements of an in-house program 7. Training and certification


1. THERMOGRAPHY OVERVIEW Temperature and thermal behavior of plant machinery, power generation and distribution equipment, control systems, and related materials are the most critical factors in the maintenance of operations. For this reason, temperature is frequently considered the key to successful plant maintenance and is, by far, the most measured quantity. Although conventional methods of temperature measurement using thermometers and thermocouples are still commonly used for many applications, infrared thermography (IR) sensors have become less expensive, more reliable, and electrically interchangeable with conventional thermistors and thermocouples. Noncontact measurement using infrared sensors has become an increasingly desirable alternative over conventional methods. Now, with the proliferation of innovative computer hardware and software, computer-aided predictive maintenance (PDM?) is feasible and efficient.


1.1 Advantages of Non-Contact Thermal Measurement The four most commonly stated advantages of non-contact thermal infrared measurement over contact measurement are that it is non-intrusive, remote,much faster than conventional methods, and that it measures the temperatureat the surface of the target (test subject) not the surrounding air. Any one, or acombination of the following conditions, warrants the consideration of anoncontact sensor:• Target in motion . When the target to be measured is moving, it is usually

impractical to have a temperature sensor in contact with its surface. Bouncing,rolling, or friction can cause measurement errors and the sensor mightinterfere with the process.

• Target electrically hot . Current-conducting equipment and components present a hazard to personnel and instruments alike. Infrared sensors place both out of harm’s way.

• Target fragile . When thin webs or delicate materials are measured, a contacting sensor can often damage the product.

• Target very small . The mass of a contacting sensor that is large with respect to the target being measured will usually conduct thermal energy away fromthe target surface, thus reducing the temperature and producing erroneousresults.


• Target remote . If a target is very far away from, or inaccessible to,contacting sensors, infrared measurement is the only option.

• Target temperature changing . Infrared sensors are much faster than thermocouples. Infrared radiant energy travels from the target to the sensor at the speed of light. A rapidly changing temperature can be monitored by infrared sensors, with a millisecond response or faster.

• Target destructive to thermocouples . When the high mortality rate of thermocouples due to jarring, burning, or erosion becomes a serious factor, an infrared sensor is a far more cost effective alternative.

• Multiple measurements required . When many points on a target need to be measured, it is usually more practical to re-aim an infrared sensor (IR Scanner, Line scanner) than it is to reposition a thermocouple or to deploy a great number of thermocouples. The fast response of the infrared sensor is important.

There are, of course, limitations to the non-contact approach conditions that might make it impractical or ineffective. These will be covered as the discussion progresses.


1.2 Heat Transfer and Infrared Radiation BasicsInfrared thermography is based on measuring the distribution of radiant thermal energy (heat) emitted from a target surface and converting this to asurface temperature map or thermogram. The thermographer requires anunderstanding of heat, temperature, and the various types of heat transfer asan essential prerequisite in preparing to undertake a program of IRthermography. This section is an overview discussion to provide the readerwith a basic understanding of how heat transfer phenomena affect non-contact infrared thermal sensing and thermographic measurements.

For a more detailed discussion of temperature and heat transfer basics, see Appendix A.

Comments: The differences in detecting principle by thermal detectors andphoton detector were not addressedThermal detector – heat sensitive?Photon detector – spectral sensitive?


1.2.1 Heat and TemperatureHeat is defined as thermal energy in transition, flowing from one place or object to another as a result of temperature difference, with the flow of heatchanging the energy levels in the objects. All of the energy must be taken intoaccount because energy can neither be created nor destroyed. What we oftenrefer to as a heat source (like an oil furnace or an electric heater) is really oneform or another of energy conversion; the energy stored in one object isconverted to heat and flows to another object.

Temperature is a property of matter and not a complete measurement of internal energy. It defines the direction of heat flow when another temperature is known. Heat always flows from the object that is at the higher temperature to the object that is at the lower temperature. As a result of heat transfer, hotter objects tend to become cooler and cooler objects become hotter, approaching thermal equilibrium. To maintain a steadystate condition, energy needs to be continuously supplied to the hotter object by some means ofenergy conversion so that the temperatures and, hence, the heat flow, remainconstant.


1.2.2 Instruments for Temperature Measurement (Contact and Non-Contact)Conventional temperature measuring instruments use various contact sensors.

A mercury thermometer works on the principle of expansion with heat: the mercury expansion is calibrated based on its known characteristics and the reading is an indication of the temperature at the site of the mercury reservoir. Thermometers using thermocouples, thermopiles, and thermistors are based on the electrical-thermal characteristics of these sensors and produce a reading based on the temperature of the object with which the sensor is in contact. Infrared thermal instruments are non-contact devices and produce readings based on the surface temperature of objects at which the instrument is pointed.


1.2.3 Converting Temperature UnitsTemperature is expressed in either absolute or relative terms. ■ There are two absolute scales called º Rankine (English system) and

Kelvin (metric system).■ There are two corresponding relative scales called º Fahrenheit (English

system) and º Celsius or Centigrade (metric system).

For a detailed discussion of temperature units and formulas for converting from one scale to another, see Appendix A.

Table 1-1 is a conversion table to facilitate the rapid conversion of temperature between Fahrenheit and Celsius values. Instructions for the use of the table are shown at the top. For convenience, Table 1-1 is repeated in Appendix A (Table A-1). For quick reference, the conversion factors are summarized in Appendix C, Plate 1.



1.2.4 The Three Modes of Heat TransferThere are three modes of heat transfer: (1) conduction, (2) convection, and (3) radiation. All heat transfer processes occur by one or more of these three modes.

IR, Infrared thermography is based on the measurement of radiative heat flowand is, therefore, most closely related to the radiation mode of heat transfer.

For a detailed discussion of heat transfer modes and the relationship between infrared measurements and radiative heat flow, see Appendix A.


1.3 Measuring and Mapping Temperature Without ContactAll targets radiate energy in the infrared spectrum. The hotter the target, the more energy that is radiated. Very hot targets radiate in the visible spectrumas well as in the infrared. As targets cool, they no longer glow but theycontinue to radiate. The radiation can be felt on a hand placed near thetarget’s surface, but the glow can’t be seen because the energy has shiftedfrom red to infrared. Infrared detectors can sense infrared radiant energy andproduce useful electrical signals proportional to the temperature of targetsurfaces. Instruments using infrared detectors allow a fast and highlysensitive target surface temperature measurement without contact.Instruments that combine this measurement capability with the capability ofscanning a target surface area are called infrared thermal imagers. Theyproduce thermal maps, or thermograms, where the brightness intensity orcolor of any spot on the map is representative of the surface temperature ofthat spot. In other words, they extend non-contact point temperaturemeasurements to non-contact thermography.


1.3.1 The Three Elements of a Non-Contact Temperature MeasurementIn using infrared instruments for making non-contact temperature measurements, three sets of characteristics need to be considered:

• Target surface• Transmitting medium between the target and the instrument• Measuring instrument

Figure 1-1 shows how the instrument is aimed at the target and makes the measurement through the medium.


Figure 1-1- Categories of Conditions for Infrared Thermal Measurements



Every target surface above absolute zero radiates energy in the infrared. The hotter the target, the more radiant infrared energy is emitted. The physicallaws that define this behavior are discussed in detail in Appendix A, alongwith a detailed discussion of medium and instrument characteristics.Emissivity is a very important characteristic of a target surface and must beknown in order to make accurate non-contact temperature measurements.

Methods for estimating and measuring emissivity are discussed throughoutthis guide, and the emissivity setting that is needed to dial into the instrumentcan usually be estimated from available tables and charts. The proper settingneeded to make the instrument produce the correct temperature reading canbe learned experimentally by using samples of the actual target material. Thismore practical setting value is called effective emissivity.


Although the transmitting medium is usually air, non-contact temperature measurements can be made through a vacuum, gas, or certain solidmaterials. The characteristics of the medium need consideration and adetailed explanation of this is included in Appendix A. Figure 1-2 shows thenecessary components of an infrared radiation thermometer that makes asingle point non-contact temperature measurement on the target surface.

Collecting optics (that is, infrared lenses, etc.) is necessary in order to focusthe energy radiated from the target onto the sensitive surface of an infrareddetector. The detector converts this energy into an electrical signal that isrepresentative of the temperature of a spot on the target. Adding scanningelements between the target and the detector (also shown in Figure 1-2)allows the instrument to scan the target surface and to produce a thermogram.Most currently available infrared thermal imagers incorporate multi-detector focal plane array (FPA) sensors that are electronically scanned and that eliminate the requirement for an opto-mechanical scanning mechanism (single sensor type?) .


When an infrared radiation thermometer (point-sensing instrument) is aimed at a target, it collects energy within a collecting beam, the shape of which isdetermined by the configuration of the optics and the detector. The cross-section of this collecting beam is called the field of view (FOV) of theinstrument and it determines the size of the area (spot size) on the targetsurface that is measured by the instrument. On scanning and imaginginstruments this is called the instantaneous field of view (IFOV) and becomesone picture element on the thermogram.


Figure 1-2 Components of an Infrared Sensing Instrument (non FPA?)


1.4 Performance Parameters of Thermal Sensing InstrumentsThis section previews the performance parameters of point-sensing instruments and scanning and imaging instruments. For a detailed discussionof these parameters and how to specify and testthe performance of instruments, please refer to Appendix A.1.4.1 Point-Sensing InstrumentsPoint-sensing instruments are defined by the following performance parameters:• Temperature range . The high and low limits over which the target

temperature might vary• Absolute accuracy . As related to the NIST

(National Institute of Standards and Technology) standard• Repeatability . How faithfully a reading is repeated for the same target


• Temperature sensitivity . The smallest target temperature change that the instrument needs to detect

• Speed of response . How fast the instrument responds to a temperature change at the target surface

• Target spot size and working distance . The size of the spot on the target to be measured and its distance from the instrument

• Output requirements . How the output signal is to be utilized• Spectral range . The portion of the infrared spectrum over which the

instrument will operate• Sensor environment . The ambient conditions under which the instrument

will operate


1.4.2 Line Scanners and Imagers - Qualitative and QuantitativeThe parameters used for assessing the performance of infrared thermal line scanners and imagers are more complex because a thermal line-scan orimage is made up of a great number of discrete point measurements.

Many of the performance parameters of infrared thermal line-scanners andimagers, such as accuracy, repeatability, and spectral range, however, are the same as those of radiation thermometers. Others are derived from, or areextensions of, radiation thermometer performance parameters.

Some types of thermal imagers show comparative temperatures and not actual temperature measurements. For users of these thermal viewers (see section 3), parameters dealing with accuracy and repeatability do not apply. Parameters exclusive to thermal line-scanners and imagers are as follows:


1. Total field of view (TFOV) . The thermogram image size, in terms of scanning angle. (example: TFOV=20° Vertical x 30° Horizontal) The TFOV of a line scanner is considered to be the TFOV of one scan line.

2. field of view (IFOV) . The spot size represented by one detector element atthe target plane: Imaging spatial resolution. (example: IFOV= 2 milliradians)(1° = 35 milliradians)

3. Measurement spatial resolution: (IFOVmeas) . The spatial resolution that describes the minimum target spot size on which an accurate temperature measurement can be made. (example: IFOVmeas = 5 milliradians)

4. Frame (or line) repetition rate . The number of times every point on the target is scanned in one second. (example: Frame rate = 30/second or 30 Hz; Scan rate = 60 lines/second)

5. Minimum resolvable temperature (MRT) . The smallest blackbody equivalent target temperature difference that can be observed: Temperature sensitivity. (example: MRT=0.1°C @ 30°C target temperature)

6. Other parameters such as spectral ranges, target temperature ranges, accuracy and repeatability, and focusing distances are essentially the same as those for point-measuring instruments.


1.4.3 Thermal Imaging SoftwareIn order to optimize the effectiveness of thermographic measurement programs, the thermographer needs a basic understanding of the thermalimage processing techniques. The following is a list of broad categories ofthermal image processing and diagnostics currently available. A discussion ofeach of these categories is included in Appendix A. A detailed description ofcurrently available thermal imaging and diagnostic software is provided insection 2. Thermal imaging software can be categorized into the following groups:

• Quantitative thermal measurements of targets• Detailed processing and image diagnostics• Image recording, storage, and recovery• Image comparison• Archiving and database*

*Although data and image database development is not an exclusive characteristic of thermal imaging software, it should be considered animportant part of the thermographer’s tool kit.


2. A compendium摘要 of commercial infrared sensing and imaging instruments This chapter begins with a classification of infrared sensing and imaging instruments by type and application. The list includes commercially available instruments, from single-point thermal probes to on-line control sensors, to high-speed, high-resolution thermal imaging (thermography) systems. A detailed overview of performance characteristics and features follows, along with a discussion of the typical thermographic display approaches that are used by various imager manufacturers. This is followed by a discussion of currently available thermographic image processing software and image hard-copy recording accessories. Finally, a tabulation of currently available instruments by category and manufacturer is appended, including a digest of performance characteristics and features. A current index of manufacturers’ addresses, phone numbers, Web sites (where available), and/or e-mail addresses is also included.


2.1 Classification of Instruments Infrared sensing instruments are traditionally classified into three groups: ■ point-sensing, ■ linescanning, and■ thermographic (two-dimensional scanning).

Point-sensing devices (commonly called Infrared Radiation Thermometers)collect radiant energy from a spot or area on the surface of an object to bemeasured (the target) and provide an output indication, usually in terms oftarget temperature. Line-scanning instruments provide an output, generally an analog trace, of the radiant energy (or, in ideal cases, temperature) distribution along a single straightline projection from the target surface.Thermographic instruments (imagers) provide an image of the energydistribution over a scanned area on the target surface. This is presented inthe form of an intensity-modulated black and white picture or a synthesizedcolor display called a thermogram.


Point sensors, line scanners, and imagers can be further divided into sub-groups. This section will review commercially available instruments along thelines of this breakdown:Point-Sensing • Probes and IR thermocouples• Portable (hand-held)• On-line monitoring and control• SpecialsLine-Scanning • Opto-mechanically scanned• Focal plane array (FPA), electronically scannedThermographic • Opto-mechanically scanned imagers

(single element, mechanical manipulated)• Electronically scanned pyrovidicon imagers (?)• Electronically scanned FPA focal plane array imagers

(multi-elements array)


2.2 Instrument Manufacturers Particularly in the point-sensing category, there are many companies offering the same instrument under different private label arrangements. In order toavoid duplication, the original manufacturer or prime (U.S.) distributor will belisted in the material that follows. At the end of Section 2, a comprehensivelist of instruments is included (Table 2-1), for which descriptive literature wasavailable at the time of the preparation of this text. The performancecharacteristics are summarized rather than presented in detail. The listedmanufacturer should be contacted for detailed performance information. Alisting of current addresses, phone numbers, Web sites, and/or e-mailaddresses, for the listed equipment manufacturers, is included in a separatetable (Table 2-2) at the end of Section 2. In addition, a third table is included,which summarizes proven industrial applications for thermal imaginginstruments (Table 2-3). The information that follows will highlight theapplications for which each instrument category and group is particularlysuited, based on configuration or performance characteristics.


2.3 Discussion of Instruments ■ 2.3.1 Point Sensors (Radiation Thermometers) 2.3.1.1 ProbesTemperature probes are characterized by low price (from less than $100 to about $1,000), pocket-portability, and wide-collecting angle. They are battery-powered and are generally optically pre-adjusted for minimum spot size at ashort working distance (a 1/4" (6.35 mm) spot at a 3/4" (19.05 mm) workingdistance is typical). Some models are designed to operate into a conventionalmulti-meter and some incorporate their own readout box with a liquid crystaldiode (LCD) display. They usually feature disposable batteries and somemodels have ac adapters. Temperature ranges are from about 0°F, or slightly below, to 600°F, and a sensitivity of +/- 1°F is easily achieved. Emissivity adjustments are available on some models. Probes are ideal forclose-up measurements and are used in circuit board analysis, troubleshooting of electrical connections, the inspection of plumbing systems, and in application to biological and medical studies.


2.3.1.2 Portable Hand-HeldWith few exceptions, these instruments are pistol-shaped and designed for middle-distance measurements. They are usually optically pre-adjusted forinfinity focus. A typical 2° field of view resolves a 7.5-cm (3-inch) spot at a150-cm (60-inch) working distance, and a 30-cm (1- foot) spot at a 9-m (30-oot) working distance. Prices range from about $100 to more than $3,500.Sighting and aiming methods vary from simple aiming notches to enclosedilluminated reticles. There are instruments with extremely narrow fields ofview (0.5°) that include a rifle stock and telescopic sight. Most instruments inthis group incorporate emissivity adjustments and some includemicrocomputers with limited memory and data-logging capabilities. Most are available with a recorder output, although this feature is seldom used. A meter is always provided and, with one exception that reads in BTU/ft²-h, the readout is always in temperature units. Analog displays are still available, although they are decreasing in popularity. Digital readouts featuring light emitting diodes (LEDs) were introduced first but the LCD display, introduced more recently, is now used almost universally because its tiny power drain extends battery life.


For this reason, the more recent instruments offer replaceable rather thanrechargeable batteries and battery life approaches one year. Some instruments in this group have zeroing adjustments, but all of the newer instruments include auto-zeroing features. Temperature ranges are, typically, from 0°C to 1500°C. Temperature sensitivity and readability are usually 1°C (or °F) or 1% of scale, although sensitivities on the order of 0.1°C (or °F) are achievable.This instrument group is particularly suited to applications where spot-checking of target temperatures is sufficient and continuous monitoring is notrequired. A typical use would be for periodic maintenance checks of rotatingmachinery to detect whether or not bearings are beginning to overheat. Theseinstruments, over the past few years, have become an important part of manyplant energy conservation programs. Although many of these instrumentsprovide extremely accurate readings, accuracy, like the recorder output, isless important to most users than repeatability, ruggedness, portability,reliability, and ease of use. Some newer models incorporate microcomputerswith special features such as a data-logger, which has the capability to storeas many as 60 readings for future retrieval and printout.


2.3.1.3 On-Line Monitoring and ControlThese instruments are primarily used for monitoring and control of manufacturing processes. The one feature that distinguishes this instrumentgroup from the others is dedicated use. The instrument is generally mountedwhere it can measure the temperature of one specific target, and it remainsthere for the life of the instrument or the process. With few exceptions, theseinstruments operate on line power. The output signal of the instrument can beobserved on a meter, used to operate a switch or relay, feed a simple orsophisticated process control loop, or it can be used in any combination ofthese functions.Early on-line instruments consisted of an optical sensing head and an electronics/control readout unit at the other end of an interconnecting cable.This configuration still exists to some extent, but most of the newer unitsfeature sensing heads that are more stable electronically and, hence, moreindependent of the remote control units.


The trend is for these new sensors to mate with universal indicator/control units that accept input from various types of industrial sensors. This instrument group is selected to perform a specific task, so the manufacturer provides a shopping list ordering format to the customer, enabling them to purchase all required features.Manufacturers offer sensing head features such as variable or fixed focus, sighting tubes, light pipes, water-coolable housings, air purge fittings, air curtain devices, and see-through aiming with target-defining reticles. The shopping list for the indicator/controller unit might include digital readout, binary coded decimal (BCD) output, analog output, single, double, orproportional set point, rate signals, sample and hold, peak or valley sensor, and data-logger interface. Emissivity controls, located in a prominent place on a general-purpose instrument, are more likely to be located behind a bezel 玻璃柜on the sensor on these dedicated units, where they are set one time and locked.


Spectral characteristics are worth mentioning separately, although, technically, they are part of the sensing head shopping list. The spectral interval over which the sensing head operates is selected to optimize the signal from the target, to reduce or eliminate the effect of an interferingenergy source, or to enable the instrument to measure the surface temperature of thin films of material that are largely transparent to infrared energy. This last application has made these instruments important factors in the manufacture of thin film plastics and also of glass.

Exercise:What is the spectral filter need to measure the surface temperature of PU.


2.3.1.4 SpecialsThere are several special categories of spot-measuring instruments that are worth mentioning, although they might, by strict definition, fit into one or moreof the above categories.

(1) Two-color or ratio pyrometers are one special case of an on-line instrument. These are particularly useful in high-temperature applications and in measuring small targets. The effective emissivity of the target need not be known, providing that it is constant and that reflections are controlled. The target need not fill the field of view, provided that the background is cool,constant, and uniform. Impurities in the optical path that result in broadband absorption, do not affect the measurement because the measurement is based on the ratio of energy in two spectral bands. Ratio pyrometers are, generally, not applicable to measurements below 500°F.


Another special case is the (2) fiber optic-coupled thermometer. With thisinstrument, inaccessible targets can be measured by replacing the optic witha flexible or rigid fiber optic bundle. This, of course, limits the spectralperformance and, hence the temperature range, to the higher values, but ithas allowed temperature measurements to be made when none werepossible.


Fiber Optic-coupled Thermometer


(3) The infrared microscope is a third special case. This instrument is configured like a conventional microscope. Through the use of reflective microscope objectives and beam splitters, it enables the operator to simultaneously view and measure targets down to 0.0003" (.00762 mm) in diameter with an accuracy and resolution of about 0.5°F. Another special case, known as the

(4) laser pyrometer, has also become available. This instrument uses the reflected energy of an active laser to measure target reflectance. A built-in microcomputer calculates target effective emissivity and uses this to provide a corrected true temperature reading. The laser pyrometer is useful for high temperature diffuse target surfaces. Prices of instruments in the on-line control instrument group vary from less than $1,000 for an infrared switch, to more than $15,000 for infrared microscopes and on-line instruments equipped with many control features. Generally speaking, the price goes up when sensitivity, small spot size, and speed of response are all required and, of course, when many shopping list items, or additional features, are added.


■ 2.3.2 Line Scanners The purpose of spatial scanning is to derive information concerning the distribution of radiant energy over a target scene. Quite often, a single straightline scanned on the target is all that is necessary to locate a critical thermalanomaly. In the newer line scanners, the single-element detector is replacedby a multi-element single-line focal plane array (FPA) and the optomechanicalscanning element is eliminated. Probably the first approach to line scanningthat was adopted commercially was in an aerial-type thermal mapper in whichthe line scanner was mounted on a moving aircraft and scanned lines normalto the direction of motion. The outputs representing these individual scanlines were intensity-modulated and serially displayed in shades of gray on astrip map. This display represented the thermal map of the surface beingoverflown by the vehicle.


2.3.2.1 Opto-Mechanically Scanned Line ScannersThe earliest process-monitoring line scanners (many of which are still in use) employed a single element detector and a single scanning element, usually amirror. The instantaneous position of the scanning element is usuallycontrolled or sensed by an encoder or potentiometer so that the radiometricoutput signal can be accompanied by a position signal output and bedisplayed on a chart recorder, an oscilloscope, or some other recordingdevice. One portable, battery-powered line scanner, still used commercially,scans a single line on target, develops a visible temperature trace using lightemitting diodes and, by means of optical beamsplitting techniques,superimposes this trace over the visible scene viewed by the operator. Theoperator selects the line to be scanned by aiming the instrument’s horizontalcenterline.


Photorecording of the composite scene is accomplished by aiming a conventional instant color camera through the eyepiece of the scanner. Thisinstrument has no recorder output and is, therefore, not suited for processcontrol applications. Unlike most thermal viewers, however, absolutetemperatures are obtainable with this device. Good applications for this linescanner include electrical switchgear and transmission lines, thetroubleshooting of plumbing systems, and webprocess profiling.


2.3.2.2 Electronically Scanned Focal Plane Array FPA Line ScannersThe newest high-speed on-line commercial line scanners employ linear focal plane detector arrays that are electronically scanned. They develop highresolution thermal maps by orienting the linear array along an axis normal tothe motion of a moving target such as a paper web, a rotating kiln, or a stripsteel process. The output signal information is in real-time computercompatible format and can be used to monitor, control, or predict the behavior of the target. The best applications for this scanner are in on-line real-time process monitoring and control. In significant recent developments, families of line cameras have been made available with a wide selection of linear focal plane array detectors based on the speed, resolution, and spectral sensitivity requirements of the process being monitored.


■ 2.3.3 Thermographic Instruments An important advantage of radiation thermometers over contact thermometers is their speed of response. The measured energy travels from the target tothe sensor at the speed of light. The response of the instrument can then bein milliseconds or even microseconds. This important feature has allowed thefield of infrared radiation thermometry to expand into real-time thermalscanning and thermal mapping. When problems in temperature monitoringand control cannot be solved by the measurement of one or several discretepoints on a target surface, it becomes necessary to spatially scan (that is, tomove the collecting beam (instantaneous field of view) of the instrumentrelative to the target). The detector output is intensity-modulated in proportion to the total exitant radiant energy at each point scanned on the target surface. The image produced is presented in monochrome or color, where the gray shades or color hue are intended to represent a thermal level at the target surface.


These thermal images are called thermograms. The purpose of spatial scanning is to derive information concerning the distribution of infrared radiant energy over a target scene. Scanning can be accomplished either opto-mechanically or electronically.

Opto-mechanical scanning can be done by moving the target with the instrument fixed, or by moving (translating or panning) the instrument, but ismost practically accomplished by inserting movable optical elements into thecollected beam. Although an almost infinite variety of scanning patterns canbe generated using two moving elements, the most common pattern isrectilinear. This is most often accomplished by two elements that each scan aline normal to the other. A typical rectilinear scanner employs two rotatingprisms behind the primary lens system (refractive scanning). An alternateconfiguration uses two oscillating mirrors behind the primary lens (reflectivescanning).


This is also commonly used in commercially available scanners, as arecombinations of reflective and refractive scanning elements. Electronicscanning involves no mechanical scanning elements, the thermal pattern ofthe surface is scanned electronically. The earliest method of electronicallyscanned thermal imaging is the pyrovidicon (pyroelectric vidicon) or thermalvideo system. With this method, charge proportional to target temperature iscollected on a single pyroelectric detector surface, within an electronic picturetube. Scanning is accomplished by an electronic scanning beam. Althoughoffering them in favor of instruments based on solid-state focal plane array technology.

Most recently, electronically scanned thermal imaging is accomplished by means of an infrared focal plane array (IRFPA), whereby a two-dimensional staring array of detectors collects radiant energy from the target and is digitally scanned to produce the thermogram. All of the above approaches to producing an infrared thermogram will be discussed.


Commercial thermal imaging systems fall into the following categories and sub-categories:

• Thermal viewers, opto-mechanically scanned• Imaging radiometers, opto-mechanically scanned• Thermal viewers, electronically scanned (pyrovidicon imagers)• Focal plane array (FPA) imagers, qualitative (thermal viewers), and

quantitative (imaging radiometers)

Keywords:Thermal viewers (thermal detector) - qualitativeImaging radiometer (photon detector) – quantitative (radiometric)


A comprehensive list (Table 2-1) of all known, commercially available thermal-imaging instruments, on which descriptive literature was available atthe time of the preparation of this document, is included at the end of Section2. Performance characteristics are also briefly summarized. A listing ofcurrent addresses, phone numbers, Web sites, and/or e-mail addresses, ofthe listed equipment manufacturers, is included in a separate table (Table 2-2)at the end of Section 2. In addition, a third table is included, whichsummarizes proven industrial applications for thermal imaging instruments(Table 2-3). The information that follows will highlight the applications forwhich each instrument category and group is particularly suited, based onconfiguration or performance characteristics.


Infrared (IR) thermography is a well established technique for remotely measuring the temperature of a surface where it is impractical or impossible to do so by a contact means. The term thermography denotes an imaging capability, but the concepts are the same for non-imaging sensors. IR thermography exploits the correlation between the temperature of a surface and the IR energy emitted by the surface. This relationship is described by Stefan’s Law:

where σ is the Stephan-Boltzmann constant (= 5.67×10-8 W/(m2·K4)) and T is the temperature of the surface. The spectrum of the IR light is described by Planck’s blackbody function.


2.3.3.1 Thermal Viewers, Opto-Mechanically ScannedOpto-mechanically scanned thermal viewers are inexpensive battery-powered scanning instruments producing a qualitative image of the (thermally associated) radiant exitance distribution over the surface of a target. The battery packs are rechargeable and usually provide 2 ~ 3 hours of continuous operation. These are one-piece, lightweight instruments, designed to besimple to operate.

The first viewers required cryogenic cooling of the detector elements, whichwas accomplished by means of a small tank of compressed argon. These early units, while still in use, are no longer manufactured. Newer units feature thermoelectric detector cooling provided by a battery-powered cooler.(and sterling cooler?)

Note: Although they are being replaced gradually by focal plane arrayimagers (see section 2.3.3.4), at the time of this writing, opto-mechanicallyscanned thermal viewers are still in wide use commercially. For this reason,the following operational description is provided.


Thermal viewers are not designed for absolute temperature measurements, but they can demonstrably sense temperature differences in tenths of degrees. Some manufacturers have modified these viewers and introduced absolute temperature references so that absolute measurements are possible in certain applications. (discuss this statement, on how this pseudo absolute temperature measurement is accomplished?)This generally requires an additional box, however, and diminishes the portability that defines the instrument group. (It also increases the price.) Thermal viewers operate most effectively with cooler targets (0°C.150°C) but, through the use of optical attenuators, they can be used for targets of up to 1500°C. Typically, the area scanned (field of view) with thermal imagers is from 6° to 8° high and from 12° to 18° wide, with spatial resolution (instantaneous spot size) of 2 mRad (1 cm at 2 m). (? – see next page)Although a hard copy of the thermal image can be acquired by through-the-eyepiece recording using either conventional or instant film, currently available units offer direct video recording by means of a conventional VCR output jack and camcorder accessories.


Applications for thermal viewers are found throughout the industrial environment but are generally limited to those in which the temperature measurements are not critical and the recording quality does not need to be optimum. The combination of a thermal viewer (to locate thermal anomalies) and a handheld thermometer (to quantify them) is powerful and cost effective.Thermal viewers are particularly useful industrially in tight spaces or,conversely, when a sizable area must be traversed and user fatigue becomes a factor.

Exercise:From text: 2 mRad (1 cm at 2 m). (?)Calculation:D = α∙d, D = 2 x 10-3 x 2 = 4 x10-3 = 4mm#

Q? (4mm or 2mm?)


2.3.3.2 Opto-Mechanically Scanned Imaging RadiometersOpto-mechanically scanned imaging radiometers provide potentially quantitative temperature measuring capability and high-resolution image quality. Detector cooling is almost always required and this is done using any of several means including thermoelectric (Peltier effect) coolers, compressed argon, refillable liquid nitrogen containers, and, most recently, electricpowered Stirling cycle nitrogen coolers. Most commercial imaging radiometers use a single detector, but some manufacturers offer dual-detector or multi-detector (linear array) instruments. All provide a means of measuring target surface temperature.

Note: Although they are being replaced gradually by focal plane array imagers (see Section 2.3.3.4), at the time of this writing, opto-mechanicallyscanned imagers are still in wide use commercially. For this reason, thefollowing operational description is provided.(Could be misleading note, 未必-里根星球计划)


These imagers use refractive, reflective, or hybrid scanning systems and operate in either the 3.5 µm (MWIR) or the 8.14 µm (LWIR) atmospheric window. In addition to quantitative temperature measuring capability (Radiometers) in idealized circumstances, these instruments feature excellent capabilities for both spatial resolution (about 1 mRad) and minimum resolvable temperature (0.05°C to 0.1°C). Most manufacturers offer isotherm graphics features, spectral filtering, interchangeable optics for different total fields of view(FOVtotal) , color or monochrome (black and white) displays, flexible videorecording capabilities, and computer compatibility. Most general-purpose systems in use today feature compact, field-portable, battery-operable sensing heads and control/display units, some of which are integrated into camcorder configurations. A complete system, including battery and video recorder, can usually be handled by one person, by either mounting the components on a cart or assembling them on a harness. Detector cooling for all newer models that are intended for field operation is accomplished by means of thermoelectric or Stirling-cycle cooler, thuseliminating the inconvenience of liquid nitrogen refills in the field.


Thermoelectric Cooling - Figure below The operating principle of thermoelectric devices is depicted above which demonstrate that it is possible to convert temperature gradients into electrical currents (or vice versa) and that thermoelectric devices can be used for both cooling and recovery of waste heat.

http://www.nano.ucf.edu/research/compsim_masunov1.php


Sterling Cooling – Electromechanical Cooling

http://www.robertstirlingengine.com/cold.php

Sterling Cooling


DIY Temperature Chamber – Thermoelectric Cooling / Peltier Cooler

■ https://www.youtube.com/embed/XApTATLNEcQ

https://www.youtube.com/watch?v=XApTATLNEcQ


Stirling Cycle Engine, Two-Cylinder Alpha Type

■ https://www.youtube.com/embed/aPxRB6JNfCw

https://www.youtube.com/watch?v=aPxRB6JNfCw


Stirling Engines - How They Work

■ https://www.youtube.com/embed/gQb2sN6UWkA

https://www.youtube.com/watch?v=gQb2sN6UWkA


Ultra-Low Temperature Cooler - A Product of Precision Manufacture

■ https://www.youtube.com/embed/-B2VcNy8dNs

https://www.youtube.com/watch?v=-B2VcNy8dNs


Ronald Regent Star War


Ronald Regent Star War



2.3.3.3 Thermal Viewers, Electronically Scanned (Pyrovidicon Imagers)Pyrovidicon imaging systems are not unlike home video-recording systems except that the camera tube is a pyroelectric vidicon (pyrovidicon) rather than a conventional vidicon. It records target radiation in the infrared rather than the visible spectrum. The significant difference is that the pyrovidicon has no dc response; that is, if the camera is not continuously panned over the target or the collecting beam is optically chopped, the image fades from the screen(pyroelectric elements) . This behavior is caused by the fundamentalphotoelectric response characteristics of the detector material. Aside from thetube, which is costly, and the lens, which is generally made of germaniumand also costly, these systems use commercially available televisionequipment and recording accessories.

Note: Although they are being replaced gradually by focal plane array imagers (see section 2.3.3.4), at the time of this writing, pyrovidicon imagersare still in wide use commercially. For this reason, the following operationaldescription is provided.


By comparison with other infrared imaging systems, the picture quality and resolution are good, approaching conventional television format. The thermalimage can be viewed or videotaped with equal convenience and no cooling isrequired. The requirement for continuous target panning can be made lessobjectionable by the ability to play back an image and freeze the frame fordetailed image inspection. Compact synchronous choppers that provideflicker-free performance and enhance image quality are incorporated in mostinstruments. Pyrovidicon systems do not intrinsically offer absolutemeasurement capability, but a thermal profile feature, available on some units,provides an analog of the center scan line displayed to the side of the image.Some models incorporate a spot-measuring sensor (addition photon detector sensor?) boresighted with the scanner and its measurement superimposed on the video display, along with a defining reticle in the center of the display.Software packages are offered that are specified to provide quantitative measurements by compensating for field variations and introducing temperature references.


Thermal resolution of pyrovidicon instruments is between 0.1°C and 0.2°C in panned mode (?) and between 0.2°C and 0.4°C (half as good) in chopped mode. Another useful feature available on some models integrates a video camera into the viewing channel so that simultaneous visual and thermalimages can be seen on a split-screen or in a fade in, fade out format. Although pyrovidicon displays are monochrome (black and white), some models incorporate colorizer accessories and image-processing software packages.Pyrovidicon systems are particularly suited to moving targets, airborne scanning, and distant measurements. They operate well in the 8.4 µmatmospheric transmission window. They are susceptible to a momentary lossof sensitivity from saturation phenomena, known as depoling, when suddenlyaimed at very hot targets with the aperture improperly open. The automaticrepoling circuits require about a 30-second restoration time, resulting in someoperator inconvenience. Operating costs are very low because no coolant isrequired, and common erasable videocassettes are used for recordingpurposes. Videotapes can be monitored on conventional television receivers.


2.3.3.4 Focal Plane Array (FPA) Imagers - Qualitative and Quantitative.In the mid 1980s, detector mosaics, or staring infrared focal plane arrays, were used successfully for military night vision Forward Looking InfraRed(FLIR) viewers and have since been made widely available for use incommercial thermal-imaging instruments. In an IRFPA imager, each detectorelement is assigned one display picture element and mechanical scanning iseliminated altogether. IR focal plane array (IRFPA) radiometers areadaptations of military and aerospace FLIRs but, unlike FLIRs, they aredesigned to allow measurement of the apparent temperature at the targetsurface and to produce quantitative as well as qualitative thermograms. Theyrepresent the most recent developments in FPA imagers. Althoughmeasurement-capable IRFPA imagers were promised as early as 1987,these capabilities were slow in arriving because of the complexity of the task.It was well into the 1990s before good quality measurement capabilitiesbecame available.


At the present time, most commercial manufacturers offer a wide choice ofhigh-resolution IRFPA imagers and radiometers. Today.s IRFPA imagers offer thermal resolution that is comparable to opto-mechanically scanned imagers (0.05°C to 0.2°C) and spatial resolution that is considerably better (1 mRad or better with standard optics). With inherently faster response, no moving parts, and superior spatial resolution, IRFPA imagers andradiometers have all but completely replaced opto-mechanically scanned imagers throughout the user community.

Keywords:■ IRFPA imagers and radiometers■ IRFPA (1) imagers and (2) radiometers■ Qualitative & Quantitative


Currently, most commercially available (1) measuring and (2) non-measuring IRFPA cameras use uncooled focal plane arrays of bolometric orpyroelectric/ferroelectric thermal detectors. Although detector cooling is notrequired, the detector arrays are temperature-stabilized by means of lowpower thermoelectric devices to ensure instrument stability.

(Bolometric, pyroelectric and ferroelectric are thermal detectors ≠photon detectors?)Although there are no scanning elements, pyroelectric FPAs require a mechanical chopper because they have no DC response.


For special applications where high speed, improved sensitivity, or spectral selectivity is required, cooled photo- detector arrays are used. These include platinum silicide (PtSi), indium antimonide (InSb), mercury-cadmium-telluride (HgCdTe) and, most recently, gallium arsenide (GaAs) quantum well infrared photo-detectors (QWIP), all of which require cooling. Detector cooling can be accomplished by any of several means, including TE (thermoelectric Peltier effect) coolers, compressed argon, refillable liquid nitrogen containers and, most recently, electric-powered Stirling-cycle nitrogen or helium coolers. Most of today.s commercially available cooled imagers are equipped with either a TE cooler or a compact, high-efficiency Stirling-cycle cooler. The Stirling-cycle cooler operates like a micro-miniaturized electric refrigerator.


DiscussionSubject: For special applications where high speed, improved sensitivity, or spectral selectivity is required, cooled photo- detector arrays are used. Question: Does thermal detector (≠ photon detector) applicable to spectral selectivity?


IRFPA imagers and radiometers.


2.3.3.5 FPA Imager Performance ComparisonsMost application needs can be fulfilled by means of selecting from among five categories of instruments available in today.s commercial thermal imagermarket. These include:1. Un-Cooled FPAs (the general purpose choice) 2. Mid-Range Infrared (MWIR) Indium Antimonide (InSb) or Platinum Silicide

(PtSi) FPAs3. High-speed, high-sensitivity photo-detector FPAs (for special applications)4. NIR (near-infrared) FPAs (for telecommunications, fiber optic, and laser

profiling applications)5. Special High-Temperature FPA Imaging Pyrometers (for special high-

temperature applications, such as furnace temperature monitoring)


■ Un-Cooled FPAs (the general purpose choice) (Bolometric, pyroelectric and ferroelectric are thermal detectors ≠photon detectors?)

Un-cooled IRFPA imagers, operating within the 7.14 µm region, are suitable for most applications in:• Predictive maintenance, condition monitoring• Buildings, roofs, and infrastructure• Process monitoring and control (except where there are high-speed or

spectral considerations)• Medical and biological studies• Materials evaluation and nondestructive testing (except for high-speed or

high-resolution applications)• Security, surveillance, night vision, search and rescue, firefightingTypical performance characteristics of imagers in this category are:• Temperature sensitivity (noise-equivalent temperature difference [NETD]):

0.08°C (80 milliKelvins) @ 30°C• Spectral range: 7.5 ~ 13 µm• Spatial resolution: 1.3 milliradian (320x240 element micro-bolometric FPA)• Frame repetition rate: 50/60 Hz


■ Mid-Range Infrared (MWIR) Indium Antimonide (InSb) or Platinum Silicide (PtSi) FPAs (these are photon detector?)

Cooled platinum silicide (PtSi) or indium antimonide (InSb) imagers are preferable where spectral selectivity at shorter wavelengths is important (such as in some manufacturing processes) or for high-temperature applications (such as furnace measurements).A typical imager in this category could have the following performance characteristics:• Temperature sensitivity (NETD): 0.07°C (70 milliKelvins) @ 30°C• Spectral range: 3.4.5 µm• Spatial resolution: 1.2 milliradian (256x256 element PtSi FPA)• Frame repetition rate: 50/60 Hz

InSb-based imagers have somewhat better thermal sensitivity than PtSi-based imagers and are somewhat more expensive.


■ High-speed, high-sensitivity photo-detector FPAs (for specialapplications)

For special applications involving high-speed phenomena, high thermal sensitivity, and processing flexibility at longer wavelengths, the detector of choice has become the gallium arsenide (GaAs) QWIP FPA.A typical imager in this category could have the following performancecharacteristics:• Temperature sensitivity (NETD): 0.02°C (2 milliKelvins) @ 30°C• Spectral range: 8.9 µm• Spatial resolution: 1.1 milliradian (320x240 element GaAs QWIP FPA)• Frame repetition rate: selectable from 50/60 Hz to 750/900 Hz


DiscussionSubject:MWIR: Cooled platinum silicide (PtSi) or indium antimonide (InSb) imagers are preferable where spectral selectivity at shorter wavelengths is important (such as in some manufacturing processes) or for high-temperature applications (such as furnace measurements).LWIR: For special applications involving high-speed phenomena, high thermal sensitivity, and processing flexibility at longer wavelengths, the detector of choice has become the gallium arsenide (GaAs) QWIP FPA.

Could the reasons for preferences/ selections for/ of SWIR be:■ Manufacturing processes requirements?

(selective transmissivity or specific temperature measurements)■ High temperature applications?What are the others?Could the reasons for preferences/ selections for/ of LWIR be:■ Manufacturing processes requirements?

(selective transmissivity or specific temperature measurements)■ High thermal sensitivity?■ High responsivity?


Figure 3.2: Response Curves of Various Infrared Detectors


IR detector spectral detectivity



http://www.intechopen.com/books/advances-in-optical-fiber-technology-fundamental-optical-phenomena-and-applications/sige-based-visible-nir-photodetector-technology-for-optoelectronic-applications





http://pe2bz.philpem.me.uk/Lights/-%20Laser/Info-999-LaserCourse/C04-M08-OpticalDetectors/mod04_08.htm



http://www.intechopen.com/books/optoelectronics-advanced-materials-and-devices/advances-in-infrared-detector-array-technology


■ NIR (near-infrared) FPAs (for telecommunications, fiber optic, and laser- profiling applications)

A typical imager in this category could have the following performance characteristics:• Radiant sensitivity Noise Equivalent Irradiance (NEI): 1x1010 ph/cm2/sec

(Because the applications for this type of instrument are concerned with measuring radiant power rather than temperature, sensitivity is expressed in NEI rather than NETD.)

• Spectral range: 900 - 1700 nm (0.9 - 1.7 µm)• Spatial resolution: 1.2 - 1.6 milliradian (320 x 256 element InGaAs FPA)• Frame repetition rate: 30 Hz


■ Special High-Temperature FPA Imaging Pyrometers (for special high-temperature applications, such as furnace temperature monitoring)

A typical imager in this category could have the following performance characteristics:• Temperature sensitivity (NETD):• Spectral range: 700.1100 nm (0.7.1.1 µm) selected filters for ranges from

600°C to 2400°C• Spatial resolution: 1.2.1.6 milliradian (776x484 near-infrared FPA detector)• Frame repetition rate: 30 Hz


2.4 Thermal Imaging Diagnostic SoftwareThe new generation of thermal imagers features image processing capabilities that can be generally categorized into four groups. Applicationsfor thermal imaging often require the use of more than one of these four groups:• Quantitative thermal measurements of targets• Detailed processing and image diagnostics• Image recording, storage, and recovery• Image comparison


2.4.1 Quantitative Thermal Measurements of Targets This is the temperature value of any point (or all points) on the target surface. For true radiance measurements, the system throughput attenuation must betaken into consideration as well as losses through the measurement medium(atmosphere, in most cases). For true temperature measurement, the targeteffective emissivity must also be considered. In order to provide true radiancevalues, the system calibration constants are fed into the computer on initialsetup and a system of prompts assures the operator that changes in aperturesettings, target distance, interchangeable lenses, etc. are fed into thekeyboard each time a change in operating condition occurs. For truetemperature values, it is necessary for an effective emissivity value to beinserted by the operator. The temperature readings that are then displayedassume that the entire target surface effective emissivity is equal to thisinserted value. In operation, a color scale (or monochrome gray scale) isprovided along one edge of the display with a temperature showncorresponding to each color or gray level.


The operator can also place one or more spots or cross hairs on the image and the temperature value of that pixel will appear in an appropriate locationon the display. Some systems allow the assignment of several different effective emissivities to different areas of the target, as selected by the operator, with the resulting temperature correction.

One system, developed for the thermal imaging of semi-conductor devices and other micro-targets, offers a spatial effective emissivity correction basedon the actual measurement of the surface effective emissivity of the target. Bymeans of a precision-controlled heated sub-stage, the operator heats theunpowered device to two known temperatures in sequence. At eachtemperature, a radiance image is recorded. Using the known temperature andthe known radiance for two temperatures, the effective emissivity matrix iscomputed, pixel by pixel, and stored. This matrix is subsequently used tocorrect the powered radiance image of that specific device and to provide atrue temperature thermogram.


2.4.2 Detailed Processing and Image Diagnostics Detailed processing and image diagnostics is a phrase that describes the capability of the computer to analyze each pixel of the thermal image and topresent information in a wide variety of qualitative and quantitative forms for the convenience of the user. Some (by no means all) of these forms are discussed below. In addition to the spot meter capability discussed previously, the operator might call for profile displays. The analog trace (in x, y, or both) of the lines on the image that intersects at the selected spot will then appear at the edge of the display.

Some systems allow the operator to display as many as seven sets of profiles simultaneously. Profiles of skew lines can also be displayed on some systems. The operator can draw areas on the display in the form of circles, rectangles, or point-to-point free forms. These areas can be shifted, expanded, shrunken, or rotated. They can be used to blank out or analyze portions of the image. On command, the computer will provide a detailed analysis of the entire image or the pixels within the area including maximum, minimum, and average values, number of pixels, or even a frequency histogram of the values within the area.


Although a standard (default) color scale is usually provided by the manufacturer, color scales can be created by the operator in almost infinitevariety from as many as 256 colors stored within the computer. Zoomfeatures allow the operator to expand a small area on the display for closerexamination, or to expand the colors for a small measurement range. Auto-cale features provide the optimum display settings for any image that isselected. 3-D features provide an isometric thermal contour map of the targetfor enhanced recognition of thermal anomalies.


2.4.3 Image Recording, Storage, and Recovery This is the capability to index, record, and retrieve images and data. Most commercial thermal imaging systems offer limited image storage by means ofon-board removable floppy disks, PCMCIA cards, or other reusable storagedevices. Limited image analysis software can also be incorporated into thefield-portable instrument. Images can be stored from a frozen-framethermogram of a live target on operator command, or the operator can set upan automatic sequence and a pre-set number of images will be stored at pre-et time intervals. Most systems also offer VCR options so that an entiremeasurement program can be recorded on videotape. These videotapes canthen be played back into the system and images can be stored on playbackfrom videotapes. Stored images can be retrieved from storage and displayedat the operator.s command.


Diagnostic software is generally offered separately from the basic imaging instrument, although some limited diagnostic software is usually included in the basic package for on-site analysis. The current trend by manufacturers is to offer more and more onboard image analysis capabilities but, for extensive image storage and analysis, the images are more often downloaded from the cards to computers with large storage capacities and memory. The extensiveimage and data analysis software is resident on the computer hard drive.


2.4.4 Image Comparison Image comparison is a very significant capability in that it allows the automatic comparison of images taken at different times. The computerallows the operator to display two images, sideby- side or in sequence, and tosubtract one image from another, or one area from another, and to display apixel-by-pixel difference thermogram. This provides the capability forarchiving thermal images of acceptable components, assemblies, andmechanisms, and for using them as models for comparison to items producedsubsequently. Subtractive routines produce differential images illustrating thedeviation of each pixel (picture element) from its corresponding model. Imageaveraging allows the computer to accumulate several scan frames and todisplay the average of these frames. Comparison (subtraction) of images canbe derived from two real-time images, two stored images, or a real-time and astored image.


2.5 Recording, Hard Copy & Storage of Images and DataThermal image recording and storage has evolved dramatically from Polaroid® instant photos of the display screen, to magnetic storage andarchiving of images and data (such as labels, dates, conditions ofmeasurement, and instrument settings), to the instant digital image storagecapabilities incorporated into most of today.s thermal imagers. Hundreds ofimages can be recorded in the field and stored on removable, reusablememory cards. The problem of making a hard copy of the displayed imagehas also been solved with the advent of miniaturized digital cameras andphoto-quality color printers that can print high-resolution images directly fromcamera outputs or from downloaded images and process them on thecomputer. Thermal images are saved in any one of several digital imageformats such as .bmp, .tif, and .jpeg for archiving and future analysis.Corresponding visible reference images of the same targets can be recordedin the same format by digital cameras. Some manufacturers have integrateddigital visible photo-recording capabilities into their new models of thermalimagers. Both thermal and visible images can be printed independently or aspart of a detailed report, as described in Section 2.6.


2.6 Report Preparation Stimulated by the demand of the predictive maintenance community for timely and comprehensive reporting of the findings of IR surveys, mostmanufacturers of thermal imagers have developed comprehensive reportpreparation software. These packages provide templates that allow thethermographer to prepare reports in standard word processor formats (suchas Word for Windows®), into which digital thermal images and visible imagesimported from various imaging radiometers and digital cameras, can bedirectly incorporated. Additional diagnostic software is customarily provided inthese packages so that post-analysis and trending can be added to the report.

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

Table 2-1 Instrument Characteristics

Manufacturers Models Characteristics

Point-Sensing

Probes and IR Thermocouples

Dickson D161 Various models -40°C to +500°C, hold button LCD display, laser pointer, emissivity control (e set).

Exergen SnakeEye and Smart IRt/c series

Wide range of infrared thermocouples with standard and custom configurations.

Horiba IT580 32°F to 572°F, 0�300°C, LCD display, e set, hold button.

Ircon Ultimax Jr -40°C to +500°C, e set, LCD display, laser aiming spectral range: 8�14 µm.

Linear QuickTEMP, C500, C1600, and C1700 series

-18°C to +315°C, QuickTEMP has LCD display and optional laser pointer, C500 connects to a multi-meter, C1600 has multiple models with various ranges, some models have e set. C1700 reads heat flow in BTU/sq ft/hr.

Mikron Model M50, M500 IR thermocouples

Various temperature ranges from 0°C �500°C.

OS36, OS37, and OS38 series IR thermocouples

Modular and hand-held infrared thermocouples, various ranges. Omega

OS200, 500, 600, 88000 and OS20 series

Close-focus probes with LCD readouts.

Raytek Raynger IP series A family of plug-in accessory probes that convert a digital multi-meter (DMM) or thermocouple meter into a close focus, non-contact IR thermometer. -18°C to 250°C, 8�14 µm.

Telatemp TH1-440S and TemptestR Ranges from -50°C to +500°C, LCD display, LED aiming available e set.

2-16

EPRI Licensed Material

A Compendium of Commercial Infrared Sensing and Imaging Instruments

Table 2-1 (cont.) Instrument Characteristics


Point-Sensing, Hand-Held

Dickson D160 series Various models -40°F to +950°F, -45°C to +538°C, hold button LCD display, laser pointer, emissivity control (e set).

Everest Model 100.3ZL and ZH Two models from -30°C to +1100°C, LCD display, analog output, aiming light, peak sampler, differential available. Rechargeable battery.

E series Microscanner -50°F to +550°F or -5°C to +285°C, one piece with LED bar graph and numerical scale, high- and low- hold feature, audio alarm.

Exergen

DX series Close-up sensor with reflective cone for target emissivity correction; ranges from -4.5°C to +871°C, digital read-out.

Ircon ULTIMAX series Various models from -30°C to +3000°C, thru-the-lens sighting, spectral ranges 0.65, 0.96�1.06, and 8�13 µm (some models are ratio-pyrometers), LCD display, analog and RS-232 outputs, replaceable batteries.

Irtronics Sniper series Laser or visual sights, 8 wavelengths, 0�3000°F/C.

Land Cyclops series (Minolta), 33, 41, 52, Compac 3

High- and low-temperature (to 5500°C), small targets, variable focus, reticle display, Compac 3 has low-temperature, fixed-focus, thru-lens sight.

Linear LT, LTL, and LTS series -29°C to 1093°C, 30:1 or 60:1 optics, laser pointer or non-parallax sight available, 1% accuracy. F-C switch, LCD display.

Mikron M90, M100, M101, M102, and M103 series

Various models, including ratio pyrometers, from -40°C to +3000°C, LCD displays, options: laser aiming light, telescope, e set, various FOVs.

Omega HHM, OS520, OS631, OS900 series, others.

Wide range of models with ranges from -18°C to 2482°C, options include laser aiming, through-the-lens viewing, BTU read-out.

Palmer-Wahl Heat Spy DHS-100 series, DHS-200 series, DHS-20 series, DHS-34 series, DHS-53 series, HAS-201 series

Various models from -40°C to +1760°C, analog, LCD, and LED displays. Series DHS has e set, peak-hold, and various FOVs, including telescopic. Through-the-lens sighting and laser aiming features are available.

2-17




Point-Sensing, Hand-Held (cont.)

Pyrolaser laser pyrometer Ranges from 600°C�3000°C, uses laser to measure reflectance and correct for emissivity, thru-lens sight, rechargeable battery.

Pyrometer

Pyrofiber series Fiber-optic-coupled, ranges from 600°C�3000°C, uses laser to measure reflectance and correct for emissivity, thru-lens sights, rechargeable battery.

Raytek Raynger MiniTemp, MX, 3I, IP, ST series

Various models from -30°C to 900°C, dual LCD display, hi-lo alarms, RS232/analog output, datalogger, max-min-mean, differential, laser aiming available.

Teletemp INFRAPRO 3 and 4 Various models from -32°C to +760°C, rechargeable battery, e set, LED display. Laser aiming and scope available.

Williamson 600, Viewtemp, Truetemp Viewtemp is 25°C to 1650°C, LED inside reticle, e set, and rechargeable battery. Truetemp is 2-color, 550°C to 2200°C. 600 has analog display, various ranges from 75°F to 3000°F.

Point-Sensing On-line

E2 Technology (now part of Mikron)

Heat switch (Solar TD100 and Meteor 300), Pulsar and Quasar Series Photon, Nova, Comet, other models

Various heat pulse switches and ruggedized models from 260°C�1650°C, including ratio pyrometers.

Everest 3000 series, 4000 series Ranges from -40°C to +1100°C, spot size available down to 0.01". Multiplexes up to 8 heads through electronics.

Horiba IT-230 0°C�300°C, multiple ranges, digital output with e set, multiple control features.

Ircon Modline 3 and 4 series, SA, SR, and 1100 Series, Javelin, Mirage and MiniIRT series, others.

Various models and accessories, -18°C to +1375°C, integrated, fixed-focus, two-wire transmitters, spectral selection. Various models of two-piece, -18°C to 3600°C with thru-lens sights, LCD display, spectral selection (including ratio pyrometers), and control and output options. IR pulse switches and fiber optic-coupled heads.

Irtronics Argosy, Spartan, others Various ranges from 30°C to 3000°C, spectral selection, telephoto, multi-zones, fiber-optic-coupled heads available.

2-18





Point-Sensing On-line (cont.)

Land System 4, SOLO, UNO, CF series

Wide selection of instruments, 120°C to 2600°C, two-color, spectral selection, fiber optic, telephoto lens option, modular, many accessories. SOLO is a line of two-wire thermometers.

Linear TM1000 series, M series, MX series

TM 1000 series are modular sensors, ranges from 0°C�2000°C, spectral selection, thru-lens sights, linearized outputs, many control options. M series are lower cost, fewer options. MX series are customized units with high-temperature and high-resolution options.

M67 series Modular, ranges from 0°C�1650°C, spectral selection, fixed- and variable- focus, thru-lens sights, many accessories.

M68, M668, M600, M680 series

Fiber optic, one color and ratio pyrometers, ranges from 250°C�3500°C.

M190 series Two-piece, 0°C�3000°C, spectral selection, fixed- and variable-focus, thru-lens sights, many accessories.

Mikron

M77/78 M77 is two-color, M78 is two-color, fiber-optic-coupled.

Omega OS36, 39, 42, 65, 101, 1592 series, many others

Wide range of sensors including fiber-optic-coupled, ranges from -45°C to +3700°C.

Thermalert IT series Thermalert ET series

Various models, -15°C to +538°C, two-piece, small sensing head. Various models, -15°C to +1650°C, integrated sensing head, e set, spectral selections, processing options.

Thermalert III series Various models, -15°C to +3000°C, two-piece, LED display, e set, spectral selections, processing options.

Thermalert IV series Various models, -15°C to +3000°C, two-piece, dual LED display, set points, e set, processing options, spectral selections.

Raytek

Compact Series Intended for low-cost, multiple-sensor applications.

2-19




Point-Sensing On-line (cont.)

Raytek (cont.) Marathon Series For high-temperature applications, up to 3000°C, 1 µm spectral region, include ratio pyrometer and fiber-optic-coupled models.

Quantum Focus RM2 Infrared microscope. Spot size down to 0.0003".

PRO 80, PRO 90, PRO 100, PRO 200

Various models including two-color, fiber-optic-coupled, 30°C�2500°C, spectral selections, many accessories.

Williamson

TempMatic 4000, FiberView 5000, 500, 700, and 1000 series

Various models, ranges from 30°C�2500°C, two-wire, fixed-focus transmitters and two-wire, fixed-focus single wavelength and ratio pyrometers, some fiber-optic-coupled models.

Line Scanners

HGH (France) ATL-100 narrow angle (6 deg) ATL-020 wide angle (90 deg)

Modular thermoelectrically cooled, high-resolution analog and digital outputs, operates with control system host computer.

Ircon ScanIR II series Modular thermoelectrically cooled and un-cooled detectors for various spectral bands from 1 to 5.1 µm, high-resolution analog and digital outputs, visible laser alignment feature, operates with host computer.

Infrared Solutions IR ScanPro 1000 Scanner based on no moving parts, un-cooled 120-element thermoelectric linear array. Extensive computer interface.

Landscan LS Series opto-mechanically scanned

Modular, adjustable scan rate, six models with wavelengths from 1 to 5 µm, temperature ranges from 70°C�1400°C, high-resolution analog and digital outputs, operates with control system host computer.

Land

ScanTemp ST Series opto-mechanically scanned

Low cost, adjustable scan rate, eight models with wavelengths from 1 to 14 µm, temperature ranges from 0°C�1400°C, analog and digital outputs, operates with control system host computer.

2-20





Line Scanners (cont.)

Mikron MikroLine series, 250, 2128, 2256

128-, 160-, or 256-element arrays of PbSe, pyroelectric or GaAs and other detectors, temperature ranges of 0°C�1300°C, spectral ranges of 1.4�1.8 µm, 3-5 µm, 4.8�5.2 µm, and 8�14 µm, frame rates up to 18 kHz, full-process-analysis software.

Pyrometer ThermATrace Un-cooled, provides composite visual image and IR scan line superimposed, portable, rechargeable battery, photo-recording only.

Raytek CS-100, GS-100, TF-100, TIP-450 (all using the MP-50 Thermalert line scanner)

Each system for a different process application, modular thermoelectrically cooled, high-resolution analog and digital outputs, various wavelengths, operate with integral control system or host computer.

Thermographic

Opto-Mechanically Scanned Imaging Radiometers

Bales BSI TIP Very high-resolution desk-top imager with liquid nitrogen cooling, 2�12 µm, TFOV 20x30 deg, extensive on-board, real-time diagnostic software, advanced capability for variable frame rate, multiple simultaneous images. Part of pulsed multi-mode inspection system.

Compix PC2000 and 2000/e

PC2100 and 2100/e

TE-cooled single-element PbSe (3�5 µm) with PC card module to convert IBM-based desktop and notebook computers to thermal imagers, slow scan (10 seconds and 15 seconds per frame) 244x193 pixel image. 2100 series has magnifier lens for microscope resolution down to 0.002 inch.

CMC-Cincinnati Electronics (also markets AVIO)

AVIO TVS Series TE-cooled and Stirling-cycle cooled models featuring 10-element InSb, 3�5 µm, 10degVx15degH TFOV, lightweight and portable with on-board LCD color monitor, accessories.

Infrared Solutions IR SnapShot (also sold by Ircon as DIGICAM-IR)

120-element, un-cooled thermoelectric array for 8�12 µm operation, mounted on slide-mechanism for single image one-second frame. Extensive diagnostic software, remote operation capability.

2-21




Opto-Mechanically Scanned Imaging Radiometers (cont.)

Jenoptik Varioscan series Stirling-cycle cooled, liquid nitrogen cooled, and TE-cooled HgCdTe detector models for 8�12 µm and 3�5 µm performance, 30°x20° FOV slow-scan, high-sensitivity, extensive diagnostic software.

Land Cyclops T135 Camcorder-configured reflective scanner using TE-cooled, 12-element HgCdTe, 3�5 µm, 25 f/s, 16x16deg TFOV, monochrome viewer, separate image processor available.

FPA Thermal Viewers (Non-Measuring)

AIM µ Cam, FS, and FL FLIR families

Modular, building block cameras using cooled HgCdTe, GaAs QWIP and PtSi FPAs from 128x128 element to 640x486 element.

BAE MicroIR Un-cooled 320x240 element micro-bolometric FPA imager module in a weatherproof, ruggedized housing.

CMC-Cincinnati Electronics

Nightmaster, Night Conqueror, others

Many models of Stirling-cycle cooled 160x120, 256x256, and 640x512 element InSb FPA imagers (3�5 µm) for a wide variety of military, search, and surveillance applications.

Electrophysics PV-320 Un-cooled barium-strontium-titanate (BST) IRFPA imager, 2�14 µm or 0.6�20 µm 320x240 element array, 60 Hz frame rate, quantifiable option.

ThermaCAM E series Un-cooled miniaturized (less than 1.5 lbs) 160(H)x120(V) element micro-bolometer FPA, portable, battery-powered, 7.5�13 µm, laser aimer, non-measuring version.

FLIR

ThermoVision 1000, Sentry and Ranger; MilCAM SAFIRE, UltraFORCE, SeaFLIR, others

High-resolution, Stirling-cycle cooled InSb and PtSi, (3�5 µm) QWIP (8�9 µm) selectable TFOV-thermal viewers for military, law enforcement, air and sea, and other security and surveillance applications.

Guangzhou SAT SAT � HY600 Un-cooled amorphous silicon micro-bolometer 320(H)x240(V) element FPA, 8�14 µm.

2-22





FPA Thermal Viewers (Non-Measuring) (cont.)

Alpha NIR Miniaturized, 320x256 element InGaAs FPA, 900�1700 nm, for telecommunication, fiber optic, and laser-profiling applications.

Alpha Miniaturized, 160x128 element micro-bolometer FPA, 7.7�13.5 µm.

Merlin Family of imagers offering 320x256 element FPAs in four spectral bands: InGaAs (0.9�1.68 µm un-cooled), InSb (1.0�5.4 µm Stirling-cycle cooled), GaAs QWIP (8�9 µm Stirling-cycle cooled), and micro-bolometer (7.5�13.5 µm un-cooled).

Phoenix Family of imagers offering 320x256 and 640x512 element FPAs in three spectral bands: InGaAs (0.9�1.7 µm un-cooled), InSb (2�5 µm and GaAs QWIP (8�9.2 µm Stirling-cycle cooled).

Indigo

Omega Miniaturized, 160x128 element micro-bolometer FPA, 7.7�13.5 µm.

Infrared Solutions Modular 160 120x160 pixel un-cooled micro-bolometer FPA in miniaturized (three-inch cube) module for 8�14 µm operation.

IRISYS IXS 9004 Very low-cost portable, battery-powered viewer using un-cooled 16x16 element pyroelectric FPA, 8�14 µm spectral region, connects to IBM PC and includes image and color display software.

Marconi Argus Series Firefighter thermal imagers.

Mine Safety Appliance Corp.

VideoTherm 2000 Un-cooled 320x240 element pyroelectric FPA hand-held viewer with added measurement capability by means of boresighted radiation thermometer, monochrome or color display (8�14 µm).

Raytheon PalmIR-250 Un-cooled ferroelectric 320x240 FPA, 7�14 µm, battery-powered portable viewer, monochrome display.

2-23




FPA Thermal Viewers (Non-Measuring) (cont.)

Raytheon (cont.) Sentinal Un-cooled micro-bolometer 320x240 element FPA 8�14 µm, battery-powered portable viewer, monochrome display.

Santa Barbara Focal Plane

Various Models High-resolution front-end detector and optics for integration into user's system, based on liquid nitrogen-cooled, 128x128 element 256x256, 320x240, 320x256, 640x480, and 512x512 element InSb FPA (focal plane array) detectors, 1�5 µm.

US Infrared THERMOviewer Portable, battery-powered, un-cooled barium-strontium-titanate (BST) 320x240 element IRFPA imager, 2�14 µm spectral range, 60 Hz frame rate, boresighted IR thermometer provides spot measurement reference, color display, aimed at low-cost PdM applications.

Wuhan IR920, 922, and 923 Un-cooled micro-bolometer 320(H)x240(V) element FPA, 920 has image radio transmitter and receiver. 922 is helmet-mount, 923 is long-range monitoring/surveillance camera.

FPA Imaging Radiometers (Measuring)

Cedip Jade MW

Jade LW

Jade UC

Stirling-cycle cooled 320x256 element FPA MCT or InSb, 3�5 µm, extensive diagnostic software.

Stirling-cycle cooled 320x256 element FPA MCT, 7.5�9.6 µm, extensive diagnostic software.

Un-cooled 320x240 micro-bolometer FPA, 8�14 µm, extensive diagnostic software.

CMC-Cincinnati Electronics

TVS8500 Stirling-cycle cooled 256x256 element InSb FPA, 3�5 µ, 13.7degVx14.6degH TFOV, multiple-temperature measurement on multiple-selected pixels, emissivity compensation, lightweight and portable with on-board LCD color monitor, accessories.

2-24





FPA Imaging Radiometers (Measuring) (cont.)

ThermaCAM PM390 Stirling-cycle cooled PtSi 256x256 element FPA, portable battery-powered, 3.4�5 µm, integral display, extensive diagnostic software.

ThermaCAM E2 Un-cooled miniaturized (less than 1.5 lbs) 160(H)x120(V) element micro-bolometer FPA, portable, battery-powered, 7.5�13 µm, LCD display, laser aimer, extensive diagnostic software.

ThermaCAM P40 ThermaCAM P60

Un-cooled high-sensitivity micro-bolometer 320(H)x240(V) element FPA, portable, battery-powered, 7.5�13 µm, integral or LCD display, extensive diagnostic software. P60 has improved sensitivity, laser aimer, added LCD color display.

ThermaCAM PM545

ThermaCAM PM675

ThermaCAM PM695

Un-cooled micro-bolometer 320(H)x240(V) element FPA, portable, battery-powered, 7.5�13 µm, integral or LCD display, extensive diagnostic software.

ThermaCAM SC300 Un-cooled micro-bolometer 160(H)x120(V) element FPA, 7.5�13 µm, extensive diagnostic software, low-cost research camera.

ThermaCAM SC500 Un-cooled micro-bolometer 320(H)x240(V) element FPA, 7.5�13 µm, extensive diagnostic software, for high-performance scientific applications.

ThermaCAM SC1000 Stirling-cycle cooled PtSi 256x256 element FPA, portable battery-powered, 3.4�5 µm, integral display, extensive diagnostic software, for high-performance scientific applications.

ThermaCAM SC2000 Un-cooled micro-bolometer 320(H)x240(V) element FPA, portable, battery-powered, 7.5�13 µm, integral display, extensive diagnostic software, for high-performance scientific applications.

FLIR

ThermaCAM SC3000 Stirling-cycle cooled GaAs QWIP 320(H)x240(V) element FPA, 8�9 µm spectral response, high-speed, up to 900 Hz, high-sensitivity, broad dynamic range, extensive diagnostic software, for high-performance scientific applications.

2-25





ThermoVision 160M Un-cooled micro-bolometer 160(H)x120(V) element FPA, 7.5�13 µm, extensive diagnostic software, many lenses available, including microscope, low-cost industrial automation camera.

FLIR (cont.)

Thermovision 320 series

Un-cooled micro-bolometer 320(H)x240(V) element FPA, 7.5�13 µm, extensive diagnostic software, for multiple-process monitoring and machine vision applications, high-performance industrial automation cameras.

Guangzhou SAT SAT � HY6000 and 6800 Un-cooled micro-bolometer 320(H)x240(V) element FPA, 8�14 µm, extensive diagnostic software, and wide selection of field-interchangeable lenses.

Alpha Miniaturized, 160x128 element micro-bolometer FPA, 7.7�13.5 µm. Measuring capability by means of added diagnostic software.

Merlin Family of imagers offering 320x256 element FPAs in four spectral bands: InGaAs (0.9�1.68 µm un-cooled), InSb (1.0�5.4 µm Stirling-cycle cooled), GaAs QWIP (8�9 µm Stirling-cycle cooled), and micro-bolometer (7.5�13.5 µm un-cooled). Measuring capability by means of added diagnostic software.

Phoenix Family of imagers offering 320x256 and 640x512 element FPAs in three spectral bands: InGaAs (0.9�1.7 µm un-cooled), InSb (2�5 µm Stirling-cycle cooled) and GaAs QWIP (8�9.2 µm Stirling-cycle cooled). Measuring capability by means of added diagnostic software.

Indigo

TVS-620 Un-cooled, 320x240 element micro-bolometer FPA, 8�14 µm, portable hand-held unit with integrated display, software, removable PC card image storage.

IRISYS IRI 1001 Very low-cost portable, battery-powered using un-cooled 16x16 element pyroelectric FPA, 8�14 µm spectral region, connects to IBM PC and includes measurement and color display software.

Infrared Solutions Modular 160 120x160 pixel un-cooled micro-bolometer FPA in miniaturized (three-inch cube) module for 8�14 µm operation.

Ircon Stinger Un-cooled pyroelectric 320(H)x240(V) element FPA, spectral range: 8�14 µm, extensive diagnostic software, for multiple-process monitoring and machine vision applications.

2-26






HGH Source of AVIO and CMC Cincinnati Cameras.

Jenoptik VarioTHERM series Stirling-cycle cooled, 256x256 PtSi FPA. 3.4�7 µm, portable, battery-powered, extensive diagnostic software.

Cyclops PPM Radiometric version of the Raytheon PalmIR 250 (same as Raytheon PalmIR 500D) modified by Electrophysics and sold by Land); 320(H)x 240(V) un-cooled BST FPA, 0°C�300°C, PC memory card.

Land

FTI-6 FPA imager with on-board diagnostic software.

MikroScan 5102 Stirling-cycle cooled 255x223 element HgCdTe FPA, 8�12 µm, line- or battery-powered portable viewer, on-board display, and flip-up LCD option.

MikroScan 5104 TE-cooled 255x223 element HgCdTe FPA, 3�5.2 µm, line- or battery-powered portable viewer, on-board display, and flip-up LCD option, spectrally selective models available for working with glass or flame.

MikroScan 5104i TE-cooled 255x223 element HgCdTe FPA, 3�5.2 µm, line-powered fixed-mount camera for on-line process monitoring and control.

MikroScan 7102i Un-cooled micro-bolometer 320x240 element FPA 8�14 µm, fixed-mount camera for on-line process monitoring and control.

MikroScan 7200 Lightweight, un-cooled micro-bolometer 320x240 element FPA 8�14 µm, battery-powered portable viewer, on-board display, and flip-up LCD option.

MikroScan 7515 Lightweight, un-cooled micro-bolometer 320x240 element FPA 8�14 µm, battery-powered portable viewer, on-board display, and flip-up LCD option, upgrade version of the 7200 with remote control option and analysis and report-writing software.

Mikron

M9000 series Imaging Pyrometer, un-cooled 776x484 near infrared FPA detector for high-temperature targets, multi-range with selected filters from 600°C to 2400°C, extensive diagnostic software integrates PC with color monitor.

2-27





Nikon (see HGH) Laird S270 and 3A series 537x505 and 768x494 element Stirling-cycle cooled PtSi FPAs, (3�5 µm) battery- and line-powered, ac adapter, interchangeable color display available. Multiple temperature measurement on multiple selected pixels, emissivity compensation.

Quantum Focus Instruments

InfraScope, InfraScope II Lab-operated imager for microelectronics applications, features liquid nitrogen-cooled InSb FPA, automatic emissivity compensation, full field temperature measurement, spatial resolution down to 2.5 µm, 60 Hz frame rate.

Radiance HSX

Stirling-cycle cooled 256x256 element InSb FPA, 3�5 µm, 60 Hz frame rate (Radiance HS has selectable frame rates up to 1400 Hz, optional displays, extensive thermal analysis software).

Raytheon

PalmIR 500D Radiometric version of the Raytheon PalmIR modified by Electrophysics and sold by Land); 320(H)x240(V) un-cooled BST FPA, 0°C�300°C, PC memory card.

Thermoteknix VisIR Un-cooled micro-bolometer 160(H)x120(V) element FPA, portable, battery-powered, 7.5�13 µm, integral LCD display, image storage, radio link, extensive diagnostic software.

Thermal Wave Imaging EchoTherm

ThermoScope

EchoTherm is an NDE system, built around a selection of high-speed FPA imagers. Includes flashlamp sources, power supplies, synchronizing electronics, and analytical software for TRIR. ThermoScope is a field-portable version.

Wuhan IR912 and 913 Un-cooled micro-bolometer 320(H)x240(V) element FPA, portable, battery-powered, 8�14 µm, 912 and 913 have fold-out LCD display, extensive diagnostic software.

2-28



Table 2-2 Equipment Manufacturers

Company Name Mailing Address Phone Number Web Site or E-mail

AIM Infrarot-Module GmbH Theresienstrasse 2 D-74072 Heilbron, Germany

+49-7131-6212-460 www.aim-ir.com

BAE, Information and Electronic Warfare Systems

2 Forbes Rd., LEX01-112 Lexington, MA 02421-7306

(781) 863-3684 www.iews.baesystems.com/iris

Bales Scientific Inc., div. CTI 1620 Tice Blvd. Walnut Creek, CA 94595

(510) 945-0144 www.balesscientific.com

CEDIP, SA 19 Blvd. G. Bidault F-77183 Croissy Beaubourg, France

(+33) 01 60 37 01 00 [email protected]

CMC-Cincinnati Electronics Corp. Div BAE Systems

7500 Innovation Way Mason, OH 45040-9699

(513) 573-6744 www.cmccinci.com [email protected]

Compix 15824 SW Upper Boone�s Ferry Road Lake Oswego, OR 97035

(503) 639-8496 www.compix.com [email protected]

The Dickson Company 930 S. Westwood Ave. Addison, IL 60101

(800) 323-2448 http://www.dicksonweb.com/

Electrophysics Corp. 373 Rte 46 West, Building E Fairfield, NJ 07004

(973) 882-0211 (800) 759-9577

www.electrophysicscorp.com

E2Technology Corporation (part of Mikron)

4475 Dupont Court, Unit 9 Ventura, CA 93003

(805) 644-9544 www.e2t.com [email protected]

Everest Interscience Corp. 1891 N. Oracle Rd. Tucson, AZ 85705

(520) 792-4545 (800) 422-4342

http://www.everestinterscience.com/ [email protected]

Exergen Corporation 51 Water St. Watertown, MA 02472

(617) 923-9900 (800) 422-3006

www.exergen.com [email protected]

2-29

http://www.aim-ir.com/

http://www.iews.baesystems.com/iris

http://www.balesscientific.com/

mailto:[email protected]

http://www.cmccinci.com/

http://www.compix.com/

http://www.dicksonweb.com/

http://www.electrophysicscorp.com/

http://www.e2t.com/

http://www.everestinterscience.com/


http://www.exergen.com/


Table 2-2 (cont.) Equipment Manufacturers


FLIR Systems, Inc. World Headquarters

16505 SW 72 Ave. Portland, OR 97444

(503) 684-3771 (800) 322-3731

www.flir.com

FLIR Systems, Boston Formerly Inframetrics

16 Esquire Road N. Billerica, MA 01862

(978) 670-5555 www.flir.com

FLIR Systems AB, Sweden Formerly AGEMA

Rinkebevägen 19, PO Box 3 SE182-11 Danderyd, Sweden

+(46) 8 753 2500 www.flir.com

Guangzhou SAT Infrared Technology Co., Ltd.

10 Diongjiang Ave., Guangzhou Econ. & Tech. Dev. District, China 51073

+86-20-82229925 +86-20-82227947

www.sat.com.cn [email protected]

HGH Systemes Infrarouges 3, rue du Saule-Trapu, F91300 Massy, France

(33-1) 60110141 http://www.hgh-infrarouge.fr/ [email protected]

Horiba 17671 Armstrong Ave. Irvine, CA 92614

(800) 446-7422 (949) 250-4811

www.horiba.com [email protected]

Indigo Systems Corp. 5385 Hollister Ave. #103 Santa Barbara, CA 93111

(805) 964-9797 www.indigosystems.com

Infrared Solutions, Inc. 3550 Annapolis Lane North, Suite 70 Plymouth, MN 55447

(763) 551-0038 [email protected]

IRCON Instruments 7300 N. Natches Ave. Niles, IL 60714

(847) 967-5151 (800) 323-7660

www.ircon.com

IRISYS Towcester Mill, TowcesterNorthants NN12 6AD, UK

+44(0)1327 357824 www.irisys.co.uk [email protected]

Irtronics 132 Forest Blvd. Ardsley, NY 10502

(914) 693-6291 No e-mail address

JENOPTIK, GmbH Goschwitzer Strabe 25, D-07745 Jena, Germany

+49(3641) 65 33 11 www.jenoptik.de [email protected]

2-30

http://www.flir.com/



http://www.sat.com.cn/


http://www.hgh-infrarouge.fr/


http://www.horiba.com/


http://www.indigosystems.com/


http://www.ircon.com/

http://www.irisys.co.uk/


http://www.jenoptik.de/





Land Infrared 10 Friends Lane Newtown, PA 18940-1804

(215) 504-8000 www.landinst.com [email protected]

Linear Laboratories 42025 Osgood Rd. Fremont, CA 94538

(800) 536-0262 www.linearlabs.com

Marconi Electronic Systems 4 Westchester Plaza Elmsford, NY 10523

(914) 592-6050 (800) 342-5338

www.marconitech.com [email protected]

Mikron Instrument Co., Inc. 16 Thornton Road Oakland, NJ 07436

(201) 405-0900 (800) 631-0176

www.mikroninst.com

Mine Safety Appliances 1000 Cranbury Woods Road Cranbury, PA 16066

(800) 821-3642 (724) 776-7700

www.msanet.com

Minolta (see Land) 101 Williams Dr. Ramsey, NJ 07446

(201) 529-6049 (888) 473-2656

www.minoltausa.com

NEC (see Mikron)

Nikon (see Pyrometer Instruments and HGH)

Omega Engineering, Inc. One Omega Drive P.O. Box 2349 Stamford, CT 06906

(203) 359-1660 (800) 826-6342

[email protected] www.omega.com

Palmer Wahl Instrumentation Group

234 Old Weaverville Road Asheville, NC 28804

(828) 658-3121 (800) 421-2853

www.instrumentationgroup.com

Pyrometer Instrument Co. 209 Industrial Pkwy. Northvale, NJ 07647

(201) 768-2000 (800) HOT-PYRO

www.pyrometer.com [email protected]

2-31

http://www.landinst.com/

http://www.linearlabs.com/

http://www.marconitech.com/


http://www.mikroninst.com/

http://www.msanet.com/

http://www.minoltausa.com/


http://www.omega.com/

http://www.instrumentationgroup.com/

http://www.pyrometer.com/




Quantum Focus Instruments Corp.

990 Park Center Drive, Suite D Vista, CA 92083

(760) 599-1122 www.quantumfocus.com

Raytek, Inc. 1201 Shaffer Rd. Santa Cruz, CA 95060

(831) 458-1110 www.raytek.com [email protected]

Raytheon Corporation 5756 Thornwood Dr. Goleta, CA 93117

(805) 683-6621 (800) 990-3275

www.raytheoninfrared.com

Raytheon Corporation, Ind. Auto. Div.

P.O. Box 655012 Dallas, TX 75265

(800) 990-3275 www.raytheoninfrared.com

Santa Barbara Focal Plane Division of Lockheed Martin

69 Santa Felicia Dr. Goleta, CA 93117

(805) 562-8777 www.sbfp.com

Teletemp Corp. P.O. Box 5160, 351 S. Raymond Fullerton, CA 92635

(800) 321-5160 (714) 879-2901

www.telatemp.com [email protected]

Thermal Wave Imaging, Inc. 845 Livernois Street Ferndale, MI 48220-2308

(248) 414-3730 www.thermalwave.com

Thermoteknix Systems, Ltd.

US Infrared 1535 S. Memorial Dr. Suite 117 Tulsa, OK 74112

(918) 663-7833 www.bpcintl.com

Williamson Corp. 70 Domino Dr. Box 1270 Concord, MA 01742

(978) 369-9607 www.williamsonir.com [email protected]

Wuhan Guide Electronic Industrial Co. Ltd.

Hongshan Chuangye Ctr. Bldg. Luoyu Rd. No. 424 Wuhan, China

+86-27-87659277 +86-27-87659069

www.wuhanguide.com [email protected]

2-32

http://www.quantumfocus.com/

http://www.raytek.com/


http://www.raytheoninfrared.com/

http://www.raytheoninfrared.com/

http://www.sbfp.com/

http://www.telatemp.com/


http://www.thermalwave.com/

http://www.bpcintl.com/

http://www.williamsonir.com/

http://www.wuhanguide.com/



Table 2-3 Compilation of Typical Industrial Applications of Thermal Imaging Instruments

Typical Applications by Industry

Industry Applications

Metals Continuous casting, strip annealing, extrusion presses, rolling mills, induction heating, resistance heating, heat treating, electrolytic refining

Glass Tank refractories, glass body temperatures, mold temperatures, bottle machines, float glass, tempering and annealing, fiberglass manufacturing

Cement Kiln shell, refractory insulation, bridge delamination inspection

Textiles Permanent press heat setting, dye setting, foam lamination, carpet backing

Plastics Vacuum forming, extrusion, film process monitoring and control

Paper Dryer drums, coating ink drying

Chemical and Petroleum

Furnace tube temperatures, pipe and vessel corrosion, mixing process monitoring and control

Food and Confectionary

Rotary cooker temperatures, continuous infrared ovens, mixers, continuous baking ovens, freeze-dry processes

Asphalt Paving Road stone dryer, mixing temperature, rolling temperature

Rubber Hot rubber sheets�cooling and rolling, tire testing

Utilities Electrical systems, steam valves, motors, pumps, boilers, circuit boards, switchyards, transmission and distribution lines

2-33


Table 2-3 (cont.) Compilation of Typical Industrial Applications of Thermal Imaging Instruments

Typical Applications by Discipline

Discipline Applications

Design • Exhaust stacks, flue pipes

• Heating units (ovens, boilers, furnaces)

• Buildings (offices, schools, hospitals, plants)

• Process pipes, vessels, lines�steam and water lines

• Kilns

• Cryogenic storage vessels

• Electrical and electronic circuits and micro-circuits

Workmanship • Operational procedures

• Installation of refractory materials

• Installation of foam insulation materials

• Installation of fiberglass materials (roof insulation and so on)

• Replacement of parts and other repairs

• Roof inspection for moisture saturation

Component Failure • Steam traps, underground steam lines, plumbing lines and systems

• Electrical lines and substations

• Electrical and electronic components and modules

• Insulation�foam, fiberglass, and refractory

• Seals�low- and high-temperature

• Doors, ports, windows

• Cooling towers, heat exchangers

• Motors, pumps, ventilators, bearings

2-34


3.The Measurement MissionThe successful completion of a field measurement mission requires planning,caution, and the ability to interpret the thermographic results. The thermographer also needs a clear understanding of the thermal behavior of the targets involved in the measurement mission. The mission tasks can be subdivided as follows:■ Understanding the thermal behavior of the target■ Preparing the equipment for the mission■ Using correct instrument operating procedures


3.1 Thermal Behavior of the TargetThere are 10 sources of energy transfer at the target surface that can cause IR thermal imaging equipment to register apparent temperature changes.Some of these represent real temperature changes at the target surface andsome do not. It is important for the thermographer to understand thesephenomena and to be able to distinguish between apparent and real targettemperature changes. Examples of the 10 sources of apparent & real targettemperature differences will be described. They are tabulated as follows:

Real • Mass transport difference• Phase change difference• Thermal capacitance difference Cp

• Induced heating difference • Energy conversion difference• Direct heat transfer difference

Apparent • Emissivity difference ε• Reflectance difference ρ• Transmittance difference τ• Geometric difference G


3.1.1 Emissivity Difference As discussed in Appendix A, Section A.3.3, the radiant energy emitted by a target surface is proportional to emissivity as well as to a power of the targettemperature. If the emissivity of the target surface changes, or if the wrongeffective emissivity value is assumed for the target, the apparent temperaturereading will be in error. The resultant inaccuracy will not be the result of a real temperature change at the target surface.

3.1.2 Reflectance Difference An apparent temperature change will occur when thermal radiant energy from an external heat source is reflected off the target surface. The apparentchange will be proportional to a power of the temperature difference betweenthe actual target and that of the external heat source. It will also beproportional to the reflectance (1.0 minus the emissivity value) of the targetand to the emissivity of the external heat source. This apparent change willnot be the result of a real temperature change at the target surface.


3.1.3 Transmittance Difference An apparent temperature change will occur when thermal radiant energy from an external heat source behind the target surface is transmitted through thetarget surface. The apparent change will be proportional to a power of thetemperature difference between the actual target and that of the external heatsource. It will also be proportional to the transmittance of the target and to theemissivity of the external heat source. This apparent change will not be theresult of a real temperature change at the target surface.

3.1.4 Geometric Difference An apparent temperature change might occur as a result of the geometric shape of the target. If the target surface is shaped so as to form a cavity, forexample, multiple reflections of radiant energy between the cavity walls willresult in an apparent increase in emissivity. The corner of an enclosure withthree mutually perpendicular surfaces in close proximity is a good example ofthis. The apparent change will be similar to that caused by an emissivityvariation and will not be the result of a real temperature change at the targetsurface. (the geometric difference will affect both the reflectance and the emissivity differences)


3.1.5 Mass Transport Difference An example of a mass transport difference is air leakage from the inside of a building through the building surface that happens to be the target. The air intransit might heat or cool the target surface. This results in a real temperature change at the target surface.

3.1.6 Phase Change Difference An example of a phase change difference is water that condenses (changes from gas to liquid) on or behind a target surface and temporarily cools the surface. This results in a real temperature change at the target surface.

3.1.7 Thermal Capacitance Difference An example of a thermal capacitance difference is when solar heat stored in water-saturated sections of a roof warms the surface of the roof at night, in contrast to the non-saturated sections. This is because the water-saturated sections have higher thermal capacitance than the dry sections and it results in a real temperature change at the target surface.


3.1.8 Induced Heating Difference An example of an induced heating difference is the inductive heating of ferrous bolts that are improperly installed in an aluminum buss bar. Themagnetic field will cause inductive heating in ferrous materials, which resultsin a real temperature change at the target surface.

3.1.9 Energy Conversion Difference Most temperature rises observed in a plant environment are the result of energy conversion (friction to heat, chemical reaction to heat, and so on). Acommon example of an energy conversion difference is when the resistanceof a poor connection converts electric current to heat. This results in a realtemperature change at the target surface.

3.1.10 Direct Heat Transfer Difference A direct heat transfer difference occurs by conduction, convection, or radiation as described in Appendix A, Section A.2. Examples of direct heattransfer are found in the nondestructive testing of materials where a uniformheat flow is generated and observed thermal anomalies indicate flaws. Theseare real temperature changes at the target surface.


Thermogram - Mass Transport Difference


Thermogram - Mass Transport Difference


Thermogram - Thermal Capacitance Difference


Thermogram - Thermal Capacitance Difference


Thermogram - Energy Conversion Difference


Thermogram - Energy Conversion Difference


3.2 Equipment Preparation3.2.1 The Mission Checklist In preparation for the measurement mission, the thermographer should use checklists to ensure that there are no surprises on site. A standard checklistshould be prepared to include all items in the thermographic equipmentinventory. The list should include: instruments, spare lenses, tripods,harnesses, transport cases, carts, batteries, chargers, liquid or gaseouscryogenic coolant, if applicable, safety gear, special accessories, film,diskettes, spare fuses, tool kits, data sheets, operator manuals, calibrationdata, radiation reference sources, inter-connecting cables, accessory cables, and special fixtures. Well in advance of the mission, the thermographer can highlight all of the items that will be required for a particular job. The highlighted standard list will then become the checklist for the job.


3.2.2 Equipment Checkout and Calibration All quantitative thermography equipment (what about qualitative equipment?)should be calibrated periodically in accordance with the manufacturer’s recommendations found in the operator’s handbook. In addition, a quickoperation and calibration check should be performed by the thermographer to make certain that the equipment is in working order and in calibration.

This can be performed by using an infrared radiation reference blackbody source or by a more quick and simple means such as a two-point check. This approximate test can be performed by using two known targets such as ice water (0°C) and the palm of the thermographer’s hand (approximately 35°C).


3.2.3 Batteries Too many thermographic measurement missions have had to be postponed or prematurely terminated because the thermographer ran out of chargedbatteries. This can be very costly in terms of lost inspection time andcustomer confidence. The batteries item on the mission checklist should beunderstood to mean fully-charged batteries and it is the thermographer’sresponsibility to ensure that there is a comfortable surplus of battery poweravailable for each mission. The fact that batteries become discharged morerapidly in cold weather also needs to be considered in preparing for themission.


3.2.4 Facility Personnel Participation A knowledgeable facility representative should accompany the thermographer on the measurement mission or be available during measurements. Byproviding expert information concerning the processes taking place and thelikely sources of temperature differences, this assistance will enable thethermographer to anticipate thermal behavior and to better understand and interpret the thermographic results.


3.3 Some Cautions for Correct Instrument OperationAssuming that the instrument selected is appropriate to the measurement application, there are a few things that the thermographer should rememberto avoid common mistakes in use. These include the following:

• Learn and memorize the start-up procedure.• Learn and memorize the default values.• Set or use the correct effective emissivity.• Make sure that the target to be measured is larger than the instantaneous

field of view for measurement (IFOVmeas) of the instrument.• Aim the instrument as close to normal (perpendicular) with the target

surface as possible. • Check for reflections off the target surface. • Keep portable inspection instruments as far away as possible from very hot

targets.


3.3.1 Start-Up Procedure Thermographers that operate several different models of thermographic and thermal-sensing equipment need to be certain that they re-familiarizethemselves with the start-up procedure of the equipment selected for eachmeasurement mission. This allows the data-gathering process to begin withno unnecessary delays. It saves valuable on-site time and inspiresconfidence on the part of facility personnel. A quick review of the operator’smanual and a short dry run prior to leaving home base is usually all that isrequired.


3.3.2 Memorizing the Default Values The operator’s manual also provides default values for several important variables in the measurement such as emissivity, ambient (background)temperature, distance from sensor to target, temperature scale (°F or °C),lens selection, and relative humidity. These are the values that theinstrument processor automatically uses to compute target temperatureunless the thermographer changes these values to match the actualmeasurement conditions.

Typical default values are: 1.0 meter distance to target, emissivity of 1.0, and ambient temperature of 25°C. Failure to correct for these (for example, if the target is known to be 10 meters away, is known to have an effective emissivity of approximately 0.7, and is in an ambient of 10°C) can result in substantially erroneous results. By memorizing the default values, the thermographer will know when it is necessary to change them, and when time can be saved by using them unchanged, without having to refer to a look-up menu.


3.3.3 Setting the Correct Emissivity Table 3-1 and Table 3-2 list various targets and their approximate generic emissivities. There are emissivities shown for various temperatures and inseveral spectral bands. Where it is not otherwise indicated, temperaturesshould be assumed to be 30°C. If possible, it is always better to directlydetermine the actual effective emissivity of the surface to be measured byusing the actual instrument to be used in the measurement. Effectiveemissivity (e*) is defined as: ..the measured emissivity value of a particulartarget surface under existing measurement conditions, that can be used tocorrect a specific measuring instrument to provide a correct temperaturemeasurement..

EPRI Licensed Material The Measurement Mission

Table 3-1 Table of Normal Spectral Emissivities

Short Wave (SW) = 2�5.6 µm Long Wave (LW) = 6.5�20 µm

Material Wavelength (micrometers)

Temperature (°C)

Emissivity

Alumina brick SW 17 0.68

Aluminum, heavily weathered SW 17 0.83�0.94

Aluminum foil 3 0.09

Aluminum foil (bright) 3 0.04

Aluminum disk, roughened 3 0.28

Asbestos slate (wallboard) 3 0.96

Brick, common SW 17 0.81�0.86

Brick, facing, red SW 0.92

Brick, facing, yellow SW 0.92

Brick, masonry SW 0.72

Brick, red 5 0 0.94

Brick, waterproof SW 17 0.9

Chipboard, untreated SW 0.9

Concrete, dry 5 36 0.95

Concrete, rough SW 17 0.92�0.97

Copper, polished, annealed 10 0.01

Fibre board (hard), untreated SW 0.85

Fibre board (porous), untreated SW 0.85

Filler, white SW 0.88

Firebrick SW 17 0.68

Formica LW 27 0.937

Frozen soil LW 0.93

Glass, chemical ware (partly transparent) 5 35 0.97

Granite, natural surface 5 36 0.96

Gravel LW 0.28

Hardwood, across grain SW 17 0.82

Hardwood, along grain SW 17 0.68�0.73

Hessian Fabric, green SW 0.88

Hessian Fabric, uncolored SW 0.87

3-6


The Measurement Mission

Table 3-1 (cont.) Table of Normal Spectral Emissivities


Temperature (°C)

Emissivity

Iron, heavily rusted SW 17 0.91�0.96

Limestone, natural surface 5 36 0.96

Mortar SW 17 0.87

Mortar, dry 5 36 0.94

P.V.C. SW 17 0.91�0.93

Paint (by manufacturer)

Broma Alkyd enamel 102 gold leaf 3 40 0.98

Broma Alkyd enamel 113 light blue 3 0.95

Chromatone® stabilized silver finish� Alumatone Corp.

3 10

25 0.26 0.31

Krylon® flat black 1502 3 50 0.95

Krylon flat white 3 40 0.99

Krylon ultra-flat black 5 36 0.97

3M® black velvet coating 9560 series optical black

3 40 >0.99

Oil SW 17 0.87

black flat SW 0.94

black gloss SW 0.92

gray flat SW 0.97

gray gloss SW 0.96

Plastic, black SW 0.95

Plastic, white SW 0.84

Paper, cardboard box 5 0.81

Paper, white SW 17 0.68

Perspex®, plexiglass SW 17 0.86

Plaster Pipes, glazed SW 17 0.83

Plaster SW 17 0.86�0.9

3-7




Temperature (°C)

Emissivity

Plasterboard, untreated SW 0.9

Plastic, acrylic, clear 5 36 0.94

Plastic paper, red SW 0.94

Plywood SW 17 0.83�0.98

Plywood, commercial, smooth finish, dry 5 36 0.82

Plywood, untreated SW 0.83

Polypropylene SW 17 0.97

Redwood (wrought), untreated SW 0.83

Redwood (unwrought), untreated SW 0.84

Rendering, gray SW 0.92

Roofing Metal

Azure blue, smooth SW 0 0.54

Azure blue, textured SW 0 0.51

Burnished copper, smooth SW 0 0.54

Burnished copper, textured SW 0 0.56

Dark bronze, textured SW 0 0.7

Mansard brown, smooth SW 0 0.58

Matte black, smooth SW 0 0.73

Roman bronze, smooth SW 0 0.69

Slate gray, smooth SW 0 0.64

Stone white, smooth SW 0 0.57

Terra Cotta, smooth SW 0 0.61

Shingles�asphalt (sm. Ceramic-coated rock granules)

Adobe SW 0 0.77

Black SW 0 0.83

Bright red SW 0 0.96

Chestnut brown SW 0 0.67

Colonial green SW 0 0.83

Dawn mist SW 0 0.76

Desert tan SW 0 0.74

Frost blende SW 0 0.76

Meadow green SW 0 0.78

Noire black SW 0 0.90

3-8





Temperature (°C)

Emissivity

Shingles�asphalt (sm. Ceramic-coated rock granules) cont.

Sea green SW 0 0.83

Shadow gray SW 0 0.81

Slate blende SW 0 0.65

Snow white SW 0 0.81

Wedgewood blue SW 0 0.75

Wood blende SW 0 0.75

Average SW 0 0.89

Fiberglass�asphalt (sm. Ceramic-coated rock granules)

Frost blende SW 0 0.83

Mahogany SW 0 0.84

Meadow mist SW 0 0.98

Noire black SW 0 0.93

Snow white SW 0 0.74

Wood blende SW 0 0.81

Average SW 0 0.86

Solid vinyl

Autumn gold, textured SW 0 0.79

Butternut beige, textured SW 0 0.80

Lexington green, textured SW 0 0.86

Oyster white, textured SW 0 0.88

Quaker gray, textured SW 0 0.89

Sunshine yellow, textured SW 0 0.75

White, smooth SW 0 0.93

Average SW 0 0.94

Styrofoam, insulation 5 37 0.60

Tape, electrical, insulating, black 5 35 0.97

Tape, masking 5 36 0.92

Tile, floor, asbestos 5 35 0.94

Tile, glazed SW 17 0.94

3-9




Temperature (°C)

Emissivity

Varnish, flat SW 0.93

Wallpaper (slight pattern) lt. gray SW 0.85

Wallpaper (slight pattern) red SW 0.90

Wood, paneling, light finish 5 36 0.87

Wood, polished spruce, gray 5 36 0.86

Table 3-2 Emissivity for Wavelengths of 8�14 µm at 0°C

Material Emissivity (%)


Pure and Oxidized Metals Asbestos Board Paper Slate

96 94 96

Aluminum, polished Rough surface Strongly oxidized

5 7 25

Brick Glazed, rough Fireclay Red, rough

85 85 94 90

Brass, dull, tarnished Polished

22 3

Carbon, purified Cement Charcoal, powder Clay, fired Enamel

80 54 96 91 90

Bronze, polished Porous, rough

10 55

Fabric, asbestos 78 Cast iron, casting Polished

81 21

Glass Frosted

92 96

Chromium, polished 10

Ice 97 Copper, commercial burnished Electrolytic, polished Oxidized Oxidized to black

7 2 65 88

Lacquer, bakelite Black, dull Black, shiny (on metal) White

93 87 87 87

Gold, polished 2

Lampblack 96 Iron, hot-rolled Oxidized Sheet, galvanized, burnished Sheet, galvanized, oxidized Shiny, etched Wrought, polished

77 74 23 28 16 28

3-10



Table 3-2 (cont.) Emissivity for Wavelengths of 8�14 µm at 0°C



Oil paint, various colors 94 Pure and Oxidized Metals

Paper, black, shiny Black, dull White

90 94 90

Lead, gray Oxidized Red, powder Shiny

28 63 93 8

Porcelain, glazed 92 Mercury, pure 10

Nickel on cast iron Pure, polished

5 5

Quartz 93 Platinum, pure 8

Rubber 95 Steel, galvanized Oxidized strongly Rolled freshly Rough surface Rusty, red Sheet, nickel-plated Sheet, rolled

28 88 24 96 69 11 56

Shellac, black, dull Black, shiny on tin plate

91 82

Tin, burnished 5

Snow 80 Tungsten 5

Tar paper 92 Zinc, sheet 20

Water 98

There are several methods described in Section 4 that can be used to estimate target effective emissivity quickly. Using the instrument chosen for measurement, one method of determining the setting needed for a particular target material is to:

1. Prepare a sample of the material large enough to contain several spot sizes or IFOVs of the instrument. A 10 cm x 10 cm (4" x 4") sample is a good choice.

2. Spray one half of the target sample with flat black (light absorbing) paint; cover it with black masking tape or use some other substance of known high emissivity.

3. Heat the sample to a uniform temperature as close as possible to the temperature at which you estimate your actual measurement will be made.

4. Set your instrument emissivity control to the known emissivity of the coating and measure the temperature of the coated area with your instrument. Note the reading.

5. Immediately point to the uncoated area and adjust the emissivity set until you repeat the reading you obtained in 4. above. This is the effective emissivity, the value you should use in measuring the temperature of this material with this instrument.

For quick reference, this procedure is illustrated and summarized in Appendix C, Plate 5.

3-11


3.3.4 Filling the IFOVmeas for Accurate Temperature Measurements If you need to measure the temperature of a spot on a target, be certain that this spot completely fills the Instantaneous Measurement Field of View (IFOVmeas) of the instrument. If it doesn’t, you can still learn some useful things about the target with the instrument, but you can't get an accurate reading of target temperature. Use the quick calculation that is provided in Appendix C, Plate 2 to determine spot size based on IFOVmeas and actual working distance. If your target spot size is 5 cm or larger, for example, and the calculated spot size is 5 cm, move the instrument closer to the target or use a higher magnification lens, if either is possible. If not, expect to see some background effect in your reading. Also, be sure to allow for aiming errors and instrument imperfections; to be sure, allow an extra 30%.

(Does the IFOVmeas has the necessary allowance, for IFOVmeas = 3 x IFOVgeom?)


3.3.5 Aiming Normal to the Target Surface The effective emissivity of a target surface is due partially to the surface texture. It stands to reason, then, that if you look at a surface at a skimming angle, you won’t see the texture; the effective emissivity will change greatly and you will see misleading reflections. These can result in cold errors as well as hot errors. A safe rule is to view the target at an angle within 30° of normal (perpendicular). If the target effective emissivity is very high, you can go as high as a 60° angle if necessary.


3.3.6 Recognizing and Avoiding Reflections From External Sources If there is a source of radiant energy in a position to reflect off your target surface and into your instrument, you should take steps to avoid themisleading results of this effect. The greatest likelihood of errors due toreflections from external sources occurs when:

• The target emissivity is low. (1= ε + ρ, for τ = 0 )• The target is cooler than its surroundings.• The target surface is curved or irregularly shaped.

You can find out if a thermal anomaly is due to a point source by moving the instrument and pointing it at the target from several different directions. If theanomaly moves on the thermogram, it is a reflection. You can eliminate theeffect of an interfering source, once you identify it, by changing your viewingangle, by blocking the line of sight to the source, or by doing both (refer toAppendix A, Figure A-9). For reflections from hot backgrounds, refer toAppendix A, Section A.3.3.


3.3.7 Avoiding Radiant Heat Damage to the Instrument Unless specifically selected for continuous operation in close proximity to a very hot target, your instrument might be damaged by extensive thermalradiation from a target. Don’t leave the instrument in areas that are too warmto place your hand comfortably.


4. Inspection TechniquesThis section is divided into two sub-sections that deal with the common problems and solutions that are encountered when using infraredthermography in a plant or industrial environment. The first section deals withthe inherent or indigenous problems, such as emissivity or reflectance. Thesecond section explains the tricks of the trade that are used to get the bestpossible information out of the imaging systems. The references (Appendix D)and the bibliography (Appendix E) provide many sources of additionalinformation on a wide variety of problems, both theoretical and practical.


4.1 Mitigating Inherent EffectsThere are several factors that affect the production and subsequent proper interpretation of a thermal image. These factors include the (1) target’s emissivity, (2) reflectance, (3) distance from the imager, (4) temperature, (5) background temperature, (6) ambient temperature, (7) orientation, (8) target size, (9) and the transmittance of the intervening atmosphere.

In addition, the image, as presented on the imager, is not temperature but radiosity. Imagers measure the radiant energy emitted by the target plus the radiant energy reflected from and transmitted through the target. The sum of these radiant energies is the commonly accepted definition of radiosity. There are practical considerations that will simplify the following discussions of the inherent effects. In general, the transmittance (energy transmitted through the targets) can be ignored in most, if not all, cases for targets in a power plant. Transmittance is an important factor in industries where the temperature of a thin film of plastic or other infrared opaque targets are being observed. Also, with the exception of absolute temperature measurements being required, the transmittance through the atmosphere can be ignored as well. The major exception would be in cases where long distances were involved in a humid atmosphere (that is, hydrogen igniters or spray nozzles in containment).


4.1.1 Emissivity and Reflectivity A review of the references in the bibliography (Appendix E) will show that no one subject is discussed more than emissivity. The effective emissivity of a target clearly must be known in order to measure its absolute temperature. This is discussed in detail in Appendix A. Table 4-1 provides some values ofemissivity for common objects. Aluminum, the most commonly used electricalconductor, can range from 0.55 for a rough highly oxidized plate, to 0.039 fora highly polished plate. In practical terms, this means that 45% of theanodized plate and 96% of the polished plate’s incident energy are reflectedand that any hot or cold objects in the optical background will reflect their energy off these surfaces. These mirrors do have surface thermal patterns. It is difficult to measure them, however, because of the low emitted energy and the natural ability to reflect thermal energy as well as light. In general, if a target is acting as a visible mirror, it is acting as an infrared mirror as well. An exception to this rule is the germanium lenses used on the thermal imager. These lenses transmit more than 90% of the energy in the infrared spectrum but have light-reflecting coatings that reflect more than 90% of the energy in the visible spectrum.


Germanium Lenses - used on the thermal imager. These lenses transmit more than 90% of the energy in the infrared spectrum but have light-reflecting coatings that reflect more than 90% of the energy in the visible spectrum.


Germanium Lenses - used on the thermal imager. These lenses transmit more than 90% of the energy in the infrared spectrum but have light-reflecting coatings that reflect more than 90% of the energy in the visible spectrum.


Germanium Lenses (Night Vision) - used on the thermal imager. These lenses transmit more than 90% of the energy in the infrared spectrum but have light-reflecting coatings that reflect more than 90% of the energy in the visible spectrum.


Germanium Lenses (Night Vision) - used on the thermal imager. These lenses transmit more than 90% of the energy in the infrared spectrum but have light-reflecting coatings that reflect more than 90% of the energy in the visible spectrum.


Table 4-1 Normal Emissivity Values of Common Materials


Given that shiny objects have surface thermal patterns that are hard to image, there are several techniques that improve the ability to establish a satisfactory image. The most common way to obtain a useful thermal image from a shiny or low-emissivity surface is to add a coating to it that has a higher emissivity. (This is not practical and is not recommended for an energized electrical surface.) There are three common non-permanent materials that have been used to improve emissivity.

These are:• Foot powder• Dye check developer• Electricians’ tape


4.1.2 Foot Powder Foot powder is sprayed on a target to create a uniform layer that reduces the reflections. After the powder has reached thermal equilibrium with the surface, the temperature measurements can be made. The emissivity of foot powder has been estimated to be 0.96. Before any coating isapplied, however, the chemical composition of the coating should be determined to avoid anynegative effects from its application.


4.1.3 Dye Check Developer An alternative to foot powder is liquid dye penetrant developer. It has an estimated emissivity of 0.97 and might already have been formulated to conform to QA requirements for sulfur and halogen purity. Application of it is identical to the foot powder. Given the temperature of the target, it might take several minutes for the developer to reach thermal equilibrium as itspropellant cools the target’s surface. The best way to use this in an actual survey would be to apply it to all targets to be surveyed before commencing the actual survey. This will ensure that all target surfaces will have reached thermal equilibrium.

(Caution: Ensure that all manufacturer precautions are followed prior to use of any developer. For example, Magnaflux Zyglo® developers, such as ZP-9Eand ZP-9F, might produce chlorine gas or become flammable when theycome in contact with moderately heated surfaces.)


Dye Check Developer An alternative to foot powder is liquid dye penetrant developer. It has an estimated emissivity of 0.97 and might already have been formulated to conform to QA requirements for sulfur and halogen purity.


The target in Figures 4-1 and 4-2 is a shiny metal can of dye check developer with the label removed. There are no hot objects in or near the can. With theimager’s emissivity set at 1.0, an analysis of the temperature distribution overthe can yielded a temperature range of 74.6°F to 67.9°F (6.7°F ΔT). Thereason for the variation is reflection of the cold window plus geometricconsiderations in measuring a curved surface. Setting the emissivity at 0.10,a more realistic figure for a shiny surface, yielded a maximum temperature of66.2°F and a minimum temperature of 23.9°F (42.3°F ΔT). The room ambienttemperature was 68°F. Without changing anything, the can surface wascoated with developer and allowed to achieve thermal equilibrium. The firsteffect noted was the observation of the level of the developer in the can(Figure 4-3). This was due to the difference in the heat capacity of the liquidand vapor present inside the can.


The cooling action of the propellant developed a thermal transient that resulted in the liquid level visible on the thermogram. The emissivity was reset to 0.97 and the can was allowed to achieve thermal equilibrium with the room. After 10 minutes, the maximum temperature observed was 70.4°F and the minimum temperature was 69.5°F (0.9°F ΔT), close to room ambient of 68°F. (The 0.9°F temperature spread is normal because the dye check developer might not have uniformly coated the surface.) Clearly, the developer served its intended function of improving the surface emissivity and, therefore, the results.

4.1.4 Electricians' Tape Another alternative that improves the surface emissivity is the use of electricians’ tape (it has an estimated emissivity of 0.95). This method is easyto use and apply but can present problems if the glue on the tape containschlorine or other chemicals that can attack the target surface.


Electricians' Tape Another alternative that improves the surface emissivity is the use of electricians’ tape (it has an estimated emissivity of 0.95).


Figure 4-1 Emissivity Improvement by Coating.Setup


Figure 4-2 Thermogram of an Uncoated Shiny Metal Container


Figure 4-3 Container Has Been Coated to Improve Emissivity.Thermogram Now Reveals Fluid Level


4.2 Proven Inspection Techniques4.2.1 Mirrored Surfaces A commonly encountered situation is one where there is little or no room to place the imager and the area of interest is behind another object. This iscommonly found in electrical switchgear. One method that works well is touse a material with a high reflectivity (low emissivity) as an infrared mirror.The mirror is placed in such a manner that the reflected image is viewed froma more convenient position. This is a common technique for visual inspection.The determination of temperature, though, requires that the emissivity of thereflecting surface be taken into account. Also, as in the visual technique, themirrored image will appear reversed, thus requiring care in interpreting thedata. There are excellent front surface mirrors available for this technique.These mirrors have the reflecting material on the front surface so that theincoming energy is not refracted by the glass. Sources for these mirrorsinclude most optics manufacturers.


4.2.2 Thermal Transfer Imaging As reported in “Subsurface Flaw Detection in Reflective Materials by Thermal-Transfer Imaging”, there are a number of inspection techniques that can easily be applied in the field to handle targets with low emissivity. One ofthese techniques is called Thermal Transfer Imaging (TTI). This techniquewas developed primarily for the steel industry where low emissivity and hightemperatures exist as major problems in infrared imaging. In a case includedin “Subsurface Flaw Detection in Reflective Materials by Thermal-TransferImaging”, the surface thermal patterns of a piece of hot steel needed to bedetermined. The resultant thermal image provided too much reflection and toolittle emission to observe meaningful surface thermal patterns. The patternswere observed after they had been transferred to a material that had a higheremissivity. In other words, the surface patterns of the target were observed onthe surface of another object after the two had been in contact with eachother. If the emissivities of both materials are known and accounted for,temperature measurements can be made this way.


4.2.3 Thermal Transients Another useful inspection technique for handling targets with low emissivity is to add or subtract heat from a target. Most uses of IR are in the steady statecondition. When there are two materials with different heat capacitiesinvolved, however, a thermal transient is most useful. A graphic example ofthis is shown in Figure 4-3, dealing with the can of dye check developer. Athermal transient was induced on the can just by spraying it. The endothermicreaction of the propellant as it evaporated caused heat to transfer from theinside of the can (warmer) to the outside. In the case of the propellant inside,the liquid had a higher heat capacity (Cp) than the vapor space above it.During the transient, the liquid, therefore, caused a larger transfer andresultant temperature difference due to conduction on the can surface. Thehigher emissivity of the developer on the can’s surface allowed it to be seenmore readily.


This is an extremely useful technique. Where large masses are concerned, however, a large amount of heat transfer might be needed for observation.This technique can be used to determine relative thicknesses of material andlocations of voids, delaminations, and internal structures. The heat transfercan be induced by several methods. In the case of locating reinforcing bars(rebar) in concrete, a large induction coil placed on the concrete causes thebars to heat. The locations of the bars and their relative depth can,subsequently, be observed on the surface. When looking for voids incomposite materials, a flash lamp can be used for a short pulse of energy.Hot air from a compressor can be used for containment spray ring headernozzle inspections and for locating materials near the surface of concrete. It should be noted, however, that heating is not always the most effectiveapproach. Cooling is sometimes more effective, especially in hot areas.


4.2.4 Differential Thermography Another state of the art inspection technique is differential thermography. This method was originally developed for the U.S. Army for the identification ofdefective components on the surface of a printed circuit board. The reports, “Infrared Automatic Mass Screening (IRAMS) System for Printed Circuit-Board Fault Detection” and “Infrared Automatic Screening (IRAMS) Progress Report”, provide details on this successful technique and results. As applied in a power plant, a good example would be to observe the resultant surface thermal patterns of reflective insulation to learn about its efficiency. Given that the reflective insulation on a pipe or heat exchanger is not only reflective but large in size, coating with dye check developer or tape is impractical; an infrared imager shows the surface and all reflections from it.


The technique here involves a computer, image enhancement, and commercial software. A baseline image is taken at one temperature, forexample, during start-up. This image is digitized and stored on a computer. Asecond image, or subsequent images, are taken from the same location butat a different temperature, at full power for example. This image is alsodigitized and stored on the computer. The two images are then subtracted.The high reflectance due to the low emissivity exactly cancels out, leaving animage of true surface thermal patterns. One important assumption here is thatthe background remains the same. These patterns can then be correlatedwith a visual image for location of internal insulation damage. Also, knowingthe emissivity of the insulation and the resultant temperature patternsprovides an opportunity to measure the R-value of the insulation. This shouldhelp in determining the cost-effectiveness of insulation repair or replacement.


The differential thermography technique requires that the images be taken from the same place. There are several ways to do this. The first is called pinregistration and involves drilling small pilot holes into the floor so that the pinsof a tripod’s feet would fit in to them. The only variable then becomes theorientation of the thermal imager head on the tripod. A better application ofthis differential thermography technique is to have the computer at the imager.The original is placed on the screen as a mask. When the mask and the liveimage cancel each other out, there is exact registration (within the accuracyof the optics). In some cases, such as measuring the R-value for the entireheat exchanger, the temperatures above and below certain targets arecanceled out (chopped). The analysis is then done on the resultant images.The criteria for chopping can be due to background sources and/or hotreflective sources.


4.2.5 Using Infrared Transmitting Windows For the purpose of safety, it might be inadvisable or in violation of safety regulations, to remove bolts from operating high voltage equipment or to openpanels. However, it might be possible to install viewing windows of infraredtransmitting materials for infrared inspection. There are numerous materialsavailable for this purpose. In Appendix A, Figure A-12 shows the spectraltransmission characteristics of several of these materials, many of whichtransmit energy past 10 µm. These materials are often used as lenses andoptical elements in low-temperature infrared sensors. Installing IR transmittingwindows in critical locations is a growing trend, enabling periodic inspection ofthese locations without the hazard or inconvenience of opening panels orremoving bolts.


Thermogram of Tower


5. EXAMPLES OF INFRARED APPLICATIONS 5.1 Current Applications The applications described below are broken down into three categories: electrical, mechanical, and miscellaneous. The primary use of infraredthermography has been in the electrical area. The mechanical area involvesrotating equipment, heat exchangers, valves, and buildings. Themiscellaneous section describes research in progress and uniqueapplications. The Bibliography section of this Guide (Appendix E) providesreferences to many other publications where examples of other applicationsare presented.

5.2 Electrical Applications The primary use for infrared thermography, and usually the most straightforward application for it, is in the area of electrical predictive maintenance. Within this area, there are three main categories of problems: (1) high electrical resistance, (2) inductive currents, and (3) open circuits.


5.2.1 High Electrical Resistance High electrical resistance is the most common problem that can be identified by using an infrared imager. Based on Ohm’s law, power (watts) is calculatedas the square of the current multiplied by the resistance (P = I2R). When theresistance is high, the power that is dissipated will be high. A higher powertranslates into a higher temperature at the same location. This creates the hot spots that are detected by the infrared thermal imager. Typical problems inthis category include loose and/or corroded connections (see Figure 5-9),under-sized electrical conductors, and open individual strands of a multiple-tranded conductor. A special case in this category is phase imbalance. Thesituations that cause a phase imbalance are numerous, but all involve thesituation where the current in one phase of a three-phase circuit issignificantly different than in the other phase(s). The difference in the highercurrent phase will be seen as a heating difference. The individual phasecurrents should be measured to verify this.


Another special case within the category is high resistance within a battery cell. Normally, batteries under trickle charge will be near ambienttemperatures. High resistance, internal to the battery, can be observed on thebattery exterior as areas of higher temperature when compared to similarbatteries. These observed temperature differences on an unloaded batterycell will be very small (that is, 0.25°F to 1.0°F). Any temperature differences along the inner cell connections with the battery on float indicate a potentially serious connection problem. There have been several cases where high internal battery resistance has gone unnoticed and has subsequently led to battery failure.


5.2.2 Induced Currents In situations involving high currents, hot spots might appear, not from the primary current but from currents induced in nearby ferrous elements or structures. This is often the case near the main electrical generator. These hot spots can appear in unlikely places such as the supporting steel structure of the generator. Other inductive hot spots have been observed on the generator stator casing and on the frames of motors. Not all of the hot spots are problems, however. In the case of the steel structure, the hot spots might be at the location where the electrical fields from the generator coincide. Hot spots are also common on motors. In both cases, this type of problem should be well documented and, where necessary, trended for future evaluation.


Induced Currents


Induced Currents


5.2.3 Open Circuits One frequently overlooked application of infrared thermography is in identifying open circuits. For example, a common problem with invertershappens when one or more capacitors fail open. In this case, the failedcapacitors will appear to be cooler than other similar capacitors within theinverter.


5.3 Mechanical Applications IR applications that do not fall into the electrical category are usually described as mechanical. Within this category, there are four major subsets:(1) heating due to friction, (2) valve leakage/blockage, (3) insulation, and (4) building applications.

5.3.1 Friction In the case of rotating or moving equipment, the result of friction is readily observable as an increase in temperature. Typical situations evolve in thearea of bearings on pumps (see Figure 5-26) and motors. If a bearing orcoupling is inadequately lubricated, internal friction can cause heating, whichcan usually be observed during operation. A misaligned shaft can result inunequal loading, which causes heat generation at the point of highestmechanical resistance. This situation can be detected from the resultantelevated temperatures seen at the shaft bearing or coupling.


5.3.2 Valve Leakage/Blockage The leakage of fluid past a normally closed valve might be easy to observe with an infrared imager, provided that the insulation on the pipe is accountedfor or removed, and that there is a sufficient temperature difference between the pipe surface and ambient. Typical situations are leaking safety valves (see Figures 5-21, 5-22, 5-23, and 5-25), drain valves, and steam traps. Blockage in a pipe or a valve is a special case. In this situation, it might be necessary to add or remove heat from the area in question in order to locate the blockage. As an example, if a blockage were suspected in a boric acid transfer line, adding or removing heat in the area of the blockage would result in a thermal discontinuity at the location of the blockage. The discontinuity exists because boric acid, in the solid form, has a different heat capacity (Cp) than boric acid in the liquid form. Therefore, if a uniform amount of heat is added or removed from both areas, the areas will cool or heat at different rates. The rate difference will, for some period of time, show up as a temperature difference. The interface will be at the location of the blockage. This same mechanism, transient heating or cooling, is the mechanism that allows the remote detection of fluid levels in a tank by means of thermal imaging.


5.3.3 Insulation Insulation on piping and equipment can be tested for integrity using an infrared imager. IR applications include the assurance of complete coverageof the area, thinning/degradation of the insulation, and wet insulation. A mostchallenging application is when the insulation is a reflective type of insulationor has a reflective covering. The very low emissivity of the surface can resultin reflected hot spots from the background, thus, making temperaturemeasurements difficult. One process that can be used is to observe theinsulation over a period of time when the system is heating up or coolingdown. Using differential thermography, and subtracting two images, cancelsout the effects of emissivity and might result in an interpretable thermaldifference image.

Keywords:Differential thermography (subtracting algorithm)


5.3.4 Building Envelopes Buildings can be inspected for energy conservation with an infrared imager. Typical problems that can be found include air infiltration or exfiltration, poorinsulation, and wet roofs. These are traditional applications for infraredthermography. The bibliography (Appendix E) provides sources of further information on these types of applications.

5.4 Miscellaneous ApplicationsThere are numerous applications for infrared thermography that are unique to the nuclear industry or that require special mention. These applicationsinclude, inspecting the containment spray ring header, the hydrogen igniters,and the condensers for air in-leakage, and observing thermal plumes.


5.3.4 Building Envelopes Buildings can be inspected for energy conservation with an infrared imager. Typical problems that can be found include air infiltration or exfiltration, poorinsulation, and wet roofs. These are traditional applications for infraredthermography. The bibliography (Appendix E) provides sources of further information on these types of applications.

5.4 Miscellaneous ApplicationsThere are numerous applications for infrared thermography that are unique to the nuclear industry or that require special mention. These applicationsinclude, inspecting the containment spray ring header, the hydrogen igniters,and the condensers for air in-leakage, and observing thermal plumes.


5.4.1 Containment Spray Ring Header Due to the inaccessibility of the containment spray ring header for physical inspection, infrared imagers have proven to be quite useful in detectingnozzle blockage. In the past, verification of unblocked nozzles on the header has involved several methods including smoke tests and balloons. The infrared method involves pumping heated air into the header and observing the thermal patterns at the nozzles. A blocked nozzle will not pass any hot air and an unblocked nozzle will. Due to the small size of the nozzle and the distance involved, a telescopic lens must be used with the imager for this inspection.

5.4.2 Hydrogen Igniters Infrared thermography has been used for inspecting the containment hydrogen igniters. Through the use of telescopic attachments, the temperature of the igniters can be measured from a remote distance. This technique eliminates the need for staging for close-up inspection.


5.4.3 Condensers Infrared thermal imagers have been used for inspecting condensers for both tube leaks and vacuum leaks (air in-leakage). As the air is drawn into thecondenser, the leaks are observable as cooler areas. This inspectiontechnique, however, is very labor-intensive and requires close and careful inspection of valve stems, bonnets, flanges, penetrations, and tubes.

5.4.4 Thermal Plume Detection The use of an infrared imager in a helicopter or airplane can assist the plant in verifying thermal discharge patterns in cooling ponds or other bodies ofwater. The thermal plume, or outfall, is easily observed from the air. Thehottest spots on the surface of the water are easily located. This facilitatesroutine environmental monitoring for thermal discharge.


IR Thermogram – F1


IR Thermogram


IR Thermogram


IR Thermogram


IR Thermogram


IR Thermogram


Hydrogen/ Flame Igniters at Flare BoomInfrared thermography has been used for inspecting the containment hydrogen igniters. Through the use of telescopic attachments, the temperature of the igniters can be measured from a remote distance. This technique eliminates the need for staging for close-up inspection.








5.5 Applications Summary Table 5-1 is a composite list of potential applications for infrared thermal imaging in the areas discussed.Electrical • Electrical connections (loose/corroded) • Switchyard disconnects • Transformers (connections, arrestors, cooling) • Transformers (internals) • Misaligned contacts, brushes, fuses, fuse clips, holders • Splices, crimps • Motor Control Center (MCC) heaters • Conductors (stranded, undersized, damaged) • Inductive heating (structure, bus ducts) • Batteries (connections, cells) • Open circuits (capacitors) • Load imbalance • Printed circuit boards • Motors (frames, bearings, connections) • Motors (failed coil in stator)


Mechanical • Valves (leakage, blockage) • Bearings • Couplings • Insulation (wet, damaged, coverage) • Pipes (thin areas, blockage, missing lining) • Refractory buildings (insulation, air leakage, roofs) • Reinforcing bar location • Underground leaks • Steam traps • Boiler tubes

Miscellaneous • Containment spray ring header nozzles • Containment hydrogen igniter temperatures • Condensers (air in-leakage, tube leaks) • Thermal plumes • Heat transfer evaluation of heat exchangers


To assist utility personnel in thermal image interpretation and recognition, this section also contains a number of examples of applications. These arethermal and visual images of components that appear to be in a degradedcondition, along with a number of thermal and visual images of othercomponents that appear to be in good working order. Table 5-2 is a listing ofthe example images that follow.


Table 5-2 List of IR Application Examples

5-1 Step-Up Transformer High-Resistance Connection 5-2 250 kV Transformer 5-3 Steam Line Leaks 5-4 Isophase Bus Bellows 5-5 Electric Generator 5-6 Regulating Transformer Cooling Oil Migration 5-7 Generator Casing 5-8 Energized Ground Cable 5-9 480 V Breaker Connection 5-10 Current Transformer 5-11 Fuse Holder 5-12 Connection to Fuse Holder 5-13 Knife Switch 5-14 Motor Control Center Breaker 5-15 Motor Control Center Terminal Block


5-16 Motor Control Center Control Wire 5-17 Padmount Transformers 5-18 Vacuum Leak on Turbine Condenser 5-19 Small Transformer 5-20 Motor 5-21 Shell Relief Valve 5-22 Shell Relief Valve (Weeping) 5-23 Shell Relief Valve (Leaking) 5-24 Vacuum Leak on Turbine 5-25 Steam Trap 5-26 Pump Bearing 5-27 Office Building 5-28 Building Roof with Water Saturation 5-29 Induction Motor Air Intake Plenum 5-30 Generator Step-Up Transformer 5-31 Printed Circuit Module

EPRI Licensed Material Examples of Infrared Applications

Figure 5-1 Step-Up Transformer High-Resistance Connection

Figures and text provided by Richard Bjornson, Seabrook Nuclear Power Station, Seabrook, NH, FLIR/InfraMation 2000 Proceedings

5-8


Examples of Infrared Applications

Figure 5-1 (cont.) Step-Up Transformer High-Resistance Connection

5-9


Figure 5-2 250 kV Transformer

5-10



Figure 5-2 (cont.) 250 kV Transformer

5-11


Figure 5-3 Steam Line Leaks

Figures and text provided by Mark Lanius, PECO, Peach Bottom Nuclear Station, Delta, PA, FLIR/InfraMation 2000 Proceedings

5-12



Figure 5-3 (cont.) Steam Line Leaks

5-13


Figure 5-4 Isophase Bus Bellows

5-14



Figure 5-4 (cont.) Isophase Bus Bellows

5-15


Figure 5-5 Electric Generator

5-16



Figure 5-5 (cont.) Electric Generator

5-17


Figure 5-6 Regulating Transformer Cooling Oil Migration

Figures and text provided by James Dan Roark, Knoxville Utilities Board, Knoxville, TN, FLIR/InfraMation 2001 Proceedings

5-18



Figure 5-6 (cont.) Regulating Transformer Cooling Oil Migration

5-19


Figure 5-7 Generator Casing

Figures and text provided by Greg Stockton, Stockton IR Thermography Service, Randleman, NC, FLIR/InfraMation 2000 Proceedings

5-20



Figure 5-7 (cont.) Generator Casing

5-21


Figure 5-8 Energized Ground Cable

5-22



Figure 5-8 (cont.) Energized Ground Cable

5-23


Figure 5-9 480 V Breaker Connection

5-24



Figure 5-9 (cont.) 480 V Breaker Connection

5-25


Figure 5-10 Current Transformer

5-26



Figure 5-10 (cont.) Current Transformer

5-27


Figure 5-11 Fuse Holder

5-28



Figure 5-11 (cont.) Fuse Holder

5-29


Figure 5-12 Connection to Fuse Holder

5-30



Figure 5-12 (cont.) Connection to Fuse Holder

5-31


Figure 5-13 Knife Switch

5-32



Figure 5-13 (cont.) Knife Switch

5-33


Figure 5-14 Motor Control Center Breaker

5-34



Figure 5-14 (cont.) Motor Control Center Breaker

5-35


Figure 5-15 Motor Control Center Terminal Block

5-36



Figure 5-15 (cont.) Motor Control Center Terminal Block

5-37


Figure 5-16 Motor Control Center Control Wire

5-38



Figure 5-16 (cont.) Motor Control Center Control Wire

5-39


Figure 5-17 Padmount Transformers

Figures and text provided by Jeff Sullivan, Mississippi Power Co., Hattiesburg, MS, FLIR/InfraMation 2000 Proceedings

5-40



Figure 5-17 (cont.) Padmount Transformers

5-41


Figure 5-18 Vacuum Leak on Turbine Condenser

Figures and text provided by Mark Lanius, PECO, Peach Bottom Nuclear Station, Delta, PA, FLIR/InfraMation 2000 Proceedings

5-42



Figure 5-18 (cont.) Vacuum Leak on Turbine Condenser

5-43


Figure 5-19 Small Transformer

5-44



Figure 5-19 (cont.) Small Transformer

5-45


Figure 5-20 Motor

5-46



Figure 5-20 (cont.) Motor

5-47


Figure 5-21 Shell Relief Valve

5-48



Figure 5-21 (cont.) Shell Relief Valve

5-49


Figure 5-22 Shell Relief Valve (Weeping)

5-50



Figure 5-22 (cont.) Shell Relief Valve (Weeping)

5-51


Figure 5-23 Shell Relief Valve (Leaking)

5-52



Figure 5-23 (cont.) Shell Relief Valve (Leaking)

5-53


Figure 5-24 Vacuum Leak on Turbine

5-54



Figure 5-24 (cont.) Vacuum Leak on Turbine

5-55


Figure 5-25 Steam Trap

5-56



Figure 5-25 (cont.) Steam Trap

5-57


Figure 5-26 Pump Bearing

5-58



Figure 5-26 (cont.) Pump Bearing

5-59


Figure 5-27 Office Building

5-60



Figure 5-27 (cont.) Office Building

5-61


Figure 5-28 Building Roof with Water Saturation

Figures and text provided by Kathryn Barker, American Infrared Testing and Consulting, FLIR/InfraMation 2000 Proceedings

5-62



Figure 5-28 (cont.) Building Roof with Water Saturation

5-63


Figure 5-29 Induction Motor Air Intake Plenum

5-64



Figure 5-29 (cont.) Induction Motor Air Intake Plenum

5-65


Figure 5-30 Generator Step-Up Transformer

Figures and text provided by Mark Goff, Tennessee Valley Authority, Chattanooga, TN, InfraMation 2001 Proceedings

5-66



Figure 5-30 (cont.) Generator Step-Up Transformer

5-67


Figure 5-31 Printed Circuit Module

Figures and text provided by Richard Fishbune, IBM, Rochester, MN, FLIR/InfraMation 2000 Proceedings

5-68



Figure 5-31 (cont.) Printed Circuit Module

5-69