Trans v01 Ch08

TRANSACTIONS Volume 1 05

Non-Contact Temperature MeasurementA Technical Reference Series Brought to You by OMEGA

11

VOLUME

I N M E A S U R E M E N T A N D C O N T R O L

While many of the earlierchapters of this volumehave explored thephysics and technology

behind non-contact temperaturemeasurement, now it’s time to delveinto the wide array of products thatare available to take advantage ofradiation phenomena—and howthey’re applied to industrial use.

Non-contact temperature sensorsallow engineers to obtain accuratetemperature measurements in appli-cations where it is impossible or verydifficult to use any other kind of sen-sor. In some cases, this is because theapplication itself literally destroys acontact-type sensor, such as whenusing a thermocouple or resistancetemperature detector to measuremolten metal. If the electrical inter-ference is intense, such as in induc-tion heating, the electromagneticfield surrounding the object willcause inaccurate results in conven-tional sensors. A remote infrared sen-sor is immune to both problems.

For maintenance, no other sensoris able to provide long-distance, non-contact temperature measurementsneeded to find hot spots or troubleareas in distillation columns, vessels,insulation, pipes, motors or trans-formers. As a maintenance and trou-bleshooting tool, it’s difficult to beata hand-held radiation thermometer.

Although non-contact temperaturesensors vary widely in price, theyinclude the same basic components:collecting optics, lens, spectral filterand detector. For more detailed tech-nical information on each sensor type,see the previous chapters.

Alternative ConfigurationsThe user can select among non-con-tact temperature sensors that operateover just about any desired wave-length range, both wide and narrow.Radiation thermometer sensitivityvaries inversely proportionally withwavelength. Therefore, an instrumentoperating at 5 microns only has one-fifth the sensitivity of an instrumentoperating at 1 micron. This also meansthat optical noise and uncertainties inemissivity will result in measurementerrors five times greater in the long

wavelength instrument. Radiation thermometer optics are

usually the fixed focus type,although designs with through-the-lens focusing are available for mea-suring over longer distances. Fixedfocus devices can also be used tomeasure at long distances if the tar-get area is smaller than the lensdiameter in the optical system.

Non-contact temperature sensorsrange from relatively inexpensiveinfrared thermocouples, priced fromabout $99, to sophisticated, comput-

56 Volume 1 TRANSACTIONS

Alternative Configurations

Application Guidelines

Accessories & Options

NON-CONTACT TEMPERATURE MEASUREMENTProducts & Applications

8

WProducts & Applications

Low-End IR Pyrometer/ Thermometer

Portable and convenient

Inexpensive (from $235)

Excellent maintenance tool

Maximum probe cable length of 1 m limits use

High-End IR Thermometer

Can focus on any target at almost any distance

Portable or fixed-place operation

Camera-like operation (point and shoot)

Low to medium cost (from $350)

Measures only a fixed spot on target

Accuracy affected by smoke, dust, etc. in line of sight

Affected by EMI

Fiber Optic Works in hostile, high-temperature, vacuum or inaccessible locations

Can bypass opaque barriers to reach target

Unaffected by EMI

Fairly expensive ($1600-$2600)

Fixed Focus

Two-Color Sees through smoke, dust and other contaminants in line of sight

Independent of target emissivity

Fairly expensive (from $3600 for sensor, and $5000 for display/controller)

Linescanner Only sensor that makes full-width temperature measurements across product

Measures continuously as product passes by

Computer can produce thermographic images of entire product and its temperature profile

Very expensive (from $10,000 for sensor alone, $50,000 for complete system)

INSTRUMENT TYPE STRENGTHS WEAKNESSES

IR Thermocouple

Inexpensive (from $99)

Self-powered

No measurement drift

Plugs into standard thermocouple display and control devices

Reaches into inaccessible areas

Intrinsically safe

Nonlinear output

Susceptible to EMI

Table 8-1: Strengths and Weaknesses of Non-Contact Temperature Sensors

er-based $50,000 linescanners. Inbetween is a wide variety of hand-heldand permanently mounted measuringsystems that meet just about any tem-perature monitoring need imaginable.

• Infrared ThermocouplesAn infrared thermocouple is anunpowered, low-cost sensor thatmeasures surface temperature ofmaterials without contact. It can bedirectly installed on conventionalthermocouple controllers, trans-mitters and digital readout devicesas if it were a replacement thermo-couple. An infrared thermocouplecan be installed in a fixed, perma-nent location, or used with a hand-held probe.

Because it is self-powered, itrelies on the incoming infrared radi-ation to produce a signal via ther-moelectric effects. Therefore, itsoutput follows the rules of radia-tion thermal physics, and is subjectto nonlinearities. But over a givenrange of temperatures, the output issufficiently linear that the signal canbe interchanged with a convention-al thermocouple.

Although each infrared thermo-couple is designed to operate in aspecific region, it can be used out-side that region by calibrating thereadout device accordingly.

• Radiation Thermometers/PyrometersRadiation thermometers, or pyrome-ters, as they are sometimes calledcome in a variety of configurations.One option is a handhelddisplay/control unit, plus anattached probe. The operator pointsthe probe at the object being mea-sured—sometimes getting within afraction of an inch of the surface—

and reads the temperature on thedigital display. These devices areideal for making point temperaturemeasurements on circuit boards,bearings, motors, steam traps or anyother device that can be reachedwith the probe. The inexpensivedevices are self-contained and runoff battery power.

Other radiation thermometers arehand-held or mounted devices thatinclude a lens similar to a 35mm cam-era. They can be focused on anyclose or distant object, and will takean average temperature measure-ment of the “spot” on the target thatfits into its field of view.

Handheld radiation thermometersare widely used for maintenance andtroubleshooting, because a techni-cian can carry one around easily,focus it on any object in the plant,and take instant temperature read-ings of anything from molten metalsto frozen foods.

When mounted in a fixed position,radiation thermometers are oftenused to monitor the manufacturingof glass, textiles, thin-film plastic andsimilar products, or processes such astempering, annealing, sealing, bend-ing and laminating.

• Fiber Optics ExtensionsWhen the object to be measured isnot in the line of sight of a radiationthermometer, a fiber optic sensorcan be used. The sensor includes atip, lens, fiber optic cable, and aremote monitor unit mounted up to30 ft away. The sensor can be placedin high energy fields, ambient tem-peratures up to 800°F, vacuum, or inotherwise inaccessible locationsinside closed areas.

• Two-Color SystemsFor use in applications where the tar-get may be obscured by dust, smokeor similar contaminants, or changingemissions as in “pouring metals,” atwo-color or ratio radiation ther-mometer is ideal. It measures tem-perature independently of emissivity.Systems are available with fiber opticsensors, or can be based on a fixed orhand-held configurations.

• LinescannersA linescanner provides a “picture” ofthe surface temperatures across amoving product, such as metal slabs,glass, textiles, coiled metal or plas-tics. It includes a lens, a rotating mir-

Products & Applications8


Typical fiber optic probe, transmitter, and bench top display.

ror that scans across the lens’ field ofview, a detector that takes readingsas the mirror rotates, and a comput-er system to process the data.

As the mirror rotates, the linescanner takes multiple measure-ments across the entire surface,obtaining a full-width temperatureprofile of the product. As the prod-uct moves forward under the sensor,successive scans provide a profile ofthe entire product, from edge toedge and from beginning to end.

The computer converts the profileinto a thermographic image of theproduct, using various colors to rep-resent temperatures, or it can pro-duce a “map” of the product. The 50or so measurement points across thewidth can be arranged in zones, aver-aged, and used to control upstreamdevices, such as webs, cooling sys-tems, injectors or coating systems.

Linescanners can be extremelyexpensive, but they offer one of theonly solutions for obtaining a com-plete temperature profile or imageof a moving product.

• Portable vs. MountedNon-contact temperature measure-ment devices also can be classified asportable or permanently mounted.Fixed mount thermometers are gen-erally installed in a location to con-tinuously monitor a process. Theyoften operate on AC line power, andare aimed at a single point. Measureddata can be viewed on a local orremote display, and an output signal(analog or digital) can be providedfor use elsewhere in the controlloop. Fixed mount systems generallyconsist of a housing containing theoptics system and detector, connect-ed by cable to a remote mountedelectronics/display unit. In someloop-powered designs, all the ther-mometer components and electron-ics are contained in a single housing;the same two wires used to powerthe thermometer also carry the 4 to20 mA output signal.

Battery powered, hand-held “pis-tol” radiation thermometers typical-ly have the same features as perma-nently mounted devices, but withoutthe output signal capability. Portableunits are typically used in mainte-nance, diagnostics, quality control,

and spot measurements of criticalprocesses.

Portable devices include pyrome-ters, thermometers and two-colorsystems. Their only practical applica-tion limit is the same as a humanoperator; i.e., the sensors will functionin any ambient temperature or envi-ronmental condition where a humancan work, typically 32-120°F (0-50°C).

At temperature extremes, wherean operator wears protective cloth-ing, it may be wise to similarly pro-tect the instrument. In shirt-sleevemanufacturing or process controlapplications, hand-held instrumentscan be used without worrying aboutthe temperature and humidity, butcare should be taken to avoidsources of high electrical noise.Induction furnaces, motor starters,large relays and similar devices thatgenerate EMI can affect the readingsof a portable sensor.

Portable non-contact sensors arewidely used for maintenance andtroubleshooting. Applications varyfrom up-close testing of printed cir-cuit boards, motors, bearings, steamtraps and injection moldingmachines, to checking temperatures

Products & Applications 8


Figure 8-1: Ambient Effects on IR Thermometer Accuracy

Atmosphere Emission and Absorption

Radiation Thermometer

Surroundings

Target

Hand-held IR thermometers include such

options as laser sights.

remotely in building insulation, pip-ing, electrical panels, transformers,furnace tubes and manufacturing andprocess control plants.

Because an infrared device mea-sures temperature in a “spot” definedby its field of view, proper aiming canbecome critical. Low-end pyrome-ters have optional LED aiming beams,and higher end thermometers haveoptional laser pointing devices tohelp properly position the sensor.

Permanently mounted devices aregenerally installed on a manufactur-ing or process control line, and out-put their temperature signals to acontrol or data acquisition system.Radiation thermometers, two-colorsensors, fiber optics, infrared ther-mocouples, and linescanners can allbe permanently mounted.

In a permanent installation, aninstrument can be very carefullyaimed at the target, adjusted for theexact emissivity, tuned for responsetime and span, connected to aremote device such as an indicator,controller, recorder or computer, andprotected from the environment.Once installed and checked out,such an instrument can run indefi-nitely, requiring only periodic main-tenance to clean its lenses.

Instruments designed for perma-nent installation are generally morerugged than lab or portable instru-ments, and have completely differ-ent outputs. In general, systems thatoperate near a process are ruggedi-zed, have NEMA and ISO industrial-rated enclosures, and output stan-dard process control signals such as4-20 mA dc, thermocouple mV sig-nals, 0-5 Vdc, or serial RS232C.

For very hot or dirty environ-ments, instruments can be equippedwith water or thermoelectric coolingto keep the electronics cool, and

nitrogen or shop air purging systemsto keep lenses clean.

Application GuidelinesFor first level sorting, consider speedof response, target size (field ofview), and target temperature. Oncethe list of possible candidates for theapplication has been narrowed, con-sider things like band pass and sensi-tivity of the detector, transmission

quality of the optical system andtransmission quality of any windowsor atmosphere in the sighting path,emissivity of the target, ambientconditions, and the process dynam-ics (steady state variations or stepchanges). These are shown graphical-ly in Figure 8-1.

If 90% response to a step changein temperature is required in lessthan a few seconds, pyrometers withthermal detectors may not be suit-able, unless you use thermopiles. Apyrometer with a photon detectormay be a better choice.

Thermometers with targets of 0.3to 1 inch diameter with a focal dis-tance of 1.5 to 3 feet from the lensare common. If a target size in this

range is needed to sight on a largetarget through a small opening in afurnace, a pyrometer in which targetsize increases rapidly with distancebeyond the focal plane may be fitthe bill. Otherwise, a thermometerwith more sophisticated optics andsignal conditioning may be required.

If the temperature to be measuredis below 750°F (400°C) a more sophis-ticated pyrometer with opticalchopping can improve performance.

If the surroundings between thethermometer and the target are notuniform, or if a hot object is present,it is desirable to shield the field ofview of the instrument so that thesephenomenon have minimal effect onthe measurement.

Any radiation absorbed or generat-ed by gases or particles in the sightingpath will affect measured target tem-perature. The influence of absorbingmedia (such as water vapor) can beminimized by proper selection of thewavelengths at which the thermome-ter will respond. For example, apyrometer with a silicon detectoroperates outside the absorptionbands of water vapor and the error isnil. The influence of hot particles can



Figure 8-2: Sighting on a Specular Surface

Target

Hot Furnace Walls

Thermometer

be eliminated by ensuring they do notenter the sighting path, or by peak orvalley picking, if they are transientlypresent. A open ended sighting tube,purged with a low temperature gascan provide a sighting path free ofinterfering particles.

Thermometers selected to mea-sure transparent targets, such asglass or plastic films, must operateat a wavelength where the transmis-sion of these materials is low so hotobjects behind the target do notinterfere with the measurement. Forexample, most glass is opaque atwavelengths above 5 microns if it is3 mm or thicker. The emittance ofglass decreases at higher wave-lengths above 8 microns because ofits high reflection, so measurementat higher wavelengths is not asdesirable. If the incorrect band ispicked, the thermometer will sightthrough the glass and not read thesurface temperature.

Imagine, for example, two ther-mometers measuring the surfacetemperature of a lightbulb. One ther-mometer operates in the 8 to 14micron range, and the other operatesat 2 microns. The 8 to 14 microndevice reads the surface temperatureof the bulb as 90°C. The 2-microndevice, sees through the surface ofthe glass, to the filament behind, andreads 494°C.

Other parameters to considerwhen selecting a non-contact tem-perature sensor include:• Target material—The compositionof a target determines its emissivity,or the amount of thermal energy itemits. A blackbody is a perfect emit-ter, rated 1.0 or 100%. Other materialsare somewhat lower; their emissivitycan be anywhere from 0.01 to 0.99, or0-99%. Organic materials are very effi-cient, with emissivities of 0.95, while

polished metals are inefficient, withemissivities of 20% or less. Tables onlygive the emissivity of an ideal surface,and cannot deal with corrosion, oxi-dation or surface roughness. In thereal world, emissivity variations rangefrom 2 to 100% per 100°F temperaturechange. When in doubt, obtain anappropriate instrument and measurethe emissivity exactly.• Temperature range—The emissivi-ty and the range of expected tem-peratures of the target determine thewavelengths at which the target willemit efficiently. Choose a sensor thatis sensitive at those wavelengths.Accuracy is listed as a percent of fullscale or span, so the closer the tem-perature range to be measured canbe specified, the closer sensormatch, and the more accurate thefinal measurements.• Wavelength choice—Manufacturers

typically lists their products with agiven temperature range and wave-length, with wavelengths listed inmicrons. Note that more than onewavelength can apply in any givenapplication. For example, to measureglass, a wavelength of 3.43, 5.0 or 7.92microns can be used, depending onthe depth you want to measure, thepresence of tungsten lamps, or toavoid reflections. Measuring plasticfilms presents the same problems.You may want to use a broad spec-trum to capture most of the radiantemissions of the target, or a limitedregion to narrow the temperaturerange and increase accuracy. In manyapplications, various conditions andchoices may exist. You may want toconsult with your supplier. • Atmospheric interference—What ispresent in the atmosphere betweenthe sensor and the target? Most non-



DH

Figure 8-3: Use of Shielding and Cooling

Hot SourceHot Source

Open End Sighting Tube

Target

Cooled Shield

contact temperature sensors requirean environment that has no dust,smoke, flames, mist or other contam-inants in the sensor’s line of sight. Ifcontaminants exist, it may be neces-sary to use a two-color sensor. If thereis an obstructed line of sight, it may benecessary to use a fiber optic probe togo around the obstacles.• Operating Environment—Intowhat kind of environment will thesensor itself be installed? If it is haz-ardous, hot, humid, corrosive orotherwise unfriendly, it will be nec-essary to protect the instrument.Lenses and cases are available towithstand corrosives; air purge sys-tems can protect lenses fromprocess materials; and various cool-ing systems are available to cool thelenses, optics and electronics.

If the surrounding temperature isthe same as the target temperature,the indicated temperature from aradiation thermometer will be accu-rate. But if the target is hotter thanthe surroundings, it may be desirableto use a device with a high N* valueto minimize the emissivity error andminimize radiation from the sur-roundings reflected into the ther-mometer. Two approaches can beused when the target is at a lowertemperature than the surroundings.The first method, Figure 8-2, is pos-sible if the target is fixed, flat, andreflects like a mirror. The ther-mometer is arranged so that it sightsperpendicular to the target.

To measure the temperature of atarget with a matte surface, youmust shield the field of view of thethermometer so that energy fromhot objects does not enter. Oneapproach, shown in Figure 8-3,involves sighting the thermometerthrough an open ended sightingtube. The other approach is to use a

cooling shield. The shield must belarge enough so that D/H ratio is 2to 4. This method can not be usedfor slowly moving or stationary tar-gets. An uncooled shield can beused to block out radiation from asmall, high temperature source thatwill not heat it significantly.

A closed end sight tube is an acces-sory that can be used to protectoptics and provide a clear sight pathfor broadband thermometers. Theone end of the tube reads the sametemperature as the target (it may betouching the target or very close to it),while cooling can be used to protectthe thermometer itself, at the otherend of the tube, from high tempera-tures. A closed or open end sight tubecan prevent attenuation of emittedradiation by water vapor, dust, smoke,steam and radiation absorptive gasesin the environment.

Industrial applications invokeeither surface temperature of

objects in the open, or tempera-tures inside vessels, pipes and fur-naces. The target may need to sightthrough a window in the lattercase. The thermometer, if perma-nently installed, can be mounted toan adjacent pedestal, or attachedto the vessel. Hardware is availablefrom manufacturers to accomplishthis. The thermometer housing mayneed to be protected from exces-sive heat via a cooling mechanism,and/or may require a continuousclean gas purge to prevent dirtaccumulation. Hardware is option-ally available for both needs.

The accessories needed for diffi-cult applications, for example, topermanently install a radiation ther-mometer on the wall of a furnace,can easily escalate the cost of aninfrared thermometer into the thou-sands of dollars, doubling the priceof the standard instrument. In Figure8-4, for example, the thermocouple



Figure 8-4: Accessories for Furnace-Wall Installation

Refactory Target Tube

Silicon Carbide Sight Tube

Sight Tube

Pipe Mount Flange

Safety Shutter

Air Purge Assembly

Sensor Head in Protective Cooling

Jacket

End Cover

*Refer to page 25

sensor head and its aiming tube aremounted inside a cooling jacket. Thecoolant flow required depends onthe actual ambient conditions whichexist. Also shown are an air purgeassembly, and a safety shutter. Thelatter allows the furnace to be sealedwhenever the radiation thermometermust be removed.

If the target and the surroundingsare not at the same temperature,additional sensors, as shown inFigure 8-5 need to be supplied. Thisconfiguration allows automaticcompensation in the radiation ther-mometer electronics for the effectsof the surroundings on the targettemperature reading.

There is a lot to consider whenselecting and installing a non-con-tact sensor to measure a criticalprocess temperature. And to the

unfamiliar, the task can seem mindboggling. How do I get emissivitydata? Which wavelength(s) is best formy application? What options do Ireally need? .... and a thousand otherquestions easily come to mind. Buthelp is available. For example, manymanufacturers have open Internetsights that contain an abundance of

helpful information to assist the firsttime user in getting started. (See listof resources, p. 68.) In addition, thereare consultants, as well as the manu-facturers themselves, who can sup-ply all the assistance needed to getup and running quickly.

• Industrial ApplicationsIn most cases, at least one of the sen-sors we’ve discussed can be used tomeasure temperature in any kind of

application, from -50 to 6,500°F . Thekey is to identify the sensor that willdo the best job. This can be a verysimple or an extremely difficultchoice. Perhaps some of the applica-tions listed below will give you a fewideas on how to use a non-contacttemperature sensor in your plant. • Airplane Checkout—The sheer sizeand height of a widebody 747 aircraftmakes it very difficult for techniciansto check the operation of variousdevices, such as pitot tubes andheating tapes used to warm pipes,water and waste tanks in variousparts of the aircraft. Before, a techni-cian had to climb a 25-ft ladder andtouch the surfaces to see if thedevices were working properly.

Now, a radiation thermometer isused during final assembly to checkthe operation of various heating ele-ments. The technician stands on theground, and aims the thermometer ateach pitot tube or heating element.Boeing reports saving 4-5 construc-tion hours on each jet.• Asphalt—Asphalt is very sensitiveto temperature during preparationand application. Thermocouples nor-mally used to measure asphalt tem-perature usually have severe breakageproblems because of the abrasivenessof the material. Infrared thermocou-ples are an ideal replacement.

The sensor can be mounted sothat it views the asphalt through asmall window in the chute, or slight-ly above for viewing at a distance. Ineither case, the sensor should havean air purge to keep the lens cleanfrom vapor or splashes. Plus, it can beconnected to the control system as ifit was a thermocouple.• Electrical System Maintenance—Infrared scanning services arebecoming widely available. Typically,a scanning service brings in a



Figure 8-5: Compensation for Elevated Ambient Temperatures

Sum of Emitted And Reflected Signals

Background TemperatureSignal Processor

Corrected Object Temperature

Emissivity Reflectivity Correction

portable imaging processor andscanner twice a year to check abuilding’s switchgear, circuit breakers,and other electrical systems. The ser-vice looks for hot spots and temper-ature differences.

Between visits, maintenance per-sonnel can perform spot checks andverify repairs with an inexpensive radi-ation thermometer. Attaching a datalogger lets a technician determineheating trends of switchgear duringpeak periods, and identify the parts ofsystem that suffer the most whenelectrical consumption goes up.• Flame Cutting—In flame cutting,before a computer cuts variousshapes from steel plate, the steelsurface has to be heated by a natur-al gas or propane flame. When a“puddle” of molten metal is detect-ed by the operator, oxygen is inject-ed into the gas stream. This blowsthe molten metal through the plateand the cutting cycle begins. If oxy-gen is injected prematurely, it makesa defective cut, leaving an objec-tionable rough and wide pit-likedepression in the plate.

A fiber optic sensor can be mount-ed on the torch and aimed to lookthrough the gas stream at the platesurface. It will detect the proper platetemperature for puddling, and informthe operator.• Glass—An infrared thermometer isideal for measuring the temperatureof soda-lime-silica glass, predomi-nantly used in making sheet, plate,and bottles. The biggest problem isthat glass has relatively poor thermalconductivity, so temperature gradi-ents exist at various depths. Thethree most commonly used wave-lengths for measuring glass—3.43, 5.0,and 7.92 microns—each see a differ-ent distance into the glass. A sensorwith 7.92 microns sees only the sur-

face, while a 3.43 micron sensor cansee up to 0.3 in. into the glass.

The trick is to select a thermome-ter which is not adversely influencedby thickness variations. Your best betmay be to send samples of glassproducts to the thermometer manu-facturer, and let them advise you onwhat device to use.

During installation, select the aim-ing point so that the instrumentdoesn’t see any hot objects behind

the transparent glass, or any reflectedradiation from hot objects in front ofthe glass. Aim the sensor at an anglethat avoids reflections, or install anopaque shield to block the reflec-tions at the source. If neither is possi-ble, use either of the higher wave-length sensors, because they are notaffected as much by reflections.

Be careful of applications wherethe glass is heated with high inten-sity, tungsten filament quartz



Cement Kilns Burning zones, preheaters

Energy Conservation Insulation and heat flow studies, thermal mapping

Filaments Annealing, drawing, heat treating

Food Baking, candy-chocolate processing, canning freezing, frying, mixing, packing, roasting

Furnaces flames, boiler tubes, catalytic crackers

Glass Drawing, manufacturing/processing bulbs, containers, TV tubes, fibers

Maintenance Appliances, bearings, currentoverloads, drive shafts, insulation, power lines, thermal leakage detection

Metals (ferrous and nonferrous) annealing, billet extrusion, brazing, carbonizing, casting, forging, heat treating, inductive heating, rolling/strip mills, sintering, smelting Metals, Pouring

Quality Control printed circuit boards, soldering, universal joints, welding, metrology

Paint Coating, ink drying, printing, photographic emulsions, web profiles

Paper Blow-molding, RIM, film extrusion, sheet thermoforming, casting

Plastic Blow-molding, RIM, film extrusion, sheet thermoforming, casting

Remote Sensing Clouds, earth surfaces, lakes, rivers, roads, volcanic surveys

Rubber Calendaring, casting, molding, profile extrusion, tires, latex gloves

Silicon Crystal growing, strand/fiber, wafer annealing, epitaxial deposition

Textile Curing, drying, fibers, spinning

Vacuum Chambers Refining, processing, deposition

2=2-color sensor H=High Temperature L=Low Temperature

2 H L 2 H L

• • • •

• •

• •

• •

• • • •

• • • • • •

• •

• • • •

• • • • • •

•

• •

• •

• • •

• •

• • • •

• •

• •

Table 8-2: Successful Radiation Thermometer ApplicationsMOUNTED PORTABLES

•

lamps. These generate radiationlevels that interfere with ther-mometers operating below 4.7microns. In this case, use a 7.92micron sensor.• Glass Molds—The temperature ofthe mold or plunger used to makeglass containers is critical: if too hot,the container may exit the mold andnot retain its shape; if too cool, itmay not mold properly. Molds mustbe measured constantly to ensurethat cooling is proceeding correctly.

An infrared thermometer can beused to take mold measurements. Afew suggestions: Don’t measure newmolds. They are usually shiny andclean, so they are reflective and havelow emissivity. As they get older,

they get dull and non-reflective, andthe emissivity becomes higher andmore repeatable. Use a radiationthermometer with a short wave-length, such as 0.9 microns, or a two-color instrument. • Humidity—An infrared thermocou-ple can be used to measure relativehumidity in any situation wherethere is a convenient source of waterand flowing air. Aim the device at a

wet porous surface with ambient airblowing across. When air movesacross a wet surface, water cools byevaporation until it reaches the wet-bulb temperature, and cooling stops.The sensor can be connected to adisplay that records the lowest tem-perature, which is the wet-bulb tem-perature, and can be used to calcu-late the relative humidity.• Immersion Thermowells—Thermowells protrude into a high-pressure vessel, stack, pipe or reac-tor, allowing a temperature sensorto get “inside” while maintainingprocess integrity. An infrared ther-mocouple or fiber optic sensor canbe positioned outside the ther-mowell looking in, rather than being

mounted inside the thermowell.Conventional sensors subjected toconstant high temperatures suffermetallurgical changes that affectstability and drift. But the non-con-tact sensors, because they are out-side, do not suffer such problems.They also respond more quickly;essentially, the response time of aradiation sensor is the same as thethermowell. Also, since the sensor

is outside, it will survive muchlonger in a very high temperatureenvironment than a conventionalsensor will.

To install a radiation thermometerin a thermowell, mount it so it isaimed directly into a hollow ther-mowell, and adjust its distance sothat its “spot size” is the same diam-eter as the thermowell. This way, thesensor will monitor temperature atthe thermowell tip. If the thermowellhas a sight glass, select a sensor thatcan see through it. • Induction Heating—Measuring thetemperature of an induction heatingprocess can be accomplished withinfrared thermocouples, thermome-ters or fiber optic sensors.

An infrared thermocouple willoperate in the very strong electricalfield surrounding induction heaters.Make sure the sensor’s shield wire isattached to a proper signal ground.The preferred method is to view thepart between the coil turns or fromthe end. If there is excessive heatingon the sensor, use a water coolingjacket (you can use the same watersource used to cool the inductioncoil).

Fiber optic sensors should bemounted so the viewing end isplaced close to the target. The tip ofthe fiber can be positioned betweenthe induction coils. Replaceableceramic tips can be used to minimizedamage and adverse effects from theradio frequency field. If the fiberwon’t fit, use a lens system to moni-tor the surface from a distance. Fiberoptic sensors are not normallyaffected by induction energy fields,but if the noise is excessively high,use a synchronous demodulationsystem. The demodulator convertsthe 400 Hz ac signal from the detec-tor head to dc, which is more



Table 8-3: Typical Application Temperature RangesAPPLICATION TEMP. RANGES

General purpose for textile, printing, food, rubber, thick plastics, paints, laminating, maintenance

Life sciences, biology, zoology, botany, veterinary medicine, heat loss and research

Thin film plastic, polyester, fluorocarbons, low temperature glass

Glass and ceramic surfaces, tempering,annealing, sealing, bending and laminating

See-through clean combustion flames and hot gases. Furnace tubes

Medium to high temperature ferrous and non-ferrous metals. See-through glass

Hot and molten metals, foundries, hardening, forging, annealing, induction heating

-50 to 1000°C -58 to 1832°F

0 to 500°C 32 to 932°F

50 to 600°C 122 to 1112°F

300 to 1500°C 572 to 2732°F 500 to 1500°C 932 to 2732°F

250 to 2000°C 482 to 3632°F

600 to 3000°C 1112 to 5432°F

immune to noise.• Plastic Film—A film of plastic orpolymer emits thermal radiation likeany other material, but it presentsunique measuring problems for anysensor, including a radiation ther-mometer. As with glass, when mea-suring film temperature, it’s impor-tant to install it so the instrumentdoesn’t see any hot objects behindthe transparent film, or any reflect-ed radiation from hot objects infront of the film.

For films of 1, 10 or 100 mil thick-

nesses, a wavelength of 3.43 or 7.92microns will work for celluloseacetate, polyester (polyethyleneterephthalate), fluoroplastic (FEP),polymide, polyurethane, polyvinylchloride, acrylic, polycarbonate,polymide (nylon), polypropylene,polyethylene and polystyrene.

As with glass, be careful of appli-cations where the film is heated withhigh intensity, tungsten filamentquartz lamps. These generate radia-tion levels that interfere with ther-mometers operating below 4.7

microns. In this case, use a 7.92micron sensor.• Web Rollers—Infrared sensors canbe used to measure the temperatureof rollers used in various web process-es, even if they are chrome plated.Uncoated metal or chrome rollers aredifficult for an IR sensor to see,because they have low emissivity andthe sensor sees too many environ-mental reflections. In such a case,paint a black stripe on an unused por-tion of the roller and aim the devicedirectly at the stripe.



Aluminum

Asphalt

Automotive

Appliances

Ammunition

Batteries

Cement

Construction Materials

Fiberglass

Food Processing

Foundry

Glass-Melting

Glass-Flat

Glass Bottles

Heat Treating

Induction Heating

Kilns

Metalworking

Mining

Non-ferrous Metals

Ovens

Paper

Pharmaceutical

Plastics

Plastic Films

Rubber

Semiconductors

Steel

Textiles

Utilities

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

TYPICAL 0.65 0.9 1.0 0.7-1.08 1.55 1.65 2.0 3.43 3.9 5.0 7.9 8-14 APPLICATIONS and 1.68 and 1.68 2-color 2-color

Table 8-4: Application Wavelengths (Microns)

SOUR

CE: IR

CON

Dull metal rollers often providereliable signals. Emissivity can shift ifthe rollers get covered with dirt,moisture or oil. If in doubt, simplypaint a stripe. Non-metallic surfacedrollers provide a reliable signal nomatter where the device is pointed.

Accessories, Features & OptionsRadiation thermometers and ther-mocouples are available with a hostof features to solve a wide range ofapplication conditions. All infraredsensors are available in a wide rangeof wavelengths, temperature rangesand optical systems. Portable unitsalmost always are available with car-rying kits, and permanently mount-ed units are ruggedized. Listedbelow are other options, featuresand accessories that make thesesensors more useful for certaintypes of applications.

Backlit LCD displays, integrallyattached or remotely mountedfrom the thermometer, are avail-able. Multiple variables can beviewed simultaneously on thesedisplays. These data can includecurrent temperature, minimummeasured temperature (time based),maximum measured temperature(time based), average temperaturemeasured (time based), and differ-ential temperature (for example,between the target and the sur-roundings).

Microprocessor-based radiationthermometers have input options toallow data to be integrated into themeasurement from other sensors orthermometers in the loop. For exam-ple, a separate thermocouple or RTDinput to the thermometer can beused to compensate the measuredtarget temperature for changingambient temperature conditions.

Protection from high electromag-netic and radio frequency interfer-ence (EMI/RFI) is available if thethermometer must be installed in adifficult environments.

Most infrared thermometers canbe supplied with an emissivityadjustment. In addition, somedevices can be supplied with anadjustable field of view. This isaccomplished by installing an iris inthe optical system that can beopened or closed to provide wide ornarrow angle field of views.

• Handheld IR ThermometersHandheld instruments are generallycompletely self-contained, battery-powered units, with manual controlsand adjustments and some form ofdigital readout. Units can be mountedon tripods. Other accessories include:• Laser sights, which paint a visiblespot on the target, making it easier todetermine where the instrument ispointed. This option is available bothintegrally attached or detachablefrom the thermometer. Hand-helddevices used for up-close spot tem-perature measurement (for example,to measure component temperatureon printed circuit boards) can haveaudible focusing guides instead oflight markers.• Dataloggers, for acquiring datafrom thermometers and recording itfor future use;• Digital printers• Electrical system scanners, designedspecifically for finding hot spots inelectrical panels, switchgear, fusepanels, transformers, etc. • Handheld, shirt-pocket-size scan-ner for general surface temperaturemeasurement.• Outputs: RS232C serial and/or 1mV/degree.

• Infrared ThermocouplesThese self-powered devices generate athermocouple signal output usingradiated energy, but usually have nosignal processing or display systems.An infrared thermocouple is a sensoronly, but it does have a few optionsand accessories.• Cooling jacket kits for air or watercooling;• Handheld version for precise spotmeasurements;• Close-focus model with up to 60:1field of view;• Periscope kit for right-angle mea-surements;• Low-cost ($99) model with ABSplastic housing;• Adjustable emissivity;• Two-color pyrometry unit thatuses short-wave and long-waveinfrared thermocouples.

• Fiber Optic SensorsProbes are available in lens cells ofvarious sizes, with replaceableglass or quartz tips. Optionsinclude a ceramic/metal tip forhigh temperatures, a polymer boltfor extrusion applications, ejectorpin probe for injection molding,and right angle prisms. Sensorprobes also are available as opticalrods up to 60 cm long.

Cables can be supplied in single,bifurcated or trifurcated fiber opticbundles, and enclosed in jacketsmade of flexible stainless steel (stan-dard), ceramic, heavy duty wire braidfor abrasion resistance, or Teflon forhigh radio frequency fields. Cablestypically are up to 30 ft long.

• Indicators and Controllers Display units and controllers areavailable in models ranging from a



simple digital panel meter that dis-plays the signal as a temperature in °For °C, to complex multi-channelprocessors that perform signal con-ditioning, linearization, peak-picking,alarm monitoring, saving min/maxvalues, signal averaging, data loggingand a host of other signal processingand manipulation functions.

• Mounted IR ThermometersThe same basic features, optionsand accessories are available forradiation thermometers, two-colorsystems, and line scanners.Ruggedized for use on the plantfloor, all these devices have severalaccessories to help them survive inhostile environments.• Air purge—Attaches to front endof sensor housing and provides posi-tive air pressure in front of the lens,preventing dust, smoke, moisture andother contamination from reachinglens. In two-color systems, it canattach to front of re-imaging lens. • Air or water cooling jackets—Available for warm (35°F above ambi-ent) and hot (up to 400 °F) environ-ments, cooling jackets keep sensor

temperature at normal levels insidethe enclosure.• Peltier effect cooling—Some linescanners have electronic cooling sys-tems, using Peltier effect devices. • Sighting accessories, includingsight tubes, laser pointing devices,and scopes.

• Onboard data logging functionsare available, as well as options forthermal printers to retrieve storeddata. Data can also be remotelytransmitted digitally.• Transmitters—Ruggedized NEMA 4housing with 4-20 mAdc and/orRS232C/RS485 outputs. T



References and Further Reading• Handbook of Temperature Measurement & Control, Omega Press, 1997.• New Horizons in Temperature Measurement & Control, Omega Press,1996.• Product Previews in Temperature Measurement & Control, 21st Century™Preview Edition, Omega Press, 1997.• Temperature Measurement in Engineering, H. Dean Baker, E. A. Ryder, andN. H. Baker, Omega Press, 1975.• “Glass Temperature Measurement,” Technical Note 101, Ircon Inc., Niles, Ill.• Handbook of Non-Contact Temperature Sensors, Exergen Corp.,Watertown, Mass., 1996.• “How Do You Take Its Temperature?, ” Aviation Equipment Maintenance,February 1992.• “How Infrared Thermometers are Gaining Acceptance,” Paul Studebaker,Control, July 1993.• IR Answers and Solutions Handbook, Ircon Inc., Niles, Ill.• “On-Line Industrial Thermal Imaging Systems Evolve Expanding InfraredMeasuring Capabilities,” George Bartosiak, Industrial Heating, December 1992.• “Plastic Film Measurement,” Technical Note 100, Ircon Inc., Niles, Ill.• “Preventive Maintenance Program Averts Crashes with IRThermometer/Thermal Scanning,” Engineer’s Digest, September 1989.

Documents

Trans v01 Ch08