Embed Size (px)
Citation preview
Presented By Zaeem Sajjad Naqvi UET-2K14-ME-076
Swedish College of Engineering & Technology Wah Cantt
Temperature
scalar quantity
Degree of hotness or coldness
Molecular K.E. = Temperature
Sensors A sensor is a device that converts real world data
(Analog) into data that a computer can understand using ADC (Analog to Digital converter)
A sensor is a device that detects and responds to some type of input from the physical environment. The specific input could be light, heat, motion, moisture, pressure, or any one of a great number of other environmental phenomena. The output is generally a signal that is converted to human-readable display at the sensor location or transmitted electronically over a network for reading or further processing.
Temperature Sensors Temperature Sensors are devices that can
sense the difference amount of heat between application space and reference.
They are used to measure temperature and change of heat transfer of a medium.
Temperature SensorsTechnology Name
A-Mechanical • Thermometer• Therm
B-Electrical • Thermistor• Themocouple• Resistance thermometer(RTD’s)
C-Wirless • Pyrometer
A-Thermometer Thermometer is
temperature measuring device
It is filled with a liquid such as heat can cause expansion or evoporation on it. So that, liquid can pressurized. The pressure is related to the temperature and it may be indicated on a simple gauge.
A-Thermometer Advanteges ; Low cost , Simple construction Disadvantages;No remote measurement Range According to British Standards, correctly
calibrated, used and maintained liquid-in-glass thermometers can achieve a measurement uncertainty of ±0.01 °C in the range 0 to 100 °C
A-Therm(bi metallic) Therm is also known as bi-metallic A bimetallic strip is used to
convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper, or in some cases steel and brass
Bimetal strips are used in miniature circuit breakers to protect circuits from excess current.
B-Thermocouple A thermocouple is a comparison of at least two
metals joined together to form two junctions one is connected to the body of known temperature(hot body) and other junction is connected with the body of unknown temperature(cold body).thermocouple measure the unknown temperature of body with respect to known temperature body.
A variety of thermocouples are available, suitable for different measuring applications
They are usually selected based on the temperature range and sensitivity needed
B-ThermocoupleADVANTAGES AND DISADVANTAGES They are simple, strong, need no
batteries, measure over very wide temperature ranges.
The main limitation is accuracy; System errors of less than 1°C can be difficult to achieve
B-ThermocoupleAPPLICATIONS Thermocouples are most suitable
for measuring over a large temperature range, up to 1800 °C
These are widely used in the steel industry, heating appliances, manufacturing of electrical equipment's like switch gears etc.
B-Thermistor A thermistor is a type of resistor with resistance
varying according to its temperature.
The resistance is measured by passing a small, measured direct current through it and measuring the voltage drop produced.
There are basically two broad types 1. NTC-Negative Temperature Coefficient: used
mostly in temperature sensing 2. PTC-Positive Temperature Coefficient: used mostly in electric current control.
B-Thermistor TYPES OF THERMISTORS NEGATIVE TEMPERATURE
COEFFICIENT:A NTC thermistor is one in which the zero-power resistance decreases with an increase in temperature.
POSITIVE TEMPERATURE COEFFICIENT:A PTC thermistor is one in which the zero-power resistance increases with an increase in temperature
B-Thermistor
ADVANTAGESAND DISADVANTAGES
• Thermistors, since they can be very small, are used inside many other devices as temperature sensing and correction devices
• Thermistors typically work over a relatively small temperature range, compared to other temperature sensors, and can be very accurate and precise within that range
APPLICATIONS• PTC thermistors can be used as current-limiting devices for circuit
protection, as replacements for fuses. • PTC thermistors can be used as heating elements in small temperature-
controlled ovens. • NTC thermistors are used as resistance thermometers in low-temperature
measurements of the order of 10 K. • NTC thermistors are regularly used in automotive applications.
B-Resistance Thermometer Resistance thermometers, also
called resistance temperature detectors (RTDs), are sensors used to measure temperature.
RTD’s are the resistance of a conductor usually increase as the temperature increase.
If the properties of that conductor are known, the temperature can be calculated from the measured resistance.
The most common RTD’s are PT100, PT 1000 and Ni100
The different RTD’s analyse 0°C with different resistive values. For example, PT 100 is 100Ω at 0°C.
The temperature can be found by using The Callender Van-Dusen equations.
B-Resistance Thermometer RTD’s has different wiring
and connection type for sensitivity of application.
Lead and reference pins are depending on measurement sensitivity.
B-Resistance Thermometer
Common Resistance Materials for RTDs:
Platinum (most popular and accurate) Nickel Copper Tungsten (rare)
CONSTRUCTION OF RTD
B-Resistance Thermometer• CONSTRUCTION OF RTD • RTD elements consist of a length of fine coiled wire wrapped around a
ceramic or glass core• The element is usually quite fragile, so it is often placed inside a
sheathed probe to protect it• The RTD element is made from a pure material whose resistance at
various temperatures has been documented. • The material has a predictable change in resistance as the temperature
changes; it is this predictable change that is used to determine temperature
C-Pyrometer A pyrometer is a type of thermometer used to
measure high temperatures. It is used for measuring temperature without any physical contact. Its is used for measuring body temperature by measuring its electromagnetic radiation
Principle Its principle depends upon the relationship between temperature of a
hot body and electromagnetic radiation emitted by the body. When a body is heated it emits thermal energy known as heat radiation. It is a technique for determining a body temperature by measuring its electromagnetic radiation
C-Pyrometer Types Optical pyrometer Radiation pyrometer
Radiation pyrometer Optical pyrometer
C-Pyrometer
Optical pyrometer The Optical Pyrometer is a highly-developed
and well accepted noncontact temperature measurement device.
It is widely employed for accurate measurement of the temperature of furnaces, molten and other heated materials.
It is primarily used in the range of 1000 to 5000 ⁰F.
C-Pyrometer Working Optical Pyrometers work on the basic principle of using the human eye
to match the brightness of the hot object to the brightness of a calibrated lamp filament inside the instrument.
The radiation from the source is emitted and the optical objective lens captures it. The lens helps in focusing the thermal radiation on to the reference bulb.
The observer watches the process through the eye piece and corrects it in such a manner that the reference lamp filament has a sharp focus and the filament is super-imposed on the temperature source image.
The observer starts changing the rheostat values and the current in the reference lamp changes. This in turn, changes its intensity.
C-Pyrometer Advantages Simple assembling of the
device enables easy use of it.
Provides a very high accuracy with +/-5 degree Celsius
There is no need of any direct body contact between the optical pyrometer and the object. Thus, it can be used in a wide variety of applications.
Disadvantage• As the measurement is
based on the light intensity, the device can be used only in applications with a minimum temperature of 700 degree Celsius.
• The device is not useful for obtaining continuous values of temperatures at small intervals
C-Pyrometer Applications Used to measure
temperatures of liquid metals or highly heated materials.
Can be used to measure furnace temperatures. Technician measuring the temperature of molten silicon at
2650°F with a disappearing filament pyrometer
Temperature Measuring SensorsTechnology Names Range costA-Mechanical • Thermometer
• therm0-100°C-17.7-537.7°C
LowLow
B-Electrical • Thermistor• Thermocouple• Resistance
thermometer(RTD’s)
-20 to 120°C
-200 to 600°CLowHigh
C-Wireless • Pyrometer Upto 1400°C High
