1. By Anupam Prakash (3RD YR EIE) ROLL NO.:-18700510014
Temperature Sensors
By Anupam Prakash
(3RD YR EIE)
ROLL NO.:

2. Brief Overview Types of Temperature Sensors and how they work
Applications
Advantages
Disadvantages and
Conclusion

3. Types of Temperature Sensors
Thermocouples
Resistance Temperature Detectors (RTDs)
Thermistors
Semiconductors

4. Thermocouples Two wires of different metal alloys.
Converts thermal energy into electrical energy.
Requires a temperature difference between measuring junction and reference junction.
Easy to use and obtain.

5. Principle Of Operation
Thermocouple follows Seebeck effect
The emf produced in a thermocouple is given by
E= a ( Ɵ) + b ( Ɵ)*( Ɵ)
where Ɵ = difference in temp. b/w the hot junction and reference junction of thermocouple.
& a , b are contants.

6. Types of Thermocouple Types Composition Temp. Range B Pt 30% Roh (+)
deg. F C
Tu 5% Rhe (+)
Tu 26% Rhe (-)
deg. F E
Chromel (+)
Constantan (-)
deg. F J
Iron (+)
deg. F K
Alumel (-)
deg. F

7. Types
Composition
Temp. Range M
Ni (+)
Ni (-)
deg. F N
Nicrosil (+)
Nisil (-)
deg. F R
Pt 13% Rh (+)
Pt (-)
deg. F S
Pt 10% Rh(+)
Pt(-)
deg. F T
Copper (+)
Constantan (-)
-330 – 660 deg. F

8. Thermocouple Applications
Plastic injection molding machinery
Food processing equipment
Deicing
Semiconductor processing
Heat treating
Medical equipment
Industrial heat treating
Packaging equipment

9. Thermocouples Advantages Disadvantages Simple, Rugged
High temperature operation
Low cost
No resistance lead wire problems
Point temperature sensing
Fastest response to temperature changes
Least stable, least repeatable
Low sensitivity to small temperature changes
Extension wire must be of the same thermocouple type
Wire may pick up radiated electrical noise if not shielded
Lowest accuracy

10. Resistance Temperature Detectors (RTDs)
Wire wound and thin film devices.
Nearly linear over a wide range of temperatures.
Can be made small enough to have response times of a fraction of a second.
Require an electrical current to produce a voltage drop across the sensor

11. Resistance with temp. relationship
R=Ro (1+a1T+a2(T*T)+…… +an(T*T*T… n times))
where Ro = resistance at temp. T=0
Types of RTD
2 wire RTD wire RTD

12. RTD Applications Air conditioning and refrigeration servicing
Furnace servicing
Foodservice processing
Medical research
Textile production

13. RTDs Advantages Disadvantages High cost Most stable over time
Slowest response time
Low sensitivity to small temperature changes
Sensitive to vibration (strains the platinum element wire)
Decalibration if used beyond sensor’s temperature ratings
Somewhat fragile
Most stable over time
Most accurate
Most repeatable temperature measurement
Very resistant to contamination/
corrosion of the RTD element

14. Thermistors A semiconductor used as a temperature sensor.
Mixture of metal oxides pressed into a bead, wafer or other shape.
Beads can be very small, less than 1 mm in some cases.
The resistance decreases as temperature increases, negative temperature coefficient (NTC) thermistor.

15. Application of Thermistors
Resistance temp. characterstics
RT1= RT2 exp ( B ( 1/T1 -1/T2)
where RT1 = resistance at temp. T1
RT2 = resistance at temp. T2
B = constant
Application of Thermistors
Most are seen in medical equipment markets.
Thermistors are also used are for engine coolant, oil, and air temperature measurement in the transportation industry.

16. Thermistors Limited temperature range
Advantages Disadvantages
Limited temperature range
Fragile
Some initial accuracy “drift”
Decalibration if used beyond the sensor’s temperature ratings
Lack of standards for replacement
High sensitivity to small temperature changes
Temperature measurements become more stable with use
Copper or nickel extension wires can be used

17. Semiconductors
Are small and result from the fact that semiconductor diodes have voltage-current characteristics that are temperature sensitive.
Temperature measurement ranges that are small compared to thermocouples and RTDs, but can be quite accurate and inexpensive.

18. Semiconductor Applications
Hard Disk Drives
Personal Computers
Electronic Test Equipment
Office Equipment
Domestic Appliances
Process Control
Cellular Phones

19. Determining Factors of a Temp. Sensor
Low Power
Serial Interface
Small
Accurate
Wide temperature range
Extras
I2C Interface
Temperature Alarms

20. CONCLUSION
In this application note , the concept and usage of different temperature sensors are discussed . Among these temp. sensors
1. Thermocouple gives the fastest response to temp. change
2. RTD is most suitable over time , most accurate temp. sensor.
3. Thermistor has the highest sensitivity to small temp. change.

21. THANK YOU