1. Thermal sensor
By: Sanchari guha
15/IC/48

2. Why we use thermal sensor?
Different properties of an object change due to change in temperature.
Various changes in physical dimension.
Variation in electrical and optical properties.
Generation of thermo-electricity.
Change in frequency of vibration of piezoelectric crystals.
Change in velocity of sound.
Change of intensity of emitted radiations.

3. Types of thermal sensor
Expansion thermometer.
Electrical temperature instrument.
radiation instrument

4. Expansion thermometer
Expansion of liquid
Expansion of gas
Expansion of solid
This type of sensors is mainly used for recording environmental temperature locally. Component Brass & Invar generally.
Range : -75℃ to 540 ℃
This type of sensor is generally used for laboratory purpose and body temperature measurement. Various types of liquids are used in it.
Range : -120℃ to 320℃
This system is used to measure the temperature of open tank liquid to cooking kettle and steam line, pipe line of the fluid flow.
Range : -120 ℃ to 427 ℃

5. Electrical measurement instrument Resistance temperature detector (RTD)
Platinum RTD: Pt 100, at 0℃ resistance of Pt is 100

6. Wire wound type RTD 2 wire wound 3 wire wound 4 wire wound
(R2/R1)=(R3/(L1+L2+RT))
If R1=R2
RT+L1+L2=R3
Lead wire error : L1 & L2
(R2/R1)=((R3+L3)/(L1+RT))
If R1=R2
RT+L1=R3+L3
L1=L3 ; RT=R3
Lead wire error : L1-L3
(R2/R3)=((R1+A)/(RT+B))
RT=(R1a+R1b)/2
Lead wire error is A & B

8. thermistor SHAPE OF THERMISTOR
Positive temperature co-eff (PTC) : Made of doped polycrystalline ceramic containing barium, lead & stongtium titanate.
Negative temperature co-eff (NTC): Specific mixture of oxides of Si, Ge, Ni, Mn etc.
SHAPE OF THERMISTOR
Rod
Plate
Disc
Glass probe

9. Working formula of thermistor
Rt = Ro exp β (1/t – 1/to)
β= temperature resistance co-eff of thermistor.
ADVANTAGES
Small size, fast response, available in different shapes.
Suitable for narrow range (-60℃ to 150℃)
Low cost.
Wire resistance and contact resistance are negligible wrt thermistor resistance.
DISADVANTAGE
R & P relation is non-linear & not used for wide temp. range

11. Materials of thermocouple
J= iron constantan (-200 to 1000)℃
T= copper-constantan(-200 to 350) ℃
K= chromel-alumel(-190 to 1200) ℃
R= pt-ptRh(13%) (0 to 1600) ℃
S= pt-ptRh(10%) (0 to 1600) ℃
B= ptRh(30%) –ptRh(6%) (0 to 1820) ℃

12. Industrial use of thermocouple
ICE BATH TECHNIQUE :

13. RADIATION INSTRUMENT radiational PYROMETER
The shielding element protects thermocouple junction from direct radiation and by this thermocouple hot junction we can measure temperature of radiation receiver which is proportional to radiation energy of the target. Range: 700℃ to 3000 ℃. FORMULA RT=σT^4

14. Optical pyrometer
Brightness of target (Bt) =brightness of filament (Bf) Target temperature (Tt) =filament temperature (Tf) Intensity of radiant energy is proportional to source of known intensity

15. reference Sensors and Transducers, D.Patranabis.
Instrument Transducers, H.K.P.Nubert
Measurement system by Tata McGraw Hill.
Class notes by P.Rakshit ma’am.
Photos from Google.

16. conclusion
We conclude from this chapter that thermal sensors are used in our daily life and in industrial purposes in various ways. Thermal sensors are widely used sensors in industrial purposes as it is easily available and easy to use. It is available in various shapes for various purposes. It serves our national security and used in various military purposes. Still now a lot of researches are going on this field to serve mankind in various ways.

17. THANK YOU for your kind attention any queries???