t srt y tstr sr5tsrts5ts t sd gsf trysr y

Artg srest sr5t st st tsrt stsete tsetse tete

1. TEMPERATURE
SENSORS
NARESH J P, FINAL YEAR PRODUCTION

2. SENSORS
•Sensors are devices which are used to measure the change in external
conditions and provide an output in the form of a measurable quantity.
•The output is usually in the form of electrical signals, but it may also be
other forms, like mechanical deformation, chemical changes, etc
•Sensors used in mechatronics generally provide outputs as electrical signals
or analog/digital voltage

3. SENSORS

4. TYPES OF SENSORS
•There are many kinds of sensors which convert various types of physical
quantities into output signals (or) measurable quantities.
•Examples of such sensors are:
Temperature sensors –Convert temperature to signals
Humidity sensors-Convert the moisture content of air into signals
Pressure sensors-Used to measure the pressure in pipes, atmospheric pressure,etc
Flow sensors-These are used to measure the flow rate of fluids in many conditions
like pipes, etc

5. TEMPERATURE SENSORS
•These are sensors which measure the temperature of a body or the
environment and provides the output in various forms such as
electrical(RTD’s), mechanical(Bimetallic strip), etc.
•These may be electrical and non electrical
•The temperature sensors we will focus on are:
Bimetallic strips
RTD’s
Thermistors
Thermodiodes /transistors
Thermocouples

6. TEMPERATURE SENSOR TYPES
•Bi-metallic strips
•RTD’s
•Thermistors
•Thermocouples
•Thermodiode

7. Bimetallic strips
•Consists of 2 metallic strips of identical dimensions and different materials
which are attached together longitudinally.
•The metals used in the strips are selected in such a way that their values of
coefficient of thermal expansion are different.

8. Bimetallic Strips
Concept is that the different metals used in the strip have different values of thermal coefficient of
expansion and one metal will expand more than the other while subjected to the same temperature
change. This causes one metal to create an tensile force on the other while the other is subjected to
compressive force due to it having a lesser temperature coefficient of expansion. This causes
bending of the metal in one direction.

9. Bimetallic Strips
SPIRAL TYPE STRIP
HELICAL TYPE STRIP

10. RTD’s(Resistance Temperature
Detectors)
•These are temperature sensors which work on the principle of change in
resistance of metal due to change in temperature.
•Here a metallic element, whose resistance at a particular temperature and
the metal’s resistance-temperature relationship is known is used in a
Wheatstone bridge configuration in order to determine the change in
temperature due to the change in resistance that the metal exhibits.

11. RTD’s(Resistance Temperature
Detectors)

12. RTD’s(Resistance Temperature
Detectors)

13. RTD’s(Resistance Temperature
Detectors)
Application of RTD in a Boiler

14. Thermistors
•These function on the same principle as RTD’s but they employ metal oxides
as the resistance elements and have a different value of temperature
coefficient of resistance.
•These have 2 types:
NTC(Negative temperature coefficient)
PTC(Positive temperature coefficient)
•Another main difference between these and RTD’s are that RTD’s show a
linear variation of resistance with temperature while Thermistors show a
non linear(exponential/parabolic) resistance relationship with temperature.

15. Thermistors

16. Thermodiodes
•Semiconductor diodes allow electricity to flow in one direction and impede
the flow in the other direction. A thermal diode performs a similar gating
function, only with heat energy instead of electrical energy.
•The voltage difference across a diode decreases when temperature increases,
and so when we change the temperature associated with the diode the
voltage also changes.
•This variation in voltage can be analysed to find out the change in
temperature, as the temperature difference will contribute directly to the
change in voltage.

17. Thermodiodes
1N4007 Diode is normally used as a thermodiode

18. Thermodiodes

19. Thermocouples
•These work on the principle of Seebeck effect, i.e. when 2 dissimilar metals’
junctions are maintained at different temperatures then an emf is generated
across the circuit

20. Thermocouples
Compensation:
To eliminate errors in the temperature measurement process using
thermocouples, we employ various compensation techniques which are,
•Lead wire compensation
•Cold junction compensation
•Linearization

21. Thermocouples
Thermocouple usage in vacuum furnace

22. Parameter Bimetallic Strip
RTD (Resistance
Temperature
Detector)
Thermistor Thermocouple Thermodiode
Material
Two metals with
different coefficients of
thermal expansion (e.g.,
steel and copper)
Platinum (commonly
used)
Metal oxides (NTC or
PTC)
Various metal
combinations (e.g., Type
K: Nickel-
Chromium/Nickel-
Alumel)
Semiconductor (typically
silicon)
Temperature Range -40°C to 300°C -200°C to 850°C
-55°C to 125°C (NTC), -
100°C to 300°C (PTC)
-200°C to 1750°C
(depending on type)
-55°C to 150°C
Accuracy Moderate High (±0.1°C)
Moderate to high (±0.1°C
to ±0.5°C)
Varies by type (e.g., Type
K: ±2.2°C or ±0.75%)
Moderate (±2 mV/°C)
Response Time Slow to moderate Moderate to fast Fast Fast Fast
Sensitivity Low High
High (NTC: decreases
with temperature, PTC:
increases with
temperature)
Moderate
High (linear voltage
change with
temperature)
Stability Good Excellent Good Good Good
Applications
Thermostats,
temperature control
devices
Industrial temperature
measurement, HVAC
systems
Consumer electronics,
automotive, medical
devices
Industrial processes,
scientific research, home
appliances
Temperature sensing in
electronic circuits,
thermal management in
ICs
Construction
Two metals bonded
together
Thin film or wire-wound
platinum element
Ceramic or polymer
bead/disc
Two dissimilar metal
wires joined at one end
PN junction diode
Cost Low to moderate High Low to moderate Low to moderate Low

23. THANK YOU