Sensors are devices that produce an output signal in response to a physical input like pressure, temperature, or displacement. Transducers convert one form of energy into another. Sensor performance is characterized by static and dynamic characteristics. Static characteristics include range, accuracy, sensitivity, hysteresis, linearity, repeatability, reproducibility, stability, and resolution. Dynamic characteristics include response time, time constant, rise time, and setting time. Common sensors include displacement, temperature, light, position, fluid level, and proximity sensors that use effects like piezoelectricity, resistance temperature, photoelectricity, and capacitance.

2. Sensor
 Sensor are devices which produce a proportional
output signal (mechanical, electrical, magnetic etc.,)
when exposed to a physical phenomenon (pressure,
temperature, displacement , force etc.,).

3. Transducer
 Transducer are devices which converts an input of one
form of energy in to an output of another form of
energy.

4. Performance terminology
• Static characteristics
– Static characteristics of an instrument are the
parameters which are more or less constant or varying
very slowly with time.
• Dynamic characteristics
– Sensors and actuators respond to inputs that change
with time. Dynamic characteristics of an instrument are
the parameters which are varying with time.

5. Static characteristics
 Range –Every sensor is designed to work over a
specified range. e.g.: a thermocouple may have a range
of -100 to 1160°C
 Span : maximum value of input – minimum value of
input.
 Error : measured value – true input value
 Accuracy : is inversely proportional to error.
 Sensitivity: it is defined as the change in output per
change in input

6. Static characteristics
 Hysteresis: it is defined as the maximum difference in
output for a given input when this value is approached
from the opposite direction.
 Linearity: it is refer to the output that is directly
proportional to input over its entire range.

7. Static characteristics
• Repeatability: it is defined as the ability of the sensor
to give same output reading when the same input value
is applied repeatedly under the same operating
conditions.
• Reproducibility: it is defined as the degree of closeness
among the repeated measurements of the output for
the same value of input under the same operating
conditions at different times.

8. Static characteristics
 Stability : it means the ability of the sensor to indicate
the same output over a period of time for a constant
input.
 Resolution: it is defined as the smallest change that
can be detected by a sensor

9. Dynamic characteristics
 Response time
 Time constant
 Rise time
 Setting time

10. Displacement sensor
 Potentiometer sensor
 Strain gauge sensor
 Capacitive sensor
 Inductive sensors (LVDT)

11. Potentiometer Displacement sensor
Linear potentiometer

12. Potentiometer Displacement sensor
Rotary potentiometer

13. Potentiometer Displacement sensor
Potentiometer with voltage divider

14. Strain gauge Displacement sensor
Strain gauge with Wheatstone bridge circuit

16. Capacitive displacement sensor
Different form of capacitive sensor

17. Push – pull capacitive sensor
Capacitive proximity sensor

18. Inductive displacement sensor
Linear variable Differential Transformer (LVDT)

19. Linear variable Differential Transformer (LVDT) output

20. Rotary variable Differential Transformer (RVDT)

21. Position sensors
 potentiometer
 Capacitive sensor
 Inductive sensor
 Hall effect sensors
 Photoelectric sensor
 Optical encoder

22. Hall effect sensors
Principle of Hall effect

23. Hall effect Sensor

24. Fluid level Hall effect Sensor

25. Temperature sensors
 Bimetallic strips
 Resistance temperature detectors (RTDs)
 Thermistors
 Thermocouples
 Thermodiodes and transistors

26. Bimetallic strips

27. Resistance temperature
detectors (RTDs)

28. Thermistors
Bead type have platinum wire sintered in to a ceramic body
(bead)
Metalized surface contact thermistors are called chips or
flakes

29. Thermocouple

30. Light sensors
 Photo resistors
 Photodiode
 phototransistors

31. Photodiode

32. Phototransistors
Phototransistor light detector circuit

33. Proximity sensor
 Optical encoders
 Hall Effect sensors
 Capacitive sensors
 Eddy current proximity sensors
 Inductive proximity sensors
 Pneumatic proximity sensors
 Proximity switches

34. Eddy current proximity sensors

35. Selection of sensors
 Accuracy required
 Precision
 Sensitivity
 Operating range
 Resolution
 Speed response.
 Reliability
 Calibration and
maintenance.
 The nature of output
 Linearity
 Environmental
conditions
 Cost
 Size and weight