Transducers: Static and dynamic Characteristics of Sensor, Potentiometers – LVDT – Capacitance sensors – Strain gauges – Eddy current sensor – Hall effect sensor – Temperature sensors – Light sensors

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 – e.g.: a thermocouple may have a range of -100
to 1000°C
 Span : maximum value of input – minimum value of
input
 Error : measured value – true input value
 Accuracy :
 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.
 Dead time: it is the time taken by the sensor from the
application of input to begin its response and change.
 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. Strain gauge Displacement sensor
Strain gauge with Wheatstone bridge circuit

15. Capacitive displacement sensor
Different form of capacitive sensor

16. Push – pull capacitive sensor
Capacitive proximity sensor

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

18. Linear variable Differential Transformer (LVDT) output

19. Rotary variable Differential Transformer (RVDT)

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

21. Hall effect sensors
Principle of Hall effect

22. Hall effect Sensor

23. Fluid level Hall effect Sensor

24. Photoelectric sensor
Through beam method
Retro reflective method

25. Optical encoder
Optical encoder

26. Incremental encoder disc track
pattern

27. An 8-bit grey code Absolute encoder disc

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

29. Eddy current proximity sensors

30. Inductive proximity sensors

31. Pneumatic proximity sensors

32. Proximity switches
Magnetic read switches
Micro switches

33. Velocity and motion sensor
 Incremental encoders
 Tachogenerator
 Pyroelectric sensors

34. Tachogenerator
Variable reluctance tachogenerator

35. Pyroelectric sensors
Dual pyroelectric sensor

36. Force sensor
Strain Gauge Load Cell

37. Fluid pressure sensors
 Diaphragm pressure sensors
 Capsule pressure sensors
 Bellow pressure sensors
 Bourdon tube pressure sensors
 Piezoelectric sensor
 Tactile sensor

38. Diaphragm pressure sensors

39. Typical Diaphragm Pressure gauge

41. Capsule pressure sensors

42. Bellow pressure sensors

43. Bourdon tube pressure sensors

44. Piezoelectric sensor

45. Tactile sensor

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

47. Bimetallic strips

48. Resistance temperature
detectors (RTDs)

49. Thermistors

50. Thermocouple

51. Light sensors
 Photo resistors
 Photodiode
 phototransistors

52. Photoresistor

53. Photodiode

54. Phototransistors
Phototransistor light detector circuit

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