I. Transducers are devices that convert one form of energy into another. They may convert a physical quantity like pressure, temperature, or light intensity into an electrical signal. II. Transducers can be classified by their operating principle, type of output signal, energy conversion method, and more. Common types include resistive, capacitive, inductive, and piezoelectric transducers. III. Examples of transducers include thermocouples and thermistors for temperature measurement, strain gauges and load cells for force/pressure measurement, and tachogenerators and optical sensors for speed measurement.

1. Transducers
1

3. Transducers
• A Transducer is a device which converts one form of
energy into another form.
• Alternatively, a Transducer is defined as a device which
provides usable output response to a specific input
measured which may be a physical quantity.
• A Transducer can also be defined as a device when
actuated by energy in one system supplies energy in the
same form or in another form to a second system.

4. Classification of Transducers
• Transducers may be classified according to their
application, method of energy conversion, nature
of the output signal, and so on.
•
Transducers
On The Basis of
principle Used
Active/Passive Primary/Secondary Analog/Digital
Transducers
Inverse
Transducers
Capacitive
Inductive
Resistive

5. Active and Passive Transducers
• Active transducers :
• These transducers do not need any external source of power for
their operation. Therefore they are also called as self generating
type transducers.
I. The active transducer are self generating devices which operate
under the energy conversion principle.
II. As the output of active transducers we get an equivalent
electrical output signal e.g. temperature or strain to electric
potential, without any external source of energy being used

6. Classification of Active Transducers

7. Example of active transducers
• Piezoelectric Transducer- When an external
force is applied on to a quartz crystal, there will be
a change in the voltage generated across the
surface. This change is measured by its
corresponding value of sound or vibration.

8. Passive Transducers
• These transducers need external source of power for
their operation. So they are not self generating type
transducers.
• A DC power supply or an audio frequency generator is
used as an external power source.
• These transducers produce the output signal in the
form of variation in electrical parameter like resistance,
capacitance or inductance.
• Examples – Thermistor, Potentiometer type transducer

9. Primary and Secondary Transducers
• Some transducers contain the mechanical as well as
electrical device. The mechanical device converts the
physical quantity to be measured into a mechanical
signal. Such mechanical device are called as the
primary transducers, because they deal with the
physical quantity to be measured.
• The electrical device then convert this mechanical
signal into a corresponding electrical signal. Such
electrical device are known as secondary transducers.

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Example of Primary and secondary
transducer

11. According to Transduction principle
used

12. Capacitive Transduction:
• Here, the measurand is converted into a change in
capacitance.
• A change in capacitance occurs either by changing
the distance between the two plates or by changing
the dielectric.
d
Area=A

13. Electromagnetic transduction:
• In electromagnetic transduction, the measurand is
converted to voltage induced in conductor by change
in the magnetic flux, in absence of excitation.
• The electromagnetic transducer are self generating
active transducers
• The motion between a piece of magnet and an
electromagnet is responsible for the change in flux

15. CLASSIFICATION OF TRANSDUCERS
According to Transduction Principle
PHOTOVOLTAIC TRANSDUCTION :
•In photovoltaic transduction the measurand is
converted to voltage generated when the junction
between dissimilar material is illuminated as shown in
fig.

16. CLASSIFICATION OF TRANSDUCERS
According to Transduction Principle
PHOTO CONDUCTIVE TRANSDUCTION :
•In photoconductive transduction the measurand is
converted to change in resistance of semiconductor
material by the change in light incident on the material.

17. Analog and Digital Transducers
Analog transducers:
• These transducers convert the input quantity into an
analog output which is a continuous function of time.
• Thus a strain gauge, an L.V.D.T., a thermocouple or a
thermistor may be called as Analog Transducers as they
give an output which is a continuous function of time.
Digital Transducers:
• These transducers convert the input quantity into an
electrical output which is in the form of pulses and its
output is represented by 0 and 1.

18. Transducer and Inverse
TransducerTransducer:
• Transducers convert non electrical quantity to
electrical quantity.
Inverse Transducer:
• Inverse transducers convert electrical quantity
to a non electrical quantity. A piezoelectric
crystal acts as an inverse transducer because
when a voltage is applied across its surfaces, it
changes its dimensions causing a mechanical
displacement.

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20. TRANSDUCERS SELECTION FACTORS
1. Operating Principle: The transducer are many times selected
on the basis of operating principle used by them. The operating
principle used may be resistive, inductive, capacitive ,
optoelectronic, piezo electric etc.
2. Sensitivity: The transducer must be sensitive enough to
produce detectable output.
3. Operating Range: The transducer should maintain the range
requirement and have a good resolution over the entire range.
4. Accuracy: High accuracy is assured.
5. Cross sensitivity: It has to be taken into account when
measuring mechanical quantities. There are situation where the
actual quantity is being measured is in one plane and the
transducer is subjected to variation in another plan.
6. Errors: The transducer should maintain the expected input-
output relationship as described by the transfer function so as
to avoid errors.

21. Contd.
7. Transient and frequency response : The transducer should meet
the desired time domain specification like peak overshoot, rise
time, setting time and small dynamic error.
8. Loading Effects: The transducer should have a high input
impedance and low output impedance to avoid loading effects.
9. Environmental Compatibility: It should be assured that the
transducer selected to work under specified environmental
conditions maintains its input- output relationship and does not
break down.
10. Insensitivity to unwanted signals: The transducer should be
minimally sensitive to unwanted signals and highly sensitive to
desired signals.

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Quantity
being
Measured
Input Device
(Sensor)
Output Device
(Actuator)
Light Level
Light Dependant Resistor (LDR),
Photodiode, Phototransistor, Solar Cell
Lights & Lamps, LED's &
Displays, Fiber Optics
Temperature
Thermocouple, Thermistor, Thermostat,
Resistive temperature detectors (RTD)
Heater, Fan, Peltier
Elements
Force/Pressure
Strain Gauge, Pressure Switch, Load
Cells
Lifts & Jacks,
Electromagnetic, Vibration
Position
Potentiometer, Encoders,
Reflective/Slotted Opto-switch, LVDT
Motor, Solenoid, Panel
Meters
Speed
Tacho-generator, Reflective/Slotted
Opto-coupler, Doppler Effect Sensors
AC and DC Motors,
Stepper Motor, Brake
Sound
Carbon Microphone, Piezo-electric
Crystal
Bell, Buzzer, Loudspeaker

23. Temperature Transducer:-
1. Resistance temperature detectors (RTD).
2. Thermocouples.
3. Thermistors.

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

33. Resistance temperature detectors (RTD):-
• Detectors of resistance temperatures
commonly employ platinum, nickel, or
resistance wire elements, whose resistance
variation with temperature has a high
intrinsic accuracy.
• They are available in many configurations
and sizes and as shielded or open units for
both immersion and surface applications.

34. Resistance temperature detectors (RTD):-
• The relationship between temperature and resistance of
conductors can be calculated from the equation.
Where
R = The resistance of the conductor at temperature t (°C)
Ro = The resistance at the reference temperature, usually 20°C
= The temperature coefficient of resistance
T = The difference between the operating and the reference
Temperature
)1(0 TRR  


35. 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

36. RTDs
RTD ELEMENT MATERIAL USABLE
TEMPERATURE RANGE
Platinum -260°C to +650°C
Nickel -100°C to +300°C
Copper -75°C to +150°C
Nickel/Iron 0°C to +200°C

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

39. RTDs
• Most stable over time
• Most accurate
• Most repeatable
temperature measurement
• corrosion of the RTD
element
• High cost
• 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
Advantages Disadvantages

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45. Thermocouples
 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
Advantages Disadvantages

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

47. A little easier to read
Thermocouple
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
0 10 20 30 40 50 60 70 80 90
Temperature (∘C)
Voltage(mV)
Thermistor
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0 10 20 30 40 50 60 70 80 90
Temperature (∘C)
Resistance(KΩ)
RTD
100.00
105.00
110.00
115.00
120.00
125.00
130.00
135.00
0 10 20 30 40 50 60 70 80 90
Temperature (∘C)
Resistance(Ω)

48. Pressure Transducer
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56. Diaphram / Bellow type
transducer
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59. Bourdon type pressure transducer
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62. Capacitive displacement
transducer
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64. Capacitive
Pressure Measurement
In a capacitance-type pressure sensor, a high-
frequency, high-voltage oscillator is used to charge the
sensing electrode elements. In a two-plate capacitor
sensor design, the movement of the diaphragm between
the plates is detected as an indication of the changes in
process pressure.

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Analog Tachometer Digital Tachometer

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86. Photo Electric Tachometer
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