Definition: The device which converts the one form of energy into another is
known as the transducer. The process of conversion is known as transduction.
The conversion is done by sensing and transducing the physical quantities like
temperature, pressure, sound, etc.
The electrical transducer converts the mechanical energy into an electric
signal. The electrical signal may be voltage, current and frequency. The production of
the signal depends on the resistive inductive and capacitive effects of the physical input.
Needs of Transducer
It is quite difficult to determine the exact magnitude of the physical forces like
temperature, pressure, etc. But if the physical force is converted into an electrical signal,
then their value is easily measured with the help of the meter. The transducers convert
the physical forces into an electrical signal which can easily be handled and transmitted
The following are the advantages of converting the physical quantity into an electrical
1. The attenuation and amplification of the electrical signals are very easy.
2. The electrical signal produces less friction error.
3. The small power is required for controlling the electrical systems.
4. The electrical signals are easily transmitted and processed for measurement.
5. The component used for measuring the electrical signal is very compact and
6. The electrical signals are used in telemetry.
Parts of Transducer
The transducer consists two important parts.
1. Sensing Element
2. Transduction Element
2. The transducer has many other parts like amplifiers, signal processing equipment,
power supplies calibrating and reference sources, etc.
1. Sensing or Detector Element – It is the part of the transducers which give the
response to the physical sensation. The response of the sensing element depends
on the physical phenomenon.
2. Transduction Element – The transduction element converts the output of the
sensing element into an electrical signal. This element is also called the secondary
Factors Influencing the Choice of Transducer
The choice of the transducers used for measuring the physical quantity depends on the
1. Operating Principle – The transducers are selected by their operating
principles. The operating principle may be resistive, inductive, capacitive,
optoelectronic, piezoelectric, etc.
2. Sensitivity – The sensitivity of the transducer is enough for inducing the
3. Operating Range – The transducer must have wide operating ranges so that it
does not break during the working.
4. Accuracy – The transducers gives accuracy after calibration. It has a small value
for repeatability which is essentials for the industrial applications.
5. Cross Sensitivity – The transducers gives variable measured value for the
different planes because of the sensitivity. Hence, for the accurate measurement,
the cross sensitivity is essential.
6. Errors – The errors are avoided by taking the input output relations which is
obtained by the transfer function.
7. Loading Effect – The transducers have high input impedance and low output
impedance for avoiding the errors.
8. Environmental Compatibility – The transducers should be able to work in
any specified environments like in a corrosive environment. It should be able to
work under high pressure and shocks.
9. Insensitivity to Unwanted Signals – The transducer should be sensitive
enough for ignoring the unwanted and high sensitive signals.
10. Usage and Ruggedness – The durability, size and weight of the transducer
must be known before selecting it.
11. Stability and Reliability – The stability of the transducers should be high
enough for the operation. And their reliability should be good in case of failure of
12. Static characteristic – The transducer should have a high linearity and
resolution, but it has low hysteresis. The transducer is always free from the load
3. Applications of Transducer
The following are the application of the transducers.
1. It is used for detecting the movement of muscles which is called
2. The transducer measures the load on the engines.
3. It is used as a sensor for knowing the engine knock.
4. The transducers measure the pressure of the gas and liquid by converting it into
an electrical signal.
5. It converts the temperature of the devices into an electrical signal or mechanical
6. The transducer is used in the ultrasound machine. It receives the sound waves of
the patient by emitting their sound waves and pass the signal to the CPU.
7. The transducer is used in the speaker for converting the electrical signal into
8. It is used in the antenna for converting the electromagnetic waves into an
The classifications of the transducers depend on the various factor like by transduction,
the converting electrical signal from AC or DC, etc.
4. Types of Transducer
The transducer changes the physical quantity into an electrical signal. It is an electronic
device which has two main functions, i.e., sensing and transduction. It senses the
physical quantity and then converts it into mechanical works or electrical signals.
The transducer is of many types, and they can be classified by the following criteria.
1. By transduction used.
2. as a primary and secondary transducer
3. as a passive and active transducer
4. as analogue and digital transducer
5. as the transducer and inverse transducer
The transducer receives the measurand and gives a proportional amount of output
signal. The output signal is sent to the conditioning device where the signal is
attenuated, filtered, and modulated.
The input quantity is the non-electrical quantity, and the output electrical signal is in
the form of the current, voltage or frequency.
1. Classification based on the Principle of Transduction
The transducer is classified by the transduction medium. The transduction medium
may be resistive, inductive or capacitive depends on the conversion process that how
input transducer converts the input signal into resistance, inductance and capacitance
5. 2. Primary and Secondary Transducer
Primary Transducer – The transducer consists the mechanical as well as the
electrical devices. The mechanical devices of the transducer change the physical input
quantities into a mechanical signal. This mechanical device is known as the primary
Secondary Transducer – The secondary transducer converts the mechanical signal
into an electrical signal. The magnitude of the output signal depends on the input
Example of Primary and Secondary Transducer
Consider the Bourdon’s Tube shown in the figure below. The tube act as a primary
transducer. It detects the pressure and converts it into a displacement from its free end.
The displacement of the free ends moves the core of the linear variable displacement
transformer. The movement of the core induces the output voltage which is directly
proportional to the displacement of the tube free end.
Thus, the two type of transduction occurs in the Bourdon’s tube. First, the pressure is
converted into a displacement and then it is converted into the voltage by the help of the
The Bourdon’s Tube is the primary transducer, and the L.V.D.T is called the secondary
3. Passive and Active Transducer
The transducer is classified as the active and passive transducer.
6. Passive Transducer – The transducer which requires the power from an external
supply source is known as the passive transducer. They are also known as the external
power transducer. The capacitive, resistive and inductive transducers are the example
of the passive transducer.
Active Transducer – The transducer which does not require the external power
source is known as the active transducer. Such type of transducer develops theirs owns
voltage or current, hence known as a self-generating transducer. The output signal is
obtained from the physical input quantity.
The physical quantity like velocity, temperature, force and the intensity of light is
induced with the help of the transducer. The piezoelectric crystal, photo-voltaic cell,
tacho generator, thermocouples, photovoltaic cell are the examples of the active
Examples – Consider the examples of a piezoelectric crystal. The crystal is sandwiched
between the two metallic electrodes, and the entire sandwiched is fastened to the base.
The mass is placed on the top of the sandwiched.
The piezo crystal has the special property because of which when the force is applied to
the crystal, they induce the voltage. The base provides the acceleration due to which the
voltage is generated. The mass applies on the crystals induces an output voltage. The
output voltage is proportional to the acceleration.
The above mention transducer is
known as the accelerometer which
converts the acceleration into an
electric voltage. This transducer
does not require any auxiliary
power source for the conversion of
physical quantity into an electrical
4. Analog and Digital Transducer
The transducer can also be classified by their output signals. The output signal of the
transducer may be continuous or discrete.
Analog Transducer – The Analog transducer changes the input quantity into a
continuous function. The strain gauge, L.V.D.T, thermocouple, thermistor are the
examples of the analogue transducer.
7. Digital Transducer – These transducers convert an input quantity into a digital
signal or in the form of the pulse. The digital signals work on high or low power.
5. Transducer and Inverse Transducer
Transducer – The device which converts the non-electrical quantity into an electric
quantity is known as the transducer.
Inverse Transducer – The transducer which converts the electric quantity into a
physical quantity, such type of transducers is known as the inverse transducer. The
transducer has high electrical input and low non-electrical output.
8. Difference Between Active & Passive Transducer
The most crucial difference between the active and passive transducer is that the active
transducer does not use any external power source for producing the output, whereas
the passive transducer requires the additional energy source for working. The other
differences between active and passive transducer are explained below in the
The physical forces like pressure, humidity, displacement etc. are difficult to measure.
For measuring the physical quantities, the device is required, which converts the
physical quantities into easy measurable energy. The conversion of physical forces or
non-measurable energy into measurable energy can be done with the help of the
Content: Active Vs Passive Transducer
Comparison Active Transducer Passive Transducer
What is The transducer which generate
the output in the form of voltage
or current, without any external
energy source is known as active
The passive transducer means the
transducer whose internal
parameters like capacitance,
resistance & inductance changes
because of the input signal.
Not Require Require
Draw energy from the
Take power from the external
source which changes the physical
properties of transducer.
Design Simple Complicated
Resolution Low High
Output signal Produces from the signal to be
Output obtains by receiving the
signal from the external power
9. Examples Tachogenerator, Thermocouple,
Photovoltaic cell etc.
tube, Photovoltaic cell.
Comparison Active Transducer Passive Transducer
Definition of Active Transducer
The transducer whose output is obtained in the form of voltage or current without any
additional auxiliary source is known as the active transducer. It works on the principle
of conversion of energy from one form to another. The active transducer is also known
as the self-generating transducer because they self-develop their electrical output signal.
The energy requires for generating the output signals are obtained from the
physical quantity which is to be measured.
Example: The Piezo electrical crystal is the example of the natural active transducer.
The crystal has the property of producing the output voltage when the external force
applied to them. The piezoelectric crystal is placed between the two metallic electrodes.
When the force applied to the crystal, the voltage induces across it.
Definition of Passive Transducer
In passive transducer, the output is obtained by changing the physical properties
(resistance, inductance, and capacitance) of the material. In other words, the passive
transducer takes power from the external energy source for transduction.
The word transduction means conversion of energy from one form to another.
10. Example: The linear potentiometer is the examples of the passive transducer. It is used
for measuring the displacement. The POT requires the external power source e for
work. It measures the linear displacement x .
Consider the L is the length of the potentiometer. R is their total internal resistance and
x is their input displacement. The output voltage is calculated by the formula shown
Key Differences between Active and Passive
The transducer which gives the electrical output (in the form
of voltage and current) without any external energy source is
known as the active transducer. The transducer whose
physical properties varies because of the input or measurand
signal is known as the passive transducer.
The active transducer does not require any additional source
while the passive transducer requires the additional energy source.
Active transducer draws energy from the measurand source and gives the
electrical output while in passive transducer the transduction can be done by
changing the physical property of the material.
The design of active transducer is simple as compared to the passive transducer.
The resolution of an active transducer is low while that of the passive transducer is
Note: The term resolution means the variation occurs in the input of the
transducer causes the change in their output.
11. The active transducer produces the output signal of very low amplitude. Thus,
their output signal needs to be amplified. Whereas, the amplification is not
required in the output signal of the passive transducer.
In the active transducer, the output electrical signal is obtained from the
measurand signal. Whereas in passive transducer the output signal is obtained by
taking power from the external energy source.
The active and passive transducer both converts the physical forces into easy
measurable energy. The active transducer converts the energy without taking the
auxiliary energy supply. And in the passive transducer, the external power source is
required for energy conversion.
12. Difference Between Transducer & Inverse Transducer
One of the major difference between the transducer and the inverse transducer is that
the transducer changes the non-electrical quantity into an electrical quantity while the
inverse transducer changes the electrical quantity into the non-electrical quantity. The
other differences between the transducer and inverse transducer are shown below in the
The control action of the physical quantities like flow, rate, position, speed,
temperature, pressure etc. depends on the measurement of the physical quantities. In
simple words, the control action of the physical quantity is possible only when these
quantities are correctly measured.
For measuring the physical quantities, it is essential to convert it into an electrical
signal, and this can be done with the help of the transducer. For example, in
servomechanism, the position of the shaft is controlled by measuring the exact position
of the shaft.
Content: Transducer Vs Inverse-Transducer
Comparison Transducer Inverse Transducer
Definition The transducer converts the
non-electrical quantity into an
The inverse transducer converts
the electrical quantity into the non-
Input Non-electrical quantity Electrical quantity
Output Electrical quantity Non-electrical quantity
Examples Photoconductive transducer,
Thermocouple, Pressure gauge,
Piezoelectric Transducer, current
carrying conductor placed in an
Definition of Transducer
The transducer is a type of device that converts the physical quantities like pressure,
brightness, displacement into an electrical quantity. The process of conversion of
quantities is known as the transduction.
13. Examples: The thermocouple converts the temperature into the small voltage. And the
LVDT is used for measuring the displacement.
Definition of Inverse Transducer
The inverse transducer is the transducer which converts the electrical quantity into a
non-electrical quantity. In other words, the transducer is a kind of actuator which has
an electrical input and the non-electrical output.
Examples: The analogue ammeter and the voltmeter convert the current into a
displacement. The oscilloscope is used for converting the electrical signal into a physical
Key Differences Between Transducer and Inverse Transducer
1. The transducer transforms the non-electrical quantity into the electrical quantity.
Whereas, the inverse transducer changes the electrical quantity into the non-
2. The input of the transducer is the non-electrical quantity. Whereas, the input of
the inverse transducer is the electrical quantity.
3. The output of the transducer is the electrical quantity while the output of the
inverse transducer is always the non-electrical quantity.
14. 4. The photoconductive cell, thermocouple, pressure gauge are the examples of the
non-electrical quantities. The piezoelectrical transducer, current carrying
conductor placed in a magnetic field are the examples of the inverse transducer.
The transducer changes the physical quantity into an electrical quantity. Whereas, the
inverse transducer changes the electrical quantity into the physical quantity.