2. • 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.
3. Parts of Transducer
• The transducer consists two important parts.
• Sensing Element
• Transduction Element
• The transducer has many other parts like amplifiers, signal
processing equipment, power supplies calibrating and reference
sources, etc.
• 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.
• Transduction Element – The transduction element converts the
output of the sensing element into an electrical signal. This
element is also called the secondary transducer.
4. In this block diagram of a simple measuring
system, there are three basic elements:
5. • Sensor
• A Sensor is a device that is used to detect changes in any
physical quantity like Temperature, Speed, Flow, Level,
Pressure, etc. Any changes in the input quantity will be
detected by a Sensor and reflected as changes in output
quantity.
• Both the input and output quantities of a Sensor are
Physical i.e., non-electrical in nature.
• Signal Conditioning Unit
• The non-electrical output quantity of the Sensor makes it
inconvenient to further process it. Hence, the Signal
Conditioning Unit is used to convert the physical output
(or non-electrical output) of the sensor to an electrical
quantity.
6. • Some of the best known Signal conditioning units are:
• Analog to Digital Converters
• Amplifiers
• Filters
• Rectifiers
• Modulators
• Data Representation Device
• A Data representation device is used to present the
measured output to the observer. This can be anything
like
• A Scale
• An LCD Display
• A Signal Recorder
7. Classification of Transducers
• There are several ways in which you can classify transducers that
include but not limited to the role of the transducer, structure of the
transducer or the phenomena of their working.
• It is easy to classify transducers as Input Transducers or Output
Transducers, if they are treated as simple signal converters.
• Input Transducers measure non-electrical quantities and convert them
into electrical quantities.
• Output Transducers on the other hand, work in the opposite way i.e.
their input signals are electrical and their output signals are non-
electrical or physical like force, displacement, torque, pressure etc.
• Depending on the principle of operation, transducers can also be
classified into mechanical, thermal, electrical, etc.
• Let us see the classification of transducers based on the following
three ways:
• Physical Effect
• Physical Quantity
• Source of Energy
8. 1. Classification based on Physical Effect
• The first classification of Transducers is based on the
physical effect engaged to convert the physical quantity
to electrical quantity. An example, is the change in
resistance (physical quantity) of a copper element in
proportion to the change in temperature.
• The following physical effects are generally used:
• Variation in Resistance
• Variation in Inductance
• Variation in Capacitance
• Hall Effect
• Piezoelectric Effect
9. 2. Classification based on Physical Quantity
• The second classification of Transducers is based on the physical
quantity converted i.e. the end use of the transducer after the
conversion. For example, a Pressure Transducer is a transducer that
converts pressure into electrical signal.
• Following is small list of transducers classified based on the physical
quantity and corresponding examples
• Temperature Transducer – Thermocouple
• Pressure Transducer – Bourdon Gauge
• Displacement Transducer – LVDT (Linear Variable Differential
Transformer)
• Level Transducer – Torque Tube
• Flow Transducer – Flow Meter
• Force Transducer – Dynamometer
• Acceleration Transducer – accelerometer
10. 3. Classification based on Source of Energy
• Transducers are also classified based on the
source of energy. Under this category, there
usually two types of transducers:
• Active Transducers
• Passive Transducers
• Active Transducers
• In Active Transducers, the energy from the
input is used as a control signal in the process
of transferring energy from power supply to
proportional output.
11. For example, a Strain Gauge is an Active Transducer, in
which the strain is converted into resistance. But since the
energy from the strained element is very small, the energy
for the output is provided by an external power supply.
Passive Transducers
In Passive Transducers, the energy from the input is
directly converted into the output. For example, a
Thermocouple is a passive transducer, where the heat
energy, which is absorbed from input, is converted into
electrical signals (voltage).
12. 1. Static Characteristics
The static characteristics of a transducer is a set of performance criteria that are
established through static calibration i.e. description of the quality of
measurement by essentially maintaining the measured quantities as constant
values of varying very slowly.
Following is a list of some of the important static characteristics of transducers.
Sensitivity
Linearity
Resolution
Precision (Accuracy)
Span and Range
Threshold
Drift
Stability
Responsiveness
Repeatability
Input Impedance and Output Impedance
13. • 2. Dynamic Characteristics
• The dynamic characteristics of transducers relate to its
performance when the measured quantity is a function of time
i.e. it varies rapidly with respect to time.
• While static characteristics relate to the performance of a
transducer when the measured quantity is essentially constant,
the dynamic characteristics relate to dynamic inputs, which
means that they are dependent on its own parameters as well
as the nature of the input signal.
• The following are some dynamic characteristics that may be
considered in selection of a transducer.
• Dynamic Error
• Fidelity
• Speed of Response
• Bandwidth
• Overall, both static and dynamic characteristics of a Transducer
determine its performance and indicate how effectively it can
accept desired input signals and reject unwanted inputs.
14. Different Types of Transducers
• Basically, the two different types of Transducers are Mechanical
Transducers and Electrical Transducers.
• Mechanical Transducers are those which responds to changes in
physical quantities or condition with mechanical quantity.
• If the physical quantity is converted to an electrical quantity,
then the transducers are Electrical Transducers.
• 1. Mechanical Transducers
• As mentioned earlier, mechanical transducers are a set of
primary sensing elements that respond to changes in a physical
quantity with a mechanical output.
• As an example, a Bimetallic Strip is a mechanical Transducer,
which reacts to changes in temperature and responds with
mechanical displacement.
• The mechanical transducers are differentiated from electrical
transducers as their output signals are mechanical.
15. • The output mechanical quantity can be anything
like displacement, force (or torque), pressure
and strain. For any measuring quantity, there
can be both mechanical and electrical
transducers.
• For example, we have seen Bimetallic Strip,
which is a mechanical transducer and is used to
react to changes in temperature. In contrast, a
Resistance Thermometer, also reacts to changes
in temperature, but the response is a change in
resistance of the element. Hence, it is an
electrical transducer.
16. Quantity to be Measured Mechanical Transducer Type of Output Signal (Mechanical)
Temperature Bimetallic Strip Displacement and Force
Fluid Expansion Displacement and Force
Pressure Ring Balance Manometer Displacement
Metallic Diaphragms Displacement and Strain
Capsules and Bellows Displacement
Membranes Displacement
Force Spring Balance Displacement and Strain
Hydraulic Load Cell Pressure
Column Load Cell Displacement and Strain
Torque Dynamometer Force and Strain
Gyroscope Displacement
Spiral Springs Displacement
Torsion Bar Displacement and Strain
Flow Rate Flow Obstruction Element Strain and Pressure
Pitot Tube Pressure
Liquid Level Manometer Displacement
Float Elements Displacement, Force and Strain
17. Electrical Transducers
• As mentioned earlier, electrical transducers are those that
respond to changes in physical quantities with electrical
outputs. Electrical Transducers are further divided into Passive
Electrical Transducers and Active Electrical Transducers.
18. Applications of Transducers
1. Electromagnetic
• Antennas
• Hall-Effect Sensors
• Disk Read and Write Heads
• Magnetic Cartridges
2. Electromechanical
• Accelerometers
• Pressure Sensors
• Galvanometers
• LVDT
• Load Cells
• Potentiometers
• MEMS
• Linear and Rotary Motors
• Air Flow Sensors
3. Electrochemical
• Hydrogen Sensors
• Oxygen Sensors
• pH Meters
20. • 7. Thermoelectric
• Thermistors
• Thermocouples
• RTD (Resistance Temperature Detectors)
• 8. Radioacoustic
• Radio Transmitters and Receivers
• G-M Tube (Geiger-Muller Tube)
21. Factors Influencing the Choice of
Transducer
• The choice of the transducers used for measuring the physical
quantity depends on the following factors.
• Operating Principle – The transducers are selected by their
operating principles. The operating principle may be resistive,
inductive, capacitive, optoelectronic, piezoelectric, etc.
• Sensitivity – The sensitivity of the transducer is enough for inducing
the detectable output.
• Operating Range – The transducer must have wide operating
ranges so that it does not break during the working.
• Accuracy – The transducers gives accuracy after calibration. It has a
small value for repeatability which is essentials for the industrial
applications.
• 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.
22. • Errors – The errors are avoided by taking the input output relations
which is obtained by the transfer function.
• Loading Effect – The transducers have high input impedance and low
output impedance for avoiding the errors.
• 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.
• Insensitivity to Unwanted Signals – The transducer should be
sensitive enough for ignoring the unwanted and high sensitive signals.
• Usage and Ruggedness – The durability, size and weight of the
transducer must be known before selecting it.
• 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 the transducer.
• Static characteristic – The transducer should have a high linearity and
resolution, but it has low hysteresis. The transducer is always free
from the load and temperature.
23. Applications of Transducer
• The following are the application of the transducers.
• The transducer measures the load on the engines.
• It is used as a sensor for knowing the engine knock.
• The transducers measure the pressure of the gas and liquid
by converting it into an electrical signal.
• It converts the temperature of the devices into an electrical
signal or mechanical work.
• 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.
• The transducer is used in the speaker for converting the
electrical signal into acoustic sound.
• It is used in the antenna for converting the electromagnetic
waves into an electrical signal.
24. Displacement transducer
• What is Potentiometer?
• The potentiometer is the electrical type of
transducer or sensor and it is of resistive type
because it works on the principle of change of
resistance of the wire with its length.
• It is defined as a three-terminal resistor having
either sliding or rotating contact that forms an
adjustable voltage divider.
• In order to use the potentiometer as a rheostat
or variable resistor, it should have only two
terminals with one end and the wiper.
25. Potentiometer Working Principle
• The potentiometer is also called as pots and it one of the most
commonly used device for measuring the displacement of the
body.
• The potentiometer consists of L which is a long resistive wire and a
battery of known EMF V whose voltage is known as driver cell
voltage.
• Assume a primary circuit arrangement by connecting the two ends
of L to the battery terminals.
• One end of the primary circuit is connected to the cell whose EMF
E is to be measured and the other end is connected to
galvanometer G. This circuit is assumed to be a secondary circuit.
26. The working principle depends on the potential across any
portion of the wire which is directly proportional to the length
of the wire that has a uniform cross-sectional area and current
flow is constant.
27. • Types of Potentiometer
• There are basically two types of potentiometers that can be further
divided depending on the movement of the wiper. Following is the
table when the wiper is moving in a circular path which is known as
rotary potentiometers.
Type Description Applications
Concentric pot Two potentiometers are
adjusted individually with
the help of concentric
shafts
Found in old car radios
that were used to control
volume and tone
Single-turn pot Approximate rotation is
270 degrees in a single
rotation
Used where a single turn
is enough to control the
resolution
Servo pot Used to adjust a servo
motor automatically
Used in remote-controls
to control the volume of
an audio equipment
28. Application of Potentiometer
• Audio control: Both linear, and rotary potentiometers,
are used to control audio equipment for changing the
loudness and other audio related signals.
• Television: They are used to control the picture
brightness, colour response and contrast.
• Motion control: In order to create a closed-loop
control, potentiometers are used as position feedback
devices known as a servomechanism.
• Transducers: As these give large output signals, they
find applications in designing of displacement
transducers.
29. LVDT
• The LVDT sensor converts the linear (or rectilinear / straight-
line) movement of the object the LVDT is coupled to, into a
variable corresponding electrical signal proportional to that
movement.
• LVDT works under the principle of mutual induction, and the
displacement which is a non-electrical energy is converted
into an electrical energy.
• That movement can be from as little as 0-0.5mm up to 0-
1000mm in laboratory, industrial and submersible
environments.
• The LVDT or Linear Variable Differential Transformer is a well
established electromechanical transducer design. This
design has been used throughout many decades for the
accurate measurement of displacement and within closed
loops for the control of positioning.
30. • In its simplest form, the LVDTs design consists
of a cylindrical array of a primary and
secondary winding with a separate cylindrical
core which passes through the centre.
31. • LVDT consists of a cylindrical former where it is surrounded
by one primary winding in the centre of the former and the
two secondary windings at the sides.
• The number of turns in both the secondary windings are
equal, but they are connected in series opposition to each
other, i.e., if the left secondary windings is in the clockwise
direction, the right secondary windings will be in the anti-
clockwise direction, hence the net output voltages will be
the difference in voltages between the two secondary coil.
• The two secondary coil is represented as S1 and S2. Esteem
iron core is placed in the centre of the cylindrical former
which can move in to and fro motion as shown in the figure.
• The AC excitation voltage is 5 to 12V and the operating
frequency is given by 50 to 400 HZ.
32. • The primary windings (P) are energised with a
constant amplitude A.C. supply at a frequency of 1
to 10 kHz. This produces an alternating magnetic
field in the centre of the transducer which induces
a signal into the secondary windings (S & S )
depending on the position of the core.
• Movement of the core within this area causes the
secondary signal to change . As the two secondary
windings are positioned and connected in a set
arrangement (push-pull mode), when the core is
positioned at the centre, a zero signal is derived.
33. Working of LVDT:
• Let’s study the working of LVDT by splitting the
cases into 3 based on the iron core position
inside the insulated former.
• Case 1: On applying an external force which is
the displacement, if the core reminds in the null
position itself without providing any movement
then the voltage induced in both the secondary
windings are equal which results in net output is
equal to zero i.e., Esec1-Esec2=0
34. • Case 2: When an external force is appilied and if
the steel iron core tends to move in the left hand
side direction then the emf voltage induced in the
secondary coil is greater when compared to the
emf induced in the secondary coil 2. Therefore the
net output will be Esec1-Esec2
• Case 3: When an external force is applied and if the
steel iron core moves in the right hand side
direction then the emf induced in the secondary
coil 2 is greater when compared to the emf voltage
induced in the secondary coil 1. therefore the net
output voltage will be Esec2-Esec1
35. • Advantages Of LVDT
• No Physical Contact Between the Core and the Coils
• Long Operating Life
• Theoretically Infinite Resolution
• Easy Modification
• Low Power Consumption
• High Accuracy
• Fast Response
• Applications of LVDT:
• LVDT is used to measure displacement ranging from
fraction millimeter to centimeter.
• Acting as a secondary transducer, LVDT can be used
as a device to measure force, weight and pressure,
etc..
