Electronics Measurement &

Instrumentation
4EC3-06
Unit -5
Transducers
Dr. Girraj Sharma
Associate Professor
Department of Electronics & Communication Engineering
JAIPUR ENGINEERING COLLEGE AND RESEARCH CENTRE, JAIPUR

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
 INTRODUCTION OF TRANSDUCERS

• A transducer is a device that convert one form of energy to other form.

It converts the measurand to a usable electrical signal.
• In other word it is a device that is capable of converting the physical
quantity into a proportional electrical quantity such as voltage or
current.

Pressure Voltage

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 BLOCK DIAGRAM OF TRANSDUCERS

• Transducer contains two parts that are closely related to each other i.e.
the sensing element and transduction element.
• The sensing element is called as the sensor. It is device producing
measurable response to change in physical conditions.
• The transduction element convert the sensor output to suitable electrical
form.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 CHARACTERISTICS OF TRANSDUCERS

1. Accuracy
2. Resolution
3. Linearity
4. Repeatability
5. Precision
6. Range
7. Dynamic Response
8. High stability and reliability
9. Speed of response
10.Sensitivity
11.Small size
12.Cost

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 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.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

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.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 CLASSIFICATION OF TRANSDUCERS

The transducers can be classified as:

I. Active and passive transducers.

II. Analog and digital transducers.
III. On the basis of transduction principle used.
IV. Primary and secondary transducer
V. Transducers and inverse transducers.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 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.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 Piezoelectric Transducer

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 CLASSIFICATION OF ACTIVE TRANSDUCERS

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 PASSIVE TRANSDUCERS

• Passive Transducers :
I. These transducers need external source of power for their operation.
So they are not self generating type transducers.
II. A DC power supply or an audio frequency generator is used as an
external power source.
III. These transducers produce the output signal in the form of variation in
resistance, capacitance, inductance or some other electrical parameter
in response to the quantity to be measured.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 CLASSIFICATION OF PASSIVE TRANSDUCERS

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 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.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

•Ref fig in which the diaphragm act as primary transducer. It convert pressure
(the quantity to be measured) into displacement(the mechanical signal).
•The displacement is then converted into change in resistance using strain gauge.
Hence strain gauge acts as the secondary transducer.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 CLASSIFICATION OF TRANSDUCERS
According to Transduction Principle

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 CLASSIFICATION OF TRANSDUCERS
Transducer and Inverse Transducer

TRANSDUCER:

•Transducers convert non electrical quantity to electrical quantity.

INVERSE TRANSDUCER:

• Inverse transducers convert electrical quantity to a non electrical quantity

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
 Circuit Diagram

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
 Strain Gauge

•A strain gauge (or strain gage) is a device used to measure

strain on an object. It is also termed as Load cell
•The most common type of strain gauge consists of an insulating
flexible backing which supports a metallic foil pattern.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 Tension
Strain Gauge
Compression

l
R= => R  l l
A
R = Resistance

l  = Property of material R
l = Length of wire
R A = Effective cross sectional area of wire
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
 Strain Gauge Applications

•Measurement of pressure
•Measurement of force
•Measurement of small displacement
•Measurement of Torque
•Measurement of Load etc.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 BOURDON TUBES

• Invented by Eugene Bourdon in the year 1849.

• Bourdon tubes are an elastic type pressure
transducer.
• Used for very high range pressure measurement
of almost 1,000,000 Psi (700MPa)

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

Working Principle

• The cross-sectional of the Bourdon tubing when deformed in any way

will tend to regain its circular form under the action of pressure.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 TYPES OF BOURDON TUBES

C-Type Bourdon tube

• The C-shaped Bourdon tube has a hollow, elliptical cross

section. It is closed at one end and is connected to the fluid
pressure at the other end.
• When pressure is applied, its cross section becomes more
circular, causing the tube to straighten out.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC
 Helical type Bourdon tube
Spiral type Bourdon tube

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

ADVANTAGES OF BOURDON TUBE PRESSURE GAUGES

• These Bourdon tube pressure gauges give accurate results.

• Bourdon tube cost low.
• Bourdon tubes are simple in construction.
• They can be modified to give electrical outputs.
• They are safe even for high pressure measurement.
• Accuracy is high especially at high pressures.
• Their greatest advantage is that they are easily adapted for designs for
obtaining electrical outputs.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

LIMITATIONS OF BOURDON TUBE PRESSURE GAUGES

• They respond slowly to changes in pressure.

• They are subjected to hysteresis.
• They are sensitive to shocks and vibrations.
• Amplifications is a must as the displacement of the free end of the bourdon
tube is low.
• It cannot be used for precision measurement.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 TACHOMETERS

oA Tachometer is an instrument used to measure the rotation speed

of a shaft or disk, as in a motor or other machine.
oMeasurement unit : Revolution per Minute {RPM}.
oLinear speed is measured in m/s ξ Angular speed in rad/s or rpm.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 TACHOMETERS CLASSIFICATIONS

▪ Mechanical Tachometers
oRevolution Counter.
oHand speed Indicator.

▪ Electrical Tachometers
oEddy current tachometer.
oMagnetic pickup tachometer.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 Eddy current/Drag cup tachometer

Electrical Tachometers

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

oParts: Permanent magnet within aluminium cup, spindle
connected to cup to which a pointer is fixed by spiral spring.

oPrinciple: When the permanent magnet rotates in a drag cup

close to magnet , the eddy current is induced which produces a
torque in drag cup.

oNow, the deflection of cup due to torque is indicated by pointer

representing speed of shaft & it’s measured upto 12000 rpm.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

oAdvantage: Less maintenance, ripple free output , Inexpensive.
oDis-advantage: Hard to calibrate.
oApplication: Automobile speedometer, Locomotive speed.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 LOAD CELL

❑ Load cell is an electromechanical device.

❑ A load cell is a force transducer that converts force or weight acting on it
into an electrical signal.
❑ Load cell can be used to measure force, torque and pressure.
❑ Load cell can measure a wide range of force, from 25grams to
3,000,000lbs.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 CLASSIFICATION AND APPLICATION

Mechanical type load cell

❑ Hydraulic
❑ Pneumatic
Electrical type load cell
❑ Resistance based (strain gauge load cell)
❑ Capacitance based
❑ Inductance based (LVDT load cell)
Among the many kinds of load cell the most common type is strain gauge load
cell.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 Mechanical Load Cell

Hydraulic load cells are force balance-devices, measuring weight as a change

in pressure of the internal filling fluid. It is ideal for use in hazardous areas as
there are no any electrical component in it.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

Pneumatic Load Cells also operate on the force-balance principle.
These devices use multiple dampener chambers to provide higher
accuracy than hydraulic load cell. Pneumatic load cells are often
used to measure relatively small weights in industries where
cleanliness and safety of prime concern.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 Electrical Load Cell

Strain Gauge Load Cell

❑ A strain gauge is a device used to measure the strain of an object and convert the load
acting on them into electrical signals.
❑ Due to application of load, strain changes the electrical resistance of the gauge in
proportion to the applied load.
❑ Strain gauge shows a very high accuracy of 0.03%.

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 LOAD CELL APPLICATION

1. All types of textile testing (Instron).

2. Measurement of weight (Moisture regain testing).

3. Online measurement of tension during various

process (like printing).

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 Ultrasonic flow meter

➢ Sound generated above the human hearing range (typically 20- 20KHz) is called
ultrasound .

➢The ultrasonic flow meter operates on the principle that the velocity of the sound
in a fluid in motion is the resultant of the velocity of sound in the fluid at rest plus or
minus the velocity of the fluid

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 TYPES

ULTRASONIC FLOWMETER

TRANSIT-TIME DOPPLER
ULTRASONIC FLOWMETER
FLOWMETER

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 TRANSIT-TIME FLOWMETER

The time(TBA) for the ultrasonic energy to go from transducer B to

transducer A is given by the expression
TBA= L
C − V cos 

The time (TAB) to go from A to B is given by

L
TAB=
C + V cos 

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

The differential transit time is given by
∆T=TBA-TAB

. cos 
2.LV
T =
C

The differential transit time ∆T is proportional to fluid velocity V

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

FREQUENCY DIFFERENCE TYPE

➢The pulse repetition frequency in the forward propagating loop is 1/t1 while
in the backward loop is 1/t2

The frequency difference is

∆f=1/t1
- 1/t2
C + V cos  C − V cos 
= -
L L

= 2V cos 
L

09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC

 ADVANTAGE

➢ No obstruction in the flow path, no pressure drop

➢ No moving parts, low maintenance cost

➢ Multi-path models have higher accuracy for wider ranges of Reynolds

number

➢ Portable models available for field analysis and diagnosis

DISADVANTAGE

➢ Higher initial set up cost

➢ Single path (one-beam) models may not be suitable for flow velocities that
vary over a wide range of Reynolds number
09-07-2021 Dr. Girraj sharma, assoc. prof. ECE, JECRC