Important slideshow for the students of XII vocational bifocal electronics. This slideshow covers 3rd chapter of their syllabus. Very useful for self preparation.

1. D.S.Vidyasagar
Understanding
TRANSDUCERS

2. What is a transducer…?
Transducer is an
electrical device which
converts one form of
energy into another
form: Microphone
which converts sound
waves into electrical
signals.

3. Classification of Transducers
Active Transducer Passive Transducer
 It is a device which
works on external
battery supply
during conversion of
one form of energy
into another form.
 It is a device which
creates its own
electric voltage
during conversion. It
does not require
external battery
supply.

4. Active Transducer
Solar cell, piezo electric
crystal, thermocouple,
etc.

5. Passive Transducer
LDR, speaker,
microphone, thermister,
etc.

6. Instrumentation System
 An instrumentation system consists of three
main blocks.
Input circuit
Processing circuit
Output circuit
Along with the transducer at the input and the
output device like measuring instrument at the
output.
input
circuit
processing
circuit
output
circuit
transducer
input
final
output

7. How thermistor works?
Thermistor (Rx) is used
in a Wheatstone bridge
circuit. It can convert
change in temperature
into its corresponding
change in potential
difference across points

8. What is LDR…?
It is a photo sensitive
device which changes its
resistance with the
change in intensity of
light.
Thus in dark its
resistance is high and in

9. Details of LDR…
 It is made up of photo sensitive material
like…
Cadmium Sulphide (CdS)
Selenium (Se)
Cadmium Selenide (CdSe)
Lead Sulphide (PbS)

10. How photo relay circuit works?
As shown in the circuit,
when LDR is dark, T1 & T2
both are OFF. So the relay is
deactivated.
When light falls on LDR, its
resistance drops and both
transistors turn ON. So relay
is activated to glow the LED.

11. Capacitive Transducer
It is a passive transducer
known as pressure
transducer. It is used to
measure external
pressure as well as
displacement also. It
works on the principle of
Farad
..
d
oAK
C


Where –
K = dielectric constant
A = area of each plate
d = distance between plates

12. How it works…?
External
P R E S S U R E
plate (A)
changed position
of diaphragm (A)
insulated
support
diaelectric
medium
static plate (B)
heat isolation
cavity
enclosure
d

13. Linear Variable Differential
Transformer (LVDT)
It is a passive transducer.
It measures force in
terms of displacement of
ferromagnetic core of a
transformer. It is based
on the principle of electro-
magnetic induction.

14. How it works…?
ac
input
ac
output
(V -V )sec1 sec2
sec-2sec-1
primary coil
Ferrite Rod
A B
magnetically
saturable core
handle

15. Piezo Electric Crystal
It is a passive transducer. It
measures force in terms of
displacement of ferromagnetic
core of a transformer. It is
based on the principle of
electro-magnetic induction.
This crystal is found in
Rochelle salt and Tourmaline
materials.

16. The 3 axes of crystal
There are three imaginary
axes of piezo electric
crystal:
 x-axis or electrical axis
 y-axis or mechanical axis
 z-axis or optical axis

17. Specialty of piezo crystal
The piezo electric crystal is a dual type of
transducer.
 When its slice is subjected to pressure, it
produces proportional potential difference.
 And when it is connected to a high
frequency ac voltage, it vibrates to produce
US waves.

18. Applications of piezo crystal
This circuit is designed around
the common emitter amplifier
stage of a Colpitts Oscillator. The
input signal to the base of the
transistor is inverted at the
transistor output. The output
signal at the collector is then
taken through a 180o phase
shifting network which includes
the crystal operating in a series

19. Continued…
In the circuit, the output is also fed back to input which is IN-
PHASE with the input providing the necessary positive
feedback. Resistors, R1 and R2 bias the resistor in a Class A
type operation while resistor Re is chosen so that the loop
gain is slightly greater than unity.
Capacitors, C1 and C2 are made as large as possible in order
that the frequency of oscillations can approximate to the
series resonant mode of the crystal and is not dependant
upon the values of these capacitors.

20. What is an Opto Coupler?
An Opto coupler, also known as an
Opto-isolator or Photo-coupler, is
an electronic components that
interconnects two separate
electrical circuits by means of a
light sensitive optical interface.
It consists of one LED and a photo
transistor or photo diode for
coupling the light signals.

21. Inside the Opto Coupler…
The LED is connected
to the input signal
through a resistor. As
the LED glows, it
conducts the photo
transistor and its
collector potential
changes in accordance
with the input signal.
Thus the two circuits

22. Types of Opto Coupler
 Simple Transistor type is used
for general applications.
 Darlington pair is used for
large current output.
 SCR is used for toggling
action for DC loads.
 Triac is particularly used for
AC loads.

23. What is gas sensor?
A gas sensor is used to measure
the traces of unwanted gas present
in required gas.
It works on the principle of chemical
reaction. The gas under test is
passed
through the sensor and if it
contains
any unwanted gas it will react with
the electrolyte and will produce

24. Application of gas sensor

25. A typical gas sensor setup
A pressurized gas under test is shown on
the left. It is passed through channel which
contains particular type of electrolyte that
will react with the unwanted gas. If the
traces of such gas are present then due to
chemical reaction, the PD isproduced which is
measured with help
of a simple
voltmeter. The
scale of voltmeter is
calibrated in terms
of percentage (%).

26. Industrial transducers
Liquid pressure transducer PT-100 NTC Thermistor JR20-TC pH level sensors

27. www.yashplus.com
Designed by: D.S.Vidyasagar