SUBJECT : ELECTRONICS & PNEUMATIC INSTRUMENTATION

1. P R THUMAR

2. P R THUMAR

3. CLASSIFICATION OF ELECTRONIC
INSTRUMENTS
ELECTRONICS INSTRUMENTS
LABORATORY
INSTRUMENTS
PMMC METER
RECTIFIER TYPE
MOVING IRON TYPE
ELECTRODYNAMOMETER
S.S.G
CRO
DSO
RAMP TYPE DVM
TESTING
INSTRUMENTS
TRANSMITTER
CONTROLLER
FIELD INSTRUMENT
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4. PMMC TYPE METER
Principle of Operation
When a current carrying
conductor is placed in a
magnetic field, it
experiences a force and
tends to move.
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5. Construction:
 It consists of a light rectangular coil of many turns of
fine wire wound on an aluminium former inside which is
an iron core.
 The coil is delicately pivoted upon jewel bearings and is
mounted between the poles of a permanent horse shoe
magnet
 Two soft-iron pole pieces are attached to these poles to
concentrate the magnetic field.
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6. Continue….
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7. P R THUMAR

8. Working:
 When a current flow through the coil, it generates a
magnetic field which is proportional to the current in
case of an ammeter. The deflecting torque is
produced by the electromagnetic action of the
current in the coil and the magnetic field.
 The controlling torque is provided by two bronze
flat springs. These springs serve as a flexible
connection to the coil conductors.
 Damping is caused by the eddy current set up in the
aluminum coil which prevents the oscillation of the
coil.
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9. Continue..
The equation for developed torque is
T = BAIN
Where, T = Torque,newton-meter
B = flux density, Wb/m2
A = effective coil area(m2)
N = nUmber of turns of wire
I = Current in the movable coil
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10. Advantages
 Uniform scale.ie, evenly divided scale.
 Very effective eddy current damping.
 High efficiency.
 Require little power for their operation.
 No hysteresis loss (as the magnetic field is
constant).
 External stray fields have little effects on the
readings (as the operating magnetic field is
very strong).
 Very accurate and reliable.
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11. Disadvantages
 Cannot be used for A.C measurements.
 More expensive (about 50%) than the moving iron
instruments because of their accurate design.
 Some errors are caused due to variations (with time or
temperature) either in the strength of permanent
magnet or in the control spring.
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12. APPLICATION
• In the measurement of direct currents and
voltages.
• In d.c galvanometers to detect small currents.
• Used as Voltmeter or Ameter
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13. MOVING IRON TYPE INSTRUMENT
The moving iron instruments are classified as
• Moving iron attraction type instruments
• Moving iron repulsion type instruments
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14. MOVING IRON ATTRACTION TYPE INSTRUMENT
PRINCIPLE:
A soft iron piece if brought near the magnet gets
attracted by the magnet.
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15. CONSTRUCTION
• It consists of a fixed coil C and moving iron piece D.
The coil is flat and has a narrow slot like opening. The
moving iron is a flat disc which eccentrically mounted
on the spindle.
• The spindle is supported between the jewel bearings.
The spindle caries a pointer which moves over a
graduated scale.
• The controlling torque is provided by the spring.
• The damping torque is provided by the air friction.
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16. WORKING
• The current to be measured is flowing in the
coil,produces a magnetic field.
• Iron piece gets attracted towards center of the
magnetic field and pointer deflects on the scale.
• The scale is nonlinear.
• Mirror is provided to avoid parallax error.
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17. REPLUSION TYPE MOVING IRON INSTRUMENT
• PRINCIPLE
– There is a repulsion between two iron pieces as
they are magnetized with the same polarity.
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18. CONSTRUCTION
• The two vanes are radial strips of iron.
• The fixed vane is attached to the coil.
• The movable vane is attached to the spindle and
suspended in the induction field of the coil.
• The needle of the instrument is attached to this
vane.
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19. WORKING
• Current to be measured is passing through
stationary coil produces magnetic field .
• Both the vanes magnetizes with similar
polarities.
• As a result a force of repulsion is set up between
two vanes
• This force produces a deflecting torque on the
movable vanes, gives deflection on the scale.
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20. Advantages
 The instruments are suitable for use in AC and DC
circuits.
 The instruments are robust, owing to the simple
construction of the moving parts.
 The stationary parts of the instruments are also simple.
 Instrument is low cost compared to moving coil
instrument.
 Torque/weight ratio is high, thus less frictional error.
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21. DISADVANTAGES
1. The scale of moving iron instruments is not uniform and is
cramped at the lower end. Hence accurate readings are not
possible at this end.
2. There are serious errors due to hysteresis and frequency
changes
3. The increase in temperature increases the resistance of coil,
decreases stiffness of the springs, decreases the permeability
and hence affect the reading severely.
4. There is a difference between a.c. and d.c. calibration on
account of the effect of inductance of the meter. Hence these
meters must always be calibrated at the frequency at which
they are to be used. P R THUMAR

22. Application:
Measurement of Electric Voltage and Current
 Moving iron instruments are used as Voltmeter and
Ammeter only.
 Both can work on AC as well as on DC.
Ammeter:
 Instrument used to measure current in the circuit.
 Always connected in series with the circuit and carries the
current to be measured.
Voltmeter
 Instrument used to measure voltage between two points in
a circuit.
 Always connected in parallel.
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23. RECTIFIER TYPE INSTRUMENT
• Rectifier type of instruments are used for measurement
of A.C voltage and current by employing a rectifier
element which converts A.C to a unidirectional D.C and
then using a meter responsive to D.C indicate the value
of rectified A.C.
• The indicating instrument is PMMC instrument. This
method is very attractive since PMMC have higher
sensitivity.
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24. A full wave rectifier type instrument is shown in figure. There
is a full wave rectifier bridge of diode which converts A.C to
D.C.
The multiplying instrument Rs, is used to limit the value of the
current in order that it does not exceed the current rating of
PMMC instrument
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26. ADVANTAGES
• The accuracy of rectifier type instrument is about 5
percent under normal operating condition.
• The frequency range of operation can be extended to
high value.
• They have uniform scale on the meter.
• They have low operating value of current and voltages
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27. ELECTRO DYNAMOMETER
• Principle :
“When any current carrying conductor is
placed inside a magnetic field, it experiences a
mechanical force and due this mechanical force
deflection of conductor takes place".
• There are Two types of coils present in
the electrodynamometer.
1. Moving Coil 2. Fixed Coil
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28. P R THUMAR

29. CONSTRUCTION & WORKING
Construction:
• It consist of two fixed coil and one movable coil
• The fixed coil is made of a few turns of thick copper
wire
• The movable coil of fine copper wire and made on
aluminium frame.
• Working:
• When the instrument is connected in a circuit the
current pass through the both coils.
• The flux produced by coil is proportional to the current.
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30. P R THUMAR
• Advantages
i) These instruments can be used on both a.c &
d.c
ii) Accurate rms value
Disadvantages
(i) They have a low torque/weight ratio and hence
have a low sensitivity.
(ii) Low torque/weight ratio gives increased
frictional losses.
(iii) They are more expensive than either the
PMMC or the moving iron type instruments.
(iv) These instruments are sensitive to overloads
and mechanical impacts. Therefore, they must be
handled with great care.
(vi) They have a non-uniform scale.

31. S.S.G(standard signal generator)
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32. S.S.G
• A standard signal generator produces known and controllable voltages.
• The carrier frequency is generated by a very stable RF oscillator using an
LC tank circuit
• .
• AM is provided by an internal sine wave generator or from an external
source.
• Modulation is done in the output amplifier circuit.
• This amplifier delivers its output, that is, modulation carrier, to an
attenuator.
• The output voltage is read by an output meter and the attenuator output
setting.
• It is used as power source for the measurement of gain, signal to noise
ratio (S/N), bandwidth, standing wave ratio and other properties. It is
extensively used in the testing of radio receivers and transmitters.
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33. RAMP TYPE DVM
The operating principle of a ramp type digital voltmeter is to
measure the time that a linear ramp voltage takes to change
from level of input voltage to zero voltage (or vice versa).
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34. RAMP TYPE DVM
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35. RAMP TYPE DVM
 At the start of measurement a ramp voltage is initiated.
 A negative going ramp is shown in Fig. but a positive going
ramp may also be used.
 The ramp voltage value is continuously compared with the
voltage being measured (unknown voltage).
 At the instant the value of ramp voltage is equal to that of
unknown voltage.
 The ramp voltage continues to decrease till it reaches ground
level (zero voltage).
 At this instant another comparator called ground comparator
generates. a pulse and closes the gate.
During this time interval pulses from a clock pulse generator
pass through the gate and are counted and displayed
 The decimal number as indicated by the readout is a measure
of the value of input voltage.
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36. CRO (Cathode Ray Oscilloscope)
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37. CRT(cathode ray tube)
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38. DESCRIPTION OF CRO
• The CRO is an extremely useful laboratory instrument
used for studying waveshape of alternating voltage
and current, measurement of voltage , current , power ,
frequency etc.
• Main parts of CRO:
1) CRT
it generates the electron beam , accelerate the
beam to a high velocity , deflect the beam to create the
image and contain phosphor screen where the electron
beam become visible.
2) Horizontal and vertical deflection plate
they are fitted between electron gun and screen
to deflect the beam according to input signal.
3)Vertical amplifier
it amplifies the signal waveform to be viewed.
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39. Continue….
4)Horizontal amplifier
It is fed with a sawtooth voltage which is then applied to
horizontal deflection plates.
5)Sweep generator
It produces sawtooth voltage waveform used for
horizontal deflection of the electron beam.
6)Trigger circuit
It produces trigger pulses to start horizontal sweep.
7)Delay line
The purpose of delay line is to delay the vertical signal
enough to keep it from reaching the CRT deflection plates
before the horizontal sweep circuits are running.
8)Power supply
It’s required to operate the CRO.
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40. DSO( Digital storage oscilloscope)
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41. DSO
• The input signal is applied to the amplifier and attenuator
section.
• The attenuated signal is then applied to the vertical amplifier.
• To digitize the analog signal, analog to digital (A/D) converter is
used.
• The output of the vertical amplifier is applied to the A/D
converter section.
• The successive approximation type of A/D converter is most of
tenly used in the digital storage oscilloscopes.
• Once the input signal is sampled, the A/D converter digitizes
it. The signal is then captured in the memory.
• The digital storage oscilloscope has three
1. Roll mode
2. Store mode
3. Hold or save mode.
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42. DSO
• Advantages
1) It is easier to operate and has more capability.
2) The storage time is infinite.
3) The characters can be displayed on screen along with the
waveform which can indicate waveform information such as
minimum, maximum, frequency, amplitude etc.
4) The X-Y plots, B-H curve can be displayed.
5) Keeping the records is possible by transmitting the data to
computer system where the further processing is possible.
6) Signal processing is possible which includes translating the
raw data into finished information.
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43. CLASSIFICATION OF BRIDGE
BRIDGES
AC
BRIDGE
MAXWELL BRIDGE
ANDERSON BRIDGE
D’SAUTY’S BRIDGE
DC
BRIDGE
WHEATSTONE BRIDGE
KELVIN BRIDGE
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44. WHEATSTONE BRIDGE
• A Wheatstone bridge consists of four resistors that
are connected in the shape of a diamond with the
supply source and indicating instruments as shown
in figure
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45. From the figure,
The voltage at point D = V × RX / (R3 + RX)
The voltage at point C = V × R2 / (R1 + R2)
The voltage (V) across galvanometer or between C and
D is,
VCD = V × RX / (R3 + RX) − V R2 / (R1 + R2)
When the bridge is balanced VCD = 0,
So,
V × RX / (R3 + RX) = V R2 / (R1 + R2)
RXR1 + RXR2 = R2R3 + R2RX
R1RX= R2R3
R2/R1= RX/R3
This is the condition to balance the bridge. And for
finding the unknown value of resistance
RX = R3 × (R2 / R1)
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46. Wheatstone Bridge Applications:
• The Wheatstone bridge is used for measuring
the very low resistance values precisely.
• Wheatstone bridge along with operational
amplifier is used to measure the physical
parameters like temperature, strain, light, etc.
• We can also measure the quantities
capacitance, inductance and impedance using
the variations on the Wheatstone bridge.
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47. KELVIN BRIDGE
Kelvin Bridge is a
modified Wheatstone
bridge and provides
high accuracy
especially in the
measurement of low
resistance.
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48. MAXWELL BRIDGE
• Where,
R1,R2,R3 = non inductive
resistor
C1=variable standaed
capacitor
Lx=unkonown inductance
Rx=effective resistance of
inductor.
Lx=R2R3C1
Rx=R2R3/R1
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49. ANDERSON BRIDGE
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50. DE SAUTY’S BRIDGE
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• C1=C2(R4/R3)

51. ISOLATION
• Isolation electrically separates the sensor signals, which can
be exposed to hazardous voltages, from the measurement
system’s low-voltage backplane
• Need for Isolation
• Consider isolation for measurement systems that involve any
of the following:
• Close vicinity to hazardous voltages
• Industrial environments with possibility of transient voltages
• Environments with common-mode voltage or fluctuating
ground potentials
• Electrically noisy environments such as those with industrial
motors
• Transient-sensitive applications where it is imperative to
prevent voltage spikes from being transmitted through the
measurement system
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52. ISOLATION TECHNIQUES
• Optical Isolation
• LEDs produce light when a voltage is applied across them.
• Optical isolation uses an LED along with a photodetector
device to transmit signals.
• A photodetector receives the light transmitted by the LED
and converts it back to the original signal.
• One benefit of using optical isolation is its immunity to
electrical and magnetic noise.
• Some of the disadvantages include transmission speed,
which is restricted by the LED switching speed, high-power
dissipation, and LED wear.
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53. CONTINUE..
• Capacitive Isolation
• Capacitive isolation is based on an electric field that
changes with the level of charge on a capacitor plate.
This charge is detected across an isolation barrier and
is proportional to the level of the measured signal.
• One advantage of capacitive isolation is its immunity to
magnetic noise.
• faster data transmission rates
• it can be susceptible to interference from external
electric fields.
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54. CONTINUE
• Inductive Isolation
• Inductive isolation uses a pair of coils separated by a layer of
insulation. Insulation prevents any physical signal transmission.
Signals can be transmitted by varying current flowing through
one of the coils, which causes a similar current to be induced in
the second coil across the insulation barrier.
• Inductive isolation can provide high-speed transmission similar
to capacitive techniques.
• Because inductive coupling involves the use of magnetic fields
for data transmission, it can be susceptible to interference from
external magnetic fields.
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55. NEED FOR STANDARDIZATION OF SIGNAL
• STANDARD SIGNAL
• Range of standard electrical signal-4 to 20
ma
• Range of standard pneumatic signal- 3 to 15
psi
• To differentiate between dead zero and live
zero, it is necessary to start control signal
range other than zero.
• 4 to 20 ma and 3 to 15 psi is the range in
which we get linear output
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56. THANK
YOU
P R THUMAR