POWER ELECTRONICS

AND
INSTRUMENTATION
Prepared by
PRADEEPA S C
Asst.Professor
EC Dept.
JNNCE,Shimoga
 B. E. (EC / TC)
Choice Based Credit System (CBCS) and Outcome Based Education (OBE)
SEMESTER – III
POWER ELECTRONICS AND INSTRUMENTATION
Course Code: 18EC36 CIE Marks 40
Number of Lecture Hours/Week 03 SEE Marks 60
Total Number of Lecture Hours 40 (8 Hours/ Module) Exam Hours 03

Course Learning Objectives:

This course will enable students to:
•Study and analysis of thyristor circuits with different triggering conditions.
•Learn the applications of power devices in controlled rectifiers, converters and
inverters.
•Understand types of instrument errors.
•Develop circuits for multirange Ammeters and Voltmeters.
•Describe principle of operation of digital measuring instruments and Bridges.
•Understand the operation of Transducers, Instrumentation amplifiers and PLCs.
Course Outcomes:
At the end of the course students should be able to:
1. Build and test circuits using power electronic devices.
2. Analyze and design controlled rectifier, DC to DC converters, DC to
AC inverters and SMPS.
3. Define instrument errors.
4. Develop circuits for multirange Ammeters, Voltmeters and Bridges to
measure passive component values and frequency.
5. Describe the principle of operation of Digital instruments and PLCs.
6. Use Instrumentation amplifier for measuring physical parameters.
Text Books:
1. M.D Singh and K B Khanchandani, “Power Electronics”, 2nd Edition, Tata Mc-Graw
Hill, 2009, ISBN:0070583897
2. H. S. Kalsi, “Electronic Instrumentation”, McGraw Hill, 3rd Edition , 2012, ISBN:
9780070702066.
 Module-1
Introduction: History, Power Electronic Systems, Power Electronic
Converters and Applications.
Thyristors: Static Anode-Cathode characteristics and Gate
characteristics of SCR, Turn-ON methods, Turn-OFF mechanisms, Turn-
OFF Methods: Natural and Forced Commutation – Class A and Class B
types, Gate Trigger Circuit: Resistance Firing Circuit, Resistance
capacitance firing circuit, Unijunction Transistor: Basic operation and
UJT Firing Circuit.(Text 1)
Module-2
Phase Controlled Converter: Control techniques, Single
phase half wave and full wave controlled rectifier with
resistive and inductive loads, effect of freewheeling diode.
Choppers: Chopper Classification, Basic Chopper operation:
step-down, step-up and step-up/down choppers. (Text 1)
 Module-3
Inverters: Classification, Single phase Half bridge and full bridge inverters with RL load.
Switched Mode Power Supplies: Isolated Flyback Converter, Isolated Forward Converter.
(Text 1)
Principles of Measurement: Static Characteristics, Error in Measurement, Types of Static Error.
(Text 2: 1.2-1.6)
Multirange Ammeters, Multirange voltmeter. (Text 2: 3.2, 4.4 ) L1,L2, L3
 Module-4
Digital Voltmeter: Ramp Technique, Dual slope integrating Type DVM, Direct
Compensation type and Successive Approximations type DVM
(Text 2: 5.1-5.3,5.5, 5.6)
Digital Multimeter: Digital Frequency Meter and Digital Measurement of Time,
Function Generator.
Bridges: Measurement of resistance: Wheatstone’s Bridge, AC Bridges- Capacitance
and Inductance Comparison bridge, Wien’s bridge.
(Text 2: refer 6.2, 6.3 upto 6.3.2, 6.4 upto 6.4.2, 8.8, 11.2, 11.8-11.10, 11.14).
 Module-5
Transducers: Introduction, Electrical Transducer, Resistive Transducer, Resistive position
Transducer, Resistance Wire Strain Gauges, Resistance Thermometer, Thermistor, LVDT.
(Text 2: 13.1-13.3, 13.5, 13.6 upto 13.6.1, 13.7, 13.8, 13.11).
Instrumentation Amplifier using Transducer Bridge, Temperature indicators using Thermometer,
Analog Weight Scale
(Text 2: 14.3.3, 14.4.1, 14.4.3).
Programmable Logic Controller: Structure, Operation, Relays and Registers
(Text 2:21.15, 21.15.2, 21.15.3, 21.15.5, 21.15.6).
 Module-3
Inverters: Classification, Single phase Half bridge and full bridge
inverters with RL load.
Switched Mode Power Supplies: Isolated Flyback Converter, Isolated
Forward Converter. (Text 1)

Principles of Measurement:

• Static Characteristics,
• Error in Measurement,
• Types of Static Error. (Text 2: 1.2-1.6)
• Multirange Ammeters
• Multirange voltmeter. (Text 2: 3.2, 4.4 )
Introduction:
What is Measurement ?

“The process of comparing an unknown quantity

with an accepted standard quantity.”

Example:
a) 10kg of sugar.
b) 5lt of milk.
c) 36.75V of voltage.
d) 527mA of current.
e) 2k of resistance.
Advantages of Electronic Measurement

1.Most of the quantities can be converted by transducers into the

electrical or electronic signals.
2.An electrical or electronic signal can be amplified, filtered,
multiplexed, sampled.
3. The measurement can easily be obtained in or converted into digital
form for automatic analysis and recording.
4. The measured signals can be transmitted over long distances.
5. Electronic circuits can detect and amplify very weak signals.
Functional elements of an instruments
Calibration:

 Calibration is the process of making an adjustment or

marking a scale so that the readings of an instrument agree
with the accepted and the certified standard.
 The periodic calibration of an instrument is very much
necessary.
 If the device has been repaired, aged, adjusted or modified,
then recalibration is carried out.
Performance characteristics:
For selecting the most suitable instrument for
specific measuring jobs.
Two basic types
1. Static: unvarying process condition
2. Dynamic: rarely respond instantaneously to
change in the measured varibles
1.Static characteristics:

The static characteristics are defined for the instruments

which measure the quantities which do not vary with time.
The various static characteristics are accuracy, precision,
resolution, error, sensitivity, threshold, reproducibility, zero
drift, stability and linearity.
1. Accuracy.
2. Precision.
3. Resolution.
4. Expected value.
5. Error.
6. Sensitivity.
1. Accuracy:

• It is the degree of closeness with which the

instrument reading approaches the true value of the
quantity to be measured.
• It denotes the extent to which we approach the
actual value of the quantity.
• It indicates the ability of instrument to indicate the
true value of the quantity.

“How close the measurement is to the actual

measured quantity.”
The accuracy can be expressed in the following ways.

1) Accuracy as „Percentage of Full Scale Reading‟:

In case of instruments having uniform scale, the accuracy can be
expressed as percentage of full scale reading.
For example, the accuracy of an instrument having full scale reading of
50 units may be expressed as ± 0.1% of full scale reading.

2) Accuracy as 'Percentage of True Value' :

It is to be specified in terms of the true value of quantity being measured.
For example, it can be specified as ± 0.1% of true value.

Example:
when a voltmeter with an error of ± 1% indicates exactly 100V, then true
level of the measured voltage is somewhere between 99V and 101V.
So accuracy is of ± 1%
2.Precision:

The smallest change that can be observed

in the measured quantity .

The degree of exactness of a measurement (results

from limitations of measuring device used).
Example: a)
1) A analog voltmeter with an FSD of 100 V might have its accuracy
stated as ±2%.
2) In this case, the maximum possible error at all points on the scale is
±2% of 100 V or ±2 V.
3) Thus when the pointer is indicating exactly at 100 V, as shown in
figure.
4) The measured voltage is correctly stated as 100 V ±2 V,
5) The actual level of the measured voltage might be anywhere from
98 V to 102 V.
Example:
Consider the digital voltmeter indication shown in figure (a).
For the 7.60 V indicated quantity, a 1 on the last (right side) numeral
represents 10 mV.
If the measured quantity increases or decreases by 10 mV, the reading
becomes 7.61 V or 7.59 V, respectively.
A voltage change smaller than 10 mV is unlikely to produce a change in
the measured quantity.
Therefore, 10 mV is the smallest voltage change that can be detected in
this case. So, it can be stated that the voltage is measured with a
precision of 10 mV.
Example:
For analog voltmeter in figure (b).
The pointer position on the 10 V range can be read within one-half of
the smallest scale division.
Since the smallest scale division represents 0.2 V (on the 10 V range),
one-half of the scale division is 0.1 V. So, 0.1 V is the smallest
detectable change in this case, or the measurement precision of this
analog instrument on the 10 V range is 0.1 V.
3.Resolution:
It is the smallest increment of quantity being
measured which can be detected with certainty
by an instrument.

The smallest observable change.

EXAMPLES:
1.Digital Multimeter:
2. Digital Scale

3. Digital Stopwatch
 Error in Measurement
1. Some factors that affects the measurements are related to
the measuring instruments themselves.
2. Person using the instruments.
3. Error may be expressed either as absolute or as percentage
of error.
 Absolute Errors and Relative Errors

Relative Errors:
Percentage accuracy gives the relative
error in a measured, or specified quantity.
Absolute Errors:
The absolute error can be determined by
converting the percentage error into an
absolute quantity
Absolute Errors:
The difference between the expected value of the
variable and the measured value of the variable
e=Yn –Xn
Where,
e = absolute error
Yn =expected value
Xn =measured value
Example 2.1: An analog voltmeter is used to measure voltage of
50V across a resistor. The reading value is 49 V. Find
a) Absolute Error
b) Relative Error
c) Accuracy
d) Percent Accuracy

Solution: a) e  X t  X m  50V  49V  1V

Xt  Xm
b) % Error  100 %
Xt
50V  49V
 100 %  2%
50V
c) A  1  % Error  1  2%  0.98
d) % Acc  100 %  2%  98%
35
 Types of static errors

1) Gross errors
2) Systematic errors
3) Random error.
1. Gross errors or human error :
• The gross errors mainly occur due to
1. Carelessness.
2. Human mistakes in readings, recordings and calculating
results
3. Lack of experience of a human being.
4. These errors also occur due to incorrect adjustments of
instruments.
• These errors cannot be treated mathematically.
• These errors are also called personal errors.
• Some gross errors are easily detected while others
are very difficult to detect.
 1. Misreading of an instruments.

The digital instrument is on a 300 mA range, so its

reading is in milliamperes.
For the analog meter, the range selection must be noted,
and the pointer position must be read from the correct
scale
2) Systematic errors
• This error is due to shortcomings of the instrument, such as
defective or worn parts, or ageing or effects of the environment on
the instrument.
• The constant uniform deviation of the operation of an instrument is
known as Systematic errors.
There are 3 types
1. Instrumental errors
2. Environmental errors
3. Observational errors.
1.Instrumental errors
Inherent in measuring instruments, because of
their mechanical structure.
Ex: D,Arsonval movement, friction in bearing
,irregular spring tensions, stretching of
springs.
How to Avoid.
i) Selecting a suitable instrument.
ii) Applying correction factor.
iii) Calibrating the insrtuments.
Measurement Error Combinations
When a quantity is calculated from measurements made on
two (or more) instruments, it must be assumed that the errors
due to instrument inaccuracy combine is the worst possible
way.
Sum of Quantities
Where a quantity is determined as the sum of two
measurements, the total error is the sum of the absolute
errors in each measurement.
 Module-3
Inverters: Classification, Single phase Half bridge and full bridge
inverters with RL load.
Switched Mode Power Supplies: Isolated Flyback Converter, Isolated
Forward Converter. (Text 1)

Principles of Measurement:

• Static Characteristics,
• Error in Measurement,
• Types of Static Error. (Text 2: 1.2-1.6)
• Multirange Ammeters
• Multirange voltmeter. (Text 2: 3.2, 4.4 )
Voltmeters and Ammeters
Basic meter:
 A basic d.c. meter uses a motoring principle for its
operation.
 It states that any current carrying coil placed in a
magnetic field experiences a force, which is
proportional to the magnitude of current passing
through the coil.
 This movement of coil is called D'Arsonval
movement and basic meter is called D'Arsonval
galvanometer.
D.C instruments:
a) Using shunt resistance, d.c. current can be measured.(d.c.
microammeter, milliammeter or ammeter.)
b) Using series resistance called multiplier, d.c. voltage can be
measured. ( d.c. millivoltmeter, voltmeter or kilovoltmeter.)
c) Using a battery and resistive network, resistance can be measured.
(ohmmeter).

A.C instruments:
a) Using a rectifier, a.c. voltages can be measured, at power and audio
frequencies. The instrument is a.c. voltmeter.
b) Using a thermocouple type meter radio frequency (RF) voltage or
current can be measured.
c) Using a thermistor in a resistive bridge network, expanded scale for
power line voltage can be obtained.
The voltmeter must be connected across the two points
or a component, to measure the potential difference,
with the proper polarity.
The multiplier resistance can be calculated as:
The multiplying factor for multiplier is the ratio of full range
voltage to be measured and the drop across the basic meter.
 Ammeters
DC Ammeter:
 PMMC Galavanometer constitutes basic movement DC ammeter.
 Coil winding are small and light.
 For large currents its necessary to bypass a major part of the current
through a resistance called a shunt.
 The resistance of shunt can be calculated using conventional circuit
analysis. Where,
Rm =internal resistance of the movement.
Ish = shunt current.
Im = full scale deflection current of the
movement.
I=full scale current of the ammeter
+shunt(total current)
Multirange Ammeters
Multirange voltmeters:
• The range of the basic d.c. voltmeter can be extended
by using number of multipliers called a selector switch.
• Such a meter is called multirange voltmeter .