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LECTURE NOTES ON MEASUREMENTS AND INSTRUMENTATION
LECTURE NOTES ON MEASUREMENTS AND INSTRUMENTATION 29
EI1202 – MEASUREMENTS AND
Ms.B.DEVI, L/ EEE
COLLEGE OF ENGINEERING AND
UNIT I FUNDAMENTALS
Functional elements of an instrument – Static and dynamic characteristics – Errors in
measurement– Statistical evaluation of measurement data – Standards and calibration
UNIT II ELECTRICAL AND ELECTRONICS INSTRUMENTS
Principle and types of analog and digital instruments –Voltmeters – Ammeters - Multimeters –
Single and three phase wattmeters and energy meters – Magnetic measurements – Determination
of B-H curve and measurements of iron loss – Instrument transformers – Instruments for
measurement of frequency and phase.
UNIT III COMPARISON METHODS OF MEASUREMENTS
D.C and A.C potentiometers – D.C and A.C bridges – Transformer ratio bridges – Self-balancing
bridges – Interference and screening – Multiple earth and earth loops – Electrostatic and
electromagnetic interference – Grounding techniques.
UNIT IV STORAGE AND DISPLAY DEVICES
Magnetic disk and tape – Recorders, digital plotters and printers – CRT display – Digital CRO,
LED, LCD and dot-matrix display – Data Loggers
UNIT V TRANSDUCERS AND DATA ACQUISITION SYSTEMS
Classification of transducers – Selection of transducers – Resistive, capacitive and inductive
transducers – Piezoelectric, optical and digital transducers – Elements of data acquisition system
– A/D, D/A converters – Smart sensors.
1. Doebelin, E.O., ―Measurement Systems – Application and Design‖, Tata McGraw Hill
Publishing Company, 2003.
2. Sawhney, A.K., ―A Course in Electrical and Electronic Measurements and
Instrumentation‖, Dhanpat Rai AND Co, 2004
1. Bouwens, A.J., ―Digital Instrumentation‖, Tata McGraw Hill, 1997.
2. Moorthy, D.V.S., ―Transducers and Instrumentation‖, Prentice Hall of India, 2007.
3. Kalsi, H.S., ―Electronic Instrumentation‖, 2nd Edition, Tata McGraw Hill, 2004.
4. Martin Reissland, ―Electrical Measurements‖, New Age International (P) Ltd., 2001.
5. Gupta, J.B., ―A Course in Electronic and Electrical Measurements‖, S.K.Kataria and Sons,
UNIT I FUNDAMENTALS
Functional elements of an instrument – Static and dynamic characteristics – Errors
in measurement– Statistical evaluation of measurement data – Standards and
FUNCTIONAL ELEMENTS OF AN INSTRUMENT
PART – A
1. What are the functional elements of an instrument? (2)
2. What is meant by accuracy of an instrument? (2)
3. Define international standard for ohm? (2)
4. What is primary sensing element? (2)
5. What is calibration? (2)
6. Define the terms precision & sensitivity. (2)
7. What are primary standards? Where are they used? (2) 8. When are static characteristics important? (2)
9. What is standard? What are the different types of
10. Define static error. Distinguish reproducibility and
11. Distinguish between direct and indirect methods of
12. With one example explain “Instrumental Errors”. (2)
13. Name some static and dynamic characteristics. (2)
14. State the difference between accuracy and precision of a
15. What are primary and secondary measurements? (2)
16. What are the functions of instruments and measurement
17. What is an error? How it is classified? (2)
18. Classify the standards of measurement? (2)
19. Define standard deviation and average deviation. (2)
20. What are the sources of error? (2)
21. Define resolution. (2)
22. What is threshold? (2)
23. Define zero drift. (2)
24. Write short notes on systematic errors. (2)
25. What are random errors? (2)
PART – B
1. Describe the functional elements of an instrument with its block
diagram. And illustrate them with pressure gauge, pressure
thermometer and D’Arsonval galvanometer. (16)
2. (i) What are the three categories of systematic errors in the
Instrument and explain in detail. (8)
(ii) Explain the Normal or Gaussian curve of errors in the study
Of random effects. (8)
3. (i) What are the basic blocks of a generalized instrumentation
Draw the various blocks and explain their functions. (10)
(ii) Explain in detail calibration technique and draw the
Calibration curve in general. (6)
4. (i) Discuss in detail various types of errors associated in
Measurement and how these errors can be minimized? (10)
(ii) Define the following terms in the context of normal
Frequency distribution of data (6)
a) Mean value
c) Average deviation
e) Standard deviation.
5. (i) Define and explain the following static characteristics of an
c) Sensitivity and
(ii) Define and explain the types of static errors possible in an
6. Discuss in detail the various static and dynamic characteristics
of a measuring system. (16)
7. (i) For the given data, calculate
a) Arithmetic mean
b) Deviation of each value
c) Algebraic sum of the deviations (6)
X1 = 49.7, X2 = 50.1, X3 = 50.2, X4 = 49.6, X5 = 49.7
(ii) Explain in detail the types of static error. (7)
(iii) Give a note on dynamic characteristics. (3)
8. (i) What is standard? Explain the different types of standards(8)
(ii) What are the different standard inputs for studying the
Dynamicresponse of a system. Define and sketch them. (8)
UNIT II ELECTRICAL AND ELECTRONICS INSTRUMENTS
Principle and types of analog and digital instruments –Voltmeters – Ammeters -
Multimeters –Single and three phase wattmeters and energy meters – Magnetic
measurements – Determinationof B-H curve and measurements of iron loss –
Instrument transformers – Instruments formeasurement of frequency and phase.
Principle and types of analog and digital instruments
A multimeter ora multitester, also known as a volt/ohm meter or VOM, is
an electronic measuring instrument that combines several measurement functions in one unit. A
typical multimeter may include features such as the ability to
measure voltage, current and resistance. Multimeters may use analogor digital circuits—analog
multimeters and digital multimeters (often abbreviated DMM or DVOM.) Analog instruments
are usually based on amicroammeter whose pointer moves over a scale calibration for all the
different measurements that can be made; digital instruments usually display digits, but may
display a bar of a length proportional to the quantity measured.
A multimeter can be a hand-held device useful for basic fault finding and field service work or
a bench instrument which can measure to a very high degree of accuracy. They can be used to
troubleshoot electrical problems in a wide array of industrial and household devices such
as electronic equipment, motor controls, domestic appliances, power supplies, and wiring
Multimeters are available in a wide ranges of features and prices. Cheap multimeters can cost
less than US10, while the top of the line multimeters.
The first moving-pointer current-detecting device was the galvanometer. These were used to
measure resistance and voltage by using a Wheatstone bridge, and comparing the unknown
quantity to a reference voltage or resistance. While useful in the lab, the devices were very slow
and impractical in the field. These galvanometers were bulky and delicate.
The D'Arsonval/Weston meter movement used a fine metal spring to give proportional
measurement rather than just detection, and built-in permanent field
magnets made deflection independent of the 3D orientation of the meter. These features enabled
dispensing with Wheatstone bridges, and made measurement quick and easy. By adding a series
or shunt resistor, more than one range of voltage or current could be measured with one
Multimeters were invented in the early 1920s as radio receivers and other vacuum tube electronic
devices became more common. The invention of the first multimeter is attributed to United
States Post Office (USPS) engineer, Donald Macadie, who became dissatisfied with having to
carry many separate instruments required for the maintenance of
the telecommunications circuits. Macadie invented an instrument which could
measure amperes (aka amps), volts and ohms, so the multifunctional meter was then
named Avometer. The meter comprised a moving coil meter, voltage and precision resistors,
and switches and sockets to select the range.
Macadie took his idea to the Automatic Coil Winder and Electrical Equipment
Company (ACWEEC, founded in 1923). The first AVO was put on sale in 1923, and
although it was initially a DC. Many of its features remained almost unaltered through to the last
Pocket watch style meters were in widespread use in the 1920s, at much lower cost
than Avometers. The metal case was normally connected to the negative connection, an
arrangement that caused numerous electric shocks. The technical specifications of these devices
were often crude, for example the one illustrated has a resistance of just 33 ohms per volt, a non-
linear scale and no zero adjustment.
The usual analog multimeter when used for voltage measurements loads the circuit under test to
some extent (a microammeter with full-scale current of 50ampere, the highest sensitivity
commonly available, must draw at least 50 milliamps from the circuit under test to deflect fully).
This may load a high-impedance circuit so much as to perturb the circuit, and also to give a low
Vacuum Tube Voltmeters or valve voltmeters (VTVM, VVM) were used for voltage
measurements in electronic circuits where high impedance was necessary. The VTVM had a
fixed input impedance of typically 1 megohm or more, usually through use of a cathode
follower input circuit, and thus did not significantly load the circuit being tested. Before the
introduction of digital electronic high-impedance analog transistor and field effect
transistor (FETs) voltmeters were used. Modern digital meters and some modern analog meters
use electronic input circuitry to achieve high-input impedance—their voltage ranges
arefunctionally equivalent to VTVMs.
Additional scales such as decibels, and functions such as capacitance, transistor
gain, frequency, duty cycle, display hold, and buzzers which sound when the measured
resistance is small have been included on many multimeters. While multimeters may be
supplemented by more specialized equipment in a technician's toolkit, some modern multimeters include even more additional functions for specialized applications (e.g., temperature with
a thermocoupleprobe, inductance, connectivity to a computer, speaking measured value, etc.).
Contemporary multimeters can measure many quantities.
The common ones are:
Voltage, alternating and direct, in volts.
Current, alternating and direct, in amperes.
The frequency range for which AC measurements are accurate must be specified.
Resistance in ohms.
Additionally, some multimeters measure:
Capacitance in farads.
Conductance in siemens.
Duty cycle as a percentage.
Frequency in hertz.
Inductance in henrys.
Temperature in degrees Celsius or Fahrenheit, with an appropriate temperature test probe,
often a thermocouple
Digital multimeters may also include circuits for:
Continuity; beeps when a circuit conducts.
Diodes (measuring forward drop of diode junctions, i.e., diodes and transistor junctions)
and transistors (measuring current gain and other parameters).
Battery checking for simple 1.5 volt and 9 volt batteries. This is a current loaded voltage
scale. Battery checking (ignoring internal resistance, which increases as the battery is
depleted), is less accurate when using a DC voltage scale.
Various sensors can be attached to multimeters to take measurements such as: