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Anna University

DEPARTMENT OF ELECTRONICS AND COMMUNICATION

ENGINEERING


EC2351 MEASUREMENTS AND INSTRUMENTATION

Prepared By,

H.Christal Beni



EC2351 MEASUREMENTS AND INSTRUMENTATION

UNIT-I

BASIC MEASUREMENT BASIC MEASUREMENT BASIC MEASUREMENT BASIC MEASUREMENT CONCEPTSCONCEPTSCONCEPTSCONCEPTS

1. What is meant by measurement?

Measurement is an act or the result of comparison between the quantity and

a predefined standard.

2. Mention the basic requirements of measurement.

· The standard used for comparison purpose must be accurately defined and

should be commonly accepted.

· The apparatus used and the method adopted must be provable.

3. What are the 2 methods for measurement?

· Direct method and

· Indirect method.

4. Explain the function of measurement system.

The measurement system consists of a transducing element which converts

the quantity to be measured in an analogous form. The analogous signal is then

processed by some intermediate means and is then fed to the end device which

presents the results of the measurement.

5. Define Instrument.

Instrument is defined as a device for determining the value or magnitude of a

quantity or variable.

6. List the types of instruments.

· The 3 types of instruments are

· Mechanical Instruments

· Electrical Instruments and



· Electronic Instruments.

7. Classify instruments based on their functions.

Indicating instruments

Integrating instruments

Recording instruments

8. Give the applications of measurement systems.

· The instruments and measurement systems are sued for

· Monitoring of processes and operations.

· Control of processes and operations.

· Experimental engineering analysis.

9. Define static characteristics?

Static characteristics are the set of rules or criteria that is defined for those

instruments that varies very slowly with time or remains a constant.

10. Define Dynamic characteristics?

Dynamic characteristics are the set of rules or criteria that is defined for

those instruments that varies very rapidly with time.

11. What are the various Dynamic characteristics?

Various Dynamic characteristics are

Fiedality

Speed of Response

Time Delay

Lag

Dynamic error

12. What are the various Static characteristics?

Various Static characteristics are



Accuracy

Precision

Error

Threshold

Bias

Linearity

Stability

Reproducibility

Hysterisis

Range

Dead Space

Sensitivity.

13. What are the various units of measurements?

Units are the fundamental quantities of physics;

Various units of measurements are

Fundamental Units e.g.: Length (m), Mass (kg), and time (S)

Supplementary

Derived Units

14. Name the different essential torques in indicating instruments.

Deflecting torque

Controlling torque

Damping torque

15. Name the types of instruments used for making voltmeter and ammeter.

PMMC type

Moving iron type

Dynamometer type

Hot wire type



Electrostatic type

Induction type.

16. State the advantages of PMMC instruments

Uniform scale.

No hysterisis loss

Very accurate

High effuiciency.

17. State the disadvantages of PMMC instruments

Cannot be used for ac m/s

Some errors are caused by temperature variations.

18. State the applications of PMMC instruments

m/s of dc voltage and current

used in dc galvanometer.

19. How the range of instrument can be extended in PMMC instruments.

In ammeter by connecting a shunt resister

In voltmeter by connecting a series resister.

20. State the advantages of Dynamometer type instruments

Can be used for both dc and ac m/s.

Free from hysterisis and eddy current errors.

21. State the advantages of Moving iron type instruments

Less expensive

Can be used for both dc and ac

Reasonably accurate.

22. State the advantages of Hot wire type instruments

Can be used for both dc and ac

Unaffected by stray magnetic fields

Readings are independent of frequency and waveform



23. What are the various types of Bridges?

There are basically two types of bridges

24. Name any one Bridge that is used to measure the frequency?

Wein Bridge

UNIT-II

BASIC ELECTRONIC MEASUREMENTSBASIC ELECTRONIC MEASUREMENTSBASIC ELECTRONIC MEASUREMENTSBASIC ELECTRONIC MEASUREMENTS

1. What are the constructional parts of wattmeter?

Fixed coil

Moving Coil

Current limiting resister

Helical spring

Spindle attached with pointer

D.C Bridge A.C Bridge

Maxwell’s

Bridge

Wheatstone

sBridge

Hay’s

Bridge

Schering’s

Bridge

Andreson’s

Bridge

Kelvin’s

Bridge

Wein Bridge



Graduated scale

2. Write down the deflecting torque equation in dynamometer type wattmeter.

Td á VI CosÖ

3. What is the principle of CRO

Cathode ray oscilloscope works on the the principle of deflection of the

electron beam in the horizontal and vertical directions and creates the trace on the

fluorescent screen.

4. Name the errors caused during measurement

Error due to pressure coil inductance

Error due to pressure coil capacitance

Error due to methods of connection

Error due to stray magnetic fields

Error due to eddy current.

5. What is meant by special Oscilloscope

The oscilloscope which is not only meant for viewing the waveform , but

also used to perform some special functions such as storage of information, retrival

of waveform, stability etc..


Various types of special oscilloscopes are

• DSO

• Delayed time base oscilloscope

• Dual trace oscilloscope

• Dual Beam oscilloscope

• Sampling oscilloscope

7. Name the methods used for power measurement in three phase circuits.

(i)Single wattmeter method



(ii) Two wattmeter method

(iii) Three wattmeter method.

8. What is meant by Phosphor burning?

The process in which the trace of the waveform is obtained on the phosphor

screen, and when the trace is present for long time, the heat generated is capable of

destroying the phosphor screen, which is known as phosphor burning.

9. How is phosphor burning avoided.

The destructive method phosphor burning is avoided by coating the

fluorescent screen with a layer of Willemite, which is the composition of zinc and

Mno2

10. What is meant by fluorescence?

The ability of the material to emit energy is known as fluorescence. When

phosphor exhibit the fluorescence property, it is known as phosphorescence.

11. What is meant by Q-factor

Q-factor is known as the quality factor. It is used to measure the quality

factor of the coils such as inductors, Capacitors etc..

12. What is meant by Q-meter

Q-meter is generally used to measure the Q-factor of the coil.

13. Name the constructional parts of induction type energy meter.

Current coil with series magnet

Voltage coil with shunt magnet

All disc

Braking magnet

Registering mechanism.

14. What is a True RMS meter

The true RMS meter is used to determine the rrot mean square value of the

current and voltage.



15. What are the various types of storage oscilloscopes

The various types of storage oscilloscopes are

• Analog storage oscilloscope

� Mesh storage oscilloscope

� Bistable phosphor storage oscilloscope

• Digital storage oscilloscope

16. What is the DSO

DSO is known as digital storage oscilloscope, it is used for storing the

waveform in a digital form. It consits of a sample and hold circuit, control logic

and an A/D converter the waveform can be stored in a buffer amplifier.


The oscilloscope which is not only meant for viewing the waveform , but

also used to perform some special functions such as storage of information, retrival

of waveform, stability etc..

18. What is the purpose of braking mechanism.

It provides necessary braking torque.

19. What are the applications of CRO

CRO is used in

Medical field

Waveform analysis

Study of time period and amplitude of the waveform

Military applications.

20. What are the various methods of RF power measurement?

The various methods used in RF power measurements are

• Caloriemeter power meter



• Power measurement at high frequencies by

• Bolometer power meter

UNIT –III

SIGNAL GENERATORS AND ANALYZERSSIGNAL GENERATORS AND ANALYZERSSIGNAL GENERATORS AND ANALYZERSSIGNAL GENERATORS AND ANALYZERS

1. What is Function Generator?

The function generator is the device which is capable of producing several

functions based on the trigger input given.

2. Name the potentiometer material used.

German silver

Manganin wire

3. Define standardization.

It is the process by which adjusting the current flows through the

potentiometer coil to make the voltage across the std cell is equal.

4. State the applications of potentiometer.

Used for m/s of unknown emf

Used for ammeter calibration

Used for Voltmeter calibration

Used for wattmeter calibration

5. What are the various types of signal generators?

• Sweep signal generator

• Audio frequency signal generator

• RF signal generators

6. What are the types of frequency synthesizer?

There are two methods of frequency synthesis, they are



Direct frequency synthesis

In-direct frequency synthesis

7. What is meant by harmonic distortion?

Any unwanted harmonics that are present along with the needful information is

known as Harmonic Distortion.

8. How the phase angle is measured in polar type potentiometers.

It is measured from the position of phase shifter.

9. Name some ac potentiometers.

Drysdale Tinsley potentiometer

Gall Tinsley potentiometer

10. State the advantages of ac potentiometers.

Can be used for m/s of both magnitude and phase angle

Can be used for m/s of inductance of the coil.

It is used in m/s of errors in CTS

11. State the applications of ac potentiometers.

M/s of self inductance.

Ammeter calibration

Voltmeter calibration

Wattmeter calibration.

12. What are Detectors?

Detectors are used in an attempt to adequately map the correct signal power

to the appropriate frequency point on the display. There are in general three types

of detectors: sample, peak, and average

• Sample detection – sample detection simply uses the midpoint of a given

interval as the display point value. While this method does represent random

noise well, it does not always capture all sinusoidal signals.



• Peak detection – peak detection uses the maximum measured point within a

given interval as the display point value. This insures that the maximum

sinusoid is measured within the interval; however, smaller sinusoids within

the interval may not be measured. Also, peak detection does not give a good

representation of random noise.

• Average detection – average detection uses all of the data points within the

interval to consider the display point value. This is done by power (rms)

averaging, voltage averaging, or log-power averaging.

13. State the disadvantage of instrument transformers.

Cannot be used for dc measurements.

14. What are the constructional parts of current transformer?

Primary winding

Secondary winding

Magnetic core.

15. Name the errors caused in current transformer.

Ratio error

Phase angle error

16. What is meant by Resolution Bandwidth?

As discussed in the operation section, the resolution bandwidth filter or

RBW filter is the bandpass filter in the IF path. Adjusting the bandwidth of this

filter allows for the discrimination of signals with closely spaced frequency

components, while also changing the measured noise floor. Decreasing the

bandwidth of RBW filter decreases the measured noise floor and vice-versa. This

is due to higher RBW filters passing more frequency components through to the



envelope detector than lower bandwidth RBW filters, therefore a higher RBW

causes a higher measured noise floor.

17. What is meant by Wave analyzer?

Wave analyzer helps to evaluate the characteristics of wave such as

frequency, amplitude and Phase angle.

18. What is a Spectrum Analyzer?

Spectrum analyzer measures the magnitude of an input signal versus

frequency within the full frequency range of the instrument. The primary use is to

measure the power of the spectrum of known and unknown signals. The input

signal a spectrum analyzer measures is electrical, however, spectral compositions

of other signals, such as acoustic pressure waves and optical light waves, can be

considered through the use of an appropriate transducer

19. What are the types of Spectrum Analyzer?

Spectrum analyzer types are dictated by the methods used to obtain the

spectrum of a signal. There are swept-tuned and FFT based spectrum analyzers:

• A swept-tuned spectrum analyzer uses a superheterodyne receiver to down-

convert a portion of the input signal spectrum (using a voltage-controlled

oscillator and a mixer) to the center frequency of a band-pass filter. With a

superheterodyne architecture, the voltage-controlled oscillator is swept

through a range of frequencies, enabling the consideration of the full

frequency range of the instrument.

• A FFT spectrum analyzer computes the discrete Fourier transform (DFT), a

mathematical process that transforms a waveform into the components of its

frequency spectrum, of the input signal.



Some spectrum analyzers, such as real-time spectrum analyzers, use a hybrid

technique where the incoming signal is first down-converted to a lower frequency

using superheterodyne techniques and then analyzed using fast fourier

transformation (FFT) techniques.

20. What is meant by center frequency?

In a typical spectrum analyzer there are options to set the start, stop, and

center frequency. The frequency between the stop and start frequencies on a

spectrum analyzer display is known as the center frequency. This is the frequency

that is in the middle of the display’s frequency axis. Span specifies the range

between the start and stop frequencies. These two parameters allow for adjustment

of the display within the frequency range of the instrument to enhance visibility of

the spectrum measured.

UNIT-IV

DIGITAL INSTRUMENTSDIGITAL INSTRUMENTSDIGITAL INSTRUMENTSDIGITAL INSTRUMENTS

1. What is a Voltmeter?

A voltmeter is an instrument used for measuring electrical potential

difference between two points in an electric circuit. Analog voltmeters move a

pointer across a scale in proportion to the voltage of the circuit; digital voltmeters

give a numerical display of voltage by use of an analog to digital converter.

2. What is a Digital Voltmeter?

Digital voltmeters (DVMs) are usually designed around a special type of

analog-to-digital converter called an integrating converter. Voltmeter accuracy is

affected by many factors, including temperature and supply voltage variations. To



ensure that a digital voltmeter's reading is within the manufacturer's specified

tolerances, they should be periodically calibrated against a voltage standard such as

the Weston cell.

3. What is a multimeter?

A multimeter or a multitester, also known as a VOM (Volt-Ohm meter), 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 analog or digital

circuits.

4. Where high resistance measurement is required?

Insulation resistance of cables

High resistance circuit elements

Volume resistivity of a material

Surface resistivity.

6. What is the function of a Frequency Counter?

A frequency counter is an electronic instrument, or component of one, that

is used for measuring frequency. Frequency is defined as the number of events of a

particular sort occurring in a set period of time. Frequency counters usually

measure the number of oscillations or pulses per second in a repetitive electronic

signal. Such an instrument is sometimes referred to as a cymometer, particularly

one of Chinese manufacture.

7. What is extension of frequency range?

Frequency extension of signal is defined as the deliberate process of

expanding the frequency range (bandwidth) of a signal in which it contains an

appreciable and useful content, and/or the frequency range in which its effects are



such. Its significant advancement in recent years has led to the technology being

adopted commercially in several areas including psychacoustic bass enhancement

of small loudspeakers and the high frequency enhancement of coded speech and

audio.

8. What is Automation in digital instruments?

It is used to fabricate a wide range of instruments and equipment for

instrumentation, process controls, automation and condition monitoring

applications.

9. Define megger.

The megger is an instrument used for the measurement of high resistance

and insulation resistance.

10. What are the technical specifications of computer controlled test systems?

Technical Specifications

• Maximum load of 10N.m

• Intelligent Torque Loadcell capacities: 0.3N.m, 1.5N.m, 3N.m, 6N.m,

10N.m (2.7lbf.in, 13lbf.in, 26lbf.in, 52lbf.in, 90lbf.in)

• Maximum sample height of 448mm (17.6") *

• Width between columns 280mm (11")

• Capacity of upper mounting table from 10 to 78mm (0.39 - 3.07")

• Capacity of lower mounting table from 10 to 190mm (0.39 - 7.5")

• Load accuracy is ±0.5% of full scale

• Load resolution is 1:6500

• Speed range of 0.1 - 20 revs/min (clockwise and counter-clockwise)

• Maximum displacement of 2440 revs



• 5kg top loading capability

• Weight 19.5kg (43lb)

11. What is the range of low resistance?

Resistance of about 1 ohm and under are included in this class.

12. What is the range of medium resistance?

Resistance of 100 kilo ohms and above are usually termed as high resistance.

13. What ranges of resistance can be measured by using doctor ohmmeter.

0 to 500 micro ohms

0 to 5 milli ohms

0 to 50 milli ohms

0 to 500 milli ohms

0 to 5 ohms.

14. How resistance is measured in direct deflection method.

The deflection of galvanometer connected in series with the resistance to be

measured gives a measure of the insulation resistance.

15. Classify the cables according to their sheathing.

Armoured cables

Unarmoured cables.

16. What is meant by automatic Zeroing?

Earth lead

Line lead

Guard lead.

17. How resistance is measured by using ohm meter method.

Series ohm meter method

Shunt ohm meter method.



18. Why Is LabVIEW Ideal for Creating Virtual Instruments?

LabVIEW is an integral part of virtual instrumentation because it provides

an easy-to-use application development environment designed specifically with the

needs of engineers and scientists in mind. LabVIEW offers powerful features that

make is easy to connect to a wide variety of hardware and other software.

19. What are the views in VI?

• Front panel and

• Grid panel

20. What is meant by Virtual instrumentation?

Virtual instrumentation is a method of creating a Real time Environment in a

virtual platform by Using software.

UNIT-V

ACQUISITION SYSTEMS AND FIBER OPTIC MEASUREMENTSACQUISITION SYSTEMS AND FIBER OPTIC MEASUREMENTSACQUISITION SYSTEMS AND FIBER OPTIC MEASUREMENTSACQUISITION SYSTEMS AND FIBER OPTIC MEASUREMENTS

1. What is DAQ?

DAQ is known as Data Acquisition system, it is meant for collecting the

data, organizing the data, processing the data and storing the results.

2. What is meant by multiplexing?

Multiplexing is the the process of combining several input signals. Many

inputs are multiplexed and the result is produced based on the select signal.

3. What is IEEE 488 bus?

IEEE 488 bus is formerly known as Hewlett Packard interface Bus. And

later it was given IEEE standard and was known as IEEE 488 bus. It is used to

interface the digital multimeters, digital voltmeters and so in.

4. What are the various devices in IEEE 488 Bus?

Various devices in IEEE 488 Bus are



Talkers.

Listeners and

Controllers.

5. Name the bridge circuits used for the m/s of mutual inductance.

The Heaviside Campbell bridge

The Campbell bridge.

6. Which type of detector is used in ac bridges?

Vibration galvanometers are used.

7. Name the ac sources used in ac bridges.

AC supply with step-down transformer

Motor driven alternator

Audio frequency and radio frequency oscillator.

8. In which cases audio frequency oscillators are used as ac source.

For high frequency ac requirement audio frequency oscillators are used.

9. Name the sources of errors in ac bridge m/s.

Errors due to stray magnetic fields

Leakage errors

Eddy current errors

Residual errors

Frequency and waveform errors.

10. State the advantages of Maxwell-wein bridge.

The balance equation is independent of frequency and therefore more

accurate.

11. State the disadvantage of Maxwell-wein bridge.

This method needs a std variable capacitor. Variable Capacitor is costliest.

12. State the disadvantages of Hay’s bridge.



The balance equation is dependent of frequency and therefore any changes

in frequency will affect the measurements.

13. What is Total internal reflection?

When the light ray travels from the optically rarer medium to the optically

denser medium the ray gets refracted and some of the rays gets reflected, when the

angle of incidence is increased, the angle of refracted also get increased and at a

particular point all the rays get reflected and no refraction occurs. This is known as

Total Internal reflection

14. What are the various methods of fiber optic power measurement?

various methods of fiber optic power measurement are

Bolometer power meter

Power meter

Autoranging power meter

15. What is meant by inductometer?

The std variable mutual inductance meter is called as inductometer.

16. Define Q-factor of the coil.

It is the ratio between power stored in the coil to the power dissipated in the

coil.

17. Name the components of iron loss.

Eddy current loss

Hysterisis loss.

18. Name the faults that occur in cables.

Break down of cable insulation

Short circuit fault

Open conductor fault.

19. Name the loop test methods used in location of fault in fiber.

Murray loop test



Varley loop test.

20. What is OTDR?

OTDR is known as Optical Time Domain Reflectometer. It is used for the

measurement of the fiber optic system loss. In this method the directional coupler

is used so that losses are reduced.

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