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Measurements and Instrumentation (EE2201)

UNIT I

INTRODUCTION

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.

Absolute Instruments

Secondary Instruments

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8. What are the 2 modes of operation of secondary Instruments?

Analog mode and

Digital mode

9. What are analog devices?

Signals that vary in a continuous fashion and take on an infinity of values in

any range are called analog signals. The devices that produces these signals are

called analog devices

10. What are digital devices?

Signals that vary in discrete steps and thus take on only finite differentvalues in a given range are called digital signals. The devices that produces these

signals are called digital devices.

11. Mention the functions performed by the measurement system.

Indicating function

Recording function

Controlling function.

12.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.

13. List the functional elements of the measurement systems.

Primary sensing element.

Variable conversion element and Data processing element.

14. What is signal conditioning?

The performing of non-linear processes like modulation, detection,

sampling, filtering, chopping and clipping etc. on the signal to bring it to desired

form is called signal conditioning.

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15. What is data transmission element?

When the elements of an instrument are actually physically separated, it

becomes necessary to transmit data from one to another. The element thatperforms this function is called a data transmission element.

16. Give the function of the variable manipulation element.

The function of the variable manipulation element is to manipulate the

signal presented to it preserving the original nature of the signal.

17. What are the characteristics of the measurement system?

Static characteristics

Dynamic characteristics

18. Why calibration of instrument is important?

The calibration of all instruments is important since it affords the

opportunity to check the instrument against a known standard and subsequently to

errors in accuracy.

19. Explain the calibration procedure.

Calibration procedure involves a comparison of the particular instrument

with either.

A primary standard

A secondary standard with a higher accuracy than the instrument to be

calibrated or

An instrument of known accuracy.

20.What are the static characteristics? (AU April 2004)

Accuracy Sensitivity

Reproducibility

Drift

Static error and

Dead zone.

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21.Define true value

True value of a quantity to be measured is defined as the average of aninfinite number of measured values when the average deviation to the various

contributing factors tends to zero.

22.Define scale range.

The scale range of an instrument is defined as the difference between the

largest and smallest reading of the instrument.

23. What is meant by reproducibility?.(AU Nov 2004)

Reproducibility is the degree of closeness with which a given value may be

repeatedly measured. It may be specified in turns of units for a given period of

time.

24. Define repeatability.(AU Nov 2004)

Repeatability is defined as the variation of scale reading and is random in

nature.

25.Define noise.

Noise is defined as any signal that does not convey any useful information.

26. What is accuracy?(AU may 2005)

Accuracy is the closeness with which an instrument reading approaches the

true value of the quantity being measured.

27.What is precision?

Precision is measure of the reproducibility of the measurements, i.e. given afixed value of a quantity; it is a measure of the degree of agreement within a group

of measurements.

28. Mention the characteristics of precision.

Conformity and

Number of significant figures.

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29.What are the different types of errors?(AU Nov 2004)

*Gross error

* Systematic error

* Random error

30.Define Fidelity.

Fidelity of a system is defined as the ability of a system to reproduce the same

output in the same form as the input.

31. What is Dynamic error?

Dynamic error is difference between the true value of the quantity changing with

the time and the value indicated by the instrument if no static error is assumed.

32.Define relative limiting error.

Relative limiting error is defined as the ratio of the error to the specified to the

magnitude of the quantity.

33.Define static error.(AU Nov 2004)

Static error is defined as the difference between the measured value and true value

of the quantity.

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UNIT IIELECTRICAL & ELECTRONICS INSTRUMENTS

1. Mention the two main differences between a flux meter and a BallisticGalvanometer.

Flux meter Ballistic

Galvanometer

Controlling torque is very small controlling torque is high

Heavy electromagnetic damping electromagnetic damping is not heavy

Less sensitive more sensitive

Less accurate more accurate

2. What are the adjustments in energy meter?

Main speed adjustment

Power factor adjustment

Friction adjustment

Creep adjustment

3. Write about DC tests in magnetic measurements.

These are used to determine B-H curve and hysteresis loop of Ferro-

magnetic materials. The direct current is used to have variable m.m.f. and

flux meter is used to measure the flux density. A ballistic galvanometer can

be used to measure flux density. Such tests are also called ballistic tests.4. Give two differences between analog and digital type phase meters.

Analog type Digital Type

This is called balanced modulator method this is called flip-flop method

Accuracy is very less high as 0.1o

can be achived

Less stable, sensitive & reliable high stable, sensitive and reliable

DC meter is used at the output display unit is used at the output

5. What is creeping?

Without any current through current coil, disc rotates due to the

supply voltage exciting its pressure coil. This is called creeping.

6. Write some advantages of instrument transformer.

The normal range ammeters and voltmeters can be used along with

these transformers to measure high currents and voltage.

The rating of low range meter can be fixed irrespective of the value of

high voltage or current to be measured

These transformers isolate the measurement from high voltage and

current circuits. This ensures safety of the operator and makes the

handling of the equipments very easy and safe.

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These can be used for operating many types of protecting devices such

as relays or pilot lights.

7. Define the terms digitizing and digitizing period.

In the digital voltmeters, it is necessary to convert the analog signal to

digital signal. Various techniques used to achieve this conversion. The circuits

which are used to achieve such conversion are called digitizing circuits and

the process is called digitizing. The time required for this conversion is called

digitizing period.

8. What are the requirements of a shunt?

The temperature coefficient of shunt and the meter should be low and

should be as equal as possible.

The shunt resistance should be stable and constant with time.

The shunt resistance should not carry currents which will cause excessive

temperature rise.

The soldering joints should not cause a voltage drop.

The values of resistance should not change due to soldering.

The resistance should have low thermal electromotive force with copper.

9. Mention any two precautions to be taken while using a voltmeter.

It should be always connected across the circuit or component whose

voltage is to be measured.

The polarities must be observed correctly.

First use the highest range and then decrease the voltage range until the

sufficient deflection is obtained.

Take care of loading effect.

10. Mention the two main differences between an ammeter and a

voltmeter.

Ammeter Voltmeter

It is a current measuring device it is a voltage measuring deveice

Always connected in series with circuit Always connected in parallel with circuit

The resistance is very small The resistance is very high

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11. What are the adjustments in energy meter?

Main speed adjustment Power factor adjustment

Friction adjustment

Creep adjustment

12. Write about AC tests in magnetic measurements.

When a ferro-magnetic material is subjected to cycle of magnetization

and demagnetization then the eddy current and hystereis losses occur. Hence

alternating current is used to determine iron losses, having provision of a

variable frequency and form factor. Such tests are carried out at power, audio

or radio frequencies.

13. Mention the errors in Moving iron instruments.

Hysteresis error

Temperature error

Stray magnetic field error

Frequency error

Eddy current error

14. How can we prevent creeping in energy meter?

Two holes are drilled in the aluminum disc 180o

opposite to each other.

When this holes comes under the shunt magnet pole, it gets acted upon by a

torque opposite to the rotation.

15. Mention the purpose of Schmitt trigger in frequency meter.

To convert the amplified signal from sine wave to square wave with fast

rise and fall times.

16.Define torque to weight ratio in electrodynamometer instrument.

To have reasonable deflecting torque, mmf of the MC must be enough.

Thus mmf=NI, hence current through MC should be high or no. Of turns

should be large. The current cannot be made high because it may cause

excessive heating of spring. Large no. of N hence is the only option but it

increases weight of the coil.

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17.What are the requirements of a Multiplier?

Their resistance should not change with time

The change in their resistance with temperature should be small. They should be non-inductively wound for a.c. meters.

18.Mention any two precautions to be taken while using an Ammeter.

It should never be connected across any source.

The polarity must be observed correctly.

First use the highest range and then decrease the voltage range until the

sufficient deflection is obtained.

19.What are instrument transformer?

Transformers used in conjunction with measuring instrument for measuring

purposes are called instrument transformers. The transformers used for

measurement of current is called current transformers. The transformers used for

measurement of voltage are called potential transformers.

20.What are the different types of frequency meters?

The different types of frequency meters are:

1.Mechanical resonant type2.Electrical resonance type

3.Electrodynamometer type

4.Weston type

5.Ratiometer type

6.Saturable core type

21.What are the different types of electrical resonance type frequency

meters?

The two types of electrical resonance type frequency meters are :1. Ferrodynamic type frequency meter

2. Electrodynamometer type frequency meter.

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UNIT III

COMPARISON METHODS OF MEASUREMENTS

1. Define D.C potentiometer

A potentiometer is an instrument designed to measure an

unknown voltage by comparing it with a unknown voltage.

2.List the application of D.C potentiometer.

Measurement of Voltage

Calibration of Voltmeter

Calibration of Ammeter Calibration of Wattmeter

3.What is A.C potentiometer?

A.C potentiometer is user for measurement of alternating voltages

and currents.

4.Give the purpose of bridge circuits. What are the different type?

The bridge circuits are used in instrumentation systems for the

measurement of resistance , inductance and capacitance.

Types:

DC type and

AC type.

5.What are the 2 types of wheatstone bridge?

Null type bridge

Deflection type bridge.

6.What are the different types of AC bridges?

Maxwells Inductance bridge

Maxwells inductance-Capacitance bridge

Hays bridge

Andersons bridge

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Owens Bridge

High voltage Schering

7. Define slew rate

Slew rate is defined as the maximum output voltage change per unit time.

8. What is the basic principle used in potentiometer.

In potentiometer the unknown emf is measured by comparing it with a std

known emf.

Name the potentiometer material used.

German silver

Manganin wire

9. 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.

10. State the applications of potentiometer.

Used for m/s of unknown emf

Used for ammeter calibration

Used for Voltmeter calibration

Used for wattmeter calibration

11. State the advantages of crompton potentiometer.

More accurate

Easy to adjust

12. What are the practical difficulties in ac potentiometers.

More complicated

Accuracy is seriously affected

Difficulty is experienced in standardization.

7. Classify ac potentiometers.

Polar potentiometer

Coordinate potentiometer.

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

It is measured from the position of phase shifter.

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14. Name some ac potentiometers.

Drysdale Tinsley potentiometer

Gall Tinsley potentiometer

15. 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

16. State the applications of ac potentiometers.

M/s of self inductance.

Ammeter calibration

Voltmeter calibration

Wattmeter calibration.

17. State the advantages of instrument transformers.

Used for extension of range

Power loss is minimum

High voltage and currents can be measured.

18. State the disadvantage of instrument transformers.

Cannot be used for dc measurements.

19. What are the constructional parts of current transformer?

Primary winding

Secondary winding

Magnetic core.

20. Name the errors caused in current transformer.

Ratio error

Phase angle error

21. Define ratio error.

The ratio of energy component current and secondary current is known as the

ratio error.

22. How the phase angle error is created.

It is mainly due to magnetizing component of excitation current.

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23. State the use of potential transformer.

Used for m/s of high voltage

Used for energizing relays and protective circuits.

24. Name the errors caused in potential transformer.

Ratio error

Phase angle error.

25. How the CT and PT are connected in the circuits.

CT is connected in series and PT is connected in parallel.

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UNIT- IV

STORAGE AND DISPLAY DEVICES

1. List the components of a magnetic tape recorder.( AU Nov 2005)

Magnetic tape

Reproducing head

Tape transport mechanism

Conditioning devices.

Recording head

2. Mention the different methods of magnetic tape recording.(AU May 2005)

Direct recording

Frequency modulation (FM) recording and

Pulse duration modulation (PM) recording.

3. What is the purpose of erase head?

In the erase head, a signal of high frequency and level sweeps the magnetic

tape thereby completely wiping out the information contained there in. this renders

the magnetic tape to be used fresh for smother signal.

4. What is drop out?

In direct recording, some portions of the tape may not be perfectly recorded

owing to dirt or poor manufacturer and this is called drop out.

5. Mention the 2 factors in FM recording

Percentage deviation and

Deviation ratio

6. What is the operation of a serial printer?

The serial printer produces a single character at a time, usually moving

from left to right across a page. It prints 200 characters per second.

7. Mention the purpose of line printers.

The line printers are used to print and entire line simultaneously. It points

4000 lines per minute.

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8. Give the operation of pare printers.

The page printer prints in a line at a time mode, but can be stopped and

restarted only on the page basis. The top speed is 45,000 lines per minute.

9. List the classification of printers.

Impact and non-impact printers.

Fully formed character and dot matrix character printer.

Character at a time and a line at a time.

10. What is daisy wheel printer?

Daisy wheel printer is a fully formed character printer, designed forcomputer usage and has characters mounted on the periphery of a spinning print

head similar to a daisy flow. They are capable of bi-directional printing.

11. Give short notes on dot-matrix printers.

In dot-matrix printers, the characters are formed by printing a group of dots

to form a letter, no. or other symbols. It can print any combination of dots with all

available print position in the matrix.

12. List the important features of CRTs.

Size

Phosphor

Operating voltages

Deflection voltages

Viewing screen .

13. What is meant by deflection sensitivity in CRT?(AU may 2005)

The deflection sensitivity of the CRT is usually stated as the DC voltagerequired for each cm of deflection of the spot on the screen.

14. What is meant by recurrent sweep in CRT?

When the saw tooth, being an AC voltage alternates rapidly, the display

occurs respectively, so that a lasting image is seen by the eye. This repeated

operation is known as recurrent sweep.

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UNIT V

TRANSDUCERS AND DATA ACQUISITION SYSTEMS

1. Define transducers.

Transducers are defined as a device which when actuated, transforms

energy from one form to another. Generally, any physical parameters is

converted into electrical form.

2. What are the 2 types of transducers?

Electrical and

Mechanical

3. Name the parameters that dictate the transducer capability

Linearity

Repeatability

Resolution and

Reliability

4. Define sensitivity

Sensitivity is defines as the electrical output per unit change in the

physical parameter. High sensitivity is generally desirable for a transducer.

5. Classify electrical transducers.

Active

Passive

6. Name the 2 parts of a transducer

Sensing element

Transduction element

7. Mention the factors considered while selecting a transducer.

Operating range

Sensitivity

Frequency response & resonant frequency

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13.Write notes on LVDT

It is the linear variable differential transformer which is used to translatethe linear motion into electrical signals. It consists of a single primary

winding and 2 secondary winding.

14. List the advantages of LVDT

High range of displacement measurement

Friction & electrical isolation

Immunity from external effects

High I/p and high sensitivity

Ruggedness

Low hysterisis & low power consumption.

15.What is a digitizer?

It is a digital encoding transducer that enables a linear or rotary

displacement to be directly converted into digital form without intermediate

forms of analog to digital (A/D) conversion.

16.What are the disadvantages of LVDT?

The disadvantages of LVDT are:

1.Relatively large displacements are required for appreciable

differential input.

2. The transducer performance is affected by vibrations.

3.The receiving instrument can be selected to operated on ac

signals or a demodulator network must be used if a D.C output is required.

17.Write down the principle of operation of capacitive transducers.

The principle of operation of capacitive transducers are given as,

Where , A=Overlapping area of plates in m2

d= distance between two plates in m.

r= relative permittivity

o= Permittivity of free space(8.85*10-12

F/m)

18.List out the advantages of capacitive transducer.

The advantages of capacitive transducer are

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1.They require extremely small forces to operate

2.They are extremely sensitive

3.They have a high input impedance and hence minimum loading effects

4.They have a good frequency response and require small power tooperate them.

20.What is the disadvantage of piezo electric transducer?

The disadvantage of piezo electric transducer is that it cannot measure

static conditions.The output voltage is affected by the temperature variation of

the crystal.

21.What is digital transducers?

Digital transducers are called as encoders. They are normally in the form

of linear or rotary displacement transducers .Hence they require digital to

analog converter to realize the digital data.

22.What is meant by Data acquisition?

Data acquisition relates to the process of collecting the input data in

digital form as rapidly, accurately and economically as necessary.

23. List the instruments that are needed for data acquisition system.

*DPM with digital outputs

* a shaft digitizer

*sophisticated high speed resolution device

24.List the basic components of D/A converter.

*flip flop register

* DAC modules

25.List the methods used for analog to digital conversion.

The methods used for analog to digital conversion are

1.Successive approximation type

2.Voltage to time conversion method

3.Voltage to frequency conversion method

4.Dual slope integration method