NOORUL ISLAM COLLEGE OF ENGINEERING,

KUMARACOIL

DEPARTMENT OF ELECTRONICS AND

COMMUNICATION ENGINEERING

EC61 – MEASUREMENTS AND INSTRUMENTATION

S6, ECE – B BATCH

PREPARED BYANGELIN KIRUBHA SLECTURER, EEE

TWO MARK QUESTIONS AND ANSWERS

UNIT I1. What is meant by measurement?

Measurement is an act or the result of comparison between the quantity and apredefined standard.2. Mention the basic requirements of measurement.

The standard used for comparison purpose must be accurately defined andshould be commonly accepted.The apparatus used and the method adopted must be provable.

3. What are the 2 methods for measurement?Direct method andIndirect 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 bysome intermediate means and is then fed to the end device which presents the results ofthe measurement.5. Define Instrument.

Instrument is defined as a device for determining the value or magnitude of aquantity or variable.6. List the types of instruments.

The 3 types of instruments areMechanical InstrumentsElectrical Instruments andElectronic Instruments.

7. Classify instruments based on their functions.Indicating instrumentsIntegrating instrumentsRecording instruments

.8. Give the applications of measurement systems.The instruments and measurement systems are used forMonitoring of processes and operations.Control of processes and operations.Experimental engineering analysis.

9. 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.10. Explain the calibration procedure.

Calibration procedure involves a comparison of the particular instrument witheither.

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

calibrated or an instrument of known accuracy.11. Define Calibration.

It is the process by which comparing the instrument with a standard to correct theaccuracy.12. Name the different essential torques in indicating instruments.

Deflecting torqueControlling torqueDamping torque

13. Name the types of instruments used for making voltmeter and ammeter.PMMC typeMoving iron typeDynamometer typeHot wire typeElectrostatic typeInduction type.

14. State the advantages of PMMC instrumentsUniform scale.No hysteresis lossVery accurateHigh efficiency.

15. State the disadvantages of PMMC instrumentsCannot be used for ac measurementsSome errors are caused by temperature variations.

16. State the applications of PMMC instrumentsmeasurement of dc voltage and currentused in dc galvanometer.

17. How the range of instrument can be extended in PMMC instruments.In ammeter by connecting a shunt resisterIn voltmeter by connecting a series resister.

18. State the advantages of Dynamometer type instrumentsCan be used for both dc and ac measurements.Free from hysteresis and eddy current errors.

19. State the advantages of Moving iron type instrumentsLess expensiveCan be used for both dc and acReasonably accurate.

20. What are the basic elements of a generalized measurement system?The basic elements of a measurement system are primary sensing element,

variable conversion element, variable manipulation element, data transmissionelement and data presentation element.

21. Define the term precision.Precision is the measure of the consistency or repeatability of a series of

measurements.Precision=1-|Xi-X/Xi|

Xi=the value of the ith measurements.X=the average value of n measurements

22. What is the difference between accuracy and precision?

Accuracy : It is the closeness with which an instrument reading approaches the truevalue of the variable being measured.

Precision: It is the measure of reproducibility of the measurements.23. List the different types of possible errors in measurements.

The types of errors in measurements are systematic errors, Random errors andgross errors.

24. List any 4 static characteristics of a measuring system.The static characteristics of a measuring system are accuracy, sensitivity,

resolution, precision, drift and dead zone.25. What are the different types of standards?

The different types of standards are international standards, primary standards,secondary standards and working standards.26. Define Accuracy.

Accuracy is defined as the measure of the closeness with which an instrumentmeasures the true value of a quantity.27. Define span.

Span is defined as the algebraic difference the highest and lowest scale values of aninstrument.28. What is random error?

Random error is an error due to unknown causes and observed when themagnitude and polarity of a measurement fluctuates in a unpredictable manner.29. Define standard deviation.

Standard deviation or root mean square deviation is a statistical measure foranalyzing grouped data by quantifying the dispersion of individual data points about theirmean value.30. Define primary standards.

They are basic fundamental or derived unit standard maintained by a country’snational standards laboratory. They are absolute standards of high accuracy that can beused as ultimate reference standards.31. Define sensitivity of an instrument.

Sensitivity of an instrument is a measure of the change in reading of an instrumentfor a given change in the measured quantity.32. Define resolution of an instrument.

Resolution of an instrument is the smallest change in the measured quantity thatwill produce a detectable change in the instrument reading.33. What is meant by systematic error?

Systematic errors are those errors that remain constant with repeatedmeasurements, such as zero, scale, response time and loading errors.34. Show the block diagram indicating functional elements of measurement system.

35. Define limiting error.In most instruments, the accuracy is guaranteed to be within a certain percentage

of full scale reading. Manufacturers have to specify the deviations from the nominalvalue of a particular quantity. The limits of these deviations from the specified value aredefined as limiting errors or guarantee errors.

Limiting error = accuracy x full-scale value.36. Define probable error.

The probable error is defined as probable error r = ± 0.6745 σwhere σ is the standard deviation. Probable error is a measure of precision.37. Define arithmetic mean.

It is the most likely value obtained from a series of independent measurements ofa given quantity.

Arithmetic mean x = ∑x1

N38. What is meant by time-domain response?

Time-domain response is a graph that shows the output or response of themeasurement systems as a function of time. The input signal is applied to the system andthe behaviour of the system is studied as a function of time.39. Define calibration.

Calibration is the process of checking the accuracy of instruments by comparingthe instrument reading with a standard or against a similar meter of known accuracy. It isalso defined as marking the scale of an instrument.

UNIT II

40. Mention any two types of electronic voltmeter.1. Direct coupled electronic DC voltmeter.2. Chopper stabilized electronic DC voltmeter.

41. What is a multimeter?It is an instrument used for measuring AC and DC voltage, AC and DC current

and resistance.42. What for a Q-meter is used?

A Q-meter is used for finding the effective inductance of a coil at radiofrequencies.43. What are the different methods available for measuring RF power?

Primarysensingelement

Variableconversionelement

Variablemanipulationelement

Datatxionelement

Datapresentationelement

Quantity tobe measured

Data conditioning element

i) Voltage and current methodii) photometric comparison methodiii) Bolometeriv) Calorimetric measurementv) Directional wattmeter

44. What is a RF probe?It is a rectifier circuit used with a high impedance voltmeter to measure RF

voltages.45. What are the difference between AC and DC electronic voltmeter?

Electronic AC voltmeters differ from their DC counterpart only in that Acvoltage must be converted to DC before being applied to the meter movement.

Meter scale in the AC voltmeter is calibrated in terms of the RMS value of awaveform instead of the average value.

DC voltmeter has high sensitivity than AC voltmeter.46. What is Q-factor?

It is the ratio of resistance and a standard capacitance.47. What are the advantages of electronic voltmeter?

Negligible loading effect. High accuracy Cheap and rugged Can measure very low voltages

48. What is vector voltmeter?It is an electronic meter used for measuring the amplitude of two points in a circuit and

simultaneously measures the phase difference between the voltage waveforms at thesetwo points.49. What is true RMS voltmeter?

True RMS voltmeter is an instrument which produces a meter indication bysensing waveform heating power, which is proportional to the square of the RMS valueof the voltage. It is used for measuring voltages of complex waveforms.50. What is a CRT?

It is an electron beam tube in which electrons emitted by a hot cathode are formedby an electron gun into a narrow beam that is focused onto a phosphor coated screen.51. What is a CRO?

It is a test instrument using a cathode ray tube to make visible on a phosphorcoated-screen instantaneous values and waveforms as functions of either time or someother quantity.52. Define vertical amplifier.

It is an amplifier in an oscilloscope for signals intended for vertical deflection onthe screen.53. Define horizontal amplifier.

It is an amplifier in an oscilloscope for signals intended for horizontal deflectionon the screen.54. Why is a delay line used in the vertical section of the oscilloscope?

Delay line is used in the vertical section of the oscilloscope to produce a timedelay of signal.55. What is a sampling oscilloscope?

A sampling oscilloscope is a special type of CRO used for high frequencyapplications, by means of sampling the input waveform and reconstructing its shape fromthe many samples taken during recurrent cycles of the input waveform.56. Mention any two applications of digital storage oscilloscope.

i) To analyse the waveforms by storing them in memory.ii) To compare the two waveforms.

57. List the special types of CRO. Sampling CRO Storage CRO Digital storage CRO

58. What is meant by phosphorescence?The property of a phosphor material continuing to emit light after its excitation

source has been removed is called phosphorescence.59. Mention the different parts of vertical deflection system.

Input selector switch, Input attenuator, Vertical amplifier and Probe

UNIT III

60. What is the difference between a wave analyzer and a harmonic distortionanalyzer?

A wave analyzer is an instrument that measures amplitudes of the harmoniccomponents of complex signal. A harmonic distortion analyzer is an instrument thatmeasures total harmonic distortion by determining the harmonic components of a givenwaveform.61. State the applications of spectrum analyzer.

It is used for Observing purity of a signal Analyzing modulated signals Studying harmonic components of a signal Finding the intermodulation content.

62. Give two applications of function generators.It is used for Generating sine, square, triangle, sawtooth waveforms etc. Modulating amplitude, frequency and pulse width of the signal.

63. What is harmonic distortion?It is a form of distortion caused by a signal passing through a non-linear system in

which harmonics are added to the fundamental signal.64. Define rise time and fall time of a pulse.Rise time : It is the time required for a pulse to rise from 10 to 90% of its normal /final

amplitude.Fall time: It is the time required for a pulse to fall from 90 to 10% of its normal /final

amplitude.65. What is a distortion analyzer?

It is an instrument that measures total harmonic distortion by determining theharmonic components of a given waveform.

66. What is a pulse generator?It is a device which generates pulses of controlled amplitude, width and repetition

rate.67. Define frequency modulation.

It is a modulation of the carrier such that the carrier frequency is proportional tothe amplitude of the modulating signal.68. What is meant by frequency synthesis?

The generation of stable output frequency derived from multiples or submultiplesof one or more crystal controlled oscillators is called frequency synthesis.69. What is a sweep generator?

It is a device which generates a waveform whose frequency can be varied at aselected rate between a minimum and maximum value.70. What is a spectrum analyzer?

It is an instrument with a CRT that displays the frequency components ofcomplex signal.71. List the types of spectrum analyzer?

Swept tuned radio frequency spectrum analyzer Swept superheterodyne frequency spectrum analyzer High frequency spectrum analyzer

72. Define duty cycle.It is a ratio of pulse width time to the signal period.

73. What is settling time?The time required for a signal to decrease to a given percentage typically 1 to 5 %

of its peak value is called as settling time.74. What is ringing?

The positive and negative peak distortion excluding overshoot or undershoot, onthe pulse top or base line is called as ringing.75. What are the types of wave analyzers?

Wave analyzer Distortion analyzer Spectrum analyzer Digital fourier analyzer Audio analyzer

76. What is a wave analyzer?It is an instrument designed to measure the relative amplitude of single frequency

components in a complex or distorted waveform.77. What are the uses of wave analyzers?

Measuring the amplitudes of individual components of a complexfrequency system.

Measuring the signal amplitudes in the presence of noise and interferingsignals.

Measuring the energy in a specific well defined bandwidth.78. Write the expression for deriving the % harmonic distortion.

%Nth harmonic distortion = VN x 100 %V1

Where VN = RMS voltage of the Nth harmonicV1 = RMS voltage of the fundamental component.

79. Give the drawbacks of tuned circuit harmonic analyzer. At low frequencies, very large values for L and C are required and their

physical size becomes rather impractical. Harmonics of the signal frequency are often very close in frequency, so

that it becomes extremely difficult to distinguish between them.

UNIT IV

80. What are the advantages of digital meters over analog meters? High accuracy High precision Better resolution No parallax error No observation error

81. What are the disadvantages of digital meters? They need external power supply unit because of the use of ICs. Testing of diodes cannot be done normally, and a special additional circuit

has to be provided for this purpose in some meters.82. What is a digital voltmeter?

The digital voltmeter displays measurements of DC or AC voltages as discretenumerals instead of a pointer deflection on a continuous scale as in analog devices.83. List the characteristics of a DVM.

Input range Accuracy Stability Resolution Calibration

84. Define sensitivity.It is the smallest change in voltage that the meter can respond.

85. What are the types of DAC? Weighted resistor D/A converter R – 2 R ladder D/A converter Inverted R-2R ladder D/A converter.

86. State the disadvantage of weighted resistor D/A converter.It is very difficult to obtain stable and precise resistors over a wide range of

values from R to 2 n-1 R where n is the number of bits of the binary word.87. State the advantages of inverted R – 2 R ladder D/A converter.

It is constructed by resistors having two values only. They are R and 2 R. The R-2R ladder networks are available on monolithic ICs thus giving a

high degree of precision.88. Define resolution.

The resolution of a D/A converter is defined as the smallest change in the analogoutput voltage corresponding to the change of one bit in the digital input signal.

89. Define stability.It is the constancy of the fullscale output with age and variations in temperature

and power supply.90. What is a frequency counter?

A frequency counter is a device that counts selected input signal transitions for afixed period of time and displays the resultant frequency on a multidigit display.91. What is called extension of frequency range?

The measurement of frequencies greater than 50 MHz often presents problems asthese frequencies are often beyond the upper range of frequency counters. This isovercome by using either one of the plug- in modules such as prescalers, frequencyconverters etc.92. Write the use of digital multimeter.

This is used for measuring quantities such as AC voltage, AC current, DCvoltage, DC current and resistance.93. List the main parts of digital multimeter.

Current to voltage converter DC voltage attenuator AC voltage attenuator AC to DC converter

94. List the special features of DMM. Diode test Touch hold Peak hold Bar graph display Digital interface

95. Give the disadvantage of DVM.The direction and relative magnitude of a signal’s change during an adjustment

may be less apparent using digital voltmeter.96. State the principle of heterodyne frequency converter.

The principle states that it is used to extend the upper range of frequencies thatcan be measured with electronic counters.97. State the properties of analog instruments.

They require no power supply They give a better visual indication of the changes They suffer less from electrical noise and isolation problem. They are simple and inexpensive.

98. Define linearity.D/A converter is said to be ideal or perfectly linear, if it gives equal increments in

analog output voltage for equal increments in the numerical value of the digital input.99. Define speed.

It is defined as the amount of time required to settle to a particular desiredaccuracy.

UNIT V

100. What is meant by data acquisition system?A data acquisition system is used for collecting the data in digital form which

consists of signal conditioning, data conversion, data processing, multiplexing, datahandling and associated transmission, storage and display system.101. What are the elements of data acquisition system?

The elements of a data acquisition system are: Sensor / transducer Signal conditioner Multiplexer A/ D converter Display device

102. Mention the factors that decide the configuration of DAS.The factors that decide the configuration of DAS are:

Accuracy and resolution Number of channels Analog or digital signal Cost Single channel and multichannel Sampling rate / channel

103. What are the objectives of DAS?The objectives of DAS are:

1. It must acquire the necessary data at correct speed and at correct time2. it must monitor the complete plant operation3. it must be flexible and capable of being expanded for future requirements.

104. What is meant by signal conditioning?Signal conditioning is a process which performs linear operations like

amplification, attenuation, integration, differentiation, addition and subtraction and non-linear operations like modulation, demodulation, filtering, squaring etc.105. What is an instrumentation amplifier?

An instrumentation amplifier is a high performance differential amplifieroperating with a high gain, high input impedance and high common-mode rejection.106. List the important features of instrumentation amplifier.

The features of instrumentation amplifier are: Selectable gain with high gain accuracy and gain linearity. High CMRR Low output impedance Low DC offset High stability of gain with low temperature co-efficeint.

107. Define a filter and classify it.A filter is an electronic circuit which allows certain frequencies and attenuate

others. They are classified as low pass filter, high pass filter, band pass filter and bandreject filters.108. What is a sample and hold circuit?

It is an electronic circuit which samples the output of the signal conditioner at aspecified time and holds the voltage level at its output.109. List the types of signal converters used in DAS.

Voltage to current converter Current to voltage converter Voltage to frequency converter Frequency to voltage converter.

110. Define a multiplexer.It is a device which accepts multiple inputs ( inputs from number of channels )

and connects them to a single, measurement device.111. Mention the types of multiplexing.

Analog to digital multiplexer Digital to analog multiplexer

112. What is meant by computer-controlled measurement system?It is an automatic test equipment (computer operated test and evaluation system)

which consists of computer, computer compatible test equipment, software toperform the desired test and communication system to connect the computer tothe test equipment.

113. What is GPIB?GPIB (IEEE 488) is one parallel interface which connects programmable instruments

to the computers.114. Define listener, talker and controller and give example for each.

Listener: It is a device capable of receiving data to other devices. Eg. Signal generator.Talker: It is a device capable of transmitting data to other devices. Eg. Counter.Controller: It is a device capable of managing communications over the GPIB by

sending addresses and commands. Eg. Computer.115. What are the types of loss measurements in optical fibers?

Cut-back method Insertion loss method Optical time domain reflectometer (OTDR) method.

116. Give the advantages of cut-back method. It is a simple method for measuring total attenuation loss. It is a precise and accurate method.

117. Write the merits of OTDR method of measuring loss in optical fibers. It requires access to one end of the fiber only. It provides positional information about the properties of fiber. It is easy to locate the faults.

118. What limits the data rate in the IEEE 488 system?The operation of the IEEE 488 bus is completely asynchronous, which requires

one task to be completed before another task can commence. So the data rate is low.119. What is the recommended maximum cable length for the IEEE 488 system?

The bus has a maximum length of 20m.