Measurements and Instruments Viva Short Questions and Answers PDF

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DEPARTMENT OF ELECTRONICS AND

COMMUNICATION ENGINEERING QUESTION BANK

MEASUREMENTS & INSTRUMENTATION

MEASUREMENTS AND INSTRUMENTATION 

UNIT-I 

BASIC MEASUREMENT CONCEPTS 

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 i)Fidelity, (ii)Speed of Response,(iii)Time Delay,(iv)Lag,(v)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 efficiency.

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 MEASUREMENTS 

1. What are the constructional parts of wattmeter? 

Fixed coil Moving Coil Current limiting resister Helical spring Spindle attached with pointer 

Graduated scale

2. Write down the deflecting torque equation in dynamometer 

type wattmeter.

Td á VI CosÖ <PDF Download>

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..

6. What is meant by special Oscilloscope 

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 Mno

2

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.

17. 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..

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 ฀ Calorimeter power meter ฀ Power measurement at high frequencies by ฀ Bolometer power meter

UNIT –III SIGNAL 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. 

(i)German silver (ii)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. 

(i)Used for m/s of unknown emf (ii) Used for ammeter calibration (iii)Used for Voltmeter calibration(iv)Used for wattmeter calibration

5. What are the various types of signal generators? 

(ι) Sweep signal generator (ii) Audio frequency signal generator (ιιι) RF signal generators

6. What are the types of frequency synthesizer? 

There are two methods of frequency synthesis, they are (i) Direct frequency synthesis (ii)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. 

(i)M/s of self inductance.(ii)Ammeter calibration, (iii)Voltmeter calibration (iv) 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 agiven interval as the display point value. This insures that the maximumsinusoid is measured within the interval; however, smaller sinusoids withinthe 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 theinterval 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? 

(i)Primary winding,(ii)Secondary winding (iii)Magnetic core.

15. Name the errors caused in current transformer?. 

Ratio error and Phase angle error.

16. What is meant by Resolution Bandwidth? 

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 downconvert 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 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? (i)Insulation resistance of cables (ii) High resistance circuit elements (iii)Volume resistivity of a material (iv)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) 

<PDF Download>

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. 

(i)0 to 500 micro ohms. (ii)0 to 5 milli ohms (iii)0 to 50 milli ohms (iv) 0 to 500 milli ohms (v)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 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 (i)Talkers.(ii)Listeners and (iii) Controllers. 

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

(i) The Heaviside Campbell bridge (ii) 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. 

(i)AC supply with step-down transformer.(ii) Motor driven alternator (iii) 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. 

(i)Errors due to stray magnetic fields. (ii) Leakage errors.(iii) Residual errors (iv)Eddy current errors (v) 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 changesin 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

(i)Bolometer power meter. (ii) Power meter. (iii)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. 

(i)Eddy current loss. (ii)Hysterisis loss.

18. Name the faults that occur in cables. 

(i)Break down of cable insulation. (ii) Short circuit fault (iii) Open conductor fault.

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

(i) Murray loop test. (ii)

<PDF Download>

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