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Electrical Measurements and Instrumentation

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Electrical Measurements and Instrumentation

shape Introduction

Electrical Measurements and Instrumentation include the methods, devices and calculations used to measure electrical quantities. Example: Ammeter is a device used to measure the current. Electrical parameters such as current, voltage, capacitance, inductance, etc. are measured with the Instrumentation.

shape Quiz

Q1. A man hold both the terminals of a 500 V meager, but still safe due to
    A. high voltage B. very low current C. high resistance of the body D. low resistance of the body Answer: B

Q2. On testing an electric iron on meter, the reading of the meter is infinity. This indicates
    A. short circuit of the heating element B. short circuit of the supply terminal C. loose terminal connections D. open circuit of the heating element Answer: D

Q3. Using a C.T. has
    A. poorer overload capacity than a P.T. B. the same overload capacity as a P.T. C. a higher overload capacity than a P.T. D. none of the above Answer: C

Q4. An alternator is being synchronized to the bus bars of frequency 50 Hz. The synchroscope lamp flickers at a frequency of 5 Hz. The frequency of the alternator is
    A. 45 Hz B. 55 Hz C. 45 of 55 Hz D. none of the above Answer: C

Q5. Tow voltmeters of 0-300 V range are connected in parallel to an ac circuit. One voltmeter is moving iron type and reads 200 V. If the other volmeter is moving coil type, its reading will be
    A. 200 3V B. 200 × 1.41 V C. slightly less than 200 V D. zero Answer: D

Q6. Which of the following meter mechanisms is adaptable to a greater variety of measurement?
    A. Inclined coil B. Moving-iron vane C. Electrodynamometer D. Permanent magnet-moving coil Answer: C

Q7. To measure 2 volts, if one selects 0-100 volt range voltmeter which is accurate within +1%, the error in his/her measurement may be upto
    A. + 0.02 % B. +1 % C. +2 % D. +50 % Answer: D

Q8. In a two wattmeter method of measuring power in a 3-phase system one of the wattmeters reads negative implying
    A. wattmeter connection is faulty B. load is unbalanced C. power flow is in the reverse direction D. power factor is less then 0.5 Answer: D

Q9. Which of the following is not an advantage of semi-conductor gauges as compared to conventional strain gauges?
    A. Excellent hysteresis characteristics B. Least sensitive to temperature changes C. High fatigue life D. Smaller size Answer: B

Q10. In indicating instruments the damping is usually adjusted
    A. at critical value B. to the value slightly higher than critical value C. to the value slightly higher than critical value value D. to any value Answer: B
Q11. Electro dynamometers are used extensively for the measurement of
    A. magnetic lines of force B. resistivity C. capacitor networks D. power Answer: D

Q12. Electrostatic instruments
    A. can be used on dc only B. when used on ac measure rms value whatever the waveform C. are highly sensitive to eddy current errors D. none of the above Answer: B

Q13. Before connecting a meter to measure an unknown current or voltage, it is best to
    A. start with the h ighest ran ge and work down B. start with the lowest range and work down C. select an estimated mid-range D. use the trial and error method Answer: A

Q14. Quadrant type electrostatic instruments can be used for measurement of ac voltage
    A. only when heterostatically connected. B. only when idiostatically connected. C. in either heterostatic connection or idiostatic connection D. None of the above Answer: B

Q15. Capacitor potential transformers are used
    A. for primary voltage exceeding 100 kv (Phase) B. because these are cheaper than the conventional type above a certain voltage C. for keeping the transformation ratio constant irrespective of the burden with certain adjustments D. all of the above Answer: D

Q16. For measuring a low resistance by ammeter-voltmeter method, the voltmeter is connected directly across the resistance under measurement
    A. there is an error in measurement as the ammeter measures current flowing through the voltmeter in addition to the current flowing through the resistance under measurement B. there is an error in measurement as the voltmeter measures voltage drop across the ammeter in addition to that across the resistance under measurement C. both (a) and (b) D. none of above Answer: A

Q17. The rectifier instrument is not free from
    A. Temperature error B. Frequency er ror C. Wave shape error D. All of the above Answer: D

Q18. An accurate ammeter must have a resistance of
    A. High value B. Low value C. Very low value D. None of the above Answer: C

Q19. The source of energy for operating an ohmmeter is obtained from
    A. the line being measured B. any 120 volt source C. a rectifier cell D. a battery Answer: D
Q20. Which of the following is not the method for reducing residual inductance in resistors?
    A. Faraday's winding method B. Card wound resistor C. Chaperon winding method D. Curtis and Arower winding method Answer: A

Q21. W1 and W2 are the readings of two wattmeters used to measure power of a 3-phase balanced load. The reactive power drawn by the load is
    A. [latex]W_{1}[/latex] +[latex] W_{2}[/latex] B. [latex]W_{1}[/latex] – [latex]W_{2}[/latex] C. [latex]\sqrt{3}{W}_{1} + {W}_{2}[/latex] D. [latex]\sqrt{3}{W}_{1} – {W}_{2}[/latex] Answer: D

Q22. Half wave rectifier type AC meters are used as voltmater. They cannot be used as ammeters because
    A. pointer would oscillate with AC B. AC current would be too small to read C. AC current would be excessive D. AC is changed to DC Answer: A

Q23. Which of the following does not have the same units as the others? The symbols have their usual meanings.
    A. L/R B. R C C. [latex]\sqrt{LC}[/latex] D. 1/[latex]\sqrt{LC}[/latex] Answer: D

Q24. The ratio of maximum displacement deviation to full scale deviation of the instrument is called the
    A. static sensitivity B. accuracy C. linearity D. precision E. dynamic deviation Answer: D

Q25. Two 200 V D.C. voltmeters having resistances of 15 k-ohm and 10 k-ohm are connected in series. The safe voltage which can be measured by this combination will be
    A. 400 V B. 200 2V C. 200 V D. 100 V Answer: C

Q26. The Q-meter works on the principle of
    A. mutual inductance B. self inductance C. series resonance D. parallel resonance Answer: C

Q27. The pressure coil of a dynamometer type wattmeter is
    A. highly inductive B. highly resistive C. purely resistive D. purely inductive Answer: B

Q28. The bridge method commonly used for finding mutual inductance is
    A. Heavyside Campbell bridge B. Sch ering bridge C. De Sauty bridge D. Wien bridge Answer: A

Q29. What is the correct sequence of the following types of ammeters and voltmeters with increasing accuracy?
    1. Moving-iron 2. Moving-coil permanent magnet 3. Induction Select the correct answer using the codes given below A. 1, 3, 2 B. 1, 2, 3 C. 3, 1, 2 D. 2, 1, 3 Answer: C

Q30. Which of the following bridges can be used for inductance measurement?
    1. Maxwell’s bridge 2. Schering bridge 3. Wein-bridge 4. Hay’s bridge 5. Wheatstone bridge Select the correct answer using the codes given below A. 1 and 2 B. 2 and 3 C. 3, 4 and 5 D. 1 and 4 Answer: D
Q31. Which one of the following digital voltmeters is most suitable to eliminate the effect of period noise?
    A. Ramp type digital voltmeter B. Integrating type digital voltmeter C. Successive approximation type digital voltmeter D. Servo type digital voltmeter Answer: D

Q32. Electrostatic instruments are normally used for
    A. low current measurements B. high current measurements C. low voltage mesurements D. high voltage measurements Answer: D

Q33. Which instrument has necessarily the ‘square law’ type scale?
    A. Permanent magnet moving coil. B. Hot wire instruments C. Moving iron repulsion D. None of the above Answer: B

Q34. In a single-phase power factor meter, the controlling torque is
    A. provided by spring control B. provided by gravity control C. provided by stiffness of suspension D. not required Answer: D

Q35. If an induction type energy meter runs fast, it can be slowed down by
    A. lag adjustment B. light load adjustment C. adjusting the position of braking magnet and moving it closer from the centre of the disc D. adjusting the position of braking magnet and moving it away from the centre of the disc. Answer: D

Q36. Which one of the following statements is correct? The deflection of hot wire instrument depends on
    A. r.m.s. value of the a.c. current B. r.m.s. value of the a.c. voltage C. average value of the a.c. current D. average value of the a.c. voltage Answer: A

Q37. Which one of the following decides the time of response of an indicating instrument?
    A. Deflecting system B. Controlling system C. Damping system D. Pivot and Jewel bearing Answer: C

Q38. Piezoelectric crystal is generally employed for the measurement of which one of the following?
    A. Flow B. Velocity C. Acceleration D. Temperature Answer: C

Q39. The deflection expression qm [latex]V^{2}[/latex] = dC/dq corresponds to
    A. moving iron type instrument B. electrodynamic type instruments C. electrostatic type instrument D. induction type instruments Answer: C

Q40. The full range of audibility in audio frequency oscillator is
    A. 0 to 20 Hz B. 20 Hz to 2 kHz C. 20 Hz to 20 kHz D. 20 Hz to 20 MHz Answer: C
Q41. Which devices used to measure the temperature of an object?
    A. Potentiometer B. Odometer C. Thermometers D. Galvanometer Answer: A

Q42. A liquid crystal display requires
    A. An AC drive B. A DC drive C. Both AC and DC drive D. None of the above Answer: A

Q43. A moving iron frequency meter consists of
    A. Two inductive circuits connected in parallel B. One inductive and one non inductive circuit connected in parallel C. Two non inductive circuits connected in parallel D. One inductive and one non inductive circuit connected in series Answer: D

Q44. The earth resistance can be measured by
    A. Fall of potential method B. Using an earth tester C. Ductor ohmmeter method D. Only (a) and (b) Answer: D

Q45. In AC bridges, the Wagner earth devices are used to
    A. Remove all the earth capacitances from the bridge circuit B. Remove harmonics C. Reduce error caused by stray electric field D. All of the above Answer: D

Q46. Electrostatic voltmeter instruments are suitable for
    A. AC work only B. DC work only C. Both AC and DC work D. None of these Answer: C

Q47. Electrostatic instruments are generally used as
    A. Voltmeters B. Ammeters C. Wattmeters D. Watt-hour meters Answer: A

Q48. In a measurement system,
    A. A single measurement components may have both random errors and systematic errors B. A measurement system consists of several components with each component having separate errors C. Both the statement (a) & (b) are trueĊ D. Neither statement (a) nor statement (b) is true Answer: C

Q49. Which of the following instruments used for the measurement of pressure?
    A. Bellows B. Diaphragms C. Fiber optic pressure sensors D. All of the above Answer: D

Q50. The errors mainly caused by human mistakes are
    A. Gross error B. Instrument error C. Observational error D. Systematic error Answer: A
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