BEE Measurement and Instrumentation 2 — Questions and Answers
Question 1: Which bridge circuit is most commonly used to measure inductance?
- Wheatstone bridge
- Maxwell bridge (Correct answer)
- Kelvin bridge
- Schering bridge
Correct answer: Maxwell bridge
The Maxwell bridge balances inductance against a known capacitance and resistance to measure unknown inductance values.
Question 2: A current transformer (CT) should never be operated with its secondary:
- Short-circuited
- Open-circuited (Correct answer)
- Connected to an ammeter
- Loaded at rated burden
Correct answer: Open-circuited
An open-circuited CT secondary causes dangerously high voltages due to the high magnetizing current in the primary.
Question 3: The sensitivity of a voltmeter is expressed in:
- Ohms per volt (Correct answer)
- Volts per ohm
- Amperes per volt
- Watts per volt
Correct answer: Ohms per volt
Voltmeter sensitivity (Ω/V) indicates how much resistance the meter presents per volt of full-scale deflection; higher is better.
Question 4: In a CRO, the time base is generated by:
- A sinusoidal oscillator
- A sawtooth wave generator (Correct answer)
- A square wave generator
- A pulse generator
Correct answer: A sawtooth wave generator
The sawtooth (ramp) wave sweeps the electron beam linearly across the screen at a controlled rate to create the time axis.
Question 5: Which error results from the loading effect of a voltmeter on a circuit?
- Systematic error (Correct answer)
- Gross error
- Random error
- Observational error
Correct answer: Systematic error
Loading error is a systematic error because it consistently affects every measurement in the same direction due to the meter's finite input impedance.
Question 6: A megohmmeter (megger) is used primarily to measure:
- Low resistances in motor windings
- Insulation resistance of cables and equipment (Correct answer)
- Contact resistance of switches
- Ground resistance of electrodes
Correct answer: Insulation resistance of cables and equipment
A megger applies a high DC voltage (typically 500–5000 V) to measure insulation resistance values in the megaohm range.
Question 7: The Lissajous figure on a CRO shows a straight line at 45°. What is the phase difference between the two signals?
- 0° or 180° (Correct answer)
- 90°
- 45°
- 270°
Correct answer: 0° or 180°
A straight-line Lissajous figure indicates 0° (same phase) or 180° (opposite phase) between the two input signals.
BEE Measurement and Instrumentation 2
Which bridge circuit is most commonly used to measure inductance?