BEE Measurement and Instrumentation 5 — Questions and Answers
Question 1: Hysteresis error in a measurement system means the output depends on:
- The rate of change of input
- The direction from which the input is approached (Correct answer)
- The ambient temperature
- The frequency of the input signal
Correct answer: The direction from which the input is approached
Hysteresis causes different output readings for the same input depending on whether the input is increasing or decreasing.
Question 2: Which instrument is best suited for measuring very low resistances (below 1 Ω) accurately?
- Wheatstone bridge
- Kelvin double bridge (Correct answer)
- Megohmmeter
- Schering bridge
Correct answer: Kelvin double bridge
The Kelvin double bridge eliminates the error due to lead and contact resistance by using a second set of ratio arms, making it ideal for milliohm measurements.
Question 3: In a spectrum analyzer, the x-axis represents:
- Time
- Amplitude
- Frequency (Correct answer)
- Phase
Correct answer: Frequency
A spectrum analyzer displays signal amplitude (power or voltage) as a function of frequency, unlike an oscilloscope which uses time on the x-axis.
Question 4: The accuracy of an instrument is best defined as:
- The smallest change in input the instrument can detect
- The closeness of the measured value to the true value (Correct answer)
- The ability to reproduce the same reading repeatedly
- The range of inputs over which the instrument is calibrated
Correct answer: The closeness of the measured value to the true value
Accuracy is the degree of conformity between the instrument's reading and the true value of the quantity being measured.
Question 5: A power factor meter used in a single-phase circuit has how many current coils and voltage coils?
- One current coil and one voltage coil
- One current coil and two voltage coils (Correct answer)
- Two current coils and one voltage coil
- Two current coils and two voltage coils
Correct answer: One current coil and two voltage coils
A single-phase power factor meter has one current coil carrying load current and two crossed voltage coils — one in series with a resistor and one in series with an inductor.
Question 6: When a voltmeter of 1000 Ω/V sensitivity is set to the 100 V range, its internal resistance is:
- 1000 Ω
- 10,000 Ω
- 100,000 Ω (Correct answer)
- 1,000,000 Ω
Correct answer: 100,000 Ω
Internal resistance = sensitivity × range = 1000 Ω/V × 100 V = 100,000 Ω (100 kΩ).
Question 7: The term 'dead zone' in an instrument refers to:
- The range where output is nonlinear
- The range of input values that produce no change in output (Correct answer)
- The maximum overload the instrument can withstand
- The frequency range where the instrument is inaccurate
Correct answer: The range of input values that produce no change in output
The dead zone (or dead band) is the largest range of input change that fails to produce any detectable change in the instrument's output.
BEE Measurement and Instrumentation 5
Hysteresis error in a measurement system means the output depends on: