BEE Measurement and Instrumentation 4 — Questions and Answers
Question 1: Which type of ADC offers the fastest conversion speed?
- Successive approximation ADC
- Dual-slope ADC
- Flash (parallel) ADC (Correct answer)
- Sigma-delta ADC
Correct answer: Flash (parallel) ADC
A flash ADC uses 2ⁿ−1 comparators simultaneously to determine all bits at once, making it the fastest but most hardware-intensive ADC type.
Question 2: In a digital multimeter (DMM), the term '4½ digit display' means the meter can show:
- Up to 4999 counts
- Up to 19999 counts (Correct answer)
- Up to 9999 counts
- Up to 99999 counts
Correct answer: Up to 19999 counts
A 4½ digit display has four full digits (0–9) and one half-digit that can only display 0 or 1, giving a maximum reading of 19999.
Question 3: The primary purpose of a shunt resistor in an ammeter is to:
- Increase the voltage drop across the meter
- Bypass excess current around the galvanometer movement (Correct answer)
- Increase the meter's internal resistance
- Protect the meter from voltage surges
Correct answer: Bypass excess current around the galvanometer movement
A low-resistance shunt in parallel with the galvanometer carries most of the current, extending the ammeter's range while keeping the movement current small.
Question 4: Which phenomenon causes the zero-shift error in a strain gauge measurement when temperature changes?
- Gauge factor variation
- Thermal expansion mismatch between the gauge and substrate (Correct answer)
- Change in supply voltage
- Increase in lead wire inductance
Correct answer: Thermal expansion mismatch between the gauge and substrate
Differential thermal expansion between the metallic gauge element and its bonded substrate generates a spurious apparent strain signal with temperature.
Question 5: In frequency measurement using a CRO, if the time period of one complete cycle is 4 ms, the frequency is:
- 25 Hz
- 250 Hz (Correct answer)
- 2500 Hz
- 4000 Hz
Correct answer: 250 Hz
Frequency = 1/T = 1/0.004 s = 250 Hz.
Question 6: A resistance temperature detector (RTD) uses which property to sense temperature?
- Change in contact potential
- Predictable change in electrical resistance with temperature (Correct answer)
- Change in capacitance with temperature
- Generation of EMF at junctions
Correct answer: Predictable change in electrical resistance with temperature
RTDs (e.g., PT100) exploit the nearly linear increase in metal resistance with temperature, offering high accuracy and stability.
Question 7: The resolution of a 12-bit DAC with a full-scale output of 5 V is approximately:
- 1.22 mV (Correct answer)
- 2.44 mV
- 4.88 mV
- 9.77 mV
Correct answer: 1.22 mV
Resolution = Full-scale / (2ⁿ − 1) = 5 V / 4095 ≈ 1.22 mV, representing the smallest output voltage step.
BEE Measurement and Instrumentation 4
Which type of ADC offers the fastest conversion speed?