Instrumentation and measurement: board exam questions with solutions
On the ECE exam under Electronics Engineering and the REE exam under Electrical Engineering Professional Subjects. Try each question before you open its solution, then practise with fresh numbers below: 2 computed question types on this topic.
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Build it in the lab
Using a multimeter · Using an oscilloscope · Oscilloscope: comparing two signals: the same circuits on a live bench, with meters you can move.
Questions
1. A 1 mA, 100 Ω meter movement is to be used as a 0–1 A ammeter. What shunt resistance is required?
- 0.1000 kΩ
- 1.000 Ω
- 99.9 Ω
- 0.1001 Ω
Show the answer and solution
Answer: D. 0.1001 Ω
Rsh = Im·Rm/(I − Im) = (0.001 × 100)/(1 − 0.001) = 0.1001 Ω.
2. A 1 mA, 100 Ω meter movement is converted to a 0–100 V voltmeter. What series multiplier resistance is needed?
- 100.1 kΩ
- 10.0 kΩ
- 99.9 kΩ
- 99.9 Ω
Show the answer and solution
Answer: C. 99.9 kΩ
Rs = V/Im − Rm = 100/0.001 − 100 = 99900 Ω = 99.9 kΩ.
3. What is the sensitivity of a voltmeter built from a 50 µA full-scale movement?
- 50 kΩ/V
- 20 kΩ/V
- 2 kΩ/V
- 200 kΩ/V
Show the answer and solution
Answer: B. 20 kΩ/V
Sensitivity = 1/Ifs = 1/(50 × 10⁻⁶) = 20 000 Ω/V.
4. A Wheatstone bridge balances when R1/R2 = R3/Rx. With R1 = 100 Ω, R2 = 200 Ω and R3 = 150 Ω, what is Rx?
- 300 Ω
- 75 Ω
- 133 Ω
- 450 Ω
Show the answer and solution
Answer: A. 300 Ω
Rx = R3 × R2/R1 = 150 × 200/100 = 300 Ω.
5. Two 100 kΩ resistors in series are across a 10 V supply. A 20 kΩ/V voltmeter on its 10 V range is connected across the lower resistor. What does it read?
- 5.00 V
- 2.50 V
- 3.33 V
- 4.00 V
Show the answer and solution
Answer: D. 4.00 V
Rmeter = 20 kΩ/V × 10 V = 200 kΩ; 100 k ∥ 200 k = 66.67 kΩ; V = 10 × 66.67/(100 + 66.67) = 4.00 V (true value 5 V).
6. A voltage whose true value is 50.0 V is measured as 49.0 V. What is the percentage error of the measurement?
- +2.0%
- −1.0%
- −2.0%
- −4.0%
Show the answer and solution
Answer: C. −2.0%
%error = (measured − true)/true × 100 = (49 − 50)/50 × 100 = −2.0%.
7. A sine wave on an oscilloscope spans 4 divisions peak-to-peak with the vertical setting at 2 V/div. What is its rms value?
- 5.66 V
- 2.83 V
- 8.00 V
- 4.00 V
Show the answer and solution
Answer: B. 2.83 V
Vpp = 4 × 2 = 8 V, Vp = 4 V, Vrms = 4/√2 = 2.83 V.
8. A 0–150 V voltmeter is accurate to ±1% of full scale. When it reads 75 V, what is the limiting error as a percentage of the reading?
- ±2.0%
- ±1.0%
- ±0.5%
- ±1.5%
Show the answer and solution
Answer: A. ±2.0%
Limiting error = ±0.01 × 150 = ±1.5 V; relative to 75 V this is ±1.5/75 = ±2.0%.
Worked examples with computed numbers
These numbers are fixed on this page; in practice they change every time.
9. A 50 mA, 500 Ω meter movement is to read 2 A full scale. What shunt resistance is needed?
- 975 Ω
- 12.5 Ω
- 20 kΩ
- 12.8 Ω
Show the answer and solution
Answer: D. 12.8 Ω
The shunt carries I − Im = 1.95 A at the meter's voltage Im·Rm = 25 V: Rs = 12.8 Ω.
10. A 100 µA, 500 Ω movement is to read 50 V full scale. What series multiplier is needed?
- 25 kΩ
- 749 kΩ
- 500 kΩ
- 501 kΩ
Show the answer and solution
Answer: C. 500 kΩ
Total R = V/Im = 500 kΩ; subtract the movement's 500 Ω: 500 kΩ.
Other topics in the same subjects
DC circuits · AC circuits · Transients (RC, RL, RLC) · Semiconductors and diodes · BJT and FET circuits · Operational amplifiers · Oscillators and feedback · Power electronics · Digital electronics · Microprocessors and microcontrollers · Control systems · Three-phase systems · Transformers · DC machines · Induction motors · Synchronous machines · Power systems and transmission · Protection: fuses, breakers, relays · Illumination · Power plant engineering · PEC: branch circuits, ampacity and protection
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