ISCET Test Equipment and Measurement 2 — Questions and Answers
Question 1: When using an oscilloscope to measure a signal, the timebase is set to 2 ms/div and you count 4 divisions for one complete cycle. What is the frequency of the signal?
- 125 Hz (Correct answer)
- 250 Hz
- 500 Hz
- 1 kHz
Correct answer: 125 Hz
Period = 4 divisions × 2 ms/div = 8 ms; frequency = 1/0.008 s = 125 Hz.
Question 2: A clamp-on ammeter measures current by sensing which electrical property?
- Voltage drop across a shunt resistor
- The magnetic field surrounding the conductor (Correct answer)
- Resistance of the wire insulation
- Capacitance between the clamp jaws
Correct answer: The magnetic field surrounding the conductor
A clamp meter uses a current transformer that responds to the magnetic field produced by current flowing through the conductor.
Question 3: On a spectrum analyzer, the resolution bandwidth (RBW) setting primarily controls which display characteristic?
- The vertical amplitude scale
- The ability to distinguish two closely spaced signals (Correct answer)
- The sweep time across the full span
- The reference level at the top of the display
Correct answer: The ability to distinguish two closely spaced signals
A narrower RBW filter allows the analyzer to resolve signals that are close together in frequency.
Question 4: Which DMM function would you select to test whether a diode junction is forward-biased and intact?
- DC voltage
- Resistance (Ω)
- Diode test mode (Correct answer)
- Capacitance
Correct answer: Diode test mode
The diode test mode applies a small forward voltage and displays the junction voltage drop (typically 0.5–0.7 V for silicon).
Question 5: A signal generator's output impedance is specified at 50 Ω. To avoid reflections and achieve maximum power transfer to the load, the load impedance should be:
- As high as possible (open circuit)
- 0 Ω (short circuit)
- 50 Ω (Correct answer)
- 100 Ω
Correct answer: 50 Ω
Maximum power transfer and reflection-free operation occur when load impedance matches source impedance.
Question 6: When an oscilloscope probe is switched to the ×10 position, how does this affect the observed waveform amplitude compared to ×1?
- The displayed amplitude appears 10 times larger
- The displayed amplitude appears 10 times smaller (Correct answer)
- The amplitude is unchanged but bandwidth increases
- The amplitude doubles and noise decreases
Correct answer: The displayed amplitude appears 10 times smaller
The ×10 probe divides the signal by 10 before it reaches the scope input, so the displayed voltage must be multiplied by 10 to get the actual signal.
Question 7: Which instrument is best suited to measure the total harmonic distortion (THD) of an audio amplifier output?
- Digital multimeter
- Oscilloscope only
- Spectrum analyzer or distortion analyzer (Correct answer)
- LCR meter
Correct answer: Spectrum analyzer or distortion analyzer
A spectrum analyzer or dedicated distortion analyzer can identify and quantify individual harmonic levels relative to the fundamental.
ISCET Test Equipment and Measurement 2
When using an oscilloscope to measure a signal, the timebase is set to 2 ms/div and you count 4 divisions for one complete cycle.
What is the frequency of the signal?