ISCET Test Equipment and Measurement 4

Question 1

Which measurement technique is used to eliminate the resistance of test leads when making a precise 4-wire (Kelvin) resistance measurement?

Accepted Answer

Current is forced through two leads while voltage is sensed on two separate leads

Answer

In Kelvin sensing, current flows through the outer pair of leads while the voltmeter's high-impedance inner leads sense voltage with negligible error from their own resistance.

Question 2

A power supply's output has 50 mV of ripple superimposed on 12 V DC. To best display the ripple on an oscilloscope without saturating the input, the technician should:

Accepted Answer

Use AC coupling and set sensitivity to 20 mV/div

Answer

AC coupling blocks the 12 V DC component so the oscilloscope can be set to a sensitive range that reveals the small ripple without overdrive.

Question 3

What does the term 'true RMS' mean in the context of a digital multimeter?

Accepted Answer

The meter computes the actual RMS value of non-sinusoidal AC waveforms

Answer

True-RMS meters calculate the root-mean-square mathematically, yielding accurate readings for distorted, non-sinusoidal waveforms.

Question 4

When measuring small resistances (less than 1 Ω) with an ohmmeter, which factor is most likely to cause significant measurement error?

Accepted Answer

Test lead and contact resistance comparable to the measured value

Answer

Lead and contact resistance can easily be a significant fraction of 1 Ω or less, introducing large percentage errors in the measurement.

Question 5

A network analyzer measures the S11 (return loss) of an antenna and displays −20 dB. This means the antenna is reflecting what percentage of the incident power?

Accepted Answer

1%

Answer

−20 dB return loss means reflected power = 10^(−20/10) = 0.01 = 1% of incident power.

(ISCET) International Society of Certified Electronics Technicians Practice Test

(ISCET) International Society of Certified Electronics Technicians Practice Test

ISCET Test Equipment and Measurement 4