Testing & TroubleshootingQuestion 505 of 521
You must measure current on a circuit feeding electronic (nonlinear) loads such as LED drivers and VFDs. Which meter feature gives an accurate reading?
a.A true-RMS meter
b.An averaging (non-true-RMS) meter
c.An analog swinging-needle meter only
d.Any meter reads distorted waveforms accurately
Explanation
Nonlinear loads draw distorted, non-sinusoidal current, and only a true-RMS meter computes the real heating value accurately. Averaging meters (b) assume a clean sine wave and under- or over-read on distorted waveforms. An analog meter (c) is also averaging-type, and not all meters handle distortion (d).
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