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A true rms multimeter with a crest factor limit of 3 is used on a waveform whose peak is five times its rms value. The reading will be

  • A.low, the peaks being clipped by the input circuit
  • B.high, the instrument overestimating the contribution of the peaks
  • C.correct, the crest factor limit applying only to average responding types
  • D.zero, the instrument refusing to display a reading outside its limits

Answer: A

The input amplifier saturates on the peaks, so part of the waveform never reaches the computing circuit and the squared average comes out too small. There is no warning indication, which makes it a genuine hazard when measuring rectifier currents.

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