| 摘要 |
PROBLEM TO BE SOLVED: To reduce a converting time period by retaining the conversion accuracy by a method wherein a capacitance of an averaging capacitor circuit connected to an effective value converting circuit is switched corresponding to a frequency of a signal to be inspected. SOLUTION: An averaging capacitor circuit 13 that sets an averaging time constant by switching it corresponding to a capacitance selected from a plurality of selectable capacitances is connected to an effective value converting circuit 12 that converts an amplitude of a signal to be inspected by retaining the conversion accuracy and conversion time corresponding to the averaging time constant, then a capacitanceΣCj of the averaging capacitor circuit 13 is varied to be set corresponding to a frequency of the signal to be inspected. The capacitance of the averaging capacitor circuit 13 is optimized by two stages of tuning such as rough tuning based on an output of a zero-cross comparator 15 and fine tuning based on an output of a ripple detecting circuit 16. As a result, it is possible to detect the accurate effective value in a necessary minimum time irrespective of a frequency band or a kind of a waveform of the signal to be inspected.
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