| 摘要 |
PURPOSE:To enable measurement not affected by switching frequency or higher harmonics, by multiplying a voltage and a current by a multiplier and reducing the frequency of the ripple component of the multiplication output of said multiplier to 1/2 prior to measurement. CONSTITUTION:Voltage V is set to a switching wave form shown by a drawing (a) and a current I contains higher harmonics shown by a drawing (b). Voltage V and the current I are applied to a multiplier 30 through a transformer 10 and a current transformer 20. The multiplication result is not affected by the switching wave form and the higher harmonics and comes to a signal shown by a drawing (c) having the ripple component of frequency two times the fundamental wave of both inputs. The DC components contained in this multiplication signal is cut by a filter 40 and only an AC component having a twofold frequency component is subjected to wave-form shaping by a wave-form shaping circuit 50. The number of output pulses of the circuit are counted by a counter 60 while contracted to 1/2 and this count value corresponds to the frequency in a power line and is displayed on a display device 70.
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