PURPOSE: To compensate the fluctuation of sensitivity characteristics of a current transformer automatically by feeding a low-frequency signal with a specific current to the coil winding of the current transformer and adjusting the gain of an amplifier so that the amplifier output level of the signal reaches a specific value.
CONSTITUTION: A coil winding N3 is newly provided to a residual current transformer ZCT and the output of an oscillator OSC1 for oscillating a low-frequency signal frequency f2 via a capacitor C0 is energized by a specific current content. A commercial frequency leak current component and the component of a frequency f1 are returned to a grounding conductor. However, since the current with the specific value of a frequency f2 flows to the new coil winding N3, the three types of current components are input to an amplifier A1. In a loop- shaped automatic gain adjustment circuit consisting of a variable resistance element Vr, an amplifier A2, a filter F2, and a current transformer DT, only the component of the frequency f2 is passed through the filter F2 and an element Vr is controlled by the use of the voltage which is obtained by rectifying it (DT) so that the component of the frequency f2 contained in the output of the amplifier A2 is constant, thus automatically compensating the sensitivity fluctuation of the current transformer ZCT.
TERAOKA TOMOZOU
WAKIMOTO OSAMU
KASHIWAZAKI SHUNJI
