| 摘要 |
An improved DC stabilization system is provided in an electronic digital power meter of the type utilizing current transformers (30) to scale and isolate the power line current (Ip1) and an analog to digital converter (not shown in Fig. 2) to convert the meter currents to a digital signal for signal processing. An unmodulated square wave signal is provided (46) to trigger a chopper switch (42) which connected the current transformer to an amplifier (5) and provides a current signal output (Io1). A feedback current from the amplifier is provided through the feedback (33) and sense (32) winding of the current transformer by the chopper to compensate for the effects of DC offset voltage at the input of the amplifier. The square wave is a low frequency such that its harmonics and those of the power lines are different, to minimize the gain bandwidth requirements of amplifiers in the system. The timing signals for the analog to digital converter are controlled to avoid sampling at the transition of the square wave signal to enhance conversion accuracy, and means are provided to remove the signal inversion in the current signal introduced by the chopper.
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