| 摘要 |
PURPOSE:To reduce an error in digital effective value by correcting an AC input value and a 90 deg. phase leading AC value according to the sample measured value and detected frequency of an AC input and processing the two corrected AC quantities at every sampling period. CONSTITUTION:The AC input is counted by a data sampler circuit 10 at a specific sampling period and outputted to a frequency detecting circuit 20 and a 90 deg. leading AC generating circuit 30. The circuit 30 receives the AC input value and frequency from the circuit 20 and compute the 90 deg. phase leading AC value. This AC value is supplied to the correction part of the circuit 30 to correct the difference between the AC input value and an AC input value measured actually. The circuit 30 outputs the AC input value and 90 deg. phase leading AC value to an effective value arithmetic circuit 40 at every sampling period. The circuit 40 performs square averaging arithmetic operation at every sampling period to calculate the digital effective value of the AC input. Therefore, even if the AC input varies abruptly in case of the fault of an electric power system, corrections are made following up the variation to suppress errors due to the variation.
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