| 摘要 |
PROBLEM TO BE SOLVED: To dispense with external memory of large capacity and always cancel a residual portion based on new data of zerophase waveform by using a ring buffer formed on the built-in RAM of a CPU. SOLUTION: Output waveforms of voltage or current sensor input from the input terminals 1 of three phase are synthesized, zerophase waveform is converted to a digital signal by an A/D converter, and input to a CPU 7. A ring buffer 9 formed on the built-in RAM 8 of the CPU 7 stores the residual portion of the zerophase waveform. At every sampling, the average value of data is computed, and this average value is subtraced from the newest sampling data to perfom cancelling. The effective value of data after cancelling is compared with the set value, and in the case under the set value, by substituting the newest sampling data for the oldest data of the ring buffer 9, data is renewed, Further in the case of exceeding the set value, renewal of data is locked.
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