| 摘要 |
PROBLEM TO BE SOLVED: To accurately eliminate the unbalanced voltage of a Hall element causing an error, and the offset voltage of a differential amplification means. SOLUTION: In the watthour meter, a Hall element outputs a Hall voltage corresponding to the product of measurement voltage and current, switching means Swa1 to Swb2 invert the positive and negative polarities of the Hall voltage at each specific period, differential amplification means 3 and 4 carry out differential amplification, an invert means 9 inverts the polarity of differential amplification output to a state where polarity invert is returned by the switching means again, and an integration means 10 performs integral calculus. Hall elements 1 and 2 for outputting an unbalanced voltage with the polarity being different from that of the Hall voltage with the same polarity are used, adjustment is made by an unbalanced voltage adjustment means 7 so that the unbalanced voltage of the two Hall elements becomes equal, and each differential amplification output of the two Hall elements is added by an addition means 8 before the integral calculus is made by the integral means 10.
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