POWER METER

PURPOSE:To measure electric power in a short sampling period with one arithmetic unit by sampling the input voltage and current at the same time in a fast period, A/D-converting them, once storing the data, and reading them out in an optional period. CONSTITUTION:The input voltage (e) and input current (i) are sampled at the same time by S/H circuits 1, 2 whenever a clock signal SC is generated and converted 3, 4 into digital data De, Di. Address counters 8, 9 count the data De, Di stored in memories 6, 7, and the storage is stopped when these numbers reach the preset values. An arithmetic unit 11 reads out the sampled data DV, DA from the memories 6, 7 at the same time, they are multiplied 11a to calculate the instantaneous power, and this instantaneous power is averaged 11d to obtain the average power, i.e., effective power. The A/D conversion period and the calculation period are separated, thus the calculation period is not restricted even if the A/D conversion is performed at a high speed, complex calculation requiring a long time can be performed, and a power meter with many functions can be realized.