| 摘要 |
PROBLEM TO BE SOLVED: To accurately measure the frequency of an a-c power source if the noise exists by providing sample value storing means, etc., for storing sampled sample values being shifted one after another. SOLUTION: A sampling means 21 samples signals to be measured at a fixed period and sends the sampled values to a sample value storing means 22 and a product sum means 23. The sample value storing means 22 stores up to m inputted sample values which are shifted one after another, the product sum means 23 multiplies the sampled values by (m-n+1) values at the tail side of the storing means 22, respectively and adds the obtained values to (m-n+1) values stored in the product sum means 23, respectively. The obtained result is restored in a memory means 24 and sent to a max. value deciding means 25 which compares the inputted product sum values, selects a max. value, and calculates the frequency of the signal to be measured from its registered number.
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