| 摘要 |
PROBLEM TO BE SOLVED: To enable the measurement of frequency without using division by obtaining AC electric quantity frequency with a specific formula, on the basis of continuous number of times that the same sign of samble values contained in a rating frequency specific cycle time is a specific number -1 or +1. SOLUTION: The set frequency value of a frequency memory region 134 previously calculates a value (F-S) about an electric angle defining the sampling period adopted by a frequency measuring circuit 1, and obtains a frequency (f) of, e.g. an electric angle 30 deg. and a frequency f0 =50Hz, from the relation f=f0 +f0 /2ab×(F-S) where (a) and (b) are positive integers, and F and S are continuous number of times that the same sign of sample values during the time interval of rating frequency (b) cycles is (a-1) and (a+1), respectively. A control part 15 A/D converts 12 sample values of AC electric quantity every time interval (t), and turns a reversible counter 133 into +1(-1) every detection of the number of times F(S). As a result, the count value turns to (F-S) at the self reference time and every constant time by a f b cycle timer. The frequency (f) corresponding to the value (F-S) is outputted 14 from the region 134.
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