APPARATUS FOR OPERATING AMPLITUDE VALUE

PURPOSE:To operate an amplitude value, by using a product of a square value of digital data obtained by sampling an AC signal at every predetermined time interval and digital data obtained by sandwitching said digital data in a time sequential manner and shifting the same by 90 deg. before and behind in a phase. CONSTITUTION:The outputs of CT1 and PT2 connected to a power system are introduced into an input converter 4. The converted digital data are written in a memory region 6 at every definite sampling interval by DM5 and CPU7 uses the data of the memory 6 according to the program of ROM8 to perform operation represented by formula (wherein im is digital data coming to the standard of an input AC and im-n and im-n+l are digital data shifted by 90 deg. before and behind in a phase when im is sandwitched in a time sequential manner). By this method, a operational error due to the frequency variation of the input AC is reduced and an amplitude value E can be operated.