Systematic error of time-division wattmeters when voltage and/or current are distorted

A method of compensation of the frequency dependent systematic error of the time-division watt-converter using two multipliers

“…Because the whole previous analysis and derivations are based on the statement that systematic amplitude error can be with sufficient accuracy expressed by (3), it was necessary to determine with which accuracy the expression (3) approximates the real relation betweerr error and frequency of the input signals, and up to which value of f/fc the approximation (3) is acceptable. Conceming the choice of the conversion frequencies, the upper limit for the higher conversion frequency is determined by quality and performances of the technical solution of the multiplier (converter) and also depends on required precision.…”

“…The lower conversion frequency has to be enough apart from the upper conversion frequency, but not too much low, i.e. not outside the range in which TDM is linear and not out of the f/fc range in which the approximation (3) is acceptable. In determining the optimal value of the ratio kfc=fc2/fc1 one should take into account also the values of the input signals of the summing block (Fig.…”

“…The precision of these measuring instruments is a few tens 10" [2]. A TDM of the Goldberg type, however, introduces a systematic amplitude (in phase) error depending on the square the ratio of the input signal frequency to the conversion frequency [3], [4], thus making this measuring method, and measuring devices based on this method, applicable to signals of only one frequency or to the signals of very narrow bandwidth. Recently there are requirements for the precise measurement of the electric power not only at the network frequency of the input signals but at a significantly extended range of frequencies (ranging to 10 kHz and more).…”