GB1372978A - Circuit arrangements for measuring electrical energy - Google Patents

Abstract

1372978 Measuring electrical energy LANDIS & GYR AG 25 May 1973 [7 June 1972] 25061/73 Heading G1U Apparatus for measuring electrical energy (v x i) comprises two modulators 1, 2 for forming respective pulse trains wherein the ratio of the difference to the sum of mark duration and space duration is proportional to an input voltage and current respectively a coincidence circuit 5 which is preferably an AND gate for providing an output indicative of coincidence between the pulses of the two trains, a clock pulse source 10 which is coupled to a counter 13 via a second gate 8 such that the counter counts the clock pulses in dependence on the output of the circuit 5, and a symmetrical, rectangular pulse generator 15 which periodically reverses the polarity of one of the input signals and simultaneously reverses the direction or count at 13. The period of the generator 15 is much greater than that of the modulators 1, 2, and the counter 13 is arranged to count the clock pulses when coincidence between pulses of the trains is detected. The theory is explained in the Specification and it is shown that if the mark duration of the two modulators 1, 2 is respectively: T 1 /2 + K 1 v; T 2 /2 + K 2 i, where T 1 , T 2 are the periods of the modulators, k 1 , k 2 are constants, then the time averaged frequency of pulses reaching the counter is f r Àk 1 Àk 2 vi/T 1 ÀT 2 where #r is the frequency of the source 10 and v, i are time-averaged values. The reversals controlled at 15 nullify the effects of asymmetry in the outputs at 1, 2. In a modification, Fig.2 (not shown) the gate 5 is an EX-OR which responds to coincidence of both pulses and gaps and gate 8 is replaced by an EX-OR (19). During the first ¢-cycle of the generator 15, which provides an input to gate (19), pulses from the source 10 are counted into counter 13 when a state of coincidence exists, and are counted out otherwise. In the second ¢-cycle, the situation is reversed.