Electronic device for measuring electrical power supply to a load

Claim 1

An electrical power measuring device comprising: input means for producing first and second analogue signals respectively representative of the instantaneous values of the voltage and current supplied to a load; modulator means for producing, in response to one of said first and second analogue signals, an output modulator signal which during periods of equal duration has a first or a second value such that the ratio of the number of the periods of the first value to the number of periods of the second value over an interval varies with the value of said one of the first and second analogue signals; an analogue-to-digital converter connected to said input means for producing at a converter output, first and second output digital signals respectively representative of the magnitude and polarity of the other of said first and second analogue signals; and accumulator means connected to said converter output which, in response to the output modulator signal of said modulator means during each said period, accumulates said first digital signal during that period in a sense dependent on the value of the output modulator signal of the modulator means and the polarity of said other of said first and second analogue signals, as represented by said second digital signal, said accumulator means being operative to produce an output pulse each time the accumulator means reaches a predetermined count, thereby to produce an output power signal comprising pulses at a rate indicative of the power supplied to the load.