Power measuring device

Claim 1

Apparatus for determining average power consumption by an electrical load comprising: means resistively coupled to the load operative to generate first and second electrical signals respectively proportional to the voltage across and the current through the load; multiplier means coupled to the means to generate the first and second signals, operative to generate at a multiplier means output a third signal proportional to the product of the first and second signals; a reference offsset signal source and signal summing means coupled to the reference offset signal source and to the multiplier means output for combining a reference offset signal with the third signal, the reference offset signal having a magnitude and polarity such that the combined reference offset signal and third signal will have a constant polarity regardless of the polarity of the third signal; converter means coupled to the signal summing means operative to generate a pulse train signal having a frequency proportional to the amplitude of the combined reference offset signal and third signal; and utilization means including counter means having a counting input coupled for receipt of the pulse train signal, and microcomputer means coupled to the counter means, operative to periodically read contents of the counter means at predetermined time intervals and to convert the read contents into an average power consumption indicating signal that is a function of the frequency of the pulse train signal.