Electrical measuring apparatus employing magneto-electric devices

Claim 1

An electrical measuring apparatus for use with an alternating current electrical power supply system, comprising: a carrier domain magnetometer responsive to a voltage input representative of the system voltage and a magnetic flux input representative of the system current to produce a train of pulses whose frequency varies with the product of said inputs; first counter means responsive to the output of the magnetometer to produce an output count representative of the number of pulses in the magnetometer output during a preceding predetermined period; bias compensating means arranged to produce a count equal to the output count of the counter means when said voltage and magnetic flux inputs are zero; subtracting means for producing an output equal to the difference between the count of the compensating means and the output count of the counter means, and hence representative of the active power supplied by the system; comparator means responsive to the outputs of the magnetometer and the compensating means to produce an output when the frequency of the magnetometer output has a value below its value when said voltage and magnetic flux inputs are zero; an AND gate having a first input connected to the output of the comparator; a clock pulse generator connected to a second input of the AND gate; and second counter means responsive to the output of the AND gate to produce an output count representative of the number of clock pulses applied to the AND gate while the comparator produces an output, and hence representative of the phase angle between the system voltage and current.