Automatic compensation technique for alternating current metrology based on synchronous filtering

In alternating current electrical metrology, the balancing procedure is the act of reduction to zero of a measured terminal-pair voltage (or current), accomplished via injection of a compensation voltage (current) in the circ uit. An automatic compensation technique is described here: the terminal-pa ir voltage is continuously sensed, by means of vector synchronous detection , and the injected voltage is directly synthesized from the main circuit so urce. An implementation of the compensation technique, realized with analog electronics, permits compensation of audio frequency small voltages down t o the nV range, with settling time in the order of milliseconds. (C) 1998 A merican Institute of Physics. [S0034-6748(98)02812-3].