Calibration of Standard Wattmeters Using a Capacitance Bridge and a Digital Generator

A method for calibrating high-accuracy wattmeters is described. The technique is a modification of a previously described approach that utilizes a power bridge based on a current comparator. In such a bridge the test current of the wattmeter is balanced with a known current that is proportional to the test voltage. The measurement circuit described employs a high-voltage capacitance bridge in place of a special current comparator that was used in the previous system. High sensitivity and large ratios of the capacitance bridge enable using high impedances, such as stable gas-dielectric capacitors and resistors having low-power dissipation for the generation of reference currents. The voltage on the standard impedances is adjusted with inductive dividers to obtain any power factor between zero and one, lead and lag. A digitally synthesized dual-channel signal source serves as a stable source of voltage and current, and thus of "phantom" power.