A digital three-phase watthour meter

A microprocessor-controlled three-phase digital watthour meter is described. The wattmeter is based on a sampling method and on an analog-to-digital (A/D) conversion; only one 10-b A/D converter, integrated in a microprocessor, is used. The resolution of the converter is improved by superimposing noise on current and voltage signals, and its uncertainty is reduced via an external resistive voltage divider. A wide current range is achieved by passing voltage signals. proportional to input currents, through a programmable-gain amplifier. The overall uncertainty of the meter is less than 0.1%. A block diagram of the wattmeter is presented. >