부산대학교 도서관

An electrical measurement device for monitoring the current and power taken by a plurality of electrical loads that may be powered by a selected one of multiple AC power sources comprises sampling the voltage of said sources and the current taken by said loads at a integral number of samples per cycle at sample times determined by an independent processor clock. The integral number of samples of each measured parameter for each cycle are processed to determine a complex number for each parameter representative of the amplitude and the phase relative to the independent processor clock. The phase drift of the substantially constant source voltages may be determined as a measure of frequency of the sources, and may be used to cancel drift of the current measurement to enable averaging. When the source feeding a load is changed, the phase drift is removed from its current measurement by selecting the voltage samples of the source now feeding it to use for drift cancellation or for average power computation and cumulative energy computation.