Abstract: A power supply for an instrument that measures waveforms on AC (alternating current) power systems. Under ordinary circumstances, the power supply draws its power from the signal that the instrument measures. The power supply includes energy storage means. When the instrument must make a precise measurement that could be affected by the power drawn by its power supply, the instrument temporarily disconnects its power supply from the measured signal and draws power from its energy storage means, effectively coasting on the stored energy. At the conclusion of the precise measurement, the instrument reconnects its power supply to the signal being measured.

Abstract: An instrument employs a high-pass filter and an associated amplifier to reduce the number of Analog-to-Digital-Converter bits required to determine the amplitude of harmonics contained in digitally sampled AC (alternating current) power system voltage or current waveforms. The instrument is coupled to a power system having a line conductor and a neutral conductor for obtaining time-domain representations of the current flowing in the line conductor and the voltage difference between the line conductor and the neutral conductor. The time-domain representations are converted to frequency-domain representations by a single-chip microprocessor.