An accurate RMS-DC voltage comparator

An accurate RMS-DC voltage comparator based on an inexpensive solid-state dual-heater-type converter has been developed. The instrument is designed to operate as a null meter with a range of +or-1000 p.p.m. of nominal test voltages used in high-accuracy AC calibrations. Test results show that the comparator can determine the RMS value of AC voltages for its 5- and 7-V inputs with an accuracy of better than +or-50 p.p.m. for frequencies of 50 Hz to 200 kHz. Voltage inputs of 100 and 120 V can be measured with an accuracy of better than +or-30 p.p.m. for frequencies of 50 Hz to 100 kHz.>