Thermal converters as AC-DC transfer standards for current and voltage measurements at audio frequencies

Thermal con verters and associated equipment that are used as ac-dc transfer standards at t he National Bureau of Standards for the precise measurement of current and voltage at power and audio frequencies are described. The tandards and t h e equipment are primarily used to standardize a-c ammeters and voltmeters submitted to the Bureau for certification. Th e ac-dc transfer may be made with t hese thermal converters at currents from 1 milliampere to 50 amperes, voltages of 0.2 to 750 volts, with an accuracy of 0.01 percent at frequencies from 25 to 20,000 cycles per second.