A multirange standard for AC/DC difference measurements

A standard for ac/dc difference measurements which incorporates an integrated circuit thermal sensor is described. The basic instrument (SL851) is intended for use in the frequency range of 100 Hz to 1 MHz and for voltage levels of 600 mV to 200 V. Coupled with an amplifier or high-voltage range resistors, the full-scale ranges can be extended down to 200 mV and up to 1000 V. This new standard is being developed to take advantage of the capabilities of the National Bureau of Standards (NBS) to give uncertainties of 10 ppm, under special conditions, in the frequency range of 100 Hz to 20 kHz, and for voltages of 5–100 V. It is expected that the SL851 will have ac/dc differences of only a few parts per million for levels up to 60 V at frequencies up to 100 kHz. Other advantages, as compared to vacuum thermoelements, are a shorter settling time and an output level of 2 V instead of a few millivolts. A power supply which can be operated on batteries was also developed. This paper provides a brief description of the SL851 instrument and associated high-voltage range resistors, preamp, and power supply. The factors that were considered in the physical construction are also addressed. A test configuration is described and the data obtained are presented and discussed.