A micropotentiometer-based system for low-voltage calibration of alternating voltage measurement standards

The paper describes a new ac-dc transfer standard developed at the National Measurement Laboratory. It enables the calibration or ac-dc transfer and ac voltage standards to be made in the range of voltages from (1-500) mV, with a standard uncertainty of (10-500) μV/V in the frequency range 10 Hz-1 MHz. The standard is based on the micropotentiometer principle. It incorporates single-junction thermal converters and nonreactive radial resistors using thin Evanohm films. Precision current shunts have been introduced into the millivoltmeter calibrations as terminating resistors of the micropotentiometers resulting in an uncertainty of 25 μV/V at 2 mV. Errors produced by the loading effect of the instrument under test on the micropotentiometer resistance and simple techniques for measuring these errors are also discussed