NIST Sampling System for Accurate AC Waveform Parameter Measurements

This paper summarizes efforts at the National Institute of Standards and Technology (NIST) to develop a waveform sampling and digitizing system with accuracy comparable to that of an ac-dc thermal transfer standard for ac voltage measurements over the frequency range of 10 Hz to 1 MHz. In the frequency range from 1 kHz to 1 MHz, the sampler's gain flatness is better than that available from the best commercial digital multimeter. In ac-ac comparisons referenced to 1 kHz, the system agrees with a NIST-calibrated thermal transfer standard to within 17 muV/V from 20 Hz to 100 kHz for measurements made at both 1 and 0.1 V. The sampler's excellent dynamic linearity and flat input impedance are also discussed