An intercomparison of AC voltage using a digitally synthesized source

An AC voltage intercomparison was conducted by the National Institute of Standards and Technology (NIST) to determine the consistency of AC voltage measurements made at various standards laboratories. The transport standard used for this purpose was an NIST-developed, digitally synthesized sinusoidal voltage source whose RMS (root mean square) value was calculated by measuring the DC level of each of the steps used to synthesize the sine wave. The uncertainty of the calculated voltage at approximately 7 V RMS is typically within ±10 parts per million (p.p.m.) from 15 Hz to 7.8 kHz. This approach incorporates a technique of determining AC voltage with reference to a measured standard DC voltage, which is independent of the traditional thermal voltage converter approach. Preliminary measurements made at each of the participating laboratories agree with the calculated value to within ±20 p.p.m. These results indicate that at 7 V, in the low audio-frequency range, the AC voltage measurement techniques implemented at these laboratories are near the state of the art