An intercomparison of AC voltage using a digitally synthesized source

An AC voltage intercomparison was conducted to determine the consistency of AC voltage measurements made at various standards laboratories. The transport standard used for this purpose was a 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 (ppm) from 15 Hz to 7.8 kHz. This approach incorporates a measured standard DC voltage and 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 ppm. 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