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This paper describes a sampling system designed using a commercial sigma-delta analog-to-digital converter (Sigma-Delta ADC). In addition to characterization measurements using a conventional high-quality signal generator, a Josephson waveform synthesizer that provides ultimately noise- and drift-free voltages was used. To evaluate the suitability of this sampling system as part of a transfer power standard, additional comparisons of the root-mean-square (RMS) values measured were performed against a thermal converter and the primary power sampling standard at the Physikalisch-Technische Bundesanstalt, Braunschweig, Germany. Initial analysis of the measurement data shows an effective resolution in the range of 18-19 bits at an equivalent sampling rate of 64 kHz. The integral nonlinearity error of the system was measured to be within plusmn7 muV/V or one least significant bit at this resolution.