AC-DC Transfer Instruments for Current and Voltage Measurements

The basic electrical units are maintained by groups of standard cells and resistors. With these standards and a de potentiometer, measurements of direct voltage and current are readily made with an accuracy of 0.01 per cent or better. Corresponding measurements of alternating voltage and current at power and audio frequencies depend, at the present time, upon ac-dc transfer instruments which have nearly equal ac and de response. Such instruments may be calibrated on direct current and then used on alternating current, or alternatively, may be used directly to make ac-dc difference measurements, as in the certification of other instruments.