An automated AC-DC transfer calibration system

The paper describes recent improvements in the NRC ac-dc transfer capabilities. They were achieved through full automation of the ac-dc transfer comparator, extensive redesign of the control software, and modification of the voltage buildup procedure. Hardware additions to the comparator design include several stepping motor driven switches and a range changer of the highest accuracy commercial electronic transfer standard. Redesigned Visual Basic software is very flexible, and can be easily modified to accept new instruments and new procedures. The NRC buildup procedure has been modified at the 500 V and 1000 V levels. The expanded uncertainty assigned to the NRC working standard is given and its components are briefly discussed