AC-DC difference precision measurement of /spl mu/pot

Many electrical standard laboratories use /spl mu/pots as the primary standards for low ac voltage measurement. To determine the ac-dc difference of a /spl mu/pot usually requires a transfer standard which has high input impedance for the standard values transferred from a standard /spl mu/pot through a step-down procedure. In order to lower the uncertainty of the /spl mu/pot ac-dc difference measurement, after several step-down procedures at low voltage range, a precision comparison method is introduced.