Sub-PPM linearity testing of a DMM using a Josephson array

The design and operation of a system that uses a 10-V Josephson array to measure automatically the linearity of precision digital multimeters (DMMs) are described. Software automatically sets the array voltage to appropriate levels over the range of interest, controls the data collection at each data point, performs data reduction, and stores the data on disk for archival and future recall. The results reported demonstrate the ability of the system to measure the linearity more accurately than 0.1 p.p.m. of 10 V. Tests on some DMMs demonstrated peak linearity errors as small as 0.03 p.p.m.<>