Experiences with a new sampling-based four-terminal-pair digital impedance bridge

Abstract

Digital impedance bridges are emerging as instruments suitable for the realization of impedance scale. The paper describes a new realization of a sampling-based four-terminal-pair electronic fully digital impedance bridge. Using a new high-performance source of digitally synthesized AC voltages, in conjunction with synchronous PXI sampling, the bridge can compare any two impedances across the entire complex plane in the frequency range of 20 Hz to 20 kHz. Operation of the bridge is validated using calibrated standards and the triangle method. Comparisons of calibrated standards and consistency checks performed at 100 Hz, 1 kHz and 1.59 kHz with impedances in the range from several hundred Ω to several kΩ demonstrate that the bridge has an accuracy better than 10-5. We discuss the uncertainty of the bridge in more detail and specifically measure the main digitizer nonlinearity errors which limit the accuracy of the bridge for 1:n comparisons. In the future, the accuracy of the bridge could be improved by correcting for this nonlinearity.