Evaluation of Automatic Coaxial Mechanical Scanners for Precise Resistance and Capacitance Measurements

In this paper, we evaluated automatic four-terminal-pair and two-terminal-pair coaxial mechanical scanners for precise dc resistance and capacitance measurements. These scanners mechanically change a set of four-terminal-pair or two-terminal-pair BNC connections with coaxial cables using servo-controlled motors. Although originally designed for calibrating the impedance, we evaluated their performance in automating and improving high-resistance measurements. We compared the measured resistance ratios with and without the scanners in the range 1 Ω-1 TQ. The results are found to agree to within about 10% of the expanded uncertainty. We also used the scanners to conduct precise 10-pF capacitance measurements at 1 and 1.592 kHz. The measured capacitance differences and the loss angle differences agree with the direct measurements to within the expanded uncertainty.