Instrumentation for Measuring Dry-Circuit Contact Resistance

An automated contact resistance measurement and recording system was designed and constructed for evaluating the dry-circuit performance of electrical contacts. To assure dry-circuit conditions the voltage across the contacts was limited to less than 30 millivolts regardless of contact resistance. The signal used to measure the resistance was a dc biased 400 Hertz sinusoid. The basic repetitive sequence of operation consisted of mechanically cycling the switch, then measuring and recording the contact resistance as falling within one of an adjustable set of five contiguous resistance ranges.