Contact-Resistance Data Processing Using an On-Line Digital Microprocessor

Instrumentation which automatically measures and records dry-circuit contact resistance as lying within one of five adjustable resistance ranges has been previously devised and reported by Jedynak [ 1 ]. In this paper, we report on a major modification and improvement of the equipment involving the use of a cation and improvement of the equipment involving the use of an on-line digital microprocessor, to greatly improve the resistance measurement resolution and to convert the voluminous stream of data into more useful forms. The new system uses a special-function digital-to-analog converter controlled by the microprocessor to measure and record, for each operation of the contact, the dry-circuit contact resistance as lying within any one of 4096 contiguous 0.1-m12 resistance bins ranging from 0 to 0.41 . The microprocessor also computes a running mean and standard deviation of the contact resistance based on the previous several hundred measurements. After every several thousand contact operations and concurrent measurements, the mean and standard deviation are printed out on a standard Teletype. During this normal printout time, the contact-resistance distribution of the last several hundred measurements is graphically displayed on the Teletype also. Numerical guard bands are placed on the mean and deviation computations so that if the contact resistance characteristic changes significantly between normal display points then the on-going results are automatically printed out on the Teletype on what amounts to an expanded time base: Thus the experimenter is assured that his data always accurately reflect the dry-circuit contact behavior even over millions of contact operations.