A new test equipment for high dynamic real-time measuring of contact resistances

It is well known that the resistance of a wearing contact may rise from less than a milliohm to more than a kiloohm within months or maybe in less than a microsecond. The automobile industry has considerable trouble with short-term intermittences of contacts under vibration stress. The vibration of the vehicle can be simulated quite well with a shaker. Measuring the long-term increase of the resistance can be done by switching off the shaker from time to time. But the electromagnetic field of the shaker prevents the measurement of the resistance-changes with standard equipment while the shaker is working. A test equipment and a test method have been developed that make it possible to measure contact resistances in real-time and over a resistance-range of six decades. As this can be done while the shaker is running, intermittences not only can be detected but also measured. This equipment can be used for finding out whether a certain contact system can be used for a concrete application. Also it assists the research work on the mechanisms of contact intermittences. A set of contacts has been tested and their electrical behaviour has been compared with the status of their contact surface.