Contact Resistance measured in milli-ohms, is the electrical resistance of a reed contact in closed state, as measured terminal to terminal, at their associated terminals.
This is usually measured with a coil at 25% overdrive. Four-terminal Sensing and shielded cables should be used for accurate contact resistance measurements.
Electrical contact resistance (ECR, or simply contact resistance) is resistance to the flow of electric current caused by incomplete contact of the surfaces through which the current is flowing, and by films or oxide layers on the contacting surfaces. It occurs at electrical connections such as switches, connectors, breakers, contacts, and measurement probes. Contact resistance values are typically small (in the microohm to milliohm range).
Contact resistance can cause significant voltage drops and heating in circuits with high current. Because contact resistance adds to the intrinsic resistance of the conductors, it can cause significant measurement errors when exact resistance values are needed.
Contact resistance may vary with temperature. It may also vary with time (most often decreasing) in a process known as resistance creep.
Electrical contact resistance is also called interface resistance, transitional resistance, or the correction term. Parasitic resistance is a more general term, of which it is usually assumed that contact resistance is a major component.
William Shockley introduced the idea of a potential drop on an injection electrode to explain the difference between experimental results and the model of gradual channel approximation.
