Contact resistance

The contact resistance – always present, but mostly undesirable

Contact resistance is the electrical resistance that arises at the contact point when components are connected. It depends on the material used and the quality of the connection. A distinction must be made between intentional and unintentional contact resistance. In switching and plug-in contacts and in cable and line connections, the transitions must always be kept to a minimum, because every resistance means the loss of energy and thus causes costs, and in data lines the signals can no longer be passed on, so data transmission is no longer guaranteed. But also the material of the cable can be affected by a bad transition and thus fatigues much faster. Furthermore, with mechanical connections, the contact resistance is a measure of the quality of the welded or screwed connection. An intentional application of the contact resistance is the pressure dependence of the contact resistance of a carbon microphone, but the contact resistance is also used in the relationship between current and voltage in varistors.

Determining the contact resistance

The contact resistance is determined with the aid of a micro ohmmeter. This is much more detailed and accurate than a standard multimeter for resistance measurement. This is because the resistance values for connections of metals are in very low ranges and therefore the accuracy and tolerance is very important. Furthermore, the temperature dependence must always be taken into account with contact resistances, because this negatively influences the resistance value. Of course, the contact resistance can also be calculated, but this only results in a theoretical value, which does not take into account the quality of the junction. Conclusions about the quality can therefore only be drawn by measuring with a micro-ohmmeter.

Minimize the contact resistance

To increase quality in connection technology and minimize losses, resistance must be kept extremely low. This can only be achieved by a perfect connection of the contact points. These must be properly processed and protected from external influences. The contact points and thus the contact resistance can also change over time, for example due to mechanical stress or moisture from the connection point. Basically, the importance of the transition resistance is very often underestimated.

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