Kontaktsmotstånd

Kontaktsmotstånd, or contact resistance, is the electrical resistance encountered at the interface between two conducting surfaces in electrical contact. It arises from the real contact points where microscopic asperities meet, as well as from any insulating films, oxides, or contaminants that may be present. While individual contact spots can conduct well, the overall resistance across the interface can be a significant portion of a circuit’s total resistance, especially in high-current or precision applications.

The resistance at a contact interface comprises mainly two parts: the constriction (or contact) resistance at the microscopic contact areas, and the resistance of any intervening surface films such as oxides or dirt. Holm theory provides a framework for estimating constriction resistance based on material resistivity and the effective contact radius. In practice, contact resistance depends on surface roughness, hardness, and the applied contact force, as well as temperature and the condition of surface films. Oxidation, contamination, wear, and moisture can increase contact resistance over time, while proper materials and surface treatments can reduce it.

Measurement and implications: Contact resistance is typically measured using four-wire (Kelvin) techniques or by determining the voltage drop across the interface at a known current. It is commonly expressed in milliohms or micro-ohms for a given contact force and material pairing. Elevated contact resistance can cause unwanted voltage drops, heating, power loss, and reliability issues in switches, relays, connectors, battery contacts, and other interfaces.

Mitigation strategies include increasing real contact area, ensuring adequate and stable contact force, using wear- and corrosion-resistant coatings (such as noble metal platings), maintaining clean surfaces, and employing design practices that minimize oxide formation and contamination.