Fyrtrådsmetoden

Fyrtrådsmetoden, meaning "four-wire method" in Swedish, is a technique used in electrical measurements to determine the resistance of a conductor. This method is particularly effective for measuring low resistances where the resistance of the connecting wires can significantly influence the reading of a standard two-wire measurement.

The core principle of the fyrtrådsmetoden involves using four separate conductors. Two of these conductors are used to pass a known current through the resistance being measured. The other two conductors are used to measure the voltage drop across the same resistance. By keeping the current-carrying conductors separate from the voltage-measuring conductors, the resistance of the current leads does not affect the voltage measurement, and thus, the calculated resistance.

This technique is crucial in applications where precise low-resistance measurements are necessary. Examples include measuring the resistance of shunts in ammeters, contact resistances in switches and relays, or the resistance of cables and busbars. The accuracy gained by eliminating the influence of lead resistance makes the fyrtrådsmetoden a standard for high-precision resistance determination in various scientific and industrial settings. It is often implemented using specialized equipment like an ohmmeter designed for four-terminal measurements.