Measurement Topology
Electrical measurement circuits designed to isolate lead wire resistance deploy separate conductor pairs for current excitation and voltage measurement across a device under test. Four-wire Kelvin sensing eliminates voltage drop errors caused by wiring resistance and contact impedance by using dedicated force and sense paths. Current flows through high resistance force leads, while high impedance voltmeters measure potential across sense terminals without drawing load current.
Instrumentation systems measure low resistances accurately across long cable distances using this four terminal arrangement. Industrial RTD transmitters and precision shunt monitors rely on this network to achieve sub-milliohm accuracy in field installations.
Parasitic Drop
Lead wire resistance creates parasitic voltage drops in conventional two wire sensing configurations. High currents flowing through excitation wires produce offset voltages that skew resistance readings. Isolating measurement leads prevents excitation current from generating voltage drops inside the sensing loop.
Contact Impedance
Terminal oxidation and connector pin wear alter connection resistance over time. Four wire arrangements prevent contact resistance changes from affecting voltage measurements at the sensing element. Voltmeter input impedance remains orders of magnitude higher than lead line resistance.
Accuracy Verification
Metrology laboratories calibrate current shunts using four terminal reference standards. Automated verification checks sense wire continuity before recording high precision measurements. Four-wire Kelvin sensing sets the standard for precision low impedance measurement in automated test systems.
