What is thermal electromotive force during resistance measurement?

A

Thermal electromotive force (thermal EMF)  is the potential difference that occurs at the junction of two dissimilar metals, including between the probe tips and the lead wire of the measurement target. If the difference is sufficiently large, it can cause erroneous measurements. The amplitude of thermal EMF depends on the temperature of the measurement environment, with the force generally being greater at higher temperature.

Increasing thermal EMF examples
• The measurement target is a fuse, thermal fuse, thermistor, bimetal, or thermostat.
• The voltage detection lines incorporate a single stable relay as a contact.
• An alligator clip is used as a voltage detection terminal.
• A voltage detection terminal is held by hand.
• There is a large temperature difference between the measurement target and the instrument.
• Wire materials differ between the SENSE A and SENSE B.

Low resistance measurement may be affected by the thermal electromotive force generated at the contact of different metallic materials probe contact).
OVC function compensates the effect of this thermal electromotive force in order for the Resistance Meter RM3545A to measure low resistance accurately.
This is useful for measuring the contact resistance of connectors or relays,welding resistance of busbars, etc.