Ohmmeter:
A portable instrument for measuring relatively low values of electric resistance. The Ohmmeter is ideal for use in the workshop, field or test lab. The range of resistance measures is typically from .1 microhm to 1999 ohms. Ohmmeters maybe either analog or a digital instrument. It uses a 4 terminal measurement method in which a constant current source is applied to the current terminals of a resistor via the current terminals on the Ohmmeter. Some Ohmmeters use special measuring probes (Kelvin Clips) consisting of a set of leads with combined current probes and potential probes.
To calculate resistance manually one must use Ohm's Law. Ohm's Law deals with the potential difference (voltage) across an ideal conductor is proportional to the current through it. In short V=IR, that is voltage equals current multiplied by resistance, as a result R=V/I.
The reason for the use of Ohmmeters is that they enable uses to solve quickly and easily a variety of different measurement problems. These include measuring the resistance of cladding and tracks on printed circuit boards, electrical connectors, and switch and relay contacts, as well as detecting the quality of ground conductor continuity and bonding, cables, bus-bar and weld connector tags.
