ohmmeters

An ohmmeter is a measuring instrument used to determine the electrical resistance of a component or circuit. Most devices supply a small direct current through the test leads and measure the resulting voltage drop, or alternatively apply a voltage and measure current, computing resistance from Ohm's law.

Ohmmeters come in analog and digital forms. Analog models use a calibrated scale with a moving-coil galvanometer; digital models employ an analog-to-digital converter and display the reading numerically. They can be standalone units or integrated into multimeters. For high accuracy at low resistances, four-wire (Kelvin) configurations separate the current-carrying leads from the sense leads to reduce lead and contact resistance errors.

Operation and usage details. Ohmmeters offer manual or auto-ranging options and may require a zero adjustment or short-circuit compensation to account for lead resistance. Measuring resistance in a circuit can be misleading if the circuit is powered or if parallel paths exist, so it is best to de-energize the circuit and remove or isolate the component when possible. Temperature, contact resistance, and measurement leads all influence readings.

Limitations and safety. Ohmmeters generally measure DC resistance and are unsuitable for measuring resistance in live circuits. Very low resistances demand careful lead technique and sometimes specialized equipment; very high resistances or insulating materials may be challenging to measure accurately. Users should de-energize circuits, discharge capacitors, and avoid applying excessive test current to sensitive components.

Applications. Ohmmeters are used for troubleshooting electrical and electronic devices, verifying resistor values, checking continuity, component testing, and calibration procedures. They are commonly standalone instruments or part of digital multimeters.