Ohmmeter (Resistance Meter)
An ohmmeter measures the electrical resistance between the input terminals, in ohms (Ω), kilohms (kΩ) or megohms (MΩ).
Unlike an ammeter or voltmeter, which take measurements while the test circuit is powered (or 'live'), the circuit must be turned off, or the resistance removed from the circuit, prior to measuring resistance with the ohmeter. An ohmmeter typically operates by applying a small voltage to the circuit and measuring the resulting current, from which resistance may be determined using Ohm's law.
Specialised applications of the ohmeter include the continuity tester and insulation tester. The continuity tester indicates a low resistance circuit path using an audible beep or visual indicator, either to confirm correct circuit operation, or as a fault-finding aid. At the opposite extreme, an insulation tester tests electrical insulation (in MΩ) at a high applied voltage, but correspondingly very low current.
An ohmeter is typically found as a component part of a digital multimeter, rather than as a separate measuring device, but may also be encountered as a virtual instrument in electronics design software.