A LCR meter (Inductance (L), Capacitance (C), and Resistance (R)) is a piece of electronic test equipment used to measure the inductance, capacitance and, resistance of a component. In the usual versions of this instrument these quantities are not measured directly, but determined from a measurement of impedance. The necessary calculations are, however, incorporated in the instrument's circuitry; the meter reads L, C and R directly with no human calculation required.
Usually the device under test (DUT) is subjected to an AC voltage source. The meter detects the voltage over, and the current through the DUT. From the ratio of these the meter can determine the magnitude of the impedance. The phase angle between the voltage and current is also detected and between that and the impedance magnitude the DUT can be represented as an L and R or a C and R. The meter must assume either a parallel or a series model for these two elements. The most useful assumption, and the one usually adopted, is that LR measurements have the elements in series (as would be encountered in an inductor coil) and that CR measurements have the elements in parallel (as would be encountered in measuring a capacitor with a leaky dielectric).It can also be used to judge the inductance variation with respect to the rotor position in permanent magnet machines.
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