Impedance: why do LCR meters exist? #EE

In a recent introductory article on electronics, lcamtuf’s blog talked about impedance: the tendency for components and circuits to resist the flow of current. The phenomenon can be divided into three categories: resistance (R), capacitive reactance (C), and inductive reactance (L, um, yeah). All of these can be thought of as the contributors to apparent resistance — and indeed, their effects can be difficult to distinguish at a glance.

On the face of it, an LCR meter looks like a nerfed DMM, only capable of measuring inductance, capacitance, and resistance. One has to wonder how this piece of gear survived this long, and why it commands a considerable premium for such a limited feature set.

It does so by outputting an AC signal, comparing the resulting voltage amplitudes and currents, and then calculating Z = V/I. Just like in a DMM, the measurement represents the combined effect of resistive, capacitive, and inductive effects; it tells us nothing about the exact values of L, C, or R. That said, the other parameter the meter computes with high accuracy is the phase offset between the voltage and current (θ) — and that extra bit of information changes everything.

See the full discussion in the post here.


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