Used LCR Meters & Impedance Analyzers for Sale

An LCR meter measures inductance (L), capacitance (C), and resistance (R) of passive components and materials. Most modern LCR meters display derived parameters alongside these: impedance magnitude (|Z|), phase angle (θ), dissipation factor (D or tan δ), quality factor (Q), ESR (equivalent series resistance), and admittance (Y). Measurements are made by applying a known AC test signal and measuring the resulting voltage and current. The instrument computes the complex impedance and decomposes it into the parameter pair selected by the user (L+Q, C+D, R+X, Z+θ).

The distinction is frequency range and measurement capability depth. An LCR meter (HP 4284A, Keysight E4980A) operates at a fixed set of test frequencies — typically 20 Hz to 1 MHz or 20 Hz to 2 MHz — and is optimized for component characterization at those frequencies. An impedance analyzer (HP 4192A, Keysight E4990A, Keysight 4294A) sweeps continuously across a wide frequency range and displays the full impedance spectrum, including resonant frequencies, self-resonances, and parasitic behavior. For production testing of individual capacitors, inductors, and resistors, an LCR meter is the right tool. For characterizing materials, ceramic resonators, quartz crystals, and transformer windings across frequency, an impedance analyzer is required.

The HP 4284A is a 20 Hz to 1 MHz precision LCR meter that became the lab standard in semiconductor manufacturing and electronics R&D during the 1990s. It has 0.05% basic accuracy, a four-terminal Kelvin measurement configuration for low impedance, and a built-in bias voltage source for capacitance-voltage characterization of MOSFETs and dielectrics. HP made it in very large quantities, so used units are widely available and well-understood. The most common failure mode is the DC bias output stage — typically a failed pass transistor or op-amp in the bias circuit. Measurement accuracy rarely drifts without a visible failure.

1 kHz is the standard test frequency for most capacitor specifications (electrolytic, film, ceramic) and is the frequency most component manufacturers specify on datasheets. 100 kHz is standard for measuring high-Q ceramic capacitors and SMD inductors where 1 kHz measurements are dominated by ESR rather than reactance. For power inductors used in switching regulators, measurements at the actual switching frequency (100 kHz to 2 MHz) are more relevant than at 1 kHz. For electrolytic capacitors in audio applications, 120 Hz is the traditional test frequency. The HP 4284A, Keysight E4980A, and Wayne Kerr 6430 all support user-selectable frequencies across their full range.

ESR (Equivalent Series Resistance) is the total resistive loss in a capacitor at a given frequency — it combines the resistance of leads, plates, and dielectric losses. Low ESR is critical for capacitors in power supply decoupling and switching converter output filters, where high ESR causes voltage ripple and heat. A capacitor with nominal capacitance but high ESR will fail in a switching power supply even though it measures correctly on a basic capacitance meter. LCR meters measure ESR directly as the real part of the series impedance model. HP 4284A, Keysight E4980A, and dedicated ESR meters (ESI 290A) are all used for production ESR screening.

A standard two-terminal measurement injects current and measures voltage through the same two leads — lead resistance adds directly to the measured impedance, causing errors when measuring low-value components. A four-terminal Kelvin configuration uses four separate terminals: Hcur and Lcur carry the test current, while Hpot and Lpot sense the voltage at the component itself with zero current flowing through the sense leads (Kelvin sensing). This eliminates lead resistance from the measurement. For components below about 100 Ω, Kelvin connection is required to get accurate readings. All HP/Agilent 428x series LCR meters and most Wayne Kerr instruments use four-terminal Kelvin configuration.