Overview: This article explains the importance of LCR meters in electronics testing, quality control, and industry applications, highlighting features, working principles, and their role in ensuring device reliability.

Electrical circuits are fundamentally built from three passive elements: resistors, capacitors, and inductors. Resistors provide opposition to current flow, ideally following Ohm's law (V = IR) regardless of frequency. Capacitors store energy in electric fields, with impedance decreasing as frequency increases. Inductors store energy in magnetic fields, with impedance increasing with frequency.

Unlike resistance in direct current circuits, impedance is a fundamental concept in AC circuit analysis, representing the total opposition a circuit presents to alternating current. It is a complex value that consists of two components:

  • Resistive (real) part: Represents pure resistance, where energy is  dissipated as heat.
  • Reactive (imaginary) part: Represents reactance, where energy is  temporarily stored and released by inductors (as magnetic fields)  and capacitors (as electric fields).

A standard digital multimeter can measure the primary value of a resistor, capacitor, or sometimes an inductor at a single frequency or DC. However, it cannot reveal how these components behave across a range of frequencies. Instruments like the LCR meter (or impedance meter) show how a component's impedance varies with frequency.

What Is an LCR Meter?

An LCR meter is an electronic test instrument that provides detailed measurements of resistance, capacitance, and inductance over a broad frequency spectrum, essential for advanced circuit design and troubleshooting.

Working Principle

Modern LCR meters are designed to accurately quantify the complex impedance. They achieve this by

  • Applying an AC test signal: The meter sends a known AC voltage or current through the component under test.

  • Measuring voltage and current: It simultaneously measures the magnitude of the voltage across and the current through the device.

  • Determining the phase angle: The meter calculates the phase  difference between the voltage and current waveforms.

From the measured impedance and phase angle, the LCR meter can easily derive resistance, inductance, and capacitance.

LCR meters also determine secondary parameters such as dissipation factor (D or tan (δ), and quality factor (Q), which reflect the "purity" of a component---how closely it behaves as an ideal resistor, capacitor, or inductor.

  • D is the ratio of resistance to reactance and is particularly important for capacitors, where a low D indicates low losses.

  • Q, the reciprocal of D, is important for inductors, with a high Q  indicating low resistance relative to reactance.

LCR meters often include a sweep function, allowing users to automatically measure parameters over a defined range of frequencies, voltages, or currents. This feature is important for identifying frequency-dependent behaviors and parasitic effects. Additional measurements such as conductance, susceptance, phase angle, and equivalent series resistance (ESR) provide the component\'s electrical behavior.

Key Parameter in Selecting an LCR Meter

Frequency selection: The behavior of resistors, capacitors, and inductors changes with frequency. Accurate characterization of the circuit depends on measuring components at frequencies that match their intended use.

Signal level: Using the highest available test signal level within the component's and circuit's safe limits improves measurement accuracy and resolution. However, excessive signal levels can damage sensitive components or introduce nonlinearities.

Circuit model: Choosing the correct measurement parameter (series or parallel model) and understanding the difference between them is important for accurate interpretation.

Fixtures and Leads: Electronic components are manufactured in a variety of packages, such as axial, radial, surface-mount, and custom forms, which require appropriate fixtures to connect. The quality, length, and condition of test leads, connectors, and fixtures directly impact measurement accuracy.

Applications

LCR meters are used across a wide range of applications, including the characterization of passive components, assessment of transformer or cable losses, and evaluation of antenna inductance in RFID modules. LCR meters are widely used for component testing and quality assurance in manufacturing.

It is also used for characterizing filters, transmission lines, and cables, and network analysis in RF and communication systems.

Effective LCR Meters to Consider

Keysight's LCR meters offer a wide range of handheld and benchtop instruments that deliver high accuracy, speed for measuring. This article elaborates on such an effective model.

Keysight U1730C Series Handheld LCR Meters

They are compact, battery-powered instruments designed for quick and accurate measurement of inductance, capacitance, and resistance, impedance, ESR, DC resistance (U1733C only), dissipation factor, quality factor, and phase angle.

These meters offer a high resolution of 20,000 counts and a basic accuracy of 0.2%, enabling precise component testing. They support multiple test frequencies---up to 1 kHz for the U1731C, 10 kHz for the U1732C, and 100 kHz for the U1733C---making them suitable for a wide range of components.

The meters feature automatic identification of component type, auto and manual ranging, tolerance sorting, data hold, and recording of maximum, minimum, and average values.

U1733C handheld LCR meter

Fig. 1 U1733C Handheld LCR Meter Source: Keysight

Keysight E4980A/E4980AL Precision LCR Meter

It is a high-accuracy instrument designed to measure a broad range of electrical parameters, including capacitance, inductance, resistance, impedance, reactance, conductance, susceptance, dissipation factor, quality factor, and phase angle. It offers a broad frequency range, with the E4980A model covering 20 Hz to 2 MHz, and the E4980AL model available in options up to 1 MHz.

The meter supports both parallel and series equivalent circuit models. The instrument features a four-terminal measurement setup, multiple cable length options, and several measurement time modes to balance speed and precision.

The meter also includes advanced functions like deviation measurement, auto/manual impedance range selection, and multiple trigger and averaging modes, making it suitable for both laboratory and production environments where reliable and precise component characterization is required.

These features make the E4980A suitable for demanding R&D, quality control, and manufacturing test environments requiring high accuracy and fast throughput.

E4980AL precision LCR meter

Fig. 2 E4980AL Precision LCR Meter Source: Keysight

Summarizing the Key Points

  • LCR meters measure impedance, resistance, capacitance, and inductance across frequencies for reliable electronic circuit design.

  • They identify frequency-dependent behaviors and parasitic effects, with parameters like Q factor and dissipation factor, enhancing accuracy in quality control and component testing.

  • Modern handheld and benchtop LCR meters feature auto-ranging, multiple test frequencies, and advanced functions, ensuring fast, accurate measurements in R&D and manufacturing environments.

  • LCR meters are essential in quality assurance, helping detect faults  early, optimize product designs, and reduce failures, thus > ensuring electronic device performance and durability.

Reference

Burnik, U., Križaj, D., Topčagić, Z., & Meža, M. (2018). Measuring impedance using an open-source instrumentation platform. International Journal of Electrical Engineering Education, 55(2), 168--185. https://doi.org/10.1177/0020720918761764

Simic, M. (2014). Realization of digital LCR meter. 2022 International Conference and Exposition on Electrical and Power Engineering (EPE), 769--773. https://doi.org/10.1109/icepe.2014.6970014

Inácio, P. M. C., Guerra, R., & Stallinga, P. (2022). An Ultra-Low-Cost RCL-Meter. Sensors, 22(6), 2227. https://doi.org/10.3390/s22062227

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Rohde & Schwarz. (2022, March 18). Understanding LCR meters [Video]. YouTube. https://www.youtube.com/watch?v=vi9t5gdog7Q

Zurich Instruments. (2022, April 5). LCR meter or impedance analyzer - what's the difference? [Video]. YouTube. https://www.youtube.com/watch?v=Gw0xx1bG9zg