LCR Meter Guide: How to Measure Inductance, Capacitance, and Resistance

An LCR meter is the only instrument that can directly and accurately measure inductance (L), capacitance (C), and resistance (R) as individual component parameters — not as the blunt DC resistance a multimeter sees, but as the true impedance components at a specific test frequency. If you work with electronics, power electronics, transformers, or motor drives, an LCR meter removes the guesswork from component qualification, PCB debugging, and incoming inspection.

What an LCR Meter Actually Measures

Every passive component — resistor, capacitor, inductor — has an impedance Z that is complex: it has both a real part (resistance, R) and an imaginary part (reactance, X). An LCR meter applies a small AC stimulus at a controlled frequency, measures the resulting current and the phase angle between voltage and current, and then calculates all the derived parameters from those two numbers.

Why Test Frequency Matters

The single most important thing to understand about LCR measurement is that every parameter depends on frequency. A 100 μF electrolytic capacitor measured at 100 Hz will show a different value than the same capacitor at 1 kHz or 10 kHz. Neither reading is "wrong" — the component's behaviour genuinely changes with frequency because ESR, lead inductance, and dielectric properties all shift.

Always match the test frequency to the frequency at which the component will operate in the circuit. Standard test frequencies and their typical applications:

• 100 Hz / 120 Hz — large electrolytic capacitors (power supply filter caps, motor-run caps), power transformers. This is the ripple frequency they'll see in service.
• 1 kHz — the most common default. Ceramic capacitors, small inductors, general component testing, incoming inspection.
• 10 kHz — small-value capacitors (nF range), RF inductors, switching power supply components.
• 100 kHz — SMD components, high-frequency transformers, ferrite cores, RF components.
• 1 MHz and above — RF inductors, chip capacitors, transmission line components.

How the Measurement Circuit Works

Inside an LCR meter, a precision oscillator generates an AC stimulus — typically a sine wave at the selected test frequency with an amplitude between 0.1 V and 2 V RMS. This signal is applied to the component under test (DUT) through a current-sense resistor. The meter then simultaneously measures:

1. The voltage across the DUT (V_DUT)
2. The current through the DUT via the sense resistor (I_DUT)
3. The phase angle θ between them using phase-sensitive detection

From these, the meter calculates: Z = V_DUT / I_DUT, R = Z × cos(θ), X = Z × sin(θ). If X is positive it's inductive; if negative, capacitive. C = 1/(2πfX) or L = X/(2πf).

Higher-end meters use a 4-terminal (Kelvin) connection to eliminate lead and contact resistance from the measurement — critical when measuring components below 1 Ω ESR or below 10 Ω resistance.

4-Terminal (Kelvin) Connection

Standard 2-wire connections introduce lead resistance into the measurement. For a resistor of 100 Ω this is negligible. For a 10 mΩ ESR electrolytic capacitor or a milliohm-level winding resistance, a 50 mΩ lead resistance is five times larger than the quantity being measured.

Kelvin connections solve this with four separate terminals — a pair for current injection (H_cur, L_cur) and a separate pair for voltage sensing (H_pot, L_pot). Because the voltage-sense path carries essentially no current, its resistance does not affect the reading. For any component below 10 Ω, always use 4-wire Kelvin connection if your meter supports it.

Measuring Capacitors

Set the LCR meter to series equivalent mode (Cs-D or Cs-Rs) for most capacitors. Series mode is correct because the real loss mechanism in a capacitor — the ESR — is in series with the capacitance.

• Electrolytic caps (≥1 μF): Test at 100 Hz. Key parameters: C (should be within ±20% of marked value), D (dissipation factor — should be below 0.1 for new caps; above 0.2 indicates a degraded dielectric), ESR (should be milliohms for large caps; high ESR causes ripple heating in power supplies).
• Film and ceramic caps (nF range): Test at 1 kHz. Q should be very high (>100 for good film caps). Low Q indicates contamination or damage.
• RF ceramic caps (pF range): Test at 1 MHz or higher. Stray inductance from leads will dominate below resonance.

Measuring Inductors and Coils

Set the meter to series equivalent mode (Ls-Rs) for most inductors, particularly at higher frequencies where winding resistance is in series with inductance. Use parallel mode (Lp-Rp) for high-Q inductors at low frequencies where core loss is the dominant mechanism.

• Power inductors: Test at 1 kHz. Check L (within ±10–20% of marked value) and Q (typically 20–100; lower Q means higher copper or core losses).
• Transformer windings: Test each winding at 1 kHz with all other windings open-circuited. Inductance proportional to N² tells you if turns are intact.
• Ferrite chokes: Test at the frequency where they are expected to suppress noise — often 10–100 kHz. At the wrong frequency they appear inductive rather than resistive and the measurement is meaningless.

Measuring Resistors

For resistors above 100 Ω, a basic multimeter resistance mode is adequate. But for precision resistors (0.01% tolerance), shunt resistors (milliohms), or resistors in high-frequency circuits, the LCR meter's AC resistance measurement is more accurate because it is free from thermoelectric EMF offsets that affect DC resistance measurement.

Use 4-wire Kelvin connection for any resistor below 10 Ω. Open- and short-circuit compensation (zeroing) must be performed before precision measurements — attach the short clip, zero the display, then detach and measure.

Open and Short Circuit Compensation

Test fixture leads, clips, and PCB pads all have stray capacitance and inductance that add to the measurement. Before measuring any component, run:

1. Open compensation: Leave the test terminals open (nothing connected). The meter measures the stray parallel capacitance and subtracts it from subsequent measurements.
2. Short compensation: Short the test terminals with a known-good shorting clip or bar. The meter measures the stray series resistance and inductance and subtracts it.

Skip this step for rough spot-checks. Never skip it for precision work — the error can exceed the component tolerance at high frequencies.

Practical Applications

Incoming inspection: Verify that capacitors, inductors, and resistors from a new batch meet specification before soldering. Counterfeits and mismarked components are common in the global supply chain. An LCR meter finds them in seconds.

PCB debugging: Test components in-circuit (with power off) to find failed capacitors, short-circuit inductors, and open resistors. Some in-circuit measurements will be affected by parallel paths — desolder one lead if readings are ambiguous.

Transformer characterisation: Measure primary inductance, leakage inductance (secondary shorted), turns ratio (by comparing primary and secondary open-circuit inductance), and winding resistance — all with one instrument.

Motor maintenance: Measure the inductance balance across phases of a three-phase motor. An unbalanced inductance reading indicates shorted turns before the motor has failed completely.

Capacitor bank maintenance: Power factor correction capacitor banks degrade over years. Periodic LCR measurement of capacitance and ESR identifies capacitors that need replacement before they fail and take the whole bank down.

Which LCR Meter to Buy

The key specifications to compare:

• Frequency range: A meter limited to 100 Hz–100 kHz is adequate for most electronic work. Measurements above 1 MHz require an RF impedance analyser.
• Basic accuracy: 0.1% accuracy is adequate for component qualification. 0.02% is needed for precision reference standards.
• Measurement range: Verify coverage of the component values you work with — especially pF-range capacitors and μH-range inductors.
• 4-wire (Kelvin) capability: Essential if you measure anything below 10 Ω.
• DC bias: Some capacitors (especially ceramics) require DC bias during measurement because their capacitance varies with applied voltage. An LCR meter with internal DC bias replicates operating conditions.
• Speed: Production testing requires fast measurement rates (>10 measurements/second). Bench work doesn't.