RLC measurements

This article is about measuring resistance, capacitance and inductance. The measurements described here talks about measuring components that not wired into any circuit.

Resistors, Inductors and Capacitors are the most commonly used passive components in almost every electronics circuit. Out of these three the value of resistors and capacitors are commonly marked on top of it either as resistor colour code or as numeric marking. Also the resistance and capacitance can also be measured using normal Multimeter. But most of the inductors, especially the ferrite cored and air cored ones for some reason does not seem to have any sort of marking on them. This becomes quite annoying when you have to select the right value of inductor for your circuit design or have salvaged one from an old electronic PCB and wanted to know the value of it.

Resistance with a multimeter

Resistance is the measure of difficulty electrons have in flowing through a particular object. Resistance can be measured with an analog or digital multimeter or ohmmeter. Resistance is can be usually usually most easily measured using an instrument such as digital multimeter.

Resistance measurement does not involve measuring the circuit’s resistance value itself. Instead, resistance is calculated by measuring the current and voltage applied to the circuit. Resistance can be calculated by measuring the current and voltage using Ohm’s Law.

Many multimeters typically apply a low current to the circuit under measurement, the circuit (resistance) exhibits a voltage a voltage drop related to resistance value. In most cases, when measuring resistance with a digital multimeter, you’ll use the two-terminal measurement method. This method applies a constant current and measures the resistance value using the instrument’s voltmeter. There are advanced meters that use a four-terminal resistance measurement for more accurate low-resistance measurement.

Capacitance measurements

Many modern “better” multimeters have a measurement range to measure capacitance. Simple DMMs can measure capacitance by just charging the capacitor with a constant current and measuring the rate of voltage build-up. This simple technique provides surprisingly good accuracy and wide dynamic range, therefore it can be implemented in almost any DMM, without significant cost penalties. There are other techniques as well: A multimeter determines capacitance by charging a capacitor with a known current, measuring the resulting voltage, then calculating the capacitance. Those multimeter capacitor measurements are simple to use, but can have limited accuracy. Capacitors measured by means of a multimeter in capacitance mode may be expected to read low by as much as 10%. This accuracy is sufficient for many applications such as the starting circuit for an electric motor or for power supply filtration. Greater accuracy is available by performing a dynamic test.

A capacitance meter is a piece of electronic test equipment used to measure capacitance, mainly of discrete capacitors. Depending on the sophistication of the meter, it may display the capacitance only, or it may also measure a number of other parameters such as leakage, equivalent series resistance (ESR), and inductance. For more details on capacitor measurements check out IFIXIT Introduction to Capacitors.

You can to check bad Capacitors in circuit boards with ESR meter and multimeter that can measure capacitance. For more details on this check out 3 Ways to Check Capacitors in Circuit with Meters & Testers video. If you are interested in capacitor ESR measurements, check my posts on ESR meters and DIY ESR meter.

Inductance measurements

Inductance is usually measured in units called millihenrys or microhenrys. It is commonly measured by using a frequency generator and an oscilloscope or an LCR multimeter. The only reason DMMs can’t measure inductances is that it is more difficult to measure inductance than resistance or capacitance: this task requires special circuitry, which is not cheap. Since there are relatively few occasions when inductance measurements are required, standard DMMs do not have this functionality, which allows for lower cost.

Theoretically, one could measure inductance by applying a constant voltage across an inductor and measuring the current build-up; however, in practice this technique is much more complicated to implement, and the accuracy is not that good. It can be also hard to separate ESR from reactive value at low frequencies unless a dc resistance measurement is also taken. The DC resistance itself is easy to measure separately with a multimeter resistance measurement range.

RLC meter instruments

LCRs are special meters designed for inductance measurements and containing the required circuitry. These are costly tools.
A basic LCR meter is very similar to a multimeter. With the RLC measurement electrical components can be measured in detail.
determine resistance (R), inductance (L) and capacitance (C).

To measure the inductance of a device, intrinsic inductance of a circuit or more widespread distributed inductance, an LCR meter is the instrument of choice. It subjects the device under test (suitably discharged and isolated from any ambient circuitry that could energize it or create irrelevant parallel impedance) to an ac voltage of known frequency, typically one volt RMS at one kilohertz.


The simplest method to measure L or C is with a series resistor and a low frequency oscillator. A cheap DMM and a cheap LCR will both use this method. The accuracy with DMM or LCR will therefore be similar. However, because inductors have more parasitic effects than capacitors, like resistance, leakage flux, saturation, non-linearity, hysteresis, eddy currents, frequency depending mu, the simple measurement of the inductivity may not be sufficient for you.
The cheaper ones are accurate enough, but don’t distinguish resistance from inductance when measuring coils, so you need to know both to get an accurate reading. Like all things, you get what you pay for.

I own Lutron LCR-9063 that I use to make RLC measurements (it is similar to VOLTCRAFT LCR-9063 LCR-meter):

There are also more advanced meters that simultaneously measures the voltage across and current through the device. From the ratio of these amounts it algebraically calculates the impedance. The measurement results from programming (stimulus) an AC voltage/current with a given frequency and the measurement of the voltage curve and the current profile.

Subsequently, advanced meters measure the phase angle between the applied voltage and resulting current. The simultaneous determination of current (I) and voltage (U) in short intervals over a period of several intervals allows for the determination of the phase angle between U and I.
They use this information to display the equivalent capacitance, inductance, and resistance of the device in question. The meter operates under the assumption that the capacitance and inductance it detects exist in either a parallel or series configuration.

Der EE DE-5000 Handheld LCR Meter is one more advanced meter I seen. It can do measurement at many frequencies. For more details on it check out Der EE DE-5000 Unboxing and Teardown.

Multi component testers

There are many cheap tester circuit boards, DIY kits and ready made instruments marketed like $20 LCR ESR Transistor checker. Those instruments can measure transistors, resistors, capacitors and inductors. You can but those from online market, and their capacitance meter usually also ESR meter built in.

For capacitance, inductance and resistance measurements I have successfully used component testers like this:

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I have tested several different component tester DIY kits and boards:
DIY Electronics Tester Kit M168
Component tester M12864
Transistor tester M12864 advanced version

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They are good for many things, but have limitations also – do not always give accurate inductance reading with some coils that use large iron or ferrite core. The reason is that those testers typically measure the inductance with a short measurement pulse that can behave somewhat differently with magnetic core than continuous waveform sent by specific RLC meters.

Audio measurement instruments

There are audio measurement tools that are designed to measure different audio system components like speaker elements and passive components. For example DATS V3 can measure the exact values of passive components like resistors, capacitors and inductors.

If you are a DIY person, it is also possible to measure RLC parameters using a sound card. You will need some inexpensive DIY hardware and suitable software. Check for example 2-Pound RLC meter article and Sound Card LCR Meter Mini-App with ESR, DF, and Q web pages.

Vector network analyzer

Vector Network Analyzers are used to test component specifications and verify design simulations to make sure systems and their components work properly together. they are typically used to verify radio frequency circuit component and wiring impedance matching. R&D engineers and manufacturing test engineers commonly use VNAs at various stages of product development. Vector Network Analyzer (VNA) helps measure both phase and magnitude related measurements. They are primarily designed to measure system impedance matching, but many VNAs can also measure resistance, capacitance and impedance values over certain range.

A Vector Network Analyzer contains both a source, used to generate a known stimulus signal, and a set of receivers, used to determine changes to this stimulus caused by the device-under-test or DUT. They have used to to be very expensive special instruments only found on advanced RF and high speed electronics circuit design laboratories.

But over last few years, cheap VNAs have come to the market. One of the most commonly used hobbyist budget VNA is called NanoVNA, which is available on many version starting at well below 100 US dollars. You can use such a Vector Network Analyzer (VNA) to measure and understand RLC parasitics in radio / wireless design and construction. it can be used to measure resistors, capacitors, and inductors and their non-ideal behaviors at radio and even microwave frequencies. I have tested first NanoVNA and S-A-A-2 NanoVNA V2. I found both to be useful for measuring RLC values in RF circuits (meaning quite low inductance and capacitance values).

Here are links to a few videos how to do RLC measurements with NanoVNA:

NanoVNA – Measuring RLC Components

nanoVNA – Measuring Inductors and Capacitors (Vers. 3)

Using a nanoVNA to determine unknown inductance value

Keep in mind that NanoVNA uses RF frequencies to measure the RLC components. The shunt method is most accurate within a range of impedances or capacitance. The impedance seen by VNA is a function of frequency, thus as the frequency of measurement moves further away from the ideal the measurement will be less and less accurate. This is one reason (not the only reason) the observed inductance changes as you go up in frequency. Stray capacitance in the test fixture, between the coils of the inductor, as well as proximity effect and skin effect… all of these things are frequency dependant and will play a role in determining the behaviour of your inductor at different frequencies while being measured with the nanoVNA. If one wishes to simply obtain a “marked value” measurement of a given inductor, a relatively crude test fixture can work.

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For accurate result it is best to perform the characterization the component at the frequency the component is designed to be used, user proper test jug and do good calibration of VNA. It all depends on what your goals are.

8 Comments

  1. Tomi Engdahl says:

    NanoVNA – Measuring RLC Components
    https://www.youtube.com/watch?v=R0mRTigYzco

    Using a Vector Network Analyzer (VNA) to measure and understand RLC parasitics in radio / wireless design and construction. Looks at resistors, capacitors, and inductors and their non-ideal behaviors at radio and microwave frequencies. Also includes brief discussions of EM fields, both in free space and around circuit components.

    Reply
  2. Tomi Engdahl says:

    Inductance measurements results with Multi component testers

    Small common mode choke (ferrite core):
    1.39 mH result
    Turn around get first 1.20 mH, then next measurement same direction 1.39 mH
    Turn around again gets 1.20 mH and then 1.38 mH

    Mains transformer low voltage coil 246 mH
    Turn around 158 mH and next measurement same direction 234 mH
    Tunr aroun 169 mH and next 245 mH

    Another signal transformer 0.53 mH
    Other way 0.52 mH next 0.53 mH

    Reply
    • Claerity AI says:

      The pandemic has entirely changed the way of working. Most of us work with common web conferencing software like Google Meet, Microsoft Teams, and Zoom to discuss the project. During the conference call, you may face external challenges like noise distortion, network connectivity, communication lag, and other background noises. For getting rid of the background trouble during your conference call, you can use the background noise removal app for better sound quality.

      Reply
  3. Tomi Engdahl says:

    https://www.edaboard.com/threads/measuring-inductance-with-network-analyser.73955/

    Hi cat
    It is easy enough to get a reasonable measurement of inductance using a network ananlyser.

    You will need an open ended coax lead with a connector to fit your network analyser.
    Make sure that the open end is large enough to connect your inductor.

    Connect the lead to Port 1 and set measurement to S11, probably the reset condition.
    Set the frequency range to 10 – 20MHz, or what ever you feel most suitable.
    Select Smith chart and turn the marker on, set to your desired frequency.

    Short circuit the open end of the coax in the same way as it will be when connected to your inductor.
    Normalise the display, Data to Memory & Data/Memeory on the HP8753.

    Add a phase offset of 180 degrees.

    The marker should now show an open circuit or close to.

    Connect you inductor in place of the short.

    Read off the inductance from the marker.

    Different analysers may disply the answer differently the 8753 reads inductance and capacitance directly. You may have to work it out from the reactance if that is al that is displayed.

    Reply
  4. Tomi Engdahl says:

    Measuring Capacitor Parameters Using Vector Network Analyzers
    https://www.researchgate.net/publication/269166796_Measuring_Capacitor_Parameters_Using_Vector_Network_Analyzers

    Fig. 3. Two terminal passive components measueremnt techniques using
    VNA: (a) reflection technique; (b) shunt-through technique; (c) series
    through technique.

    V. CONCLUSION
    Vector network analyzers can be very useful for accurate
    capacitor impedance, resonant frequency, capacitance and ESL
    measurements in broad frequency range if proper measurement
    technique and de-embedding is used. Measurement accuracy of
    several % and even lower can be achieved using proper
    measurement technique. Measurement error of capacitors
    impedance and ESR depends not only on capacitor impedance
    magnitude (and frequency) but also on the measurement
    technique used.
    The best suited technique for capacitor fres measurement is
    the shunt-through technique, because measurement accuracy of
    capacitor impedance at fres and in the vicinity of it is very good
    (even below 1%) and this technique is less sensitive to the
    experimental setup parasitics. For capacitor impedance
    measurements in broad frequency range (when capacitor |Zc|
    can change from mΩ to kΩ) it is better to use combination of
    the shunt-through and series-through techniques: when |Zc| is
    below several tens of ohms, then it is better to use shunt-
    through technique; when |Zc| is above several tens of ohms,
    then it is better to use series-through technique. The reflection
    technique should not be used for capacitor parameters
    measurements because, firstly, it can give accurate results only
    when capacitor |Zc| slightly differs from 50Ω and secondly, it is
    very sensitive to uncalibrated connectors parasitics.

    The most problematic parameter to measure accurately with
    VNA is capacitor ESR. Only shunt-through technique should
    be used for accurate ESR measurements. However there are
    some limitations. ESR can accurately be measured only at fres
    and in vicinity of it (ESR measurement error below 3% can be
    achieved). For frequencies which are much higher or lower
    than fres the measurement accuracy can be very poor, even
    using shunt-through technique, because when capacitor
    reactance is much higher than its ESR, then the measurement
    error can increase enormously. Accurate measurements of ESR
    of capacitors with C lower than several tens of nF are
    impossible. ESR measurements of small-capacitance
    capacitors using VNA is completely useless.

    Overall it can be concluded that VNA can substitute more-
    expensive impedance analyzers for accurate capacitor
    parameters measurements in broad frequency range with some
    limitations in terms of ESR measurements.

    Reply
  5. Claerity AI says:

    The pandemic has entirely changed the way of working. Most of us work with common web conferencing software like Google Meet, Microsoft Teams, and Zoom to discuss the project. During the conference call, you may face external challenges like noise distortion, network connectivity, communication lag, and other background noises. For getting rid of the background trouble during your conference call, you can use the background noise removal app for better sound quality.

    Reply
  6. Tomi Engdahl says:

    DIY transformer/inductor tester
    https://www.youtube.com/watch?v=QBbEYYWiBI8

    Shorted transformer hard to tell? Let’s build a tester of transformers and inductors. It can identify shorted windings, including just 1 short turn. It’s hard to test switching transformers and inductors for internal shorts using any other tool. This tool is very useful, especially when fixing switching power supplies and inverters. It’s a simple ring tester, testing the winding based on the number of damped oscillations it can make. An internal short will turn a high Q factor transformer or inductor into a very low Q one, resulting in way less damped oscillations (rings). The Q factor is affected by the internal short turns way more than the inductance is.

    Reply

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