How to measure inductance

By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up. I am modeling the fine behavior of interacting oscillatory circuits. I have looked up a couple of methods for measuring inductance.

I believe I am following the procedure faithfully, but the values I obtain aren't as precise as I expect. I have a Tektronix B oscilloscope and a pretty standard signal generator. I measure across two inductors in series; as a sanity check I also did both inductors separately.

L1 is the kind of inductor that looks like a resistor see the green thing in the photo below ; Lcoil is a coiled inductor see below. Are these the best numbers that I can expect?

I do not have an electronics background, so if there are some basic intuitive principles I am overlooking, please let me know!

Edit: I add a screencap of one of the calculations, which provides the values of the inductance and the inductor resistance. The method you use is very error sensitive, ESR can be an issue but also determining the exact voltage ratios isn't easy. You should aim for a frequency that the signal generator can easily generate, for example 1 MHz. Set the generator output voltage a couple of volts, the exact value does not matter because we want to determine the resonance frequency.

Vary the frequency of the generator and on the oscilloscope keep an eye on the signal amplitude. The frequency where the amplitude is the largestthat is the resonance frequency. If the signal generator is not very accurate if it is an analog signal generator then measure the frequency using your oscilloscope. You need a better than 0. Your oscilloscope is a digital one so it can measure frequencies with more enough accuracy. Sunnyskyguy outlines an excellent method. Accuracy does depend on the resonating capacitor error.

how to measure inductance

The other error term is frequency: the Tek B's crystal-controlled timebase should make frequency measurements accurate. It is worthwhile to outline the alternate test configuration: series LC. Function generator outputs a sine wave of decent amplitude:. The depth of the dip gives an indication of inductor quality Q.

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If your function generator sine wave is low distortion, you can see if non-linearities in the inductor cause harmonics to be observable at the dip-frequency. Harmonics may also be caused by function generator distortion.

The path from function generator to test fixture should be as short as possible. From test fixture to oscilloscope can be longer use a 1x probe. Many function generators have an accurate internal 50 ohm source resistance. If not, you might attach a 50 ohm attenuator, to establish a solid 50 ohm source resistance. The dip amplitude oscilloscope voltage allows a calculation of inductor's resistance.

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You can use series or parallel resonance depending on what impedance you choose at resonance and what Q you expect from either mode. This can be limited by your driver GBW product.

But I needed to buffer with output impedance lower than the DCR of the coil, if I want to measure that.

Measuring Leakage Inductance

The amplification is the Q or impedance ratio of the signal. Your mileage will vary. Usually you want to test it in the frequency region it will be used.Inductors are sometimes wound by the user instead of bought. In such cases, the inductance would not be stamped on the side but instead may need to be found empirically.

The best way to measure inductance for an inductor like a coil solenoid is to use an inductance bridge or meter. If you have neither, a more indirect way is to use an oscilloscope.

Turn on the oscilloscope and clamp the two clips of one voltmeter to the circuit on opposite sides of the coil to determine the voltage drop across the coil. Then do the same for the resistor with another voltmeter. Set the frequency of the oscilloscope such that the voltage drop across the resistor and inductor are the same.

Finding said frequency may be a matter of trial and error. At that frequency, the resistance of the resistor and the impedance of the inductor will be equal. The resistance of the resistor has not changed from the start; it is independent of the frequency. Paul Dohrman's academic background is in physics and economics. He has professional experience as an educator, mortgage consultant, and casualty actuary.

His interests include development economics, technology-based charities, and angel investing. Connect a resistor of known resistance and the coil in series with the sine wave oscilloscope. Things You'll Need. About the Author. Photo Credits. Copyright Leaf Group Ltd.Sometimes you dig around in your parts bin, desperately searching for a bit of coax cable to make a new connector to your fantastic whizzbang widget. Well, here are two easy ways of finding out. But how do you get the inductance and capacitance of your bit of cable?

Just take a piece of the cable just a short piece is enough and measure the capacitance between the center core lead and the shield of the cable on one end of it. Next up is the inductance. Then use the LCR Meter and measure the inductance at the open end of the cable. This result had me stumped for a while.

So I remeasured and came to the same results. So close enough. So now you have a quick way of checking the impedance of cables you bought from a Ham-Fest or just some random cable hidden in the cable drawer. I have written an article about measuring the velocity factor of a cable.

You can use the same technique to send a short pulse through the wire and check the reflection. By adding a potentiometer at one end of the cable and sending a short pulse through it, you could adjust the potentiometer until the reflected signal is at the lowest value. The cable is normally 75 ohm. No problem at the cable. But the measured cable length is so short. Measure the cable with min. To measure just a short piece of cable, you have to have a very very good and expensive LCR meter measurement device.

Not a hand LCR meter with cheaper one. So you need an LCR meter. Your email address will not be published. This site uses Akismet to reduce spam. Learn how your comment data is processed. Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website.

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It is mandatory to procure user consent prior to running these cookies on your website. What kind of impedance does this coax cable have?

Comments The cable is normally 75 ohm. Leave a Reply Cancel reply Your email address will not be published. This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish.

Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website.The coil is the most recognizable form of an inductor. This tool is designed to calculate the inductance of a coil of wire given the number of turns, the loop diameter, wire diameter, and the permeability of the medium. Note that you can choose the unit of measurements for the loop diameter and wire diameter. The number of turns is always assumed as a whole number it's hard to do a 3.

The capacitor in parallel with the trigger coil charged up to V using the low-resistance path provided by the SCR. However, once the capacitor was fully charged, the short-circuit path to ground provided by the SCR was removed, and the capacitor immediately started to discharge through the trigger coil.

Since the only resistance in the time constant for the inductive network is the relatively low resistance of the coil itself, the current through the coil grew at a very rapid rate. A significant voltage was then developed across the coil. This voltage was in turn increased by transformer action to the secondary coil of the autotransformer, and the flash lamp was ignited.

That high voltage generated across the trigger coil will also appear directly across the capacitor of the trigger network. The result is that it will begin to charge up again until the generated voltage across the coil drops to zero volts.

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However, when it does drop, the capacitor will again discharge through the coil, establish another charging current through the coil, and again develop a voltage across the coil. Inductors can be found in a wide variety of common electronic circuits in the home. This feature is particularly important for dimmers, since they are most commonly used to control the light intensity of an incandescent lamp. The inductor is also effective in blocking high-frequency noise RFI generated by the switching action of the triac in the dimmer.

A capacitor is also normally included from line to neutral to prevent any voltage spikes from affecting the operation of the dimmer and the applied load lamp, etc. Hello sir, do you think a Henries inductor coil normal?

The inductor is a common school use transformer turn coil, with wire diameter about 0.

how to measure inductance

Could this be possible? So it suggests the permeability of the iron core is about The calculator is very good. This is in agreement with your formula but it does not apper to be correct. By using equations from electronics texts or manuals like Bleaney,Electricity and Magnetism I obtain a value around uH.

I have actually built such a coil, and measured a value around uH. Am I using your calculator in the wrong way? Or is there some error in it? This is way out, to the point of not even being useful.July 19, Comments. Measuring inductance with a handful of cheap common parts is certainly possible. There is 1 digital output and 1 digital input, so this will work with most micro controllers.

The only thing left is to measure the rising edge to falling edge time on a square wave. LM, LM comparison and a picture showing bell like behavior. An inductor in parallel with a capacitor is called an LC circuitand it will electronically ring like a bell. We will electronically strike the LC bell, wait a bit to let things resonate, then take a measurement. Now micro controllers are terrible at analyzing analog signals. As soon as the voltage on the LC circuit becomes positive, the LM will be floating, which can be pulled high with a pull up resistor.

When the voltage on the LC circuit becomes negative, the LM will pull its output to ground. Since our wave is a true sinusoidal waveit spends equal time above zero volts and below zero volts. This measurement can then be doubled to get the period and the inverse of the period is the frequency. Since the circuit is resonating, this frequency is the resonating frequency. To the left are the equations where f is the resonating frequency, c is capacitance, and L is inductance.

Solving for inductance will result in the last equation. The RLC will still resonate, but the amplitude will die out. With a low resistance the RLC will tend to latch onto the exact resonating frequency quicker. Pick whichever circuit is better for you, but the one using the LM is better. Both the capacitors are 1uf metalized film, but anything that is non polar will work. It will need to be very close to 2 uF though.

You can not use a capacitor that marks which connection is ground. One thing you may notice is that the LM is geared for analog computing. Remember that the LC circuit will vary above and below ground. Using the common LM op amp.

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D2 is a 1N too. Code for Arduino — With large inductors, you may need to increase the timeout on pulseIn from to Not accurate enough? What does this mean? Well this means that the inductor is in between uH and uH. This method uses low current to measure inductance, so saturation characteristics will be unavailable measurements will be taken in an unsaturated state. There is this wonderful thing called permeability.

Filling an inductor with certain materials changes the inductance without changing the coils. This is similar to mutual inductance in transformers. Another method that doesn't work well with Arduino.

how to measure inductance

You could make a metal detector. If you have access to fast sampling rates, you can use the method on the right too, but it will require a p type mosfet to really pump some current into the inductor and R1 less than an ohm or so, but greater than the equivalent series resistance of the inductor. Filed under Guides. About Moser Electrical Engineer who loves to bike!This article describes some methods to measure the self-inductance and the ESR equivalent series resistance of inductors and transformers.

An inductor has as beside its most important property the self-inductance, also parasitic properties. The most important of these are the internal series resistance and the parallel capacitance. The series resistance, also known as the ESR, is mainly determined by the ohmic copper resistance of the windings. The parallel capacitance is formed by the individual isolated windings laying next to each other.

The measure methods in this article can only determine the self-inductance and ESR. To measure the parasitic capacitance too, a more sophisticated method must be used as described in the article Parasitic properties.

To get usable measuring results, the measure frequency has to be chosen correctly. The designated work frequency of the inductor can be used as a rule. The self-inductance of inductors that include an iron or ferrite core are very dependently on the driving amplitude. If possible, use the the work conditions or lower. Applying a too high drive amplitude will result in measurement errors. The first method describes a self-inductance and ESR measurement by using a triangle shaped current.

The inductor to test is connected to a function generator who is outputting a triangle shaped voltage. An oscilloscope is used to measure the voltage across the inductor. The function generator must set at a high as possible output voltage where the inductor doesn't overdrive.

The frequency is adjusted so that the voltage across the inductor is kept low as possible but high enough to be measured accurate. In this way the inductor is, as it were connected to a current source. The top-top current, or current difference is: Fig. For completeness, here is also the coil current is measured, however, this is not necessary. Self-inductance If voltage is applied to an inductor the current will increase linear in time: [A] The opposite is also true: If an linear in time increasing current flows through an inductor, a constant voltage across the inductor can be observed.

And when a triangle shaped current is flowing through an inductor, a squarewave voltage V L can be found across the coil. The oscilloscope screen shot doesn't show a clean square wave, the horizontal line shows an incline. This incline is caused by the voltage across the ohmic portion of the inductor. After all, the voltage across a resistor is proportional to the current. The voltage belonging to the inductive part is the mean top-voltage V L.

The self-inductance is than: And the ohmic resistance is: Measuring with a sinewave To measure an inductor with a sinewave voltage, the inductor is added to a halve bridge circuit who is powered by a sinewave generator.

How To Measure Inductance

The self-induction and ESR is calculated with the measured voltages and phase difference. The unknown inductor L x is connected in series with a current measure resistance R s and connected to a function generator. The shunt resistor must be kept low but high enough to measure the voltage accurate. With the use of a two channel oscilloscope the voltage across the halve bridge and the the voltage across the inductor as well as the phase difference between these voltages is measured.

The measurement With the measured values and a mathematical model the self-induction and ESR is calculated as follows. L x and R x are the inductive and ohmic components of the inductor. With the use of the resistor R s the current is measured. This resistor has a low ohmic value to be able to measure the general low ESR of inductors.

The load that the probe forms can be neglected. Usually the measure frequency will be low enough that the reactance and the ohmic resistance of the probe doesn't play any role.Leakage inductance is an inductive component present in a transformer that results from the imperfect magnetic linking of one winding to another.

Any magnetic flux that does not link the primary winding to the secondary winding acts as inductive impedance in series with the primary, therefore this "leakage inductance" is shown on a schematic diagram as an additional inductance before the primary of an ideal transformer. In certain applications, such as switched-mode power supplies and lighting ballasts, leakage inductance of the transformer may play a critical function in the product design. For this reason, accurate measurement of leakage inductance is often an important test function for transformer manufacturers.

In order to avoid confusion with other transformer characteristics, this technical note will not refer to other components of loss such as winding resistance or inter-winding capacitance.

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For a theoretical, ideal transformer, there are no losses. Voltages are transformed in the direct ratio of the turns; currents in the inverse ratio of turns figure 1. In a real transformer, some of the flux in the primary may not link the secondary winding.

This "leakage" flux takes no part in the transformer action and can be represented as an additional inductive impedance that is in series with the primary winding figure 2.

In certain transformer designs, leakage inductance must be a greater proportion of the total inductance and is specified within a tight tolerance. The increased proportion of leakage inductance is usually achieved by introducing an air gap in the core design, thus reducing the permeability of the core and therefore the value of primary inductance.

The ratio of flux that does not link the primary winding to the secondary winding will therefore increase relative to the flux that links both windings figure 3.

how to measure inductance

Leakage inductance LL may be undesirable in a wound component, in which case it is important to measure the value to show that it is low or, in some applications, such as electronic lighting ballasts and resonant power converters, leakage inductance is deliberately introduced and its value is an integral part of the circuit design. In these applications, the leakage inductance provides an energy storage medium that is essential to achieve correct operation of the finished product.

It is therefore important that the value of leakage inductance of the transformer is known to be within specified limits. When an LCR meter is connected to the primary winding of a transformer with open-circuit secondary terminals figure 4the value of inductance L comprises primary inductance LP plus leakage inductance LL.

Since LL is a function within the transformer, it is clearly not possible to measure its value directly. A method must therefore be used to subtract the value of LP from the total measured inductance.

This is achieved by applying a short circuit across the secondary terminals figure 5. A perfect short circuit will result in zero volts on the output terminals figure 6 and, through transformer action, zero volts will also appear across the primary inductance. The measured value of inductance at the primary terminals will therefore be the true leakage inductance LL. Unfortunately, achieving a perfect short circuit on the secondary of a transformer is difficult in a laboratory and completely impractical in a production environment.

In production, it is common for the short circuit to be applied manually or via a switchable relay. Under these conditions, a perfect short circuit cannot be achieved, and it follows that the secondary voltage will not be truly zero.

The voltage attributable to the imperfect short circuit will then appear across the primary inductance as a short-circuit error multiplied by the turns ratio figure 7.

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