Finding inductance of single turn inductor - Page 1
Forum section: electronics / projects

author: ocset
author_rank: Super Contributor
timestamp: June 02, 2018, 06:22:58 pm
content: Hello,We are looking to find the inductance of the following ferrite core set-up. (attached)Is the following ok..Ampere’e Law N.I = H.dl..substitute H = B/(u0.ur)N.I. = [B/(u0.ur)] * dl..substitute B = (L.i )/ (N.A)Eventually gives( [N^2] .A u0.ur) / dl = LWhere:A = minimum core pair areadl = magnetic path lengthetcAttached Files Attached Files

author: JS
author_rank: Frequent Contributor
timestamp: June 02, 2018, 06:31:15 pm
content: You usually want the inductance per turn of the given core, Ln usually called. Thay way you do L=n^2*LnTo find it having the core you do 10 turns or 100 turns and do the inverse, usually better than just relying on a single turn measurement.If you don't have the core you can sometimes find the value somewhere or you can do the math as you are doing, but having the correct μr and length is usually tricky. Also the μr could change with signal amplitude, freq and other factors, so experimentation with the actual conditions is the best way to find the value.JSEnviado desde mi LG-M250 mediante Tapatalk

author: Kalvin
author_rank: Super Contributor
timestamp: June 02, 2018, 08:33:25 pm
content: After some heavy math you may want to verify your calculations by measuring the actual inductance:http://www.dos4ever.com/inductor/inductor.html

author: Teledog
author_rank: Regular Contributor
timestamp: June 03, 2018, 04:21:46 am
content: Also, watch for your alignment on the board (if you so choose to use one).Worked on ~1Ghz oscillators years ago, was given dead boards to "fix".Simply rotating the inductor (next to the Xtal) 180 degrees was a go or no-go thing.Winding rotation/position made all the difference.Circuit sim was useless.

author: ocset
author_rank: Super Contributor
timestamp: June 03, 2018, 10:12:54 am
content: QuoteThanks, thats a really good way. Like it.For us, we need to measure the inductance at 50kHz, because our inductor will have a 50kHz sine current in it.......so i think we will just modify your method for this.

author: Kalvin
author_rank: Super Contributor
timestamp: June 03, 2018, 11:40:45 am
content: Quote from: treez on June 03, 2018, 10:12:54 amInductance is a property of an inductor, like resistance is a property of a resistor and capacitance is a property of a capacitor. When you go and buy a 1 uH inductor for example, its inductance will remain 1 uH no matter the frequency over the specified frequency range - in a similar way as when you buy a 100 ohm resistor its resistance will remain 100 ohm withing specified operation conditions and 100 nF capacitor's capacitance will remain 100nF, Of course at high frequencies there will be some parasitics introduced which will affect the impedance, but in practical terms the inductance can be taken as constant for a given inductor: Given that the inductor will not saturate the inductance of an inductor will remain practically constant over practical frequency range.Now, when you say that you need to measure the inductance at 50 kHz because you are driving the inductor with 50 kHz sine wave signal, this is not probably what you really want to do. First, you need measure the inductance of an inductor using the method in my previous post, and then you can calculate the impedance of the inductor at 50 kHz: 2*pi*f*L = 2 * pi * 50 000 * inductance in Henrys. Of course, you *could* measure the inductance at 50 kHz, but you will get more accurate value for the inductance using the method of signal generator and oscilloscope. The expected measurement accuracy should be somewhere within +/- 10% which is sufficient for practical purposes.

author: ocset
author_rank: Super Contributor
timestamp: June 03, 2018, 12:03:07 pm
content: QuoteThanks, the thing is, the LCR45 inductance meter calculates inductance at either 1khz, 15khz, or 200khz. So you infer that this is purely because of the parasitics?LCR45 inductance meter:https://www.tester.co.uk/peak-lcr45-lcr-impedance-meter?fee=3&fep=6892&gclid=EAIaIQobChMI_86M7rK32wIVBLftCh2qsgABEAQYBCABEgLyEPD_BwE

author: Kalvin
author_rank: Super Contributor
timestamp: June 03, 2018, 12:17:33 pm
content: Quote from: treez on June 03, 2018, 12:03:07 pmProbably the three ranges are for measuring the large (1kHz), medium (15kHz) and small inductances (200kHz). The instrument may also measure some parasitic values using different frequencies. If you have that instrument at hand, you can measure your inductance using the 15kHz and 200kHz ranges - the results should be the same of course if the inductance is well within the instrument's specified range.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: June 03, 2018, 02:34:55 pm
content: Common method is resonate it with a known capacitor (value to get whatever frequency you want) and measure the frequency.