DIY Standard Inductors with Reasonable Accuracy and Stability? - Page 1
Forum section: electronics / general

author: TimNJ
author_rank: Super Contributor
timestamp: September 05, 2020, 12:04:29 am
content: Hi all,I have a feeling this might be a long one so...please bear with me...Part A:A few weeks ago, I bought an HP 4332A LCR meter on eBay. My initial spot checks show that it looks reasonably accurate. But, I still want to perform a proper calibration. The adjustment procedure requires a 100uH and 1mH standard inductor.FYI, I have access to a QuadTech Digibridge 1710 (0.2% basic accuracy, 1KHz max measurement frequency) and an Extech LCR200 (0.5% basic accuracy, 100KHz max measurement frequency). I can use these meters to check the accuracy of my "standard" inductors.In the last few weeks, I've tried to cobble together a DIY 100uH and 1mH standard inductor with some Coilcraft parts mounted to a small PCB. I bought a bunch of different values and fined tuned to get within about 0.2% of the nominal inductance at 100KHz. I used a combination of Coilcraft 1812FS (ferrite) and 1812CS (ceramic) parts. These inductors use very fine gauge wire (~35AWG in my estimation) and wound on a very small core/former. The HP 4332A user manual requires the adjustment procedure to be done with 61.9ohm in series with the 100uH and 619ohm in series with the 1mH. Since the inductors use such fine guage wire, I just added the difference between the DCR and the required series resistance. (What's the point of these resistors by the way?)When measuring this series RL combination on the 4332A, on the low value/high frequency ranges (100KHz measurement), the inductances show very close to what I measured with the QuadTech and Extech. But, when switching to the high value/low frequency range (1KHz measurement) the *apparent* inductance goes up significantly..This is confusing to me. When I remove the external resistance (61R9 or 619R), the measured inductances returns closer to the expected value @ 1KHz measurement. (The coil still has a large self-DCR though.) What phenomenon is going on here? A fault with my meter? Ignorance of the user?----Part A:It's silly for me to jump ahead to an "improved" solution, when it's not even clear if my current solution even has a problem or if it ismewho is the problem. But...Ferrite cores, in general, aren't great when it comes to temperature and long-term stability. Plus, the Coilcraft inductors appear to be "open" magnetic circuits, as opposed to a toroid which is much more well contained to the core. While I'm hoping someone can clue me in on my current situation, I've been thinking ahead about trying a new approach using low permeability moly-permalloy (MPP) cores. I skimmed through some GenRed app notes about their 1481 series of inductors, which used MPP cores. If I were to "clone" the 1481, my basic approach would be as follows:1. Reach about 95-98% of the nominal inductance value with one large MPP core, and then to trim the value with 1 or 2 more small diameter MPP cores, in series. Since the inductance is basically limited to increments of 1 turn, using one large core alone probably will be an issue.2. Then, mount the cores on rubber/cork standoffs in a diecast aluminum box.3. Mount banana jacks to box, bond the negative jack to the case for interference shielding.4. Partially fill the enclosure with potting compound to keep everything in place.Anyone have any thoughts?Thanks for reading,Tim

author: Vgkid
author_rank: Super Contributor
timestamp: September 05, 2020, 02:39:26 am
content: Start reading up on the NBS inductance standards, as well as the genrad manuals for them.Found this, its a neat read.https://www.ietlabs.com/1482.html#:~:text=The%20GenRad%201482%20Standard%20Inductors,exacting%20specs%20as%20General%20Radio.Add in nbs 300https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.govinfo.gov/content/pkg/GOVPUB-C13-1dab064e1d53908b9cbf1f0d6e1e170b/pdf/GOVPUB-C13-1dab064e1d53908b9cbf1f0d6e1e170b.pdf&ved=2ahUKEwj1g83XgdHrAhVPVs0KHe0TBqYQFjAEegQIARAB&usg=AOvVaw1Ny2Ji-L9wNbq-nZn9SE8K

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 05, 2020, 03:30:54 am
content: TimNJ and the group,Tim asked:The HP 4332A user manual requires the adjustment procedure to be done with 61.9ohm in series with the 100uH and 619ohm in series with the 1mH. Since the inductors use such fine guage wire, I just added the difference between the DCR and the required series resistance. (What's the point of these resistors by the way?)The measurement frequency of the 4332A is 100kHzThe impedance of 100uH at 100kHz = 2 x Pi x F x L = 62.8 j\$\Omega\$So the 61.9resistor will make the impedance = 61.9 + 62.8jThe phase angle will be very close to 45oSimilarly 619and 1000uH (628 jat 100kHz) will also be approximately 45oThey are making sure that the LCR meter reads the imaginary impedance, the inductive part. There is a phase sensitive detector on the 4332A.Standard InductorsThe Genrad inductors are wound on Steatite toroidial cores. Steatite is essentially soapstone. So they are 'rock' steady. Magnetically they are air cored.There are lots of curves here on the MPP core materialshttps://www.mag-inc.com/Products/Powder-Cores/MPP-Cores/MPP-Material-CurvesLower permeability cores are better for this application but they will require more turns.Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: September 05, 2020, 04:57:43 am
content: Quote from: Jay_Diddy_B on September 05, 2020, 03:30:54 amThanks JDB. A few days ago, I actually postulated that it was to create a 45 degree impedance, but I don't know why I didn't bother to simply calculate it out.When trying to measure my DIY "standard" 1mH inductor in series with 619R, the 100KHz measurement ranges all show accurate results (for both L and R), but the first 1KHz range (3mH range) overloads, and the next 1KHz range (10mH) shows about 2.5mH. If I remove the R component, and just measure L (which actually still has about 20R DCR), the inductance reads correctly on the 1KHz ranges.Yet, when I grab a random 1mH drum-core inductor and 619R resistor from my parts-bin and connect them in series, L and R read perfectly on all applicable ranges. As expected, when the R component is removed, the L component still reads fine.Now...as I look at the Coilcraft 1812FS plots, the lowest characterized frequency is 10KHz, and it appears there is some tendency for the inductance to go up @ < 10KHz, compared to nominal.That said, the inductive partdoesread correct at 1KHz so long as the series resistor is removed. I feel like this has an obvious answer, but I need to spend some more time to think about it. I almost want to figure it out myself, but we'll see. Question to myself is: "What's the difference between my fabricated 1mH+619R and an off-the-shelf 1mH+619R?" By the way, the "1mH inductor" is 3*330uH + 1*10uH. Not sure I have a good reason to do it this way for the 1mH, but for the 100uH, I wanted to use ceramic core inductors, and that would only work if I put a few in series.----Regarding the MPP cores, thanks. Yes, if I tried this, I'd probably use 60u cores as a balance between permeability temperature coefficient and keeping turns count reasonable...although the GenRad Steatite core inductors have a ton of turns piled on top of each other, but maybe their frequency range is quite limited.Thanks as always.

author: TimNJ
author_rank: Super Contributor
timestamp: September 05, 2020, 05:10:12 am
content: Quote from: Vgkid on September 05, 2020, 02:39:26 amThanks. I've been reading through the GenRad app notes from the 50's and 60's the last few days:https://www.ietlabs.com/notes/inductanceThe NBS 300 publication looks terrific. Too bad the PDF is so horridly slow (at least on my computer) since all the pages seems scanned at very high resolution and with full color.

author: chris_11
author_rank: Contributor
timestamp: September 05, 2020, 09:08:09 am
content: Inductors are always lousy high order systems. You can calibrate them, that they work at one frequency but not being nominal inductive over a large frequency range. For a LISN you manage hard, that they are not below a certain impedance over a specified frequency range. They are a mixture of transmission lines with L and C circuits + frequency dependent resistance/damping due to skin and proximity effects. And that for air core. If you have magnetic permeable cores you get additional frequency and amplitude dependent losses plus inductance changes.A LCR meter is a VNA which uses discrete frequency points. Why do they not use well established calibration procedures for VNAs?brChristian

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 05, 2020, 12:08:02 pm
content: Hi,1mH at 1 kHz = 6.28 jin series with 619Impedance is 619 + 6.28jThe phase angle istan-1Zl/R = tan-16.28/619 = 0.58oIt is a tough ask to be able to measure the 1mH inductance in series with 619at 1kHz.I don't think the 4332A should be able to measure 1mH when in series with 619on the 3mH range.The 4332A uses a 1.5mV signal. Under these conditions the voltage across the inductor is 15uV.Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: September 05, 2020, 05:02:05 pm
content: JDB,Thanks again. I think I understand the fundamental issue that a small phase angle impedance is a problem for the synchronous detector, as the vast majority of the sensed voltage is in phase with the driving voltage, so the "quadrature" voltage is very small. I suppose the 4332A is measuring the peak value/amplitude of the quadrature signal?But, I guess what still confuses me is that the 4332Adidaccurately measure a different 1mH inductor in series with 619R on the 1KHz ranges, and within 5% of expected value.If the quadrature signal is so low at 1KHz, I wonder if my issue is noise or setup related. The loop area of my board is fairly big, now that I look at it. Since the actual out-of-phase component is such a low level, I reckon it would be very easy for the signal to get lost in noise with a poor setup. (Maybe noise isn't the right word.)Chris_11,Thanks. I'm well aware that, of the 3 basic electrical components, the inductor is least likely to behave ideally due to the items you mentioned. In my experience though, issues usually come about at high test frequencies with skin effect and distributed capacitance effects. A 1KHz, I was not expecting the inductor to look significantly different, but it seems (more than likely) that the true signal is buried in noise and the 4332A is having a tough time pulling it out.Regarding VNAs, an interesting point. So how are VNAs usually calibrated then?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 05, 2020, 07:18:10 pm
content: Hi,In addition to the low signal and very small quadrature component.The bobbin inductor is essentially an air core inductor with a large air gap. The MPP core might have a high inductance and the very very low flux density.Do you have the dimensions, the core material and the number of turns for your MPP inductor?My HP4275A has adjustable signal level from 1mV to 5V. I am not sure if I have any MPP.Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: September 05, 2020, 09:11:35 pm
content: Hi JDB,I’d plan to use Chang Sung OD400, MPP, 60u (CM400060) as I can get those fairly easily. Then trim with OD127 or smaller core(s). To reach 1mH, you need about 110 turns.http://www.cwsbytemark.com/images/OD400.pdfWhen you talk about the bobbin core, you’re referring to the drum core right?So far, I have not made anything with the MPP cores, it there is any confusion there. So far, I’ve just cobbles together with some SMD ferrite core inductors from Coilcraft. What’s the relevancy of the “infinite” air gap of the drum core and the flux density of a powder core to this discussion?Thanks so much!(PS I’m writing up the DO-160 LISN documentation this weekend. Will share soon. And DM/CM separator boards in progress. Too many projects, but also never enough.)

author: TimFox
author_rank: Super Contributor
timestamp: September 06, 2020, 02:40:46 pm
content: Quote from: TimNJ on September 05, 2020, 05:02:05 pmFor impedance measurements, VNAs are normally calibrated at a "plane" defined by the coaxial connector on a reflection bridge, using three standards:an open-circuit (with controlled fringe fields), a short-circuit, and a well-characterized 50 ohm standard. Everything past that is arithmetic.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 06, 2020, 03:00:50 pm
content: Loving the old ways, I found this interesting-https://nvlpubs.nist.gov/nistpubs/bulletin/02/nbsbulletinv2n1p87_A2b.pdfSome decades ago I saw and copied an article on making calculable inductance standards, possibly in a ham oriented magazine. It was practical and of reasonable accuracy. I'll try to locate it but am recovering from a surgery, so may not manage it for a while. CH

author: doktor pyta
author_rank: Frequent Contributor
timestamp: September 06, 2020, 07:14:20 pm
content: I was about to write about marble as a material for bobbin. Take look at the photos.Mine required some repair due to marble crack, but i can confirm that it is wound using litz wire.

author: TimNJ
author_rank: Super Contributor
timestamp: September 06, 2020, 08:26:51 pm
content: Thanks for the input! Why litz wire in this application? Is it mainly to reduce Rac of the inductor? I noticed that the GenRad inductors were/are wound with litz. Perhaps Rac really starts to add up with these high turns count “air core” inductors. Seems like it might be unnecessary for MPP core but could be wrong.

author: TimFox
author_rank: Super Contributor
timestamp: September 06, 2020, 10:02:44 pm
content: Litz wire is used to get more effective conductor area inside a given bundle diameter when skin depth is a problem. Typically, it is useful below 1 MHz; the complete theory is more complicated than just the skin to diameter ratio, since the actual current distribution is affected by neighboring strands. To use it properly, you must keep the strands insulated from each other except at the very ends of the long wire. See pp 37, 74, and 80 of F E Terman.Radio Engineers' Handbook, New York: McGraw Hill, 1943. That first edition is a better reference for coil design than some later editions.

author: TimNJ
author_rank: Super Contributor
timestamp: September 06, 2020, 10:06:46 pm
content: Thanks. Yes, I understand litz is primarily useful for reducing the AC resistance due to skin depth, but also know it’s also useful in reducing proximity effect losses in the presence of magnetic fields. I suppose I do not understand the relevancy of keeping Rac low in a standard inductor. Obviously, it would be nice to keep the inductor as “ideal” as possible, but for typical equipment calibration, does additional AC resistance of the inductor really matter? Is there some other benefits?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 06, 2020, 11:35:41 pm
content: Hi,The Litz wire is easier to wind, it is softer than the solid wire. I think the main advantage is that you can immobilize the winding with wax or varnish.Jay_Diddy_B

author: TimFox
author_rank: Super Contributor
timestamp: September 06, 2020, 11:45:46 pm
content: Litz wire should be similar in flexibility to stranded wire of the same configuration, but usually litz wire has far less stiff serving (overall insulation).In general, for a reactance standard, you want to minimize the ESR to concentrate on the reactance. This is a problem with air-core inductors (high ESR) but iron cores introduce non-linearity and temperature dependence of the iron. Capacitor standards are far closer to ideal.

author: TimNJ
author_rank: Super Contributor
timestamp: September 07, 2020, 06:12:27 pm
content: Thanks all. The flexibility bit makes more sense. Although, for automated toroid winding machines, I can't see it making too much of a difference(?), but I am not Gen Rad, so I do not now.Taking a look the Δu/Δt plots from CSC, for 60u MPP, the variation in permeability seems very good for a typical operating ambient range of +10 to + 40C. It's hard to tell precisely from the plots, but seems like the variation would be <0.1 or 0.2% within the aforementioned temperature range. (No mention about if that's a typical or maximum plot, but I assume typical.)Is that true "standard" inductor stability? Eh, probably not, but I just need it to be good enough to make sure my 1% accurate LCR meter is mostly telling the truth.

author: bob91343
author_rank: Super Contributor
timestamp: September 07, 2020, 09:01:27 pm
content: I find it amusing that the plot vertical axis is rather coarse, probably to give the impression that the stability is good. A full scale of 1% would be more useful. But maybe the data aren't good enough for that. Or the sample to sample variation.

author: TimNJ
author_rank: Super Contributor
timestamp: September 07, 2020, 10:10:07 pm
content: I think it’s done, in part, because they show the other core material plots (sendust, high flux, mega flux) on the same page and, for those materials, there’s much larger variation, especially at high temperature. So, it seems like they want to compare the materials. That said, even the other plots do not have the same full scale limits.It would be nice to have more detail indeed.

author: TimNJ
author_rank: Super Contributor
timestamp: September 07, 2020, 10:19:42 pm
content: Quote from: TimFox on September 06, 2020, 02:40:46 pmThanks. Yes..actually I knew that much. Just got my first VNA a few weeks ago. I guess I thought you were talking about a calibration and adjustment procedure, but maybe VNAs don’t typically need such adjustment, since they are designed to be constantly calibrated to each new measurement setup anyway.Presumably there has to be some sort of baseline calibration required though? i.e. What does a calibration service do when they check your VNA for calibration?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 08, 2020, 01:22:55 am
content: Hi,Genrad made two kinds of standard inductor. The better 1482 series were wound on steatite core. These are essential air cored. The Steatite, like the marble used by Tinsley has a very low coefficient of thermal expansion.The 1481 series described here:https://www.ietlabs.com/pdf/GR_Experimenters/1950/GenRad_Experimenter_Dec_1950.pdfThese were wound on dust cores. These have a higher Q but they are not as stable.I think if you were to wind your standards on low permeability MPP cores you will get performance that this similar to the 1481 series.I have two 1481 series inductors. They are marked 'secondary standard'.I measured the 200mH 1481 with my (uncalibrated) HP4274A:This shows how the Inductance and Q changes with frequency.I don't know the age of my 1481, but it is between 50 and 70 years old.I expect that you will give similar results if you make your standards on MPP cores. They may be good enough for the intended purpose.Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 08, 2020, 02:55:51 pm
content: Hi group,I made an attempt a recreating the Genrad 1482 1mH inductor using materials on hand.The coreThe core is an Arnold A-930157-2xxx 157, the 157 is the ALvalue 157nH/N2I believe that this crosses to Magnetics Inc MP 106125 - xThe xxx 125, the 125 is the relative permeability.I have had this core a long time. It is smaller than the ones used by Genrad.CalculationN = SQRT ( 1000uH /157nH) = 80 turns.WindingI wound 80 turns of 22awg wire. This produced a single layer winding:The winding was immobilized with homemade Q dope. This is made by dissolving old polystyrene peanuts in lacquer thinner. You have to use old peanuts made from real polystyrene. Some new 'eco-peanuts' are made from corn starch.AdjustmentI had to remove two turns from the winding to get a nominal value of 1000uH. This may be due to permeability tolerance or I lost count when winding.MeasurementI used an HP4274A for the measurement. The HP 4274A allows me to select the test frequency, in steps, and the drive level.Similar to the original GR 1481, the inductance increases with ac current.7mA of AC current at 1 kHz increases the measured inductance by 0.25%.(This is lower current than the GR original, but my core is smaller. So probably similar flux density).Regards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: September 08, 2020, 03:07:24 pm
content: Thanks very much for testing your own 1481 inductors. Always appreciate your willingness to spend time in your own lab. They look pretty good to me, although the datasheet indicates that the inductance of the 100uH version will increase by about 0.075% @ 100KHz, and the 1mH version will increase by about 1.5% @ 100KHz. On the other hand, the HP 4332A is calibrated at 100KHz, and calls for calibration with the "better" 1482 air-core model. But, the 1482, with more turns and more capacitance, has even lower resonant frequency compared to the 1481. So, how does HP rationalize calibrating the 1000uH range with a standard inductor that doesn't hold up very well at 100KHz?https://worldradiohistory.com/hd2/IDX-CATALOGS/IDX/General-Radio/General-Radio-Catalog-R-1963-OCR-Page-0182.pdfThe 1481 datasheet shows they are wound on MPP cores. I think dust core is just a catch-all name for powder/distributed air-gap cores.By the way, what do the "little zeros" signify in the Q measurement @ 1KHz and 4KHz?

author: TimFox
author_rank: Super Contributor
timestamp: September 08, 2020, 04:27:47 pm
content: I don't own that instrument, but I assume that the ".oo" means that the zeros are not significant. The Q values of 139 and 293 are only significant down to the "9" and "3", respectively, which are > 0.1% of the value..

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 08, 2020, 05:16:24 pm
content: Hi,I suspect that the Genrad 1481 inductors were no longer in production in 1972 when the HP 4332A was introduced.The 1481 Inductors are not in the General Radio 1973 catalog that I found here:https://www.yumpu.com/en/document/read/22518496/genrad-general-radio-1973-catalog-iet-labs-iet-labs-incThe HP4274A LCR manual has this to say:and this is the list of equipment required:The HP 4274A has an accuracy specification of 0.1% on the best ranges. The accuracy changes depending on value and frequency.No mention of standard inductors.Big Zero and Little ZeroA big zero is a significant 0The little zero is a less significant 0.The 4274A (and the 4275A) use this to indicate a level of uncertainty, as oppose to presenting meaningless data. I use these as a clue to increase the signal level or change frequencies.Fit for purposeInductors normally have reasonable tolerances and since most practical inductors change with bias current, temperature and frequency a great deal of precision isn't normally required.For calibrating a HP4332A the Inductor I made would be absolutely fine. I would use it as a transfer standard. I would measure it on a good meter under the same or similar conditions as the 4332A and then adjust the 4332A accordingly.The MPP construction using low permeability materials is fine for this purpose.Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 08, 2020, 05:57:34 pm
content: Hi,I found this paper:https://pdfs.semanticscholar.org/1fc6/ce314b28f6d461ea155e17cf047e09a595f7.pdfThe title is "EVOLUTION OF THE ITALIAN NATIONAL STANDARD OF INDUCTANCE"Interesting reading.Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: September 09, 2020, 05:03:09 pm
content: Quote from: Jay_Diddy_B on September 08, 2020, 05:16:24 pmThank you. That's very interesting (and logical) that the HP 4274 does not bother to calibrate to a standard inductor. The HP 4332A specifies the 100uH and 1mH versions of the GenRad 1482. The SRF is 2.2MHz for 100uH, and 800Khz for the 1mH. The 100uH version's final adjustment is made at 10KHz, and the 1mH at 1KHz. How can you reliably calibrate a 100KHz measurement range to an inductor with unknown (but likely higher than "nominal") at the 100KHz test frequency?It must not be absolutely critical. Or, is it possible HP has accounted for the fact that the GR 1482 willnotbe a true 100uH or 1mH @ 100KHz? i.e. The meter is really calibrated to a 1.107mH inductor, as an example, if that was the nominal value of the 1482-1mH @ 100KHz.It's true that fretting over tenths of a percent of accuracy is not usually necessary for inductors, as 10% tolerance is considered good for most parts. It's only with very specialized resonant circuits that I've ever needed to consider less, but even then...5% is hard to do!In the coming days/weeks, I will make something like a 1481 clone and share the results here. I do not have much specialized equipment, but I wonder if I can show the ΔL/L (with respect to frequency or drive/bias current) via oscilloscope measurement. Obviously (to most), the absolute vertical accuracy of an oscilloscope is maybe 3%, so measuring absolute values of inductance this way is not accurate. But, may be able to quantify at least relative deviation from nominal.Thanks.

author: TimNJ
author_rank: Super Contributor
timestamp: September 09, 2020, 05:08:44 pm
content: HP 4332A standard inductor requirements below.

author: TimNJ
author_rank: Super Contributor
timestamp: September 09, 2020, 05:09:23 pm
content: Quote from: TimFox on September 08, 2020, 04:27:47 pmThank you. Got it!

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 10, 2020, 08:51:01 pm
content: Hi,I have playing in the lab againThis time I built a 100uH (nominal) inductor on my Arnold A-930157-2 MPP core (relative permeability 125).I wound 28 turns evenly spaced Litz wire on the core:Then I measured the inductor on my HP4274A:These are the results at 100 Hz, 1 kHz, 10 kHz and 100 kHz.Remember the little o indicates uncertainty.Impedance measured on a VNAI measured the impedance using a HP3577A and my clone of the HP35676A R/T Test Set.The scale is in dB.The marker is 0dB at 1.56 kHz, this corresponds to 1 j.The SRF is about 6 MHz.This is certainly good enough for calibrating an HP 4332A analog LCR meter.Regards,Jay_Diddy_B

author: TimFox
author_rank: Super Contributor
timestamp: September 10, 2020, 09:10:46 pm
content: Your litz wire: how many strands of what gauge? In coil design, the devil is in the details.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 10, 2020, 09:59:39 pm
content: Quote from: TimFox on September 10, 2020, 09:10:46 pmThe label has come off the reel. However counting the strands and measuring the OD and the resistance and comparing the results to the New England Wire Catalog.Link:https://newtcdn.s3.us-east-2.amazonaws.com/wp-content/uploads/2018/03/16104646/NEW_Catalog.pdfpage 135.I believe that I have:24 awg equivalentSingle nylon serving105 strands of 44 awgarranged 3 bunches of 35 strands eachThe OD 0.029 inchesNEW suggests this wire for 350kHz to 850 kHzRegards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 10, 2020, 10:12:59 pm
content: Hi,Given that I have 27 turns.AL= 102uH / 272= 139nH26 turns = 94uH27 turns = 102 uH28 turns = 109 uHYou can't make it precise. You can and want to make itstable.I would immobilize the winding with Q dope and mount in a diecast box supported by foam, like the Genrad 1481 if I was making it to keep.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 11, 2020, 03:46:53 am
content: Hi,Playing around with LTspice. Here is the equivalent circuit of the 100uH inductor featured in this thread:The cursor is on 1.At 100 kHz:The phase angle is 89.7oThis matches the impedance measured with the VNA.Regards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: September 11, 2020, 04:11:24 am
content: Thanks JDB! I understand that calibrating the 4332A is not incredibly difficult, given it's stated accuracy. At this point I'm just interested in standard inductors!As I only have litz in larger diameters, I may try litz for the 100uH coil inductor, and solid wire for the 1mH inductor. Unless I get lucky with permeability tolerances, I will likely need an additional trim toroid (or two). I'll put them in Hammond enclosures and possibly "pot" it with some GE Silicone II. I think this stuff is okay for electronics, and it is quite flexible.I suppose I'll calibrate to 100uH and 1mH @ 100KHz, differing from the 1481 inductors which are calibrated at 1KHz and 10KHz.

author: guenthert
author_rank: Frequent Contributor
timestamp: September 11, 2020, 04:43:38 pm
content: Quote from: Jay_Diddy_B on September 10, 2020, 10:12:59 pmYou can certainly have fractional turns. In fact, I'd think it's impossible to avoid them.

author: Magnificent Bastard
author_rank: Regular Contributor
timestamp: September 11, 2020, 04:55:04 pm
content: Quote from: guenthert on September 11, 2020, 04:43:38 pmOK. I'm interested in learning how to make fractional turns on a toroid that has a relative permeability of 125. Can you elaborate?

author: guenthert
author_rank: Frequent Contributor
timestamp: September 11, 2020, 06:28:12 pm
content: Quote from: Magnificent Bastard on September 11, 2020, 04:55:04 pmFirst and last turn won't be complete 360° (EDIT: make that firstorlast turn). Further, the e/m field doesn't end at the surface of the toroid. Calculating the exact value of a coil would be quite a challenge.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 11, 2020, 06:47:57 pm
content: Hi,My understanding is:1) Any wire that pass through the center of the toroid counts as a turn. If you wind a toroid and you remove a turn the inductance follows the formula that L is proportional to N2.2) The idea of using a toroid is that the magnetic flux is contained within the toroid, so it is self-shielding.3) If you add inductance by having loops on the leads, this is adding another inductor in series. The magnetic flux in these loops is not coupled to the magnetic flux inside the toroid. You are essentially adding leakage inductance.4) You can make transformers with fractional turns. These have flux balancing, (or controlling windings), but these don't work very well because of leakage inductance.Reference (Link):https://patentimages.storage.googleapis.com/9d/23/a0/bdd72ade91b576/US6348848.pdfJay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 11, 2020, 07:29:49 pm
content: Hi group,I have just finished building and testing a 10uH air cored inductor.I chose a circular cross-section for the winding. I calculated the size of the toroid to use a single layer of 105 x 44 awg Litz wire in the center.Fusion 360 and 3D printingI drew the core shape that I wanted in Fusion 360:and printed the core in PLAhttps://www.eevblog.com/forum/Themes/default/images/bbc/url.gifThe notches help get the spacing even and remove the need to count the turns when winding.Winding and coatingThe core was wound with 52 Turns of the Litz wire. Homemade Q-dope was used to immobilize the winding.The wire is about 3m long giving a resistance of 0.3The expected Q at 100kHz was 21MeasurementsHP 4274A LCR MeterHP3577A VNA - Impedance MeasurementsThe VNA gave the expected results 20 dB(10) at 159 kHzThe SRF is about 15 MHz.Regards,Jay_Diddy_B

author: KT88
author_rank: Frequent Contributor
timestamp: September 11, 2020, 07:40:45 pm
content: It would be possible to add one or more loops outside of the core. Vary number of turns and/or area....Edit: The previous post came simultanously - covers it already..

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 11, 2020, 07:45:40 pm
content: Quote from: KT88 on September 11, 2020, 07:40:45 pmYes, you can, but it is another inductor in series. It is not a fractional turn.Jay_Diddy_B

author: guenthert
author_rank: Frequent Contributor
timestamp: September 11, 2020, 09:13:55 pm
content: Quote from: Jay_Diddy_B on September 11, 2020, 06:47:57 pmI think the misunderstanding stems from different viewpoints on whatexactshould mean. A toriod will minimize the stray magnetic flux, but won't cancel it. There's a magnetic field around any conductor carrying current. The stray magnetic flux might be insignificant, particularly when the core is ferromagnetic, but it won't be null.

author: KT88
author_rank: Frequent Contributor
timestamp: September 11, 2020, 09:28:20 pm
content: QuoteThey are calling it5/8 equivalent turnsas an example, still having complete turns.If you prefer a truly single inductor you could vary the thickness of the toroid having different flux through different windings which would also give you an equivalent of a fractional winding...

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 11, 2020, 10:35:23 pm
content: Hi,We are getting a bit off topic with fractional turns.This is one example that I have seen in a product. Tektronix did this in the SC503 (and other SC50x scopes?) They put a flux balancing winding which is a figure '8' of magnet wire on the top of the center limb:This keeps the flux in each of the two outer limbs, on the E core, the same.A wire, for the CRT filament, is passed through one side of the E. This is a 1/2 turn.They showed this on the schematic:The SC503 was introduced in 1979.The patent is the same techniqueYou need the flux balancing winding because of Lenz's law. Without it, the flux would try and go down the other side of the E.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 12, 2020, 07:09:20 pm
content: Hi,Today in the lab I wound another 10uH toroid inductor. This time I used 23 awg enameled wire instead of 24 awg (equivalent) Litz wire. I could use 1 gauge larger because the diameter of the enameled wire is still smaller than the Litz wire.Before I share the results does anybody want to have a go a predicting the results?Here is a picture of the enameled wire inductor:Regards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: September 13, 2020, 12:33:48 am
content: My guess is that the results are indistinguishable!

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 13, 2020, 01:49:46 am
content: Hi,We can start with a resistance measurement. I used the HP 4328A Milliohmmeter on the 300mscale.( This is a similar vintage to the HP 4332A LCR meter it uses 1kHz and a phase sensitive voltmeter to detect the in phase component. The skin depth in copper at 1kHz is 2mm. So using 1kHz will not be significantly different than dc.)Enameled wireThis measured 205mThis is consistent with 23 awg.Litz wireThis is consistent with 24 awg equivalent.This measured 237mRegards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: September 13, 2020, 03:56:00 am
content: Thanks for sharing. I thought your question was about the inductance value (stability over frequency). For resistance, indeed I would expect litz to read lower.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 13, 2020, 04:12:20 am
content: Hi,Here are the results of the enameled wire inductor from the HP4274A:The Q is higher for the enameled wire inductor for frequencies 40kHz and lower. This is because the DC resistance is lower, the enameled wire is one wire gauge larger.At 100 kHz the skin depth has started to show and the Q for the enameled wire is similar to the Litz wire version.Network analyzerThe impedance versus frequency is very similar. The SRF frequency of the enameled wire is higher. This is because it has a smaller diameter and therefore lower capacitance.The difference between the Litz wire and the enameled wire isn't all that great especially if you increase the gauge of the enameled wire to the same diameter as the Litz wire.SummaryRegards,Jay_Diddy_B

author: ArthurDent
author_rank: Super Contributor
timestamp: September 14, 2020, 12:46:40 am
content: Years ago I would bid on Department Of Defense surplus electronic lots, sight unseen. Among other great stuff I got in one large lot that I got for about $0.25 per pound there were two sets (15 values each set) of GR 1482 series inductors that were removed from a calibration lab. That was one of the better buys I ever got.

author: TimNJ
author_rank: Super Contributor
timestamp: September 29, 2020, 03:55:27 am
content: So far, I've only had the time to wind one inductor, but I thought I'd share:For the 1mH inductor:CSC CM400060 (OD=40mm, 60u, MPP) "Bulk inductance"~110 turns of 0.45mm UEW enameled wireCSC CM127060 (OD=12.7mm, 60u, MPP) "Coarse adjustment"~20 turns of 0.45mm UEW enameled wireCSC CM039060 (OD=3.9mm, 60u, MPP) "Fine adjustment"~3 turns of 0.45mm UEW enameled wireThe first two cores are mounted to the housing using 3/8" rubber bumpers, with 3M VHB tape on top of the bumper to make a double-sided 3/8" bumper (if you will). Then, I flooded the housing with clear GE Silicone II. (No photo yet.) It's not the best consistency to work with. Regular flexible potting compound would have been better, but I cannot justify the price. $50+ to fill just two of these little Hammond enclosures.With the 40mm core only, the closest value I could get was about 1010mH@100KHz, which really isn't so bad. But, figured I could do better. So, I removed a turn and added the 1/2" (12.7mm) toroid. This got the inductance within ~0.2%, so I added a little extra inductance with the 3.9mm toroid to get within 0.1%. However, after finalizing the mounting position in the housing and after "potting" the inductors in some GE Silicone II, the inductance crept up to about 1002mH. So, I removed the small 3.9mm toroid. (Photo shows original configuration with fine adjustment toroid.)In the end, if you try to make your own, you could just get lucky and not have to bother with any of this.Also, winding 110 turns on this core requires about 5.5 meters of wire. Took me close to two hours and extreme attention to prevent the wire from kinking, due to its very long length.The meter I have access to (Extech LCR200) shows between 996 - 997mH @ 100Hz, 1KHz, and 10KHz, and 1000.9mH @ 100KHz. I'd like to check it on a TG + SA or VNA to check its resonant frequency. It seems that the inductance is increasing ever so slightly with frequency.