Making Resistance Standards Similar to Leeds and Northrop Standards - Page 1
Forum section: electronics / general

author: ZGoode
author_rank: Frequent Contributor
timestamp: October 08, 2024, 07:34:30 pm
content: I looked around to see if anyone had tried to do this and couldn't find anything (although I could have just been searching for the wrong stuff). If someone has started a thread for this already please feel free to direct me there.I was wondering how difficult it would be to homebrew some resistance standards similar to the old Leeds and Northrop ones. I would love to have a standards set, but can't justify the eBay costs for a full set. I don't really care if my standards are say exactly 10ohms (or whatever value), more so I am looking for something that if it measures 10.12345ohms today, that it will still measure 10.12345ohms one+ years from now. I do have access to a recently calibrated 3458A (not mine, I wish it was) that I can use to record its aging over time. Any suggestions on where to start with for this and what would be the best materials to use here?

author: Victorman222
author_rank: Regular Contributor
timestamp: October 09, 2024, 08:20:04 am
content: The "easiest" way to make a resistance standard is to use a high stability commercial resistor. Here are some links for inspiration:https://xdevs.com/article/bsw104/https://www.eevblog.com/forum/metrology/my-first-10kohm-reference-resistor/https://www.eevblog.com/forum/metrology/teardown-standard-resistors/Or are you interested in winding your own resistors? Then these threads have some info on resistor construction:https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/https://www.eevblog.com/forum/metrology/manufacturing-custom-high-precision-low-tc-resistors/Also this article is very interesting to get an idea where real resistors TCR lies:https://xdevs.com/article/tcr_test/

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 09, 2024, 10:44:56 am
content: HelloIf you want to built a DIY resistor you needa box ( can ) can be a paint metal can cleaned , or a old metal coffe can or a nice bespoke made one from a stainless pipe piece ,an aluminium enclosre can do the job too4 banana sockets / post high quality as Pomona gold plated + one for the guarda round mandrel / core or a plate in bakelite or teflon or any quality material , teflon is nice as that quite cheap and easy to supply but a lot of resistor have built on bakelite .and the most important very high quality resistor wire , can be located on Ebay from some shop ( there is seller in Bulgaria with a nice range of wire )after you need to cut to length , test . adjust . solder .... and connect to 4 sockets / post by using quite stiff copper wiredesign is not complicated but making adjustment request a calibration equipment which is VERY costly .Most easy way is to built two ( on over the value one below the value ) with estimated resistance ( by length of wire or basic measurements ) send them to calibration and after you can use the two calibrated resistors to measure the value you want you a null meter in controlled temperature box as an air bath .Built a true xx.xxxxx resitor value is easier by using a foil or a ribbon and trim it with a file or abrasive to adjust , as you can trim without the request to desoldering / resolderingRegardsOS

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 09, 2024, 04:55:21 pm
content: Accepted wisdom is that to get the last ppms it's very difficult. That said, I've made nice standards from manganin, wound on a spider form, housed in glass jars from my wife's cosmetics. I install four terminals in the cap and a center rod to hold the spider. The L&N standards are wound with (I think) fabric covered wire on brass or other forms. The problem is thermal expansion probably affects them more than you'd hope. I tore down a Guildline standard and was surprised to see they just coiled the wire loose in the bottom. I've also taken apart Julie Research resistors and they also use a very loose wind on their coils. This leads me to believe a spider cut from whatever, with a loose wind, is a reasonable approach. L&N resistors probably went through one or more baking cycles to stabilize them. You should also read about making the 1 ohm NBS standards as they describe that quite well.https://typeset.io/pdf/a-new-design-of-precision-resistance-standard-4mtb5xjuhb.pdfhttps://nvlpubs.nist.gov/nistpubs/Legacy/circ/nbscircular470.pdfYes, oldies, but IMHO essential reading.

author: EC8010
author_rank: Frequent Contributor
timestamp: October 09, 2024, 06:22:35 pm
content: Interesting stuff, but I couldn't see a date for the first reference?

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 09, 2024, 06:40:00 pm
content: Hello1930 , printed last pagea very nice design is this onehttps://testequipment.center/Products/Leeds--Northrup-4361as ribbon it is easy to adjustRegardsOS

author: Victorman222
author_rank: Regular Contributor
timestamp: October 09, 2024, 09:28:35 pm
content: Thanks for sharing, Conrad. Could you please elaborate on what "a spider form" means? Is it like a former around which wire is wound like spider web?Quote from: Conrad Hoffman on October 09, 2024, 04:55:21 pm

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 10, 2024, 02:28:57 am
content: Not sure about the right terminology but long ago they made spider antennas and inductors. Do a Google search on radio spider wound inductor. Those exact words are fairly important. You took a round form and cut notches towards the center, creating something like flower petals. Then you wound the wire around, going over and under the petals. The advantage over a regular coil was very low self capacitance. I do pretty much the same, but keeping the wire loose so as not to introduce strain. The round form is mounted on a standoff in the center, up to the cap, cover or whatever, and sits in oil if desired.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 10, 2024, 06:29:05 am
content: HelloSpider web coil looks as the linked picture , the core looks as a flowerwiring of this type of coil is a bit .....to reach a perfect resultTinsley design ( see linked pics ) is easy to duplicate , comb allow to use non isolated / bare wireRegardsOS

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 10, 2024, 12:39:36 pm
content: Tinsley is nice, though if one has a small lathe it seems easier to make a "threaded" form and lay the wire in that. I suppose one could make the Tinsley spacers with a saw if carefully marked out.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 10, 2024, 02:10:23 pm
content: HelloYes that possible to use a small saw to cut the comb teeth , advantage of the combs compare to a groove / thread in the mandrel is the wire is fully in contact in the air and loose .As there is very low to no mechanical stress that also easy to wiringeasier solution for accurate adjustment is to use ribbon rather than round wire , adjustment can be done by reducing the width with a Dremel or a small file when you are near the value you wantCombs for ribbon can be done by removing teeth by using a fileCore can be done by using fiber glass tube available per metter / cut to lenght and combs can be done in plexiglass or ptfe or PEHD 1000 , that perhaps possible to make these parts by using 3D printerRegardsOS

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 10, 2024, 05:00:29 pm
content: We've been printing parts at work with a Bambu printer and the results are surprisingly good. There are materials with good properties, though I don't know how they react to being immersed in oil for a very long period of time. There are several filament materials that claim oil resistance. It would definitely be worth the experiment to create a nice former.

author: Gyro
author_rank: Super Contributor
timestamp: October 10, 2024, 06:01:30 pm
content: There's another, possibly clearer, picture in the (still current) Tinsley 5685 series datasheet...https://tinsley.co.uk/wp/?page_id=2610It is based on the UK NPL (National Physics Laboratory) F J Wilkins design rather than the NBS/NIST based one.P.S. It looks as if some degree of elevated temperature annealing treatment is still required for best stability. From the documents earlier in the thread (silk and shellac insulation) it looks as if the materials only need to be able to withstand 150'C though.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 10, 2024, 06:18:03 pm
content: Quote from: Conrad Hoffman on October 10, 2024, 05:00:29 pmHelloYes some new material are impressive in 3DI have some ceramic tube from high temp lab furnace , cut them is easy with diamond disk , drill them is possible with carbide drill and finishing with diamond grinding bits so making a core in ceramic is a possible project for the combs PTFE is the easiest material , PTFE + stainless screw + ceramic core allow 100 percent safe oil immersion at affordable costHousing / enclosure can be done by using refuse of inch pipe in SS304 pipe with a TIG welded base plateDepend if the initial choice is oil bath or air bath , for air bath 3D printing is the way to follow if the purpose is to avoid machining as mechanical tolerances do not need to be tight.RegardsOS

author: TimFox
author_rank: Super Contributor
timestamp: October 10, 2024, 06:25:42 pm
content: Another simple solution to the cylindrical housing is plumbing-fixture copper pipe fittings and copper or brass pipes.I built voltage-reference ovens using this style of cap:https://www.mcmaster.com/products/tube-fittings/shape~cap-and-plug/material~copper-2/Just putting a cap on one end of the pipe will give a reasonably tight fit and can be secured with tape.The resistor and connectors are mounted to that cap.The other end can be soldered in place.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 10, 2024, 06:45:54 pm
content: Yes, built lots of stuff out of copper pipe and caps. There are good lead-free solders now like Harris Bridgit.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 11, 2024, 06:38:48 am
content: Quote from: Conrad Hoffman on October 10, 2024, 06:45:54 pmHelloCrucial choice is to select insulated or non insulated wire or ribbon , I agree than copper pipe for insulated wire is an easy solution and also able to handle oil bath .a useful chart for plastichttps://www.plasticsintl.com/chemical-resistance-chartRegardsOS

author: EC8010
author_rank: Frequent Contributor
timestamp: October 11, 2024, 11:18:56 am
content: Not just ancient radios. I opened up my Jay-Jay Instruments decade inductor box (1mH to 1H). I suspect the term for the coils in this may be "wave wound" but they look very similar to the spider wound and are undoubtedly chasing the same low self-capacitance.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 11, 2024, 12:16:02 pm
content: HelloThat look as flat coil made by using twisted wireI link a drg of a spider coil coreWire is interwined between the core ''petals''RegardsOS

author: EC8010
author_rank: Frequent Contributor
timestamp: October 11, 2024, 02:16:17 pm
content: It does look that way, but I don't see any advantage to doing that, whereas an inductance box definitely needs low capacitance.Taking a coil apart would give a definitive answer, but I don't like to destroy it. I looked up the petal methodology and mentioned it to an elderly friend. Such coils were common as reaction coils in early super-regenerative radios and were hinged to allow the reaction to be adjusted. Naturally, the coil was a decent aerial and apparently such coils were banned because of the interference they could cause.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 11, 2024, 04:06:31 pm
content: HelloMost common use of the spider ''petal core'' is the coil for metal detector but I am not an expert in metal detectorMost standard resistor I have seen are built with a basic design IF that for DC currentRegardsOS

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 11, 2024, 08:48:43 pm
content: My hope, maybe wishful thinking, was that by keeping capacitance low the standard could be used up to some moderate AC frequency.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 13, 2024, 11:16:49 am
content: Quote from: Conrad Hoffman on October 11, 2024, 08:48:43 pmHelloOn low value resistor inductance seems also to be a concernhttps://www.zhinst.com/europe/de/blogs/inductance-smd-shunt-resistor-measured-mfiaTinsley doc provide 1.5 Hz as maximum allowed frequency to stay on the published values .RegardsOS

author: Gyro
author_rank: Super Contributor
timestamp: October 13, 2024, 11:28:52 am
content: Quote from: Overspeed on October 13, 2024, 11:16:49 am1.5kHz

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 13, 2024, 12:19:55 pm
content: Quote from: Gyro on October 13, 2024, 11:28:52 amHelloFollowing the Tinsley doc that 1.5 Hz except if there is an error on the doc.Other Tinsley ref are 400 Hz always if there is not error on the doc.RegardsOS

author: Gyro
author_rank: Super Contributor
timestamp: October 13, 2024, 01:01:58 pm
content: That's a comma, not a decimal point isn't it? same in the datasheet. Yes the cheaper 5695 is 1ppm to 400Hz, I don't think we have an image of the winding construction of that one.Hard to think they would specify single digit Hz to 3 decimal places in the datasheet. It just seems more plausible when you're talking 1592Hz.

author: ArdWar
author_rank: Frequent Contributor
timestamp: October 13, 2024, 01:12:30 pm
content: 1592 Hz was (allegedly) from10000 / 2π, making rad/s values in neat decades.It is one of the common measuring frequency for artefact metrology alongside the usual 1kHz.

author: Overspeed
author_rank: Frequent Contributor
timestamp: October 13, 2024, 01:15:20 pm
content: HelloOk that a comma and not a point so a typical UK/US systemI never use AC so as far that OK for DC /Pulsed DC that OK for mea xdev webpage with some ( all ? ) Tinsley modelshttps://xdevs.com/review/tinsleyres/85 and 95 are no the same , not the same connectors not the same housing ...RegardsOS

author: TimFox
author_rank: Super Contributor
timestamp: October 13, 2024, 02:26:11 pm
content: Quote from: ArdWar on October 13, 2024, 01:12:30 pmMy Wayne-Kerr B221 admittance bridge operates at 1592 Hz for that reason.An early 1950s model, the manual for which includes a table of reciprocals for those missing their sliderule.The bridge shows negative capacitance when measuring an inductance: it is the capacitance that would resonate that inductance at 1592 Hz.

author: Victorman222
author_rank: Regular Contributor
timestamp: October 13, 2024, 06:46:11 pm
content: What about the kind of wire that the standard is wound with?For the materials, as i see it, there are two main kinds: the manganin like materials (manganin, constantan) and the nichrome style materials (nichrome, evanohm). The nichrome materials cant be soldered so they don't seem to be very suitable for diy. A shame since evanohm alloys seem to have better TC and temperature range than manganin.Then choosing between manganin and constantan, it is said that manganin is more susceptible to mechanical stress than constantan, but constantan has a huge thermal EMF with copper of about 40 uV/K. Maybe the TEMF issue could be fixed by having the constantan wires soldered to copper wires at a point that equalizes their temperatures, for example a ceramic chip (like it's done in low TEMF reed relays).After we chose our wire material, there is the question of what kind of insulation to get. There are three main kinds avilable: bare wire (no insulation), enameled wire, and enameled wire with silk over it. Bare wire seems only suitable for lower resistance values. Enameled wire is good but with smaller diameters like 0.05mm manganin is easy to rip by hand. On the other hand the silk insulation 0.05mm wire is stronger, but there may be a problem with humdity dependence as the silk expands/contracts as described in the NBS circular 470.Also sometimes there are different anneal? grades, for example with the soviet wires there are: MT MM MС - manganin hard, manganin soft, and manganin stabilized.It would be very interesting to hear your thoughts. Have you had any experience with the different wire materials and insulation types? Have i misunderstood or missed something important?

author: shabaz
author_rank: Frequent Contributor
timestamp: October 13, 2024, 08:00:41 pm
content: Quote from: Victorman222 on October 13, 2024, 06:46:11 pmThey can be ferruled though : ) Although whether you'd want to do that or not, I have no idea, since once it is done, you'd have to find some alternate way of trimming since it's not a very reversible thing.Photo shows ferrules on resistance wire (manganin; I didn't try soldering it directly), but this wasn't a resistance standard, it was just intended to be a dummy 4-ohm/8-ohm load which worked for several hundred watts. I didn't notice any change in resistance after subjecting it to that, but again I wasn't looking out for the same performance as a resistance standard so I can't comment on that. I doubt I checked beyond a few digits but I can't recall. For a standard, I imagine you'd want to protect from even faint oxidization, so possibly it wouldn't be good to have bare wire like this in free air. But I'm speculating, I'm not an expert.

author: ZGoode
author_rank: Frequent Contributor
timestamp: October 14, 2024, 03:11:22 pm
content: I wasn't expecting this many responses to my question, lolThese are all great tidbits of information! Since I already have some basic nichrome on hand, I'm going to try and practice some of the techniques I see here before I try and replicate them using expensive manganin or evanohm wire. This might be the excuse I have been looking for to buy one of those small jewelry welding torches

author: bsdphk
author_rank: Regular Contributor
timestamp: October 14, 2024, 04:53:46 pm
content: I read a personal recollection of the history of resistance standards some years back. (Possibly one of the founders of ESI?)One of the first thing he mentions is that people thought they had soldered connections, but what they really had was a blob of solder holding a loose wire in proximity with the terminal.He mentioned point-welding as the solution, and that's certainly inside the DYI perimeter.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 14, 2024, 05:36:57 pm
content: A good place to start-https://www.eevblog.com/forum/metrology/manufacturing-custom-high-precision-low-tc-resistors/