4-wire short - 2020 - Page 1
Forum section: electronics / projects

author: felixd
author_rank: Regular Contributor
timestamp: September 29, 2020, 08:49:09 pm
content: Howdy4-Wire Shortreplaces:* Keithley General Purpose 4-Wire DMM Shorting Plug Model 8620 and 8610* Fluke 884X Short 4-Wire Short* HP, Keysight 34172B Calibration Short for Digital MultimetersFeatures:* Gold plated PCB - ENIG (RoHS)* 18 mm long, 4 mm gold plated brass banana plugs with twisted springs from Stabuli (MultiConnect) with 0,2 mOhm contact resistance(springs are made from rigid hard-drawn copper alloy sheet)* M4 screws / holes in PCB have 4.3 mm diameter* materials are selected to have minimal thermal EMF voltage* holes separation: 19,05 mm x 19,05 to 34,50 mm (should fit almost any bench DMM)It's just great, universal 4-wire DMM input short. I am looking for people who might be interested in buying one of those. Main advantage of this project are better bana plugs that are going to be used. They are longer (18 mm) and have slightly better contact forces/lower resistance(twisted spring)Thank toJay_Diddy_Bwe were able to test 3D printed prototype on many different DMMsMore pictures are in his response to this thread:https://www.eevblog.com/forum/projects/4-wire-short-2020/msg3259760/#msg3259760Example from HP 34401A:Edit: We havev1releaseThis project is "under design" since I am waiting for Your requests for PCB variants. Should we make one universal PCB or ones with exact plug separaion? What is your opinion?

author: ArthurDent
author_rank: Super Contributor
timestamp: September 29, 2020, 10:46:04 pm
content: One modification I've made on banana pins to be sure there is good contact is to slide the springy sleeve thingy to the end where the wire connects and solder the sleeve just at that one end. It is important to slide the sleeve to one end before soldering or the sleeve may not compress properly. I found with some pins that may be of lesser quality or contaminated that there wasn't the best contact between the sleeve and the inner pin. I first noticed this on some leads that were rated 20A (and had 254 strand wire) That I was testing at rated load that had slightly higher drop than I expected. If I were using these leads with a power supply I'd use remote sensing to compensate for any drops but I wanted to see how the leads reacted to carrying 20A.In this application and with good quality gold plated pins like those shown, and basically no current flow, this probably isn't a real problem.

author: eblc1388
author_rank: Frequent Contributor
timestamp: September 30, 2020, 07:05:24 am
content: Quote from: ArthurDent on September 29, 2020, 10:46:04 pmYou would think they would use brass for the inner pin?Check if the inner pin is not made of iron, as it will cause excessive voltage drop. I just binned some of mine which stuck fast to a magnet.

author: ArthurDent
author_rank: Super Contributor
timestamp: September 30, 2020, 07:11:55 pm
content: Quote from: eblc1388 on September 30, 2020, 07:05:24 amWhen I say the leads had “slightly higher” drops I was talking of the scale that I’m measuring on my LTZ1000 10.00000VDC voltage reference where I had to be concerned about which end of a 3” long wire I sensed the voltage from. For average use I’d never notice the difference but I was curious to know what the lead resistance and voltage drop of these 20A leads were.The high current leads I bought have banana pins that are not steel and use 254 strand silicone insulated wire that is very flexible. Most of the lower power leads I have are Pamona which are high quality and do not have steel in the banana plugs.Long ago I had some ultra cheap alligator jumpers that had 7 strand untinned copper wire that wasn’t even soldered to the clips. The insulation on the wire was just stripped and the bare strands bent back over the insulation and then lightly crimped into the clip. The boot over the clip was stiff plastic and you needed pliers to pinch hard enough on the clip to open them. If I pulled on the wire while holding the clip the wire would easily pull out of the clip. As you might imagine the resistance of these short leads was quite high. I got rid of those leads the same day I picked them up at a flea market.Back on topic, for the board used for the shorting plug, I like the one with the slotted holes that would be universal. I would like to see the 'HI' and 'LO' screened on that board along with the broad lines between holes to visually indicate that all pins are connected together.

author: bdunham7
author_rank: Super Contributor
timestamp: September 30, 2020, 08:06:40 pm
content: I'd like a version that is not actually shorted so that other things can be made, or it can be shorted if you wish.I'd also second what Arthur Dent said about the rotating bits, I'd rather have a good-quality fixed banana plug like the old Pomonas. I always get a little bit of resistance and noise from the spinners after a while, even good ones. I solder them as well, but I always feel I might be giving up a bit in thermal quality when I do that, especially with gold plated.

author: felixd
author_rank: Regular Contributor
timestamp: October 01, 2020, 09:44:39 am
content: Should do the job. Contacting manufacturers for gold plated version.

author: felixd
author_rank: Regular Contributor
timestamp: October 01, 2020, 07:15:42 pm
content: Updates: PCB holes separation have been corrected a bit. They should now easily handle:X = VerticalY = Horizontalt* X = 19.05, Y = 19.05 mm (0.75'' x 0.75')' - HP 34401A, 34410A, 34460A, Keithley 2000/2001/2002/2010/2015, Advantest R6581T, Rigol DM3068, Siglent SDM3065X* X = 19.05, Y = 22.225 mm (0.75"x 0.875") - HP 3478A* X = 19.05, Y = 25 mm (Datron 4708)EDIT: * X = 19.05, Y=34.5mm -> Datron 1072 (thanks "doktor pyta") ... now it's time to think if we can fit those all sizes on one PCBI have also contacted Stabuli, they give 1 year warranty for their products. Catalog states also that they should survive 1 million mating cyclesWell...for sure I should receive some free samples for all those ads I am doing for them

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 01, 2020, 09:27:04 pm
content: Hi,This is a picture of an official Keithley 4W-short:Notice how the tracks are placed on the board. This is arranged to measure the resistance of a wide track that is very short.This is from this message:https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/msg999334/#msg999334In this message I built my own version.Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 01, 2020, 09:39:06 pm
content: Hi,When you build the short like Keithley did there is a right way and wrong way to use it.Wrong wayRight WayDetail[ Specified attachment is not available ]Regards,Jay_Diddy_B

author: Cerebus
author_rank: Super Contributor
timestamp: October 02, 2020, 12:33:04 am
content: It's a 4-way short for establishing a zero input for offset calibration, not a 3000ppm/C resistance standard.Assuming the worst case 23.5resistance, and a (worst case for a decent meter) 1 nA leakage current heading in exactly the wrong direction, that will result in a 23.5 nV offset error when using it as a short. That'll be less than 1 LSB on anything less exotic than an HP3458A. I personally wouldn't copy the Keithley style layout, I can't see any good reason for it*, and would personally opt for a solid pour (faster thermal equilibrium would be my theory for this), but I also can't see the Keithley design realistically causing any practical problems as a 4-way short.*If someonedoesknow of a good reason why Keithley did it that way,pleasespeak up. It looks like a deliberate choice, and I've seen a lot of very fussy, careful PCB layout in Keithley kit, so it'd be unlike them to just chuck any old layout at the board. Or, it's so non-critical in design that they just let the layout junior get on with the job with a spec of "just short all four pins together".

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: October 02, 2020, 05:40:48 am
content: Quote from: Cerebus on October 02, 2020, 12:33:04 amFluke has a good discussion of shorting devices for high-resolution DVMs here:https://au.flukecal.com/literature/electrical-calibration/watch-out-those-thermoelectric-voltages-cal-lab-journal-reprinttwo design goals for the device are low thermal EMFs, and low thermal mass. The latter means the temperature difference between the shorting device and the DVM quickly settles, but not to 0. From the article, discussing a setup with an 8.5 digit DVM:QuoteFluke recommends gold flash on PCB traces, to prevent oxidation (hence lower thermal EMFs). The Keithley and Fluke approaches differ greatly.

author: felixd
author_rank: Regular Contributor
timestamp: October 02, 2020, 07:01:44 am
content: Since I haven't provided public link yet to the project sources and notes I will do it now:This is mydirty development and notes branch! WIP - Work in Progressone but hold some more information and good links.https://gitlab.com/metrology101/hardware/4-wire-short/-/tree/felixdOnce project is finished (first release, PCB manufactured) it will be merged into master branch.Right now I am more focused on physical board shape. We will focus on traces once, first step is doneI have some nice idea btw for this project. Stay tunedBTW,https://www.keysight.com/en/pd-1108290-pn-34172B/calibration-short-for-the-34401a-34410a-34411a-l4411a-digital-multimeter?cc=US&lc=engDoes it also shorts Current input with LO? What's the good (any?) reason for doing that?

author: Cerebus
author_rank: Super Contributor
timestamp: October 02, 2020, 02:05:32 pm
content: Quote from: thermistor-guy on October 02, 2020, 05:40:48 amYeah, I perhaps should have been clearer. I was thinking in terms of reasons for the specific trace layout that Keithley choose, with that anaemic trace connecting two much heavier traces. I can't see any logic behind that particular choice. In terms of thermalmass, the pins are considerably more significant than the traces so simply reducing the mass of copper on the board can't be the driving force in the decision, and they'd have made all the traces very thin if it was.

author: felixd
author_rank: Regular Contributor
timestamp: October 02, 2020, 04:00:59 pm
content: Updates, updates, updates.There was a request in the beginning of this journey to fit Datron 1072 inputs with this project. I believe it has been done!By a mistake I took 25 mm as vertical separation (it's from Datron 4708). Real distance is 34,5 mm. This is being reflected in this update. Final mechanical layout I truly believeNow it's to do quickly redraw it in KiCAD. I will post an update soonBoard will fit HP 34401A. If you have any objections, You think that this PCB won't fit your DMM please let me know while there is still chance to make changes.Stay tuned.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 02, 2020, 06:07:05 pm
content: Hi,Here are some files for those playing along at home.I drew 1/4 and then mirrored it twice to get the full design.I have attached the Fusion 360 file and the STL file.I have 34401A, 3457A, K2001 and Datron 1281. I will print and try.Regards,Jay_Diddy_Beevblog_felix_4W_short.zip(68.79 kB - downloaded 91 times.)

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 02, 2020, 06:51:19 pm
content: Hi,Here are some photographs from a non-functional prototype.AssemblyDatron 1281 26mmHP Agilent 33401A 19.05 mmKeithley 2001 19.05mmHP 3457A 22mmIt looks okay to me, at least on the front terminals.Regards,Jay_Diddy_B

author: felixd
author_rank: Regular Contributor
timestamp: October 02, 2020, 07:05:45 pm
content: Jay_Diddy_B Thats greatThanks a lot. Can you also checkhorizontalinstallation in 34401A (front and rear)? Rear is specially need as we are "tight" thereMy F360 files:https://a360.co/3jpQ9Rr- boardhttps://a360.co/3nfaBH2- aseembledhttps://a360.co/3in6mpd- assembled - sandwich

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 02, 2020, 09:03:10 pm
content: felixd and the group,I just did aa test on the rear terminals of a HP 34401A:It looks okay.I also joined the two Fusion 360 models together, to check that they are the same:They are the same.Regards,Jay_Diddy_B

author: felixd
author_rank: Regular Contributor
timestamp: October 02, 2020, 11:09:46 pm
content: Thanks a mill!So my caliper and sheet of paper measurements were correctLet's call this mechanical drawing as done. I will post more updates in the morning (it's 1 AM in Poland now).Cheers and thanks again for help.

author: felixd
author_rank: Regular Contributor
timestamp: October 04, 2020, 10:45:21 am
content: FCC, CE, RoHS marks placed. Now we can go for mass production.Anybody in need of such a solution we are fighting here for last few days?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 06, 2020, 10:30:51 pm
content: Hi felixd and the group,I took a little time today make a couple of prototypes using my LPKF Protomat c60.3D Model from KICADBoardsI made two boards. One has the obvious X pattern. The other is in the Keithley style H pattern.Which do you think will be better?Regards,Jay_Diddy_B

author: coppercone2
author_rank: Super Contributor
timestamp: October 07, 2020, 04:01:43 am
content: Why not just get a thick copper block, then drill and tap 4 holes in it to make the short, without the PCB?If you use thermal shielding compound (its like wet tissues), you can braze the banana jacks.I think it would be better because then you don't need to buy a PCB to make it. It should work as one piece and spread heat better also, from touching it, then you can add bakelite handles to make 'handling' insulators. I think clamping on epoxy is always going to be less stable then solid metal, I am just not sure about how thermal EMF looks like, but if its built heavy, it should equalize really well?

author: Vgkid
author_rank: Super Contributor
timestamp: October 07, 2020, 10:26:13 am
content: @Coppercone2That would work as a low resistance, but due to its massit would never reach thermal equilibrium, and would induce a large thermal emf.

author: mawyatt
author_rank: Super Contributor
timestamp: October 07, 2020, 01:23:33 pm
content: Early this year we developed a few of the direct plug-in type PCBs for use with our HP34401A, Agilent 34401A and KS 34465A. These are 42.3mm square, have 19.05mm plug spacing in both directions, and fit the front and rear terminals of the mentioned DMMs.Best,

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 07, 2020, 05:58:05 pm
content: Hi,I am going to share some measurements that I made using an IET LOM-510A Micro-Ohmmeter.Link:https://www.ietlabs.com/lom-510.htmlThis may be one of the best instruments available for measuring very small resistances.The 4W-shorts are directional. The best results are obtained if you connectedSource + to Source - with a thick traceSense+ to Sense- with a thick tracea short, wide trace connecting the two together.I am going to call this the preferred orientation. The other orientation I will call non-preferred.Keithley DesignPreferred OrientationThis reads 0.000 mThis make sense, you are measuring a very short, very wide track.Non-Preferred OrientationThis measures 20.23 mYou are measure a long, thin track.Universal Design (Keithley Style)Preferred orientationThis is a very wide, very short track.Non-Preferred Orientation28.17 m\$\Omega\$. This makes sense, the track is a little longer than the design above.Felixd DesignPreferred orientation4 u(4 Micro Ohms)Non-Preferred Orientation1.389 mThe 'X' pattern is not as sensitive to the orientation as the Keithley 'H' style design. But, it is not as good as the Keithley 'H' in the preferred orientation.Note:The Datron 1281 requires a different 'H' design than the HP 3457A. The 'H' has to be rotated 90o.Regards,Jay_Diddy_B

author: coppercone2
author_rank: Super Contributor
timestamp: October 07, 2020, 08:07:45 pm
content: the instrument rack they tested it on is a bit suspicious, i suspect there could be a draft there from the instrument under it possibly, and its unknown what alloy its made of, and how the banana plugs are attached to the copper

author: tooki
author_rank: Super Contributor
timestamp: October 08, 2020, 02:39:17 pm
content: Quote from: felixd on September 29, 2020, 08:49:09 pmFYI, that’s “Stäubli” (pronounced ‘shtoyblee’), formerly Multi-Contact.Nice choice, I REALLY like their products.Quote from: ArthurDent on September 29, 2020, 10:46:04 pmDon't do this to a Stäubli plug. These aren’t el-cheapo plugs, in fact, they’re ultrapremium ones that make Pomona look like trash. (And I say that as someone who likes Pomona products!) They absolutely do not need that to make good contact. In bad plugs it’s needed to overcome excessive tolerances and awful plating. Stäubli plugs have excellent plating and insanely good tolerances. The spring “basket” (as they call it in German) fits very snugly onto its shaft, requiring a bit of force to move.Also, wouldn’t solder potentially cause more thermal EMF problems, since it introduces another metal to the mix?

author: Cerebus
author_rank: Super Contributor
timestamp: October 08, 2020, 03:43:38 pm
content: Quote from: tooki on October 08, 2020, 02:39:17 pmNot really, think of each dissimilar metal to metal contact as a little temperature dependant battery, then draw a circuit of the metal/solder/metal contact - two temperature dependant batteries back to back with close thermal coupling => no potential difference across the whole assembly, the two dissimilar metal interfaces cancel each other out. Still, like you, I don't like the whole idea on principle.

author: tooki
author_rank: Super Contributor
timestamp: October 08, 2020, 05:04:53 pm
content: Quote from: Cerebus on October 08, 2020, 03:43:38 pmOhhhh, gotcha, that makes complete sense!

author: mawyatt
author_rank: Super Contributor
timestamp: October 08, 2020, 05:15:32 pm
content: Quote from: Jay_Diddy_B on October 07, 2020, 05:58:05 pmThat's some really good 4-wire short readings!!I get ~50 micro-ohms with a KS34465A using the resistor calibrator rotated shown above your post.Best,

author: DavidKo
author_rank: Frequent Contributor
timestamp: November 18, 2021, 06:58:31 pm
content: After many thoughts I have created version with 2 distances and various connecting wire width.If someone interested the KiCad pcb files and gerber files from production tohttps://github.com/konarik/4-wire-short.Some pictures below

author: bdunham7
author_rank: Super Contributor
timestamp: November 18, 2021, 09:03:54 pm
content: Quote from: DavidKo on November 18, 2021, 06:58:31 pmThanks for posting that. What banana plugs did you use?

author: DavidKo
author_rank: Frequent Contributor
timestamp: November 19, 2021, 10:26:50 am
content: I have usedhttps://za.rs-online.com/web/p/banana-connectors/2263095In my case I have ordered them from Germanyhttps://www.buerklin.com/en/4-mm-Panel-plug-Screw-connection-0-5-mm%C2%B2-4-mm/p/12F168I already find some flaws/possible improvements:distance is not marked on the PCBYokogawa uses different distance between posts (probably 20mm)connections need to be cut with a hack saw - the holes to them should be addedmaybe it is better to pick one width of middle wire and use various spacing between holes to have one universal PCB

author: sequoia
author_rank: Unknown
timestamp: December 28, 2021, 07:39:10 pm
content: Quote from: DavidKo on November 18, 2021, 06:58:31 pmThanks!Btw, I tested uploading the zip file from github to JLCPCB, and from the preview (and 3D gerber viewer on the size), it looks as if the 3x3 panel won't be routed?Only showing holes for the banana plugs.... Is that to be expected?

author: DavidKo
author_rank: Frequent Contributor
timestamp: December 28, 2021, 07:59:09 pm
content: Quote from: sequoia on December 28, 2021, 07:39:10 pmIn jlcpcb 3D viewer you should see thin milled shape, but the scrap material is still there. I have not found what I'm doing wrong. In theory the scrap material shoud not be shown.Final result you can see on the picture in my posthttps://www.eevblog.com/forum/projects/4-wire-short-2020/msg3821228/#msg3821228.

author: jonpaul
author_rank: Super Contributor
timestamp: December 29, 2021, 09:32:01 am
content: Bonjour a tous: Just found this post now, fascinating reading.I think this iis a bit overwrought, and wonder any PCB at all? Why the 4 wire layout?My experience leads to a simple plane of copper.Also Both DCV (2 term) and resistance (4 term) should be checked.Experiment: Using a new Keysight 34465A warm up 2 hrs , ACAL.I have a variety of shorting plugs, some copper foil, gold plated foil and gold plated bananas, (eg from Gen Rad standard resistor).With the gold bananas bare copper foil across all 4 connectors, OR 4 mm wide copper braid no plating,About same with gold plated copper sheet or HP CAL shorting from 4195A. \\DCV 200 nV4 wire R ~500...800 uOhmGood enough for me, the meter seems in CAL and in SPEC.problem solved, NO fancy 4 wire PCB just a stupid sheet of copper foil and 4 holes.Your thoughts and critique?Bon Soiree,JonPS: The fancy bananas seem to have a very tight fit into the 34465A input, hard to remove.

author: tooki
author_rank: Super Contributor
timestamp: December 29, 2021, 10:37:24 am
content: Quote from: jonpaul on December 29, 2021, 09:32:01 amBecause of thermal EMF. See the attached PDF.

author: jonpaul
author_rank: Super Contributor
timestamp: December 29, 2021, 01:09:59 pm
content: Tooki: Fine paper on thermal EMF. I do not have a level of equipment like the Fluke 8508A of Mr Kidd , just the Keysight 34465AI believe that Thicker copper (than a PCB) gives more isothermal system.Found a Copper plate 44 x 76 mm , 3.175 mm thick, drilled for gold bananas, and added gold foil between the bananas and the plate.The 34465A is approaching 1 uV as it stabilizes.Finally I wonder why this thread is not in the Metrology forum?With Kind Regards,Jon

author: tooki
author_rank: Super Contributor
timestamp: December 29, 2021, 02:29:57 pm
content: Quote from: jonpaul on December 29, 2021, 01:09:59 pmThis concept has been proposed, and the response why it's a bad idea, earlier in this thread:Quote from: coppercone2 on October 07, 2020, 04:01:43 amQuote from: Vgkid on October 07, 2020, 10:26:13 am

author: jonpaul
author_rank: Super Contributor
timestamp: December 29, 2021, 02:54:50 pm
content: Very interesting discussion,I am getting 1..2 uV with the plate.Fluke paper mentions bare Cu wire as low mass and low thermal.I have some #24ga Bell System unplated, solid Cu insulated PVC wire, I will make another test with just the bare Cu and then the bare Cu wire on the gold bananas.Jon

author: DavidKo
author_rank: Frequent Contributor
timestamp: December 29, 2021, 07:10:49 pm
content: But this thread is about 4 wire short, not 2 wire like on your picture.I do not want to say that you are wrong. I have had the same idea at the start (take Cu plate, drill 4 holes and put bananas), but than I have read more about that and changed my mind. For sure you can use bare copper wire like is mentioned in HP 3458A manual.

author: Cerebus
author_rank: Super Contributor
timestamp: December 29, 2021, 07:53:33 pm
content: The point is being missed here. Yes, a simple wire short, of low thermal mass, is best. It is however completely useless with a meter with shrouded sockets instead of binding posts - e.g. HP 34401A. It is forthosestyle of meters that these PCB 4 wire shorts are designed.

author: Shonky
author_rank: Frequent Contributor
timestamp: August 02, 2023, 11:53:22 pm
content: Bit of a thread dig. I took @felixd 's design and made some "improvements"- There were a number of "bonus" (i.e. duplicate) tracks some of which threw up some DRC warnings. One was a track right in the middle of one of the holes- I made the tracks a bit smaller including the link track- I changed the soldermask to expose the link tracks so when getting ENIG finish, the whole track is ENIG. There's not a huge point in getting ENIG otherwise. You're just going gold to gold from the banana plugs on the pad then to the copper track then back to gold on the other pads. Yes this should largely cancel out any thermal EMF but better to just stay gold all the way. This necessitated moving the silkscreenPictures from my JLCPCB order.Update PCB file and gerbers attached too.I have a couple of spares that I can share basically at my cost (about $7 + say A$1 to post in Australia), if anyone wants one. Or just order your own from JLC or whoever.PM me if you want one.

author: coppercone2
author_rank: Super Contributor
timestamp: August 03, 2023, 02:01:20 am
content: if you really wanna be precise don't you need a tellurium copper PCB and tellurium copper plugs? preferably welded on.harder to make though. Best one would probobly be to weld 4x plugs to a copper plate, put it upside down in a fixture so the plugs are underneath, then grind it thin, glue it to a panel, then use a press to cut out the shape. and glue it to a thicker substrateno interconnects then.preferable equipment is a custom vacuum clamp grinding block, cbn abrasive wheel, micro plasma or micro tig torch, helium box, custom space rated bakelite panels, space rated epoxy. Not sure about cutting it into shape, I guess a custom die, or maybe a fast sharp router is good enough.

author: Shonky
author_rank: Frequent Contributor
timestamp: August 03, 2023, 02:19:13 am
content: Impressive sarcasm.

author: coppercone2
author_rank: Super Contributor
timestamp: August 03, 2023, 02:26:12 am
content: not really someone is probobly going to need the stability eventually?the other thread had super conductor shunt talk, that means copper shunts on superconductive substrates for 100 nanoohms

author: donlisms
author_rank: Frequent Contributor
timestamp: August 05, 2023, 03:14:35 am
content: Frank Wenner's article (a hundred years ago) on four terminal conductors has a whole lot of good theory that applies directly to these shorting devices, though that wasn't its original purpose. It shows why some of the intuitive approaches won't work, and provides background for how to do it right. (It also walks right up to the door of tetrajunctions, without really going through.)The other thing that always bugs me around these discussions is the lack of good explanations of Seebeck and thermal EMF. The potential difference(s) are within conductors that have different temperatures at their ends. A junction between the two conductors merely provides a place for the current to flow between them, and generally, a place to make one end of each conductor the same temperature. The difference in the two potentials appears between the other (non-joined) ends.It is not the junction that "generates" the voltage, as seems to be commonly thought. It took me nearly forever to dig up good explanations of this; there are so many explanations, even from otherwise authoritative sources, that say, or imply, that the voltage "comes from" the junction - the point of contact between the two metals. Having a more correct explanation helps deal with the issue more effectively, e.g. why plating has no effect, and other ideas.

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2023, 04:15:40 am
content: A junction is what everyone talks about because there is documentation that supports this, i.e. the voltage generated by different types of solder joints, and the use of specialty solders to reduce the effect. That is identical structures will generate different voltages depending on what solder you use, according to the documentation.And a standard thermocouple works by measuring the junction temperature,and different wires make different voltages.I don't see how you could get around talking about the junction? short and long thermocouples seem to work pretty much the same other then noise pick up. so do different wire gauges.

author: donlisms
author_rank: Frequent Contributor
timestamp: August 05, 2023, 06:37:26 pm
content: I suppose the main point is that the junction is not where the voltage "comes from". The potential is (pretty much) the same in both sides of the junction - the thermocouple voltage does not appear there. It's a different way if thinking about things than what some writers present.

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2023, 08:36:21 pm
content: but its important to think about the joint because its the parameter that you can change to reduce the effect.the plating increases drift by a order of magnitudehttps://www.edn.com/wp-content/uploads/5.3.01_Minimizing_thermocouples_maintains_20-bit_DAC_precision.pdf

author: mawyatt
author_rank: Super Contributor
timestamp: August 05, 2023, 09:06:18 pm
content: Quote from: coppercone2 on August 05, 2023, 08:36:21 pmBelieve that reference has an error in Figure 6, the op-amp is configured with the 500 ohm and two 500K resistors and has the op-amp inputs reversed. As shown it has positive feedback, which should be negative feedback for a stable result.Best,

author: alm
author_rank: Super Contributor
timestamp: August 08, 2023, 09:05:25 am
content: Quote from: donlisms on August 05, 2023, 06:37:26 pmI would love too see a detailed description of the Seebeck effect on the molecular level. Plating and oxidation makes a huge difference (see Jim Williams article posted by coppercone2), while it's hard to imagine there being much of a gradient across the plating: in copper-nickel copper, both copper nickel junctions would be at pretty much the same temperature. This suggests to me that there might be more to it than just two junctions with a different temperature across them.But I've not found a reference supporting this, so maybe I'm wrong and it is just about copper atoms on both sides of the plating being at different temperatures.

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: August 09, 2023, 03:40:48 am
content: Quote from: donlisms on August 05, 2023, 03:14:35 amThere is a good introduction, to the Seeback effect in thermocouples, in a National Measurement Laboratory monograph. The third edition (2004) is here:https://shop.measurement.gov.au/products/monograph-5?variant=1042647327I have the second edition (2003). There is bold text at the bottom of page 9:QuoteThe monograph also touches on the Peltier and Thomson effects, but states, in the context of metallic thermocouples (2nd ed. page 6):Quote

author: alm
author_rank: Super Contributor
timestamp: August 09, 2023, 01:53:09 pm
content: Quote from: thermistor-guy on August 09, 2023, 03:40:48 amThanks for the reference! The full text is available fromCSIRO(first result with "full text" written under it). I find this indeed a very helpful description that gives intuition for the physics behind the Seebeck effect, how it is really about the gradient across the conductor, and not about the interface. If you had material in between with a very high Seebeck coefficient relative to copper, but the material was entirely isothermal, then it wouldn't contribute towards the Seebeck voltage.

author: Miti
author_rank: Super Contributor
timestamp: July 11, 2024, 11:18:24 pm
content: Necro posting but it’s related.I,ve tried quite few banana plugs with this project, nickel, gold plated, but the best is a 5/32 copper tube from a hobby store. It doesn’t have the flexible contacts but it wedges well enough and after 15 minutes you’ll have a dead zero on a properly calibrated meter.Cheers,Miti

author: coppercone2
author_rank: Super Contributor
timestamp: July 12, 2024, 05:35:03 am
content: ehhh you sure that it won't damage your banana jacks? especially if your meter has gold plated ones, I would be really worried jamming copper in there. maybe you should cut a X into it and debur it very well to give it some complianceIts almost unheard of in precision mechanics to have jammed together pipes in a system that is meant to be assembled more then once. Every connector in exsitance pretty much uses proper spring shapes (tempered too).My guess is poor cycle life and damage to connectorsand it should also be polished, that looks rather gnarlyamusing if our calibration guy found that jammed inside of the fluke MFCklingons!!

author: donlisms
author_rank: Frequent Contributor
timestamp: July 12, 2024, 08:00:12 am
content: I have experimented with copper tubing also.It may be helpful to saw an end-wise slit into the copper tube and push something springy into the tube, to get some compliance.It might help to shape the tube leaves carefully to get good contact, but also make sure the cut ens of the tube is shaped so that it isn't scraping the inside of the socket.It may help to smooth and almost polish the surface, e.g. put the tube in a drill and use some very fine abrasive on it. At the very least, deburr any cuts.A quick investigation suggests that beryllium copper has horrible conductivity compared to pure copper, e.g. 15% to 30%. If that's what the tube is made of, it's something to think about.

author: Miti
author_rank: Super Contributor
timestamp: July 12, 2024, 04:51:12 pm
content: Quote from: coppercone2 on July 12, 2024, 05:35:03 amNo, no plating in the 34401 jacks, they are bare copper. I don’t jam them hard inside the jack, just a light push. And there’s a little flexibility in them. And you don’t use them every day but once a year to adjust the zero and eventually once in awhile to verify it, if necessary.

author: Miti
author_rank: Super Contributor
timestamp: July 12, 2024, 04:57:19 pm
content: Quote from: donlisms on July 12, 2024, 08:00:12 amYes, I thought about that but I found it unnecessary. Also, it looks rough in the picture but I polish it once in awhile with Scotchbrite. The material is pure copper.

author: donlisms
author_rank: Frequent Contributor
timestamp: July 13, 2024, 07:51:02 pm
content: Your confidence that it’s pure copper is inspiring… but if I may ask, how do you know? I might see those words on an auction site, for example, but don’t trust them! Maybe you have a more reliable and more technical source?

author: coppercone2
author_rank: Super Contributor
timestamp: July 13, 2024, 08:43:12 pm
content: you will know BeCu if you handle it compared to any kind of pure copper. its stiff as hell and you will feel it fight you with vibration/spring back. its unpleasant as a material to work with and you will immediately know something is wrong. Threading it by hand feels like fighting a spring lolalso its expenisve and toxic so don't sand thatits like normal bushes vs mean impale yourself on a stick bushes. if you ever made a bow and arrow when your young, its the wood you look for with to make a bow

author: Miti
author_rank: Super Contributor
timestamp: July 14, 2024, 01:17:52 am
content: Quote from: coppercone2 on July 13, 2024, 08:43:12 pmBeCu is expensive. It is used in some high quality connectors an specialty non-sparking tools, not in some hobby tubing.See here:https://ksmetals.com/products/cut014-5-32

author: Miti
author_rank: Super Contributor
timestamp: July 14, 2024, 01:20:01 am
content: Quote from: donlisms on July 13, 2024, 07:51:02 pmYes, I do. The manufacturer specifications. Now, there's nothing pure in this world as in 100% but it is copper.https://ksmetals.com/products/cut014-5-32

author: Miti
author_rank: Super Contributor
timestamp: July 14, 2024, 01:29:07 am
content: To be honest I did not expect this kind of replies. Don't damage the jacks, how do I know it is copper, what if it is Be-Cu, like I'm a complete idiot and I don't know what I'm doing, but nothing about the main goal, finding a solution that gives me the lowest thermoelectric voltage for calibrating the zero of a precision multimeter.34401A has copper plugs, I think 3458 also has copper plugs... I think.This is one simple solution that I found, it is not intended to be professional nor commercial.

author: Miti
author_rank: Super Contributor
timestamp: November 27, 2024, 01:21:07 pm
content: This is a more gentle version using these copper banana plugs, which should be pure copper. Also thinner so they should reach the thermal equilibrium faster.https://www.aliexpress.com/item/32810453016.html?spm=a2g0o.order_list.order_list_main.10.18e71802SYs0qR