what is the deal with DC shorts and offset - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 12:10:59 am
content: So I have two shorts I made up for my newly repaired Keithley 2001One is a double banana jack (pomona) with a piece of 14 AWG copper bare wire (from the wall) soldered across the turret terminals. This one gets close to zero in the meter.I just made another one that I thought would be better, this time from 12 AWG soft magnet wire that is soldered into two banana jacks to make a U shape. These are the banana jacks that have the screw on plastic bit. I soldered it maybe 1/2 hour ago. The offset from this one is massive (3.6uV instead of 100nV). If I reverse the polarity, the polarity of the offset changes. This makes me think thermocouple. The wire is bent into a U and soldered into the well.Is this just because the heavy assembly without plastic is sinking heat away from the meter and making a thermocouple? Or is it from the plating type? The solder is the same on both of them.35 min later:This one just does not want to settle, even after 30 min. I thought it was better made because I don't know how the pomona solder turrets are mounted on the dual connector. I had them basically "spin" before on a damaged connector, which made me think it might be some mechanical seat (not one piece)....It was at 3.4 microvolts after settling for 1/2 hour in the meter. I just put the pomona one back in, and it settled to 0.2uV immediately.Am I correct in thinking that this thing is too good of a heat sink for the front panel that its making a inordinate amount of heat come out of the front of the meter? because there is air flow around the U shaped wire, where with the other one it has a plastic part blocking air flow in the middle of the arc. ?I am going to try it in the rear connector. I thought to pot it in a container of clear epoxy mixed with fiberglass too (low thermal conductivity), like a matchbox, so all the exposed metal is covered.What would a good one look like? I thought to bend egg-beater terminals out of fine silver plated spring copper wire, since it carries no current. Would that be good? It should have a high degree of thermal isolation from the banana receptacle body.Hmm its doing alot better on the back of the meter. I think its because its a U shape and it was hanigng off the table making alot of air flow. I stuffed a sock in the U and on the back it already dropped down to 1uV. Actally I wonder what would happen if you mix epoxy and like powdered or sanded styrofoam, like with a rasp. The pink one that is really good.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 02:53:16 am
content: oK SO Like the room temperature was swinging and everything was going wildWhat I did is I got a piece of silver plated spring brass (not copper) about the thickness of a good resistor lead, and bent a [ clip out of it with like P's on each end of the [ so it kinda sits in the banana hole (using round pliers and carefully adjusting it until it fit snug but not tearing it up, and I wrapped the exposed part of the [ with a cotton cloth.High precision mode with filter set to 100 counts (not advanced filter), it gets ~000.0002 with it going as low as 000.00003 sometimes, I can feel room temperature swinging a little because of computer use.I think I have proper BeCu spring that is silver plated thick some where to make another one thats better then brass of the same kind, and it will get a small styrofoam grip and insulation.Lol, I have all these different jumpers and I can't tell. It could just be the meter fooling me. My big jumper with the 12awg wire is definately bad, but as for the other ones I can't really tell the difference. Maybe the thin brass one seems like the best... it seems like it jumps around the least, but I thought the spring copper one would be the best but it looks like it jumps more. I guess I would need computer data logging and long time periods and enviromental control and what else to actually see there is no difference between any of them ?Though, I tried a cigarette lighter test. The BeCu does less offset. But its also thicker. I need the same dimension rod to compare. But it went less even when I held it alot longer then the brass does just for a split second but thats not scientific. At least its fun to stick music note shapes into a meter.

author: PascalNE
author_rank: Regular Contributor
timestamp: May 17, 2025, 04:47:26 am
content: Apologies if Im misunderstanding but does your 12AWG one have different banana jacks (non-pomona) so maybe they are causing offsets. And I think you’re right the 12AWG will have a pretty big thermal mass and when it’s acting like a heat sink it’ll cause bigger temperature differences. I think protecting it from air movement as much as possible would be good.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 04:49:04 am
content: I don't know. I think it was pomona. But they are like bulky in comparison.Actually I think the brass spring might work the best.this shape out of a spring (but the jumper in the middle part is only 1 wire, not twoI have some really fine BeCu silver plate wire that takes the cake on thickness for all of them, I might try it tommorow. Does it make sense that the really thin wire equilibriates the best at the contact?Because the current is so small... only temperature matters?

author: PascalNE
author_rank: Regular Contributor
timestamp: May 17, 2025, 04:58:28 am
content: Not really my area of expertise but I’d assume that thinner wire will reach a temperature equilibrium much faster than a big piece of copper. Super low thermal EMF cables are often made with thin 22AWG wire. And maybe poking the wire into the hole is making better contact than your banana plugs were reducing resistance and reaching equilibrium faster.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 05:02:56 am
content: Well, its very hard to see any difference between the dual banana pomona and the wire notes. But my DIY dual banana is attrocious.I will throw it in the ultrasonic maybe, the contacts are a little oxidized on that one. But it measures OK.I think the fire test might point to the copper one being the best material.The tiny spring copper I have is like something less then 32AWG but it should be springy enough for a good contact if you bend it right.It's called a instrument, putting notes into it just makes sense

author: Kleinstein
author_rank: Super Contributor
timestamp: May 17, 2025, 08:39:30 am
content: Surface layers or plating have very little effect. There is just not much thermal gradient over the thin layer. HIghly oxidized contacts could still be bad from acting as a rectifier for EMI.There are 2 possible ways to get thermal EMF errors: one a thermal gradient over the connector part and the other it drawing heat away from the usually warmer meter and than causing a change in the temperature gradient inside the meter, e.g. at the sockets.For the 2nd effect it can help to cover the connector part with some cloth for extra thermal isolation.

author: zlymex
author_rank: Frequent Contributor
timestamp: May 17, 2025, 11:20:58 am
content: I use these for many years.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 11:35:05 am
content: Hmm those look really thick.Could it really be a corrosion rectifier then...I did not want to try to stick thick bent wire in there because I thought it might scratch things. If you bend thin wire like a 'note' then only polished rounded wire is being pushed into the banana receptacle. I will just try a clean shiney 14 awg piece of copper, lightly bent into a simple U , without the connectors

author: tggzzz
author_rank: Super Contributor
timestamp: May 17, 2025, 12:03:57 pm
content: Have a look at this conversation...https://www.eevblog.com/forum/testgear/why-rotary-tip-on-4mm-banana-plugs/msg5634873/#msg5634873

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 01:36:33 pm
content: The contact area increases thermal transfer though, unless you have thinner contact leafs. To me it seems like you should be using something different for no current measurements. If you solder them it will eventually break.What I had in mind is to make egg beaters out of the 34 or whatever gauge spring wire, then silver braze two of them together in a [ shape. But I am not good enough with wire yet to make that. The contact should be good and the thermal transfer should be neglegible.That's why I thought brass too, because the thermal transfer is worse. Same with BeCu. But there is thermocouples then.Stainless also has very low thermal conductivity, with titanium being around there too.Other idea was to make mini stainless egg beaters and dip them in my crucible 'silverer' but it would loose spring.... it would need silver electroplating (which I don't want to get into).But I have seen those banana connectors before and they probobly do have very low thermal mass. The pipe onesAnother option is to have a helix leaf spring with a 'thing' in the middle, so you can hold it, "wind it" (and pull on it), insert it into the connector and have it expand in there. When you twist a helix leaf spring it should shrink a little in diameter . This one would need some kind of 'key' for installation and removal though. And it would have a single fine wire inside bonded to the spring, so the spring is the contact, but the contact weld is deep inside of the spring (near the depth of the bore)Kind of like a reusable heli-coilLow mass design gets ridiculous and annoyingI am sure the metrology guys would love to have a micro sized 'utilities key' for installing DC shorts.https://inspectoroutlet.com/products/sewer-cap-wrench(this one is a meter long)https://www.yamamoto-ms.co.jp/en/product/b-72-p14/- spiral contact for testing electroplating (inspired the idea)https://specialtytest.com/product/spiral-contractometer-includes-two-calibration-weights-0-5oz-one-teflon-coated-spiral-instructional-dvdextra-wire-repair-kit/- device- instructionsOh yeah and the entire assembly would be two of these special micro leaf helix springs, connected by something like a 30AWG wire that has two styrofoam plugs on it (which you insert into the banana connector when you insert it), and then a tiny two piece Styrofoam clam shell that you put over the tiny wire loop after its installed (with micro magnets), and you would need to wait 30 minutes for it to equilibrate before you measure zero. I think it would make employees happy and calm to use this robust assembly.Just thinking about it makes me want to reject technology and go to a tibetan monestary

author: Simmed
author_rank: Frequent Contributor
timestamp: May 17, 2025, 01:55:59 pm
content: found itthere is this thread about zero ohmhttps://www.eevblog.com/forum/metrology/zero-ohm-diy-4-wire-standard/?all

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 02:04:08 pm
content: Well I did find a electroplating recipe for mu-metal that you can deposit on the styrofoam insulator that protects the wirebut realistically you should have a heat flux meter built into the DMM front panel so you can calibrate it for the expected test leads that will be usedFor those interested, the pink hard styrofoam in home depot is one of the best insulators you can getI actually had to park my ass in front of the Fluke MFC before for a few days to measure things, and I assure you the laughter is purely sadistic with thoughts about the poor operator that has to do this stuff. The thermocouple calibration stuff was theworst.ALSO with how SLOW it goes, even with the helper programs, what fluke should do on the next one, is make the machinequiet. Fucking NO ONE wants to be near that thing. Seriously the people that are actually interested in nano volts and stuff are NOT people that like machine fan noises. I really think that maybe they think companies are hiring former blacksmiths or heavy machine gun operators for doing calibrations ?? ( I always imagined that the guy that approved it might have been involved with using the 16 inch cannons on the USS Missouri). I am not even joking, I feel like I see ex-navy people around this stuff ALOT. Like ok, I know why you are questioning my ability to tolerate noise, its because you are half deaf from working on the flight deck on an aircraft carrier.I did kind of like seeing what the meters are really measuring, but the noise is not tolerable.I did put a noctua fan in my k2001 BTW

author: TUMEMBER
author_rank: Regular Contributor
timestamp: May 17, 2025, 04:21:58 pm
content: Quote from: zlymex on May 17, 2025, 11:20:58 amThis is an economical and common sense solution. I opted for the "clover", it worked for "zeroOhm" and "zeroVolt". The photo shows how easy it was to prove what a "shit" the "leading product of the world's leading industrial hegemon" turned out to be at some point. For those who are visually impaired, the range is 100 mV, slow, full short circuit. And several hundred thermocouples were measured with something like that.It is enough to "bathe" copper wire in citric acid from time to time and rinse it in distilled water, and it will remain without an oxidized layer.

author: TUMEMBER
author_rank: Regular Contributor
timestamp: May 17, 2025, 04:38:13 pm
content: Quote from: Kleinstein on May 17, 2025, 08:39:30 amYou can try to measure the socket temperature using a PT100 sensor. The diameter must be matched closely to the socket diameter, i.e. 4 mm, and at the same time it must be a "short" sensor, i.e. the length of the socket channel, to prevent "extraction" of heat through the "jacket" of the temperature sensor. Unfortunately, each meter will have a different time constant and it will change with the change of the ambient temperature in the laboratory. But the order of magnitude itself can be determined. In my case, the SOLARTRON 7062 is a task for Herakles, it has an exceptionally "thought-out FISHER connector" - their ass should swell for this choice.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 05:03:51 pm
content: are you sure those are good the fluke one is a acrylic block on a circuit board with tiny traces for copper. I think that your copper wire flower is losing alot of heat. I feel the heat on the side vent of the keithley and the topI put two notes in the sense and source terminals and hung a third note in the middle (so its just hanging on the bits that are hanging out, and the offset for 4W is 80 micro ohms. I hung a transistor off it to weigh down the contact and its staying mostly the same. (0.75 inches of fine wire and 2 silver contacts). That is really bootleg but its low thermal mass, im not going to solder today, but I think I might try to make a single piece one with a dot of solder in the middle to try to make a real kelvin short that is also very thin (like a tripod with 4 legs). I can use silver to bond it in the middle instead of solder too.like this, but with loops on the legs so it stays in placeIDK if it makes sense to compare 4 wire ohms shunts, 2 wire ohm shunts and 2 wire voltage shunts? (depending on current, but volts is really low). Well, I doubt you can get the stuff thin enough to matter

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 05:27:58 pm
content: how does your flower clover shunt do in another meter?

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 05:48:24 pm
content: I got a piece of 14 awg zinc wire that I just bent into a simple U and shoved into the banana jacks because it came in the mailstill does better then the banana connector one. Like alot. The zinc wire, copper wire, brass wire, pomona plug are all very similar.The meter has been on a long time, and I think that the copper one is the bestLol, this banana plug could troll someone to hell. its basically a power source. I wonder if it can charge a capacitorits free energy machine

author: mawyatt
author_rank: Super Contributor
timestamp: May 17, 2025, 06:03:18 pm
content: Here's a 4 Wire Short/Shunt with #12 Solid Cu Wire we use, and a Precision Resistor with a Thermistor attached by heat shrink tubing.We found that with our KS34465A DMMs show a temperature rise of ~2C on the thermistor, other meters such as DMM6500 showed less rise. This indicates the KS DMM Banana Sockets are at least 2C above ambient, likely 3~4C at the socket inside the DMM.Anyway, they are for use with our multiple 6 1/2 digit meters.Best

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 06:13:35 pm
content: I put a small leatherman in there and it works way better then the bad banana jumperACtually it drifts more, so the banana plug is betterima stop before I have to buy new socketssomeone should not plug a leatherman into a 3458a(I put two steel rods into the front panel and lightly wedged a leatherman in there to act as the DUT)Offset is 5mV. bad banana is like 4mV, copper is 0.01uV. Leathermans down to 3mV so its like the bad bananasMan the leatherman with the keithley electrometer range switch bolts is beating out my copper short. I thought this short can handle like 30 amps.How the fuck did I manage to build something so impressively bad. I was proud of this thing! And god damn zinc wire too.

author: TUMEMBER
author_rank: Regular Contributor
timestamp: May 17, 2025, 06:33:38 pm
content: It doesn't work because such a solution is not applicable in my private meter. K2700 was a service meter at work - I don't work there anymore and it's not my problem. Explanation in pictures. What's the harm in trying the clover? The cost is small, a bit of work with pliers to bend it into the right shape to fit the meter sockets. K2700 had an advantage - it didn't have a fan, although it's only 6 1/2 digits.

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 06:42:53 pm
content: I don't think you understood what i said. I just wanted to know if it worked in another meterwhat happens if you plug it into another meter?

author: TUMEMBER
author_rank: Regular Contributor
timestamp: May 17, 2025, 06:55:29 pm
content: Quote from: coppercone2 on May 17, 2025, 06:42:53 pmIt seems that I wrote it quite "legibly". Not everyone is an American and has 10 DMM at home for their own needs. These are expensive toys, in Poland you have to consider whether to spend it on a used car or a gadget. My next meter does not meet the criterion of accuracy and reproducibility in this type of measurement, because it is SOLARTRON 7150. Find its metrological parameters and draw conclusions. I am "registering from the topic".

author: coppercone2
author_rank: Super Contributor
timestamp: May 17, 2025, 11:48:43 pm
content: I just want to know if that clover is actually a good 4-wire shunt or not. I left that meter on with my bad banana shunt for many hours now and its just not gonna settle. I thought the shunt would be great because it looks beefy, well soldered, low impedance. If I made a judgement on the K2001 with that bad shunt I would be wrong (because I tried it with good shunts). At most I can say that maybe the keithley has a thermal problem where it does not like measuring voltage with heavy gauge wires. (which is a interesting observation because naturally people might just got for 12AWG test leads for everything and not realize there is a potential benefit in some meters for say having a different pair of thin gauge leads for measuring voltage).If you actually put that shunt in another meter that is similarly accurate and it worked it would at least tell us something about it. All I know right now is that for sure it does not agree with that meter, not if the meter is bad, because the design is unorthodox and contrary to things I hear (and saw with purchased calibration artifacts) about low thermal mass being the 'norm'My 34401A reads the bad shunt that the keithley disagrees with as good (2uV offset) ,and if I plug in my low thermal mass shunts I also get 2uV offsets. Something is different about it, but I need to let it warm up for 24h before I make any conclusions. Things are slow to settle but its peculiar that the same shunt reads say 5uV in the K2001 and only 500nV in the 34401A (on power up 15 min after being off for a while). I am curious to see how things will look after an hour,. I tried to set the filters so they update similar intervals. I see it started negative and its moving up. For all I know in a few hours it will drift up to +5uV and be just as bad as the keithley, then I really know that its not a great shunt if it causes problems in two different DMM. But This thing looks BOSS for say shorting out a power supplyThe difference is that the 34401A has a soldered or brazed copper pipework for the front panel, and the K2001 has little panel mount connectors with small pins (2mm IIRC) that go to a teflon wire. The k2001 is totally different then 34401A (which is basically a fucking heat exchanger for a nuclear reactor)It looks like because HP used heavy hardware for the front panel instead of little crap, it looks more stable. (and this is a hallmark of keithley where they won't make any parts for themselves that are bad ass). Maybe keithley needs to buy a 500W iron for their factory. Or maybe there is something more to ithttps://www.ftm-technologies.com/produit/600w-heavy-duty-soldering-station/?lang=enThough, given that the 34470A also uses heavy pipe work for the front panel, I think keithley is just cheap.

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2025, 12:19:45 am
content: Hmm after a good half hour now, the little note jumper reads as 300nV on 34401A and the bad banana reads as 3uVits bad even with the big pipes. its just badsome how it looks like I have soldered together evilAnd 5uV. I pulled it out and put in the note and it fell down to 500nVI don't have a third manufacturers meter but I will just say that this jumper is... bad unless you are using it to short a DC power supply or something.I think I will give the leaf a going over with some polish to see if it improves, and then try the ultrasonic cleaner. Just scrubbing the bananas with IPA had no effect. Maybe I can try some kind of acid too (I need to see which acid works for what I am guessing is nickel), I don';t mind pickling the whole part to see if it improves it.A rather substantial amount of crud came off the banana from rotary polishing with a buff and compound. Maybe offset went down a little. I wonder if there is crud on the leaf pole interface. Ultrasonic pickling should take care of that. Now its hanging out at 2.8uV. The towel is on it but the room is getting drafty from a outside wind rainThe copper wire was from a big ass renco inductor BTWNope, its back to 4uV.and the note is 1uV , maybe the meter drifted a little its really starting to get to what people might say is stable zone for 34401AI gave the bad one 15 minutes in the ultrasonic with alconox. Still the same. I am out of citric acid to try to pickle it

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2025, 04:29:57 am
content: damnit I made another one with new banana plugs that have more leafs that I bought a few months ago from DK with a thinner piece of bus wire that fits in there and it works OK (but its not stiff enough to insert good, its not a good 'standard'). Maybe I will drill it to accommodate that big ass wire that is in the bad banana and try it again. The new plugs go in deeper because their not threaded for the insulating collarI will make a big long copper loop that sticks out like an inch to compensate for the shorter plug. If the same wire (longer and extending more for thermal mass) on different banana plugs gives me a better comparison for thermal mass and heatsink. Or maybe I should just solder it to a big 1/4 inch copper U shape to make a really exadurated heat sink Or I can solder it to a freaking bus barHmm I noticed this one has a temperature meter on it. I wonder if it measures thermocouples.Can the thermocouple meter on the K2001 tell me something about my jumpers? It has alot of settings.I put it on T mode and plugged in various jumpers. The bad banana reads 0000.2 c immediately . The other ones are 0 or 0.0001Ehh its not really conclusive.What can I use to study the different jumper wires behaviors, etc?Something like a special thermocouple meter? I mean to get more resolution/clarity.Like some rig with heater resistors and temperature sensors attached to some faux banana connector ior something

author: Kosmic
author_rank: Super Contributor
timestamp: May 18, 2025, 01:50:11 pm
content: For reference, This is how the Agilent 34172A is constructed (I was expecting something better).I'm also including some documentation from Fluke about thermal EMF and the characteristics of a good short (low thermal mass).Watch Out for Those Thermoelectric Voltages!

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2025, 07:00:06 pm
content: My feelings on the matter so far is that you might be paying for the insulation ,the alloy choice/plating *thick gold, hopefully?), but not their handywork . And that they probobly tested in in 10,000 meters before putting it on the market. And the injection mold lol... withENGRAVEDletteringI have been chronically disappointed taking apart various adapters and such lol. I need to remind myself its the ergonomic clam shell I paid for, not what is inside. And that I can write a official sounding PN in a document.I had my own banana clam shell thing made up for some specific thing we do. 70% of the work was on the plastic enclosure , and this one was 3d printed. Two of them kept not fitting right into the front panels and it got reprinted 50 times. Good puzzle for bored co worker (they just want a extra measure of 'touch safety' for low voltage things, personally I just used it 'bare', though it looks like kind of shady to have it sticking out of a expensive device without a housing ). Now he knows the specifics on why 3d printer is a wild animalI am wondering if that Agilent one on purpose does not have a PCB inside. Because mine used a BAKELITE board (screw mountings for the parts) inside of it with a plastic covering. But theoretically theirs has higher thermal isolation between the connectors if its all polystyrene plastic. that might be the magic of it.... IIRC its great insulator . But mine is a high current device and I don't care about microvolts there, its just essentially a weird adapter for some test probes, and its not like bakelite is a heat sink anyway, and @ 3/16 inch thickness its really tough and also easy for machine shop to make, unlike PCB (no glass)

author: Ismsanmar
author_rank: Regular Contributor
timestamp: May 18, 2025, 10:45:16 pm
content: Quote from: coppercone2 on May 18, 2025, 07:00:06 pmThat is just a 34171A repurposed. Are you sure that you are not paying for their handywork? One of the current model connectors, 34171B, costs $170.5 directly from their website, and the 34172B costs $341. That's exactly $123.5 for their handywork (plus the wire, solder and the sticker with the model number), and they also take the gold-plated copper nuts as part of the payment.

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2025, 11:20:47 pm
content: What I mean to say is that you won't find like anything expensive or difficult inside. all of those you take em apart and its like what? especially the LCR things, like $1000 component testers/adapters that are like a spring and a capacitor with some bus wire or whateverYou might get the impression that it will be something legendary like a resistance box switch or something in there that makes your jaw drop for the priceI feel the same way about pump things from the chemistry side of it. You get the worksmanship of a childrens china 1990 toy with some dead bug parts and a cheap motor for like $1000+ . For the chemistry side of 'lab tools' . From like VWR etc. I love the ones that don't bother with wire (they use component leads) or insulation (try to wedge it between plastic pegs and stuff. or PCB's, brackets (they like foam), connectors, cheap battery contacts, etcSometimes those companies are kinda selling junk on the side (even if they have some really nice equipment)I took apart both a scandously priced electronic motorized pipette and a 'micro pump' that were like that from the big expenisve brandsI have a feeling that its not the same designers either. Just the badgeHave you never encountered the brand image part of product design where you get some enclosure that is basically selling because of looks and then there is no money to work on the inside and stuff, and its super irritating because of the enclosure features ? The way I always saw it work is sales says "we need something that LOOKS like this" and then engineering goes "well....." and then sales go "it has to look LIKE THIS or it WONT SELL" and then when it comes down to the remaining money for the parts there is none? Or you can't fit anything in there because of decorative features?Their always expensive lab tools that would look good on a star trek set. It's what apple does but for test equipmentI think its especially valued in chemistry labs because it looks cleaner and visitors are less anxious about being in there if its some total desk jockey that thinks a belt pump is going to explode and spray them with plutonium or something. They love doing lab tours and facilities tours and as a result of that there is pressure to make everything look as chic as the board room. We are NOT just another company boiling metal cuttings in acid because our hot plates and microscopes have sloped beveled miters ! (process was unchanged since 1942)

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2025, 01:54:44 am
content: I am going to try to make spider-shortI lashed 4 spring copper wires together using some kind of soft brass jewlery 'lacing' wire and I will dip it in a silver pot. Then I will shape it and trim the excess. It's not the same idea that they have now with using thick traces for everything but the short, and instead its a bunch of thin wires that converge at one point in hopefully a low temperature offset braze.I am wondering if there is data about brazes and thermal EMF. I have 56% silver braze and also pure silver. Its hard to do pure silver. I suspect its going to have a better result though?Does anyone have a table for this weirdness? For all I know it can be horrible performance. I just wanna try some experiments. I have some Cd solder too IIRC (low temp)https://www.ni.com/docs/en-US/bundle/ni-switch/page/thermal-emf-and-offset-voltage.htmlThough I wonder if I can just weld it together.......I suspect that it will be difficult to control. The braze version has zinc and nickel in there, which look like bad performance. It seems hardly worth doing over just soldering it with electronics solder.Damn I did it in pure silver but then I thought Oh I will just give it one more quick dip to make sure and it totally melted and contaminated some valuable silver. And zirconia for ghetto work is no good (it cracked), graphite however is excellent. The melting point are so closeAnyway I did it with the braze alloy. I wonder how this will read

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2025, 02:55:15 am
content: spider 4w short using 4x becu spring wires and a 56% silver dip braze in the middle reads 500 micro ohms on 34401A slow 6 digit. At least it was fun to makeThough I don't have a commercial 4W short to test it with and htis meter was calibrated long ago200 now. sometimes it gets to all 00 to 100 micro ohms now so it looks like it went to the last digit. I wonder if it will go negativeOk so even without a box it looks like it can get a 34401A to all zeros. Nice. IDK if the 34401A reads negative like some SMU dolets see what k2001 saysIt says its 300 micro ohms. I wrapped it in a tissue or possibly toilet paper and will let it settleIf its inserted and I put it on DCV it reads 500nVI don't remember if i ever tried the keithley 4W short with the 34470A when it was available. But I do recall someone having problems with this at work, they ended up getting one that is an acrylic block to I guess block air currents. Not sure what the 'passing grade' is for a calibrationFor 3458A the test limit is 0.00007 ohms for the 4 wire shortdamn that means my short sucks if their fail is 70 micro ohms and I can't get it under 233The conductivity of spring copper is bad however, I just thought it was cool that it has good contacts for the banana holes and it should like stay.. dimensionally correct for longer. I can try to make the same thing with just copper wire. I think the BeCu could have conductivity as low as 20% of copper. But I don't even know what I am measuring here, because their so tight together. The silver solder? Parts of BeCu and silver solder intermetallics etc?Do you actually see all 0 on a 7.5 or 8.5 digit meter from putting the factory shorting 'block' in?Or are they just used to set zero? What is their actual resistance. I am thinking about buying one for $100They just say its low "However, the absolute resistances of 2- or 4-wire configurations as well asthermal voltage offsets are not specified, and metrology traceable applications are not recommended."What is a specified one at?Mine is down to 182 micro ohms. I guess the trick is to not measure a solder joint. Unless I can get the pure silver to work with very careful dunking it should be made out of one copper piece in that location. Perhaps I can try welding this

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2025, 05:43:39 am
content: this measures 180 on keithley, but it does appear to totally zero a 34401A out.How do you get something to less then 5 micro ohms?

author: laichh
author_rank: Regular Contributor
timestamp: May 19, 2025, 06:00:41 am
content: For up to 7½ digit DMM, I use either Keysight 34172B or Stäubli KS4-19 (Item No: 24.0002-21).Keysight 34172B Calibration Short for Digital Multimetershttps://www.keysight.com/us/en/product/34172B/calibration-short-digital-multimeters.htmlStäubli KS4-19 (Item No: 24.0002-21)https://www.buerklin.com/en/p/staeubli-electrical-connectors/short-circuit-connectors/24-0002-21/40F436/For 8½ digit DMM, nothing beats a piece of AWG14 pure Copper wire.

author: Vgkid
author_rank: Super Contributor
timestamp: May 19, 2025, 06:06:04 am
content: Since you are now wanting Zero ohm resistance VS zero thermal emf see this thread:https://www.eevblog.com/forum/metrology/zero-ohm-diy-4-wire-standard/

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2025, 07:10:02 am
content: what do you actually get when you plug it in though. Is it actually all zeros?I like sawed at the silver with a sharp knife because it wet two wires, and now its at 160 micro ohms.I am asking how much better the number will be If I buy the commercial thingLike if you bought it and plugged it into some NIST 8.5 digit super meter, what would the front panel say ?The only number I found is that the 3458A has a value that says "less then 0.00007 ohms" for "pass" on their test sheet.What do they actually measure at??I want to understand the value I am getting. The best I can try to make vs some thing that costs money online. In micro ohms or nano ohms per dollar.1 inch of 14AWG copper wire is 200 micro ohms. Its around what my thing is getting. How much better do they do?Like I can buy the keithley one, I can buy a chinese one, I can try to rig some shit up with PCB, etc. I will buy the real one if it actually gives a low number instead of messing around

author: TUMEMBER
author_rank: Regular Contributor
timestamp: May 19, 2025, 07:58:11 am
content: Quote from: coppercone2 on May 19, 2025, 05:43:39 amYou built a nice thermocouple. I showed you how to make "zeroVolt" but with the stubbornness of a maniac you do everything "your way" and against the grain. There should be only one metal - pure copper. There should be no soldered joints - the second metal creates the thermocouple. A 2 mm wire bent and pulled together creates a closed loop without the need for soldering.1. There are no different metals in contact with each other, there is no difference in potential.2. There is no temperature difference "at the beginning of the wire and its end", there is no difference in potential. Work on the Seebeck effect.3. Work on the "Law of the Third Metal".In terms of whether you can have "all zeros on 7 1/2 digits on the lowest range" - see photo. Similarly, when it comes to the "zeroOhm" range in multimeters, you can when measuring using the zeroing function + 4W measurement. Multimeters are not resistance bridges, they have "limited resolution and accuracy of resistance measurement" they are "blind" to certain minimum measurable values.

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2025, 08:06:15 am
content: I just bought the keithley one its easier then trying to get a ohms number from aggressive wacko with a vendetta, I will just plug it in and find out

author: Kleinstein
author_rank: Super Contributor
timestamp: May 19, 2025, 08:16:38 am
content: A proper 4 wire short for the ohms zero is mainly connecting the 2 sense wires to each other. The 2 drive wires are connected separate. Between the 2 parts there is a weaker link connected at 1 point for each end. The main point is avoiding voltage from the current to enter the sense link.A simple version is a wire from drive H - drive L - sense H - sense L.

author: miro123
author_rank: Frequent Contributor
timestamp: May 19, 2025, 12:56:51 pm
content: Keithley DMM6500 has default option to compensate the thermocouple effect. Many discrete sd-adc from TI has those option too. just do the measurement with and without excitation current

author: J-R
author_rank: Super Contributor
timestamp: May 19, 2025, 11:26:15 pm
content: I picked up one of these a while back, seems to be decent:https://www.ebay.com/itm/326409377777

author: zlymex
author_rank: Frequent Contributor
timestamp: May 20, 2025, 01:19:26 am
content: A simple 4-w short for Hioki RM3545 (buttom left PCB) made by bg2iax.

author: coppercone2
author_rank: Super Contributor
timestamp: May 22, 2025, 09:04:27 pm
content: I got the keithley 4 wire short for a not so low price and its reading like 190 counts on 4 w high accuracy mode. not too different from my spring spider short (233 counts) but its built very differently. Whatever parasitic effects it has don't contribute more then like 100 micro ohm of errorso its like a 50 micro ohm difference ON drifty startup. I just need to get the voltage shunt (the $10 pipe banana connector) and this issue is settledAfter about an hour the acrylic block keithley is reading 210 and IIRC the DIY one was like 233, so there is a 20 micro ohm difference between them. I don't have what it needs for the calibration yet, but anyway I think that means my spider spring design idea is not that terrible. So this instrument has offset that can be calibrated out, but this still IMO says that the difference between the shorts is small, considering one is about a 20 cents of spring wire, a drop of silver braze+1 tissue (with no design work other then being handy) and the other costs $150If I had 4x banana to binding post adapters (expensive) I would try the U short method using bare copper wire. Sadly this instrument does not have binding posts on it, understandably so because it might be connected up to 1kVhttps://www.digikey.com/en/products/detail/pomona-electronics/2894-0/736408?gQT=1or POMONA 5165-0 or 1286after many hours its at 142