Short for the end of test leads when using 2W Ohms - Page 1
Forum section: electronics / general

author: mendip_discovery
author_rank: Super Contributor
timestamp: April 12, 2023, 07:14:20 pm
content: During a recent assessment there was a question raised over me doing a zero on a meter. My normal practice is to just touch the two bananna ends together and NULL/zero the meter to remove the error of the leads. But that wasn't liked due to the thermals and the small contact area, two cylinders touching at a small area vs the surface area of the banana connector.Yes I know 4W is best but I do have situations where I have to measure 2W mode checking customer meters mostly, and for when doing zero checks on the meter with the 17025 assessor watching prior to doing a 2W measurement.I already have a 2W short for the meter and today I received my Marco Reps 4W short (thanks to the YouTube star).I am thinking of two banana connectors bolted onto a hefty chunk of copper. The other idea was join two banana inputs together via a copper coupling end to end.Any thoughts of a better option?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 12, 2023, 07:29:10 pm
content: Not clear to me what's on the ends of the wires. Usually it would be probe points, or do you have banana-to-banana cables for some reason?

author: mendip_discovery
author_rank: Super Contributor
timestamp: April 12, 2023, 07:41:34 pm
content: Banana to BananaIt's for meter to calibrator that I use these leads.

author: tggzzz
author_rank: Super Contributor
timestamp: April 12, 2023, 08:31:16 pm
content: What of the objective of doing the 2W null?If it is to remove the "parasitic" resistances in the next measurement, then the null measurement should represent what will occur in the next measurement - wires, contacts, etc. No surprises there.The reading that is nulled out should, of course also be stable and repeatable. Is that possible with handheld point/line contacts?

author: coppice
author_rank: Super Contributor
timestamp: April 12, 2023, 09:04:27 pm
content: What makes sense for a resistance measurement depends very much on the size of the resistance being measured, and the precision needed. For low enough values of resistance, like a 100 micro-ohm current shunt, even an attached 4W approach can be useless. You need to measure those in a systematic way.

author: mzzj
author_rank: Super Contributor
timestamp: April 12, 2023, 09:19:47 pm
content: I think your auditor got bit into "academic wanking" but it is your responsibility to prove otherwise by showing measurements x y z and calculations a+b+c that it doesn't really have practical importance.I have done some tests and based on that assumed that good banana connectors repeat to <1 milliohm but not much better than that.BUT there is a huge variation between different banana connectors and female receptable bore sizes.I just did some measurements and for example this banana connector performs quite poorly as the loose spring adds another rather random contact:https://nl.farnell.com/hirschmann-testmeasurement/934062101/test-lead-red-1m-60v-16a/dp/523744barrel to barrel approx 1 milliohm clamped between fingersbarrel spring to barrel spring approx 10 to 50 milliohms clamped between fingers and quite often I see contact resistance go up with more clamping!copper shorting block 10 milliohms initially, after few insertions and rotations this drops to 1 milliohm.This on the other hand is one of the best I have tested:https://fi.farnell.com/hirschmann-testmeasurement/930727700/conn-banana-plug-30a-solder-blk/dp/2914769Gold plated and the springs are integral part of construction.barrel to barrel approx 0.5 milliohm clamped between fingersbarrel spring to barrel spring 0.6 to 1.0 milliohms clamped between fingerscopper shorting block 0.2 to 0.4 milliohms pretty much every time.So one of them is about 50 times better than the other.I made the copper shorting block from a piece of 10x40mm copper busbar by drilling two 4 millimeter holes on it.If taken to wanking contest the bores need to be cleaned with deoxit and measured for size and surface roughness before each use.

author: alm
author_rank: Super Contributor
timestamp: April 13, 2023, 01:00:04 pm
content: Are they low thermal EMF copper banana leads, or standard brass banana plug? If the latter, then I'd just use a banana jack coupler likePomona 6252.For low thermal EMF I'd look for something copper, but I'm not quite sure if there's an off the shelf item.

author: manganin
author_rank: Regular Contributor
timestamp: April 13, 2023, 01:57:47 pm
content: Quote from: mzzj on April 12, 2023, 09:19:47 pmThe best repeatability of those that I have tested.Wear doesn't increase the contact resistance. When the curved surface flattens, it actually slightly decreases.Also my favourite in low thermal EMF applications: single piece and very low mass.Unfortunately the quality of those that I recently bought was not as good as the old ones.The current version required some sanding. Only the smooth side should contact the socket, not the corrugated.

author: tggzzz
author_rank: Super Contributor
timestamp: April 13, 2023, 02:10:48 pm
content: Quote from: manganin on April 13, 2023, 01:57:47 pmA few years ago I went to a Maker Faire in Hannover. The German PTB had a stand with some rather lovely old and new equipment on it, and offered to "calibrate" equipment brought to them.The connectors they were using had similar shafts to those, and may have been the same type.

author: mzzj
author_rank: Super Contributor
timestamp: April 13, 2023, 03:49:48 pm
content: Quote from: manganin on April 13, 2023, 01:57:47 pmI have bunch of similar but chinese gold plated versions. I haven't tested them throughly but they seemed to perform pretty well considering they were something like 50 cents a piece.For low thermal EMF use you can also solder the wire inside the tip of the connector so that there is very minimal lenght of banana connector body involved. In theory I'd expect this to be advantage when hunting last nanovolts.

author: mawyatt
author_rank: Super Contributor
timestamp: April 14, 2023, 04:34:48 pm
content: Quote from: mzzj on April 13, 2023, 03:49:48 pmWhere did you find these versions, we've only been able to find the Multicomp Pro PSG03597 and 98 types? Also, couldn't locate the Staubli MC types.Best,

author: tggzzz
author_rank: Super Contributor
timestamp: April 14, 2023, 05:04:44 pm
content: Quote from: mawyatt on April 14, 2023, 04:34:48 pmI bought these Staubli MChttps://uk.rs-online.com/web/p/banana-connectors/0531453

author: mzzj
author_rank: Super Contributor
timestamp: April 14, 2023, 05:41:25 pm
content: Quote from: mawyatt on April 14, 2023, 04:34:48 pmCan't wouch for any of the sellers but here is few:https://www.aliexpress.com/item/1005001732071011.htmlhttps://www.aliexpress.com/item/32781819650.htmlUnlike Staubli these are not stackable and at least the ones I got are quite "springy" requiring some force for insertion.(Wouldn't be my first choice for general purpose lab banana connector because of this)This model has been also decent:https://www.aliexpress.com/item/1005005321775778.html

author: mawyatt
author_rank: Super Contributor
timestamp: April 14, 2023, 07:47:34 pm
content: Quote from: mzzj on April 14, 2023, 05:41:25 pmThanks, we have and use the the type directly above, and have had some issues with some being slightly large and very difficult to insert, but like them better than the lattern type.We've never used the jagged slit type before, but understand they are good. The ones you've identified are brass based, not copper, the Staubil MC types data sheet show a copper alloy....not sure how much this matters in actual use tho. If the connector has low thermal mass, then seems as the connector plug and instrument jack should reach thermal equilibrium quickly and without a significant temp difference across the plug/jack the induced thermal EMF should be small. We haven't done any tests to qualify such tho.Best

author: mendip_discovery
author_rank: Super Contributor
timestamp: April 15, 2023, 11:52:37 am
content: Quote from: mzzj on April 12, 2023, 09:19:47 pmI was trying to do a MATH NULL on the 3458A and was getting a little tired and failed to spot I was doing MMATH NULL, I'm such a noobAs it was near the end of the second day and I was tired I just put the leads between my fingers and that was enough for him to make a comment. He also didn't like that I did a 0 mV check I plugged the 3458A into the 3050A Transmille and set it to 0.000 mV DC, we got all the zeros and noise of 2.I already have some of the same 30A HIRSCHMANN plugs with Gold plating. They are rather nice. I used them to make up some test leads that go with the onsite calibrator but I need to source some PTFE-coated wire so that I can make a collection of test leads. As I know with the 3458A I will need to be very aware of the effects the leads can have on a measurement. Annoyingly I have some Gold plated test leads which don't stack and are for audio use so I am starting to notice the gold plating is starting to rub off. I have a customer that does aircraft wiring so they have miles of rather nice wire there but I haven't been sent to that job for months as it's "too easy" for me.Thanks for the comments. I will try and report back on what I found best (easiest) to do as I like to have something repeatable and neat. I know 4W is better than 2W but I still have to prove the meter is capable of 2W.https://docs.rs-online.com/3f7d/0900766b8145e3c2.pdf Don't ask me what they are, the MD bought them on Amazon as they were cheaper than going to RS to buy proper connectors. as a friend of mine said once the best thing you can use is the thing you will use. Make it too complicated and hard and you won't do it, best to make it easy to do then you will do it.

author: manganin
author_rank: Regular Contributor
timestamp: April 17, 2023, 02:03:37 pm
content: Quote from: mzzj on April 13, 2023, 03:49:48 pmIt's all about the spring. Multi-Contact (now Stäubli) knows how to do it, so better use the original.Northern Europe:Elfa stocks them (in metrology friendly colors!). Impossible to find with their search engine, so here are the order codes:140-48-007140-48-061 black140-48-058 red140-48-059 blue140-48-063 green

author: alm
author_rank: Super Contributor
timestamp: April 17, 2023, 02:28:53 pm
content: Quote from: mendip_discovery on April 15, 2023, 11:52:37 amSounds like gold plated brass. So a nickel or gold plated brass short sounds the best match in terms of thermal EMF, and the jacks of non-metrology-grade multimeters will also be nickel plated brass.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: April 19, 2023, 02:57:14 am
content: i folded a copper foil in a spiraled shape. copper oxidized quite fast need to clean itit it proper connector or really not ? in overall my result repeatable

author: martinr33
author_rank: Frequent Contributor
timestamp: April 24, 2023, 04:34:19 am
content: I can see why the auditor had a problem. Finger pressure is totally uncontrolled, as is the location of the measurement.My suggestion would be:- zero the meter by pressing the probe tips into one of the terminals, thereby creating a short that replicates the metal-metal contact of the measurement.- Adjust the angle and pressure a little bit to prove that the contact is good and not variable.- For extra confidence, measure the resistance of the probes and contact on a regular basis (use a 4W short as the zero reference).- Record also the zero reading of the meter without null. A 2W offset has been a common problem for me of late, traced to bad wires (!), bad switches, and bad contacts.(2W resistance unnulled zero is a good test for a meter).You could write up something like this as a little process, which would give the lab reproducibility.

author: mendip_discovery
author_rank: Super Contributor
timestamp: April 25, 2023, 08:31:23 pm
content: Thanks martinrr.Now that I have got all the close outs from the assessment done I can look to my list of bits to look at that the assessor mentioned.I plan to do some checks of the 2W zero at the terminals and then again with the leads just to get an idea of the values I am dealing with. Some how the 2W short I have has vanished, I suspect the MD had a tidy up when I wasn't there.For the moment I have been pressing the two banana connectors together and holding them using croc clips it's doing a ok job for now, as the bananas are making the contact and not the crocs. They provide a constant pressure and I use two, to provide pressure from two angles.I don't do much if any 2W measurments but I like to keep it checked as I compare the performance of the 2 vs the 4 as part of my currently weekly normally monthly checks on the 3458A vs the Transmille 3050A.I might just take the ptfe wire I have and swap the connectors to the stackable gold plated ones I have as this would remove the issue I currently have.I really need to get some sort or GPIB going so I can devise some tests to graph out the best ways to use the 3458A either settings, connectors and even wire.