DIY Kelvin/4-Wire Probes - A Few Questions, Please - Page 1
Forum section: electronics / testgear

author: t1d
author_rank: Super Contributor
timestamp: November 29, 2019, 09:37:49 am
content: I have a new multimeter that has Kelvin/4-Wire capability; it is smarter than I am, at this point. It did not come with Kelvin probes. I have been pricing them and the top brands are expensive. I like to DIY, so I am moving toward making a set. I have a few questions…Researching other DIYs, I found these clips that appear to be worthy and I have ordered a set.https://www.banggood.com/2Pcs-Copper-Gwinstek-LCR-Kelvin-Test-Clip-Bridge-Test-Clip-Microresistivity-Clip-p-1043337.html?rmmds=myorder&cur_warehouse=CNI already have these wires in stock. (Too many to ever use them all… I caught them on a really good sale.) So, I am thinking of cutting off the alligator clips and using the wires. (If I am smart, I will leave a good bit of wire on the alligator clips, for other uses.)https://www.banggood.com/DANIU-5Pcs-1M-4mm-Silicone-Banana-Plug-to-Crocodile-Alligator-Clip-Test-Probe-Lead-Wire-Cable-p-1062184.html?rmmds=myorder&cur_warehouse=CNHere are my questions…- A few OEMs have a fifth wire that I surmise is to ground a coax shield. Would it be an improvement to use coax and ground it? If so, the ground would not be tied to the clips in any way, it would just shield the lengths of wire; correct?- The wires I have in stock do not have any particular specifications, other than that they are copper. And, I can tell they are stranded, by their flexibility. What wire specifications do I need and how can I test the wires that I have to verify that they would be appropriate for the job?Thank you for your help!

author: Vgkid
author_rank: Super Contributor
timestamp: November 29, 2019, 12:56:17 pm
content: Looking at ehat you have, it seems good. Hopefully the stock bananna plugs are decent. You don't need to use coaxial cable, or the shield for most useage(unless you are using a shielded enclosure)What multimeter are you using?

author: t1d
author_rank: Super Contributor
timestamp: November 29, 2019, 01:03:10 pm
content: Thanks Vg. Good information. I appreciate your effort to respond.J-u-s-t received a new Siglent SDM3065X. I'mverygreen on it.I saw these on AdaFruit. A trio was on T-day sale at Amazon for the same price Ada wants for just one. Plus, free Prime shipping... So, I grabbed a couple of sets, just to have some options.https://www.amazon.com/gp/product/B07K49H8XR/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

author: t1d
author_rank: Super Contributor
timestamp: November 29, 2019, 01:13:16 pm
content: Quote from: Vgkid on November 29, 2019, 12:56:17 pmForgot to add my thought about this... The wires are amazingly good quality, for the price. Heavy metal jaws with good clamping strength. Very supple coverings. Flexible. Very long, a full meter, IIRC. They have a good reputation within the DIY community. They're not on sale, now, but they are still a decent value at the higher price.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 24, 2020, 01:11:43 am
content: Re-surfacing this somewhat old thread....Question: if the someone were to use four conventional banana to alligator clip leads (similar to what the OP posted) to measure some small resistance - like half a meter of 18 gauge wire with an expectation that the resistance should be approximately 10 milliohms - how much different (better?) would you expect the measurement to be when using a set of "true" Kelvin leads (four wires with two Kelvin clips) vs the four wires with four alligator clips? I'm guessing the difference might be on the order of a milliohm (or less) in this example (10 milliohms total) but maybe that's not correct?Thx

author: JohnPi
author_rank: Regular Contributor
timestamp: August 24, 2020, 03:07:44 am
content: It might actually be better using 4 separate wires & alligator clips.With those small Kelvin clips, the 'force' and 'sense' positions are indeterminate by the width of the contacts at the end of the clip. Thus the precise length of the wire you are measuring isn't well defined. With 4 alligator clips, you can position the 'force' lines well outside the sense lines, and therefore the length of conductor you are measuring is defined only by the alligator clips -- if you arrange that only one side of the jaw is contacting, then the position is quite precisely defined.Not that for resistances of 10 mΩ, you'll need to be careful about offsets and thermal effects.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 24, 2020, 04:42:32 am
content: Quote from: JohnPi on August 24, 2020, 03:07:44 amThanksI can believe that the precise position as defined by the point of contact can make an impact, and of course thermal too.But if 4 clips are potentially advantageous, why do 2 (Kelvin) clips seem so popular rather than using 4? Is it strictly convenience? Thx again

author: serg-el
author_rank: Regular Contributor
timestamp: August 24, 2020, 10:51:17 am
content: https://radiokot.ru/forum/viewtopic.php?p=3687780#p3687780My conversion of probes from China. The quality is good.