does this 'kelvin clip' cable even make sense? - Page 1
Forum section: electronics / testgear

author: linux-works
author_rank: Super Contributor
timestamp: February 06, 2014, 08:08:16 pm
content: I bought one of these, recently, and it does not make sense to me:http://www.ebay.com/itm/UNI-T-Parts-Kelvin-Test-Line-Wire-Cable-Cord-For-UT612-UT611-PA-7-/161179519462first of all, the cables are shielded but the shield is left unconnected at the clip. there is a shield that goes to one of the black bananas but only the center conductor is connected at both black and red clip ends.what's the point of this? its NOT able to be used for 4wire R work. isn't that the whole purpose of kelvin clips?in real kelvins, isn't each clip two red wires OR two black wires? but they have a pair of black/red going to each single kelvin clip.maybe this is meant for something else, but it seems wrong to call this kelvin.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 06, 2014, 08:11:53 pm
content: No, it is correct.Use one color to carry the current and the other one for sensing voltage.If polarity matters, left red in + current, right black in - current, right red in + volt and left black in - voltage.Here is the Gossen version:

author: linux-works
author_rank: Super Contributor
timestamp: February 06, 2014, 08:24:36 pm
content: but again, only ONE wire per clip is connected! I cut and examined the wire (maybe I'll post a pic of it) and there was not even an attempt to solder the shield to the other end of the same kelvin.so, red wire to one kelvin, other red wire to the other kelvin, black wires go to shield from bananas but left unconnected at the clip end.that's not 4wire. there's no continuity from any of the black bananas to anything!

author: robrenz
author_rank: Super Contributor
timestamp: February 06, 2014, 08:27:21 pm
content: I don't know if this is industry standard but it's how I use mine. I use blacks for the drive current and the reds for voltage sense.Don't listen to that fool (me) that does not match the traditional colors of the 4 wire jacks of a meter. What Wytnucls said is correct.As long as a source and sense are connected to each clip the worst that would happen is the polarity is backwards giving a negative voltage reading. Just make sure that with the clips open there is no continuity from black to red. If there is they are cheating and have both wires on one side of the clip or the clip halves are not properly insulated from each other.Edit: sorry posted too soonThe red banana should have continuity to one half of the clip only. The black banana should have continuity to the other half of the clip only. The shield is optional and typically all 4 shields would be connected together and have continuity to one black banana only that would be inserted in the input LO of the 4 wire inputs. The shields at the clip ends would not be connected to anything.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 06, 2014, 08:43:10 pm
content: It may be faulty, reconnect the black wires to their side of the clips and forget about shielding.

author: sync
author_rank: Frequent Contributor
timestamp: February 06, 2014, 08:44:22 pm
content: The cable is for the UT612. The UT612 doesn't use 4 wire measurement. The two inner sockets are connected to the ground plane. They are only for shielding.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 06, 2014, 08:47:53 pm
content: Ok, that makes sense now, but they shouldn't be called Kelvin clipsHey, that's my picture! lol

author: robrenz
author_rank: Super Contributor
timestamp: February 06, 2014, 08:51:15 pm
content: But they really are Kelvin clips!!! does it matter that its not a Kelvin connection?

author: linux-works
author_rank: Super Contributor
timestamp: February 06, 2014, 08:57:13 pm
content: I did get the impression that they are meant for something other than 4wire measurements.but shielding single conductors is not kelvin! there are not 4 wires in use, here, and the clips have one metal jaw wired and the other metal jaw (on the same clip) floating!maybe the seller just posted the wrong description? hard to believe uniT would call them kelvin when they clearly are not.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 06, 2014, 08:59:35 pm
content: I checked the UNI-T Chinese online catalogue and it is nowhere to be found.

author: ot1
author_rank: Contributor
timestamp: February 06, 2014, 09:00:45 pm
content: I agree with you Linux, those clips can't be 4-wire kelvin! To prove this fact with a kelvin designed meter, clipping the leads together should give you a zero ohms reading. If one refers tohttp://www.allaboutcircuits.com/vol_1/chpt_8/9.htmlthe clips you have cannot provide a Kelvin reading accuracy intended for 4-wire measurement without connecting the shields at the clip end !

author: linux-works
author_rank: Super Contributor
timestamp: February 06, 2014, 09:02:14 pm
content: Quote from: robrenz on February 06, 2014, 08:51:15 pmlolyou have a pointI was also able to buy the 'raw' clips (in solid red and solid black; none of that stupid grey stuff) and I'll soon make my own; but this pre-made cable looked cheap enough and so I gave it a try.funny that when I gave the seller a neutral feedback on ebay, they tried to bribe me (with only $4!) to change my review. I didn't slam the seller but I slammed the product as not being as-advertised, which it wasn't!

author: ron
author_rank: Regular Contributor
timestamp: February 06, 2014, 09:07:15 pm
content: "does this 'kelvin clip' cable even make sense?"I love puns

author: robrenz
author_rank: Super Contributor
timestamp: February 06, 2014, 09:18:55 pm
content: Quote from: ot1 on February 06, 2014, 09:00:45 pmShields are not a necessary part of a Kelvin connection. The pictures in that link are showing a 4 conductor cable not shielding.

author: linux-works
author_rank: Super Contributor
timestamp: February 06, 2014, 09:24:13 pm
content: you can't tell from the photo, but when I CUT OPEN the wire, I found it was cheap shielding (like you'd find on an rca stereo red/white cable that was included in an audio system for free) and the shield was not connected at the clip-end of things.

author: robrenz
author_rank: Super Contributor
timestamp: February 06, 2014, 09:43:32 pm
content: I was talking about the pictures in this linkQuote from: ot1 on February 06, 2014, 09:00:45 pm

author: Psi
author_rank: Super Contributor
timestamp: February 06, 2014, 09:50:55 pm
content: The shielding is probably just because shielded wire was cheaper at the time. Typical china.Just because a wire has extra conductors (the shielding) doesn't mean it has to be used for anything.4 wire measurement is done with 4 single conductors going to 4 terminals.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 06, 2014, 10:12:29 pm
content: On the UT612 LCR meter, the external leads have to be shielded, otherwise the meter internal calibration doesn't work. That's probably the reason for using shielded cable on this rig.https://www.eevblog.com/forum/testgear/review-and-tear-down-of-uni-t-ut612-lcr-meter/43/Post 43

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 06, 2014, 10:24:40 pm
content: Hi,You can find many instances on eBay where the word Kelvin is used incorrectly. Sometimes it is used when alligator or crocodile would be more appropriate.http://www.ebay.ca/itm/6pcs-1000V-32A-Battery-Alligator-Kelvin-Test-Clip-to-4mm-Banana-jack-6-Colors-/181314838482?pt=LH_DefaultDomain_0&hash=item2a3734dfd2Why would you need 32A Kelvin clips?Also what would do with these leads, other than cut them in half?Jay_Diddy_B

author: free_electron
author_rank: Super Contributor
timestamp: February 06, 2014, 10:31:54 pm
content: Quote from: Jay_Diddy_B on February 06, 2014, 10:24:40 pmoh for fuck's sake... anything to make a buck

author: linux-works
author_rank: Super Contributor
timestamp: February 06, 2014, 11:04:43 pm
content: Quote from: Jay_Diddy_B on February 06, 2014, 10:24:40 pmI think those are meant to be loop-backs.(lol)

author: linux-works
author_rank: Super Contributor
timestamp: February 06, 2014, 11:06:27 pm
content: Quote from: free_electron on February 06, 2014, 10:31:54 pmjust thought of another reason: extra reliability. in case one wire breaks, you still have the other.and yes, with china involved, this (whimsical) concept might actually apply.sad, that, though...

author: robrenz
author_rank: Super Contributor
timestamp: February 06, 2014, 11:40:02 pm
content: Quote from: Jay_Diddy_B on February 06, 2014, 10:24:40 pmSome micro Ohm meters use up to 100A of drive current

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 06, 2014, 11:41:53 pm
content: Quote from: free_electron on February 06, 2014, 10:31:54 pmI might have guessed that they were for Audiophile applications, but I did not see any mention of:1) Oxygen Free2) Single crystal3) Arrows showing the direction4) Burned in5) Cryogenic treatment6) Snake oil ....More seriouslyI believe these clips are copies of ESI clips. I have some of the original ones. I am trying to find some suitable rubber for the spring. I think have seen somebody using O-rings. I might give that a try.Jay_Diddy_B

author: robrenz
author_rank: Super Contributor
timestamp: February 06, 2014, 11:47:39 pm
content: Quote from: Jay_Diddy_B on February 06, 2014, 11:41:53 pmLooks like a length of thin wall silicone tubing.

author: ot1
author_rank: Contributor
timestamp: February 07, 2014, 01:42:27 am
content: Quote from: robrenz on February 06, 2014, 09:18:55 pmYes I don't know anymore because I can't tell how the red wires are connected to the clips ... Thinking it was through the black shielding although that seems unlikely now

author: scientist
author_rank: Frequent Contributor
timestamp: February 07, 2014, 03:47:03 am
content: Quote from: Jay_Diddy_B on February 06, 2014, 10:24:40 pmJumpstarting a car? That wire is pitifully narrow for that though.

author: free_electron
author_rank: Super Contributor
timestamp: February 07, 2014, 12:42:57 pm
content: Quote from: robrenz on February 06, 2014, 11:47:39 pmEbay me tions. Heat shrink tubing...

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 07, 2014, 01:27:52 pm
content: Hi,The real application for these Kelvin jumpers is for 4-Wire measurements of series-connected resistors:If you don't know what is wrong with this picture, you need to go back to school.Jay_Diddy_B

author: robrenz
author_rank: Super Contributor
timestamp: February 07, 2014, 01:46:07 pm
content: Thanks for posting that Jay_Diddy_B. Now that I can see how useful they are I am going to have to make some up. But I think I am going to include some offset compensation circuitry in mine

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 07, 2014, 02:34:47 pm
content: Robrenz,I would also make some in a Y configuration, with three Kelvin clips, they would be useful for 4-Wire measurements of parallel connected components.Jay_Diddy_B

author: The Electrician
author_rank: Frequent Contributor
timestamp: February 08, 2014, 07:02:49 am
content: Quote from: Jay_Diddy_B on February 06, 2014, 10:24:40 pmAre these for sale on eBay, or somewhere else? If so, do you have a link?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 08, 2014, 01:34:24 pm
content: Hi,I found them here:http://www.ebay.ca/itm/1pair-1M-3-3FT-Double-Gold-plated-Copper-Kelvin-Clip-4-wires-Silicon-Test-Cable-/400488747789?pt=LH_DefaultDomain_0&hash=item5d3efd530dThe same seller also offers the clips separately, which make a more sense:http://www.ebay.ca/itm/2x-12-0014-Gold-plated-Copper-10A-Kelvin-Clip-with-20cm-8mm-Heat-Shrinkable-Tube-/181136611941?pt=LH_DefaultDomain_0&hash=item2a2c955a65Jay_Diddy_B

author: linux-works
author_rank: Super Contributor
timestamp: February 09, 2014, 07:12:40 pm
content: Quote from: ron on February 06, 2014, 09:07:15 pmthat brings up another bad ebay purchase of mine. I once bought a palindrome but they actually just sent me a pun.

author: nadona
author_rank: Regular Contributor
timestamp: February 09, 2014, 10:05:43 pm
content: Quote from: Jay_Diddy_B on February 08, 2014, 01:34:24 pmI am looking for 30A Kelvin clips to make 30A connections for my micro ohm meter.I couldn't find mentioning of 35A in the first URL's page. 2nd URL's title says 10A clip. Maybe different clips they are using in the first webpage product?I am planing to buy 30A clip and use car battery jump cables to the meterAnd put spade lug on the other end. Better idea?Thank you.

author: linux-works
author_rank: Super Contributor
timestamp: February 10, 2014, 02:39:47 am
content: do you plan to use that for, uhm, constantcarrant?

author: nadona
author_rank: Regular Contributor
timestamp: February 10, 2014, 03:15:43 am
content: I think yes because it has voltmeter inside to use ohm's law. No?

author: staxquad
author_rank: Frequent Contributor
timestamp: February 10, 2014, 04:24:46 am
content: Quote from: robrenz on February 06, 2014, 11:40:02 pmthese beefy kelvin cables made by Mueller have a 100A capacity, used in a GE double bridge (marked Cornish Coroprene 14/2 type SJO 300V on the cables)pictured with an 87 for size referencefor example, they were used to find ground faults on aircraft