Kelvin leads for DMM - Page 1
Forum section: electronics / testgear

author: Traceless
author_rank: Frequent Contributor
timestamp: March 07, 2022, 08:43:16 pm
content: Currently I'm looking for a set of kelvin leads to go along with a new DMM. Does anyone have any experience withthese? Is there any good reason (other than the extra ground lead) to go withtheseortheserather than the ebay ones? This seems to be one of the cases where you pay almost 6 times the price just for a brand name, or am I mistaken and there is any real value that justifiesthatkind of surcharge?

author: TimFox
author_rank: Super Contributor
timestamp: March 07, 2022, 08:48:27 pm
content: I like the idea of shielded wires and a fifth wire for ground, but most modern DMMs seem to lack a "ground" connection on the front panel.When measuring high resistance values with such a DMM, I have a noticeable problem with hand capacitance, even with the metal chassis near the resistor connected to the LO terminal on the ohmmeter (usually two-terminal for high values).

author: mawyatt
author_rank: Super Contributor
timestamp: March 07, 2022, 09:12:00 pm
content: Have a few DIY versions.LeftRight is dual with 2 wires & shields,rightleft is cut off BNC types and replaced with Banana plugs, each wire is shielded,topbottom is small Kelvin clips with unshielded wires and Banana plugs.All seem to work OK for what we need, the best are the individual shielded wire types.Best,Edit: Whoops image came out inside down!! So changed above!

author: Someone
author_rank: Super Contributor
timestamp: March 07, 2022, 10:34:03 pm
content: time to start sellingaudiophilevoltnuttery cryo treated individual triax wired palladium clips with optional antitriboelectric PTFE wire stands?

author: alm
author_rank: Super Contributor
timestamp: March 07, 2022, 10:54:59 pm
content: The clips on the "GW-Instek" leads look quite cheap to me. Also, the way the wire is coiled makes it look quite stiff. The nicer clips, wire and higher-quality gold-plated banana plugs is probably where the extra money goes, beyond brand name and paying for a fairly low-volume item compared to normal DMM probes. Whether this is worth paying 6x as much is of course debatable.You may already know this, but you don't need Kelvin clips to do a four-wire (Kelvin) measurement. It works pretty much as well if you use four separate wires. The only downside is the extra hassle of having to attach four clips, and possibly extra noise pickup unless you twist the wire together (sense with sense, force with force).These kind of Kelvin clips are usually quite large. So they'll fit on unsoldered leaded resistors, but good luck clipping them to a 1/4W resistor that's tightly bent and soldered to a PCB. Never mind any SMD. Four small hook / pincer clips may very well work better for PCB work unless you're measuring a large through-hole current shunt resistor. I only use purpose-built Kelvin clips when measuring loose resistors. For any other four-wire measurement, like in circuit, I'll usually use some other way of attaching the four wires.

author: Hydron
author_rank: Super Contributor
timestamp: March 08, 2022, 12:17:35 am
content: The ebay GW Instek seem to work fine for me, though they are a bit chunky as noted, and the gold plating doesn't seem to be the thickest (am seeing some discolouration). They are certainly higher quality than the top two types of clips in mawyatt's collection. I also have some of these with shielded wires and didn't notice any benefit when I tried them versus the unshielded ones. Wire isn't super flexible like nice test-lead silicone wire, but it's not problematic either.

author: duckduck
author_rank: Frequent Contributor
timestamp: March 08, 2022, 01:17:36 am
content: Quote from: Traceless on March 07, 2022, 08:43:16 pmHaven't tried the fancy ones. I've got a set of these:https://www.ebay.com/itm/201604885284( Cheap  leads from "AST Labs" ) and they work very well for fancy-hobbyist level work. If I made a living making 4-wire measurements I would buy a fancy set from one of the big test equipment manufacturers.

author: mawyatt
author_rank: Super Contributor
timestamp: March 08, 2022, 02:41:15 am
content: Here's some higher quality Kelvin clips and tweezers from Tonghui, use these with the TH2830 LCR meter. The Kelvin clips came with the instrument and they all have a 4 BNC interface so not compatible with DMMs. The tweezers work really well with SMD devices, also have a dedicated SMD device fixture for discrete SMD work.There might be DMM versions of these Tonghui tweezers and SMD fixture for use with DMMs with banana jacks, but we don't have them. Been thinking about making some adapters so these could be used with DMMs and the DE-5000.Also shown are some cheap tweezers with added banana jacks, these work but nowhere as easy as the quality Tonghui tweezers. Also added some Kelvin clips to the DE-5000, these work well as do the supplied DE-5000 Tweezers, and Gator clips.Anyway, all this was created to help support an ongoing project, various precision components became unavailable because of Covid, and we decided to characterize and match the components we could get as required for the project, many of these components required 15~16 bit equivalent matching. There were quite a lot of components and gave us anexcuserequirement to assemble all these Kelvin clips, fixtures and suchAfter measuring many thousands of components with various instruments we found the inexpensive Kelvin clips worked almost as well as the OEM Tonghui supplied clips, but the cheap tweezers didn't!! The SMD fixture allowed the best use with discrete SMD devices tho, but of course you must use tweezers for mounted SMD devices.Best,

author: Electro Fan
author_rank: Super Contributor
timestamp: March 08, 2022, 03:30:29 am
content: I tried a few less expensive products and then settled on these after doing some tests with a 34465A.https://www.tequipment.net/BK/TLDK1/Kelvin-Test-Leads/Had I just started with these I could have saved the price of the others.Edit to add a link:https://www.eevblog.com/forum/testgear/4-wire-2-wire-resistance-tests-various-cheap-kelvin-clips-various-meters/msg3240888/#msg3240888

author: JohnG
author_rank: Frequent Contributor
timestamp: March 08, 2022, 02:11:30 pm
content: I have two sets.The less expensive set: Pomona 6303https://www.pomonaelectronics.com/products/dmm-test-leads-and-probes/kelvin-probe-setThis set is Kelvin connected only to the needle tip probes, not all the way to the component terminations. But, it turns out that they are good enough for about95%98% of what I need, and the needle points are far more user-friendly than the clips on my expensive set. Since the majority of the error-inducing impedance is normally the test leads, and these take care of most of that, they work well.The expensive set: Keysight 11059Ahttps://www.keysight.com/us/en/product/11059A/kelvin-probe-set.htmlIf I am measuring low single digit milliohms or less, and I care, and the component has leads or some big features to grab onto (PCB traces or copper busses), I use these. For that, they work great. For surface mount anything, not so much.John

author: alm
author_rank: Super Contributor
timestamp: March 08, 2022, 02:40:15 pm
content: I have a set of true four-wire probes:Keithley 5805. I bought them used years ago, and definitely didn't pay anywhere near $300. They are nice for measuring PCB traces with negligible error from contact resistance, but the distance between the two probe tips makes it quite hard to use: finding spots you can use it on a PCB with solder mask is often difficult.

author: mawyatt
author_rank: Super Contributor
timestamp: March 08, 2022, 04:00:09 pm
content: Quote from: Electro Fan on March 08, 2022, 03:30:29 amThose B&K TLDK1 Kelvin probe clips look like the Tonghui supplied ones on the TH26011CS fixture, and much higher quality clips than the cheaper Kelvin types found on eBay. Couldn't find them sold individually anywhere tho.While searching I came across some R&S Kelvin clips and cables with BNC ends, these looked like the cheap eBay cables with the low quality Kelvin clips. Recall the price was ~$330!!!Anyway, thanks for pointing out the B&K Kelvin cables, with those quality Kelvin clips they are certainly better than anything we conjured up!!Best,

author: TomWinTejas
author_rank: Regular Contributor
timestamp: March 08, 2022, 04:40:38 pm
content: I purchased some banana plug patch cords directly from AST Labs last week and added some Kelvin leads since I was already paying for shipping, even though I don't have a 4 wire meter just yet. The quality looks better than what I've seen from typical AliExpress vendors, but unsurprisingly doesn't match what I've ordered from Probemaster. The leads are nice and flexible, appear to be silicone. The clamps are made of what feels like a cheap plastic, but the clamping action feels solid. The actual alligator clips on the clamp look solid and have good alignment on the teeth. I just verified they are fully isolated up to the actual teeth, the spring is insulated from the terminals. For around $20, I think it was a good deal.https://ast-labs.com/product-category/test_cables/kelvin/

author: SHTechnics
author_rank: Regular Contributor
timestamp: March 08, 2022, 09:02:21 pm
content: I got these from Banggood and they work fine :https://www.banggood.com/Y238-2Pcs-LCR-Bridge-Test-Cable-Universal-Digital-Multimeter-Plug-Milliohm-Test-Line-Test-Clips-p-1482576.html?imageAb=2&rmmds=myorder&cur_warehouse=CN

author: MegaVolt
author_rank: Frequent Contributor
timestamp: March 09, 2022, 12:27:55 pm
content: These beautiful clips seem to belong to Tonghui. I think somewhere else should be the same ending bananas.https://aliexpress.ru/item/1005002208013017.html

author: mawyatt
author_rank: Super Contributor
timestamp: March 09, 2022, 12:56:26 pm
content: Yes, those are from Tonghui. Seems the banana versions are also from Tonghui (same unique Kelvin Clips) and rebranded by B&K TLDK1 as shown by Electro Fan. Tonghui stuff seems first class, and much is rebranded by others. Took a peak inside at the TH2830 we have, it's as well made as present day Keysight equipment (KS34465A for example).Best,

author: mawyatt
author_rank: Super Contributor
timestamp: March 09, 2022, 07:13:13 pm
content: Ran some long term tests while working other things. After about 4~5 hrs we have DIY Kelvin leads connected to one KS34465A and DMM6500. Another KS4465A has 4 wire DIY Zero ohm shunt. The KS34465A Kevin setup has each wire shielded with clips shorted. The DMM6500 Kelvin setup has 4 individual wires all within one overall cable that's shielded with clips shorted.Everything is in open room with AC at ~45% Humidity and ~26C, no attempts to shield for air flow or by not being close by.Results of long term average are:4 Wire short 50u ohms with SD of 21u ohms (KS34465A)Individual Shielded Kelvin 4 leads 161u ohms SD 19u ohms (KS34465A)Single shielded 4 lead Kelvin -80n ohms SD 5u ohms (DMM6500)All meters had Offset Compensation and AZ active and no null (KS34465A) or reference (DMM6500) were used. Line Synch with 10 for KS and 5 for DMM, averaging filter 50 readings for KS and 20 for DMM. Should have made all these settings close to each other, but didn't think about it when we started the test early this morning, so just reported what we found.Don't have any proper quality non-DIY Kelvin clips with banana jacks to compare with, however the shorted clip tests seem to indicate these DIY Kelvins are acceptable for our needs at the moment, although they likely won't last long with heavy use since the plating is questionable...gold??...how thick??Edit: Took an image of the Web Server screen showing the 3 meters before changing things, top KS is Kelvin setup, bottom is 4 wire short, left is DMM6500 with Kelvin setup.Best,

author: Kean
author_rank: Unknown
timestamp: March 09, 2022, 08:08:23 pm
content: I have a set of the Keysight 11059A I bought in late 2015 a few months before I bought my 34465A.I also have some of the Tonghui measurement sets for my LCR meter - SMD fixture, tweezers, and Kelvin clips. They are pretty good but in my opinion not as nicely constructed as the 11059A set. I haven't tried the Pomona Kelvin leads but generally Pomona quality is reasonable.For things that I rely on as a consultant, I prefer to pay once and cry once. As a hobbyist I'm also happy to buy cheaper stuff that isn't critical and hope it is decent (often it is virtually identical). In this case I believe the 11059A were on special at the time, and I got them a lot cheaper than the current price.

author: tooki
author_rank: Super Contributor
timestamp: March 09, 2022, 08:50:25 pm
content: Quote from: mawyatt on March 09, 2022, 07:13:13 pmPlease use thescreenshot features of your operating systemto take screenshots. Photographs of the display suck in so many ways.As for the plating: you do realize the whole point of Kelvin measurement is to eliminate the effects of test lead and contact resistance?

author: mawyatt
author_rank: Super Contributor
timestamp: March 09, 2022, 09:00:20 pm
content: Edit: @ KeanThose look very nice, and price ($213) isn't that high for KS!!Know what you mean about regarding cheaper stuff for "real " work, and not wasting time. That's why we got the Tonghui TH2830 first with various Tonghui fixtures, including Kelvin clips, Tweezers and Slotted fixture for components with wires. Since our main project tied up the TH and we needed to also to make other measurements and decided to go the cheap approach, since we could "verify" the cheap clips & fixtures with the Tonghui. Later when we needed accurate capacitance measurements, we got the DE-5000 to supplement the TH2830, the DE-5000 is very accurate and spot on when compared to the TH2830, great value IMO!!Over time we would periodically "spot check" the cheap stuff, and trash the inferior/defective items..... so a few clips, cables, connectors, adapters and such ended up in the can!!Best,

author: mawyatt
author_rank: Super Contributor
timestamp: March 09, 2022, 09:10:34 pm
content: Quote from: tooki on March 09, 2022, 08:50:25 pmPlease use thescreenshot features of your operating systemto take screenshots. Photographs of the display suck in so many ways.Will do!!QuoteActually in reality it doesn't "eliminate the effects" of test lead and contact resistance, it attempts to reduce these effects. There are many different types of "Kelvin" type fixtures/clips/tweezers available, and not all fit the same measurement situation.Best,

author: Hydron
author_rank: Super Contributor
timestamp: March 09, 2022, 09:20:40 pm
content: Quote from: Kean on March 09, 2022, 08:08:23 pmI think there is a chance that all of these are made by pomona (with small differences between runs - they seem to have been around a while), in which case you have tried the pomona oneshttps://uk.farnell.com/pomona/5940/test-lead-set-kelvin-clip/dp/4136020~=https://uk.farnell.com/keysight-technologies/11059a/kelvin-probe-set-0-8m-42v/dp/2853359~=https://uk.farnell.com/keithley/5809/set-clip-lead-kelvin/dp/2131248edit: missed these too!https://www.warwickts.com/1311/PJP-440-Kelvin-Clips-Lead-Set@Kean - have you specifically tried the BK precision/Tonghui clip style from the following link vs the Keysight ones?https://www.tequipment.net/BK/TLDK1/Kelvin-Test-Leads/It looks like the TLDK1 would have an advantage in ease of use, only needed to plug in 2 connections vs 4 or 5.

author: Traceless
author_rank: Frequent Contributor
timestamp: March 09, 2022, 09:27:54 pm
content: Thanks to everyone for the feedback. So far the TL;DR I get from all the responses is:"Expensive probes are kinda nice and can make a difference but probably are not really worth the money, cheap or diy ones do the job at a fraction of the cost."@mawyatt that is a nice collection of probes you have there, also thank you for posting your test measurements, the probes you tested all seem to be pretty good. The most impressive were of course the single shielded ones tested on the DMM6500. It would be interesting to see a comparison where you swap one of the probes you tested with the KS with those tested on the Keithley just to see if the probes are that good or if it is the DMM or a combination of both.Quote from: alm on March 07, 2022, 10:54:59 pmYes thats a good point using four seperate clips/grabbers and not touching the probes is surely the best way to go in many cases. There is at least one case where Kelvin probes, especially @JohnGsPomonaprobes are really useful (IMO): Following the lowest resistance path to trace a short. With regular two wire probes your test leads keep influencing the measurements and may send you on a goose chase, but with these 4-wire-2-point probes you pretty much eliminate the effect of your leads. Tracing shorts with 4 seperate wires especially when SMD components involved is cumbersome . In the past I used my "poor man's version" of the Pomona 6303 probes, with varying degree of success. Here is a picture for the amusement of everyone aroundWhile they don't perform actual 4-point measurements and thus may not give the most accurate absolute value they give pretty good relative measurements and eliminate any influence of the test leads. If anyone knows cheaper alternatives to the Pomona 6303 let me know.@Electro Fan I was also looking at the BK TLDK1 and liked them but they are also rather expensive here. You can expect to pay 100€ in Germany.@TomWinTejas, @duckduck: The AST probes look nice but don't seem to be easily available in Germany. Importing them from the US will make them a lot more expensive due to shipping + import fees.@alm: I did a quick search on ebay for the Keithleys, the cheapest 5805s currently available are 172,93€ + shipping. Maybe there pops up a bargain at some point.@SHTechnics: I do likethe banggood ones you linkeda lot, are affordable and also look like they are less bulky and more flexible than the ebay-GW-Instek ones I posted. I think I might buy a pair of these to give them a try.@Hydron: Thanks for reporting back on your experience the GW-Instek ones I linked in my original post. Before you and alm mentioned it i didn't recognize how wide the clip-tips are. Indeed I was looking for something more filigree.

author: Hydron
author_rank: Super Contributor
timestamp: March 09, 2022, 09:44:06 pm
content: Thought this might be useful for reference:

author: Electro Fan
author_rank: Super Contributor
timestamp: March 09, 2022, 11:13:10 pm
content: fwiw, I've found that where the BK TLDK1 Kelvin clips and leads will measure my reference DUT (45 cm of 18 gauge copper wire) as being approx 9.5 milliohms (depends on ambient temp, settling time, etc.) I can get a very similar reading (within about 0.1 milliohms, ie about 100 microohms) by using four separate just plain old every day nothing special leads with banana to alligator clips and banana to minigrabber clips. I am very happy with the TLDK1 Kelvins (they provide convenience and confidence inspiring measurements) as companions to the 34465A but unless you are going deep(er) into metrology 4 regular separate clips and leads can probably suffice.

author: Someone
author_rank: Super Contributor
timestamp: March 09, 2022, 11:14:01 pm
content: Quote from: Traceless on March 09, 2022, 09:27:54 pmTiny kelvin clips:https://www.eevblog.com/forum/testgear/best-way-to-securely-attch-probe-to-a-passive-smd-component/msg1310826/#msg1310826BYO cabling, "standard" 0.025" pin header plugs. They will take more than the 1A rated current.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 09, 2022, 11:31:39 pm
content: Quote from: Someone on March 09, 2022, 11:14:01 pmThanks for posting. The product in the photos at your link above looks good but the link at your link doesn't seem to go to the product and the product number doesn't seem to be findable. Maybe a double check? Thxhttp://www.keysight.com/my/faces/partDetail.jspx?partNumber=1400-3652Edit: found it, I think:https://www.keysight.com/my/partDetail/1400-3652

author: Someone
author_rank: Super Contributor
timestamp: March 10, 2022, 12:41:01 am
content: Quote from: Electro Fan on March 09, 2022, 11:31:39 pmOr if you read that (short and concise) thread, a whole 2 posts along:https://www.eevblog.com/forum/testgear/best-way-to-securely-attch-probe-to-a-passive-smd-component/msg1310906/#msg1310906you get the OEMs part number.

author: alm
author_rank: Super Contributor
timestamp: March 10, 2022, 01:05:29 am
content: Quote from: Electro Fan on March 09, 2022, 11:13:10 pmWell, if you talk about metrology, high-end standard resistors will just have four binding posts to be used with four leads with spade lugs. The leads may be twisted and shielded, have low thermal emf connections and have a high insulation resistance, but that's pretty much all there is to it. There's really nothing in having force and sense combined in one clip that improves accuracy.To me the main advantage of the 'real' Kelvin clips is that they are quick to clip on. Clipping on and off four clips each gets old real soon if you're measuring 20 resistors (like for matching / binning).

author: Electro Fan
author_rank: Super Contributor
timestamp: March 10, 2022, 04:07:22 am
content: Quote from: Someone on March 10, 2022, 12:41:01 amThanks! Looks like same part at a better price.https://www.newark.com/hirschmann-testmeasurement/972416100/clip-test-micro-smd-black-mln/dp/67C8450

author: Gary350z
author_rank: Regular Contributor
timestamp: March 10, 2022, 11:37:17 am
content: I have theseB&K TLDK1 Kelvin probes:They work very good and have good build quality.Mine have a moderate amount of that cheap Chinese plastic smell, which I don't like.https://www.tequipment.net/BK/TLDK1/Kelvin-Test-Leads/-----------------------------------------------------------------------Previously, I bought some of the these GWInstek Kelvin type clips to make my own probes.https://www.ebay.de/itm/231777696119?epid=1501720482&hash=item35f706f977:g:saQAAOSwp5JWZq5gThey are supposedly made by ETA (Electronic Test Accessories); ETA3105 Kelvin Test Cliphttp://www.tw-eta.com/index.php?c=show&id=149I don't know if I got the real deal or a clone, but mine were very bad. They are supposedly gold plated, but the surface of the metal looks bad, and when testing conductivity of the surface of the metal with good gold plated meter probes, many times they don't even make contact. I threw them away.

author: Gary350z
author_rank: Regular Contributor
timestamp: March 10, 2022, 11:43:29 am
content: B&K TLDK1 Kelvin probes teardown photo:

author: mawyatt
author_rank: Super Contributor
timestamp: March 10, 2022, 02:11:57 pm
content: Of course with just a 4 wire Kelvin banana interface this begs the question, "where to connect the shield(s)"?? What's interesting about the above image is that the transition from the 4 wire individually and overall shielded grey cable is that none of these shields is terminated!! The connection to the 2 dual prong banana adapters are using a shielded single wire connection and the shield as the other connection to connect to the dual banana jacks!!Our DIY versions, we brought all the shields together and a separate banana jack, so a 5 wire setup. The 5th or shield wire can be connected separately, and usually we just connect to the source negative on the DMM since these have no ground or chassis connection on the front panel, although we found little difference in resistive measurements with the shield wire connected or not, or connected to another DMM terminal. This might make a difference with very high resistive measurements, although we haven't done any of these measurements yet (high resistive measurements don't usually require Kelvin measurements tho).Having the shields connected to chassis or line ground may improve EMI/RFI susceptibility, and may provide a more stable measurement environment (in our case this didn't make much difference).With any of the Kelvin clip type cables getting accurate small capacitance readings will be difficult, these are best left to a mechanically and electrically stable test fixture, and not generally the place for using banana jacks and DMMs, this is the purpose for dedicated LCR instruments and fixtures.Here's what the Tonghui TH26011CS Kelvin Clip BNC interface box to the instrument looks like. Note how each individual lead shield is terminated at BNC chassis connection, and all shunted together (doesn't seem the overall cable shield is connected tho).This illustrates the difference between a LCR instrument and DMM Kelvin Clip banana jack type interface.Anyway, interesting topic and thanks for posting the innards of the B&K TLDK1.Best,

author: 2N3055
author_rank: Super Contributor
timestamp: March 10, 2022, 08:08:38 pm
content: Fairly convenient place to connect shield to analog ground of multimeter is a high current input. I use 10A input on my DM3068.

author: mawyatt
author_rank: Super Contributor
timestamp: March 10, 2022, 08:30:53 pm
content: Yes that is a good spot, however we haven't seen any change in readings when connected or not, but measuring low value resistors (<100k) also.Best

author: Electro Fan
author_rank: Super Contributor
timestamp: March 10, 2022, 09:15:47 pm
content: 2N3055, mawyatt, others?Anyone up for posting a summary explanation or "theory of operations" regarding the role of the shield and the practical connection considerations? Maybe touch on how a fifth conductor is supposed to work with 4 wire Kelvin leads. Thx"Fairly convenient place to connect shield to analog ground of multimeter is a high current input. I use 10A input on my DM3068.""Yes that is a good spot, however we haven't seen any change in readings when connected or not, but measuring low value resistors (<100k) also."

author: Someone
author_rank: Super Contributor
timestamp: March 10, 2022, 09:32:34 pm
content: Quote from: Electro Fan on March 10, 2022, 09:15:47 pmhttps://www.tek.com/en/documents/product-article/keithley-low-level-measurements-handbook---7th-edition

author: mawyatt
author_rank: Super Contributor
timestamp: March 10, 2022, 09:43:14 pm
content: One issue is with measuring small capacitance, any coupling between the leads can create errors. Also if the cables move, bend, or change position this can create a change in the setup residual capacitance and corrupt measurements. Having each individual wire shielded reduces the coupling IF the shields are terminated. These are reasons mentioned for using a rigid mechanical fixture for small capacitance readings where things are fixed and don't move.Another issue is potential EMI susceptibility, where shields help reduce the actual external signal coupling onto the inner signal lead, although most DMMs have pretty good EMI filtering since they are designed to work with unshielded cables/probes.With high valued resistance measurement leakage can corrupt measurements, and having shields terminated helps keep the leakage current controlled and confined, in some cases the shield can act as a"guard" where the shield is driven by a voltage similar to the one on the conductor the shield is guarding. This reduced the differential voltage between the inner lead and shield and reduces leakage. This very technique was employed eons ago to effectively reduce the cable capacitance as "seen" by the signal on the cable inner conductor, since displacement capacitive current is proportional to dV/dT, by making dV~0, or shield voltage approximately equal to the conductor signal (unity gain buffer amp to drive the shield), then the displacement current is reduced and capacitance as "seen" by the conductor signal is reduced. We patented a 2 dimensional similar technique to reduce the electron leakage between adjacent pixels in an ultra-sensistive night vision imaging chips (patent 8102452), this is where every electron counted!!Anyway, I'm sure 2N3055 and others can elaborate much more on this issue as we're certainly no expert on this.Edit: That's a great article mentioned by Someone, must readBest,

author: 2N3055
author_rank: Super Contributor
timestamp: March 10, 2022, 11:21:44 pm
content: Between what "not an expert"Mike wrote and Keithley LLM handbook, not much for me to add.These are simply electrostatic shields. As Mike also said, not needed for low impedance circuits, and source of leaks with really high impedance circuits, where you use triax, that combines driven guard and shield. God triax cables also have conductive layer to reduce triboelectric effects ( a cousin of piezoelectric effect in other materials) from moving or vibrating cables.For DC ohm measurements all of that is probably not necessary. For LCR meter OTOH, very useful.I use current socket as a point to connect shield when measuring low voltage AC together with shielded twisted pair for inputs.That is to reject both magnetic (twisted pair) and electric field (shield) coupling into circuit.Microphones use same type of connection: differential + shield.

author: Kean
author_rank: Unknown
timestamp: March 11, 2022, 12:41:03 pm
content: Quote from: Hydron on March 09, 2022, 09:20:40 pmThe only set I have apart from the KS 11059A is a set for the LCR meter with the 4 BNC box, so I can't do a comparison. I thought my LCR meter set were Tonghui, but they are just an unbranded clone of the TH26011 with the common low-cost plastic handled Kelvin clips. Only my LCR SMD adapter is Tonghui branded, and that is the primary adapter I use.The thing I really like about the 11059A set (and the Pomona/Keithley equivalents) is that the Kelvin clips are a really simple design. The only plastic part is at the pivot, and the rest is just bent metal, heatshrink, and O-rings. Almost as simple as a common clothes peg, so very easy to maintain/repair if ever needed.

author: gamalot
author_rank: Super Contributor
timestamp: March 11, 2022, 02:13:53 pm
content: I compared the difference when the shield of the test leads were grounded or left floating on my Hioki RM3545 DC resistance meter. You can see that the difference is 'huge' when the resistance under test is 100K ohms, and there is still a 'tiny' difference when the resistance is as low as 100 ohms.

author: tooki
author_rank: Super Contributor
timestamp: March 11, 2022, 04:49:11 pm
content: Where it would get interesting is with very high resistances. (Like the 40MOhm resistor I had to measure a few weeks ago.)

author: TimFox
author_rank: Super Contributor
timestamp: March 11, 2022, 05:16:28 pm
content: I recently built some shielded banana-plug leads from Pomona patch cords and shield braid because of difficulty measuring resistors > 100 k ohms with a bench DMM.This improved body- and hand-capacitance effects when the shields were connected to "LO", but I had better results with a different setup and a "real" ground connection to the shields.

author: gamalot
author_rank: Super Contributor
timestamp: March 11, 2022, 07:42:11 pm
content: I tested the highest value resistor I could find, a cheap 1G ohm/5 watt high voltage resistor I bought from China. At such high resistance values, without any well-grounded shield, the results would be obviously bad.

author: Someone
author_rank: Super Contributor
timestamp: March 12, 2022, 01:39:11 am
content: Quote from: gamalot on March 11, 2022, 07:42:11 pmThe periodicity of that interference is rather "suspicious" bench DMMs are usually excellent at rejecting external interference when correctly configured.

author: Traceless
author_rank: Frequent Contributor
timestamp: March 12, 2022, 09:07:15 am
content: Quote from: Someone on March 10, 2022, 09:32:34 pmI just took a look at that Tektronix article, can anyone explain why they measure resistance in watts?

author: tooki
author_rank: Super Contributor
timestamp: March 12, 2022, 09:11:29 am
content: Quote from: Traceless on March 12, 2022, 09:07:15 amThey don’t: That’s practically guaranteed to be a typo caused by conversion from one file format to another. If you download the book as a PDF (the “DOWNLOAD FILE” button at the top of the page), it uses the ohms symbol there.

author: Traceless
author_rank: Frequent Contributor
timestamp: March 12, 2022, 09:25:02 am
content: @tooki: Yeah that was my first thought as well but they mad a lot of typos then. At first I thought it might be an auto-conversion issue, but it is not consistent even on the screenshot I posted there is actually the Omega used for resistance correctly as well. They just switch back and forth between the "" and "W". The first time it already happens in 1.1:Quote from: Keithley link=https://www.tek.com/en/documents/product-article/keithley-low-level-measurements-handbook---7th-edition

author: tooki
author_rank: Super Contributor
timestamp: March 12, 2022, 09:42:40 am
content: Quote from: Traceless on March 12, 2022, 09:25:02 amBelieve me, it’s a conversion issue. Who knows what the original source format is. But it’s eminently possible to have inconsistent conversions. Or the conversionwasconsistent, but the person using search-and-replace to fix it didn’t catch them all.Again, the PDF is correct, just look at it.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 13, 2022, 04:01:27 am
content: Quote from: Electro Fan on March 10, 2022, 04:07:22 amI ordered a pair of these. They are pretty small: about 2.5 cm long with the plastic housing and about 5mm wide on the jaws, so they are a good size for SMDs but they are a bit finicky to keep in place as you try to make measurements. If you have steady hands and your leads are long enough to reach your DUT they will hold, somewhat. You have to make your own leads. I had some female to female Dupont connectors about 6 cm long that attached to the male pin inside each jaw clip handle and then I extended those 60 cm with 22 gauge solid wire and then attached the wires to banana jacks. When it was all put together they read within about 0.1 milliohms of the TLDK1 Kelvins on my reference 45 cm copper wire. Unless you are really into low ohm SMD readings I'd say the TLDK1 leads and clips are a better use of the budget but it was an interesting look-see.

author: gamalot
author_rank: Super Contributor
timestamp: March 13, 2022, 08:01:53 am
content: Quote from: Electro Fan on March 13, 2022, 04:01:27 amI bought it on eBay for a slightly higher price.

author: tooki
author_rank: Super Contributor
timestamp: March 13, 2022, 01:26:03 pm
content: For those in Europe (or placing orders from USA, etc large enough to warrant the shipping cost), Reichelt.com has those for just over €10:https://www.reichelt.com/ch/de/miniatur-pruefclip-smd-bauteile-0-64-mm-schwarz-micro-smd-clip-p106195.html

author: Electro Fan
author_rank: Super Contributor
timestamp: March 13, 2022, 09:59:22 pm
content: Quote from: tooki on March 13, 2022, 01:26:03 pmThat's a good deal even if you have to ship a couple from Europe to the U.S. At the reichelt price they make sense if you are doing SMD, and to be square they hold onto regular resistor and other wire leads ok too. Definitely not as much clamping force as conventional Kelvin clips but ok for taking a measurement.

author: alex-kv
author_rank: Contributor
timestamp: March 14, 2022, 01:02:54 pm
content: I use these multicontact kelvin crocodile clips for the low resistance measurements. The cable is silicone-insulated coaxial. The measurement is far more stable than with the 4 wire+clip I used before.https://www.staubli.com/content/dam/spot/66.9795_en.pdf

author: MegaVolt
author_rank: Frequent Contributor
timestamp: March 14, 2022, 02:53:04 pm
content: Similar:https://aliexpress.ru/item/1005001422956990.html

author: Traceless
author_rank: Frequent Contributor
timestamp: March 17, 2022, 08:03:09 am
content: Quote from: SHTechnics on March 08, 2022, 09:02:21 pmI just found adealon those leads SHTechnics mentioned before and thought I'd share that here in case someone else is interested in giving these a try as well.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 30, 2023, 01:51:44 am
content: Resurrecting an old thread but it's sort of relevant.Awhile back in trying to compare a few models of Kelvin clips I made some posts (earlier in this thread) measuring the resistance of 45cm of 18 AWG copper wire. I got about 9.5 to 9.7 milliohms with some slight variations depending on room the clips/leads I used and maybe some temperature variation.In thinking about jumpering acrosss some traces on a circuit board using 30 AWG kynar wire I figured I should check to see what the current carrying capacity of 30 AWG kynar wire is. After looking that up I decided to test it. When I started the test I noticed that the results looked like about 150 milliohms and I then went back to doing some other work. When I looked up I noticed the test was still running but I couldn't explain why the pattern appears as it shows below. I can believe that my room temperature changes but probably not with such a symmetrical pattern. Anyone have some ideas on why the resistance pattern looks like this? ThxEdit: Kind of duh....Looks like the original copper wire measurement was done with the histogram and the first kynar measurement was done with the trend display. In looking at the new (2nd image) posted here the histogram for the kynar measurement sort of resembles the copper wire histogram. I'm guessing that if I had done the copper wire measurement with the trend display I might have seen the variable pattern. However in thinking about it, I'm still not sure what accounts for the symmetry in the kynar trend display.

author: mawyatt
author_rank: Super Contributor
timestamp: August 30, 2023, 02:09:57 am
content: Seen this type of display before, it was attributed to the AC cycling in our case.Best,

author: BillyO
author_rank: Super Contributor
timestamp: August 30, 2023, 02:38:31 am
content: Quote from: Electro Fan on August 30, 2023, 01:51:44 amIs the environment air conditioned?

author: Electro Fan
author_rank: Super Contributor
timestamp: August 30, 2023, 03:07:07 am
content: Quote from: BillyO on August 30, 2023, 02:38:31 amYes, it is. Do you think the AC comes and goes that symmetrically? Seems slightly hard to believe but maybe....

author: BillyO
author_rank: Super Contributor
timestamp: August 30, 2023, 03:12:57 am
content: Quote from: Electro Fan on August 30, 2023, 03:07:07 amYour collection was over only 2 hours so the external temperature likely would not have changed much in which case the AC would cycle fairly regularly. As for symmetry .. luck of the draw in most cases but to be expected for a well designed system.One way to test would be turn the AC off for a couple of hours and re-run the data collection.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 30, 2023, 03:25:56 am
content: Ok, fwiw, since my earlier post I went back to run the 45 cm 18 AWG copper wire test. Below is the trend chart for that; doesn't appear quite so symmetrical but it's only about 9.6 milliohms vs roughly 150 milliohms for the 45 cm 30 AWG kynar wire.I have restarted the kynar wire test and I'm going to shut the AC off and let the room warm up. We'll see what that looks like after the test runs for awhile.

author: mawyatt
author_rank: Super Contributor
timestamp: August 30, 2023, 01:52:20 pm
content: Quote from: Electro Fan on August 30, 2023, 03:07:07 amOur AC operates on a "Bang-Bang Servo" concept, where the AC comes ON until a lower set temperature is achieved, then OFF until a higher set temperature occurs, then the cycle repeats. The AC period is shorter during the day, but longer at night when the outside is cooler.Copper has a very high TC and thus becomes a temperature sensor rather than a fixed stable resistor. You can cover the entire measurement with a blanket or thermal insulating box, this will reduce the measurement excursions.If you have another plotting meter, get a thermistor and plot the temperature along with the measurement, they should correlate well.Best,

author: Electro Fan
author_rank: Super Contributor
timestamp: August 30, 2023, 03:17:11 pm
content: Quote from: mawyatt on August 30, 2023, 01:52:20 pmThanks for your post. I didn't see it until just now so the measurements have been running overnight since my last post with the AC off.Here is the latest....

author: Electro Fan
author_rank: Super Contributor
timestamp: August 30, 2023, 05:26:33 pm
content: Looks like the symmetric pattern was just the Air Conditioning cycling on and off.I haven't given as much attention to the exact room temperature as I should have but my guess is that overnight the room reached about 78F and since I turned the AC back on it's been cycling just a little above and below 74F (the current target temp).No doubt there is a relationship between resistance and temperature.

author: Kean
author_rank: Unknown
timestamp: August 30, 2023, 08:47:50 pm
content: Note that your last few photos are titled Histogram but are actually Trend Charts.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 30, 2023, 10:44:26 pm
content: Quote from: Kean on August 30, 2023, 08:47:50 pmKean, thank you for pointing that out. Fixed now.