Kelvin Clip Zero Ohm Calibration - Page 1
Forum section: electronics / testgear

author: mawyatt
author_rank: Super Contributor
timestamp: September 03, 2025, 01:13:09 am
content: We posted something on another thread here.https://www.eevblog.com/forum/testgear/new-lcr-meters-zoyi-zt-dq01-and-zoyi-zt-dq02-(march-2025)/msg6021271/#msg6021271And felt it better to post separately here.According to Hioki there is aProperandImpropermethod for Zero Ω Calibration with Kelvin Clips. We made a crude model of the Kelvin Clips and for the Zero Ω Connection with some simple calculations shown below. This show's that Zero Ohm Kelvin Clips with Hc->Lc->Hp->Lp connection per Hioki should produce the better result. This makes sense as the test current flows from Hc to Lc and not thru the Hp and Lp clip tips, whereas when reversed Hc->Lp->Hp->Lc test current flows thru Lp and Hp tips which produces a voltage drop with Hp and Lp and sensed by the meter.So we decided to see if this proved out in actual tests and first we did a Zero Ω Cal with Hioki IM3536 LCR Meter using Tonghui TH26011CS Kelvin Clips in the recommended configuration of Hc->Lc->Hp->Lp, the measurements are shown in Correct_Short. Then reversed the Kelvin Clips to Hc->Lp->Hp->Lc (improper per Hioki), shown as Reversed_Short. Note the difference in parameters Rs, Rdc, Ls, Z and Short Voltages and Currents (AC and DC). After this we returned the Kelvin Clips to the recommended configuration of Hc->Lc->Hp->Lp and remeasured shown as Reconnect_Short, compare with the 1st readingsThen we did a Zero Ω Cal with theimproperKelvin configuration Hc->Lp->Hp->Lc and repeated the above sequence shown as Improper, ImpReversed and ImpReconnect. Note that the reversed becomes theproperconfiguration and actually showed much better repeatability even tho with significant Zero errors.Anyway, these simple tests show the proper Kelvin Clip configuration for Zero Ω Cal produces much better results as a Hc->Lc->Hp->Lp setup rather than Hc->Lp->Hp->Lc. Hopefully some folks will find this useful when doing quality low Z measurements with Kelvin Clips.Best

author: mawyatt
author_rank: Super Contributor
timestamp: September 03, 2025, 01:20:28 am
content: Awhile later we repeated the Zero Ω Cal with the proper Kelvin Clip connections Hc->Lc->Hp->Lp with same sequence. Compare these results like above.Best

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: September 03, 2025, 01:35:59 am
content: I admire your dedication!This reminded me of the times at university when a PhD student would sometimes swap Kelvin wires for fun during lab to see what would we do seeing suddenly strange results

author: mawyatt
author_rank: Super Contributor
timestamp: September 03, 2025, 03:42:23 pm
content: Thanks!!Sometimes things like proper use of Kelvin Clips aren't obvious.Just for fun we checked our Tonghui TH2830 using the same Kelvin Clips and procedure as above. First Zero Ω Cal with TH2830 Source set to 2V and 30Ω to increase Short Test Current (~66.7ma), note the Hioki IM3536 used ~110ma AC, 10ma DC. This helps resolve the meter very low Zero Ω voltage measurement. First a Zero Ω Cal with proper Hc->Lc->Hp->Lp Kelvin connection, then measurement Ls and Rs (TH_Proper), then reversed Kelvin Clips and measure (Reversed), then return (Reconnect) to proper Kelvin Clip connection.No surprise, we see same behavior as with IM3536Best

author: mawyatt
author_rank: Super Contributor
timestamp: September 03, 2025, 03:55:45 pm
content: Now with the TH2830 Zero Ω Cal withImproperHc->Lp->Hp->Lc Kelvin Clip connections. Note the variability in the Rs result between the First (TH_Improper) to Reconnect (Th_ImpReconnect)!!Edit: BTW we just tried the cheap AliX $20 BNC to Kelvin Clips and see similar results, not quite as good as the quality Tonghui Kelvin Clips wrt to repeatability tho. Also see better results with popular handheld milliohm meters YR1035, and YR2050, altho HRM-10 doesn't show any improvement.Best

author: mawyatt
author_rank: Super Contributor
timestamp: September 03, 2025, 06:04:09 pm
content: Update, checking with DMM6500 and KS34465A.With a DMM6500 we see a significant (over 500X) improvement using these cheap BNC Kelvin Clips wired for dual banana jacks when usingproperKelvin Zeroing vsimproper. Hereproperrefers to HiForce->LowForce->HiSense->LowSense connections, whereasimproperReversed is HiForce->LowSense->HiSense->LowForce. In fact theproperreads in the <1 uΩ average with SD of ~19uΩ region, so using the DMM "Relative" or Null isn't necessaryl!!The KS34465A isn't as good as the DMM6500 for low-Z measurements (why we have such) so results aren't as good, but still highly worthwhile to use the proper Kelvin connections.Normally these DMM Kelvin Clips were not labeled, now there areBestBest

author: djsb
author_rank: Super Contributor
timestamp: September 03, 2025, 06:38:59 pm
content: I don't understand what the > symbol and the letters that you have next to them and how they relate to how the leads on your kelvin clips are plugged into the DMM6500. Have you got a photo of how you've plugged them in? Thanks.

author: mawyatt
author_rank: Super Contributor
timestamp: September 03, 2025, 07:09:26 pm
content: Quote from: djsb on September 03, 2025, 06:38:59 pmLeads for LCR meter use are normally Lc Lp Hp Hc in that order on the meter, thus Hc->Lc means Hc Kelvin Clip Tip connected to Lc Kelvin Clip Tip. DMMs use a Red Hi Force and Sense and a Black Low Force and Sense in a:Hi Sense Hi ForceLow Sense Low Force4 Banana socket arrangement.So this equate to a Proper Kelvin Zero Ω Kelvin connection of:Red Hi Force->Black Low Force->Red Hi Sense->Black Sense arrangement at the Kelvin Tips.If you follow the simple analysis we provided above, but with DMM connection terminology. The DMM Test Current flows from the Hi Force to the Low Force and the Hi Sense and Low Sense measure the voltage together (they have Hi Z Inputs, so no current flowing into these clips). The contact impedance between them and the contact impedance between the Low Force and Hi Sense has no current flow, thus no voltage drop. This also removes any contact impedance form the Hi and Low Force tips because the voltage is detected "outside" the Test Current flow.If you study the test current flow from the Hi Force to the Low Force you will see it doesn't pass thur the Hi and Low Sense tips, only between the Force tips (Proper). Whereas if the tips are reversed (Improper) where the Hi Force tip is connected to the Low Sense tip, then the test current flows thru the Low Sense tip thur the Hi sense tip and to the Low Force tip. This causes a voltage drop across the Hi and Low Sense tips due to test current flowing thru the tip contact impedance (and measured), and is difficult to get consistent between measurements.BTW this just works over everything we've tried so far, including the cheap AliX BNC Kelvin Clips (and modified for DMM use), and cost nothingHere's some images of the DMM Kelvin Clips discussed. Note the "Extra" Black lead is the shield from all 4 coaxial leads and connected to Low Force.Anyway, hope this helps explain the Kelvin Lead setup.Best

author: gamalot
author_rank: Super Contributor
timestamp: September 03, 2025, 07:18:28 pm
content: Here's a picture I took two years ago showing the order Hioki recommends.

author: mawyatt
author_rank: Super Contributor
timestamp: September 03, 2025, 07:34:01 pm
content: Yeah, that shows the "V" marking of the Kelvin Blades which should be connected together for a proper Zero Ω Kelvin Cal. Those are probably better than the Tonghui Kelvin Clips we have.Best

author: KungFuJosh
author_rank: Super Contributor
timestamp: September 03, 2025, 08:48:44 pm
content: Quote from: mawyatt on September 03, 2025, 07:34:01 pmThe Hioki L2000 kelvin clips are indeed better than the TongHui clips. They have better shielding, and easier repeatability IME. I don't have the TH clips anymore to make any new comparisons.

author: NANOJOLTS
author_rank: Contributor
timestamp: September 07, 2025, 08:57:29 pm
content: What's you all's take on this AP?

author: KungFuJosh
author_rank: Super Contributor
timestamp: September 07, 2025, 11:00:30 pm
content: Quote from: NANOJOLTS on September 07, 2025, 08:57:29 pmThat might be useful for their specific product, but it's not normally a short if everything isn't...shorted together.This is what I get when I try their method with the probes pointed tip-to-tip with a gap in the middle:This is what I get when I try their method with the probes pointed tip-to-tip withnogap in the middle (actually shorted):And this is what I get following Hioki's method:Thanks,Josh

author: mawyatt
author_rank: Super Contributor
timestamp: September 07, 2025, 11:55:39 pm
content: Quote from: NANOJOLTS on September 07, 2025, 08:57:29 pmOur IM3536Failsto calibrate when connected as recommended in the Ap Note for a Zero Ω Calibration!!This method doesn't seem workable as how does the Hp and Lp sensing tips acquire a proper voltage reading at the Kelvin Tips when they are both insulated from the Hc and Lc tips and both connected together and are just High Z "sense" terminals?Best

author: Ian.M
author_rank: Super Contributor
timestamp: September 08, 2025, 01:05:18 am
content: Yep. If you don't have the specific Tegam instruments, don't use their AN102 method.Thanks Mawyatt, I've just updated my hackspace's Red Pitaya LCR meter / Impedance analyser notes on our wiki, and marked the leads so we can now zero correctly!

author: mawyatt
author_rank: Super Contributor
timestamp: September 08, 2025, 02:36:03 pm
content: Interestingly our Tonghui TH2830 allowed a Zero Ω Cal with the Tegam App Note technique, so it must have an internal connection between the Force and Sense BNCs. However, when we did a simple comparison between the Hioki method and the Tegam method the results favored the Hioki method as expected.The results become progressively worse for the Tegam method as the test frequency is increased which again should be no surprise as the Kelvin Cable comes more into play as this method the Force and Sense High and Low side Zero Ω Cal "points of connection" are totally different. With the Hioki method all the "points of connection" are at the Kelvin Tips where the eventual DUT connections will be made.Anyway, folks should pay close attention to "how" the Zero Ω Cal is performed with their particular LCR Meter if they are after quality repeatable low Z measurements.Best

author: gitm
author_rank: Regular Contributor
timestamp: September 09, 2025, 12:33:54 am
content: My CKT515 user manual shows essentially the same procedure as Hioki's for the short cal. In the text it notes "if the fixture of the test cable is connected reversely, the data of the test cable will change greatly or display a large negative resistance value"

author: Zucca
author_rank: Unknown
timestamp: September 09, 2025, 02:30:17 am
content: Just to say thanks to Mike not only for the excellent post, but also because after seeing his paper and pencil investigation I do feel less alone.In times where everybody is asking AI for explanations, real EE still use paper and pencil to get answers!Please do not stop to use them, the risk is to get our brain out of shape!

author: KungFuJosh
author_rank: Super Contributor
timestamp: September 09, 2025, 04:09:26 am
content: Quote from: Zucca on September 09, 2025, 02:30:17 amThat's no joke. Allegedly, people that rely on AI to do work for them show a decline in intelligence.

author: trobbins
author_rank: Frequent Contributor
timestamp: September 11, 2025, 12:42:44 am
content: I notice a residual difference in R from shorting the Kelvin clips on a MCP BR2822 meter when the probe tips are overlapped more, or less towards the tip ends. At least the construction of the Kelvin leadset makes it more difficult to short the tips with a FSSF config, rather than a 'default' FFSS tip config.

author: 2N3055
author_rank: Super Contributor
timestamp: September 11, 2025, 09:55:50 am
content: What has been discussed is basically this:You short two force terminals together, two sense terminals together. Then you establish a link between those two.Null out.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 11, 2025, 10:19:10 am
content: Thanks for your nice Kelvin Clip research.Zero Ohm calibrations is not as easy as one would think.We discussed it here in the metrology section:https://www.eevblog.com/forum/metrology/zero-ohm-diy-4-wire-standard/

author: 2N3055
author_rank: Super Contributor
timestamp: September 11, 2025, 10:20:03 am
content: What you do is connect the clips so two sense are together on one side, and two force are on the other side.You insert a piece of copper wire in the middle, between those two groups.That makes it that you have single point connection between sense and force current paths. And makes sure both groups make their contacts nicelyAnd then you have results. Meter is in 100 NPLC, no auto zero, no relative mode.

author: mawyatt
author_rank: Super Contributor
timestamp: September 11, 2025, 03:54:12 pm
content: Quote from: 2N3055 on September 11, 2025, 09:55:50 amThat's a good analogy to the proper Kelvin Clip connections. Awhile back we made a 4 wire Zero Ω Short for our DMMs with #12 Cu wire as shown, works OK.Best