Author Topic: Kelvin leads for DMM  (Read 10086 times)

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Offline gamalot

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Re: Kelvin leads for DMM
« Reply #50 on: March 13, 2022, 08:01:53 am »
@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.
Tiny kelvin clips:
https://www.eevblog.com/forum/testgear/best-way-to-securely-attch-probe-to-a-passive-smd-component/msg1310826/#msg1310826
BYO cabling, "standard" 0.025" pin header plugs. They will take more than the 1A rated current.

Thanks 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?  Thx

http://www.keysight.com/my/faces/partDetail.jspx?partNumber=1400-3652

Edit:  found it, I think:
https://www.keysight.com/my/partDetail/1400-3652
Or 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/#msg1310906
you get the OEMs part number.

Thanks!  Looks like same part at a better price.
https://www.newark.com/hirschmann-testmeasurement/972416100/clip-test-micro-smd-black-mln/dp/67C8450

I 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.

I bought it on eBay for a slightly higher price.

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Offline tooki

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Re: Kelvin leads for DMM
« Reply #51 on: March 13, 2022, 01:26:03 pm »
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
 
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Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #52 on: March 13, 2022, 09:59:22 pm »
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

That'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.
 

Offline alex-kv

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Re: Kelvin leads for DMM
« Reply #53 on: March 14, 2022, 01:02:54 pm »
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
 
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Offline MegaVolt

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Re: Kelvin leads for DMM
« Reply #54 on: March 14, 2022, 02:53:04 pm »
 
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Offline TracelessTopic starter

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Re: Kelvin leads for DMM
« Reply #55 on: March 17, 2022, 08:03:09 am »
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

I just found a deal on 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.
 
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Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #56 on: August 30, 2023, 01:51:44 am »
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?  Thx 

Edit:  Kind of duh....  :palm:

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.
« Last Edit: August 30, 2023, 02:08:48 am by Electro Fan »
 

Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #57 on: August 30, 2023, 02:09:57 am »
Seen this type of display before, it was attributed to the AC cycling in our case.

Best,
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Offline BillyO

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Re: Kelvin leads for DMM
« Reply #58 on: August 30, 2023, 02:38:31 am »
Anyone have some ideas on why the resistance pattern looks like this?  Thx.

Is the environment air conditioned?
Bill  (Currently a Siglent fanboy)
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Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #59 on: August 30, 2023, 03:07:07 am »
Anyone have some ideas on why the resistance pattern looks like this?  Thx.

Is the environment air conditioned?

Yes, it is.  Do you think the AC comes and goes that symmetrically?  Seems slightly hard to believe but maybe....
 

Offline BillyO

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Re: Kelvin leads for DMM
« Reply #60 on: August 30, 2023, 03:12:57 am »
Yes, it is.  Do you think the AC comes and goes that symmetrically?  Seems slightly hard to believe but maybe....
Your 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.
Bill  (Currently a Siglent fanboy)
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Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #61 on: August 30, 2023, 03:25:56 am »
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.
 

Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #62 on: August 30, 2023, 01:52:20 pm »

Yes, it is.  Do you think the AC comes and goes that symmetrically?  Seems slightly hard to believe but maybe....

Our 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,
Curiosity killed the cat, also depleted my wallet!
~Wyatt Labs by Mike~
 

Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #63 on: August 30, 2023, 03:17:11 pm »

Yes, it is.  Do you think the AC comes and goes that symmetrically?  Seems slightly hard to believe but maybe....

Our 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,

Thanks 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....

« Last Edit: August 30, 2023, 10:46:37 pm by Electro Fan »
 

Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #64 on: August 30, 2023, 05:26:33 pm »
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.   :-+
« Last Edit: August 30, 2023, 10:43:17 pm by Electro Fan »
 

Offline Kean

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Re: Kelvin leads for DMM
« Reply #65 on: August 30, 2023, 08:47:50 pm »
Note that your last few photos are titled Histogram but are actually Trend Charts.
 
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Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #66 on: August 30, 2023, 10:44:26 pm »
Note that your last few photos are titled Histogram but are actually Trend Charts.

Kean, thank you for pointing that out.  Fixed now.
 


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