Author Topic: Suggestions for Kelvin probes??  (Read 1111 times)

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Offline Andrew_Debbie

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Suggestions for Kelvin probes??
« on: October 16, 2021, 03:35:09 pm »
I'm looking for a set of 4-wire Kelvin probes for my Dana 5100 DMM.     It uses Banana binding posts.  Shrouded plugs will not work.

 I have less than £50 invested in the meter.   I can't quite bring myself to spend £100 for a Pomona 6303.      Suggestions?



Pomona 6303:
 

Offline AVGresponding

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Re: Suggestions for Kelvin probes??
« Reply #1 on: October 16, 2021, 05:00:34 pm »
Make your own?   :-//
nuqDaq yuch Dapol?
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Offline rvalente

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Re: Suggestions for Kelvin probes??
« Reply #2 on: October 16, 2021, 05:07:51 pm »
Just grab a probe and add two cables, of course you won't ever  compensate the tip, but...
 

Offline bob91343

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Re: Suggestions for Kelvin probes??
« Reply #3 on: October 16, 2021, 05:45:31 pm »
I made my own with some cheap Chinese clips.  Search on ebay.
 

Offline jchw4

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Re: Suggestions for Kelvin probes??
« Reply #4 on: October 16, 2021, 10:08:13 pm »
Pomona 6303:

Don't buy. Wires are connected inside the tip, so you don't compensate for the contact resistance.

My personal favourite (I am not a professional EE) is this:

Sold as "UNI-T compatible". Goes for $25-30 delivered on ebay or $20 on aliexpress. Very solid construction, gold-pated clips, flexible wire.

I have some cheap "traditional" clips from ebay, but the plating matters  :-[

If you need "tip" connection as oppposed to the "crocodile"-style connection, you may consider Mueller BU-7042-F-48-2 (and there is a mating black one):

but the tip spacing is about 4mm and it does not really work for SMD.

I think that the best SMD-style kelvin probe could be two parallel pogo pins. Solder wires, wrap one tip with scotch tape, put botth of them in a heatshrink tube so that they are parallel, put result into an old pen, and you should have good kelvin clips!  Haven't tried it myself though.
« Last Edit: October 16, 2021, 10:20:14 pm by jchw4 »
 
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Offline J-R

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Re: Suggestions for Kelvin probes??
« Reply #5 on: October 17, 2021, 01:59:53 am »
I've done this plenty of times: just use a 2nd set of cheap leads with alligator clips and you'll get 0.1mOhm results, nothing fancy needed.  But I won't deny a set of Kelvin clips/probes would be nice, wires are bundled, easy to use....
 
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Offline Andrew_Debbie

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Re: Suggestions for Kelvin probes??
« Reply #6 on: October 17, 2021, 07:52:58 am »
Pomona 6303:

Don't buy. Wires are connected inside the tip, so you don't compensate for the contact resistance.

My personal favourite (I am not a professional EE) is this:
Sold as "UNI-T compatible". Goes for $25-30 delivered on ebay or $20 on aliexpress. Very solid construction, gold-pated clips, flexible wire.



Unfortunately shrouded plugs won't work.  My Dana 5100 has incompatible binding posts.


Quote
consider Mueller BU-7042-F-48-2

~£70 each!  :o   £140 is too expensive.  Otherwise I like them.



« Last Edit: October 17, 2021, 08:37:23 am by Andrew_Debbie »
 

Offline TERRA Operative

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Re: Suggestions for Kelvin probes??
« Reply #7 on: October 17, 2021, 08:47:31 am »
These :
https://www.ebay.com/sch/i.html?_nkw=kelvin+clips

Combined with this:
https://www.ebay.com/sch/i.html?_nkw=silicone+wire+16+awg

And these:
https://www.ebay.com/sch/i.html?_nkw=banana+plug+dual+gold

Will work well. I made a few (Using banana jacks sourced locally) and they work fine.
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Offline bdunham7

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Re: Suggestions for Kelvin probes??
« Reply #8 on: October 17, 2021, 05:40:35 pm »
I'm looking for a set of 4-wire Kelvin probes for my Dana 5100 DMM.     It uses Banana binding posts.  Shrouded plugs will not work.

 I have less than £50 invested in the meter.   I can't quite bring myself to spend £100 for a Pomona 6303.      Suggestions?

As posted by others, you can make your own if you want the Kelvin-clip style. 

However, if you (or anyone else here) is looking for the almost-Kelvin single contact probes like the Pomona 6303, I am working on one for SMD use and would appreciate input.  Specifically, what levels of resistance do you need to measure and how accurately?  For component identification and short tracing, down to a few milliohms seems a reasonable target, it is very hard to do better than that due to variability in contact resistance.  Also, what size/type probe end would you want?  The options are a single sharp point, a dull/round point and some sort of multi-toothed lamprey-style end?  The sharp point would seem best, but the tip resistance becomes larger and more variable with a narrow point.  Contact resistance is an issue with rounder and flatter styles.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline mawyatt

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Re: Suggestions for Kelvin probes??
« Reply #9 on: October 17, 2021, 06:21:27 pm »
Will be interesting to see what you come up with. Think one type will not serve all uses well, but maybe a more blunt large area contact end and a sharp small area contact. The sharp tip type will be difficult to get the sense point near the tip end. Had thought about using a sharp needle type tip and soldering a small diameter magnet type wire very near the tip end for the sense probe.

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Wyatt Labs by Mike~
 

Offline ScottW

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Re: Suggestions for Kelvin probes??
« Reply #10 on: October 17, 2021, 07:36:59 pm »
I have a pair of these, nicely made and decent price. Not sure about availability outside the U.S. though...
  https://ast-labs.com/shop/test_cables/kelvin/test-lead-kelvin-clip-4-channel-banana-plug-3-feet/
 

Online Cerebus

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Re: Suggestions for Kelvin probes??
« Reply #11 on: October 17, 2021, 08:02:43 pm »
When I wanted some I couldn't find fully assembled leads that were "cheap enough" by my skinflint criteria. I ended up making my own up come ça:



The Kelvin clips I used were cheap Chinese ones and although they don't look much in either this photo or the original vendor's photos they are reasonable quality. Ditto the dual banana plugs. Add a bit of silicone test lead (yes, our friends in the Middle Kingdom again), some nylon expandable sheathing and some heatshrink and they're served me well for a couple of years now. The knit sheathing was definitely a good idea it makes handing the lead a lot easier; a couple of times I've wished that I left a bit more unsheathed cable at the business end so that I could place the clips a bit further apart. Overall length is a metre give or take.

An hours work, all the bits apart from the Kelvin Clips were things that I keep on hand anyway so I'm not sure what I spent in total but I'd be surprised if I spent more than £10, perhaps £15 at the outside.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 
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Offline bdunham7

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Re: Suggestions for Kelvin probes??
« Reply #12 on: October 17, 2021, 11:11:15 pm »
Will be interesting to see what you come up with. Think one type will not serve all uses well, but maybe a more blunt large area contact end and a sharp small area contact. The sharp tip type will be difficult to get the sense point near the tip end. Had thought about using a sharp needle type tip and soldering a small diameter magnet type wire very near the tip end for the sense probe.

For a lot of SMD work getting two good contact points is a near impossibility and may not help all that much anyway.  At very low resistances, the voltages are also very low and the thermal voltages in the sense circuit are large enough to be an issue.  So the plan is to use a single contact with the SENSE and SOURCE leads connected as close to the end as possible.  My goal is to make a workable system that uses the low standard test currents of a precision DMM and also, if needed, has very low OCV.  My test DMMs use 10mA, 5mA and 1mA currents and I want the OCV well below 100mV--so quite unlike a typical milliohmmeter.   

 I have working prototypes, but the needle tip is stainless steel.  This is good for repeatable contact resistance, but there is high overall resistance and some other geometrical issues I should have anticipated, but didn't.  So my final challenges are to get the resistance of the tip to be as low as possible and to find the bests shape(s) and material for the contact tip. 
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline mawyatt

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Re: Suggestions for Kelvin probes??
« Reply #13 on: October 17, 2021, 11:58:25 pm »

For a lot of SMD work getting two good contact points is a near impossibility and may not help all that much anyway.  At very low resistances, the voltages are also very low and the thermal voltages in the sense circuit are large enough to be an issue.  So the plan is to use a single contact with the SENSE and SOURCE leads connected as close to the end as possible.  My goal is to make a workable system that uses the low standard test currents of a precision DMM and also, if needed, has very low OCV.  My test DMMs use 10mA, 5mA and 1mA currents and I want the OCV well below 100mV--so quite unlike a typical milliohmmeter.   

 I have working prototypes, but the needle tip is stainless steel.  This is good for repeatable contact resistance, but there is high overall resistance and some other geometrical issues I should have anticipated, but didn't.  So my final challenges are to get the resistance of the tip to be as low as possible and to find the bests shape(s) and material for the contact tip.

Might want to research what the semiconductors folks do with the wafer probes, those seem to work very well and obviously suited for probing small devices.

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Wyatt Labs by Mike~
 

Offline bdunham7

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Re: Suggestions for Kelvin probes??
« Reply #14 on: October 18, 2021, 12:11:41 am »
Might want to research what the semiconductors folks do with the wafer probes, those seem to work very well and obviously suited for probing small devices.

LOL, I'm already perusing the Harwin catalog for exactly those style of probes.  The pogo-pin assemblies won't work because their sleeve resistance is ~50mR, but I'm thinking of extracting the pin part and pressing it into a solid copper part.  If I can manage to set things up so the pin parts can be changed by the user that would be even better.  The real challenge is designing for cost-effective manufacturability.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline Andrew_Debbie

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Re: Suggestions for Kelvin probes??
« Reply #15 on: October 18, 2021, 06:46:12 am »
I investigated DIY using Pomona MDP dual bananas and Mueller BU-75K  kelvin clips.         Total was just under the minimum for free shipping from Mouser.

In the end I get to about £45 which is a lot less than buying a premade set.   

Cables are coming from AliExpress.   Dana suggest RG196U.   Yikes.  Too expensive and possibly overkill??   I ordered some RG178.



« Last Edit: October 18, 2021, 07:16:54 am by Andrew_Debbie »
 

Offline Andrew_Debbie

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Re: Suggestions for Kelvin probes??
« Reply #16 on: October 18, 2021, 07:07:55 am »



However, if you (or anyone else here) is looking for the almost-Kelvin single contact probes like the Pomona 6303, I am working on one for SMD use and would appreciate input.  Specifically, what levels of resistance do you need to measure and how accurately?

>10mΩ

The 5100 is ±(.007%+6) counts on the  0.2KΩ scale  or about   6mΩ.     

I am designing a stand alone power monitor / checker for wall power supplies.   Like the common USB testers, but for various DC wall power supplies.    Initial design has a ~20mΩ surface mount shunt resistor.     I may end up using a larger value and putting 2 to 4 of them in parallel so I can check the parts with the 5100.     


My 5100 does not have the current option.   I'd like to make a current shunt box for it  and measure the resistance of the shunt at the accuracy of the meter.


« Last Edit: October 18, 2021, 08:38:22 am by Andrew_Debbie »
 

Offline blacksheeplogic

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Re: Suggestions for Kelvin probes??
« Reply #17 on: October 18, 2021, 07:32:56 am »
Unfortunately shrouded plugs won't work.  My Dana 5100 has incompatible binding posts.

What is the problem? It took me all of 30 secs with a blade to remove the shroud when I needed to 'convert' a set of leads I had.
 

Offline Andrew_Debbie

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Re: Suggestions for Kelvin probes??
« Reply #18 on: October 18, 2021, 08:35:43 am »

What is the problem? It took me all of 30 secs with a blade to remove the shroud when I needed to 'convert' a set of leads I had.


Maybe cut off  the plugs and replace them with Pomona MDP dual bananas.    Hmmmm.....  Thinking ......
« Last Edit: October 18, 2021, 08:39:45 am by Andrew_Debbie »
 


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