Author Topic: Kelvin leads for DMM  (Read 10084 times)

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Offline TracelessTopic starter

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Kelvin leads for DMM
« on: March 07, 2022, 08:43:16 pm »
Currently I'm looking for a set of kelvin leads to go along with a new DMM. Does anyone have any experience with these? Is there any good reason (other than the extra ground lead) to go with these or these rather 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 justifies that kind of surcharge?
 

Offline TimFox

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Re: Kelvin leads for DMM
« Reply #1 on: March 07, 2022, 08:48:27 pm »
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).
 
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Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #2 on: March 07, 2022, 09:12:00 pm »
Have a few DIY versions.

Left Right is dual with 2 wires & shields, right left is cut off BNC types and replaced with Banana plugs, each wire is shielded, top bottom 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!
« Last Edit: March 08, 2022, 01:41:59 am by mawyatt »
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Offline Someone

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Re: Kelvin leads for DMM
« Reply #3 on: March 07, 2022, 10:34:03 pm »
time to start selling audiophile voltnuttery cryo treated individual triax wired palladium clips with optional antitriboelectric PTFE wire stands?
 

Offline alm

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Re: Kelvin leads for DMM
« Reply #4 on: March 07, 2022, 10:54:59 pm »
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.
 
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Online Hydron

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Re: Kelvin leads for DMM
« Reply #5 on: March 08, 2022, 12:17:35 am »
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.
 
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Offline duckduck

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Re: Kelvin leads for DMM
« Reply #6 on: March 08, 2022, 01:17:36 am »
Currently I'm looking for a set of kelvin leads to go along with a new DMM. Does anyone have any experience with these? Is there any good reason (other than the extra ground lead) to go with these or these rather 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 justifies that kind of surcharge?

Haven't tried the fancy ones. I've got a set of these: https://www.ebay.com/itm/201604885284 ( Cheap [USD21] 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.
 
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Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #7 on: March 08, 2022, 02:41:15 am »
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 an excuse requirement to assemble all these Kelvin clips, fixtures and such ;D

After 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,
Curiosity killed the cat, also depleted my wallet!
~Wyatt Labs by Mike~
 
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Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #8 on: March 08, 2022, 03:30:29 am »
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
« Last Edit: March 08, 2022, 03:35:59 am by Electro Fan »
 
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Offline JohnG

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Re: Kelvin leads for DMM
« Reply #9 on: March 08, 2022, 02:11:30 pm »
I have two sets.

The less expensive set: Pomona 6303 https://www.pomonaelectronics.com/products/dmm-test-leads-and-probes/kelvin-probe-set

This 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 about 95% 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 11059A https://www.keysight.com/us/en/product/11059A/kelvin-probe-set.html

If 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
« Last Edit: March 08, 2022, 02:13:05 pm by JohnG »
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Offline alm

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Re: Kelvin leads for DMM
« Reply #10 on: March 08, 2022, 02:40:15 pm »
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.
 
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Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #11 on: March 08, 2022, 04:00:09 pm »
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

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

Offline TomWinTejas

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Re: Kelvin leads for DMM
« Reply #12 on: March 08, 2022, 04:40:38 pm »
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/
 
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Offline SHTechnics

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Offline MegaVolt

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Re: Kelvin leads for DMM
« Reply #14 on: March 09, 2022, 12:27:55 pm »
These beautiful clips seem to belong to Tonghui. I think somewhere else should be the same ending bananas.

https://aliexpress.ru/item/1005002208013017.html
 
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Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #15 on: March 09, 2022, 12:56:26 pm »
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,
Curiosity killed the cat, also depleted my wallet!
~Wyatt Labs by Mike~
 

Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #16 on: March 09, 2022, 07:13:13 pm »
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,
« Last Edit: March 09, 2022, 07:33:01 pm by mawyatt »
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Offline Kean

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Re: Kelvin leads for DMM
« Reply #17 on: March 09, 2022, 08:08:23 pm »
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.
 
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Offline tooki

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Re: Kelvin leads for DMM
« Reply #18 on: March 09, 2022, 08:50:25 pm »
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,
Please use the screenshot features of your operating system to 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? 
 

Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #19 on: March 09, 2022, 09:00:20 pm »
Edit: @ Kean

Those 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,
« Last Edit: March 09, 2022, 09:34:13 pm by mawyatt »
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Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #20 on: March 09, 2022, 09:10:34 pm »

Please use the screenshot features of your operating system to take screenshots. Photographs of the display suck in so many ways.
[/quote]

Will do!!

Quote
As for the plating: you do realize the whole point of Kelvin measurement is to eliminate the effects of test lead and contact resistance?

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

Online Hydron

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Re: Kelvin leads for DMM
« Reply #21 on: March 09, 2022, 09:20:40 pm »
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.
I 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 ones :P
https://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/2131248
edit: 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.
« Last Edit: March 09, 2022, 09:26:45 pm by Hydron »
 

Offline TracelessTopic starter

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Re: Kelvin leads for DMM
« Reply #22 on: March 09, 2022, 09:27:54 pm »
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.

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).

Yes 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 @JohnGs Pomona probes 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 around ;)

1434877-0

While 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  ;D. Maybe there pops up a bargain at some point.

@SHTechnics: I do like the banggood ones you linked a 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.

« Last Edit: March 09, 2022, 09:56:28 pm by Traceless »
 

Online Hydron

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Re: Kelvin leads for DMM
« Reply #23 on: March 09, 2022, 09:44:06 pm »
Thought this might be useful for reference:
 
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Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #24 on: March 09, 2022, 11:13:10 pm »
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.
« Last Edit: March 10, 2022, 04:02:57 am by Electro Fan »
 
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