Author Topic: Kelvin leads for DMM  (Read 10092 times)

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Re: Kelvin leads for DMM
« Reply #25 on: March 09, 2022, 11:14:01 pm »
@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.
 
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Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #26 on: March 09, 2022, 11:31:39 pm »
@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
« Last Edit: March 09, 2022, 11:38:16 pm by Electro Fan »
 

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Re: Kelvin leads for DMM
« Reply #27 on: March 10, 2022, 12:41:01 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.
 
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Offline alm

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Re: Kelvin leads for DMM
« Reply #28 on: March 10, 2022, 01:05:29 am »
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.
Well, 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).
 
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Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #29 on: March 10, 2022, 04:07:22 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
 

Offline Gary350z

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Re: Kelvin leads for DMM
« Reply #30 on: March 10, 2022, 11:37:17 am »
I have these B&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:saQAAOSwp5JWZq5g
They are supposedly made by ETA (Electronic Test Accessories); ETA3105 Kelvin Test Clip
http://www.tw-eta.com/index.php?c=show&id=149
I 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.
 

Offline Gary350z

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Re: Kelvin leads for DMM
« Reply #31 on: March 10, 2022, 11:43:29 am »
B&K TLDK1 Kelvin probes teardown photo:
 
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Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #32 on: March 10, 2022, 02:11:57 pm »
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,
« Last Edit: March 10, 2022, 02:23:41 pm by mawyatt »
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Online 2N3055

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Re: Kelvin leads for DMM
« Reply #33 on: March 10, 2022, 08:08:38 pm »
Fairly convenient place to connect shield to analog ground of multimeter is a high current input. I use 10A input on my DM3068.
"Just hard work is not enough - it must be applied sensibly."
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Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #34 on: March 10, 2022, 08:30:53 pm »
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
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Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #35 on: March 10, 2022, 09:15:47 pm »
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."
 

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Re: Kelvin leads for DMM
« Reply #36 on: March 10, 2022, 09:32:34 pm »
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.
https://www.tek.com/en/documents/product-article/keithley-low-level-measurements-handbook---7th-edition
 
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Offline mawyatt

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Re: Kelvin leads for DMM
« Reply #37 on: March 10, 2022, 09:43:14 pm »
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 read  :-+

Best,
« Last Edit: March 10, 2022, 09:50:10 pm by mawyatt »
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Online 2N3055

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Re: Kelvin leads for DMM
« Reply #38 on: March 10, 2022, 11:21:44 pm »
Between what "not an expert" :P 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.
"Just hard work is not enough - it must be applied sensibly."
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Offline Kean

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Re: Kelvin leads for DMM
« Reply #39 on: March 11, 2022, 12:41:03 pm »
@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.

The 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.
 
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Offline gamalot

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Re: Kelvin leads for DMM
« Reply #40 on: March 11, 2022, 02:13:53 pm »
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.

« Last Edit: March 11, 2022, 02:21:40 pm by gamalot »
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Offline tooki

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Re: Kelvin leads for DMM
« Reply #41 on: March 11, 2022, 04:49:11 pm »
Where it would get interesting is with very high resistances. (Like the 40MOhm resistor I had to measure a few weeks ago.)
 

Online TimFox

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Re: Kelvin leads for DMM
« Reply #42 on: March 11, 2022, 05:16:28 pm »
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.
 
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Offline gamalot

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Re: Kelvin leads for DMM
« Reply #43 on: March 11, 2022, 07:42:11 pm »
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.

« Last Edit: March 11, 2022, 07:49:00 pm by gamalot »
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Re: Kelvin leads for DMM
« Reply #44 on: March 12, 2022, 01:39:11 am »
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.
The periodicity of that interference is rather "suspicious" bench DMMs are usually excellent at rejecting external interference when correctly configured.
 
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Offline TracelessTopic starter

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Re: Kelvin leads for DMM
« Reply #45 on: March 12, 2022, 09:07:15 am »
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.
https://www.tek.com/en/documents/product-article/keithley-low-level-measurements-handbook---7th-edition

I just took a look at that Tektronix article, can anyone explain why they measure resistance in watts?

 

Offline tooki

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Re: Kelvin leads for DMM
« Reply #46 on: March 12, 2022, 09:11:29 am »
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.
https://www.tek.com/en/documents/product-article/keithley-low-level-measurements-handbook---7th-edition

I just took a look at that Tektronix article, can anyone explain why they measure resistance in watts?
They 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.
« Last Edit: March 12, 2022, 09:13:49 am by tooki »
 

Offline TracelessTopic starter

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Re: Kelvin leads for DMM
« Reply #47 on: March 12, 2022, 09:25:02 am »
@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 "\$\Omega\$" 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
Generally, these instruments are adequate for meas­urements at signal levels greater than 1µV or 1µA, or less than 1GW.

 

Offline tooki

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Re: Kelvin leads for DMM
« Reply #48 on: March 12, 2022, 09:42:40 am »
@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 "\$\Omega\$" 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
Generally, these instruments are adequate for meas­urements at signal levels greater than 1µV or 1µA, or less than 1GW.
Believe 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 conversion was consistent, but the person using search-and-replace to fix it didn’t catch them all.

Again, the PDF is correct, just look at it.
 

Offline Electro Fan

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Re: Kelvin leads for DMM
« Reply #49 on: March 13, 2022, 04:01:27 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.
 
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