Building Kelvin (4-Wire) Test Leads

RE: Building Kelvin (4-Wire) Test Leads

Andrew J — Thu, 11 Jun 2020 16:02:26 GMT

These looked so good, I made some:

[View:/resized-image/__size/620x544/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-5218bb24-ad0f-431f-8543-273d2720558b/5554.contentimage_5F00_188405.jpg:620:544]

Readings with these,

25cm, 16 AWG stranded copper:

2-wire: 0.063Ohms

4-wire: 0.009Ohms

50cm, 28 AWG (0.32mm) single strand copper:

2-wire: 164 mOhm

4-wire: 106.7 mOhm

25cm, 28 AWG (0.32mm) single strand copper:

2-wire: 108 mOhm

4-wire: 052.3 mOhm

I also made some Micrograbbers, redred and blackblack:

[View:/resized-image/__size/620x504/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-5218bb24-ad0f-431f-8543-273d2720558b/5444.contentimage_5F00_188406.jpg:620:504]

These were a little awkward - the Grabber cap had only a small outlet for the wire, approximately 1mm, maybe 1.5mm:

[View:/resized-image/__size/620x612/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-5218bb24-ad0f-431f-8543-273d2720558b/6014.contentimage_5F00_188407.jpg:620:612]

Farnell did have some that used a 4mm banana plug connection but the red ones were out of stock; the datasheet for these made no mention of the wire size to use so I got these rather than wait. I used a 3mm bit in a pin drill and a chisel tip craft knife to enlarge the hole and wire slit to around 2.5mm which is the size of wire I have:

[View:/resized-image/__size/620x681/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-5218bb24-ad0f-431f-8543-273d2720558b/4861.contentimage_5F00_188408.jpg:620:681]

Bit blurry, but it did the job reasonably neatly. For connecting to Banana Plugs I used some bootlace ferrules and a crimpercrimper:

[View:/resized-image/__size/620x360/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-5218bb24-ad0f-431f-8543-273d2720558b/7103.contentimage_5F00_188409.jpg:620:360]

This one is a bit different to the tool you used here and there seem to be 3 types - the one above that creates a flat, 'serrated' pentagon crimp; a hexagon crimp and a square crimp. This one is a heck of a lot cheaper than the one you used though and it makes a good crimp:

[View:/resized-image/__size/620x419/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-5218bb24-ad0f-431f-8543-273d2720558b/5050.contentimage_5F00_188410.jpg:620:419][View:/resized-image/__size/620x359/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-5218bb24-ad0f-431f-8543-273d2720558b/4454.contentimage_5F00_188411.jpg:620:359]

The Deltron banana plugs I had are not very good so I need to change them - the pin pushes out of the housing if not careful, rather than into the meter.

Now all I need to do is make some SMT tweezers!

RE: Building Kelvin (4-Wire) Test Leads

mcb1 — Wed, 19 Sep 2018 10:58:53 GMT

Never really had the need (or desire) for low impedance measuring, but your sleeve idea is a good way to make some longer leads and stop them being a nuisance.

My old leads are getting very tired, so perhaps some new ones are needed ... especially with some added flexibility.

Thanks for this.

Mark

RE: Building Kelvin (4-Wire) Test Leads

luislabmo — Fri, 14 Sep 2018 13:48:41 GMT

Hi [mention:b0bc65b9ecdc4307bd967592f00e340a:e9ed411860ed4f2ba0265705b8793d05]!,

Very useful tutorial -as usual-, I definitely learned something new today!. I had to google 4-wire sensing to see what kind of equipment this may be used with.

[View:/resized-image/__size/251x335/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-5218bb24-ad0f-431f-8543-273d2720558b/contentimage_5F00_188403.png:251:335]

Luis

RE: Building Kelvin (4-Wire) Test Leads

jw0752 — Thu, 13 Sep 2018 03:58:22 GMT

Hi Shabaz,

This looks like a fun and practical project. I have everything I need except the Kelvin clips but they are now on the want list.

Thanks John

RE: Building Kelvin (4-Wire) Test Leads

genebren — Thu, 13 Sep 2018 00:34:02 GMT

Well done! This is an excellent addition to any meter that provides this capability. This a good example of a simple, clean and well thought out project.

Thanks for sharing!

Gene

RE: Building Kelvin (4-Wire) Test Leads

Gough Lui — Wed, 12 Sep 2018 22:52:33 GMT

That's quite a good project - in fact, I should probably build some myself. My excuse for not bothering with 4W mode on most of the instruments boils down to either the sense terminals being at the back (way out of reach and not a nice set of banana jacks) or the unwieldy cable arrangement of separate cables and extra clips on small terminals. Considering what some companies charge for it, it's definitely worth building yourself [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-5218bb24-ad0f-431f-8543-273d2720558b/contentimage_5F00_1.png:16:16].

Thanks,

Gough.

RE: Building Kelvin (4-Wire) Test Leads

fmilburn — Wed, 12 Sep 2018 18:51:23 GMT

Very nice. Another project added to my list :-)

RE: Building Kelvin (4-Wire) Test Leads

three-phase — Wed, 12 Sep 2018 18:46:00 GMT

Nice blog, 4 wire measurement is definitely more accurate for lower resistance measurements. I use the methodology a lot for measuring winding resistances of rotating plant down to a few milli-ohms and busbar joints down to micro-ohms. Needs an instrument with 4 wire measurement capability to get the most out of it, although sometimes I do use a voltmeter and current meter setup, record the readings and then do the math, although obtaining stable readings can be an issue. I also tend to like to use a reasonably high test current for the apparatus I work on.

Kind regards