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27) Four Wire Kelvin Resistance Measurement

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I can't afford a fancy benchtop multimeter with 4-wire measurement capability, so I made a current source and will show you how to make an accurate low-resistance measurement with this setup. There's a cool water-circuit that shows how current flows in a 4-wire system which turned out a lot cooler than I thought it would. Hope you guys enjoy!
Here's a link to the Kelvin connection clips I mentioned in the video:
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Опубликовано:

6 сен 2024

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Комментарии : 18

@AirborneSurfer 7 лет назад

Great video! I especially enjoy the water circuit demo! Thanks!

@ronniepirtlejr2606 4 года назад

Cool, I have some resistors exactly like the one you are using. I pulled it out of some vintage equipment.

@DrTune 6 лет назад

great video; good length, interesting info. Spot on

@setSCEtoAUX 7 лет назад

We do this in the PCB flying prober world too. Set up a current source (HEH!) with a pair of probes somewhere on the nets, and then use another pair right on the device pins to measure voltage of the device under test. NOW DO GUARDING! :) Would be fun to visualize it with the water analogy also. Maybe with some glitter or plastic pellets in the water to show flow (or not-flow in the case of guarding).

@AmRadPodcast 7 лет назад

That would be interesting to do guarding... don't know if I've seen a video on that before. Got about 20 more videos to do first!

@carls.6746 6 лет назад

can you make a vid on the pcb and the parts you used?

@hedgeberg 7 лет назад

This is a great video, you went through a lot of effort just to get a pretty simple visualization, and I really dig it. Also, its nuts that you cant find any other pictures of probe cards, wonder why that would be considering their prevalence in semiconductor labs...

@AmRadPodcast 7 лет назад

+hedgeberg thanks! It was a lot of work for that 5 sec shot. I found a lot of probe card images, but none free use. Last thing I need is a RU-vid slap on the wrist. If I was still in the fab, no prob...

@hedgeberg 7 лет назад

The Current Source oh you also did fab work? I really miss it, there's so much cool stuff you get to do at fab you can't do anywhere else.

@RS_83 5 лет назад

Great education channel! Subscribed!

@cdsmith 7 лет назад

Are Kelvin clips really necessary for 4 wire measurement? I scored a GDM-8251A benchtop multimeter on eBay but it didn't come with Kelvin clip test leads. I've tried 4 wire measurements using two sets of normal leads and it seems to work fine. So I guess I'm wondering if it is really necessary to be injecting current and measuring at the exact same point on the device under test. If you clip the sense leads just outside of the other (non-sense?) leads there shouldn't be any significant voltage drop in the device leads for that fraction of an inch anyway. Or am I missing something?

@AmRadPodcast 7 лет назад

Hi Carl. Yes, for general electronics work you can just use some regular ol' meter leads. I had some clips laying around, so chose to use them. The added resistance that would be added from not sensing directly on the source leads wouldn't matter at all. My mindset was coming from the semiconductor/test world where it is important. I should have pointed this out in the video... in fact after reading your comment, I went back and tried to somehow annotate that fact, but alas, RU-vid has completely disabled annotations or any other text that one used to be able to overlay on the video. So hopefully anyone else that has the same question will read your comment. Thank you for your input!

@cdsmith 7 лет назад

I may still get a set of Kelvin clip leads just for the convenience, but I had a bit of sticker shock when I found that a good quality set cost close to half what I paid for the meter (I got a really good deal on the meter).

@johnhopkins6260 4 года назад

100mA source: LM338 w/ 12.5 Ohms across Out/Adj. (15Ohm parallel with 75Ohm = 12.5Ohm)... simplifies the math. For1A: 1.25ohm across Out/Adj. (4@ 5 ohm in parallel = 1.25Ohm)... FWIW, 100mA is less likely to cook loads than 1A... or 120Ohm resistor in series from 12.6vdc battery should give roughly 100mA... ballpark measurements.

@rochellbolivar3262 6 лет назад

Thank you for the video. :)

@AmRadPodcast 6 лет назад

Thank you for watching!

@felixcat4346 6 лет назад

Nice demo, but the only reason to measure resistance this way in to increase the sensitivity of your multimeter. Expensive multimeter today provide enough accuracy for any real world applications unless you are just doing experiments.

@ZacksLab 5 лет назад

You use 4 wire when you're measuring resistance that's on the order or much less than the resistance of your leads and contact resistance. Regardless of how expensive your multimeter is, it can't measure a 1 mOhm resistor unless it is in 4 wire mode because of physics. Very small resistances show up often in real world electronics in the form of precision shunts. Also, a lot of manufacturing tests in industry involve measuring very small resistances, for example, checking the integrity of wirebonds or laser welds by measuring their resistance (which is generally in the order of a few 100 microohms). These are all done with 4 wire measurements.