Did you understand the principle of Kelvin probes properly?

The idea of using those sewing machine needles is great, as well to use the coax cable from an old SCART cable. Very nice and smart. An interesting implementation could be to make a Milliohm meter using low voltage AC instead of DC, to measure also the capacitor ESR

Would love to see you revisit this, your milliohm meter, and any other DIY test gear/ troubleshooting tools you've thought up.

The sense wires need to be down at the probe end, not back at the power supply end. These are not Kelvin probes. Preferably they will be on separate probes, but if you are close enough to the tip you will mostly get away with this.

@richardlangner

2 ай бұрын

Thanks, I realsied that and the later version had the wire soldered to the eye of the needle near the point. In any case the video was for comparative readings, not as an accurate instrument.

Great topic, thanks 👍

@richardlangner

26 күн бұрын

Thank you!

Very smart.

Excellent tutorial !!!

@richardlangner

Жыл бұрын

Thank you. After I made the video I thought of improvements... It will be better if you the measuring wire solder to the eye of the needle to reduce the commoned resistance of each probe.

I found it surprising you could solder to hardened steel. Interesting none the less. Thank you.

@lenslens7379

Жыл бұрын

For soldering stainless steel search for acid sulfuric+zinc flux there's many DIY tutorial

For soldering stainless steel search for acid sulfuric+zinc flux there's many DIY tutorial

@DaveEtchells

Ай бұрын

If you can find it, Almit KR-19RA solder has an amazing flux that lets it solder just about anything. I've used it to solder to stainless steel and regular steel in the past.

They are not real 4 wire probes. The 2 wires of each probe must be in contact only on the resistance to measure, to remove the effect of contact resistance.

@richardlangner

8 ай бұрын

Thanks for your feedback. The video project was not for accurate measurement, but for comparative readings. You are correct of course, and that's why I made a later video with twin needles.

@we-are-electric1445

8 ай бұрын

You also have to think how much accuracy do you need ? There is no point in having accuracy just for the sake of it. It wastes time ( and money). if you really want to be accurate you reverse the test current, subtract the two voltages and divide by 2 - but is it necessary to get you to where you want to be ?

@alainblazit9504

8 ай бұрын

@@we-are-electric1445 I used 4 point resistance measurements to locate short ciccuits on populated PCBs. I needed to measure very low resistances with a not too high current.

@gblargg

10 күн бұрын

@@we-are-electric1445 The question is how much connection resistance can vary. The nice thing about true four-point probes is that you can have a crappy connection yet still accurately measure resistance (assuming your power supply can deliver a high enough voltage to overcome connection resistance).

@we-are-electric1445

10 күн бұрын

@@gblargg Reversing the test current and subtracting the two voltages and divide by 2 is a standard way of obtaining accuracy. A crappy connection implies inconsistent readings. If you have poor connections the obvious question to ask is why?

To be true kelvin probes you need separate tips for voltage or current so the contact resistance at the tips isn't measured.

@richardlangner

Жыл бұрын

Thanks Lars. This video was about a quick and easy aid to finding short circuits. If you need more accuracy, I made a two needle probe which is shown in a later video. Neither of these have great accuracy but it should help people to understand the need for, and use of, Kelvin probes.