Author Topic: Looking for good quality test leads  (Read 254 times)

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Offline sdouble

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Looking for good quality test leads
« on: October 19, 2019, 01:51:42 pm »
Hi folks,
I own a bunch of reasonnable quality meters (agilent 1242B) but I do need to replace the leads.
I am after low resistance measurement and contact surface of the agilent leads is too little.
I do need to measure 0.1 ohm without pressing the surface of the Device under test.
Any idea of low impedance/ reliable leads ?
 

Online nctnico

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Re: Looking for good quality test leads
« Reply #1 on: October 19, 2019, 01:59:29 pm »
Measuring .1 Ohm with regular leads is borderline impossible if you want some accuracy (=meaningfull numbers).
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline TimFox

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Re: Looking for good quality test leads
« Reply #2 on: October 19, 2019, 02:08:21 pm »
If you need accuracy at the 0.1 ohm level, you must use four-lead measurements.  If your meter does not support four-lead ohms, your best bet is two meters, one to measure the current applied to the DUT, and the other to measure the voltage across the DUT, being careful to connect the voltmeter directly to the part to avoid voltage drop across any part of the current-forcing wires.  This can be done with a "Kelvin clip" or similar to fixture the four wires, but needs two meters and an external power supply.  The external power supply need not be expensive, so long as it has current limiting or an external (power) resistor to get the desired current level.  With 1 ampere, you will get 100 mV across the 0.1 ohm DUT, which is appropriate for the voltmeter.
 

Offline sdouble

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Re: Looking for good quality test leads
« Reply #3 on: October 19, 2019, 02:10:36 pm »
I need to measure within 50% accuracy. What I forgot to mention is that I will not sense PCB (copper) trace but aluminium which suffers from superficial oxydation
 

Offline jackthomson41

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Re: Looking for good quality test leads
« Reply #4 on: October 19, 2019, 02:23:07 pm »
Don't think it would be possible with leads at all, you will need to buy some measuring instrument ... designing one could work.
 

Online ThickPhilM

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Re: Looking for good quality test leads
« Reply #5 on: October 19, 2019, 03:59:37 pm »
I'm a little confused...

You seem to imply that you can't break the surface oxidation layer of the aluminium to measure the resistance; sorry but you really aren't going to be able to measure the resistance without doing this.

The oxidation layer is rather thin, and easily broken with any form of physical contact. If not for this aluminium would be almost unusable as a conductor.

I agree that Kelvin clips are your likely best option, either with a 4-wire meter or using 2 meters in the described configuration.

If any form of physical pressure (even the lightest of touches) is not possible, then how about attaching some very thin and flexible flying leads to the physical points you want to measure at, using conductive glue or paint?

Perhaps a little more information on the exact usage context would help us come to a solution
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nuqDaq yuch Dapol?
 

Offline sdouble

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Re: Looking for good quality test leads
« Reply #6 on: October 19, 2019, 08:13:12 pm »
I seems that I was a touch cryptic.
I have an aluminium foil, 1.5 mil thick, glued onto a frame (carbon steel ring, 8 mil thick). The ensemble constitute an electrode of an ionization chamber.
The foild got glued using conductive (containing Silver) epoxy.
It appears that we have a conductivity issuebetween the foil and the ring.
The ring is relatively stiff but the foil is kind of fragile. I can not push .onto the foil : that would deform and hamper its flatness.
I plan is gently sand a tiny fraction of the foil to remove the tiny layer of oxyde and apply immediately a good quality flat electrode
 


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