Contact resistance
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Posted by Yzordderrex on July 3, 2008, 12:38 pm
Please log in for more thread options I am using a gold pogo pin to make contact in a 2amp application. The metal it is in contact with is stainless steel. I am measuring 0.12 ohms across the interface. Does this seem correct? I would like to know if anyone has a link to a paper which would discuss this. I might have to take a look at changing the stainless to something else. regards, Bob N9NEO | |||||||||||||||||||||||||||||||
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Posted by on July 3, 2008, 5:43 pm
Please log in for more thread options What method are you using to measure the resistance? Hopefully not an ohm meter alone. I can't say 0.12 ohm is correct but at 2-amps that's a 0.24v drop. How about getting 4-clip leads, a constant current source and a voltmeter and make a 4-point measurement. Tie the current source to the pogo pin and the steel plate, connect the voltmeter to the pogo and steel plate near the point of pogo contact then touch the pogo to the steel plate and measure the voltage. Apply ohms law and determine the resistance. If the measurement point is away from the point of contact you may be measuring the resistance of the steel plate. Perhaps you could apply multiple pogo's and/or a sensing scheme to minimize the losses. good luck! al | |||||||||||||||||||||||||||||||
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Posted by DaveM on July 3, 2008, 6:57 pm
Please log in for more thread options >> Greetings,
>> >> I am using a gold pogo pin to make contact in a 2amp application. The >> metal it is in contact with is stainless steel. I am measuring 0.12 >> ohms across the interface. Does this seem correct? I would like to >> know if anyone has a link to a paper which would discuss this. I >> might have to take a look at changing the stainless to something else. >> >> regards, >> Bob >> N9NEO >
> What method are you using to measure the resistance? Hopefully not an > ohm meter alone. I can't say 0.12 ohm is correct but at 2-amps that's > a 0.24v drop. How about getting 4-clip leads, a constant current > source and a voltmeter and make a 4-point measurement. Tie the current > source to the pogo pin and the steel plate, connect the voltmeter to > the pogo and steel plate near the point of pogo contact then touch > the pogo to the steel plate and measure the voltage. Apply ohms law > and determine the resistance. If the measurement point is away from > the point of contact you may be measuring the resistance of the steel > plate. Perhaps you could apply multiple pogo's and/or a sensing scheme > to minimize the losses. > > good luck! > al What kind of pogo pins are you using? If they're needle points, then it's possible that they don't have enough pressure to dimple the stainless plate adequately to lower the resistance. Two amps is a bit much to push through a needle point contacting a hard surface. Possible to use a round tip pogo pin??... more contact area and higher pressure pins might help. -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Experience: What you get when you don't get what you want | |||||||||||||||||||||||||||||||
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Posted by on July 3, 2008, 9:24 pm
Please log in for more thread options > Greetings,
> > I am using a gold pogo pin to make contact in a 2amp application. =A0The > metal it is in contact with is stainless steel. =A0I am measuring 0.12 > ohms across the interface. =A0Does this seem correct? =A0I would like to > know if anyone has a link to a paper which would discuss this. =A0I > might have to take a look at changing the stainless to something else. Stainless steel is stainless because it is covered with a coherent layer of not-all-that-conductive chromium oxide - 0.12 ohms sounds very like the sort of resistance levels that caused me to dump stainless steel electrodes in a conductivity meter and go for platinum. For you application gold would be traditional. Printed circuit manufacturers used to routinely selectively plate a micron or so of hard gold onto the contact fingers on plug in printed circuit boards. Even that couldn't take enough pressure to force metal-to-metal contact through the gold sulphide that builds up - someone had to polish the connector pins every six months or so to keep the contacts reliable - and two part connectors eventually took over. Pogo pins do provide enough force but they will probably wreck the target surface if you make contact more than a few hundred times, which is plenty for production testing (where they are normally used). -- Bill Sloman, Nijmegen | |||||||||||||||||||||||||||||||
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Posted by Archimedes' Lever on July 3, 2008, 11:04 pm
Please log in for more thread options On Thu, 3 Jul 2008 18:24:49 -0700 (PDT), bill.sloman@ieee.org wrote:
>Stainless steel is stainless because it is covered with a coherent
>layer of not-all-that-conductive chromium oxide Stainless gets abrasively polished. Any coating placed on the raw stock before polishing gets abraded off. Everything that stainless is, is throughout the alloy matrix that makes up the medium. > - 0.12 ohms sounds
>very like the sort of resistance levels that caused me to dump >stainless steel electrodes in a conductivity meter and go for >platinum. He should go by a set of lawn mower engine points. Easy to find and nice-n-cheap. Both contacts are platinum plated, which NEVER oxidizes, and is the proper point contact medium if longevity is a concern. All that would be needed then is an actuation mechanism. | |||||||||||||||||||||||||||||||
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>
> I am using a gold pogo pin to make contact in a 2amp application. The
> metal it is in contact with is stainless steel. I am measuring 0.12
> ohms across the interface. Does this seem correct? I would like to
> know if anyone has a link to a paper which would discuss this. I
> might have to take a look at changing the stainless to something else.
>
> regards,
> Bob
> N9NEO