[volt-nuts] Best way to measure micro Ohms

Wed Sep 20 07:13:10 EDT 2017

I once repaired a Valhalla 2555A Current Calibrator <https://valhallascientific.com/DataSheets/2555A_Data_Sheet.pdf>  (good for up to 100A output). It uses aluminum bus bars inside to route the current.  The junctions between the bars had become higher than normal impedance and it could no longer deliver 100A.  I disassembled all joints, cleaned them with emery cloth, then applied a drop of Caig Deoxit and re-assembled.  That was over four years ago and no complaints from the customer so far.

Best regards,

mitch

-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces at febo.com] On Behalf Of Andre
Sent: Wednesday, September 20, 2017 3:54 AM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Best way to measure micro Ohms

Hi, just my $0.02 worth.
I have some instrumentation amplifiers here also looked into low resistance connections for my other projects.

If I recall correctly you need to look at the electrochemical series. For interconnects on Al you want a metal similar on the ES.
The oxide is a problem but if you connect it properly eg with an oil droplet and clamp connnector using compatible vernier it should be fine.

Looking at how wiring in the US is done might give you some ideas.

Kind regards, -Andre
________________________________________
From: volt-nuts <volt-nuts-bounces at febo.com> on behalf of Charles Steinmetz <csteinmetz at yandex.com>
Sent: 19 September 2017 21:30
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Best way to measure micro Ohms

David wrote:

> A practical problem is the tools available to me. The U-channel was 
> machined by someone in my radio club, and the rest I made myself using 
> nothing more than a drill and hand tools. It would be nice to make 
> more out of one piece, but it would require better tools than I have 
> readily available. There are certainly engineering companies that 
> could do a better job, but it would be quite costly.

If you can make a decent drawing of what you need (it doesn't have to be a draughtsmanlike job, as long as the form and measurements are clearly shown), I bet you can find someone in your radio club, or a personal friend, or someone on a list you frequent to make it for a nominal cost (you would probably need to pay for the raw material, although I don't charge for anything that comes out of my scrap pile and this is true of many other home shop machinists).  HSMs are behind every third or fourth garage door in the UK.

Another option would be to build up the parts as you have done, then have someone TIG weld the pieces together.

Best regards,

Charles

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