** Using 1oz PCB material, a 0.01ohm trace could be 0.5mm wide and 10mm long OR any trace with a similar ratio.
IMO, with a 5mm x 100mm trace, you *might* have a predictable result that was not too sensitive to self heating error.
No surprise you never see it done.
.... Phil
If you can deliver a known current step, you know your track resistance. If there's already a switchable current consumer in place accurate enough, hardware costs nothing.
NT
... And you have the nerve to criticize others for their misuse of English.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
Even if you use an accurate resistor, the end connections could have variable resistance.
If you really want accuracy at low resistance values, you will need to use a four-terminal system. You could probably get away with using an ordinary through-hole resistor on a double-sided board, with the current connections on the underside and the voltage connections on the top side or vice-versa (don't plate through the hole!).
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
Yep, there's surface mount versions like this:
but it's not a ten cent part...
Sure. The Farnell Australia web-site had a number of similar parts, but they did cost a dollar or more. I posted a url for one on Sunday.
-- Bill Sloman, Sydney
I use a thick track and take 'nicks' out of it to calibrate. If you have the space you can lay down multi tracks in parallel and cut through one or two to get the accuracy.The strips will current share fine batch to batch.
If you're going to cut tracks, to get useful accuracy without an excessive number of tracks you'd need to use track resistances in a ratio of 1,2,4, etc. The ratios may well be off, due to the nature of the process, but you only need to get so close.
Or you could use one track with lots of along slots in it, creating lots of short sections you can cut.
NT
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