http://pdfserv.maxim-ic.com/arpdf/MAX471-MAX472.pdf on Maxim site has a
short
discussion on using PCB traces as Rsense. Take a look at the end of
page 9 ('Cost') and the top of page 10 (Fig 6).

Tal

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Olin Lathrop
> Sent: Saturday, May 11, 2002 4:40 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Measuring automotive current....
>
>
> > The new question then is how to figure out the resistance
> > of a PCB trace.  From AWG/resistance tables for copper wire,
> > I can calculate the resistance of the copper layer with the
> > known thickness/width, but the solder coating adds an unknown
> > factor, as I haven't seen any PCB house specs on that.
>
> The board house should be able to spec the copper thickness, usually in
> "ounces", which can be translated to ohm/square after some figuring.
> However, they will usually spec only the minimum thickness, and I would
> worry about differences between boards and production batches.  This could
> be overcome by doing calibration at production time and storing values in
> EEPROM or whatever.  It's going to be tough to get a PCB trace to handle
> 100A though.  I still think that measuring the drop accross the existing
> wire or inserting a calibrated wire is a better solution.
>
>
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