Re: [PEDA] AW: Spiral trace construction?

[van de Werken, Matthew (DEM, PH)]

> -----Original Message-----
> From: Abd ul-Rahman Lomax [mailto:[EMAIL PROTECTED]]
> Sent: Friday, 15 June 2001 12:28
> To: "Protel EDA Forumm"@bastion.qld.csiro.au;
> [EMAIL PROTECTED]
> Subject: Re: [PEDA] AW: Spiral trace construction?
> 
> 
> At 01:15 PM 6/14/01 -0500, David Cary wrote:
> >In my case, I
> >finally got enough documentation to prove that PWB traces 
> varied in resistance
> >far more than the 1% we wanted in our current-sense 
> resistor. (Mostly due to
> >variations in the tin plating over copper, I hear).
> 

<snip>

> 
> That might be usable as a sense resistor, even for accurate 
> measurements, 
> if it could be trimmed or calibrated. The variation of 
> resistance with 
> temperature would need to be considered. There might be 
> applications where 
> this would make sense.
> 

Maybe it would be feasible to set-on-test a system whereby the sense
resistor section is tapped off one of several places on the sense trace (or
one of several pads is joined):

Sense track:

++++========||||||=========|=========+++++
            ||||||         |  
pads--------^

That way, you could choose which point at build time is the ideal spot. This
wouldn't be ideal, but it would make it easier to allow for variations in
manufacturing.


> Using thin track as fuse is a well-known bad idea, precisely 
> because of the 
> problems noted above plus a few, though, again, even bad 
> ideas can have 
> their day.
> 

I can't think of a single good use of using a track as a fuse - if the
"fuse" blows, you basically have to toss the board. Surely it would be
(marginally) better to use a low-ohm resistor as a fuse?? Of course, the
ideal situation is to use a fuse as a fuse, but as we all know we don't
always live in the ideal world...

Cheers,
MvdW


> [EMAIL PROTECTED]
> Abdulrahman Lomax
> P.O. Box 690
> El Verano, CA 95433
> 

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