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From: "Michael A. Terrell"
Subject: Re: Short Circuit Detector
Date: Fri, 11 Oct 2002 20:40:20 -0400
Organization: Do I have to? Well, Ok. If you insist!
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References: <email@example.com> <firstname.lastname@example.org>
Jim Thompson wrote:
> On Fri, 11 Oct 2002 18:17:07 +0200,
> "fred bartoli" ,
> In Newsgroup: sci.electronics.design,
> Article: <email@example.com>,
> Entitled: "Re: Short Circuit Detector",
> Wrote the following:
> |For copper planes, sheet resistance is about 0.5mohm/square for 35um and
> |1mohm/square for 17um thickness.
> |So you'd better have a sensitive meter, (maybe add a gain stage).
> |Then set to say 100/500mA the current, and protect your circuit with a
> |schottky between vcc-gnd : it's easy to have the psu voltage button
> |accidentally turned in case it happens the short opens... by himself. (I had
> |that and once corrected for the short I just had to drop the fried board :-(
> |> Steve
> |> "Nico Coesel" wrote in message
> |> news:firstname.lastname@example.org...
> |> > "red rover" wrote:
> |> >
> |> > >Does anyone have link to a design for
> |> > >short circuit detector? I recall that Bob
> |> > >Pease had a design for one in his Analog
> |> > >Troubleshooting book. I believe it was
> |> > >basically a micro ohmeter with an audio
> |> > >output and you worked your way around
> |> > >the pcb homing in on the fault.
> |> > >
> |> > >Anybody here made one? Any good success?
> |> >
> |> > I've found that most short circuits on a PCB are in power
> |> > distribution. In case of such a short circuit I simply connect a PSU
> |> > set at a -safe- low voltage (current limit set to 1A; depending on
> |> > minimum trace width) to the board. By measuring the voltage accross
> |> > the decoupling capacitors (to start with) I can determine the area
> |> > where the short should be. The closer you get to the short circuit,
> |> > the less voltage you measure.
> |> >
> |> > --
> |> > Reply to nico@nctdevpuntnl (punt=.)
> I once cured some shorted thick-film substrates by applying a 5V/200A
> supply ;-)
> ...Jim Thompson
> | James E.Thompson, P.E. | mens |
> | Analog Innovations, Inc. | et |
> | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
> | Phoenix, Arizona Voice:(480)460-2350 | |
> | Jim-T@analog_innovations.com Fax:(480)460-2142 | Brass Rat |
> | http://www.analog-innovations.com | 1962 |
> For proper E-mail replies SWAP "-" and "_"
> I love to cook with wine. Sometimes I even put it in the food.
I had a guy bet me I couldn't find the short and fix a shorted piece
of RG/8 coax with a PL-259 at each end. I popped the hood on my car,
center pin to one terminal, shell to the other. It started to smoke and
burn near one connector so I cut it off at the burn and put the
connector back on.
My motto: "Always use the right test equipment for the job!" Since
he considered the cable scrap and no one had a TDR it didn't really
matter if the cable was destroyed, so I had to show him that it could be
Michael A. Terrell
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