On Fri, 16 Jan 2004 08:53:49 +0800 budgie wrote:

On Thu, 15 Jan 2004 16:44:35 -0600, "Steve Nosko"
wrote:

Seems to me there's a way to use a moderate current and sense the
_magnetic_ field. Follow the field around the board along the runners.
However, I don't remember what was used to sense the field.

HP used to make a hall effect (IIRC) probe for current tracing. One of their
Bench Briefs technotes described the probe and the process.

It was the HP 547A Logic Current Tracer combined with the HP 546A
Logic Pulser. These worked only with TTL or CMOS circuits. The pulser
would drive current into any point you wanted and the tracer could be
used to follow the current path.

You would set the pulser to put out a continuous pulse train, and then
adjust the sensitivity of the tracer so that it would just trigger on
the current pulses sent out by the pulser. It would thus ignore other
current that was flowing in the same trace as long as that current was
either DC or consisted of pulses which were smaller than those put out
by the logic pulser. I think the logic pulser could put out an amp or
so, but they were short enough that they didn't damage anything.

They work well, but the current tracers are rather hard to come by now
and they are rather expensive when you find them.

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Jim Adney
Madison, WI 53711 USA
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