Re: [EE] measuring the magnetic field from a small trace carrying a < 50uA load?

Martin -

I remember during a summer job in college working with a ditch digging
crew - it was mostly standing around watching the guy with the
excavator work and then waiting for the sod delivery.

But before the excavator could dig there was a gas company guy out
marking the pipeline - he had on headphones attached to a search
thingy - but thinking about it now, how did he get a signal from a gas
pipelne ?   I'll have to do a search on that :)

Chuck

On Mon, Jan 6, 2025 at 4:40 PM Martin McCormick <[email protected]> wrote:
>
> Chuck Olson <[email protected]> writes:
> > Martin -
> >
> > You are correct, I should have said something about moving the head
> > across the conductors, cassette tapes moved less than 2 inches per
> > second so the head wouldn't have to be moved super fast ?.
> >
> > The thing I've noticed with Hall effect devices was that they are
> > really noisy, 50 uA probably not going to give much of a signal above
> > the noise.
> >
> > Chuck
>
>         I figured it was something like that plus one would have
> to have some sort of low-pass filter because 60 or 50 HZ magnetic
> fields are going to be common due to all the transformers and
> motors in our world.
>
>         I was once part of a group of people who dug a hole for
> the base of an amateur radio tower and the neighborhood in
> question had buried power and telephone lines.  A fellow from the
> power company came out and had a portable detector which was
> probably inductive but had a speaker so you could hear the hum of
> the 60-HZ magnetic field around the underground power cable.  He
> marked the ground across the yard, following the buzz so we knew
> where not to dig.
>
>         Too bad the telephone line which was also buried near
> didn't radiate much because we only found that out when we came
> across one heck of a tree root and, after the shovel cut it, the
> man's wife who had been on the phone and wasn't too keen on this
> whole deal came out to inform us we had cut their telephone wire.
> That root had a lead shield and 4 black wires.  Ah, what they are
> doing with recombinant DNA these days.
>
>         We patched the cable  temporarily so the phone worked
> again and, I guess, AT&T fixed it right a few days later.  I'd
> much rather accidentally cut a phone wire than 200 amps at 240
> volts phase to phase.  An analog telephone line pulls a few
> milliamps DC when a conversation is going on plus a little more
> if it rings but in the year 1975 when this all happened, there
> wouldn't have been any ADSL carriers or anything much on that
> line to radiate through the few feet of soil to make precise
> location easy.  When a phone is on the hook with no conversation,
> there is 0 DC current being drawn.  It would have taken a pretty
> good metal detector to find that line.  I digress.
>
> Martin
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> https://mailman.mit.edu/mailman/listinfo/piclist

-- 
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
https://mailman.mit.edu/mailman/listinfo/piclist