Re: DC cable puzzle

>Terry, East Grinstead, UK

Maybe something underground is full of water or ants or something. Possibly the wire insulation got nicked.

There are some fun instrumentation possibilities, like probing the soil at the surface and measuring/listening for AC potentials.

A map of the surface potentials of some chunk of land, color coded by frequency, would be fun.

We were on the roof yesterday and speculated how cool it would be if we could see RF, all the microwaves and cell phones and wifis and transmitters. That's not possible. But a surface potential map is.

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John Larkin         Highland Technology, Inc 

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John Larkin
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ay. It?s a long run, with an intermediate outdooor mains socket, th en a (supposedly) waterproof case with the relay.

I wanna see B-fields, from DC to maybe 60 Hz. Maybe from whomever sells x-ray glasses :^)

George H.

Reply to
George Herold

oday. It?s a long run, with an intermediate outdooor mains socket, then a (supposedly) waterproof case with the relay.

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Reply to
bloggs.fredbloggs.fred

I've often thought of that. You'd need eyes bigger than Zoey Daschanel and Irene Bordoni combined.

You know that famous chaotic function that can be modelled with a circuit of 2 multipliers and fed into a scope in XY mode to produce a pair of spirals? There's a complete circuit on Paul Horowitz's website. I might have made one for fun if the multipliers weren't $20 each.

Well, it would also be neat to put one in the cabinet under that old scope in your lobby.

Reply to
Tom Del Rosso

To my surprise the mains cabling seemed OK, giving readings outside my DMM's 200Mohm at various points.

A side issue arose has me puzzled. I found about 1V DC across a twisted pair cable, disconnected at both ends, buried in several places. How does that come about? Even the short section I've cut out, with gaffer tape around connector blocks, has about 0.5V DC.

Terry, East Grinstead, UK

Reply to
Terry Pinnell

What are you using to measure the potential difference? A high input impedance meter?

What's the reading if you have a, say, 10kohm resistor between the conductors?

Reply to
Tom Gardner

You can display anything you want on a XYZ scope:

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with just a few transistors, even TV.

Reply to
<698839253X6D445TD

Long ago, in the TV media center there was a periodic interference in the video. It turned out to be induction by the electric trains from the train station next to it into the miles and miles long coax cables in studios.

That studio complex had, IIRC, a metal roof just against RFI, but that did not help against the trains. But basically I would prefer a metal roof in the lab.. over seeing all sorts of RF stuff interfering.

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train track on the right, low flat buildings studios.

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<698839253X6D445TD

happened fredbloggs wrote

mm, using paper and metal filings is much higher resolution, put a camera on it.

Reply to
<698839253X6D445TD

DC voltages below 1 V could indicate some electrochemical pair between dissimilar metals, such as the multimeter probes and the actual wire. If the conductors were supposed to be separated, a well conducting fluid could cause such phenomenon.

Did the multimeter show anything on the AC range ? Some multimeters show some DC reading even with a symmetric AC voltage. Asymmetric AC (even harmonics) could also cause a DC indication.

Reply to
upsidedown

That's great but for an old scope on display it might be more appropriate to have a presentation that is more vector and less raster.

Of course you don't want to burn it in so have it come on when a motion sensor detects someone.

Reply to
Tom Del Rosso

Jou just re-invented the battery, two different metals with a bit of groundwater.

Reply to
Sjouke Burry

Ask Geordi La Forge...

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David Lesher

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