Measure electric fields underwater...

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Externet
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Measure electric fields underwater...

Post by Externet » Sun Apr 30, 2006 8:19 am

Hi everyone.
Two different metals in seawater produce an electric field as far as I know.

Electric fields underwater are used to keep fish from trespasssing certain areas in farming them, as it is also used to repel sharks in diving.

How adverse effect would lead and stainless, brass and steel used in fishing gear hooks and weights and things have in annoying the fish that is being lured at the same time?
How to measure such electric field or to prove/disprove its effect on fish?

And a side question; about range... - if some aluminium equipment is dumped into the ocean a mile away from a steel pipeline, would that create a mile long electric field ? :sad:

Miguel

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Chris Smith
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Post by Chris Smith » Sun Apr 30, 2006 12:45 pm

In theory yes, but then Resistance has a habit of stopping electricity even in a long good conductor.

TWO metals in salt water produce an electric field, not necessarily a magnetic field of any practical strength.

A fishing hook, is only one piece of metal.

By the way, two dissimilar pieces of metal in the presence of sun light also produces a electric field.

How do you test any of these theories, torture your gold fish I suspect?

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Externet
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Post by Externet » Sun Apr 30, 2006 9:25 pm

Hi Chris :grin:

Yes, would be nice to torture a goldfish !

Lets say a steel hook and a lead weight; that is for sure two dissimilar metals, if there is not a third of bronze (that little thing that spins so the line does not twist, whatever be its name)

Now how to measure the voltage (or current?). Probes with insulated wires, but the probes tips may be copper, or bronze, tossing another variable to the task? :sad:

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Post by dyarker » Sun Apr 30, 2006 10:30 pm

Probes in water with only hook, take measurement. Probes in water with only lead weight. Algebraic sum. Probes in water with hook and lead weight, take measurement; difference between this measurement and previous sum is caused by hook to lead weight field. The positions of objects in the water must be the same for all measurements.

The strongest fields are when dissimilar metals are in direct contact with each other and water completes the loop. Like a brass propeller on a steel shaft.
Dale Y

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Externet
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Post by Externet » Sun Apr 30, 2006 11:14 pm

Thanks, Dale.
When the metals are in contact as the propeller and shaft are yes, the galvanic current happens; am in doubt if a lead weight and a steel hook not connected, but both isolated and suspended on a nylon line would have a current between them.

Or in another example, an aluminium hull boat next to a steel hull boat will have an electric current between them, none using methods of corrosion protection metals attached, no physical contact between them, just floating apart...

Now, for probing with a voltmeter... one probe tip submerged and the other touching the hook underwater ?

Miguel :smile:

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Chris Smith
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Post by Chris Smith » Mon May 01, 2006 1:10 pm

I think the problem here is not if there is a current, but how small is it.

I think a hook, and a seperated lead weight [sealed in by the oxide] , and even the finish coating on most copper items would only produce nano amps or even Pico amps.

Perhaps a shark and other fish could detect these levels, but a lab set up might vary more, just resetting the test from one to the next?

The margin for error would be great.

I Know there is a list in my op amp book for building Nano and Pico amp setups using their op amps, but .....?

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Post by JPKNHTP » Mon May 01, 2006 1:37 pm

-JPKNHTP
-God Bless

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Post by Robert Reed » Mon May 01, 2006 1:39 pm

I don't think the fish will even notice any galvanic action. or if they do they must enjoy it. Case in point--I have caught many fish over the years fishing right be side boats of all desciptions, even in the crowded marinas. And these included all combinations of metals common to the marine industry. and sometimes in massive amounts on the larger cruisers.

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Post by Gary » Wed May 03, 2006 5:23 pm

Hammer Head Sharks special head shape helps them find animals under the sand by electric field.

A great white shark in captivity was found to bang into the side of the concrete tank wall almost every time it tried to swim around. It turned out there was an electrical anomaly there due the way the steel rebar was positioned in the concrete wall.

Some fish are very sensitive to electric fields. But these may be the exceptions rather than the rule.

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Post by haklesup » Fri May 05, 2006 4:02 pm

To measure the potential between two dissimilar metals in an electrolyte (battery) use a volt meter. Just put a probe on each piece of metal.

I doubt a lead fishing weight would do much due to the thick oxide on it and the very weak dielectric of water. Use a mV meter or bridge to measure what your talking about.

I believe it is the difference in the charge in the valence shell of the metal that has the greatest effect on the voltage (i.e. the column on the periodic table), the conductivity of the water would regulate the current that is possible.

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