Measuring voltage in salt water

[Gary Fletcher]

I am trying to solve a problem I've just started thinking about which is a bit out of the ordinary.

I want to measure voltage fluctuations in salt water, we know salt water is conductive and that when we move our muscles it generates small electrical currents - my question is does anyone know how or where to start on this? Any ideas or pointers on kit?

Thanks

Gary

[Richard Ibbotson]

My first thoughts are that there will probaly be lots of sources of electrical potential in a setup in salt water. A fairly sensitive microvoltmeter is probably required.

Also you need to know what the signals you are looking for are like. Here is a page I found on google for electromyography:

http://www.pef.uni-lj.si/eprolab/comlab/sttop/sttop-bm/bm-elephy.htm

So you probably should start with electrodes to understand what you are looking for, then experiment to see if you can get the same signals without electrode contact.

 

I've got some isolation amplifiers that might be of use for you, and maybe feed them into an A2D or storage scope.

[Gary Fletcher]

That makes some great reading, thanks for sending it through!

Are you around Wednesday to discuss in more detail?

Also I think I was talking to you about switching power supplies for Raspberry Pi from 12v input to 5v output. I think you mentioned you found a source on ebay for £1 - do you have a link by any chance?

Thanks

Gary

[Robert Thomas]

In a fluid, you do have extra issues: namely suability of the saline solution. So much so that people measure fresh water ingress to salty sea by potential difference. Then there is temperature: this causes differences not only directly but also via thermal currents and saline density.

Are you measuring a tank or free water?

R

[Nigel Worsley]

> switching power supplies for Raspberry Pi from 12v input to 5v output.

Search Ebay for LM2596, there are loads of them.

Nigle

[Gary Fletcher]

To explain the concept in more detail I was thinking about the feasibility of attracting large pelagic fish using electrical signals.

 

Richards email gave me an idea that it may be possible to take an ecg of a fish under stress and somehow play those minute electrical signals back underwater as an attractant.

 

The ocean obviously has a pretty stable salinity 1.026 and temperature between 20-26 degrees so we know those parameters.

 

I was using the hand muscles as I recently saw a study on this for attracting sharks with hand movements underwater.

 

Anyone wanna have a play and a behind the scenes visit at the National Marine Aquarium?

[Robert Thomas]

Nice invite, but I am not your man (I think). Google is my best friend. Seems that electric eels sense via a/c or disturbances via that field. That makes sense because dc will crete it's own stable field (e.g. electrolysis). So a high hertz a/c carrier and measuring offsets to that might be the way to (google)

R

p.s. you are aware of the electric fishers in (I think) the USA? It was on an "extreme Fisher program" I think.

On 20 Nov 2012, at 14:25, Gary Fletcher <garygf...@hotmail.com> wrote:

To explain the concept in more detail I was thinking about the feasibility of attracting large pelagic fish using electrical signals.

 

Richards email gave me an idea that it may be possible to take an ecg of a fish under stress and somehow play those minute electrical signals back underwater as an attractant.

 

The ocean obviously has a pretty stable salinity 1.026 and temperature between 20-26 degrees so we know those parameters.

 

I was using the hand muscles as I recently saw a study on this for attracting sharks with hand movements underwater.

 

Anyone wanna have a play and a behind the scenes visit at the National Marine Aquarium?

 

[Richard Ibbotson]

I will be down on Wednesday.

 

I've had a few more ideas on sensors/amplifiers and temporal/spacial analysis of signals, we can discuss then.

 

Will also bring some RPi stuff

[Richard Ibbotson]

My first thoughts on a measurement and simulation setup would be to use a stereo 24 bit soundcard for the sampling, because the signals of interest are in the low audio spectrum.

There is plenty of audio analysis software available too.

 

For the input, I was thinking a couple of Moving Coil cartridge transformers would give the step up and the isolation at the input. The impedance of seawater apears to be very low.

 

I guess playback could be done with a small audio amplifier.

 

Electrodes, not sure. I gues material that is corrosion resistant based on a resistive layer is not good. The silver chloride type electrodes may not have the bandwidth needed.

 

Anyone got any comments and better ideas, or any components for a test ?

[Richard Ibbotson]

If we are going to test in a saltwater aquarium, are there any specific health and safety rules for the equipment, people and the fish ?

Any maximum voltages in the water ?

 

Would batteries be better as power source ?

[Gary Fletcher]

I would say we didn't get that far, but batteries would probably be a far better source.

I just had an email that tomorrow is going to be delayed a week because there dive guy is ill and can't dive.

Are you about this evening? I'll catch up with you at the space?

---

Date: Wed, 12 Dec 2012 04:15:43 -0800
From: richard....@btinternet.com

[Robert Thomas]

I've been thinking about this a bit. If you sent out a relatively high frequency a/c and then demodulated the return, then the electrode make up is not as important. I believe I read that most signals from fish are a/c. Naturally, I could easily be talking out of my hat.

Plus, my guess is that affecting the fish with electricity is a whole heck of a lot easier than "seeing" what they are sending out.

Regards,

Rob.