Using Electric 'Field' To Detect Leak In Pool

[MrAl]

Hello there,


Another quick query...


Anyone here ever use the electric field to detect where a leak is in a swimming pool with a liner (not an in ground pool but an above ground with a liner).

The idea is that the place where the hole is will conduct much better than places without a hole so the electric field near the hole should be stronger when (possibly) the ground and water is energized.

Any ideas appreciated

 

[dougy83]

If the leak forms a path to ground, can you just measure the resistance between ground and a probe that you move around the pool? Resistance should be lowest when the probe is closest to the hole I would think.

 

[alec_t]

That sounds promising. If DC polarisation of the probe proved a problem it might be necessary to use an AC measuring method.

 

[JimB]

I have never used a technique like this for anything other than the very first "Lab session" in Electrical Engineeing at college about 45 years ago!

The Lab was entitled "Equipotential Plotting" and involved measuring voltages in a perspex tray filled with water while a current was flowing from conductive bars at opposite ends of the tray.
The tray was about 10" long and the water was about 0.25" deep.
The purpose of this was to illustrate current flows in irregular shaped conductors and that not all the conductor material actually contributes to the flow of current.

So, back to the future and Mr Als question.
If it is possible to establish a current flow from an electrode in the pool to an electrode in the earth surrounding the pool, then measure the potential gradients in the pool, they should point to the area of the leak.

So Mr Borman, I did learn something in your classes after all!

JimB

 

[MrAl]

Hi,


Ha ha

Yes i was thinking of energizing the probe with voltages starting at 9v, then progressively working up from that in case that's not enough. Of course safety is a big issue too as there will be water around.
Since the pool shell would be steel or aluminum, i'd say the water level should be low enough so it never comes in contact with it or it would create an unwanted path to ground. Just another thought.

 

[MikeMl]

I'd use AC from an isolated winding on a small transformer, for safety and to minimize electrolysis of the electrodes. I would try an AC voltmeter as a detector, or possibly a set of high-z earphones (listen for the null). The field lines should neck down where the leak is.

I recently did this (using a 12V Malibu low-voltage yard lighting transformer) to do a four-point measurement of soil conductivity. I was passing about 4A through the outer pair of electrodes...

 

[MrAl]

Hello again,

I would have no problem with trying various frequencies from 1Hz to 1MHz, but what i feared about using AC is there might be abundant capacitive effects due to the shear size of the pool liner. The interface water|liner|steel makes a huge capacitor

alec:
What where your thoughts about why DC might not work well enough?

 

[alec_t]

alec: What where your thoughts about why DC might not work well enough?

DC results in electrolysis, which can cause probe corrosion and change the probe properties/effectiveness. Brief DC pulses might be ok.

 

[MrAl]

DC results in electrolysis, which can cause probe corrosion and change the probe properties/effectiveness. Brief DC pulses might be ok.

Hello alec,


Oh yes, good thinking there

In the worst case, the trick is to disassemble an old carbon zinc battery and remove the carbon rod, and use that for the probe. They make good electrodes.

But really for this a ball of aluminum foil would probably be ok, just replace when necessary. The current would be very low, and the rate of transfer of atoms is proportional to the current, so the removal of atoms should be fairly slow anyway i would think.

Your idea is also interesting because if we could find a chemical additive that could be added but not hurt the water quality too much we might find something that reacted with the plastic liner and actually filled the hole. That would be really nice