pool water level sensor

[Les Jones]

Another possible solution would be to use the same method that is used on washing machines to control the fill level. They use a pressure switch which is triggered by the air pressure in a pipe which connects near the bottom of the drum. As water enteres the drum it tries to force it's way up the pipe which increases the air pressure in the pipe. The presuure switch operates without the water coming in contact with the pressure switch just by the increase of air pressure in the pipe. Most of these pressure switches seem to have two sets of contacts that operate at different pressures so that two different fill levels can be selected. (Or maybe one is to confirm the water has been pumped out.)

Les.

 

[spec]

Another possible solution would be to use the same method that is used on washing machines to control the fill level. They use a pressure switch which is triggered by the air pressure in a pipe which connects near the bottom of the drum. As water enteres the drum it tries to force it's way up the pipe which increases the air pressure in the pipe. The presuure switch operates without the water coming in contact with the pressure switch just by the increase of air pressure in the pipe. Most of these pressure switches seem to have two sets of contacts that operate at different pressures so that two different fill levels can be selected. (Or maybe one is to confirm the water has been pumped out.)

Les.

Your a clever fellow Les

spec

 

[spec]

Why not make your own capacitive sensor. Two insulated metal strips 20cm long, 2cm wide and 5mm apart will have a capacitance of 570pF when under water and 7pF when in air (or with 200pF parallel cap 207 to 770pF) . Combined with something similar to Roman Black's capacitance meter and you've got all the basic parts.

Mike.

Hi Pommie,

Interesting information. I did not know the difference in capacitance between wet and dry would be so great.

My recommended construction would be two stainless steel plates, of the dimensions you list with wires bolted to the plates (or soldered). Then cast the whole thing in epoxy resin or similar.

Of course, you would have a slot in the casting between the two plates, but the plates would sill be covered in a layer of epoxy.

I recon that the sensors would then last at least until the sun goes super nova.

spec

 

[camerart]

Hi,
Does the fact that the bolts are being corroded by the water mean that it could be used as an electrolite between two probes of a battery, so giving a voltage to work with?
Camerart.

 

[MikeMl]

Couldn't you just use one of these...?

.. or two of them if you need three pool levels; add water, ok, remove water.

 

[earckens]

Couldn't you just use one of these...?

.. or two of them if you need three pool levels; add water, ok, remove water.

Hi Mike, no: float switch I explicitely don't want. Too exposed to all sorts of issues: leaves, dirt, ..

 

[MikeMl]

Hi Mike, no: float switch I explicitely don't want. Too exposed to all sorts of issues: leaves, dirt, ..

Have you heard of a "water level"? Put the float switches in a covered container (but open to atmosphere) some distance from pool. If you do it right, the container could even be in your house, tens of meters from the pool. All it takes is some tubing, or inexpensive plastic pipe like Pex.

 

[spec]

OK so this is an ideas thread.

Try this one:

You have a low frequency transmitter permanently in the water that transmits continuously.

You then have two hydrophones, one positioned for high water level and one positioned for low water level.

Once again, a little Arduino and a bit of code will do the processing.

Have you seen those WW2 submarine films- if you made the transmitter ping like the ASDIC equipment, that would really impress your neighbors.

spec

 

[spec]

Have you heard of a "water level"? Put the float switches in a covered container some distance from pool. If you do it right, the container could even be in your house, tens of meters from the pool.

Hell- now that is clever.

spec

 

[earckens]

Have you heard of a "water level"? Put the float switches in a covered container (but open to atmosphere) some distance from pool. If you do it right, the container could even be in your house, tens of meters from the pool. All it takes is some tubing, or inexpensive plastic pipe like Pex.

Yes, that is the principle of communicating containers (I don't know the correct english terminology).

Then I can just as wel make a plastic tube and insert it with the gizmo in the pool. No, I don't want piping for this added to the pool: drilling holes etc in the poolwall is a no-go.

So far I can see these options if I want to toss out the current control system and replace the sensor..
1. ..with something that does not corrode
2. ..with something that does not move
3. ..with something that does not just measure "yes or no" but measures proper levels
4. ..with something that is no Chinese clone nor industrial grade quality but something in between

and these options are:
A. item 5 in my original list: https://www.adafruit.com/products/463
B. as cowboybob suggested stick to regular (every 2 years) replacing the stainless steel nuts (this does not comply with item 3 above but heck, sometimes you compromise)

That last option would also allow me to replace the current control system and build something that uses this 2 level "sensor" that is in place now.

So, if we decide on something like the eTape from Milonetech then there is the issue of IP conformance (I asked the manufacturer: he has not certified for IP rating..). The top connectors will need to be insulated from immersion. And this sensor can be built into a open plastic 1" tube so that it gets mechanical strength and can be attached to the pool wall.

I may seem like a difficult customer but I get a lot of usefull info from you all here.

 

[MikeMl]

... No, I don't want piping for this added to the pool: drilling holes etc in the poolwall is a no-go.
...

If the pool has a filtration system, or a heater, then there is already a pipe coming from the side of the pool to a remote location that could be used to indicate level. In that case, it is a simple as adding a Tee to the existing plumbing.

If you are concerned about probes corroding, it is because you are not using the proper method to measure their impedance. If you use a DC-blocked, low-amplitude AC signal to make the impedance measurement, that will eliminate the electrolysis...

 

[cowboybob]

... 36 months by now- to corrode. ...

I'd suggest (from my experience) that a 36 month life span is above average. And given the simplicity of the current system and its apparently satisfactory (thus far) performance, replacing the one corroded probe would certainly be easiest.

... 3. ..with something that does not just measure "yes or no" but measures proper levels

Not sure why you want to complicate the issue to this degree. It is certainly a high(er) tech solution but will produce, IMHO, data of little use other than when the pool needs water added.

All of the ideas thus far put forward will work and each has its advantages/disadvantages. Interfacing any one of them, however, to your existing water level control (valves, relays and such) is another issue altogether and will be far more difficult than you may imagine.

Lastly, (and I'll get off my soapbox), an example replacement **broken link removed** is also pretty cheap. I don't know, of course, of its availability in your area.

 

[earckens]

If the pool has a filtration system, or a heater, then there is already a pipe coming from the side of the pool to a remote location that could be used to indicate level. In that case, it is a simple as adding a Tee to the existing plumbing.

If you are concerned about probes corroding, it is because you are not using the proper method to measure their impedance. If you use a DC-blocked, low-amplitude AC signal to make the impedance measurement, that will eliminate the electrolysis...

Hi MikeMl, pipes to and from the pool are buried.

The corrosion is indeed caused by a probably not well adjusted or engineered control board.

 

[earckens]

I'd suggest (from my experience) that a 36 month life span is above average. And given the simplicity of the current system and its apparently satisfactory (thus far) performance, replacing the one corroded probe would certainly be easiest.

Not sure why you want to complicate the issue to this degree. It is certainly a high(er) tech solution but will produce, IMHO, data of little use other than when the pool needs water added.

All of the ideas thus far put forward will work and each has its advantages/disadvantages. Interfacing any one of them, however, to your existing water level control (valves, relays and such) is another issue altogether and will be far more difficult than you may imagine.

Lastly, (and I'll get off my soapbox), an example replacement **broken link removed** is also pretty cheap. I don't know, of course, of its availability in your area.

Cowboybob, I must agree with you on all points.

And the actual level measurement instead of the current yes/no is indeed a "nice to have".

 

[SPDCHK]

I don’t know if this might be helpful to you or not....

I have a PLC system at home performing many a function, once of which is the irrigation system.

I have a soil moisture meter (SMM) (a design made, or modified by our very own Audioguru). It too makes use of probes in the ground at it too have the corrosion problem if power is continuously left on. (BTW, my probes are simple 9” steel nails). The probes are inserted in a pot filled with dirt, and this pot is located well away from my irrigation system. The pot is exposed to open air environment, meaning it will dry out in warm sunny days, and will get wet when its raining.

My PLC runs the irrigation program always at night. It starts by switching on the power to the SMM. Allows a few seconds for the SMM to sense and detect the moisture level of the dirt, and then replies the status to the PLC.

Once the PLC has executed the result of the SMM, power to the SMM is switched off again, and it will stay off till tomorrow the same time. With this power saving option, I have been using the same metal nail probes for many a year, and they are still good. Yes, they are rusting up from the moisture in the dirt, but not from corrosion.

You might consider installing a timer on your probe sensor electronics. You will just need to latch the power ON when the probe does sense low level. Power must stay on to detect high level and then close your water SOV. Then power to the level sensor can be removed, and the timer will check again the next day?

Yes, No, Maybe?

 

[earckens]

I don’t know if this might be helpful to you or not....

I have a PLC system at home performing many a function, once of which is the irrigation system.

I have a soil moisture meter (SMM) (a design made, or modified by our very own Audioguru). It too makes use of probes in the ground at it too have the corrosion problem if power is continuously left on. (BTW, my probes are simple 9” steel nails). The probes are inserted in a pot filled with dirt, and this pot is located well away from my irrigation system. The pot is exposed to open air environment, meaning it will dry out in warm sunny days, and will get wet when its raining.

My PLC runs the irrigation program always at night. It starts by switching on the power to the SMM. Allows a few seconds for the SMM to sense and detect the moisture level of the dirt, and then replies the status to the PLC.

Once the PLC has executed the result of the SMM, power to the SMM is switched off again, and it will stay off till tomorrow the same time. With this power saving option, I have been using the same metal nail probes for many a year, and they are still good. Yes, they are rusting up from the moisture in the dirt, but not from corrosion.

You might consider installing a timer on your probe sensor electronics. You will just need to latch the power ON when the probe does sense low level. Power must stay on to detect high level and then close your water SOV. Then power to the level sensor can be removed, and the timer will check again the next day?

Yes, No, Maybe?

Well what do we have now? We will be talking in the future! I plan on exactly this in the coming years for our holiday home: full automatic garden sprinkler system with sensors, weather detection, IP connection, GSM transmission etc.. combined with pool automation, ect. I already have a full burglary detection and camera system in place (my job, my company), the rest will follow. My wife declares me nuts (she may be right ) but this may well be something to retire on