Projet of PH Sensor for swimming pool

[battika]

I bought the PH sensor module and probe in post 2 last summer, managed to find some info regarding calibration so bought three different buffer liquid and calibrated it at 25 Celsius. Then built a super basic system that posts PH value every 15 minutes at Thingspeak and placed it next to the pool. The problem is the module does not have auto compensation for temperature and I did not find anything regarding how to take temperature into account. So, the readings were very different during the day (around PH6) and during the night (PH7)

So, it was not possible to trust the readings so I gave up on this project. Hope you guys will have better luck with your sensors.

[bertrand]

The sparky boards are i2c also arnt they?

Yep, that makes it easy to have one node that reads all your water parameters:
pH, EC, Temp... and if you're into Ions, then you can add more probes.

[sel303]

Anyone get further with this? Trying to get the i2c to read acurate numbers started to take time away from other projects. I'm thinking about getting the Atlas board.

[nowd1976]

thanks

[Shardan]

A word about temperatur compensation with pH probes.

Some basics:
Usually it is said that pH probes should be calibrated with buffer solutions at 25°C.
This is not really correct, it is just the usual compromise so the buffer solutions are made for use at 25°C.
Beware: Buffer solutions vary their pH value with temperature too!

For really exact pH gauging the solution should have the same temperature as the water you want to check.
Remeber you have to use buffer solutions made for this temperature - makes things somewhat complex.

To make things even more complex:
If you want to meter values above ph7 you have to calibrate with ph7 buffer and pH 9 or pH 10 buffer.
If you want to meter values below ph7 you have to calibrate with ph7 buffer and pH 4 buffer.
The output curve of the probe differs between above / below pH7 slightly.

The temperature compensation depends on 2 factors.
- The deviation of the temperature (for example calibrated at 25°C, gauging at 15°C)
- Deviation of the pH value from the neutral point (pH 7).

On pH7 you don't have any temperature deviation. If water has pH 7, it has pH7 at 10°C and it has pH 7 at 50°C.

For a pool or a fishtank the temperature deviation usually is negligible.

Let me give an example.
Requierement: You calibrated your pH probe at 25°C.

Your fishtank or your pool shows a pH of 6 at 25°.
What pH would be shown without temperature compensation if you raise or lower the temperature by 20°C?
At 5°C it would show pH 5.93. (Difference -0.07 pH)
At 45°C it would show pH 6.07. (Difference +0.07 pH)

Lets say at 25°C you see pH 5.
At 5°C it would show pH 4.86. (Difference -0.14 pH)
At 45°C it would show pH .14. (Difference +0.14 pH)

As you can see temperature compensation is not the most important thing for most home users.

Anyways, you may simply use a DS18B20 waterpoof sensor and calculate the temperature compensation
with a rule.
A table with some compensation values is shown in the attached picture.
left column shows deviation from calibration temperature.
(Sadly picture is in German language, but the table should be clear enough).

temp-pH.jpg (489.75 KiB) Viewed 18169 times

Regards
Shardan

[TD-er]

But then the question is: How to waterproof your sensor for a pH far from neutral? :0
Or do you just measure the glass containing the concentration?

[randytsuch]

Have you guys seen this project?
http://www.domoticz.com/forum/viewtopic ... a1736e75e2

He provides lots of information.

I've thought about trying to implement a chlorine sensor for my pool, but haven't make any progress yet.

Randy

[Shardan]

But then the question is: How to waterproof your sensor for a pH far from neutral? :0
Or do you just measure the glass containing the concentration?

No problem. pH-probes are cabled sensors so the electronics can be somewhat distant to the probe itself.
Electronics should be mounted in a IP65 waterproof case.

More industrial solution: There are glands for pH probes in the market similiar to cable glands.
These glands can be fixed to a tube where the liquid is flowing.

100_4820.JPG (10.8 KiB) Viewed 18135 times

[alli21]

Hello Guys,

I am having a swimming pool at my house. I have not so much knowledge about the PH sensor. Can anyone tell me something about this? Is it a necessary equipment to be installed in the swimming pool? Please help me with this.

Thanks