Hello Everyone - I am working on a project to measure ph of my pool and make adjustments accordingly. ph is dependent on the sample temperature. I am not going to have a method in the project to measure temperature. Right now, pool temperature is hard coded in my sketch. I would like to add a potentiometer an input to easily adjust pool temperature through the season and not need to reload a sketch. Based on this, how stable is the resistance of a potentiometer for a temperature range of say 60 deg F and 95 deg F? What other options do I have without measuring temperature directly? Another option I have thought about was using the buttons on my lcd to launch a call that would read buttons up and down and store in eeprom. This may be beyond my capabilities.
I'd say that the stability over such small ranges is much better than your ability to eyeball the position and the actual temperature.
Alternatives to a pot is several jumpers, each for a predetermined temperature value.
But seriously, how much do you expect the temperature to fluctuate? And more importantly how large are the variations in ph with the change of temperature?
Uh, whatever the change in ph due to temperature, it's actual ph, isn't it? Are you sure you should compensate? Perhaps the ph probe needs compensation?
Thank you for the response. PH will move by 0.009 for each deg C of temp which would result in a ph difference of bout 0.14 over a range that the pool would be operating with the swg in use. rage of ph to be maintained is 7.5 to 7.8 so the .14 is about 1/2 of the range. the board i have will measure temperature but that would only be its temperature which will be fluctuating a lot since it doesnt have a 13,000 gal mass slowing it down. i wasnt planning on eyeballing the pot position but measure a reading ans show it on the lcd. i am not sure how the jumpers would work, are you saying rwead a high low signal at several inputs and run that through some logic?
Ok, why don't you put the temperature sensor in the water next to the ph probe?
Jumpers would be connected to resistors of different values hooked up in parallel, leading to an analogue input. Depending which jumper you short, you get different readings.
But I still don't get it. The ph changes with temperature. It's not that you get false readings - the actual ph changes, right? So who cares what temperature the water is? You need to adjust ph regardless.
thanks again, maybe i am missing something but the ph meter will be calibrated at one temp and them reading a solution at another temp. it is my understanding that the ph meter floats based on temp, not the fluid. so a fluid at 20 deg and at 35 deg has the same ph but the meter sees it differently. commerical ph meters quite oftem have a temp comp built in but only work well if both the solution and the meter have time to soak at the ambient temp. the ph board i have has a temp reading on its board, i cant put it in the water.
on the resistors, are you implying that they maintain a given resistance over temp.
I am not going to have a method in the project to measure temperature.
You can add a temperature sensor for about $2 USD. Take a look at [u]this[/u] and [u]this[/u].
The LM35 puts-out a voltage proportional to Centigrade and the LM34 puts-out a voltage proportional to Fahrenheit. But, since the Arduino can do math you can use either one.
the sensor that are listed do not look like they can get wet. i was hoping to just break into the piping once for the ph probe. can the arduino read a thermocouple or thermistor?
