DIY Continuous pH probe

pH probes can be very maintenance-intensive. If you really need a pH measurement system that does not require a lot of maintenance, you could try building your own auto-clean system where the probe is routinely pressure-washed with water spray to help keep it clean. Use a PLC to time the cleaning cycles, and of course "freeze" the pH measurement value while it's being cleaned so that the control system does not take action while the probe is hit with water. You will still need to calibrate the probe on a routine basis against standard buffer solutions, so I'm not sure just how much this approach would help.

Conductivity measurement is not a substitute for pH measurement because pH probes are ion-selective (H+) while conductivity is not. I've heard of some specialized applications where conductivity can be used in lieu of pH, but that is only in really strong solutions where H+ ion activity dominates above all other ion species.

Like the idea of auto calibration system - without removing the probe, easy as well would need a few Sol valves and all ingredants stored in different bottle. could work out well.

From your previous pH thread,
>Another way is to have some indicator that is 'adsorbed' on to a surface which will react to the material and later is to be washed. This thing has already worked so thats well. But the accuracy is questionable unless i use a colorimeter or a spectrometer to measure it..

That sounds a lot like liquid chromatography.

The axial path around porous wood spools in a probe loaded with a large volume of potassium chloride seems to be big in the industrial world, it takes longer to pollute a probe of this design than conventional designs.

What are you doing that does not justify purchasing commercial instruments?

Thanks for your replies,

@ Tony...

I was wondering... if i know the concentration of a salt solution... knowing the dissociation constants of all the ionic species... is it not possible to figure out the contribution due to H+ ions just by some sort of ratio? (I understand this is a very special and simplistic case).

@Iris

Yes, these is some colorimetry involved in the previous measurement. The pH sensitive balls were like a hybrid of liquid chromatography and ion exchange (column). Like i said, it worked then, but i cannot keep replacing them on saturation now. If a wash could be performed without taking the probe out of the immersion then, that would be interesting.

Also, i like your idea about the pH probe.Will check that out.

Purchasing commercial instruments tends to cut down on the time i get to think about a given problem, is too expensive and is rarely precisely what i need. So, though purchasing may be the final step in many endeavors, for the time being I prefer brainstorming. In the last few years it has lead to new designs using standard parts that turn out working better than expected.

Cheers!

I remember Honeywell having a solid state pH probe that can be an alternative to glass based, maintenance intensive pH electrodes.

If I am correct, the same could also survive insitu cleaning even at elevated temperatures as is the case in pharma industries.

Please however check honeywell catalogues.

Also, a simple cyclic timer ciruit that cuts in at regular intervals triggering a solenoid valve with a nozzle directed at the target should be no big deal for cleaning the set up. However, as said ealier, holding the pH value constant helps in avoiding errors by the control system.

Litmus paper and a colour CCTV should do the trick.