PLC-5/40 and a pH Probe

I have a PLC-5/40, and currently have a pH Probe that is reading to its own GLI controller. That controller opens and closes a relay that enables and disables a dosing pump for caustic. As you could imagine, I do not have very good control of the pH while this process is running. It is the solution in our scrubber as HF and H2 gases are exhausted from the retort, to the scrubber. The dosing pump tries to keep up and then, as the set point pH is reached, the dosing pump still will pump a few more times which then drives the pH up. It is a constant tug-of-war. I would like to get rid of the pH controller and have the PLC-5 control the dosing pump. I have a 1771-IFE for the analog input and a 1771-NOC/A for the analog outputs. Thank you.

If you decide to do away with the controller, keep in mind that you will have to decide how to scale the ph value based on the process temperature. Im sure there is a way, just something to be aware of before going into it.

we've been dealing with a similar situation in a water based cleaning machine that has an acid and alkali tank, with rinse tanks after each.

good luck.

dwoodlock said:

If you decide to do away with the controller, keep in mind that you will have to decide how to scale the ph value based on the process temperature.

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I know, that's why I wanted to throw it out here on the forum. So far I haven't had a situation that someone here hasn't already dealt with and succeeded.