ORP (Oxidation Reduction Potential) analyzers are also common but a bit more complex, but it is all about the chemistry of your scrubber process.
A lot of it has to do with the incoming gas composition and the amount of makeup (water in some cases) needed to keep the concentration of the under control.
Not sure but I think the conductivity will go up with increased solids while the pH may stay the same, but you want to keep the pH stable to prevent corrosion.
Depend on what you are scrubbing out of course.
What I know of is the scrubber is using sodium hydroxides to pump into the water tank, and it is used to scrubber acid air. The thing I am I am not sure is the relationship of having the ph and conductivity monitoring devices.
Do you have a P&ID (Process and Instrument Drawing)? That should show what the instruments are there for. The signals may go to a controller, just an indicator, or something else. The drawing will also show if there are any alarms, etc. Sometimes the loop drawing will give a clue also.
They must have been put there by the process engineer for something.
You add caustic to keep the pH within a certain range of neutral,
pH =7 +/-
Acid gas (H2SO4, H2SO3, etc.) can cause corrosion problems in the piping, valves, and pumps. The allowable pH range is set by the materials of construction, the service temperature, and impurities.
Typically the scrubber will use the proper materials with continual makeup water with pH monitoring in the pump recycle, with a separate neutralization process for more complete treatment. The flow to neutralization is typically under level control of the scrubber level.
It is a process system.
if you are dealing with acid gas with caustic added to the scrubber liquid, the pH tells you if too much caustic or not enough and may be useful for online monitor/control.
The conductivity tells you the ion content only, but not the acid level.
For example you can look most scrubbers might look at conductivity to control make up water, with neutralization of the scrubber bottoms in a separate waste water treatment process consisting of several gas blanketed vessels/tanks.
Acid gas contains H2S so you need to fully understand your process before changing your design. It is not a gas you can afford to make a mistake with.