Automatic Control of pH

There is equpment out there that will do this, it tends to be rather expensive for a fully automated system. The measuring cell may need to be custom designed, it depends on the volume of water, flow rates and such like.

A search should bring up a few companies... probably easiest to get a rep' in to go through the requiremnet and details.

The company I work for in the UK does a system for swimming pools where the readings are entered manually (they have to be taken anyway as a legal requirement) the system then doses appropriately to achieve the target ph.

Any automated system will still need manual checks as the measurement cells can be wildly off.

Del

So the following will be needed:

• A pH transmitter
• Somewhere to mount it
• A pH electrode
• Somewhere to mount it
• A cable connecting the transmitter to a controller
• Somewhere to support it
• A 3-term controller
• Somewhere to support it
• Some power for it
• A low-voltage power supply for the transmitter
• Some terminals and interconnecting wires
• Something to protect them
• A dosing set
• Somewhere to put it
• Some chemicals to put in it
• Some calculations to determine the optimum dosing rate
• A tank for the chemicals to give the optimum refill time determined by local conditions
• An injection point upstream of the pH electrode
• A static mixer, perhaps, depending on whether there is any other mixing equipment downstream of the dosing point or not
• Some pipe to connect the dosing unit to the injection point
• Some power for the dosing pump
• A cable for the dosing pump
• Somewhere to support it
• Some commissioning time
• Some experience of tuning three-term controllers that can be used during the commissioning time.

<....automatically modify the pH set-point based on other measurrments in the process...>

These will determine what else is needed to the above list.

Dear friend

pH is a highly non linear variable. You need to something like a DCS type system along with a good strategy for control. PID type control alone will not do.

Best you can do is manually control

Regards

Manmeet

A DCS is desirable but would be an exergeration in this particular application.A pH sensor in a suitable holder and a transmitter,loop powered or other wise with 3 a term stand alone controller coupled with,yes hands on experience tuning the PID in a process plant should do the trick.

Usually the wwtp consists of several unit processes in series. The pH may not be constant across each unit operation as you move along the train.

jb

The minimum set-up you'll need are a 4-20mA pH sensor & transmitter, 2 storage tanks for the pH adjustment chemicals (1 acid, 1 alkali), 2 dosing pumps (1 for each chemical), a mixing tank, a mixer, and a control panel. If you're not one, talk to a water engineer about this. He'll be able to advise you on your requirements based upon your plant wastewater output & production process.

If I understood you well:

You are measuring the treated water PH, and the output is 4-20 mA. at the same time you need to change the PH preset point according to your 4-20mA, while measuring the resulted PH as well. That means you have two variables?. If this is the case you will need more than just a PH controller, It will have to use a simple programmable PLC or a PC combined with two controllers.I am sure, that this is not a complicated matter, although maybe a bit more complicated to implement due to other factors as your total Q, and PH tolerance. If your set point is 7.0 than you will also need 2 separate injection ports etc.

I maybe wrong in my assumptions though...

Wangito.

OP stated that his application was wastewater, not water. He did not describe the process at all beyond that. In some areas groundwater is considered hard and needs to be softened before it can be used. The pH needs to be lowered and alkalinity removed. OTOH, soft water lacks such minerals and often it is necessary to add chemicals to raise the pH.

But again, OP gave no clue as to process.

Talk with you local Honeywell process solutions distributer. They have the equipment and expertise necessary.

SIR CAN YOU EXPLAINE ME HOW YOU CONTROL PH

THANKS