Hi everyone,
I would like know if it is possible to control the tank level by controlling two flow inlets (two control valves) and how to implement the control.

Thanks a lot

e-mail: [email protected]

 

There are many ways to implement such a control, depending on what you are trying to do. If the two inlet valves are of different size, then you can use that to your advantage by opening both valves when the tank level is far from its desired level, and then closing the larger inlet as the tank level gets closer to the desired level. I assume you have a continuous level sensor?

Robert Scott
Real-Time Specialties

 

If you try to do this then you get a PID with a variable open loop gain depending on which valves are open. Tuning this becomes a problem.

What do you want to do? Assuming both inlet flows are controlled by a variable valve...

1. As suggested by Robert you can use one valve as a booster when you are far from setpoint. You will need variable control tuning to get this to work properly.

2. You can use a split range control to open one valve then the other. You will need variable control tuning if the valves are of different sizes.

3. You can open both valves by the same percentage. You won't need to change the control tuning.

My 2c.

Rob
www[.]lymac.co.nz

 

You could send the output of you level controller to both valves so they operate together or if one stream is more important have one valve operating on 0-50% of the signal and the other 50-100% "split range". This is quite common, for example the first valve to open would supply recycle water while the second would supply fresh water.

If you give a few more details we can help further.

Roy