Proportional and integral control of tank system


Thread Starter


Hi Everyone,

I have a question and perhaps many of you will find this very simple but to me its perplexing as I am new to control systems and the theories behind it.

My questions is if I have a simple tank system and am using proportional and integral controllers and step up the desired value 10% given my PB = 100% and time = 30 seconds how I can show these graphically for both open and closed loop controller outputs?

What are the formulas I need to graph the output?

If you could explain in detail (in layman's terms) how and what both closed loop and open loop outputs are doing over time given the step change of 10% with PB = 100 I would be very appreciative.
You can't graph the output knowing only the controller settings - you have to know the actual Process Gain, Time Constant and Deadtime as well.

Once the first output action has been made, all further output changes made by the PID controller are dependent entirely upon the actual response of the process.

If this isn't a university exam question, most of us cheat and use a tool something like this ..

In simple terms, you have a PI controller.

The P action reacts to the change in error since the last control action (in a digital system, the last PLC scan).

The I action reacts to the time that the error has been present in the system. The longer the error remains, the greater the total I action.

See here for more info ...