HI 

Even when we set the Process value and Set point equal, the output of the PI controller does not become zero. How can we make the output zero when the two quantities are equal and I also give enough time to the integral part? What is the point that I am not considering?

AND

Is it correct that the controller only operates in one direction, meaning if the PV is behind the SP, it works, but if the SP is less than the PV, the controller no longer works? If so, what is the solution to enable control in both directions?

 thanks Ixo65

What about the first question?

AND

Could you modify my example to work in both directions?

ixo65

The PI controller of the LOGO! can control in one direction. But the direction can be selected.
The PI controller therefore regulates upwards or downwards, depending on the preselection.

If you want to regulate both upwards and downwards with a PI controller, you need 2 PI controllers, one regulating upwards and one regulating downwards.

Dear Ixo65,

Not at all; it's a different question. I would like to understand why the output of the PI controller doesn't become zero, even when the PV and SP are equal.

P.s.

I completely understand your response that the PI controller is not suitable for digital output.

ixo65

I think you are still interested in this topic.

Pi controller

MSDHJP

The ship's rudder angle control includes

-two solenoid valves (on/off) as outputs

-and a 4-20mA feedback signal as input

- and an analouge 0-10 V as disiered location that selected by captain.

.

Each solenoid, when activated, turns the angle in one direction (right or left).by oppening hydrolic valve.

Is a PI controller useful for this system, as we know,  in the system output is 24V digital signal to  on  solenoid valve.

If yes, how can we convert its analog output to digital in program?

In my opinion, PI control is the wrong approach if you ultimately want to control simple valves.
For this reason, I am withdrawing from the topic.