My question is:

How many posts will you make for the same problem?

Dear user,

I understand this might be unrelated, but this is my first time here and I am facing commissioning deadline.

I am using CONT_C  in a function block. I call the FB in a Cyclic Program (OB32).  when the PID is in manual I can change the Block CV  by entering a manual value of 0-100%.  The problem is starts when I put the loop in Automatic.  It is a simple Flow control loop. As soon as I put the loop in Automatic, the loop becomes very unstable. Proportional gain is 0.1, Ti is 0 ms, PV_FAC=1.  Derivative is also 0.  SP=1100, PV (0-1800).

My Question:  Why is this loop become so unstable with such a very small gain?  Is this because my SP and PV can only be between (-100 to 100 %)?

 Ti=0 is the main cause of oscillation and the FB41 itself rectify that by putting Ti=cycle that is around 100ms as you selected.Please, start again with Ti=200s and decrease it step by step (150s -->100-->50) for a fast action.

I hope it helps,

hdhosseini

You can use FineTuning to obtain pid parameters.