S7-1200 PID slow startup

[grnick50]

Hello all,

I have set up a PID loop which works fine except it is a bit slow during the startup.
I wish that it would reach near the setpoint faster. What should I look into?

The PID controls the flow of a pump. I am happy after the startup, it is only the startup I want to improve.
It takes about 15sec to stabilize.
I noticed that if I make P larger and I smaller, then I get a faster response and big overshoot followed by a big undershoot. If I remove D then I get a huge oscillation until it stabilizes.

P=0.004
I=3.2
D=0.935

 

[Pete.S.]

Only run the loop when the pump is running.

You could do this for instance by setting the loop to manual mode as you stop the pump. Now the output signal (speed for the pump) is locked.

When you start the pump, you keep the PID in manual mode for a set period of time (until the pump has had a chance to build up the pressure) then you switch it over to automatic.

PS. For tips on tuning, do you have a graph that shows the pressure like the one above but together with the output of the PID?

I assume your pump is run by a VFD. Check so that you don't have any large ramp up/down times setup in the VFD.