Vacuum pump control via S7-300

Our customer did a project that vacuum pump controlling via S7-300.Setpoint entry on Operator panel,S7-300 make Pid conrol ( SFB41 CONT_C used )Analog output module giving 0-10 V to ABB inverter,and this inverter driving a vacuum pump.Setpoint value always minus number due to vacuum.I want to learn ;Pid value (Kp)gain must be minus or not?Which parameters must use like this applications for sensitive,that is P,I,D?Have any experience?Thanks in advance...

pumps

Lot's of experts here on PLCS who can help you more then me.
But, when I have such an application, then I use the PID CONROL PARAMETER ASSIGNMENT tool from Simatic. I never use the D. Do I use PI regulation. I start with I = 0 and KP (P) 1, then I look how it responds, you can increase or decrease untill you see regulation. Then you can add I time to make it more stable.

tulip said:

Our customer did a project that vacuum pump controlling via S7-300.Setpoint entry on Operator panel,S7-300 make Pid conrol ( SFB41 CONT_C used )Analog output module giving 0-10 V to ABB inverter,and this inverter driving a vacuum pump.Setpoint value always minus number due to vacuum.I want to learn ;Pid value (Kp)gain must be minus or not?Which parameters must use like this applications for sensitive,that is P,I,D?Have any experience?Thanks in advance...

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Instead of using a setpoint value of -x the programmer could multiply the gain by -1 just before passing it to the FB41. It's just a different way of doing the same thing. Positive gain to the FB41 makes the loop go one way, negative gain makes it go the other way. I prefer to handle this inside the PLC program and use positive numbers for setpoints, but there are as many ways to program as there are programmers.

There are applications where you need D, do a search here for discussions. All of my applications have been PI.