PID control of motor drive considering the diameter and an external Potentiometer

Hai friends

I want to write a PLC program to control an wire extruder based on PID algorithm. I have a PLC with PID in it. I have configured the PID. I took the diameter as PV. The CV is taken out through an analog output and is from 0 to 10V. In industry at first operator will set the line speed through a 0 to 10V potentiometer by connecting it to drive (considering the required diameter). Then they shift to PID control. For example at first for 6v the motor rpm will be 600. Then they shift to PID. PID should monitor the variation in diameter according to set diameter and should control the voltage from potentiometer. Again they want to increase the production speed they will raise the potentiometer value ,for example to 8V then motor speed will be 800rpm then they will shift to PID. Before using PLC they use a standalone PID controller. How can we use PID in PLC by considering the potentiometer input????? How will be the connection??? What will be the SETPOINT either potentiometer input or set diameter??? I am in a great confusion Please help me!!!!!!!!!!!

I am a beginner!!!!!!!!!!!

When running in PID mode, you cannot have both a speed input command and a PID setpoint in control.

Either the motor must be free to vary its speed to keep the error between the setpoint and the process variable at a minimum or, the speed input defines the motor speed and there is no PID control.

Thanks DICKDV

But without considering potentiometer output we can't control the line speed. For example the operator set the potientiometer for a particular diameter and will shift to PID , the output of PID should be that of potentiometer otherwise the whole wire will get wasted because the line speed is 100m/sec. I think the potientiometer input should be added or subtracted with a factor and it should be defined by PID according to set diameter. Can anyone help me on this????