PID advanced function

dear plc-holic, i wish to hear from you about how do you use PID controller,
1. what is the purpose of that machine.
2. what is the advantage of the PID installed there.
3. how happy are you, after the machine run.
4. what makes you un-happy, if any..

iam happy to read all your reply post.

great regards,
reza

( cos i never used it )

A PID (Proportional Integral Derivative) controller is simply a device for process control. It compares a process variable like pressure to a setpoint or target pressure, and calculates the output to a control device like a valve required to keep the process variable at the target.

PID has the advantage of being widely available from hundreds of suppliers and almost all PLCs. It has been used for over 50 years.

It has the disadvantage of being difficult to tune, in all cases for a novice and in some cases for a professional.

It creates happiness when it is properly tuned and applied to a well behaved process with short lag times.

It creates dissatisfaction when improperly tuned, resulting in instability or poor control of the process. This often happens if there is a lot of lag time in the process or the control devices.

I've read many articles claiming that 25% to 50% of PID controls are actually operated in manual because the operators get better control than when the system is in manual.

Tom, do you think the 25 - 50% figures are due to the PID not being tuned correctly?

Up until recently I can honestly say that I would not have a clue how to tune a PID properly. The company has been paying a genuine expert in advanced control to come to site once a month and both train us in advanced control techniques and to improve some circuits of our plant.

I have learnt first order and integrator tuning process but I am lead to believe they are easy compared to the more difficult processes.