Hi all the experts here, I have a project with me now, it is a PID controller for X-Y positioning table.

I have tried to read the relevant DIY project set (PR24) in your site, I am able to understand the concept and idea of the project, but for the source codes I still need to go deep into it before fully understand them.

I have some questions regarding to PID controller...is it all PID controller have similar algorithmic with the one in the codes ( Integral = Integral + Error; Derivative = Current error - Previous error).

Apart from this, what is the typical way to implement PID controller? Is it make it controlable from the external world (like what you all did in the project), or get the precise value of P, I, D and set the value fixed in the codes??

Another question here, from what I learned in control system, I know that a system require mathematical modeling in order to obtain its relevant transfer function. In a typical closed-loop block diagram, a controller is needed before the plant transfer function, and PID controller is acted as a compensator for the controller in order to fully meet the system specification.

But I am quite confused if I relate the theoretical part with practical application...In real time application, how are we going to obtain the system mathematical model and transfer function, what is the use of this transfer function after obtaining it, is it used for simulation??

Hope to hear from you all soon...

Thanks a lot...best regards.