Saturday, August 27, 2011

Tutorial of PID Control Theory





The P stand for proportional control, I stand for integral control and D stand for derivative control. This is called a 3 controller term. The essential function of a controller is to perform an algorithm according to the input of control engineer the operators wished operating value and the present value of plant process. The necessity for the controller to proceed so that the value of process is as near to the set point as possible in the majority cases. The engineer of control utilizes the algorithms of PID to realize this in the fundamental process control loop.

The algorithm of PID control is utilized for the control of nearly all loops in the industrial process, and is the source for a lot of control advanced strategies and algorithms. The PID loop has to be properly tuned in order for loops of control to work properly. Standard ways for correction loops and criteria for the loop tuning judging have been applied for many years, but should be re-evaluated for use on systems of modern digital control.

How a PID Controller Operates
The controller job of PID is to keep up the output at a stage so that there is no error between the PV (process variable) and the SP (set point). The valve could be running the gas going to a heater, the pressure in a pipe, the cooler chilling, the flow via a pipe, the level in a tank, or other system of process control. What the controller of PID is looking at is the "error" the SP between and the PV. It seems at the rate of change of error and the absolute error. The rate of change of error means the difference between the SP or PV acquiring larger or smaller as time goes on. Absolute error means there is a large difference in the SP and PV or a slightly difference?

When the SP or PV quickly changes, the controller of PID has to rapidly modify the output to find the process variable back identical to the set point. If you have a running cooler with a controller of PID and someone opens the door and walks in, the temperature (PV) could increase very fast. Thus the controller of PID must raise the cooling or output to recompense for this increase in temperature. Once the controller of PID has the PV equivalent to SP, a good controller of PID will not diverge the output. You desire the output to be very stable. If the valve is continually varying, this could case more put on the element of control.



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