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A block diagram of a PID controller in a feedback loop. r(t) is the desired process variable (PV) or setpoint (SP), and y(t) is the measured PV. The distinguishing feature of the PID controller is the ability to use the three control terms of proportional, integral and derivative influence on the controller output to apply accurate and optimal ...
The Ziegler–Nichols tuning method is a heuristic method of tuning a PID controller.It was developed by John G. Ziegler and Nathaniel B. Nichols.It is performed by setting the I (integral) and D (derivative) gains to zero.
An everyday example is the cruise control on a road vehicle; where external influences such as gradients cause speed changes (PV), and the driver also alters the desired set speed (SP). The automatic control algorithm restores the actual speed to the desired speed in the optimum way, without delay or overshoot, by altering the power output of ...
Within modern distributed control systems and programmable logic controllers, it is much easier to prevent integral windup by either limiting the controller output, limiting the integral to produce feasible output, [5] or by using external reset feedback, which is a means of feeding back the selected output to the integral circuit of all ...
Several different control strategies have been devised in the past years. These vary from extremely general ones (PID controller), to others devoted to very particular classes of systems (especially robotics or aircraft cruise control). A control problem can have several specifications. Stability, of course, is always present.
A typical application is a PID controller fed by a flow meter and using a control valve as the final control element. The DCS sends the setpoint required by the process to the controller which instructs a valve to operate so that the process reaches and stays at the desired setpoint. (see 4–20 mA schematic for example).
and the normal methods for PID controller tuning can be applied. In this way the complicated nonlinear control problem has been reduced to a relatively simple linear control problem. References
The Smith predictor (invented by O. J. M. Smith in 1957) is a type of predictive controller designed to control systems with a significant feedback time delay. The idea can be illustrated as follows. The idea can be illustrated as follows.