File Name: self regulating and non self regulating control system .zip
A self regulating control is a system that compares a measured value of a process with a desired set value called set point and processes the resulting error signal to change some input to the process, in such a way that the process stays at its set point despite disturbances. Only 1 degree Celsius deviation from the body core temperature set point will make a difference between being healthy or suffering hypothermia or fever and hyperthermia. So what a great self regulating control system we have in our body!
The two most common categories of process responses in industrial manufacturing processes are self-regulating and integrating. A self-regulating process response to a step input change is characterized by a change of the process variable, which moves to and stabilizes or self-regulates at a new value. An integrating process response to a step input change is characterized by a change in the slope of the process variable. From the standpoint of a proportional, integral, derivative PID process controller, the output of the PID controller is an input to the process. Figure 1 compares the response of the process variable to a step change of the PID controller output for a self-regulating process and for an integrating response.
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In other words, a self-regulating process will exhibit a unique process variable value for each possible output valve value. A corollary to the principle of self-regulation is that a unique output value will be required to achieve a new process variable value. This presents a fundamental problem for a proportional-only controller. This increase in process variable drives the error back toward zero, which in turn causes the controller to decrease its output value back toward where it was before the setpoint change. Even if the gain is not great enough to cause sustained oscillations, excessive values of gain will still cause problems by causing the process variable to oscillate with decreasing amplitude for a period of time following a sudden change in either setpoint or load. Just how much integral action a self-regulating process can tolerate depends on the magnitudes of any time lags in the system.
The case studies on this site largely focus on the control of self regulating processes. The principal characteristic that makes a process self regulating is that it naturally seeks a steady state operating level if the controller output and disturbance variables are held constant for a sufficient period of time. Cruise control of a car is a self regulating process. If we keep the fuel flow to the engine constant while traveling on flat ground on a windless day, the car will settle out at some constant speed. If we increase the fuel flow rate a fixed amount, the car will accelerate and then steady out at a different constant speed. The heat exchanger process that has been studied on this site is self regulating. If the exchanger cooling rate and disturbance flow rate are held constant at fixed values, the exit temperature will steady at a constant value.
Unless you adequately understand the nature of the process you intend to control, you will have little hope in actually controlling it well. This section of the book is dedicated to an investigation of different process characteristics and how to identify each. Quantitative PID tuning methods see section The goal of this section is for you to understand various process types by observation and qualitative analysis so you may comprehend why different tuning parameters are necessary for each type, rather than mindlessly following a step-by-step PID tuning procedure.
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In almost all industrial process applications, control of process variables is critical to the safe and efficient operation of the process.