The controller’s response characteristics are determined by the PID constants provided to the controller. Conversely if control is not aggressive enough (over-damped), the system may require too much time to recover-or not recover at all. If the controller is too aggressive (under-damped), it may cause the process to become unstable and oscillate, preventing repeatability. However, each time an error is calculated, the controller must decide how much to alter the process. If an error exists, the controller adjusts its output to alter the process to bring it closer to the desired point, thus minimizing the error. The PID controller measures the process output and calculates the difference (error) between what is measured and the set point. While these controllers can be built using analog circuits, implementing them using a digital controller provides greater flexibility in adjusting the control algorithm and in fine-tuning the controller settings. The purpose of a controller is to compensate for the effects of disturbances on process variables and to force a process variable to track a desired set point.
Industrial controllers utilizing this technique are used for controlling processes like those found in chemical plants, those for temperature control, for certain automotive applications, etc. One of the most common automatic control methods used in industry is the Proportional-plus-Integral-and-Derivative (PID) controller. The architecture of data acquisition and control systems which have their own DSP processors makes them well-suited for use in PID applications.
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