Embedded Systems October 2000 Vol13_11

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TIM WESCOTT PID Without a PhD PID (proportional, integral, derivative) control is not as complicated as it sounds. Follow these simple implementation steps for quick results. solved with imple conu-ollers, without resorting L t wOl-k, I am one of three designated "servo guys," and the only one who implemenlS control loops in software. As a result, I often have occasion to design digital control loops for various projects. I have found that while Lhere certainly are conu-oJ problems th at require all the expertise J can bring to bear, a great number of conu-ol problems can be O any conU-ol theOl), at all. This article will tell you how to implement and tune a sim ple controller without getting into heavy mathematics and withoUL requil-ing you to learn any conu-ol th eo I u-ue method that can be applied to almost any control problem with success. PID control The PID controller has been in use for over a centlll)' in various forms. It has enjoyed popularity as a purely mechanical devi ce, as a pneumatic device, and as an elecu-onic device. The digital PID controlle r using a microprocessor has I -ecently come into its own in indusu)'. As you will see, it is a straightforward task to embed a PID conu-oller in to your code. PID stands for "proportional, integral, derivative." These three tel-ms describe the basic elements of a PID controller. Each of these elements per- fornls a different task and has a different effect on the functioning ofa system. In a typical PID controller these elements are driven by a combinatio n of the system command and tile feedback signal from the object th at is being controlled (usually referred to as the "pla nt"). Their outputs are added together to form the system output. )'. The technique used to tune the controller is a uied and

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