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Unformatted text preview: Questions: PID control; Tuning techniques Copyright c 2002-2003 Tony R. Kuphaldt Learning Objectives: Explain the importance of understanding the process, and of verifying the proper function of instruments in a control loop, before proceeding to tune a controller. Identify practical means of analyzing a process control loop to determine if tuning is necessary. Identify the characteristics of the so-called stick-slip cycle in a control loop, and describe both its cause and its solution. Explain how to experimentally determine whether or not a process has a variable gain . Identify some of the practical concerns with perturbing a live process. Determine whether a process is self-regulating , or non-self-regulating (integrating) from inspection of the P&ID. Determine whether a process is self-regulating , or non-self-regulating (integrating) from inspection of process response to a step change in controller output. Contrast the relative stability of integrating versus non-integrating processes. Describe the difference between dead time and lag in a process. Define the phrase quarter-amplitude damping . Calculate P, I, and D constants for a controller using the Ziegler-Nichols closed loop (Ultimate) method. Calculate P, I, and D constants for a controller using the Ziegler-Nichols open loop method. Calculate P, I, and D constants for a controller using the Cohen-Coon open loop method. Introduction This worksheet is the fifth in a series teaching the so-called PID (Proportional-Integral-Derivative) control algorithm. Here, we investigate the art and science of tuning the P, I, and D constants of a PID controller for optimum process control quality. Understanding the principles of Proportional, Integral, and Derivative control modes allows the techni- cian to adjust these constants (called tuning a controller) for optimum performance. Optimum performance in a control system usually translates to increased profitability, decreased maintenance costs, increased safety, and decreased emissions in the system being controlled. Controller tuning is a widely misunderstood subject, to the detriment of process control quality worldwide. People with a solid understanding of PID control are rare, possessing a very valuable and sought-after skill set. It is well worth your time to become one of them. A serious fault of many PID tuning curricula and tutorials is the failure to teach how to identify when tuning is needed versus when tuning is not needed . It is just as dangerous to unnecessarily adjust the tuning constants of a PID controller as it is not to tune a controller requiring tuning. Many control problems are caused by faults in instruments, and/or mis-engineered loops, and cannot be rectified by tuning. Often, attempts to tune such a loop only serve to mask the real problem, and greater problems may later arise as a result. Here, you will learn theory and techniques helpful for avoiding such mistakes.as a result....
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This note was uploaded on 12/09/2011 for the course ECON 101 taught by Professor Azul during the Spring '11 term at NE Texas CC.
- Spring '11