I Preface are not communicated to the people who must apply them. Control problems arise in the plant and must be solved in the plant. Until plant engineers and control designers are able to communicate with each other, their mutual problems await solution. I do not mean to imply that abstract mathematics is not capable of solving control problems, but it is striking how often the same solution can be reached by using good common sense.
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I Preface are not communicated to the people who must apply them. Control problems arise in the plant and must be solved in the plant. Until plant engineers and control designers are able to communicate with each other, their mutual problems await solution. I do not mean to imply that abstract mathematics is not capable of solving control problems, but it is striking how often the same solution can be reached by using good common sense. High-order equations and high-speed computers can be manipulated to the point where common sense is dulled.
Some months ago I was asked to give a course on process control to a large group of engineers from various departments of The Foxboro Company. If the subject were presented through the traditional medium of operational calculus, the effort would be wasted, because too few of the students would have this prerequisite.
Rather than attempt to teach operational calculus, I chose to do without it altogether. It then became necessary to approach control problems solely in the time domain.
Once the transition was begun, I was surprised at the fresh point of view which evolved. Some situations which were clouded when expressed in frequency or in complex numbers were now easily resolved. Dead time, fundamental to any transport process, is naturally treated in the time domain. The value of this new approach was evident at once. In the very first session the student was able to understand why a control loop behaves the way it does: why it oscillates at a particular period, and what deter- mines its damping.
The subject was tangible and alive to many students for the first time. Interest ran high, and the course was an immediate success. The great demand for notes prompted the undertaking of this book. Through the years, I have observed many phenomena about control loops which have never been explained to my satisfaction. Why does a flow controller need such a wide proportional band, whereas a pressure controller does not?
Why is derivative less effective in a loop contain- ing dead time than in a multicapacity loop? Why are some chemical reactors impossible to control? What makes composition control SO difficult? Why cannot some oscillations be damped? These and many other observations are explained in this book and perhaps nowhere else. It is always very satisfying to learn the reasons behind the behavior of things which are familar, or to see accepted principles proven in a new and different way.
Therefore i expect that those who are accustomed to the more conventional approaches to control system design will find this treatment as interesting as those who are not familiar with any. In spite of the simplicity of this presentation, we are not kept from Preface I ix applying the most advanced concepts of automatic control. Feedfor- ward control has proven itself capable of a hundredfold improvement over what conventional methods of regulation can deliver. Recent developments in nonlinear control systems have pushed beyond tradi- tional barriers-achieving truly optimum performance.
These advances are not just speculation-they are paying out in increased throughput and recovered product. The need for economy will make it so. But the most brilliantly conceived control strategy, by itself, is noth- ing. By the same token, the most definitive mathematical representa- tion of the process, alone, is worthless.
The control system must be the embodiment of the process characteristics if it is to perform as intended. Without a process, there can be no control system. Anyone who designs controls without knowing what is to be controlled is fooling himself.
A pressure regulator cannot be used to control composition. Neither can a temperature controller on a fractionator perform the same function as one on a heater. For these reasons this entire text is written from the viewpoint of the needs of the process. Each type of physical- chemical operation which has a history of misbehavior is treated in- dividually.
Not every situation can be covered, because plants and specifications differ, and so do people. If for no other reason, this book will never be complete. But enough attention is given to basic prin- ciples and typical applications to permit extension to a broad area of problems. The plant engineer can take it from there.
In appreciation for their assistance in this endeavor, I wish to express my gratitude to Bill Vannah for providing the initiative, to Molly Dickinson, who did all the typing, and to John Louis for his thoughtful criticism. Although their impact on the process industries Greg Shinskey.
Process Control Systems
McMillan and Sigifredo Nino Oct 26, The teachings and writings of Greg Shinskey have had a profound effect on many process automation professionals, including these authors. Since that time, I have had the opportunity and pleasure of implementing many of his ideas throughout my successful career as process control engineer-turned-consultant. Thanks to my professional relationship with Shinskey, I have become closely familiar with his thinking, methods and creative process. His tutelage and experience continue to guide my work today, and this unique experience has given me huge insight into his approach, more so than any of his books and papers ever could have, no matter how many times I read them. Nonetheless, there is a wealth of priceless process control information in his prolific written production, which I recommend you tap into. If you tally that up, that is over half a century of invaluable contribution to process control and a confirmation of his profound interest, commitment and dedication to developing techniques and practical methods for real-life applications. Furthermore, true experts in process control are an endangered species.
McGraw Hill - Process Control Systems (Shinskey)
The real time values of these parameters will be fed to a central control system. These values are compared with the preset set-points through feedback systems and the necessary alerts are output on the display system, so that corrective action can be taken. It is then converted in digital form and picked by the processor. The cost-performance trade off is to be balanced to implement application-specific peripherals for achieving the desired core performance. Once the core is optimized for working with the desired peripherals, and speed, the rest of the system may be designed as per budget considerations.