[Luyben] Process Mod.. - Student subdomain for University of Bath

12 PROCESS MODELING, SIMULATION, AND CONTROL FOR CHEMICAL ENGINEERS
No degree of sophistication in the control system (be it adaptive control,
Kalman filters, expert systems, etc.) will work if you do not know how your
process works. Many people have tried to use complex controllers to overcome
ignorance about the process fundamentals, and they have failed! Learn how the
process works before you start designing its control system.
1.6.2 Languages of Process Control
As you will see, several different approaches are used in this book to analyze the
dynamics of systems. Direct solution of the differential equations to give functions
of time is a “time domain” technique. Use of Laplace transforms to characterize
the dynamics of systems is a “Laplace domain” technique. Frequency
response methods provide another approach to the problem.
All of these methods are useful because each has its advantages and disadvantages.
They yield exactly the same results when applied to the same
problem. These various approaches are similar to the use of different languages
by people around the world. A table in English is described by the word
“TABLE.” In Russian a table is described by the word “CTOJI.” In Chinese a
table is “ $ 5.” In German it is “der Tisch.” But in any language a table is still
a table.
In the study of process dynamics and control we will use several languages.
English = time domain (differential equations, yielding exponential time
function solutions)
Russian = Laplace domain (transfer functions)
Chinese = frequency domain (frequency response Bode and Nyquist plots)
Greek = state variables (matrix methods applies to differential equations)
German = z domain (sampled-data systems)
You will find the languages are not difficult to learn because the vocabulary that
is required is quite small. Only 8 to 10 “words” must be learned in each language.
Thus it is fairly easy to translate back and forth between the languages.
We will use “English” to solve some simple problems. But we will find that
more complex problems are easier to understand and solve using “Russian.” AS
problems get even more complex and realistic, the use of “Chinese” is required.
So we study in this book a number of very useful and practical process control
languages.
I have chosen the five languages listed above simply because I have had
some exposure to all of them over the years. Let me assure you that no political
or nationalistic motives are involved. If you would prefer French, Spanish,
Italian, Japanese, and Swahili, please feel free to make the appropriate substitutions!
My purpose in using the language metaphor is to try to break some of the
psychological barriers that students have to such things as Laplace transforms
and frequency response. It is a pedagogical gimmick that I have used for over
two decades and have found it to be very effective with students.