Practical Process Control (eBook)

Practical Process Control (loop tuning and troubleshooting). This
book differs from others on the market in several respects. First,
the presentation is totally in the time domain (the word "LaPlace"
is nowhere to be found). The focus of the book is actually
troubleshooting, not tuning. If a controller is "tunable", the
tuning procedure will be straightforward and uneventful. But if a
loop is "untunable", difficulties will be experienced, usually
early in the tuning effort. The nature of any difficulty provides
valuable clues to what is rendering the loop "untunable". For
example, if reducing the controller gain leads to increased
oscillations, one should look for possible interaction with one or
more other loops. Tuning difficulties are always symptoms of other
problems; effective troubleshooting involves recognizing the clues,
identifying the root cause of the problem, and making
corrections.

Furthermore, most loops are rendered "untunable" due to some aspect
of the steady-state behavior of the process. Consequently, the book
focuses more on the relationship of process control to steady-state
process characteristics than to dynamic process characteristics.
One prerequisite to effective troubleshooting is to "demystify"
some of the characteristics of the PID control equations. One
unique aspect of this book is that it explains in the time domain
all aspects of the PID control equation (including as the
difference between the parallel and series forms of the PID, the
reset feedback form of the PID equation, reset windup protection,
etc.) The book stresses an appropriate P&I (process and
instrumentation) diagram as critical to successful tuning. If the
P&I is not right, tuning difficulties are inevitable.
Developing and analyzing P&I diagrams is a critical aspect of
troubleshooting.