TABLE OF CONTENTS E. H. Bristol
Research Department, The Foxboro Company
(a Siebe Company), Foxboro, Massachusetts.
(Basic Control Algorithms)
G. A. Hall, Jr.
Westinghouse Electric Corporation, Pittsburgh, Pennsylvania.
(Control Principles prior edition)
Peter D. Hansen
Systems Development and Engineering, The Foxboro Company
(a Siebe Company), Foxboro, Massachusetts. (Techniques for
Process Control)
Stephen P. Higgins, Jr.
Retired Senior Principal Software Engineer, Honeywell Inc.,
Phoenix, Arizona. (Techniques for Process Control prior edition)
Richard H. Kennedy
The Foxboro Company (a Siebe Company), Foxboro,
Massachusetts. (Techniques for Process Control prior edition)
E. C. Magison
Ambler, Pennsylvania. (Safety in Instrumentation and
Control Systems)
Joe M. Nelson
Applications Systems, Honeywell Inc., Billerica, Massachusetts.
(Techniques for Process Control prior edition)
Robert L. Osborne
Manager, Diagnostics and Control, Westinghouse Electric
Corporation, Orlando, Florida. (Techniques for Process Control
prior edition)
John Stevenson
West Instruments, East Greenwich, Rhode Island.
(Control Principles)
by John Stevenson [*]
In this article the commonly measured process variable temperature is used for the basis of discussion. The principles being discussed apply also to other process variables, although some may require additional sophisticated attention, as discussed in the subsequent article, which deals with techniques for process control.
In contrast with manual control, where an operator may periodically read the process temperature and adjust the heating or cooling input up or down in such a direction as to drive the temperature to its desired value, in automatic control, measurement and adjustment are made automatically on a continuous basis. Manual control may be used in noncritical applications, where major process upsets are unlikely...
