Complex digital control systems

Guthikonda V. Rayo, Van Nostrand Reinhold (1979), 516 pp, £2Z40 This massive book, over 500 pages of A4 format, deals with its subject in three main topics. The first is control systems, theory, the second is the application of the control theory to a complex digital control system, and the third is computer-controlled digital control systems.

The complex digital control system used as a design example concerns the design of the interacting digital control systems of a Quadruplex Colour Videotape Recorder (Q-CVTR). The design example treats the design of the sampled data feedback control systems for the headwheel, capstan and vacuum guide in a tutorial manner. Emphasis is placed on the derivation of simplified mathematical models which can be realised in electronic circuit design. In particular the application of a 'measure and optimize' technique is described. This is a heuristic tech- nique where measured variables are used to optimize designated parameters to meet the requirements of an engineer- ing specification.

The stated intention of the book

is to be a tutorial text for the under- graduate, graduate and practical electrical engineer. Some knowledge of Laplace and Z transforms is assumed.

The primary concern is the corre- lation of theory and technology in the implementation of modern control systems, and to expose the student to the reality of the elaborate circuit design involved in realising the imple- mentation. It is in this last aspect that the book falls short of its intentions. The design example, while dealing well with the derivation of the mathe- matical algorithms, including good sections on data sampling and digital filtering, stops short at a block diagram of the system.

However it is in the large section, more than a quarter of the book, devoted to microcomputer controlled digital control systems, that the book fails to the greatest extent to meet its stated intentions. Despite the apparent importance given to this subject, as illustrated by the length of the section, the important topics of transducer input and actuator output interfacing, software design, and implementation of real-time control algorithms in soft-

ware are treated superficially. The importance of designing soft-

ware, either by flowchart or pseudo code, is neglected and program flow- charting is dealt with in less than one page with one simple example. The problems of using high level languages (I-ILL) for the porduction of real-time control algorithms, particularly with regard to run time, are not discussed. The advantages of HLL are stated reasonably correctly but no disadvant- ages are given. Moreover the availability of HLL compilers in a microprocessor environment requires some qualification. A HLL compiler operates only with the operating system for which it has been designed.

The book is well produced and illustrated, with many block dia- grams. The contents summary, biblio- graphy and index are satisfactory.

Although much general information may be derived from this book it is essentially for the specialist, especially designers of tape transports. The micro- computer engineer requiring access to control systems theory will gain more from this book than the control engineer requiring information on the application of microcomputers in digital control systems.

Joe Gallacher, Praxis Instruments B V

vo/ 417o 6/u/y/august 1980 227