An integrated approach to software design for programmable controller systems.

Programmable Logic Controllers (PLCs) belong to a class of industrial control devices that has come into existence only recently. PLCs are an important and widespread new technology in the American Industrial Complex. All electrical design engineers who are involved with industrial applications, will find knowledge of PLCs to be useful, and in many cases necessary, in the performance of their employment duties.

This thesis is a discussion of design methods used for producing quality PLC software. The information presented is based upon the author's several years experience in the design of PLC based industrial control systems. Practical examples are presented which illustrate how design procedures were applied in the case of a large industrial manufacturing process.

The designer of PLC software faces a challenging and interesting task. While borrowing many of the methods of the computer programmer, the designer must have a detailed knowledge of the process to be controlled and of the interface hardware. As a design methodology, three features are presented as being mandatory for quality software. These features are specification, simulation, and documentation.

While not intending to define a "cookbook" approach to PLC software design, a broad base of information is presented upon which the engineer can formulate design procedures appropriate to his work assignment. Successful completion of the engineer's project involvement requires that these procedures correctly address the importance of quality in PLC software design.