How control languages should be designed, with an integrated example design

Abstract

For 20 years, digital process control applications have been programmed and “configured” in a variety of general-purpose languages and special-purpose packages. During this time, some advances have been made, notably the concepts of application languages based on established diagrammatic documentation techniques, such as the block diagram or the ladder diagram. But these languages have been incomplete; much of the control application has required general-purpose languages not reflecting any particular application view and, therefore, requiring a lot of user reinvention. In all of this effort, no one in the computer or process control field has attempted to formalize a concept of language quality for human use. This paper presents a listing of the weaknesses of existing general-purpose and application languages, and outlines principles for overcoming these weaknesses. While the references develop previously shown techniques for demonstrating reduced human programming and analysis effort through use of specialized language features, the validation of an entire language, in these terms, is beyond the scope of this paper. Instead, we will show a videotape demonstrating the impact and range of an illustrative example control language, designed according to the discussed principles, through four quite different application examples: 1. 1. A Two-Loop Cascade Startup 2. 2. A Subsystem I/O Variables Definition 3. 3. A Major Plant Startup 4. 4. A Complex Multi-Unit Continuous Control System From these examples, the overall power and characteristics of the example language and the underlying techniques should be apparent.