An expert system for diagnostic interpretation and relay ladder logic test generation for programmable logic controllers

System test of modern state of the art programmable logic control lers Is an effort which attempts to provide an absolute standard of product qual ity for an Increasingly complex product. Indeed product complexity has scaled classic control tasks of data acquisition and manipulation towards process control solutions. Control systems have reached a level of functional ity that couples with the dynamics of the industrial controls market to eliminate exhaustive testing as an economic quality assurance option.

This thesis project involves the knowledge engineering, design, development and analysis of an expert system which performs diagnostic interpretation and generates relay ladder logic (RLL) test programs for a programmable logic controller. The system captures principles of error resolution, test adequacy, and RLL program construction and utilizes them on any arbitrary PLC configuration for the Texas Instruments 560 product. The effort is singular in that it is architecturaly independent of target configurations and it offers an empirical measure of test adequacy, both of which are of vital importance with a product which cannot be exhaustively tested and which may contain configuration sensitive errors. Two versions of the system are in use at the Industrial Systems Division of Texas Instruments.