Automates Fault Analysis for Hydraulic Systems: Part 1 - Fundamentals

This paper is the first of two parts and describes the fundamental research into software techniques for automating fault analysis in hydraulic circuits. Part 2 (see Hogan et al. (1)) provides a detailed description of some important aspects of the software development and the applications and experimental procedures used to test its effectiveness. The objective of the project is the development of a software toolkit, DESHC (Diagnostic Expert System for Hydraulic Circuits), which can be used to automate the two techniques used in an assessment of the integrity of a hydraulic system, Failure Mode and Effects Analysis (FMEA) and Fault Tree Analysis (FTA). The purpose of an integrity assessment is to highlight potential problem areas in a system so that they can be dealt with at the design stage. The toolkit has been used to build model-based expert systems for the analysis of faults in a number of hydraulic circuits. It consists of a library of re-usable objects representing hydraulic, mechanical and electrical components which can be called and linked together at run-time to represent the particular circuit under analysis. This approach obviates the need to re-write the expert system for each new circuit under consideration. A robust expert system for analysing faults in engineering systems should use both heuristic knowledge (empirically derived shallow knowledge) and knowledge of the structure and behaviour of the system (deep knowledge). The second section of this paper examines the advantages and disadvantages of these different types of knowledge. This is followed in the third section by a description of the use of deep knowledge alone to model the components of hydraulic circuits as software objects. The fourth section provides an outline of software development an..