Extended event signatures for fault diagnosis using ladder logic

The lack of effective run-time diagnostics is a major irritant in the discrete manufacturing industry. This is partly attributed to the ubiquitous ladder logic diagrams (LLD) used to process the factory information for control and diagnostics. In this paper, we examine the efficacy of LLDs to produce useful diagnostics. For this, we have followed and extended the event signature (ES) method proposed by Chand (1992). Our study shows we can extract useful diagnostic knowledge from the control logic in the form of LLD and this refines the diagnosis related to input sensors in the factory. Predefining suitable run-time experiments for anticipated faults helps in further localizing the fault.