Fault Simulation under the Multiple Observation Time Approach using Backward Implications

We present an improved procedure for fault simulation under the multiple observation time approach based on state expansion. Under state expansion, an incompletely specified state reached during fault simulation is replaced by 2 k states, each one assigning a different combination to k unspecified present state variables. For each expanded state, additional output values are then implied. As a result, a fault that cannot be identified as detected using conventional simulation may now be identified as detected. The procedure proposed here enhances state expansion by backward implications to take advantage of every present state variable value specified under state expansion. As a result of using backward implications, fewer states need to be considered after state expansion, fewer state expansions are potentially needed for every fault, and the number of faults that can be efficiently considered is increased. Experimental results are presented to support these claims. 1. Introduction..