Variable-Length Distinguishing Sequences and Their Application to the Design of Fault-Detection Experiments

Abstract—A variable-length distinguishing sequence (VLDS) is a preset distinguishing sequence X0 such that, if the machine is started in an unknown state, the output response of the machine to some prefix of X0 will identify the initial state. The length of the required prefix is a function of the initial state. The properties of such sequences are investigated and a method which employs a modified version of the diagnosing tree is developed for generating and displaying all such sequences. The fixed-length distinguishing sequence (FLDS) is shown to be a special case of the more general VLDS. The VLDS is next applied in the design of simple and efficient preset fault-detection experiments for sequential machines.