A sequential failure detection technique and its application

An integral element of a highly reliable, fault-tolerant system is an efficient failure detection and isolation (FDI) technique. This short paper presents an FDI system whose design criterion is the minimization of the mean time to detect system failures subject to constraints on false-and miss-alarm error probabilities. The cost of missed failure is measured by system performance degradation, while the loss of unfailed components due to false alarm is unacceptable for practical levels of redundancy. An on-line recursive FDI technique is developed through an application of sequential analysis and information feedback. The feedback control is derived by utilization of a monotonicity property of the performance. The analytical performance in terms of mean detection and isolation time is presented. This sequential FDI technique is applied to the problem of second sensor failure isolation to provide fall operational-fail safe capability to the space shuttle's redundant inertial reference units.