Interval Time for Reconfiguration after Sensor Loss

This article deals with remaining time before non-estimability (RTBNE) after sensor fault occurrence in view of fault tolerant estimation. When faults occur in the measurement devices, the system reconfiguration uses only healthy sensors. In some cases, with these remaining sensors, the state or the functional of the state to estimate becomes unobservable and therefore unestimable. Because of unobservability of the state, unknown behaviour can occur. So after sensor fault occurrence, it could be interesting to reconfigure the system before the loss of estimability of the state. Thus, the new concept of RTBNE, based on pseudo-observability indexes, corresponds to the remaining time the system is still estimable after sensor fault occurrence. Thus, in order to avoid unknown behaviour, in case of fault occurrence, the reconfiguration should last less than this RTBNE. This new concept can be handled either for linear or nonlinear system; to simplify, this will be presented for linear system and applied to a simple example