Estimator schemes for instrument fault detection and isolation: structure, function and application limits

This paper deals with output-estimator based structures to solve the robust-fault-detection-and-isolation problem (RFDIP). These estimator schemes use analytical redundancy to generate and evaluate residuals. The residuals have to be robust against internal inaccuracies and decoupled from external disturbances (unknown inputs) to allow a unique detection of malfunction and isolation of a faulty actuator, component or sensor. For the case of instrument fault detection and isolation, seven groups of estimator schemes are described and analysed regarding their structure, function and application limits. The analysis is a basis for the proposed method that allows one to compare the schemes and to select the most convenient scheme for solving the RFDIP. Design procedures for residual generators and evaluators have not been considered in this analysis. The results are presented in a table and the application of this table is exemplified