Maximizing Fault Detectability with Closed-Loop Control

This paper addresses the fault detectability problem for PCA-based process monitoring methods under closed-loop control. Unlike previous research assuming the same process variation for both modeling and monitoring periods, the impact of controller on data variation is considered. The effective fault direction is given in order to describe the effect of process variation on fault detection index under different controllers. The minimum variance along the effective fault direction is developed by introducing the concept of block-lower-triangular interactor matrix and conditional minimum variance control. The sufficient condition for a fault to be detectable under any controllers is provided. The proposed method is demonstrated with the simulation examples.