Orthogonal nonnegative matrix factorization based local hidden Markov model for multimode process monitoring

The HMM-based monitoring indication named negative log likelihood probability is utilized for fault detection. In Case 1, measurement x1 is contaminated by a bias fault of some magnitude in 101-200 samples. NLLP detects all faults from samples 100-200 while they hardly trigger false alarms for the normal observation from samples 1-100.