“…Coupled techniques for fault detection are considered as a strategically important research area (Gelegenis et al, 1989;Frank, 1996;Patton, 1996;Zhang & Morris, 1996;Jain & Jain, 1997). Recent work on hybrid intelligent systems for diagnostic purposes includes research by, among others, Terpstra et al (1993), Rengaswamy and Venkatasubramanian (1993), Pfau-Wagenbauer and Nejdl (1993), Kordon and Dhurjati (1996), Shen and Hsu (1998), Heiming and Lunze (1998) and Norvilas et al (1998) where expert systems technology is combined with neural networks or signal information from sensors.…”