fault analysis[′fȯlt ə‚nal·ə·səs]
The detection and diagnosis of malfunctions in technical systems. Such systems include production equipment, transportation vehicles, and household appliances. While the need to detect and diagnose malfunctions is as old as the construction of such systems, advanced fault detection has been made possible only by the proliferation of the computer. Fault detection and diagnosis actually means a scheme in which a computer monitors the technical equipment to signal any malfunction and determine the components responsible for it. The detection and diagnosis of the fault may be followed by automatic actions enabling the fault to be corrected, such that the system may operate successfully even under the particular faulty condition.
Fault detection and diagnosis applies to both the basic technical equipment and the actuators and sensors attached to it. Actuator and sensor fault detection is very important because these devices are quite prone to faults.
The on‐line or real‐time detection and diagnosis of faults means that the equipment is constantly monitored during its regular operation by a permanently connected computer, and any discrepancy is signaled almost immediately. On-line monitoring is very important for early detection of any component malfunction, before it can lead to more substantial equipment failure. In contrast, off-line diagnosis involves the monitoring of the system by a special, temporarily attached device, under special conditions (for example, car diagnostics at a service station).
The diagnostic activity may be broken down into several logical stages. Fault detection is the indication of something going wrong in the system. Fault isolation is the determination of the fault location (the component which malfunctions), while fault identification is the estimation of its size.
Fault detection and isolation can never be performed with absolute certainty, because of circumstances such as noise, disturbances, and model errors. There is always a trade-off between false alarms and missed detections, the proper balance depending on the particular application.