Due to the increasing complexity of modern control systems, availability of accurate information on the actual operating condition of these systems becomes increasingly important. The technology that is concerned with the determination of this operating condition is referred to as condition monitoring. The operating condition of a control system includes the stages of wear of the different parts of the system. But it also includes faults that can occur in the different parts. The information obtained from condition monitoring can be used in several ways. One way is to notify an operator about the system condition and let him decide on the actions that should be taken. He can, for example, conveniently schedule a maintenance  action for an almost worn part. Another, more advanced way is to use a controller that can adapt or reconfigure itself automatically to changing conditions such as faults. Controllers that have the ability to adapt to faults are known as fault-tolerant controllers and can make control systems more reliable.

A schematic diagram of a fault-tolerant control scheme is displayed in the figure above. The controlled system consists of actuators that control the system, the system itself and sensors that measure information from the system. In all of these three parts faults may occur. The inputs to the condition monitoring block are the observations taken from the monitored system. These observations, in general, are measured time signals such as the input and output of the system. Furthermore, model information can be used for condition monitoring. Condition monitoring techniques that use model information are known as model-based condition monitoring and have the advantage that less or no extra hardware is required as opposed to condition monitoring techniques that do not use a model. ReliaCon has a strong background and expertise in model-based condition monitoring. Based on the measured time signals and the model information an analysis is made of the current operating condition of the system. The output of such an analysis can then be used to reconfigure the controller or to notify the operator about a fault.

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