Diagnosis of instrument fault

The diagnosis of faults in instrumentation equipment can often be confused with faults in the system. The correct diagnosis of instrument faults is of importance. Here it is described how to detect instrument faults in non-linearity. Time-varying processes that include uncertainties such as modelling error, parameter ambiguity, and input and output noise. The design of state estimation filters with zero sensitivity to the uncertainties and maximum sensitivity to the instrument faults is described together with the conditions for the existence of such filters. The idea was applied to the fault diagnosis of a heat exchanger. The heat exchanger can be described by a bilinear model with modelling uncertainties. The cause of the fault is estimated from a fault dictionary which was compiled