Patent ID: 8042568

Claim:
A fluid controller operable to control a flow of a fluid from a source of pressurized fluid to a pressure operated device, the controller comprising: a housing defining an inlet port connected to the source and an outlet port connected to the pressure operated device, a valve member movable within the housing and cooperating therewith to provide the flow between the inlet port and the outlet port at a flow rate which depends on the position of the valve member relative to the housing, a processor providing a reference which is indicative of a desired position of the valve member relative to the housing, an actuator adapted to move the valve member in accordance with the reference, a sensor adapted to provide a sensor output indicative of an obtained position of the valve member relative to the housing, an observer adapted to determine a model output based on the reference, and to determine a residual value indicative of a difference between the sensor output and the model output, and a fault detection system adapted to compare the residual value with a threshold value, wherein the fluid controller is adapted to provide a gradient that is calculated based on the reference and another reference provided by the processor earlier in time, and to scale the threshold value based on the gradient.