Control system actuator position synthesis for failure detection

Apparatus for diagnosing failures in an actuator loop of a digital electronic engine control (DEEC) which controls the actuator position in each of a plurality of successive sample intervals in dependence on the difference signal magnitude between an actuator position command signal sample and an actual actuator position signal sample selected from one of two sensed actuator position signals provided from first and second position sensors associated with the actuator, comprising:

• model means, for simulating the signal response of the actuator loop to the difference signal magnitude between the actuator position command signal sample and the selected actual position signal sample from a preceding sample interval, to provide a synthesized actuator position signal sample representative of the expected actuator position in a present sample interval;
• signal selection means, responsive to the actual position signal samples of each sensed actuator position signal and responsive to said synthesized signal sample,
• for determining the difference signal magnitude between each actual position sample and said synthesized sample to select for use by the DEEC, a first one of the actual samples whose difference value is within a maximum position difference limit,
• for rejecting for use in a sample interval an actual sample having a difference signal value greater than said maximum position limit,
• for providing a fail signal identifying as failed any of said position sensors providing an actual signal sample having a difference magnitude greater than said maximum limit in a successive number of sample intervals;
• and
• recording means, for recording each of said fail signals from said selection means to provide a failure diagnosis record for the actuator loop.