A steam turbine is provided with an automatic digital computer controller and a backup analog controller which are interfaced with an electrohydraulic position control for the turbine throttles and governor valves. Valve position signals are generated by transducers and applied to the valve position control along with position setpoint signals from the computer or the backup controller for the purpose of generating valve control signals which drive the valves until the position setpoints are satisfied. The position signals are also applied to the computer where they are compared to the computer valve position setpoints. The automatic controller and the analog backup controller each have a speed/load control which generates the valve position setpoints in accordance with a speed or load reference, and the backup control tracks the computer setpoints during automatic control. The backup control position setpoint signals are also applied to the computer during automatic control there they are also compared to the computer valve position setpoints. If any comparison results in a difference in excess of a predetermined deadband valve, the computer generates a contingency signal to indicate a valve not functioning or backup not tracking.
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