Arrangement for monitoring a rudder control system

Claim 1

Arrangement for monitoring a rudder control system, containing a transmitter for generating a set-point signal corresponding to the respective desired angular position of the rudder and facilities for turning the rudder subsequently to the angular position provided by the set-point signal, the actual angular position of the rudder being picked up by a receiver which supplies a corresponding control-point signal, further containing a first limit circuit (5) to which the difference between the set-point signal and the control-point signal is applied and which supplies an error signal if the applied difference between the set-point signal and the control-point signal exceeds a predetermined limit, a second limit circuit (10), which supplies an error signal corresponding to the turning rate of the rudder, an evaluation circuit (14) to which the output signals of the two limit circuits (5,10) are applied for supplying a drive signal for an alarm generator if two error signals are present, dependent upon an input signal coming from the first (5) and the second (10) limit circuits, and a delay circuit (20) responsive to said first limit circuit for enabling the alarm generator to be triggered by a drive signal, present at the output of the evaluation circuit (14), only after a predetermined period of time has elapsed during which an output has been provided by said first limit circuit, characterized by the provision of a differentiating circuit (9) to which the control-point signal is applied for producing a signal corresponding to the rate of change of the control-point signal and supplying it to the second limit circuit (10); the provision in said second limit circuit of two limit elements (11,12), one for producing a first signal when the rate of change of said control point signal in a positive-going direction exceeds a predetermined minimum and otherwise producing a second signal, and the other for producing a first signal when the rate of change of said control-point in a negative-going direction exceeds a predetermined minimum and otherwise producing a second signal; the provision in said first limit circuit of two limit elements (6,7), one of which (6) supplies an error signal when a positive signal limit is exceeded and the other one (7) of which supplies an error signal when a negative signal limit is exceeded; provision of a pair of logic circuits (15,16), one for each polarity of error signal, in said evaluation circuit (14) for responding to the presence of an error signal from the limit element of said first limiting circuit relating to said polarity during the presence of said first signal from the limit element of said second limit circuit (10) corresponding to the same polarity; provision of the error signals of the two limit elements (6,7) also at the same time to an additional logic circuit (27) for supplying an activation signal to the delay circuit (20), and provision of a final logic circuit (18) for producing an alarm signal in response to the output of said evaluation circuit (14) after the delay circuit (20) has provided a signal to said final logic circuit indicating that said delay circuit has been activated for a predetermined period.