OSCILLATORY SERVO-VALVE MONITOR

An oscillatory servo-valve fault monitor is provided for identifying faults attributable to servo-control system components. In particular, both low frequency and high frequency (oscillatory) fault responses are identified. Such oscillatory fault responses are distinguished from normal position control adjustments and transient responses. As the reaction to a fault condition is to shut down the faulty actuator and corresponding servo-control, such capability avoids inadvertent shut-downs. Independent detection paths are provided for sensing low frequency responses and high frequency responses. Each path includes a respective window comparator and up-down counter. For a given path, the window comparator defines two thresholds--in effect, a window. If the monitored signal amplitude is outside the window, then a counter or count signal is incremented. If the signal amplitude is within the window, then the counter or count signal is decremented. The time constant for counting up is less than that for counting down, so that more up counts would occur in a given time period, than would down counts for the same period. As a result, faults causing an oscillatory amplitude beyond the thresholds of the window comparator are quickly identified. If the count signals (or the count in either of the up-down counters) exceed a respective value, then the monitor indicates that a fault condition is present.