GB853674A - Improved fault detection means in servo control systems - Google Patents

Abstract

853,674. Controlling aircraft. SHORT BROS. & HARLAND Ltd. Jan. 21, 1958 [Feb. 7, 1957 ; Sept. 13, 1957], Nos. 4234/57 and 28906/57. Class 4. An electric control system on aircraft between an input control member and an output controlled member such as a control surface comprises three transmission channels supplied with input signals responsive to the movement of the input member, means for sampling the signal in each channel, and for comparing each sample with each of the other two, and warning means responsive to any disparity between the samples to indicate the identity of a defective channel. A control column 10 is connected to the pick-off arms of three ganged rheostats 11, 21 and 31 each energised from a common source, not shown, to provide identical input signals to three channels I, II and III, the input signals being amplified at 13, 23 and 33 to energise output members 15, 25 and 35 which each comprise a transducer driving the spindle of a valve in a hydraulic servo mechanism which operates control surface 50. Feedback circuits 16-17, 26-27 and 36-37 are provided to the respective amplifiers and a fault detector 14 is arranged to sample the amplifier output in each of the three channels and is connected at 54 to indicators respectively associated with each channel. The detector 14 comprises three similar relays A, B and C each comprising a pair of opposed coils 41, 42, an armature 44 pivotally mounted between the coils ; a warning switch 51 and a supply switch 52, the movable contacts of these switches being respectively attached to the ends of the armature. The movable contact of each warning switch 51 is connected to the fixed contacts of the supply switch of one of the other relays and the movable contact of each supply switch 52 is connected through lead 53 to a source of power, conveniently tapped from the channel which is not sampled by the relay. The fixed contacts of each warning switch 51 are connected to one of three warning circuits 54 connected to a warning lamp (not shown). Each channel is sampled two coils of different relays e.g. channel I is sampled by coil 41 in relay A and coil 52 in relay C, channel II by coil 42 in relay A and coil 41 in relay B, and channel III by the coil 42 in relay B and coil 41 in relay C. If a fault develops, for instance in channel I the disparity in the signals sampled from this channel actuates relays A and C and closes the switches in these relays. The warning switch 51 in relay A and supply switch 52 in relay C being closed, and interconnected, the warning circuit associated with channel 1 is energised. The warning circuit for channel III is not energised for it derives its power source from dejective channel I. A further embodiment is described incorporating additional feed-back circuits. It is stated in the first Provisional Specification that means may be provided for " holding " an indicator in warning condition and/or for automatically isolating a faulty channel.