Smiths Industries Plc

Edward S Eccles

Harry Gibson

Michael P Barnsley

Ralph Taylor

A hydraulic control system has two fluid supply circuits which control fluid pressure supplied to respective chambers of a fluid-controlled actuator, each chamber having an individual piston mounted on a common actuator rod. In normal operation, a major part of the pressure is supplied to the actuator by the first circuit in accordance with control signals derived from an external source. The second circuit supplies pressure to its respective chamber at a lower level in accordance with control signals derived from the differential pressure across the piston in that chamber, the pressure supplied by the second circuit acting to reduce the differential pressure across the piston. The system also includes a control unit that responds to malfunction of the first circuit or error in the control signals supplied to the first circuit, by disconnecting the first control circuit from control of the actuator, such as by equalizing pressure across the piston in the first chamber. Upon detection of a malfunction or error, the control unit also supplies to the second circuit, instead of the signals derived from the differential pressure, control signals nominally-identical to the control signals supplied to the first circuit and derived from an external source. In this way, following detection of a malfunction in the first circuit, the second circuit controls the major part of the pressure supplied to the actuator.

Control systems

An electrical indicator has a consecutive series of light-emitting diodes which are arranged along a straight or curved reference scale. A limited region of the series, comprising several diodes, is energized and this illuminated region is displaced along the scale upon change in an electrical input variable supplied to the indicator such that the position of the region provides an analogue indication of the value of the input variable. To improve the appearance of the display and reduce power consumption, the brightness of the region varies along its length with one or both of the outermost diodes being energized at lower levels than another of the diodes. The indicator may include a shift register having a number of storage locations, each for storing signals representative of a corresponding one of the light-emitting diodes, the signals at these locations being displaced in accordance with change in value of the input variable. Signals output from each storage location of the shift register are supplied to a gate which controls switching of a transistor that is connected in series with a resistor in the energizing circuit of each light-emitting diode. Each energizing circuit includes two such transistors and associated gates which control the degree of brightening of each light-emitting diode by switching one or more resistors in parallel in the circuit. The gates are connected to control brightening of one diode in accordance with brightening of one or more other diodes.

Analogue electrical indicators having a series of

Control apparatus for controlling an aircraft gas-turbine engine, having two control lanes operated in parallel with one another and each of which is capable of performing the function of the control apparatus individually, includes a computer and a monitor unit associated with each lane for performing checks on the integrity of the components of both lanes. Transducers in each lane sense engine parameter values and pass signals in accordance therewith to the computer that sends control signals to a control unit and thence to an actuator for adjusting engine variables in accordance with engine-thrust requirements. The control unit includes a pair of cam-operated switches that respond to difference in the values of the control signal from each lane indicative of a fault in the lanes and that trigger operation of the monitor unit in each lane. The monitor units disengage the control signals of the computers from the actuator and cause each computer to pass to the monitors the results of signal comparisons it has made involving signals values of each lane, so that the monitor units can determine in which lane the fault lies. The monitor units reconnect to the actuator control signals from a lane that is found to be operating correctly.

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Bishops Cleeve, United Kingdom

Edward S Eccles