Abstract: An instrument for detecting penetration of the epidural space comprises a barrel within which a plunger is urged forwardly by a resilient strap. The barrel has a nose on which a Tuohy needle is mounted. The inner surface of the barrel has a groove that extends along the barrel, being spaced from the nose. In operation the assembly is pushed forwardly until the tip of the needle contacts the spinal ligaments. The plunger is then pulled rearwardly past the end of the groove so that air enters the barrel and becomes trapped when the plunger is released and urged forwards by the strap. Penetration of the epidural space by the tip of the needle allows the trapped air to escape through the needle thereby providing an indication of penetration of the epidural space by causing the plunger to be moved forwards.

Abstract: A circuit is provided which accepts digital position information from a graphics generator. This information serves as an input to a look-up table to determine whether the position information would cause any portion of a symbol from the graphics generator to be inside a clipping boundary, which boundary frames higher priority symbology. If this is found to be the case, the circuit excludes or clips the symbol portion that would otherwise interfere with the higher priority symbology.

Abstract: A connector assembly for a capacitive fuel-gauging probe comprises a socket assembly, mounted on the probe, and plugs. The socket assembly has several sockets each of which has an elongate contact element. The inner surface of each socket has a number of axial rails and channels which engage with rails and channels formed on the outer surface of the housing of a cooperating plug. The cooperating surfaces of the plugs and sockets differ one from the other so that only the correct plug can be inserted in the correct socket. The contact element of each plug is in the form of a resilient loop, the upper portion of which has a projection that locks with an aperture in the socket contact element. Pulling the plug housing out of the socket moves the projection out of the aperture so that the plug can be withdrawn.

Abstract: Head-up display units and other display systems are tested by means of a camera having an array of light-responsive elements. The signals supplied to the display system to control the disposition of the display representation in the display area of the system, are compared with the output from the camera so as to derive an indication of the difference between the signalled disposition and the actual disposition of the representation. The display unit is mounted for angular displacement about two axes at right angles to the line-of-sight. The width of the display representation is determined by measuring the distance between two points of the same brightness on opposite sides of the center of the representation; this is done by displacing the image formed on the array across an individual element of the array. The brightness of the display representation is determined by comparison with a source that is switchable between two known brightness levels.

Abstract: An optical displacement transducer for providing a digital output representative of the displacement of a variable from a datum value comprises a light beam emitter and a light beam receiver disposed on a common optical axis, a digital encoding element comprising an optical grating disposed between the light beam emitter and receiver, the grating extending in a circular path with the grating lines extending substantially radially of the path, means for causing relative rotation between the light beam and the grating about the center of the circular path whereby the light beam as seen by said receiver is in the form of a series of light pulses, a first reference position at a stationary position on the circular path, a second reference position on the circular path and angularly displaced about the center of the circular path from the first reference position whereby a predetermined light pulse count is produced during the relative rotation through the angle between the first and second reference positions, an

Abstract: A system for use in a gas-turbine engine, for controlling the clearance between the tips of the blades and a surrounding shroud, has a probe mounted in the shroud. A microwave oscillator supplies microwave energy to the probe which propagates energy towards the blades and receives energy reflected from the blades. A mixer is mounted remote from the probe and mixes the energy reflected from the blades with a reference signal derived either from energy transmitted by the oscillator or from the energy reflected by the tip of the probe. This produces interference dependent upon the phase difference between the energy reflected by the blades and the reference signal. From this phase difference, the system derives an indication of the separation of the blades from the probe and uses this to displace the shroud along its length, thereby altering the clearance between the tips of the blades and the shroud.

Abstract: A cathodoluminescent display device, for example a low-voltage vacuum fluorescent display device, has a source of low-voltage electrons and cathodoluminescent layer for excitation by the low-velocity electrons which comprises particles of phosphor material, for example a sulphide, selenide, telluride or oxy-sulphide phosphor, thar are treated to increase their surface conductivities by, for example, deposition of a surface coating comprising conductive or semi-conductive material.

Abstract: Gyroscope apparatus includes a tubular rotor that is supported at opposite ends by bearings, such as a gas-lubricated bearing, for rotation about its axis. A gimbal ring encircles the rotor and is resiliently supported with the rotor, for angular displacement about an axis at right angles to the rotor axis, by a pair of flexure pivots located intermediate the ends of the rotor. An inertia ring is mounted concentrically with the gimbal ring by another pair of flexure pivots for angular displacement about an axis at right angles to the rotor axis and the axis of displacement of the gimbal ring. The major part of each flexure pivot is contained within the radial thickness of the gimbal ring. Displacement of the inertia ring is sensed by pick-offs the outputs of which are used to control the restoring torque applied by torquers located outwardly of the pick-offs.

Abstract: A control system for an aircraft gas-turbine engine has positive and negative acceleration control units. Each control unit has a memory storing values of the maximum or minimum desired rate of change of fuel flow at different speeds beyond which surge or extinction will occur. The control units produce output signals, in accordance with the engine speed and acceleration, for controlling fuel flow so that it follows closely within the surge or extinction curves. The system also has amplitude gates that pass one or the other of these output signals to the engine if the speed of engine demanded by the pilot is such as to cause surge or extinction.

Abstract: A pressure transducer cross-check system (10) in which a pair of low precision pressure transducers (12, 14) which detect parameters related to each other in content are alternately periodically calibrated during the operation of the system by cross-checking by a solenoid actuated valve (18) which alternately connects one of the pair of low precision pressure transducers (12, 14) to its associated pressure input (20, 22) while connecting a common high precision pressure transducer (16) to the other of the related pressure parameter inputs (20, 22) for selectively alternately providing one of the pair of parameter input signals as a high precision pressure responsive input signal to the system controller on alternate cycles of the low precision pressure transducer pair in accordance with the cycling of the valve (18).

Abstract: A mach airspeed indicator capable of internally determining mach number and VMO from measured altitude and airspeed information directly. An internal microprocessor, capable of storing a plurality of selectable VMO curves and a table of mach number versus q.sub.c /P.sub.s, receives the measured altitude and airspeed information, determines VMO and mach number therefrom, and directly drives the VMO and mach number displays where q.sub.c represents the impact pressure and P.sub.s represents the static pressure. The measured altitude and airspeed signals are analog synchro signals. In order to drive the VMO display, the received analog altitude synchro signals are digitized in a synchro-to-digital converter comprising a single multiplying digital-to-analog converter for both sin .theta. and cos .theta. synchro functions, and fed to the microprocessor which verifies the appropriate VMO from the preselected VMO curve, and drives the VMO analog pointer via a stepper motor servo loop closed by the microprocessor.

Abstract: An aircraft head-up display system has a combiner comprising a block of transparent glass and a plate of transparent glass cemented to the rear of the block. The plate carries a reflection holographic element on its front surface abutting the block. Light from a display on the screen of a cathode-ray tube is projected into the combiner through one edge, at an acute angle onto its front face. The light is then reflected rearwardly through the holographic element to the rear face of the plate where it is reflected forwardly again. The holographic element is arranged such that some of the light incident on it from the successive reflections within the combiner is reflected at right angles to the surface of the plate, forwardly through the front face of the combiner and into the line-of-sight of the observer. Successive reflections cause light to emerge at several locations along the length of the combiner so as thereby to increase the field of view of the system.

Abstract: An automatic door operator for opening and closing a door such as a cold storage door which is mounted in a frame for sliding movement in a vertical plane has a hydraulic control system which includes an electric motor for rotating a reversible hydraulic pump, an electric control circuit which activates the electric motor to rotate the pump in the appropriate direction, and a reversible rotary hydraulic motor driven by the pump to rotate a chain drive which draws the door to its open and closed positions. The hydraulic control system also includes a means for cushioning the rapid start and stop of the door to provide smooth operation which includes a pair of check valves disposed in the control system such that one check valve is on either side of the hydraulic pump, and a first set of pressure relief valves disposed in the control system on either side of the pump between the pump and the check valves, and a second set of pressure relief valves between the check valves and the hydraulic motor.

Abstract: A connector for medico-surgical tubing has a plastics body with a male Luer tapered forward portion that is shaped for engagement with a coupling member having a cooperating Luer tapered bore. The body has a rear portion of prismatic shape and square cross-section that is embraced by a square aperture in a rear flange of a locking ring. The locking ring has a cylindrical portion which extends axially of the connector and which has an internal screw thread for engaging cooperating projections on the coupling member. The locking ring is thereby free to slide axially along the prismatic portion of the connector body but is prevented from rotation relative to it. The rear of the Luer tapered portion projects above the surface of the prismatic portion to limit forward displacement of the locking ring.

Abstract: A system for indicating the mass of fuel in several fuel tanks of an aircraft has a capacitive depth sensor and a permittivity cell located in each tank. Signals from the sensors and cells are supplied to a computing unit which computes the volume of fuel in each tank and its approximate density. The system has a densitometer and another permittivity cell which receive a sample of all the fuel supplied to the tanks, and supply output signals to the computing unit. The computing unit derives a correction factor by comparing an approximate value of density derived from the other permittivity cell with a more accurate measure of density derived from the densitometer. The correction factor is used to correct the approximate values of density derived from the permittivity cell in each tank.

Abstract: In a cathode-ray tube display system, signals defining the coordinates of the element of the screen on which the cathode-ray beam is incident in its raster scan are supplied to a comparator together with signals defining the coordinates of a series of points defining the image to be displayed. The comparator derives a brightness-weighting signal in respect of each element in accordance with the proximity of that element to those of the points defining the image within a predetermined proximity. The predetermined proximity may be equal to the separation between the points. The system also includes a store, brightness-weighting signals being added together in the store to produce a total signal for each element that is used to control bright-up of the element.

Abstract: A fuel-gauging system has a capacitive sensor that is mounted in a fuel tank and supplied with an alternating electric signal from an oscillator. The oscillator output is supplied to a diode-pump circuit that produces a D.C. voltage proportional to the product of the amplitude and the frequency of the oscillator output. The D.C. voltage is supplied to the input of a comparator that receives a constant voltage at its other input. The comparator produces a D.C. output voltage, dependent on the difference between its inputs, which is supplied to an input of the oscillator, the oscillator being arranged such that the amplitude of its output voltage is dependent upon the amplitude of the input voltage. In this way, the product of the amplitude and frequency of the oscillator output is maintained substantially constant.

Abstract: 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.

Abstract: A valve assembly comprises a resilient housing of plastic material and a valve element in the form of a unitary plastic body located within the housing. The body is closed at one end by a dish-shape portion having a circumferential lip which forms a seal with the housing. The body has a tongue formed in its wall, one end of the tongue being provided with an inwardly directed tooth. By inserting a tube or rod within the valve element to engage the tooth, the tongue can be displaced outwardly and the overlying part of the housing can thereby be distorted away from the lip to permit fluid flow through the housing. The valve assembly may be used to seal one end of the inflation line of a cuffed medico-surgical tube.

Abstract: A drive wheel for rotating a workpiece while the latter is in contact with a grinding wheel during a grinding operation. The drive wheel is in the form of a pneumatic tire with a tire valve which permits easy variation of the internal pressure in the drive wheel. Thus the relative softness or hardness of the drive wheel can be changed in accordance with requirements attendant to the grinding operation. The drive wheel is motor-driven and a speed control device operates to slow the motor drive shaft when high torque loads are applied to the drive wheel by the workpiece, during heavy cutting of the workpiece by the grinding wheel. Thus the workpiece rotates slowly during heavy cutting and faster during light cutting.