Smiths Industries Public Limited Company

Smiths Industries Plc

Peter D Baker

Douglas V Luke

Denys V Hollands

An aircraft fuel gauging system has three or more optical pressure sensors 1 and 3 mounted in a tank 10. One sensor 1 is mounted on the floor 14 of the tank, the other sensors 2 and 3 being displaced from the first sensors and from each other in the x, y and z directions. The output of each sensor 1 to 3 is representative of the mass of fuel above the sensor and is supplied to a processor 20. The processor 20 is also connected to an three-axis accelerometer system 21, a pressure sensor 24 above the liquid and a density sensor 25. Utilizing these inputs the processor 20 computes the location of the fuel surface and, from information in the store 22 of tank shape, calculates the mass of fuel.

Liquid quantity gauging

A coupling between two optical fibre cables has a ceramic ferrule at the end of each cable through which its fibre projects. Each fibre is melted into a spherical termination which sits in a frusto-conical recess at the end of the ferrule. A layer of a transparent resilient adhesive lies between the termination and the recess. The ferrules extend respectively into recesses at opposite ends of a ceramic tube which has a passageway coated with a reflecting layer so that radiation from one cable is focussed by its termination on the termination of the other cable and stray radiation is reflected by the reflecting layer.

Optical fibre couplings

A probe has an inlet and outlet by which a fluid flows over an optical sensing element in the sensing probe. Broad band optical radiation is supplied to the element and radiation transmitted through the optical sensing element is supplied to three photodiodes responsive respectively to radiation at different wavelengths. The transmission characteristic of the optical sensing element varies in different ways with change in temperature and pressure respectively. A store of temperature and pressure against amplitude of radiation at different wavelengths is addressed by the outputs of the photodiodes to give an indication of pressure and temperature at the sensing element.

Systems for sensing pressure and temperature at a common location

A fibre-optic cable has a silica optical fibre within a fluoropolymer sleeve. The optical fibre extends between two couplings and is protected by a sheath that is fixed at each end to the couplings. The sheath comprises parallel silica filaments that extend between two braided aramid sleeves. The sheath is completed by an outer tube of a fluoropolymer resin extruded onto the braided sleeves so that its material flows through them and the filaments. The filaments restrain thermal expansion of the sheath to an expansion closely matched to that of the optical fibre.

Fibre-optic cable assemblies

An optical fibre connector or similar entry for an optical fibre cable to an aperture in a enclosure has a metal shell supporting a resilient insert made of an elastomeric polymer loaded with up to about 30% of a material such as carbon particles so that the insert is absorptive of microwave energy at wavelengths similar to the size of the aperture. The faces of the insert have electrically-conductive layers thereon. The optical fibres of the cable are terminated in metal ferrules supported in apertures in the insert.

Fibre-optic entry to an enclosure

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.

Proximity sensing

A fibre-optic cable has a bundle of glass-fibre or silica-fibre strands extending along its length, each end of the fibre-bundle being sealed in a metal ferrule. A sheath of woven glass-fibre or silica-fibre extends about the fibre-bundle and is secured at each end to a respective ferrule in tension, such that the sheath is constricted onto the fibre-bundle along its length. The cable has an outer convoluted metal shell which is sealed at each end to a respective ferrule. A sleeve of elastic material extends around the fibre-bundle and the sheath, within the outer shell, and serves to support and cushion the fibre-bundle along its length. The sleeve may be of a woven fibre including glass-fibre or silica-fibre, and asbestos-fibre, or the sleeve may be of an elastomeric substance. A metal braid sleeve covers the outer surface of the convoluted metal shell. The cable may be included in a radiation pyrometer to transmit radiation to a radiation sensor.

Fibre-optic cable

A fibre-optic cable includes a fibre-bundle, for transmitting light along the cable, that is sealed at either end to a metal ferrule. Each end of the fibre-bundle projects a short distance from its respective ferrule and is enclosed by a metal collar which is welded to the ferrule. The projecting ends of the fibre-bundle are sealed to the ferrules by melting a glass tube within each collar about the ends of the fibre-bundle. A thread of glass or Silastomer material extends between the two ferrules and is helically wound about the fibre-bundle so as to hold together the fibres of the fibre-bundle. Convoluted outer metal tubing extends about the fibre-bundle and is welded at each end to respective ferrules. The fibre-bundle is cushioned within the outer tubing by a sleeve of woven fibre which also extends between the two ferrules about the fibre-bundle and the helical thread. The outer tubing may be evacuated or contain an inert gas at low pressure, or the outer tubing could contain a lubricant such as powdered polytetrafluoroethylene. Alternatively, a silicone oil could be used as a lubricant and, where the cable is to have one end mounted at a hot location, the silicone oil could be chosen to be a gel at that end while being a liquid where cooler, away from that end.

A radiation-detecting device which is mounted on a gas-turbine engine to receive radiations from the afterburner combustion-zone, includes a gas-filled electrical discharge tube that is located within a tubular nose of the device and is pulse energized. The ultra-violet component of radiations from the zone and distinctive of the presence of flame in the afterburner, is transmitted to the discharge tube via a sapphire plano-convex lens, the infra-red component being attenuated by a thin gold-film coating on the planar face of the lens, whereby discharge takes place in the tube with each energizing pulse only while the flame is present. The sensitivity of the detecting device to ultra-violet radiation is enhanced by internal reflections from reflective coatings on the inner surface of the tubular nose and the glass envelope of the discharge tube. The count of a counter is advanced stepwise with each pulsing of the discharge tube towards a maximum count of 8 (or 16), and is reset to zero in response to each tube discharge so that the counter overflows only after the tube remains quiescent through more than 8 (or 16) consecutive pulsings. Overflow of the counter signifies positively the flame-out condition and initiates warning and relighting action by a control unit.

Radiation-detecting devices and apparatus

A surface-discharge igniter having concentric electrodes includes a gap at its operative tip which separates one of the electrodes from the exposed semiconductive surface of a semiconductive pellet that is interposed concentrically with the two electrodes. The said one electrode, which may be either the inner or outer electrode, is connected electrically to the pellet at the bottom of the gap away from the operative tip, whereas the other electrode makes contact with the pellet at, and in the region of, the exposed surface but is otherwise insulated electrically from it. Where the gap separates the inner electrode from the semiconductive surface then the outer electrode may be flared inwardly to establish its electrical connection with that surface. On the other hand, where the gap separates the outer electrode from the semiconductive surface the inner electrode may be flared outwardly, or provided with a cap that extends outwardly across the surface, to establish the connection with it. Holes for draining the gap may be provided through the outer electrode, and the pellet, which may be of material including silicon-carbide particles, may be brazed to the electrodes.

Growing community of inventors

Basingstoke, United Kingdom

Peter D Baker