Abstract: A position measuring device includes a conventional encoder, a scale member and an index member together arranged to provide two periodic waveforms of the same frequency and in quadrature with one another. Errors in the waveforms are corrected, and the corrected waveforms used to produce an indication of the position represented by the waveforms. The two positional indications are combined to give a high-resolution output. The conventional encoder may be absolute or incremental, and the device may be used to measure linear or angular position relative to a datum.

Abstract: A marine mine 10 (FIG. 4) is arranged to have a buoyancy state in which the force of gravity and/or buoyancy act on the mine in a vertical direction to move the mine through the water and includes control means operable to control guidance surfaces 16, 17, 18 projecting from the mine to impart a lateral gliding movement to the mine to steer it to intercept a target. The buoyancy state is determined by a buoyancy compartment forming part of the mine body which may be flooded to lay the mine at a submerged station. Sonar sensing means detecting a target causes air from a cartridge to displace water from the buoyancy compartment to provide an upward buoyancy force which is used to give lateral movement to the mine which is steered on a trajectory intercepting the target.

Abstract: Capacitance measuring apparatus comprises a variable capacitor VC and a reference capacitor FC. Circuits D, ID, are provided for generating a periodic waveform for application directly to the variable capacitor, and in inverted form to the reference capacitor. Switches means SM are operated by control logic CL to connect the two capacitors in sequence to the input of an integrating amplifier IA, the output of which is applied to a comparator CM to which is also applied a reference level. The output of the comparator controls the control logic. Output of the control logic is converted to an indication of the capacitance of the variable capacitor relative to that of the reference capacitor.

Abstract: A liquid display device comprises two spaced electrodes each having a resistance characteristic such that a potential gradient may be developed across the electrode. A liquid crystal material is located between the two electrodes. Voltage supply means are provided which apply an alternating potential across each electrode, such that the two potentials are of the same frequency, and, preferably, in quadrature with one another.

Abstract: A circuit assembly having a plurality of planar substrates 14 with modules and/or components 13 mounted thereon, has the substrates comprising at least parts of walls of substantially enclosed hollow structures 15, for example, the substrates comprising two opposing and parallel walls of each structure, the structures are mounted spaced apart within a container 10, and the arrangement is such that cooling fluid is to flow from a supply to the circuit assembly, and is to be discharged from the circuit assembly, the cooling fluid to flow between the regions within the container surrounding the structures and the interiors of at least some of the structures, via holes 26 in the walls of the structures, so that the cooling fluid can be supplied easily and efficiently to points within the circuit assembly where generated heat is required to be removed, the construction of the circuit assembly being flexible in this manner.

Abstract: Laser cutting apparatus comprises a laser (20), means (24,25) for directing the output beam of the laser on to a workpiece (26), and means such as a quarter-wave plate (27) for producing circular polarization of the laser output beam. The laser may include within its optical cavity an element which produces stable linear polarization of the output beam. The quarter-wave plate (27) then covers the polarization into circular polarization.

Abstract: Correction for variations in scan period of optical image scanners includes measuring and storing the scan times at which optical events occur to cause image detector signals, detecting an optical marker near the end of the scan and the scan time of its detection, determining the difference between this scan time and a stored scan period, comprising the nominal scan time for marker detection, which difference represents the scan period error, dividing the difference by the stored scan period to provide a scan time unit error and multiplying each stored measured scan time by the unit error to provide a correction for each measured scan time, thereafter adding the correction to the stored measured scan time to give a corrected scan time.

Abstract: A circuit assembly comprises a planar substrate 10 supporting, on a surface 11, connectors 14 and modules 12, the connector pieces of the connectors, and the module leads, both extending at least substantially parallel to said one major substrate surface, and the modules are clamped to the substrate in a readily releasable manner by means 40, so that a module can be replaced readily, for example, when faulty, and there may be a resilient part 48 of the clamping means between each module and a rigid part 41 of the clamping means, so that the module is not damaged by the clamping action; possibly the resilient part being provided by a composite structure of the resilient part and insulating sleeves 13' for module leads; and the clamping means including at least part of the connectors, so that the required clamping action is at least partially between the substrate and the connectors.

Abstract: A circuit assembly comprises a planar substrate 10 supporting, on a surface 11, connectors 14 and modules 12, each module having leads 13 extending from two opposing module surfaces, with the leads from one surface extending exclusively in one or two planes parallel to the module-bearing substrate surface, and with the leads from the other surface extending exclusively in the other such plane, the connectors each having an electrical insulating block 15 comprising two separable parts stacked one on the other, and rigidly secured to the substrate, and with connector pieces 17 secured to the block, such that there is facilitated, possible, at least partial, protection of connections between the module leads and the connector pieces, by the connections being on, or within, or adjacent to the block, before the module and the block are supported on the substrate.

Abstract: In trimming a constituent layer (10) of a circuit element, through which layer current is to flow along an axis (14), a first channel (16), extending through the layer from one layer edge, (17), partially across the width of the layer, transversely to the axis, is provided in a first, coarsest trimming action, a second channel (18), extending through the layer, from the extremity of the first channel remote from the layer edge, parallel to the axis, is provided in a second finer, trimming action, and in each of at least one further trimming action a further channel (20) is provided, each further channel extending through the layer parallel to the axis, the further channels being successively between the immediately previously provided channel and the layer edge, there being successively greater accuracies associated with the constituent trimming actions, each further channel possibly extending further from the first channel than the immediately previously provided channel.

Abstract: A laser energy control circuit for a gas-discharge excited laser includes an energy source PSU to supply energy to the gas discharge. First circuit means TR1, TR2 operate to limit the energy supplied to a first value for a first time interval, after which second circuit means A1, A2 allow the energy to rise to a maximum value and then decrease gradually to a second value over a second time interval. Subsequently, third circuit means including amplifiers A3 to A6 operate to maintain the light output of the laser at a desired value.

Abstract: A cathode electrode for a gas discharge laser comprises a block of platinum black compressed into a solid mass.

Abstract: Laser apparatus operable in the range 8 to 50 microns, has an optical cavity defined by two mirrors M1 and M2, one of which is partially transmitting. The cavity contains a laser active medium AM and a reflecting polarizer RP. The reflecting polarizer comprises a substrate carrying a metallic reflecting coating covered by a dielectric layer of alumina, silicon dioxide or magnesium oxide. The wavelength of operation determines the dielectric material to be used, and the thickness of the layer determines the absorption loss introduced into one of two perpendicular planes of polarization.

Abstract: A connector for a light-transmitting cable 13 comprises a body member 10 in which are located a sleeve 11 of elastomeric material and a grip member 12. The grip member is segmented and deformable under radial pressure applied by the sleeve. The ends of two cables 13 may be inserted into the grip member 12 and means 15 are provided for applying axial pressure to the elastomeric sleeve 11 to cause it to extend in a radial direction to exert pressure on the grip member. The grip member 12 then grips the cable 13 at a number of equally-spaced points around its periphery.

Abstract: A network of different weighted resistances, for example, binary resistances, coupled in parallel with each other, is provided in a semiconductor body by providing a plurality of substantially identical resistors, with different numbers of the identical resistors being coupled in parallel to provide the required different weighted resistances of the network, possibly, the constituent identical resistors of the different weighted resistances of the network being interdigitated with each other.

Abstract: An accelerometer comprises an electric coil pivotally mounted in a magnetic field about an axis extending perpendicular to the field for oscillatory movement substantially perpendicular to the field, in the manner of a D'Arsonval movement. Switching means in the form of a radition source and detector responds to movement of the coil assembly when on either side of a switching position to apply a constant current to the coil to move it in the direction of the switching position, thereby setting up an oscillation of the coil. Linear acceleration is measured by having an inertial mass, such as provided by mounting the coil away from its center of mass, displaced from the pivotal axis. An acceleration force acting on the mass of the oscillating coil alters the proportion of time spent at each side of the switching position to give an average current flow in the coil related to the magnitude of acceleration. More than one coil may be provided to measure acceleration along a number of axes.

Abstract: A method of bonding an optical element (12) to a support (10) requires the formation on the support of a thin pad (11) of material of substantially the same dimensions as the base of the optical element. The material of the pad is one to which the adhesive to be used will not adhere. The optical element (12) is positioned on the pad (11) and a fillet of the adhesive (13) is applied around the base of the element, in contact with both the base of the element and with the support. As a modification, an aperture (14) may be formed in the pad (11) and filled with a rapid-setting adhesive (15) to secure the element in position while the fillet of adhesive is applied.

Abstract: An electric connector includes a housing having a number of elongated recesses, and a plurality of contacts. Each contact has a terminal portion, two spaced parallel support members extending between the terminal portion and a web, and two contact members located between the support members and extending one from the terminal member and one from the web.

Abstract: An electrical resistor comprises a tube of resistive material having a closed end. An electrical connection is made to the open end of the cylinder, and a further connection comprises a conductor passing through the open end of the cylinder and connected to the closed end. A pair of voltage-measuring connections are made to the outer surface of the cylinder.

Abstract: Electric motor control apparatus includes a variable-frequency oscillator 10, a counter 11 clocked by the oscillator, and signal generating means 12 arranged to generate two sinusoidal voltages in quadrature with one another. The two voltages are applied through separate amplifiers 22, 23 to separate stator windings 24, 26, of the motor, the stator windings being 90.degree. apart. Control means includes a bistable circuit 28 producing a signal lagging 45.degree. behind one sinusoidal voltage, and a phase sensitive detector 29 arranged to vary the frequency of the oscillator 10 to maintain a constant phase difference.