Abstract: The invention relates to a technique for providing a so-called `pedestal` voltage on the rear surface of the target of a pyroelectric camera. This is a positive voltage required to ensure efficient discharge, by the electron beam, of the pyroelectric charge. In the invention, the pyroelectric material is in the form of a plurality of islands of pyroelectric material connected individually to the signal plate. Each island is coated on its rear surface and on at least one side, by a conductive film. By applying a positive bias voltage to the signal plate, the rear surface of the pyroelectric islands are similarly biassed to provide the pedestal.

Abstract: The invention provides an image intensifier arrangement in which for each stage either the luminescent screen or the photo cathode thereof is decoupled by resistive decoupling with respect to the capacitances of a power supply source which is provided to supply high tension thereto. In each case the resistive decoupling consists of a resistor of such value as to provide a time constant with the capacitance of the relevant output point of the power supply which is many times greater than the duration of a typical high energy flash to which the intensifier is likely to be exposed in operation.

Abstract: The aluminium-backed phosphor layer on the output window of conventional image intensifier tubes of the photoemissive/luminescent screen type can be seriously damaged by the extremely high energy density pulse of electrons resulting from exposure of the tube to very bright light (such as a shell flash). The invention prevents or minimises the damage by placing in between and in contact with the phospher layer and the aluminium layer a layer of material (for example, potassium silicate) whose thermal properties are such as to cause it to act as a heat sink and so absorb most, if not all, of the thermal energy released by the electron pulse.

Abstract: The invention provides a multi stage image intensifier arrangement in which, for any stage, means are provided responsive to the photo current of the stage for discharging capacitance associated with that stage so as to limit the level of current density to which the anode screen of that stage is subjected as a result of a high intensity input flash of light.

Abstract: A magnetron consists of a cathode structure mounted within an anode cavity arrangement. In order to prolong the operational life of the cathode structure electron emissive material is located within recesses formed in the outer surface of a cylindrical support. As the electron emissive material erodes away during operation of the magnetron its surface area remains substantially unreduced.

Abstract: An image intensifier device is provided with color filters on its input and output surfaces so as to intensify a color image without losing the color content. Each filter consists of an array of red, green and blue elements and these elements are precisely aligned in both input and output filters to avoid degradation of the color content. A method of producing the output filter in situ is described to provide the required accuracy of alignment.

Abstract: A switch device comprising at least two switches (12, 13) connected in parallel in a first electric path; a timing device (3) for feeding at a required time, a switching impulse along a second electric path to the switches thereby switching at least one of them (12) to a conductive state so that current flows along the first path; and a transformer (18) having a primary (20) in the said first path and a secondary (17) in the said second path arranged so that the aforementioned current induces a further switching impulse or reinforces the first switching impulse thereby switching or assisting the switching of the other switch (13) to a conductive state.

Abstract: The invention provides a magnetron of the strapped anode type having three strapping members each co-axial but at different diameters from the center of the anode block of the magnetron. The middle strapping member is connected to alternate vanes and the innermost and outermost strapping members are connected to the remaining ones of the anode vanes.

Abstract: The invention concerns thyratrons and in particular thyratrons which are required to be able to conduct protectively in a reverse direction. In order to assist in such reverse conduction an electrode which at such times acts as a cathode e.g. a conventional anode is formed or includes material of low work function such as tungsten impregnated with barium aluminate. Where the electrode in question is a plate anode the disc or plate is itself formed of the low work function material. Where the anode is a so-called hollow anode material of low work function may be introduced within the interior of the hollow anode. Where the anode electrode is in the well known form of an inverted cup material of low work function may be provided as a layer on the surface thereof facing the cathode.

Abstract: A streaking image tube having a suppression mesh electrode spaced between the normally provided accelerating mesh electrode and anode. Appropriate potentials are applied to the electrodes so that undesirable secondary emission from the accelerating mesh electrode is returned to that said electrode.CROSS REFERENCE TO RELATED APPLICATIONSThe above-entitled application is a Rule 60 continuation of Ser. No. 885,192, filed Mar. 10, 1978 and now abandoned; Ser. No. 885,192 being a rule 60 continuation of Ser. No. 599,465 filed July 28, 1975 and now abandoned.

Abstract: A co-axial magnetron in which the microwave output frequency can be rapidly altered within a particular frequency band. A movable tuning plate is coupled to a mechanical tuning fork which is set into vibration by an alternating voltage applied to a solenoid.

Abstract: The invention relates to light biassed camera tube arrangements of the kind in which the light bias source within the overall outline of the tube envelope has one terminal connected to a heater pin in order to provide a source of power. The other terminal of the light bias source is connected to a lead extending to a terminal carried by a protecive end base cap for the tube and a removable disc is provided to fit between the base of the tube and a valve base into which the tube is plugged, the removable disc bearing circuitry and terminals provided to contact selected ones of the terminals carried by the protective end base cap so that the nature of the light bias provided may be selected.

Abstract: The invention relates to combustible gas detectors of the kink in which a heatable wire filament exhibits a change in resistance due to a change in its temperature caused by the oxidation of a combustible gas passing over it. In order to avoid poisoning the heatable wire filament is embedded in a pellet consisting of a homogeneous mixture of an oxidation catalyst material and zeolite material the latter preferbly of type X, Y, L or mordenite of large pore size. Additionally layers of catalytically active material and/or inactive non-catalytic porous material may be provided around the outside of the pellet.

Abstract: In a co-axial multi cavity anode magnetron spurious resonances which would otherwise occur in the space between a magnetic pole piece and an anode shell are suppressed. The resonances may be suppressed by means of short circuit pins located within the anode shell.

Abstract: A display arrangement is provided with two opposite display surfaces so that a display can be seen from both directions. The display arrangement consists of an evacuated envelope and fluorescent screens are provided at both display surfaces which are irradiated by a common electron emissive cathode. This enables a display arrangement to be provided which is very thin, but which is capable of providing very bright displays in an economical manner. Segmented mesh electrodes are positioned adjacent to both fluorescent screens so as to selectively control the regions of the screen which fluoresce, and this enables the nature of the display to be readily altered.

Abstract: A rotatable thermal shutter for use with a pyroelectric camera tube is provided with blades having opening and closing edges in the shape of a spiral. The use of a spiral shape allows the rotatable shutter to have a particularly small diameter while still providing satisfactory performance.

Abstract: A mesh electrode for a c.r.t. display device consists of a number of coplanar portions of mesh insulated from each other, and secured to a support plate by means of two layers of refractory compound. The first layer is applied to the support plate and allowed to set before the second layer is applied so as to space the mesh portions from the support plate by at least the thickness of the first layer.

Abstract: The invention is concerned with monitoring the temperature distribution of a surface which may not be a good emitter of thermal radiation. In the invention a member which is of relatively low thermal conductivity and high thermal emissivity is placed in contact with the surface the temperature distribution of which it is required to monitor so that a thermal image transfers from the latter to the former. A pyroelectric vidicon camera tube then examines the temperature distribution of the member.

Abstract: An addressable display in which data is presented in the form of a rectangular dot array is provided by means of an evacuated cathode ray tube, which enables large bright displays to be achieved. The cathode ray tube contains two segmented mesh electrodes each consisting of separately addressable stripes. Electrons from a flood gun are passed by both electrodes only at the crossing point of two stripes, one on each electrode, when predetermined potentials are applied to them.

Abstract: This invention concerns gas filled thyratrons and is concerned with preventing the formation of arc spots on the grid when the thyratron is operated in a grounded grid mode. The thyratron provided has a grid consisting of three apertured baffle electrodes which are electrically united and occur in sequence in the cathode to anode path of the thyratron. The baffle electrodes on the cathode side of the final baffle electrode forms at least one re-entrant hollow cathode and conductive gauze covered apertures in the baffle electrodes on the cathode side of the final baffle electrode are staggered relative to apertures in the final baffle electrode.