A temperature compensated lead screw for use in a device, such as a vacuum capacitor, in which an electrical parameter is controlled by position of a shaft operating through a vacuum-sealing flexible metal bellows into an evacuated envelope. The shaft position is, in turn, the result of the lead screw acting against a threaded member. The lead screw assembly is composed of an externally threaded sleeve slip-fit onto a mandrel and welded, or other wise tightly bonded, at a single discrete location along the common mandrel/sleeve axial length. Normally the sleeve has a relatively high predetermined thermal coefficient of expansion and the mandrel a low coefficient, if the device controlled is a vacuum capacitor. The heating effect, and therefore the resulting capacitance change through expansion effects in a vacuum capacitor handling RF power, is a complex function of factors, including capacitance value. The desired counteractive shaft expansion is therefore a function of capacitance (lead screw) setting. The structure described provides a counteraction for internal heating expansion effects in devices of the character described. If the bond between the sleeve and mandrel is not at the extreme end of the lead screw assembly, then for example, positive overall lead screw expansion is obtained corresponding to thread engagement on one side of the bond, and negative for a thread engagement on the opposite side of the bond.
A vacuum capacitor and its manufacturing method are disclosed. The vacuum capacitor comprises: an insulating envelope; a pair of end electrodes, each end electrode being brazed under a non-oxidation atmosphere to a corresponding end of the insulating envelope and being formed together with the insulating envelope to constitute a vacuum vessel; a plurality of cylindrical electrode plates constituting a pair of cylindrical electrodes, each cylindrical electrode plate constituting one of the pair of cylindrical electrodes having a mutually different diameter and being extended along the insulating envelope from an inner surface of the corresponding one of the pair of end electrodes so as to be inserted into a space between the mutually adjacent cylindrical electrode plates constituting the other of the pair of cylindrical electrodes; and a positioning member to position one of the pair of cylindrical electrodes to the other of the pair of cylindrical electrodes in such a manner as to equalize a spatial interval between each cylindrical electrode plate constituting the one of the pair of cylindrical electrodes and that constituting the other of the pair of cylindrical electrodes.
