Patent GB-679963-A (GB)
Abstract: 679,963. X-ray apparatus. GENERAL ELECTRIC CO., Ltd., and BRYER, R. F. July 13, 1950 [July 14, 1949], No. 18609/49. Class 98 (i). [Also in Group XXXVIII] A timing device for controlling, for example, radiograph exposures of the order of humdredths of a second and in which the time interval may be varied comprises a uniselector having its actuating coil fed from A.C. mains such that it steps one position for each cycle or half-cycle of the supply, the timing being effected by a contact arm wiping over a predetermined set of consecutive contacts. In the embodiment shown, two uniselectors F and G are provided having their actuating coils fed from an A.C. mains supply M through oppositely connected rectifiers Fl and G<SP>1</SP> respectively. Initially, all the wiper arms are in the first position and operation of the device is initiated by pressing switch P whereupon uniselector F is stepped to the second position by the first " positive" half-cycle of current. An energizing circuit is thus completed via the second to twenty-fifth contacts of level F1 and the wipers will therefore step forward each following "positive" half-cycle until they return to the first position. The second contact of level F2 completes: an energizing circuit for uniselector G which therefore steps forward on each following " negative " half-cycle until the first position is regained. Levels F3 and G2 are used for the actual timing operation, selected consecutive contacts being connected such that terminals D and E are shorted, respectively, for a desired period. The terminals D and E are respectively connected in the control circuits of two discharge devices (not shown) adapted to pass alternate half-cycles of alternating current to supply an X-ray tube. Thus, with connections as shown, and assuming a mains frequency of 50 c/s., the X-ray tube would be supplied for a total period of five hundredths of a second. The second contacts of levels F3 and G2 are preferably not used since it is desirable to allow the uniselectors F and G to reach steady conditions of operation before timing commences. Thus, the maximum exposure time obtainable with 50 c/s. mains is nearly 0.5 second. To avoid the possibility of a double run if the press switch P is not released sufficiently rapidly, the switch P may be provided with contacts to open the circuit between the twenty-fifth contact of level F1 and the actuating coil of uniselector F. In order to vary the exposure time a separate two-bank manually operated rotary switch (not shown) may be used to connect together the desired number of contacts in levels F3 and G2. The embodiment of Fig. 1 (not shown) comprises three uniselectors, one, C, being arranged to continue sweeping over its twenty-five contacts until another uniselector, B, which steps once each time the first uniselector returns to its first contact, reaches a preselected contact and thereby causes the third uniselector, A, to. home and terminate the timing operation. This arrangement, therefore, permits timing' operations of up to nearly 12 seconds. The invention is applied to a cine-radiograph camera in theembodiment of Fig. 3 (not shown), by providing a uniselector having two actuating coils for forward and reverse rotation of the wipers respectively, the coils being alternatively connected to the supply mains by the change-over contacts of a relay that is energized by a. switch synchronized with the camera shutter. The uniselector runs forward when the camera shutter is open and certain levels on it cause an exposure to be made in a similar manner to levels F3 and G2 of Fig. 2. When the camera shutter is closed the uniselector reverses and returns to, the starting position, no exposure being effected owing to further contacts of the relay breaking the circuits, to terminals D and E. It is preferred in all embodiments to use uniselectors of the type wherein the stepping of the wipers is caused by the forward rather than the reverse stroke of the actuating coil armature. In other embodiments of the invention, not described, the timing device may control a conventional electromagnetic contactor instead of the two electric discharge devices. Also the uniselectors may be arranged to step every half-cycle, instead of every cycle of the A.C. mains, by feeding the actuating coils direct instead of using rectifiers.