Patent GB-447854-A (GB)
Title: Improvements relating to electric-time switch devices, particularly for timing x-ray photographic exposures
IPC: G03B9/58
Filed: 1935-05-01
Abstract: 447,854. Actuation of switches. DEAN, G. P., 14, Baldwins Gardens, Holborn, London, and CALDWELL, T. F., 46, Clare Road, Hounslow, Middlesex. May 1, 1935, No. 13042. [Class 38 (v)] A time-switch device for interrupting an electric circuit after a predetermined time, particularly for use in timing X-ray photographic exposures, comprises electromagnetic coupling means having a part continuously rotated at a constant speed, and another part which, when the electromagnet is energized, turns with the first part and by contact with an adjustable stop co-operating with relatively movable contacts, causes the interruption of the circuit after a predetermined time. In the arrangement shown, a synchronous motor 5 drives, through reduction gearing, a shaft 10 carrying an insulating bush 16 on which are mounted slip rings 17, 18 and the soft iron casing 20 of the coil 21 of an electromagnet, the ends of the coil being connected to the slip rings. The armature 24 of the electromagnet is normally prevented from rotating with the magnet by a spring 25, but when the magnet is energized, the armature is attracted and rotated against the action of the spring until an extension 59 of the armature engages an abutment 60 carried by a pivoted arm 61 and moves the latter to separate contacts 66, 68. The contacts are connected to slip rings 30, 31, and the arm 61 is carried by an arm 64 connected to the slip rings, the arm 64 and slip rings being connected to an operating knob 39 by means of which they can be adjusted about a fixed shaft 32. The slip rings are engaged by brushes 33, 34 connected to terminals 37, 38. The knob 39 carries a pointer 40 which co-operates with a ring of graduations outside the front plate of the apparatus, and a ring 41 with recesses 43 corresponding to the graduations is mounted on the inside of the plate. An arm 45 connected to the knob is formed with a projection 46 adapted to engage one of the recesses 43 when the knob is turned to set the apparatus for a required time interval. A fine adjustment is obtained by a second knob 51 geared to an arm 47 loosely mounted on the shaft 32, said arm carrying an arcuate strip 47A formed at its end with an abutment 47D and a short inclined plane 47B engaging an extension 47c of the arm 45. Each division on the ring 41 corresponds to a tenth of a second, while the knob 51 enables adjustments to a hundredth of a second to be obtained. The circuit connections are shown in Fig. 4. The motor 5 runs continuously as long as a main switch 81 is closed. On closing a push button switch 82 the electromagnet is energized from the secondary winding 87 of a transformer, and the armature 24 rotates until its extension 59 engages the abutment 60 and separates the contacts 66, 68. The winding 85 of a contactor 86 is energized as soon as the push button is depressed and remains energized until its circuit is opened at the contacts 66, 68. The contactor controls the circuit of the primary of the X-ray transformer, which is therefore energized for the time taken by the extension 59 to reach the abutment 60, which is determined by the setting given to the knobs 39, 51. As soon as the push button is released, the electromagnet is de-energized and the armature returns to its initial position.