GB514716A - Improvements in and relating to time switches - Google Patents

Abstract

514,716. Actuation of switches. BRITISH THOMSON-HOUSTON CO., Ltd. May 14, 1938, No. 14448. Convention date, May 15, 1937. [Class 38 (v)] A switch for timing the energization of an X- ray tube 11 comprises a synchronous motor 18 which drives through worm gearing a wheel 20 loose on a shaft 21 to which it can be clutched by means of a pin 22 engaging holes 23 in wheel 20. The pin 22 is carried on a plate 24 slidably splined on shaft 21 and movable by means of a fork 26 against the action of a spring 25 by a solenoid 27. The shaft 21 carries adjustable cams 28, 29 which engage rollers 31 on contact arms 15, 17 biassed towards engagement with a fixed contact 16. The cams 28, 29 are adjusted so that contact arms 15, 17 are operated in succession and that they both engage the contact 16 for one fifteenth of a second which is the unit of time for this apparatus and is the time for one of the holes 23 to rotate into the position of the next hole. Also driven by motor 18 through a clutch 46 controlled by a solenoid 49 and reduction gearing 42, 45, is an arm 50 which is normally held by a spring 55 against a stop pin 51 but which, when clutch 46 is engaged, moves clockwise to cause a pin 54 to close contacts 36 and later contacts 37 which are adjustably mounted on an arm 52. Arm 52 may be set by a pointer 53 co-operating with a scale 51a marked in fifteenths of a second to show the time during which the circuit is closed. Starting from the position shown, with the motor 18 running and wheel 20 idling, and pointer 53 set to a desired time interval, switch 40 is depressed on to contact 38 to energize solenoid 49 to cause arm 50 to close contacts 36. This energizes solenoid 27 through contacts 34 and shaft 21 starts to rotate until circuit is closed at 15, 16, 17 and the tube 11 is energized. Cam 33 on shaft 21 then opens the circuit of solenoid 27 at 34 and closes contacts 35 and shaft 21 remains stationary until pin 54 closes contacts 37. This again energizes solenoid 27 through contacts 35 and shaft 21 rotates to break circuit at 15, 16, 17 and completes one revolution until circuit of solenoid 27 is opened at 35 by cam 33. When switch 40 is released, clutch 46 is de-energized and arm 50 returns under the action of spring 55. The time during which the circuit is closed is thus the time due to the different settings of cams 28, 29 plus the time during which the shaft 21 is stationary, that is the time taken for arm 50 to travel from the opening of contacts 36 to the closure of contacts 37 and is shown on dial 15a. The timing is exact since it depends on the number of holes 23 which pass pin 22 between the two energizations of solenoid 27.