GB833482A - Improvements in electric timing relays - Google Patents

Abstract

833,482. Electromagnetic switches; control Of motors. M & C SWITCHGEAR Ltd. June 14, 1956 [June 29, 1955], No. 18789/55. Classes 38 (3) and 38 (5). A switch intended to control two contact sets in timed sequence comprises a contactoperating lever 17 pivoted at 21 and operated by an armature 41 through a push-rod 25 against the retarding action of the extendible rod 12 of a timing device 11 of known construction. The lever 17 is in three parts 30, 31, 32, the parts 31, 32, being clamped together by a spring device 36 and the part 31 being mounted on the fulcrum 21 and biased by a tight spring 33 so that the part 31 abuts a stop-screw 34 on the part 30. The part 32 insulatedly carries a bridging contact 19 cooperating with a pair of contacts 20 on an insulating base 16 whilst the part 31 carries a striker 22 co-operating with a normallyclosed spring-biased bridging contact 23 engaging fixed contacts 24. When the coil 40 is energized the armature arm 43 is raised to compress a spring 26 arranged between an abutment 46 on the rod 25 and a collar 45 slidable on the rod and the lever 17 is tilted against the delay action of the device 11 to close contacts 19, 20. As the armature continues its delayed movement the part 30 moves independently of the parts 31, 32 which remain stationary, the spring 33 holding the contacts 19, 20 closed against vibration. Eventually the retarding action of the device 11 ceases and the rod 25 moves rapidly upward and a tongue 35 on the part 30 " breaks " the part 31 from the part 32 so that the striker 22 opens the contacts 23, 24. On de-energization of the coil 40 the switch parts return to their initial condition without any delay action of the device 11. The time at which the contact 19 closes may be varied by adjustment of the stop-screw 34 whilst the further time taken for opertion of the striker 22 may be varied by adjustment of the threaded upper end of the rod 12 in a bore in the pivot 18. Fig. 5 shows the application of the switch to a system in which a motor 51 controlled by a starter 56 drives an endless conveyer belt through a traction-type hydraulic coupling, the conveyer having a spring brake preventing its movement until there is sufficient driving torque, the brake being released by a motor 52 having a starter 59. The circuit 53 is connected to the switch coil 40 and the solenoid 58 of the starter 59, whilst circuit 54 includes a starting relay coil 50R operating a contact 50 and the switch 23, 24 connected in parallel with a switch 60 which is closed when the brake is released. Closure of the start button 62 energizes coil 50R to close contact 50 and energize solenoid 57 of starter 56, thus starting the motor 51. Also, coil 40 is energized and after a time interval contact 19 closes to energize solenoid 58 and start motor 52. Eventually contact 23 opens but the circuit 54 is maintained through the previously closed switch 60. Thus should the brake fail to release the circuit 54 is opened by the contact 23 to open the starter 56.