Patent GB-704651-A (GB)
Title: Improvements in or relating to time delay electric switching apparatus
Inventor: FIELDING ERIC CLAY
IPC: G04F3/06
Filed: 1952-09-16
Abstract: 704,651. Time switches. STANDARD TELEPHONES & CABLES, Ltd. Sept. 16, 1952, No. 23210/52. Class 38(5) A time-delay switching apparatus intended for the control of thermionic valve equipment which ensures that power is initally withheld therefrom for a time interval Td sufficient for warming up of the valve cathodes, whilst should the supply subsequently fail for an interval less than Td, viz. Tb, the power is re-applied to the equipment after a correspondingly-less delay approximately equal to the interval Tb, comprises a clock main spring 1 which drives clockwise a gear wheel 3 and a pinion 4, the pinion 4 driving a wheel 16 adjustably carrying a time-setting dial 17 and switch-operating cam 18. The wheel 3 also drives a pinion 5 and wheel 6, the latter driving a pinion 7 and ratchet wheel 8 clockwise. A gear wheel 10 freely mounted on the arbor 9 is driven by a pawl 11 and itself drives through a pinion 13 an escapement mechanism 12, 14, 15. A synchronous electric motor X<SP>1</SP> adapted for operation by a supply having a frequency in the range 45-65 C.P.S. drives a gear wheel 26 clockwise through gearing 22-25. On energization of an electromagnet MAG a gear wheel 29 is pivoted about an axis 28 to connect the wheels 6, 26. The motor X<SP>1</SP> and magnet MAG are connected to a common supply, the motor circuit being completed through a normally-closed micro switch S<SP>1</SP> and the magnet circuit being completed through a rectifier Fig. 1 (not shown). To set the apparatus to close a normally-open micro switch S<SP>2</SP> a predetermined interval Td after switching on the supply to the motor X<SP>1</SP> and magnet MAG, the dial 17 and cam 18 are moved together on the wheel 16 until an arrow marked on the wheel edge coincides with the desired delay marked on a scale on the dial, and are then clamped to the wheel 16 by a nut 19. More than one scale may be provided corresponding to the different supply frequencies which may be connected to the motor. The drawing shows the apparatus set for a delay of 14 minutes with a 50 C.P.S. supply or 11.7 minutes with 60 C.P.S. The initial position of the apparatus is determined by a stop 21 on the wheel 16 which engages a cam 20 fixed to the end of the pinion 4, under the influence of the spring 1. On energization of the motor X<SP>1</SP> and magnet MAG the pinion 5 is rotated clockwise through the clutch wheel 29 and the spring 1 is wound up; also, cam 18 is rotated until after an interval Td it deflects a member 30 to operate switches S<SP>2</SP>, S<SP>1</SP>, substantially simultaneously but in that order. The switch S2 is thus closed and the motor circuit interrupted by switch S<SP>1</SP>. Moreover, magnet MAG remains energized and spring 1 is thus prevented from restoring the apparatus due to the locking-effect of worm gearing 23, 24. The ratchet and pawl connection 8, 11 prevents the escapement mechanism 12, 14, 15 being operated by the motor X<SP>1</SP>. If the supply fails, the magnet is de-energized, releasing the wheel 29 and spring 1 acts to restore the apparatus to its initial condition in a time determined by the escapement mechanism 12, 14, 15. Generally, the construction is such that the restoring time taken by the spring 1 is approximately equal to the time Td, the speed of the wheel 16 produced by the spring 1 being an average of the speeds produced by the motor over the range 45-65 C.P.S. i.e. a speed equal to that produced by a frequency of 55 C.P.S. Should the supply return before the spring 1 has completed its restoring operation, i.e. after an interval Tb, the motor and magnet.will be energized to reclose the switch S2 after an interval approximately equal to Tb.