Patent GB-259303-A (GB)
Title: Improvements in or relating to railway signalling systems
IPC: B61L13/04
Filed: 1925-07-07
Abstract: 259,303. Downes. F., and Tattersall, A.E. July 7, 1925. Electrical systems, non-automatic. - In a system of the kind in which a section of the track is tested for the presence of vehicles &c. immediately before a train is permitted to enter the section, a testing voltage higher than normal, and of the order of 6 volts, is applied. The high voltage, which is transiently applied for reasons of economy, breaks down the film resistance between the track rails and the wheels of any vehicle present and ensures efficient shunting of the track relav. The track rails are divided by insulation 3, 4, 5 into main sections 1, 2 and a short auxiliary section 2<1> at the entrance end. Two track relays 6, 7 are provided in parallel, the latter operating only under a higher voltage than is sufficient to operate the former. A second track relay 15 is also provided. Relays 6, 15 are normally operatively energized by current from battery 20 over a high resistance 19. With the track section clear, armature 8 closes a circuit from a battery 11 over a high resistance 10, single lever lock 13, and indicator 14, the current supplied beijng insufficient to release' the lock 13. or to restore the indicator 14 from " track occupied " to " track clear " position, but sufficient to hold the indicator in " track clear " position. When the signalman desired to lower the signal to admit a train, contacts 12 are first closed (by catch-handle, foot-plunger, or otherwise) thus short-circuiting resistance 19 and and applying higher voltage across the rails and track relays. In the presence of a vehicle efficient shunting of the track relays is ensured. The circuits through lock 13 and indicator 14 are broken at armature 8, so that the signal lever is held locked and the indicator moves to " track occupied " position. If, however, the track be clear, the higher voltage causes relay 7 to pick up its armature 9, short-circuiting resistance 10. Increased current is thus supplied to lock 13, releasing the signal lever and allowing the signal to be lowered. The indicator is automatically restored to " track clear " position by the application of higher voltage as the train leaves the section and passes over the auxiliary rail 2<1>. Current is then supplied from battery 20 over contact 16, low resistance 17, rail 2<1>, vehicle wheels, rail 1, and relays 15, 6, 7, causing arinature 9 of relay 7 to be picked up to short-circuit resistance 10. The increased current thus suplied from battery 11 restores indicator 14 to " track clear " position. Electrolitic cells may be connected in parallel with relay 7 to maintain the relay energized a short time after contacts 12 have been opened, to allow time for operation of the signal lever. An alternative arrangement is described in which the auxiliary railsection and relay 15 are dispensed with, an auxiliary relay in series with an electrolitic cell being connected in parallel with the lock 13 and indicator 14. As the train leaves the section, relay 6 is re-energized, and current is supplied to the lock 13 and indicator 14, but insufficient to operate them, and also to the auxiliary relay and electrolytic cell. The cell functions to make this current through the auxiliary relay momentary, and the relay operates a contact to shortcircuit the resistance 19, the relay 7 then functioning in the way already described. Specification 198,221 is referred to.