Patent GB-273379-A (GB)
Title: Improvements relating to block instruments for railway signalling
IPC: B61L23/12
Filed: 1926-03-26
Abstract: 273,379. Tomlinson, A. V., (Saxby & Farmer (India), Ltd.). March 26, 1926. Signalling instruments; stafftablet and ticket systems.-In block signalling for railways the release of the locking device of the instrument either to permit trans mission of the usual indications, or to release a token authorizing train movement, as the case may be, is arranged to be effected only by the receipt of a pre-determined number of alternate positive and negative impulses without undue pause. The invention is illustrated as applied at the adjacent ends of two sections, A. B being the corresponding instruments of known type, connected with the transmission lines 4, 3 and with a common controlling device comprising a selectively responsive receiver R and a transmitter T. The receiver can be connected with instrument A or B by throwing over a switch 9 to left or right, switch members 21 being similarly operated at the same time. The receiver comprises a polarized relay 1 the armature 2 of which co-operates alternately with fixed contacts when oscillated by the receipt of alternate positive and negative impulses. Movements of the armature rotate a contact disc 5 a corresponding number of steps by ratchet wheel and pawls, not shown, one pawl acting as a detent. The pawls are arranged to be in engagement only when the relay I is being energized, so that if a pause occur, the pawls disengage and the disc 5 returns to its zero position. When disc 5 is moved round a predetermined number of steps it closes a local circuit from a battery 6 over armature 2, contact 7 or 8, and one or other of two locking coils 10, 11, thus releasing the handle, &c. of the instrument. Normally the conditions are as shown. The usual bell signal current, received say over line 3, passes over normally closed contacts 18, 21a, 21, and winding of a polarized bell relay 20, which then closes a local circuit from a battery 19 over bell 24. The switch 9 is then thrown to the right connecting contacts 7, 8 to the coils 10, 11. The simultaneously operated switch 21 disconnects the line 3 from relay 20 and connects it through wire 22 with the receiver R. Receipt of the pre-determined number of alternate positive and negative impulses then energizes coil 10, 11 as described. For impulses received from line 4 the switches 9. 21 are thrown to the left, the operation being otherwise similar to that described. For transmission of impulses a clockwork operated switch 15 is closed a pre-determined number of times, intermittently energizing a coil 13 with corresponding operation of pole-changing contacts 12. To transmit the impulses to line 3, say, a switch 17 is thrown to the right, connecting battery 19 to the contacts 12. At the same time switches 21<a> are thrown to the right, thus disconnecting line 3 from relay 20 and connecting it with the outer pair of fixed contacts co-operating with the transmitter contacts 12. The clockwork device 16 controlling contacts 15 is then operated. The pre-determined number of impulses may be different for adjacent sections, and the invention is applicable to working short sections as a long section, different numbers of impulses being appropriated to short and long section working.