Patent GB-689093-A (GB)
Title: Improvements in or relating to railway signalling systems
Inventor: BROWN ANDREW
IPC: B61L23/22
Filed: 1949-08-08
Abstract: 689,093. Railway signalling systems. STANDARD TELEPHONES & CABLES, Ltd. July 28, 1950. [Aug. 8, 1949] No. 20565/49. Class 105. A railway signalling system for a layout having route-setting apparatus and with the wayside signals located to provide overlap is such that a signal for admission to a route can be cleared even if at the exit end of the set-up route the signal at the overlap point is still at danger due to the presence of a train in the section guarded by the route exit signal, provided that the train in such route-exit section is unable or unlikely to move into the route in the opposite direction. The route setting may be controlled by sequence switch apparatus. For the track layout shown in Fig. 1 a route from the signal 4 at the left hand end of the track A to the signal 29 on track B, such signal 29 being located at an overlap point with respect to the right-hand-end exit track section W38T, an appropriate sequence switch denoted by numeral 5 (but not shown) is caused to move to a position denoted by the route reference 4B3 such sequence switch thereupon closing a contact shown in Fig. 3 by the symbol J prefixed by the numeral 5 denoting the particular sequence switch and having the suffix 4B3 denoting the position on such switch to which is assigned the route denoted by 4B3. Fig. 2 shows this route. The signal 4 is cleared when a relay 4BHR is energized the circuit for which, shown in Fig. 3, extends from a positive source B over various relay and sequence-switch contacts which verify the proper positions of various points and catch points and that the track of the route is clear. Thus contact 17NWCR verifies that the crossing 17 is correct, contact 18NWCR that the points 18 are at normal, contact 21RWCR that the trap points 21 are at reverse (i.e. straight), contacts 17T, 21T, 5T, 12T that these track sections are free, contact 5ZCPR that no sequence switches are in movement, contacts 5J483 that the sequence switch 5 is in the position for route 4B3, contact 5J4B2-3 that the sequence switch 5 is in position for route 4B2 or route 4B3. Contact W380TS is a contact of a stick relay picked up when a train entered the section W38T and the signal 29 went to danger (with the train still in section W38T) and sticking until the train vacates section W38T. Contact 13TS is a contact of a track stick relay picked when the route setting means is operated. It will be seen that if a train has passed through route 4B3 but is still in section W38T nevertheless the relay 4BHR can be energized, to clear the entrance signal 4 for the route (for a second train), over contact W380TS even though front contact W38T in the circuit is open, the first train obviously being unlikely to back into the route. In the case of an oppositely travelling train in the section W38T i.e. proceeding to the left butover the points 38 at reverse and therefore unable to enter the route 4B3 then a front contact 38 RWCR would be closed to still allow energization of the relay 4BH3 for.clearance of the entrance signal 4 for route 4B3.