Patent GB-552310-A (GB)
Title: Improvements relating to block signalling systems for railways and the like
IPC: B61L23/12
Filed: 1940-05-20
Abstract: 552,310. Railway signal systems. WESTING- HOUSE BRAKE & SIGNAL CO., Ltd., PETER, L. H., and COLEY, J. P. May 20, 1940, No. 8973. [Class 105] In a block signalling system employing signalling instruments at each end of a track section to transmit and receive the usual signals requesting and permitting the entrance of a train into the section, the signals are effected by code impulses and the transmission of each impulse constituting a code element, except the first element of a code signal, is dependant on and effected by the proper transmission of the preceding code element, the indication corresponding to the signal being effected only when the code for that signal has been fully completed. As described the system uses a fourimpulse code the first element being always positive and the remaining three elements combinations of positive and negative impulses allocated as follows, the signalling being between points A, B at the ends of the section shown in Fig. 1. Code elements Signal transmitted + + + Is line clear A to B and B to A + + - "Cancel" from A to B and B to A + - + "Cancel required" from A to B and B to A + - - "Train on line coming" from B to A and "Line clear" from A to B - + + "Line closed indication" from B to A and "Train on line coming" from A to B - + - "Line clear" from B to A and "Line closed" from A to B - - + "Line closed" from B to A and "Line closed indication" from A to B - - - "Line clear received." The layout in Fig. 1 includes short insulated track-sections AXT, BXT at the ends, each with a track relay (not shown), home signals HA, HB, starter signals 5, 6, 7, 8, and release lever K (not shown) having locking coils K, K, and contacts KA, KE, Fig. 11, closed in certain positions of the lever. Figs. 4, 5 show the instrument located at A and B with its operating circuits, and provided with button 1 for sending "Is line clear ?" signal, lamp 2 for indicating receipt of the signal, button 3 for requesting "cancel," and lamp 4 to indicate that signal. The instrument comprises an armature with coil 12 pivoted between the poles of a permanent magnet 13 and carrying a pointer 15 normally held in the central "line closed" position shown by springs 14. The needle moves to right or left according to the polarity of current supplied to coil 12 and to less or greater extent as determined by inclusion or otherwise of resistances R1, R2 in the coil circuit. Fig. 2 shows the connection between A, B by lines 9, 10 with relays BL, NL responsive respectively to positive and negative line current, and batteries ALB, BLB connected to send positive and negative current respectively under control of contacts BT1, BT2, NT1, NT2 of the relays BT, NT of Fig. 3. Relays BL, NL control repeater relays BLP, NLP and at both ends of the line slow-acting "line closed" and "line open" relays LC, LO are provided, those at B not,being shown. Fig. 3 shows further apparatus provided at A, a similar arrangement not shown being provided at B. The arrangement comprises, inter alia, a set of relays ATC, ATCR, ATLB, ATLBK, ATTOLC, ATILC, ATLC, a second set of instrument relays ARLC, ARTOLC, ARLB, ARCR, ARLBK, ARC, ARILC (of which ARTOLC, ARILC are of the type mechanically latched up until released by current supplied to additional lower windings shown), a chain of counting relays 2A, 2B, 3A, 3B, 4A, 4B, a set of register relays 2BS, 3BS, 4BS for positive impulses, 2NS, 3NS, 4NS for negative impulses, and normally latched up proving relay ANPR. At each end are also provided slow release relays M, R, Fig. 13, SR, Fig. 14. The Specification traces in detail the circuits involved in the following operation. Signalman at A desiring to despatch a train from A to B presses button 1, Fig. 3, 4, energizing relay ATILC (which completes its own stick circuit), energization of relays SR, BT following automatically so that battery ALB supplies positive line current to transmit the first positive code impulse, at the same time energizing relays BL and BLP. Relays M (at A only), LC, R. also energize, closing their own stick circuits. Energization of relay BLP at A opens the circuit of relay SR which releases and de-energizes relay BT thus determining the first code impulse and releasing relays BL, BLP, followed by pick-up of relay LO and release of relay ANPR. This energizes relays LOP, 2A, BT, BL, BLP, 2BS, 2B in automatic succession, the pick-up of relay 2B breaking circuit of relay 2A leading to release of relays BT, BL; BLP completing a second positive impulse. Relay 3A then energizes, releasing relay 2B, 'followed by energization of relays BT, BL, BLP sending the third positive impulse which is terminated by pick-up of relay 3B breaking the circuit of relays 3A, BT, BL, BLP. Pick-up of relay 3B energizes relay 4A which breaks circuit of relay 3B and energizes relays BT, BL, BLP to start the fourth positive impulse. Relay 4B then energizes, breaking circuit of relay 4A, BT, BL, BLP to terminate the fourth impulse, and breaks circuit of relay ATILC. A sequence of relay operations generally similar to that described above has occurred simultaneously at B, at which point the energization of the 4B relay energizes delivery relay D which leads to relay BRILC (corresponding. to relay ARILC at A) being energized and latched up. A front contact of relay BRILC; not shown, closes the circuit of lamp 2, and a bell, at B. After period the relays other than BRILC are released at A and B and relays ANPR, BNPR (not shown), energized and latched up. The operation of the various relays automatically in sequence as described above depends on a front contact of each energized relay completing, in conjunction with front and back contacts of other relays as positioned at the time, the circuit of the next relay to be energized. In the following operations similar appropriate relay energizations occur in sequence, but the full sequence is not here described. When the appropriate code involves a negative impulse the relays NT, NL, NLP become energized in place of the relays BT, BL, BLP as described above for positive impulses. When the signalman at B wishes to accept the train by giving "line clear" signal to A he operates his release lever K, thus energizing relay BTLC (corresponding to ATLC at A) this in turn unlatching relay BRILC and stopping the bell. A front contact of relay BTLC also initiates a code transmission leading to energization of relays ARLC, BLCS. The latter closes the circuit through resistance Rl and coil 12 of the instrument at B to move the pointer one step to the right, indicating "line clear sent." Relay ARLC energizes relay ARLCP (not shown), which closes the circuit through resistance R2 and coil 12 of the instrument at A, moving the pointer one place to the left to indicate "line clear received." When the train enters section AXT the track relay of that section releases and its back contact XTR completes the circuit of relay ATTOLC, initiating a code transmission leading to energization of a relay TOLG (not shown) contacts of which close a circuit through the instrument coil which does not include resistances R1 or R2. The pointer thus moves two places to the left indicating "train on line going." The code just sent also picks up and latches relay BRTOLC at B (corresponding to ARTOLC at A), its contacts closing, an instrument circuit to indicate "train on line coming." When the train passes through section BXT the release and subsequent pick-up of the corresponding track relay initiates relay operations which result in release of relays TOLG, at A and BRTOLC at B so that both instruments return to the normal "line closed" indication. The specification describes the process when A, desiring to "cancel" after requesting and receiving "line clear" operates his button 3 to light lamp 4 at B and sound a buzzer, B responding by pressing his button 3 to light lamp 4 at A and restore the "line closed" condition. The way in which the arrangement prevents opposing operations being performed is also described in detail.