Patent GB-573056-A (GB)
Title: Improvements relating to railway signalling systems
IPC: B61L23/16
Filed: 1942-09-18
Abstract: 573,056. Railway signalling systems. TOMLINSON, A. V. (Union Switch & Signal Co.). Sept. 18, 1942, No. 13217. [Class 105] In a railway signalling system of the coded track-circuit type and using wayside signals of the kind normally biased to a central " danger " position and moved therefrom by armature or rotor to one side or the other to give corresponding " caution " and " clear " signals, the operating windings of the signal are directly supplied with energizing current from the decoding transformer, the circuits of one or more of the windings including or being controlled by a decoding unit effectively responsive to a particular frequency. Fig. 1 shows an insulated track-section 5T with parts of the adjacent section 4T, 6T to the rear and in advance respectively. Each track-section has a code-following track relay such as 5TR at its entrance end and is supplied with coded current from a battery source under control of contact 20 of a coding relay 4CR, 5CR. Each section also has the circuit arrangements shown with respect to section 5T, and a signal such as 5S located at the entrance end, the right-hand end of the diagram showing this signal as comprising a lamp L, and spectacles G, R, Y adapted to be selectively positioned in front of the lamp under control of a rotor operable according to the polarity of current supplied to a winding 15 to show signals G, Y, or, under biasing means, when winding 15 is de-energized, to give signal R. Operation of the signal also controls contacts 21, 22, 24, 25. The track relay 5TR follows the code supplied to the track in accordance with traffic conditions in advance, and its contact 10 connects alternately to the half-windings of the primary of decoding transformer 5DT, terminal B of a local source of direct current having terminals B, C. The secondary of the transformer has a winding 18 connected to a relay 5J through a resonant unit RU which is effectively energized only when the code is of predetermined frequency. As described, 180 and 75 per minute frequencies are used respectively for " clear " and " caution " conditions, and relay 5J picks up only when 180 code is supplied, as under the condition shown with the track stretch unoccupied. The transformer also has a secondary winding 12 with central tapping connected to contact 16 of relay 5J, the half-winding circuits being alternately completed over contact 11 of relay 5TR and contact 17 of relay 5J, contact 11 thus rectifying the output so that substantially direct current is supplied to winding 15 which operates the signal. Contacts 16, 17 act as pole-changers to determine the polarity of current supplied to winding 15 depending on the energized or de-energized condition of relay 5J. As shown, the current supply is in the direction which causes the clear signal G to be given. The signal-controlled contacts determine selectively according to signal position the code supplied to relay 4CR of section 4T. As shown, current is supplied over closed contact 21 and contact of code transmitter 180CT to supply 180 code to relay 4CR and this code is supplied to section 4T. When section 5T becomes occupied, shunting of relay 5TR causes de-energization of winding 15, and the signal 5S moves to its mid-position to display " danger " indication. At the same time contact 21 is opened to stop supply of 180 code, and contact 22 closes to supply 75' code (over coding contact of code transmitter 75CT) to relay 4CR, this code being repeated to section 4T. Similarly, when section 5T becomes cleared and section 6T occupied, section 5T is supplied with 75 code which is ineffective to energize relay 5.T. Current is therefore supplied through winding 15 to cause the signal 5S to move to position displaying the caution (Y) indication. At the same time contact 24 is opened to interrupt supply of 75 code, and contact 25 closes to restore supply of 180 code to section 4T. Similarly, when section 6T becomes cleared 180 code is again supplied to section 5T. Two modifications are described in which the signal has two operating windings. In one of these, one winding which, when energized, tends to move the signal to its caution position, is supplied direct from winding 12 of the transformer, its circuit being controlled by an additional signal-operated contact which is closed except when the signal is displaying its clear indication. The' other winding is supplied direct from winding 18 (relay 5J being omitted) over a resonant unit such as RU, so that the winding is effectively energized only by 180 code, and is sufficiently powerful to overcome the effect of energization in the first-mentioned winding and to move the signal to its clear position. In the second modification the transformer has one secondary winding to which both signaloperating windings are connected in parallel. One signal-operating winding is connected through a resonant unit so as to be effectively energized only by 180 code, and the other through a second resonant unit so as to be effectively energized only by 75 code.