Patent GB-562955-A (GB)
Title: Improvements relating to electrical control apparatus for railway signalling systemsand the like
IPC: B61L3/22
Filed: 1942-10-19
Abstract: 562,955. Railway signalling systems. TOMLINSON, A. V. (Union Switch & Signal Co.). Oct. 19, 1942, No. 14616. [Class 105] [Also in Group XXXVII] A four-position direct-current relay, particularly described as for use'in railway signalling but applicable to other uses, has energizing windings adapted to operate a neutral armature and one or more windings which polarize a second armature biassed to a normal midposition, this armature moving one way or the other according to the relative polarity of current in the neutral and polarizing windings. The polarized armature moves from normal position only when neutral and polarizing windings are simultaneously energized. Fig. 1 shows the relav used in a coded track current railway signalling system in which it replaces the usual three decoding relays. Current from an A.C. source BX, CX, coded according to traffic conditions by a coding device CT with one or other of usual frequencies 75, 120, 180 by correspondingly numbered contacts, is supplied to the insulated track-rail section DE through transformer TT. As shown, the code is picked up inductively by coils 4, 5 carried by vehicle W and is supplied through an amplifier A and code-following relay MR to control cab signals CS. The relay R has a core with outer limbs 15, 17 carrying neutral windings 24, shown as energized so that neutral armature 19 is picked up and contacts 26, 27, 28 operated thereby are closed. Limbs 15, 17 also have short internal polepiece projections co-operating with and acting as stops to the polarized armature 20, which is pivoted on a shorter central limb 16 of the core and is biassed to mid-position by springs 22. Limb 16 carries two windings 29, 30 respectively supplied with current from decoding units DU120, DU180. These windings are oppositely wound so that when energized they produce oppositely directed fluxes in the core, causing armature 20 to swing clockwise or anticlockwise depending on which winding 29, 30 is energized. Armature 20 controls a pivoted contact arm 35 carrying insulated contacts 32, 33 co-operating respectively with fixed contacts 38, 39, these pairs of contacts being normally open as shown, and also carrying a two-armed contact 34 normally engaging fixed contacts 36, 37. Clockwise movement closes contacts 32, 38 and breaks contact 34, 37, contacts 34, 36 remaining closed, and anticlockwise movement closes contacts 33, 39 and breaks contacts 34, 36, contacts 34, 37 remaining closed. Contact 6 of relay MR following the code frequency makes contact alternately with contacts 7, 8, thus correspondingly reversing current from a D.C. source B, C through the primary winding 9 of transformer DT. A secondary winding 10 supplies winding 24 through a full-wave rectifier 41 and as this circuit is untuned, armature 19 picks up irrespective of frequency. Windings 24 thus replace the usual detector relay. Secondary winding 11 supplies the detector units DU120, DU180 which include rectifiers and are tuned respectively to 120, 180 frequencies so that winding 29 alone is energized with code of the former frequency, and winding 30 alone with the latter frequency, neither being energized by 75 frequency. In operation, with no code current, all windings are deenergized so that armature 19 is released and contacts 26, 27 are open and back contact 28 is closed. The most restrictive lamp 43 is lit. With 75 code, contacts 26, 27, 28 pick up as shown and " caution " lamp 44 is lit. With 120, code contacts 34, 37 in circuit with lamp 44 open and contacts 32, 38 close, lighting " approach restricting " lamp 45 over closed contact 27. With 180, code circuit of lamp 44 is broken at contacts 34, 36 and contacts 33, 39 close to light " clear " lamp 46 over contact 26.