452,172. Railway signalling systems. TOMLINSON, A. V., 65, Victoria Street, Westminster.-(Union Switch & Signal Co. ; Swissvale, Pennsylvania, U.S.A.) May 15, 1935, No. 14247. [Class 105] In a railway signalling system with signals controlled by codes of interrupted current in the rails, the particular response of the track relay selects a particular interruption-rate current to energize intermittently a track feed relay, a contact of which effects the feeding of appropriate code to the rails of the rear section. The system shown in Fig. 1 employs interruption-coded direct current in the rails for the control of the wayside signals and correspondingly coded alternating current for cab signalling is superposed by means of approach relays. The section 1-3 is shown as a cut section with the coded rail current repeated by the track relay TR<2> at the cut 2. According to the ahead traffic conditions a code of interrupted direct current is applied to the rails of section 1-3 by the front contact 14 of a track feed relay CTR<3> which is energized 80. 120, or 180 times a minute according to which of the continuously operating code transmitters CT80, CT120, CT180 is connected up to the wire 24 by the control relays A<3>, H<3>, E<3>, F<3>; these relays are energized in accordance with ahead traffic conditions by the particular rail-current code applied to the track relay TR<3> of the first section ahead. The vibrating contact 4 of relay TR<3> maintains energized a relay A<3> and a relay H<3> which is energized over a front contact 7 of the relay A<3>, these relays being made slowto-release by means of rectifiers RA3, RH<3> across their terminals. The vibrating contact 10 of the relay TE<3> applies direct current alternately to the two halves W<1> W<2> of the primary length of an autotransformer DT<3> feeding relays E3, F<3> which are selectively responsive to the 120 and 180 codes. With 80 code in the ahead section, only the relays A3, H<3> are energized and thus the section 1-3 has 120 code applied thereto since the track feed relay CTR<3> is energized over front contact 23 of relay H<3> and back contacts 21, 27 of relays F<3>, E<3> and the contact of the transmitter CT120. With 120 code in the 120 ahead section then 180 code would be applied to section 1-3 by the energization of the relay CTR<3> over front contact 23 of the relay RH3, back contact 21 of the relay F<3>, front contact 27 of the relay E<3>, which responds to the ahead-section 120 code applied to the autotransformer DT<3>, and contact 180 of the code transmitter CT180. If the ahead section is occupied, the track relay TR<3> is stationary and dropped and therefore the relay H<3> is dropped since the relay A<3> being no longer energized opens its front contact 7 ; the unnecessary power supply to the autotransformer DT<3> is cut off by the opening of contact 9. The 80 code is now applied to section 1-3 by the energization of the track feed relay CTR<3> from contact 80 of the code transmitter CT80 over back contact 23 of the relay H<3>. The multi-aspect wayside signal S<3> is controlled by the relays H<3>, E<3>, F<3>. For cab signalling purposes alternating current is superposed on the direct current by an approach relay applying power to a primary winding of a transformer, the secondary of which is in series with the direct current source so that both currents are coded by the contact 14 of the track feed relay CTR<3> or contact 15 of the repeating track relay TR<2> at the cut point 2. When a west-bound train enters the section 1-3, the relay TR<1> drops and therefore relay A<1> drops so that its contact 25 de-energizes an approach relay V<2>, a back contact 11 of which applies alternating current power, from a front contact 31 of a relay A<2>, to the transformer T<2> whereby coded alternating rail current is superposed on the length 2-1 of the cut section. The relay A<2> is a slow-release relay energized over a front contact of the vibrating track relay TR<2> at the cut point 2 ; the back contact 15 of this vibrating track relay TR<2> applies the code. When the train enters the length 2-3 the vibrating track relay TR<2> drops and therefore the relay A<2> drops so that the contact 31 cuts off the alternating current code in the length 1-2, but the contact 25 of relay A<2> de-energizes an approach relay V<3> whereby alternating current is superposed on the direct current for the length 3-2 and both currents are coded by the vibrating track feed relay CTR<3>. The rear out 1-2 is now supplied with steady direct current over back contact 15 of the dropped track relay TR<2> ; this will permit clearing of any level crossing signal by means of the relay V<2>. The primary sides of the alternating current transformers are normally short circuited as by front contact 11 of relay V<2> so that the flux variation during the directcurrent coding is reduced and thus sparking at the contact is minimized. Code distortion is reduced by arranging that the vibrating track relays at successive points in a cut section apply the code alternately at the front and back contacts. The track relays, shown in Fig. 2, comprise a pivoted armature 35 surrounded by an operating winding 18 and co-operating with limbs 34 which are polarized by a magnet 40. The armature is biassed to one side by a spring so that it is only operated by current of one polarity. The relays for adjacent sections are arranged for opposite polarities and thus on any breakdown of insulation the relay being energized from the adjacent section by current of wrong polarity closes its back contact and so gives a warning. The negative resistancetemperature characteristic of the rectifiers used for the slow-release relays A<3> is compensated by including a series resistance 32 with a positive resistance-temperature coefficient.