GB476432A - Improvements relating to railway signalling apparatus - Google Patents

Abstract

476,432. Railway signalling systems. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. June 8, 1936, No. 15987. Convention date, Jan. 22. [Class 105] A relatively high voltage is impressed on a track circuit by intermittently interrupting a magnetizing direct current for a transformer connected to the rails. Similar peak voltage devices may be carried on rail cars to provide a film break-down voltage thus to ensure an adequate shunt of the usual track circuit by the axles or by a contact brush device. The interruption rate gives a coding effect and may be provided by a pair of vibrating relays R<1>, R<2> of which the relay R<1> is energized over a back contact of the relay R<2> while the relay R<2> is energized over a front contact of the relay R<1>. The relay R<1> periodically lifts its contact 3 which firstly connects up to the transformer winding 7, the lead 5 from the track rail b and shortly thereafter causes a contact 1, 2 to be opened thereby opening the circuit by which a battery B<1> feeds the transformer winding 6. The resulting rapid decay of the magnetic flux causes a high voltage to be applied to the track circuit over the leads 4, 5. When the contact 3 drops, the contact 1, 2 re-closes whereby the battery B<1> begins to build up the flux once more. At the far end of the track circuit a codefollowing relay CF is operated and energizes two slow relays SR<1>, SR<2>. Since the track circuit pulses are only of short duration it may be necessary to prolong the energization of the code-following relay and this may be achieved by the means shown in Fig. 4, where a condenser C<2> is charged during the dropped state of the code-following relay CF<2>, and discharges through a holding winding HW when a front contact 8 is closed. For different length track sections or for different ballast conditions it is necessary to provide different peak voltages. This may be obtained by the arrangement shown in Fig. 7, in which the code transmitter CT<1> has associated therewith a relay P having a slug winding 25 witii an adjustable resistance AR to delay the opening of the contact 26 in the feed circuit of the transformer 11 until a sufficiently high flux has been set up. This arrangement maintains a constant peak voltage in spite of any decay in battery voltage since with reduced battery voltage the relay P will be slower in lifting its contact ; the longer time of feed to the winding 11 then permits the lower battery voltage to produce a normal value of current in the transformer winding 11. Different coding rates may be automatically selected according to the ahead traffic conditions and the decoding means then applies the appropriate code to the rear section.