Patent GB-435036-A (GB)
Title: Improvements relating to warning signals for level crossings for railways and the like
IPC: B61L29/28
Filed: 1934-03-10
Abstract: 435,036. Level-crossing signals. ROBERTS, W. S., Newby, Ruff Lane, Ormskirk, Lancashire, and RAILWAY SIGNAL CO., Ltd., 40, Broadway, Westminster. March 10, 1934, No. 7653. [Class 105] A level-crossing signal comes into operation when an approaching train de-energizes a normally energized approach relay associated with short insulated rail sections or treadles at the two ends of the stretch and continues in operation till the train reaches a short insulated rail section or treadle at the actual crossing, whereupon an occupation relay associated with this last section renders the signal inoperative ; the approach relay is finally re-energized when the departing train reaches the remote end of the stretch. The signal may consist of flashing lamps controlled by a pair of vibrating relays. In the arrangement shown in Fig. 1, both the approach and occupation relays A, B in the normal state are energized over stick circuits including their own front contacts. The circuit for the relay A is from the battery 6, over the insulated rails 3, 5 at the two ends of the stretch, thence over the front stick contact 10 to the relay A and returns by the rail 1 to the battery 6. The circuit for the relay B is from the battery 13 to the relay B and thence by the insulated rail 4 at the crossing to the front contact 17 and so back to the battery 13. An approaching train when on the rail 3 short circuits the stick relay A which then remains dropped and by its back contact 19 completes a circuit to the signal device 18. When the train reaches the rail 4 at the crossing the stick relay B is dropped by reason of a short circuit from the positive side of the battery 13 over a back contact 26 of the relay A to the rail 1 and thence by the axles to the insulated rail 4 and the front contact 17 of relay B back to the negative side of the battery 13 ; this short circuit is opened as soon as the dropped relay B opens the contact 17, but the relay B remains dropped since it was only energized by a stick circuit. The dropping of the relay B terminates the signal, since the contact 23 opens the circuit of the signal device 18, and the back contact 29 picks up the relay A which thereafter remains energized by its stick circuit. When the departing train reaches the insulated rail 5, the relay A is again dropped and at its back contact 34 permits an electrolytic condenser 31 to be charged by a battery 32 over a back contact 36 of relay B. As soon as the rail 5 is free of axles the relay A is picked up (over the back contact 29 of the relay B) so that a front contact 37 of the relay A now allows the condenser charge to flow to an auxiliary winding of the relay B which picks up and thereafter remains energized by its stick circuit. The apparatus is now again in its normal state. In the arrangement shown in Fig. 2 the insulated sections at the ends of the stretch each comprise an outside section serving to pick up the relay A and an inside section serving to shunt out the relay A. In the normal state the occupation relay B is dead, but the approach relay A is energized by a stick circuit from battery 6 over inside section rails 3a, 5a, the winding of the relay A wires 44, 45, stick front contact 46, wire 48, and rail 1 back to the battery 6. When an approaching train is on the inside section rail 3a the stick relay A is dropped by reason of the axle shunt to rail 1 and accordingly the warning signal 18 comes into operation by the closure of back contact 49 of relay A. When the train reaches the crossing section 4 the occupation relay B is picked up by the battery 50 over wires 51, 52, rail section 4, the train axles, rail 1, wires 48, 47, and back contact 53 of the relay A ; the relay B then sticks over its front contact 56, wires 57, 47, and back contact 53 of the relay A. The opening of back contact 55 of relay B renders the signal 18 inoperative. When the departing train is on the outside section 5 the relay A is picked up by the battery 6 over inside section rail 3a, wire 42, inside section rail 5a, wire 43, the winding of relay A, wires 44, 58, the outside section rail 5, the train axles, and rail 1 back to the battery 6. The relay A then remains energized over its stick circuit which includes its own front contact 46. The opening of back contact 53 of the relay A breaks the stick circuit of relay B and the apparatus is once more in its normal state. If the relay A were to fail from some cause, it is desirable that the departing train should re-switch the signal 18 into operation. This is accomplished in the arrangement shown in Fig. 2 by providing the dotted connection 60. A departing train would then shunt out the relay B, notwithstanding that its stick circuit remains closed due to the assumed failure of back contact 53 (of relay A) to open, by reason of the battery 50 being short-circuited through wires 60, 58, section rail 5, the train axles, rail 1, wires 48, 47 and back contact 53. With the relay B thus dropped and the relay A having failed to lift, the warning signal is re-switched into operation. Alternatively, a failure of the relay A may be notified by the permanent energization of the relay B being used to open the block-signalling instrument line, this line being still, however, capable of being used for telephone messages.