Patent GB-416117-A (GB)
Title: Improvements relating to railway level crossing signals
IPC: B61L29/28
Filed: 1933-04-11
Abstract: 416,117. Level - crossing signals. NAAMLOOZE VENNOOTSCHAP MACHINERIEEN-EN APPARATEN FABRIEKEN, 30, Croeselaan, Utrecht, Holland. April 11, 1933, Nos. 10831 and 10832. Convention dates, April 12, 1932 and Dec. 31, 1932. [Class 105.] In order to avoid derangement of a trackcircuit controlled level-crossing signal by a vehicle such as an agricultural machine or a sledge runner bridging the rails at the level crossing, the system is arranged so that no potential difference exists at the rails at the crossing until a train approaches and by the track relay operates the level crossing signal. As shown in Fig. 1, the insulated rail lengths A, B at the sides of the crossing W overlap at the crossing itself where they normally are at the same potential. A train entering the length A from the left shunts the track relay GRI contact 1 of which opens the line to the clear signal Sp and back contact 4 of which picks up a secondary relay HEI. Front contact 2 of relay HEI earths the insulated rail length B and so drops the track relay GRII. Back contacts 3 of the two track relays GRI and GRII pick up a relay HRa which then sticks over back contacts 2 of relays GRI, GRII, one of these contacts alone being sufficient. When the last axle leaves the length A the relay GRI becomes live and at its front contact 2 energizes a relay HRb (over front contact 2 of relay HRa) and the clear signal Sp. The relay HRb opens the stick circuit of relay HEI and also prevents relay HEII being energized over back contact 4 of relay GRI which still continues to be de-energized by the axles in the rail length B. When the rail length B is finally empty the relay GRII becomes live, and, as GRI is likewise live, the two back contacts 2 thereof are no longer closed and the relay HRa therefore drops and in turn causes relay HRb to drop, whereby the line to the relays HEI, HEII is restored and the signal Sp is now directly energized over the front contacts 1 of the relays GRI, GRII. In the arrangement shown in Fig. 3 at the crossing W there is a short insulated rail C which is normally earthed over back contacts 2 of secondary relays HBI, HBII and is thus at the same potential as the continuous rail. A train entering at the left de-energizes relay GRI, contact 1 of which opens the line to the clear signal Sp and contact 4 of which energizes relay HBI ; this last relay at its contact 2 breaks the earth connection of rail C and at contact 3 connects it to rail length A. When the first axle enters rail length B relay GRII drops and its contact 3 completes the pick up circuit of relay HR ; relay HR sticks so long as one track relay GRI or GRII is dropped. When the last axle leaves the short rail C, the relay GRI is energized and at its front contact 2 energizes the clear signal Sp over front contact 2 of relay HR. When the rail length B is finally empty the relay HR is de-energized and signal Sp is now directly energized over front contacts 1 of the two track relays GRI, GRII. The secondary relays HEI and HEII, Fig. 1, or HBI and HBII, Fig. 3, are electrically interlocked. Another arrangement, Fig. 2 (not shown), has two opposite short insulated rails at the crossing which are normally connected one to the advance insulated rail length and the other to the rear insulated rail length, but when a train enters the front length, the short rail normally connected to the rear length is disconnected and earthed by the secondary relay. Where, adjacent to a main level crossing, there is a subsidiary level crossing which crosses an insulated rail length, there is provided in that rail length a short intermediate insulated rail normally disconnected from the rail length but which is connected thereto when the track relay drops.