Insulated rail

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The insulated rail is a safety mechanism of the German railways, which is mainly used in old mechanical and electromechanical interlockings, but also in older relay interlockings.

It consists of a short piece (approx. 25 to 30 meters) of rail that is galvanically decoupled from the rest of the track by two insulating joints. Its functionality is similar to that of a track circuit for track vacancy detection. The main purpose is to ensure the participation of a train for the back block and as a resolution criterion for the exit.

The insulated rail consists of a rail contact and a track circuit . The rail contact ensures that a train has definitely traveled (first axis). The track circuit ensures that the train that has driven has actually left the area of ​​the isolated rail (last axis).

functionality

The insulated rail consists of a rail contact and a short track circuit. Vehicles must recognize the length of the track circuit reliably, so the distance must not be less than the minimum center distance of the vehicles. A value of 30 meters is specified. The circuit is implemented using relay technology. There are wall groups for installation in signal boxes without a relay room, and in rare cases relay groups that correspond to the vascular system of the respective signal box design. The relays for the isolated rail are usually also integrated in relay block groups. For the older types, which were equipped with magnetic switches from the United Railway Signal Works, the designations Magnetic Switch Group Design 1932 and Magnetic Switch Group Design 1943 are common.

The circuit of the back block release or the route key lock is switched on by turning the signal lever (or the signal driving position), the route resolution when the route is determined. The track relay picks up because the isolated rail is free (closed-circuit principle). If the first axle of the train drives on, the track relay drops out. If this axis reaches the rail contact, it closes and the associated rail contact relay picks up. It is held by means of a self-holding contact, which means that the first axis tripping relay picks up. If the last axis leaves the area of ​​the insulated rail, the track relay picks up and then a second trigger relay, which triggers the route key lock or the back block release. This is a relay that technically releases the back block. If the section key lock is a jump key lock that is unlocked with a short pulse, the relay group is switched off again when it is triggered, whereby all relays drop out. If it is a permanent current key lock or in the case of the back block unlocking device on the relay block, the relay group is only switched off when the back block is released, and when the route is cleared when the locking relay is tightened again. In the case of relay groups with three relays, the trigger relay on the last axis is omitted; it is replaced by a contact combination of the other three relays.

If the track circuit is disturbed, for example due to insufficient bedding resistance, you can still switch to the first axis criterion. In this auxiliary operating mode, only the presence of the train is checked. Leaving the train must be checked by the operator looking. In this case, the clearing of the section is replaced by the additional actuation of the help button . Because of the otherwise possible early resolution of routes, which would enable switches to be switched while the train is still in motion, there is no possibility of switching to the first axis in route resolution groups. If the route resolution is disturbed, the auxiliary resolution must be used.

If there is an automatic track vacancy detection system in the interlocking area anyway, a track section, usually the protective section behind the entry signal, is also used. If not already available, he receives an additional rail contact. This procedure can also be used when track vacancies are reported by axle counters.

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