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sensors. More details about running several digital systems, simultaneously, are outlined
in section 15.3, “Operating Several Digital Systems Simultaneously”.
Feedback sensors are distinguished between momentary track contacts and occupancy
sensors. In TrainController the same symbol is used for both types of contacts. The
difference between both types of contacts does not play an important role as long as
trains are not operated under control of the Visual Dispatcher (see section 5, “The Visual
Dispatcher”).
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Momentary Track Contacts vs. Occupancy Sensors
Momentary track contacts are turned on for a short moment, when a train passes a certain
point on the model railroad. They stay turned on only for a short moment and are
turned off as soon as the train moves any further. In Diagram 68 to Diagram 70 you can
see a momentary contact triggered by a passing train. Momentary track contacts indicate
that a train is about to pass a certain point. Occupancy sensors are turned on when
a train enters a certain section on the model railroad. They stay turned on until the train
leaves that section completely. Occupancy sensors indicate that a train is located inside
a certain track section. In Diagram 71 to Diagram 74 you can see an occupancy sensor
turned on and off by a passing train. Occupancy sensors are able to report the presence
of a train inside a certain track section even if the train is not moving. Momentary contacts
are triggered by moving trains only. Momentary contacts can be made for instance
by mechanical track contacts, reed contacts or optical sensors. Occupancy sensors are
often based on current sensing in isolated track sections.
Unlike other programs which require occupancy sensors for automatic train control
TrainController is also able to control trains if only momentary track contacts are
used. Occupancy sensors are more safe, though, because with momentary contacts special
measures against premature release of blocks and routes must be taken.
The following diagrams show the behaviour of a momentary contact in the different
phases while a train is passing. The position of the momentary contact is marked with a
short vertical line.