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Flagmen and Conditions
It is also possible to assign a condition to a flagman (see section 12.2, “Protection and
Locking with Conditions”). The condition is additionally checked each time, after the
trigger of the flagman has been activated and before the flagman is turned on. If the
condition does not apply the flagman remains turned off. This is also analogously true
for the triggers and conditions of signals (see section 12.5).
The following example demonstrates an application of this feature.
Example: Detecting Train Direction
The condition of a flagman can be used to detect the direction of a passing train.
Trigger Flagman
Condition
Diagram 124: Detecting Train Direction
On the track section displayed above, an operation should be performed by trains running
from the left to the right. If a train passes from the right to the left, then nothing
should happen. For this purpose, a detection mechanism that is activated by trains running
from the left to the right only is needed.
In order to create this detection mechanism, two track sensors are placed on the track
section. The distance between these sensors should be smaller than the length of the
shortest train passing this section.
The following steps should be executed:
• Create a switchboard and draw the track diagram displayed above.
• Place two contact indicators (see section 4, “Contact Indicators”) in the track diagram
and specify the digital addresses of the respective track sensors.
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