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176
Indicator
Memory
Reset:
after 2 seconds
Table 4: Preventing an Indicator from Flickering
When the first axle of a passing train touches the track contact, then the indicator is
turned on. When this axle leaves the track contact, then the indicator remains turned on
until the 2 seconds have passed. If the next axle of the train touches the track contact
before the timer expires then the indicator will remain turned on for another 2 seconds
and so on. The indicator is turned off when no further axle of the train touches the track
contact, i.e. when the train has passed the contact completely. In the software the indicator
is turned on only once regardless how much cars and axles the train contains.
Preventing contacts from flickering is especially recommended when feedback indicators
are being used for automatic control of trains. Each indicator symbol, that is being
passed by a train under automatic control of the computer, should be turned
on only once by the passing train. Indicators, that are turned on two or more times by
the same passing train (“flickering”) may mislead the software and can cause unexpected
behaviour of the affected trains.
12.2 Protection and Locking with Conditions
In addition to the locking mechanisms provided by routes, there are even more possibilities
for locking and protection. It is possible to restrict the operation of switches,
signals, accessories and routes to certain conditions called conditions. For instance, it is
possible to specify that a certain switch may be operated only if a certain dependent
signal is red. Even more complex conditions, which depend on the combination of several
objects, can be specified. For instance, it is possible to specify that a certain signal
may be turned to green only if the switch behind the signal is closed and the track section
behind the switch is not occupied.
Such conditions are specified by assigning a condition to the respective element. This is
done by selecting the symbol of the element and using the Properties command of the
Edit menu. In the following dialog select the tab labelled Conditions. Now select the
state that will be affected by the condition – in the second example mentioned above,
the state green of the signal - as well as the elements that will be checked to verify
whether the condition applies or not. Also in the example, you would have to select the
switch that will be closed and an appropriate contact indicator that indicates, whether
the track section behind the switch is occupied.