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Primer: S7-300 Programmable Controller, Quick Start
C79000-G7076-C500-01
You must take into account the following safety requirements in order to
prevent any hazard to pedestrians or drivers:
S The default setting should be green for the traffic light and red for the
pedestrian light, in order to define a safe starting point.
S If the program receives a request to change the pedestrian light to green
as a result of the pushbutton being pressed, the traffic light changes from
green to red via yellow, as shown in Figure 2-3.
Apart from the safety requirements, you must now define how long the
individual signal phases are to last and when they are to start:
S The yellow phase for vehicle traffic is to last 3 seconds.
S The red phase for vehicle traffic is to last 16 seconds and it is to start
simultaneously with the green phase for pedestrians.
S The green phase for pedestrians is to last 10 seconds.
S As soon as the green phase for pedestrians has finished, the pedestrian
signal is to change to red.
S The red/yellow phase for vehicle traffic is to last 3 seconds.
S The delay for the next green request for pedestrians is to last 1 second.
Figure 2-3 gives you a schematic overview of how the TLIGHT sample
program should work:
Red for pedestrian lights
Vehicle lights switch from green
Request for green for
pedestrian lights.
Pedestrian lights switch to green
Default setting
Green for vehicle lights
Vehicle lights switch after delay
of 6 s from red via yellow
(3 s) to green.
and back to red after 10 s.
to red (16 s).
via yellow (2 s)
Delay for next green request (1 s).
Figure 2-3 Schematic Overview of the Traffic Light Control Sequence
What Safety
Requirements
Apply?
What Other
Requirements
Apply?
Defining and Structuring the Control Task
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