Siemens SIMATIC S7-300 Quick Start Manual page 16

Defining and Structuring the Control Task
What Safety You must take into account the following safety requirements in order to
Requirements
prevent any hazard to pedestrians or drivers:
Apply?
What Other Apart from the safety requirements, you must now define how long the
Requirements
individual signal phases are to last and when they are to start:
Apply?
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
via yellow (2 s)
to red (16 s).
Figure 2-3 Schematic Overview of the Traffic Light Control Sequence
2-4
The default setting should be green for the traffic light and red for the
pedestrian light, in order to define a safe starting point.
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.
The yellow phase for vehicle traffic is to last 3 seconds.
The red phase for vehicle traffic is to last 16 seconds and it is to start
simultaneously with the green phase for pedestrians.
The green phase for pedestrians is to last 10 seconds.
As soon as the green phase for pedestrians has finished, the pedestrian
signal is to change to red.
The red/yellow phase for vehicle traffic is to last 3 seconds.
The delay for the next green request for pedestrians is to last 1 second.
Default setting
Request for green for
pedestrian lights.
Delay for next green request (1 s).
Green for vehicle lights
Pedestrian lights switch to green
and back to red after 10 s.
Vehicle lights switch after delay
of 6 s from red via yellow
(3 s) to green.
Primer: S7-300 Programmable Controller, Quick Start
C79000-G7076-C500-01