Automating Manufacturing Systems - Process Control and ...

plc states - 12.7
Step 2: Define State Transition Triggers, and add them to the list of states
Description # L1 L2 L3 L4 L5 L6 transition
Green East/West 1
1 0 0 0 0 1 S1
Yellow East/West 2 1 0 0 0 1 0 delay
0 0 1 1 0 0
4sec
Green North/South 3
S2
Yellow North/South 4 0 1 0 1 0 0
delay 4 sec
Figure 12.7
State Table with Transitions
A state diagram for the system is shown in Figure 12.8. This diagram is equivalent
to the state table in Figure 12.7, but it can be valuable for doing visual inspection.
Step 3: Draw the State Transition Diagram
delay 4sec
grn. EW
pushbutton NS (i.e., S1,S2 = 10)
yel. NS
first scan
delay 4sec
yel. EW
pushbutton EW (i.e. 01)
grn. NS
Figure 12.8
A Traffic Light State Diagram
12.1.2 Conversion to Ladder Logic
12.1.2.1 - Block Logic Conversion
www.PAControl.com