Automating Manufacturing Systems - Process Control and ...

plc states - 12.11
FIRST STATE WAIT FOR TRANSITIONS
B3/1
MCR
I/1
B3/1
U
I/1
B3/2
L
MCR
Figure 12.12
Ladder Logic for First State
The second state is more complex because it involves a time delay, as shown in
Figure 12.13. When the state is active the RTO timer will be timing. When the timer is
done state 2 will be unlatched, and state 3 will be latched on. The timer is retentive, so it
must also be reset when the state is done, so that it will start at zero the next time the state
starts.