Automating Manufacturing Systems - Process Control and ...

plc states - 12.28
UPDATE OUTPUTS
ST1
L1
ST2
ST4
L2
ST3
L3
ST3
L4
ST4
ST2
L5
ST1
L6
Figure 12.30
Ladder Logic for the State-Transition Equations
The problem of prioritization also occurs with the State-Transition equations.
Equations were written for the State Diagram in Figure 12.31. The problem will occur if
transitions A and C occur simultaneously. In the example transition T2 is given a higher
priority, and if it is true, then the transition T3 will be suppressed when calculating STC.In
this example the transitions have been considered in the state update equations, but they
can also be used in the transition equations.