Automating Manufacturing Systems - Process Control and ...

plc states - 12.19
Now, simplify these for implementation in ladder logic.
ST1 = ( ST1 + ST4 ⋅ TON 2
( ST4,
4)
) ⋅ ( ST1 + S1 + S2)
+ FS
ST2 = ( ST2 + ST1 ⋅ S1 ⋅ S2) ⋅ ( ST2 + TON 1
( ST2,
4)
)
ST3 = ( ST3 + ST2 ⋅ TON 1
( ST2,
4)
) ⋅ ( ST3 + S1 + S2)
ST4 = ( ST4 + ST3 ⋅ S1 ⋅ S2) ⋅ ( ST4 + TON 2
( ST4,
4)
)
Figure 12.21
Simplified Boolean Equations
These equations are then converted to the ladder logic shown in Figure 12.22 and
Figure 12.23. At the top of the program the two timers are defined. (Note: it is tempting to
combine the timers, but it is better to keep them separate.) Next, the Boolean state equations
are implemented in ladder logic. After this we use the states to turn specific lights on.