Automating Manufacturing Systems - Process Control and ...

plc states - 12.29
STA
T5
B
T4
D
STC
A
T2
STB
C
T3
T1
first scan (FS)
T1
=
FS
STA = ( STA + T2) ⋅ T5
T2
=
STB ⋅ A
STB = ( STB + T5 + T4 + T1) ⋅T2 ⋅T3
T3
=
STB ⋅ C
STC = ( STC + T3 ⋅ T2) ⋅ T4
T4
=
STC ⋅ D
T5
=
STA ⋅ B
Figure 12.31
Prioritization for State Transition Equations
12.2 SUMMARY
• State diagrams are suited to processes with a single flow of execution.
• State diagrams are suited to problems that has clearly defines modes of execution.
• Controller diagrams can be converted to ladder logic using MCR blocks
• State diagrams can also be converted to ladder logic using equations
• The sequence of operations is important when converting state diagrams to ladder
logic.
12.3 PRACTICE PROBLEMS
1. Draw a state diagram for a microwave oven.
www.PAControl.com