Automating Manufacturing Systems - Process Control and ...

plc states - 12.16
Figure 12.17
State Diagram for Prioritization Problem
STC
MCR
D
U
STC
L
STB
MCR
Figure 12.18
State Diagram for Prioritization Problem
The Block Logic technique described does not require any special knowledge and
the programs can be written directly from the state diagram. The final programs can be
easily modified, and finding problems is easier. But, these programs are much larger and
less efficient.
12.1.2.2 - State Equations
State diagrams can be converted to Boolean equations and then to Ladder Logic.
The first technique that will be described is state equations. These equations contain three
main parts, as shown below in Figure 12.19. To describe them simply - a state will be on if
it is already on, or if it has been turned on by a transition from another state, but it will be
turned off if there was a transition to another state. An equation is required for each state
in the state diagram.
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