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Automating Manufacturing Systems - Process Control and ...

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plc states - 12.28<br />

UPDATE OUTPUTS<br />

ST1<br />

L1<br />

ST2<br />

ST4<br />

L2<br />

ST3<br />

L3<br />

ST3<br />

L4<br />

ST4<br />

ST2<br />

L5<br />

ST1<br />

L6<br />

Figure 12.30<br />

Ladder Logic for the State-Transition Equations<br />

The problem of prioritization also occurs with the State-Transition equations.<br />

Equations were written for the State Diagram in Figure 12.31. The problem will occur if<br />

transitions A <strong>and</strong> C occur simultaneously. In the example transition T2 is given a higher<br />

priority, <strong>and</strong> if it is true, then the transition T3 will be suppressed when calculating STC. In<br />

this example the transitions have been considered in the state update equations, but they<br />

can also be used in the transition equations.<br />

www.PA<strong>Control</strong>.com

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