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Automating Manufacturing Systems - Process Control and ...

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plc flowchart - 11.5<br />

STEP 1: Add labels to each block in the flowchart<br />

START<br />

F1<br />

Open outlet valve<br />

Close inlet valve<br />

F2<br />

start button pushed?<br />

no<br />

F3<br />

yes<br />

Open inlet valve<br />

Close outlet valve<br />

F4<br />

Is tank full?<br />

yes<br />

F6<br />

Open outlet valve<br />

Close inlet valve<br />

no<br />

F5<br />

stop button pushed?<br />

yes<br />

no<br />

Figure 11.3<br />

Labeling Blocks in the Flowchart<br />

Each block in the flowchart will be converted to a block of ladder logic. To do this<br />

we will use the MCR (Master <strong>Control</strong> Relay) instruction (it will be discussed in more<br />

detail later.) The instruction is shown in Figure 11.4, <strong>and</strong> will appear as a matched pair of<br />

outputs labelled MCR. If the first MCR line is true then the ladder logic on the following<br />

lines will be scanned as normal to the second MCR. If the first line is false the lines to the

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