Chapter 16 PLC Function ApplicationsMS300
680
Figure 16-39
Commonly used control circuits
Example 4: Conditional control
X1 and X3 respectively start and stop Y1; and X2 and X4 respectively start and stop Y2.
All have protective circuits. Because Y1's N.O. contact is in series with Y2's circuit, it
becomes an AND condition for the actuation of Y2. The action of Y1 is therefore a
condition for the action of Y2, and Y1 must actuate before Y2 can actuate.
X1
X3
Y1
Y1
X2
X4
Y2
Y2
Y1
X1
X3
X2
X4
Y1
Y2
Figure 16-40
Example 5: Interlocking control
The diagram below shows an interlocking control circuit. Depending on which of the start
contacts X1 or X2 becomes valid first, the corresponding output Y1 or Y2 actuates, and
when one actuates, the other does not actuate. Y1 and Y2 cannot actuate at the same
time (interlocking effect). Even if both X1 and X2 are valid at the same time, because the
ladder diagram program is scanned from the top down, it is impossible for Y1 and Y2 to
actuate at same time. This ladder diagram assigns priority only to Y1.
Figure 16-41
X1
X3
Y1
Y1
X2
X4
Y2
Y2
Y1
X1
X3
X2
X4
Y1
Y2
Y2
SET
Y1
RST
Y1
X2
X1
Top priority of start
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