Chapter 16 PLC Function ApplicationsMS300 (High Speed Model)
16-20
Example 3: Setting (SET) and reset (RST) command protective circuit
The following figure shows a protective circuit composed of RST and SET commands.
Priority stop occurs when the RST command is placed after the SET command. Because
the PLC executes programs from the top down, at the end of the program, the state of Y1
will indicate whether coil Y1 is electrified. When X1 and X2 are both actuated, Y1 will lose
power, and this is therefore priority stop.
Priority start occurs when the SET command is placed after the RST command. When X1
and X2 are both actuated, Y1 will be electrified, and this is therefore priority start.
SET
Y1
RST
Y1
X1
X2
Top priority of stop
SET
Y1
RST
Y1
X2
X1
Top priority of start
Commonly-used control circuits
Example 4: Conditional control
X1, X3 are respectively start/stop Y1, and X2, X4 are respectively start/stop Y2; all have
protective circuits. Because Y1's NO 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 be actuated before Y2 can be actuated.
X1
X3
Y1
Y1
X2
X4
Y2
Y2
Y1
X1
X3
X2
X4
Y1
Y2
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