Mitsubishi MELSEC System Q User Manual

Automatic shutdown
When a PLC is used to control motion sequences in which hazards can arise when compo
-
nents move past certain points additional limit switches must be installed to interrupt the move
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ment automatically. These switches must function directly and independently of the PLC. See
Chapter 4.9.1 for an example of such an automatic shutdown facility.
Output signal feedback
Generally, the outputs of PLCs are not monitored. When an output is activated the program
assumes that the correct response has taken place outside the PLC. In most cases no addi
-
tional facilities are required. However, in critical applications you should also monitor the out
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put signals with the PLC – for example when errors in the output circuit (wire breaks, seized
contacts) could have serious consequences for safety or system functioning.
MELSEC System Q Beginners Manual 4 – 33
An Introduction to Programming Safety First!
X000 X001
COM Y010
X002
Y011
In the example on the right a make contact in
contactor K1 switches input X002 on when out-
put Y10 is switched on. This allows the pro-
gram to monitor whether the output and the
connected contactor are functioning properly.
Note that this simple solution does not
check
whether the switched equipment is functioning
properly (for example if a motor is really turn
-
ing). Additional functions would be necessary
to check this, for example a speed sensor or a
voltage load monitor.
+24 V
K1
PLC
K2
K1 K2
K1
X000 X001
COM Y010
X002
Y011
The example on the right shows such an inter
-
lock with contactor contacts. Here it is physi
-
cally impossible for contactors K1 and K2 to be
switched on at the same time.
PLC

Mitsubishi MELSEC System Q Specifications

General

Brand	Mitsubishi
Model	MELSEC System Q
Category	Controller
Language	English