Mitsubishi Electric MELSEC Q Series User Manual page 500

(3) Fail-safe measures against C Controller system failure
The C Controller module can detect its own failure by the self-diagnostic function.
However, it may not be able to detect a failure that occurred in an I/O control part.
In such a case, all of inputs and outputs may turn on or off depending on the failure, and normal operation of the
control target and safety may not be ensured.
Though Mitsubishi Electric products are manufactured under strict quality control, it is recommended to configure
external fail-safe circuits so that a C Controller system failure will not result in mechanical damage or accidents.
The following shows a system example and a fail-safe circuit example.
*1 : The output module for fail-safe must be installed as the terminal module of the system.
(Y80 to Y8F in the above system)
Y80
C Controller module
*2 : Create a program so that Y80 alternates between ON and OFF at intervals of 0.5 seconds.
• <Q24DHCCPU-V/-VG and Q12DCCPU-V(Extended mode)>
Use the QBF_Y_Out_BitEx function.
<Q24DHCCPU-LS and Q26DHCCPU-LS>
Refer to the manual of the partner (operating system vendor), or consult the partner (operating system vendor).
*3 : Since Y80 turns on and off at 0.5s intervals, use a non-contact output module (a transistor in the above example).
498
Points per slot
Output module for fail-safe
Points per slot
*2
User program
0.5s 0.5s
Output module
Input Input
0 0 32 32
*1
Output Output Output Output
16 16 16 16
Y80
Load
Y81
Load
Y8F
24V
0V
*3
T1
Output
16
Empty
ON delay timer
T1
1s
OFF delay timer
T2
1s
MC
24VDC
T2
MC