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(3) Fail-safe measures against C Controller system failure
Failure of the C Controller module is generally detected by the
self-diagnostic function. However, if an I/O control part is faulty, the failure
may not be detected by the C Controller module.
In such a case, all the I/O may turn ON or OFF depending on the failure,
and normal operation and safety of the control target may not be ensured.
Though Mitsubishi products are manufactured under strict quality control,
the C Controller system may fail for unspecific reasons. To prevent
mechanical damage and/or accidents in that case, please configure a
fail-safe circuit outside the C Controller module.
The following shows a system example and a fail-safe circuit example.
16
points
*1 The output module for fail-safe should be loaded in the last slot of the
system. (Y80 to Y8F in the above system.)
<Fail-safe circuit example>
User program*
Y80
0.5s 0.5s
C Controller module
*2 Create a program so that Y80 alternates between ON and OFF at
intervals of 0.5 s. (Use the QBF_Y_Out_BitEx function to turn Y80
ON/OFF.)
*3 Y80 repeats turning ON and then OFF at 0.5s intervals.
Use a no-contact output module (transistor in the example shown
above).
16
16
16
16
points
points
points
points
2
Y80
Y81
Y8F
24V
0V
Output
module*
14
16
points
On delay timer
T1
Off delay timer
T2
External load
L
L
T1
T2
3
16
16
16
points
points
points
Y80 to
Y8F
Output module for
fail-safe purpose *
1s
1s
MC
24VDC
MC
1
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