Mitsubishi MELSEC-Q Series User Manual page 196

5
SETTINGS AND PROCEDURES BEFORE OPERATION
(3) Fail-safe measures against C Controller system failure
5
- 10 5.2 Fail-safe Circuit
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.
* 1 The output module for fail-safe should be loaded in the last slot of the system. (Y80 to Y8F in the
above system.)
User program *2
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).
Figure 5.6 Fail-safe circuit example
16 points 16 points
No. of slots 16 points
1
Output module for fail-safe *
No. of slots 16 points 16 points 16 points
Figure 5.5 System example
On delay timer
Y80
Off delay timer
External load
Y81 L
L
Y8F
24V
0V
Output module
T1
*3
16 points 16 points
16 points
T1
1s
T2
1s
MC
24VDC
T2
MC