Mitsubishi Q01CPU User Manual page 249

10
LOADING AND INSTALLATION
(3) Fail-safe measures against failure of the programmable controller
Failure of a CPU module or memory can be detected by the self-diagnosis function.
However, failure of I/O control area may not be detected by the CPU module.
In such cases, all I/O points turn ON or OFF depending on a condition of problem, and
normal operating conditions and operating safety cannot sometimes be maintained.
Though Mitsubishi programmable controllers are manufactured under strict quality
control, they may cause failure or abnormal operations due to unspecific reasons. To
prevent the abnormal operation of the whole system, machine breakdown, and
accidents, fail-safe circuitry against failure of the programmable controller must be
constructed outside the programmable controller.
Diagram 10.3 and Diagram 10.4 are a system example and its fail-safe circuit
example.
No. of slots 16 points 16 points
Output module for fail-safe purpose 1
No. of slots 16 points 16 points
* 1: The output module for fail-safe purpose should be loaded in the last slot of the system. (Y80 to
Y8F in the above system.)
Diagram 10.3 System example
16 points 16 points 16 points
16 points 16 points
10.1 General Safety Requirements
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