Mitsubishi Electric MELSEC iQ-R Series - Fail-Safe Measures for Programmable Controller Failure

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APPX
Appendix 8 General Safety Requirements
Fail-safe measures for programmable controller failure
A CPU module and a remote head module can detect hardware failures of themselves and their memory by the self-
diagnostic function. However, failures which occur in a part, such as an I/O control part, may not be detected.
In this case, depending on the failure, all input or output points may turn on or off, or normal operation and safety of the
control-target device may not be ensured.
Even though Mitsubishi programmable controllers are manufactured under strict quality control, they may fail due to some
reasons. Provide fail-safe circuits external to the programmable controller so that no machine is damaged and no accident
occurs.
A system example and its fail-safe circuit example are shown below.
*1 Mount an output module for fail-safe purpose in the last slot of the system. In the example above, Y80 to Y8F are assigned to the output
module.
*2 Since Y80 turns on and off at 0.5 second intervals, use a contactless output module. (In the example above, a transistor output module
is used.)
*1
Power supply module CPU module X00 to X0F X10 to X1F X20 to X2F X30 to X3F Y40 to Y4F Y80 to Y8F
Empty
Y50 to Y5F Y60 to Y6F Y70 to Y7F Power supply module
SM412
1s
1s
MC
T2T1
Y80
Y81
Y8F
24V
0V
Y80
Y80
0.5s0.5s
MC
…
…
T1
T2
24VDC
Load
Load
CPU module
Internal program
On delay timer
Off delay timer
Output module
*2