Mitsubishi Electric Melsec A Series, Руководство пользователя

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(2) Fail-safe measures to cover the possibility of PC failure
Problems with a CPU or memory can be detected by the self diagnosis function.
However, problems with I/O control area may not be detected by the CPU.
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 PCs are manufactured under strict quality control, they may
cause failure or abnormal operations due to unspecified reasons. To prevent
abnormal operations of whole system, machine breakdown, and accidents, build
a fail-safe circuit outside the PC.
The following gives an example of a fail-safe circuit.
Internal program
M9032
T1
ON delay timer
1 sec.
T2
OFF delay timer
1 sec.
L
L
MC
T2 T1
+ –
24 VDC
Y00
Y01
Y0F
24V
0V
Y00
Y00
External load
0.5 sec. 0.5 sec.
CPU module Output unit
*1
MC
*1 Since Y00 alternates between ON and OFF at 0.5 second intervals, use a contactless output
module (in the above example this is a transistor).
*2 If an OFF delay timer (especially a miniature timer) is not available, use ON delay timers to
make a fail-safe circuit as shown below.
A fail-safe circuit built with ON delay timers
Y00
Y00
MC
M2
M1
M1
M2
1s
T1
Y00
Y01
to
Y0F
24V
24VDC
0V
M9032
T1
M1
MC
L
to
L
T2
– +
Internal program
On-delay timer
External load
CPU module Output module
*1
1s
T2
M2
On-delay timer
0.5 sec. 0.5 sec.