User`s manual

11 - 7 11 - 7
MELSEC-Q
11 I/O MODULE TROUBLESHOOTING
Table 11.2 Output Circuit Problems and Corrective Actions (Continued)
Condition Cause Corrective Action
Example 5
The load
which was
turned OFF
is turned
ON for a
moment at
power-off.
(Transistor
output)
The load [2] which was turned OFF may be
turned ON due to back electromotive force at
the time of power-off [1] if an inductive load is
used.
[1]
Shut off
[2]
[3]
TB1 ON
TB2 OFF
COM+
CTL-
TB1 ON
TB2 OFF
COM-
CTL+
ON
OFF
ON
OFF
Output module,
ombined module
Source output
Load
Load
Back electromotive
force
Load
Load
Back electromotive
force
[1]
Shut off
Output module,
ombined module
Sink output
[2]
[3]
To prevent the generation of the back
electromotive force, connect diode in parallel
with load where the back electromotive force
has been generated.
Source output
[3]
Load
Back electromotive
force
Sink output
[3]
Back electromotive
force
Load