User`s manual

I/O circuit troubleshooting Troubleshooting
MELSEC System Q, Hardware 11 – 101
2 The load which was
turned off is turned on
for a moment at
power-off.
The load [2] which was turned OFF may be turned ON due
to back electromotive force at the time of power-off if an
inductive load [1] is used.
Take either of the following measure:
 To prevent the generation of the back
electromotive force, connect diode in
parallel with load where the back
electromotive force has been gener-
ated.
 Connect diode between (+) and (–) of
the external power supply so that a
sneak path circuit is porvided.
Connect the diode to C1 and R1 in
parallel when example 1 is performed
simultaneously.
* Measures will not be effective to the Output module
QY81P due to the characterictic of external power
supply circuit.
As for D1, choose a diode with following
specifications:
– Reverse current:
Approx. 10 times the rated voltage
of the spec.
– Forward current:
More than 2 times the Max. load
current (common) of the spec.
Exam-
ple
Condition Cause Corrective action
Tab. 11-1: Output circuit troubleshooting
Source output
Load 1
Load 2
Shut off
ON
OFF
Back electromotive
force
Sink output
Load 1
Load 2
Shut off
ON
OFF
Back electromotive
force
Load
Back electromotive force
Source output
Load
Back electromotive force
Sink putput
Source output
Load 1
Load 2
ON
Shut off
Back electromotive force
Example 1
OFF
Sink output
Load 1
Load 2
Load 1
Shut off
Back electromotive force
Example 1
ON
OFF