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MELSEC-Q
11 TROUBLESHOOTING
Input Circuit Problems and Corrective Actions (Continued)
Condition Cause Corrective Action
Example 5
Input signal
does not
turn OFF.
• Sneak path due to the use of two power
supplies.
Input module
E
1
E
2
>
E
2
E
1
• Use only one power supply.
• Connect a sneak path prevention diode.
(Figure below)
Input module
E
1
E
2
Example 6
False input
due to
noise
Depending on response time setting, noise is
imported as input.
Change response time setting.
Example : 1ms
5ms
(Setting of a shorter response time may produce
a higher effect on periodic excessive noise.)If no
effects are produced by the above, take basic
actions to prevent excessive noise form
entering, e.g. avoid bundling the power and I/O
cables, and suppress noise by adding surge
absorbers to such noise sources as relays and
conductors used with the same power supply.)