User`s manual

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MELSEC-Q
11 I/O MODULE TROUBLESHOOTING
Table 11.1 Input Circuit Problems and Corrective Actions (Continued)
Condition Cause Corrective Action
Example 4
Input signal
is not
turned
OFF.
• Drive by switch with LED indicator.
Leakage
current
DC input
(Positive common)
Input module
• Connect an appropriate resister, as shown
below, so that the current flowing along the
input module becomes below the OFF current.
Input module
Resistor
DC input
(Positive common)
A calculation example of a value for a
connected resistor is given on the following
p
a
g
e.
Example 5
Input signal
is not
turned
OFF.
• Sneak path due to the use of two power
supplies.
Input module
E
1
E
2
E
1
E
2
>
DC
Inpu
t
• Use only one power supply.
• Connect a sneak path prevention diode.
(Figure below)
Input module
E
1
E2
DC
Input
Example 6
Input signal
is not
turned ON
(AC input
module).
Stepwise distortion as shown below appears to
the zero cross voltage of input signal (AC).
Zero cross
voltage
Improve input signal waveform by using the on-
line system etc.
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 from
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
contactors used with the same power supply.)
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