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11 I/O MODULE TROUBLESHOOTING
11. I/O MODULE TROUBLESHOOTING
11
11.1 Input Circuit Troubleshooting
Condition
An input
signal does
not turn off.
An input
signal does
not turn off.
An input
signal does
not turn off.
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This chapter explains possible problems with I/O circuits and their corrective actions.
This section describes possible problems with input circuits and their corrective
actions.
Table 11.1 Input Circuit Problems and Corrective Actions
Cause
• Leakage current of input switch
(e.g. drive by non-contact switch).
• Drive by a limit switch with neon lamp.
• Leakage current due to line capacity of wiring
cable.
(Line capacity C of twisted pair wire is approx.
100 pF/m).
Corrective action
Connect an appropriate resistor so that the
voltage across the terminals of the input module
will be less than the off voltage.
It is recommended to use 0.1 to 0.47 F + 47 to
120Ω (1/2W) for the CR constant.
• Same as Example 1.
• Or make up another independent display
circuit.
• Same as Example 1.
• However, leakage current is not generated
when the power supply is located in the input
equipment side as shown below.
(To the next page)
MELSEC-Q
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Troubleshooting
