106
11 TROUBLESHOOTING
11.4 Examples of Troubles with the I/O Module
An input signal does not turn off No.3
■Cause
There is a leakage current due to the line capacity of the wiring cables. (The line capacity, C, of a twisted pair cable is as
follows: C = approx. 100pF/m.)
■Action
Connect an appropriate resistor so that the voltage between terminals of the input module would fall below the OFF voltage.
(Same as the action taken when an input signal does not turn off No.1)
A leakage current is not generated, however, where the power supply lies in the input device side like the figure below:
An input signal does not turn off No.4
■Cause
Even though the switch with LED indicator is turned off, leakage current exceeding the OFF current flowing through the input
module has occurred.
■Action
Connect an appropriate resistor so that the current flowing through the input module falls below the OFF current.
For the calculation example of a resistor to be connected, refer to the following.
Page 107 Calculation example
C
Power supply
AC input
Input module
Leakage
current
Power supply
AC input
Input module
DC input (sink)
Input module
Leakage current
DC input (sink)
Input module
Resistor
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