Fault Examples With I/O Modules; Faults With The Input Circuit And The Corrective Actions - Mitsubishi MELSEC-A A2USHCPU-S1 User Manual

11. TROUBLESHOOTING

11.4 Fault Examples with I/O Modules

Examples of faults concerning I/O circuits and the corrective actions are explained.

11.4.1 Faults with the input circuit and the corrective actions

Examples of faults concerning input circuits and the corrective actions are explained.
Situation
Example Input signal does not
1 turn OFF.
Example Input signal does not
2 turn OFF.
Example Input signal does not
3 turn OFF.
Example Input signal does not
4 turn OFF.
Table 11.2 Faults with the input circuit and the corrective actions
Cause
• Leak current from input switch
(driven by a contactless switch, etc.)
Leakage
current
Power supply
• Driven by a limit switch with a neon lamp
Leakage
current
Power supply
• Line capacity C of the leak current twisted pair
cable due to line capacity of the wiring cable
is about 100PF/m.
Leakage
current
Power supply
• Driven by a switch with LED indication
Leakage current
• Connect an appropriate resistor so that
voltage between the terminals of the input
module is lower than the OFF voltage.
AC input
Input
module
For CR constant,
0.1 to 0.47 F+47 to 120
• Same as the example 1.
• Or, provide a totally independent display
AC input
circuit separately.
Input
module
• Same as the example 1.
• However, it does not occur when power
supply is on the side of input device as shown
below.
AC input
Input
module
• Connect an appropriate resistance so that
voltage between the terminal of the input
module and the common is lower than the
OFF voltage as shown below.
DC input (sink)
Input
module
* An example of calculation of resistance to be
connected is provided on the following page.
11 - 23
Countermeasure
AC input
Input
R
module
(1/2W) is recommended.
AC input
Input
module
Power supply
DC input (sink)
Input
Resister
module