Mitsubishi Electronics Q172CPU9(N) ユーザーズマニュアル

 
 

 

6 - 25 

6   INSPECTION AND MAINTENANCE 

 

6.6.3 I/O modules troubleshooting 

This section describes troubleshooting with I/O circuits and their corrective actions. 

 

(1)   Input circuit troubleshooting and corrective action 

This section describes troubleshooting with input circuits and their corrective 
actions. 

 

Input Circuit Troubleshooting and Corrective Action 

 Condition 

Cause 

Corrective 

action 

Example 1 

Input signal 
is not 
turned 
OFF. 

• Leakage current of input switch  

(e.g. drive by non-contact switch). 

Leakage

current

Input module

AC input

Power supply

 

• Connect an appropriate resistor which will 

make the voltage across the terminals of the 
input module lower than the OFF voltage 
value. 

AC input

Input module

 

It is recommended to use 0.1 to 0.47µF + 47 to 
120

(1/2W) for the CR constant. 

Example 2 

Input signal 
is not 
turned 
OFF. 

• Drive by a limit switch with neon lamp. 

Leakage

current

AC input

Input module

Power supply

 

• Same as Example 1. 
• Or make up another independent display 

circuit. 

Example 3 

Input signal 
is not 
turned 
OFF. 

• Leakage current due to wiring capacity of 

wiring cable.  
(Wiring capacity C of twisted pair wire is 
approx. 100 PF/m). 

Leakage

current

AC input

Input module

Power supply

 

• Same as Example 1. 
• However, leakage current is not generated 

when the power supply is located in the input 
equipment side as shown below. 

AC input

Input module

Power supply

 

Example 4 

Input signal 
is not 
turned 
OFF. 

• Drive by switch with LED indicator. 
 
 
 

Leakage

current

DC input

(plus common)

Input module

 

• Connect a register which will make the voltage 

between the input module terminal and 
common higher than the OFF voltage value, 
as shown below. 

DC input
(plus common)

Input module

Resistor

 

(Note-1) : A calculation example of a value for a 

connected resistor is given on the 
following page.