Internal Input Circuit Troubleshooting - Mitsubishi Electric Melsec-Q172DCPU User Manual

6 INSPECTION AND MAINTENANCE

6.6.4 Internal input circuit troubleshooting

Table 6.4 Internal Input Circuit Troubleshooting and Corrective Action
Condition
• Drive by switch with LED indicator.
Internal input
signal is not
turned OFF.
• Sneak path due to the use of two power
supplies.
Internal input
signal is not
turned OFF.
This section describes possible problems with internal input circuits and their corrective
actions.
(1) Internal input circuit troubleshooting
The following describes possible problems with internal input circuits and their
corrective actions.
Cause
Leakage
current
DC input
E1 E2
E1>E2
<Calculation example of Example 1>
If a switch with LED display is connected to Motion CPU, and current of 4 [mA] is
leaked.
3.6k[ ]
(a) Because the condition for OFF voltage (0.9[mA]) of Motion CPU is not
satisfied. Connect a resistor as shown below.
3.6k[ ]
QDS
• Connect an appropriate resistor so that the current
across the Motion CPU becomes lower than the off
current.
DC input
(plus common)
Motion CPU
(Note): A calculation example of the resistance to be
• Use only one power supply.
• Connect a sneak path prevention diode.
(Figure below)
Motion CPU
Motion CPU
Leakage
Input signal
current 4[mA]
part
24VDC
Motion CPU
4[mA]
Iz=0.9[mA]
Iz=3.1[mA]
Input impedance
5.6k[ ]
24VDC
6 - 30
Corrective action
Resistor
connected is shown below.
E1 E2
DC input
(plus common)
Motion CPU
DC input
Motion CPU