Prevention Of Erroneous Inputs And Outputs To/From Remote I/O Modules - Mitsubishi FX3UC SERIES User Manual

FX Series Programmable Controllers
3UC
User's Manual - Hardware Edition

12.7.5 Prevention of erroneous inputs and outputs to/from remote I/O modules

In order to prevent erroneous inputs to and outputs from remote I/O modules, design the system under
consideration of the contents described below.
1. When setting the power to ON or OFF
When using a power supply adapter or dedicated power supply, turn ON the power of the remote I/O units
(power supply adapter and dedicated power supply) before starting data link.
Stop the data link first, and then turn OFF the power to the remote I/O modules (power adapter or dedicated
power supply).
Built-in master
(data link status)
Remote I/O module
(power supply status)
2. When the power is interrupted instantaneously in a remote I/O module
When the power (24V DC) supplied to a remote I/O module is interrupted instantaneously, erroneous inputs
may occur.
3. Cause of erroneous inputs due to instantaneous power interruption
The hardware of a remote I/O module converts the unit power (24V DC) into 5V DC before using it.
If instantaneous power interruption occurs in a remote I/O module:
Time until 5V DC inside remote I/O module turns OFF > Response time for "ON → OFF" of input unit
As a result, if refresh is executed in the period shown in (A) below, erroneous inputs occur.
(Erroneous inputs may occur especially while the input response time is set to high-speed input type.)
Remote I/O module
(Unit power supply and external
power supply to input area)
Remote I/O module
(internal 5V DC)
Input (Xn)
408
Data link start
Executing
Stopped
ON
OFF
When the external power supply to the
input area is set to OFF, the input (Xn)
turns OFF after the response time for
"ON→OFF" of the input unit.
12 Test Operation, Adjustment, Maintenance and Troubleshooting
12.7 FX3UC-32MT-LT Built-in CC-Link/LT Troubleshooting
Data link stop
(A)
When the external power supply to the
input area is set to ON, the input
(Xn) turns ON after the response time for
"OFF→ON" of the input unit.