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2 SYSTEM CONFIGURATION
MELSEC-QnA
2.2.2 Precautions when configuring a system
Design the system with the following considerations to prevent mis-input from the
remote I/O module:
(1) During power on and power off
Start the data link after turning on the power for the remote I/O module.
Turn off power for the remote I/O module after stopping the data link.
During stop
During
operation
ON
OFF
Master module
(Data-link status)
Remote I/O module
(Power supply status)
Data link start Data link stop
(2) During momentary power failure of the remote I/O module
When momentary power failure occurs with the power (24VDC) supplied to the
remote I/O module, mis-input may occur.
(a) Cause for mis-input due to a momentary power failure
The remote I/O module hardware uses the power after internally converting
the module power (24VDC) in to 5VDC.
When momentary power failure occurs with the remote I/O module, the
following condition occurs:
(Time for the 5VDC in the internal remote I/O module to turn off) > (input
module on
off response time)
Therefore, mis-input is caused when a refresh is performed within the time
indicated by
1
) in the diagram below.
Remote I/O module
(Module power supply
and input external-power
supply)
Remote I/O module
(Internal 5VDC)
Input (Xn)
Because the input external-power supply is turned off,
the input (Xn) turns off after the response time of input
module is turned off.
1