Mitsubishi Electronics MELSECNET-H User Manual
Mitsubishi PLC
MELSECNET/H Network Module
QJ71LP21S-25
2002 No.189E
NEW PRODUCT RELEASE
New!
The QJ71LP21S-25 is suitable for systems where the operation cannot be interrupted, such as LCD (Liquid
Crystal Display) and semiconductor production lines.
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[Features]
zExternal power supply prevents station from failing when power supply fails
(1) When the PLC system power supply is accidentally stopped, the QJ71LP21S-25 works as a repeater using
the power supplied from an external power supply, which inhibits the communication disruption. While
more than one station fails, the stations located between the failed ones will continue with data link.
When the normal power supply is resumed, the QJ71LP21S-25 stops as a repeater and restarts its normal
operation.
(a) Network system using only QJ71LP21S-25
Control station (station No.1)
External
power supply
External
power supply
Normal station (station No.2)
External
power supply
External
power supply
Normal station (station No.3)
External
power supply
External
power supply
When the power to normal stations
(No.3 and No.5) fails, the network
line is not disconnected, because
of external power supply to
QJ71LP21S-25.
The network line remains connected
and normal station (No. 4) continues
data link.
Normal station (station No.6)
(b) Network system using only QJ71LP21-25
Control station (station No.1)
Loopback
Normal station (station No.6)
(c) Network system using both QJ71LP21-25 and QJ71LP21S-25
Control station (station No.1)
Normal station (station No.5)
Normal station (station No.2)
Loopback
Normal station (station No.5)
Normal station (station No.2)
External
power supply
Normal station (station No.4)
Normal station (station No.3)
Normal station (station No.4)
Normal station (station No.3)
External
power suppl
When the power to normal stations
(No.3 and No.5) fails, the network
line is disconnected, therefore
normal station (No.4) cannot
continue data link.
Normal station (station No.6)
Normal station (station No.5)
Normal station (station No.4)
The station with power failure that works as a repeater does not execute data link same as a conventional
system. Therefore, normal communication stations detect this station as a data link error station, and the
B/W device hold the status before failure.
(2) When a module other than a network module fails, the faulty module can be replaced without the data link
disruption.
(3) The QJ71LP21S-25 guards against the consequence of power failure and loopback, the link scan time of the
network is kept stable.
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