Mitsubishi Electric Q Series Reference Manual page 69

3 SPECIFICATIONS
Q25H
CPU
Q25H
CPU
3 - 18
(5) Prevention of station failure by using external power supply (Optical
loop system)
Direct power supply (24 V DC) from outside to network modules will prevent the
loopback operation. Because of this, station(s) placed between faulty stations
will not go down when more than one station go down, (The QJ71LP21S-25 is
the network module where power can be supplied from outside.)
Even if the distance between normally operating stations (1Ns2 and 1Ns4, 1Ns4
and 1Ns6) is 1 km or more, normal data link will be available
External power
supply
1M 1
P
QJ71LP
21S-25
1km
QJ71LP21S-25
Q25H
1N 6
S
External power
supply
If the network modules without external power supply (QJ71LP21-25)
are placed in 1Ns3 and 1Ns5, stations between them will go down.
REMARKS
Even if the Q25HCPU of the control station is powered OFF, the control station
status will not shift to other station since the network module functions normally.
External power
supply
1Ns2
QJ71LP
Q25H
21S-25
CPU
1km
QJ71LP21S-25
CPU
1N 5
S
External power
supply
Loopback
1M 1 1N
P
1N 6 1N
s s
Loopback
External power
supply
1N 3
S
QJ71LP
Q25H
21S-25
CPU
QJ71LP21S-25
Q25H
CPU
1N 4
S
External power
supply
2 1N 3
s s
5 1N 4
s
Down
MELSEC-Q
3 - 18