Mitsubishi Electric MELSEC FX3U Programming Manual page 95

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
2. Latched (battery backed) type
When the power is turned OFF while the PLC is operating, all of the output relays and general type auxiliary
relays turn OFF.
When restoring the power again, all of the output relays and general type auxiliary relays remain OFF except
those whose input condition is ON. In some output relays and auxiliary relays, however, the ON/OFF status
just before power failure should be stored and then replicated when restoring the power, depending on control
targets. In such a case, use latched (battery backed) type auxiliary relays.
In FX /FX PLCs, latched (battery backed) type devices are backed up by the battery built into the PLC.
3U 3UC
In FX PLCs, latched type devices are backed up by the EEPROM built into the PLC. When the optional
3G
battery is installed, the battery backs up some general type devices.
X000 X001
M600
Backup against power failure
(self-holding circuit)
X000
X001
Backup against power failure
1) Application example of latched (battery backed) type auxiliary relays
Limit switch
Left limit
LS1 (X000)
Table in reciprocating motion
X000 X001
M600
X001 X000
M601
2) Method for using a fixed latched (battery backed) type auxiliary relay as a general type auxiliary relay
When using a fixed latched (battery backed) type auxiliary relay as a general type auxiliary relay, provide
a reset circuit shown in the figure below around the head step in the program.
Ex. Fx /FX
3U 3UC
M8002
Initial pulse
M600
PLC
SET M600
RST M600
PLC
(set/reset circuit)
Limit switch
Right limit
LS2 (X001)
Motor with brake
M600
Rightward
drive
command
M601
Leftward drive
command
PLCs
FNC 040
M1024
ZRST
M1024 to M1999 are initialized.
→ For details on backup method against power failure,
The figure on the left shows an operation example of
M600 (latched [battery backed] type device) in a self-
holding circuit.
When X000 turns ON and M600 turns ON in this circuit,
M600 holds its operation by itself even if X000 is
opened.
Because M600 is a latched (battery backed) type
device, it remains activated when the operation is
restarted even after X000 has turned OFF due to power
failure. If an NC contact of X001 is opened when the
operation is restarted, however, M600 is deactivated.
The figure on the left shows a circuit using the SET and
RST instructions.
In some cases, the table should be restarted in the
same direction as the direction selected just before
power failure.
X000 = ON (at the left limit) → M600 = ON→ The table
is driven rightward. → The power is turned OFF. → The
table is stopped in an intermediate position. → The table
is restarted (M600 = ON). → X001 = ON (at the right
limit) → M600 = OFF, M601 = ON → The table is driven
leftward.
M1999
4 Devices in Detail
4.3 Auxiliary Relay [M]
refer to Section 2.6.
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