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FX Series Programmable Controllers Devices in Detail 4
4-4
4.3.2 Battery Backed/ Latched Auxiliary Relays
There are a number of batter
y
backed or latched rela
y
s whose status is retained in batter
y
backed or EEPROM memor
y
. If a power failure should occur all output and
g
eneral purpose
rela
y
s are switched off. When operation is resumed the previous status of these rela
y
s is
restored.
The circuit shown on pa
g
e 4-3 is an example of a self retainin
g
circuit. Rela
y
M507 is activated
when X0 is turned ON. If X0 is turned OFF after the activation of M507, the ON status of M507
is self retained, i.e. the NO contact M507 drives the coil M507.
However, M507 is reset (turned OFF) when the input X1 is turned ON, i.e. the NC contact is
broken.
A SET and RST (reset) instruction can be used to retain the status of a rela
y
bein
g
activated
momentaril
y
.
X0
SET M507
RST M507
X1
External loads:
• Auxiliar
y
rela
y
s are provided with countless number of NO contact points and NC
contact points. These are freel
y
available for use throu
g
h out a PLC pro
g
ram. These
contacts cannot be used to directl
y
drive external loads. All external loads should be
driven throu
g
h the use of direct (Y) outputs.