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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 battery backed or latched relays whose status is retained in battery
backed or EEPROM memory. If a power failure should occur all output and general purpose
relays are switched off. When operation is resumed the previous status of these relays is
restored.
The circuit shown on page 4-3 is an example of a self retaining circuit. Relay 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 relay being activated
momentarily.
X0
SET M507
RST M507
X1
External loads:
• Auxiliary relays are provided with countless number of NO contact points and NC
contact points. These are freely available for use through out a PLC program. These
contacts cannot be used to directly drive external loads. All external loads should be
driven through the use of direct (Y) outputs.