Commissioning
UPS functionality
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LDCDS−EL100 EN 8.0
7.6
UPS functionality
An "EL 1xx PLC" is equipped with an internal UPS which − in the event of a supply voltage
failure − keeps the EL 1xx alive until the values of the retain variables have been saved
fail−safe.
Note!
The PLC program indicates retain variables by the keyword RETAIN. The value
of these variables remains unchanged both after an uncontrolled and a normal
PLC exit. After restarting the PLC, the values will be available again.
An application example is a unit counter in a production plant which is to
continue counting after a restart.
After a supply voltage failure, the following steps will be carried out automatically:
1. To bridge voltage fluctuations, the system waits for a defined time and sees if the
supply voltage is applied again (delay time = 500 ms).
If the supply voltage is applied again within this time, the system continues operation
as usual.
2. Otherwise, the background light of the display is switched off, the run−time
system/controller is stopped and the CAN telegram only transmits zeros.
3. All retain variables are saved within the buffer time of 2 seconds.
4. After the buffer time, the system checks cyclically whether the supply voltage is
applied again.
When the supply voltage is applied again, the system is restarted.
Otherwise, the system continues running until the buffer capacitors have drained.
