Siemens S5-155U System Manual page 475

Configuring
Switching off the CC
Separate or common
shutdown of the CC/EU and
load power supply
System Manual
C79000-B8576-C109-03
You must observe the following when configuring systems:
Switching on At the latest 100 ms after power-up of the PLC, the
voltage must be present at the enable inputs of the I/O
modules.
Switching off When the PLC has been switched off, the voltage at
the enable inputs of the I/O modules must still be
present as long as the internal 5 V voltage is present.
However, you must ensure that the 24 V load supply
for analog output modules is switched off together
with the PLC. If the supply voltage is still present at
the modules and the PLC is switched off, the output
values can drift. (The analog holding elements for the
outputs will no longer be refreshed with the current
value, because there is no 5 V supply to the modules
from the bus.)
You should observe the following instructions for switching off CCs
and equipment for supplying power to the enable inputs.
When there is a need to switch off the load power supply separately
without affecting the enabling of modules, there are the following
possibilities for producing the enable voltage. These exist even when
the load power supply is used without an additional capacitor and
common shutdown.
• • 230 V AC supply for CC/EU and load power supply
a)
-951
Power Supply
230 V AC
Load Power Supply
Supply for the enable inputs from:
a) 6ES5 951-4LB11 load power supply
b) Battery
c) Terminals for 24 V on the front plate of the power supply
The 470 Analog Output Module
b)
I/O Modules
F +
CC/EU
L +
L +
24 V
9
Battery
c)
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