Siemens S5-135U/155U - Manual (Page 482)

9-100
System Manual
C79000-G8576-C199-06
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 lon-
ger 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.
S
230 V AC supply for CC/EU and load power supply
F+
L+
I/O Modules
230 V AC
CC/EU
–951
a)
c)
b)
Battery
L+
Power Supply
Load Power Supply 24V
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
Configuring
Switching Off the
CC
Separate or
Common
Shutdown of the
CC/EU and Load
Power Supply
Analog Input/Output Modules