Siemens S5-135U/155U System Manual page 387

Enable Input
The enable circuit requires an external 24 V voltage at enable inputs F+/F- in
the front connector. If there is no voltage at F+/F-, the modules will not
acknowledge.
When the front connector is swivelled away from the front strip of the
module, the supply of power to the enable input is interrupted, i.e. the
module is switched off and can no longer be addressed by the user program: a
timeout (QVZ) occurs in the CC.
Switching Off the
The 460 module additionally offers the facility for changing the enable
Enable Input
mode. The module has a jumper accessible from above in the vicinity of the
addressing switch.
When the enable jumper is inserted, you can define the behaviour of the 460
analog input module as follows:
Figure 9-2
Jumper inserted:
Jumper open:
Examples of functioning of the enable inputs:
System Manual
C79000-G8576-C199-06
When the enable voltage and load voltage are obtained from the same
load supply, a shutdown of the 24 V load voltage will result in a timeout.
When the enable voltage and load voltage are obtained from different
load supplies, a shutdown of the 24 V load voltage will not result in a
timeout. (With the 460-4UA11/12 modules, a shutdown of the load
voltage will result in a timeout.)
Enable Jumper
Enable Input and Enable Jumper
Enable input (F+/F-) active (factory setting)
Enable input (F+/F-) switched off
To switch off individual subprocesses, i.e. outputs of various modules can
be operated from a common load supply and yet activated separately.
The load voltage of individual modules can be monitored without
additional circuitry. Any reactions to failure of the load voltage can be
programmed in the QVZ (timeout) organization block.
Analog Input/Output Modules
9-5