Siemens S7-300 Installation And Operating Manual page 81

External sensor supply
The figure below shows how you can connect the sensors to an external sensor supply (for
example, from another module: L+). All 6 channels of a channel group (0 to 5; 6 to 11; 12 to
17 or 18 to 23) must be connected to the same external sensor supply.
Figure 8-5
Note
Note that the errors outlined cannot be detected when operating with external sensor supply:
 Short-circuit to L+ on the unconnected sensor line (open contact)
 Short-circuit between channels of a channel group
 Short-circuit between channels of different channel groups
For electronic sensors (and therefore with external sensor supply), you can meet these three
points by short-circuit proof routing of the sensor lines.
Fail-safe signal modules
Installation and Operating Manual, 01/2010, A5E00085586-10
External sensor supply for SM 326; DI 24 x DC 24V
Digital modules
8.3 SM 326; DI 24 x DC 24V
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