Rockwell Automation 1791-I0VX BLOCK I/O - Manual (Page 11)

Introducing Block I/O
Chapter 1
1-5
In sourcing input modules (Figure 1.4), the +V on dc circuits is bussed on
the module supplying (sourcing) the current for each input circuit. The
field device switches the circuit to the common (side of the power supply,
sinking the circuit and causing current to flow from the module’s input.
Figure 1.4
Sourcing Input Example
Field
Device
Input
+V
10917-I
Block I/O
DC Power
Supply
dc Common Bus
-V
In sinking outputs (Figure 1.5), the current flow is reversed. The dc
common is bussed on the module and the current is sourced from the field
device being actuated. When an output is turned on, the output switch in
the module sinks the circuit, causing current to flow from the +V bus
through the field device to the module.
Note: The outputs must be externally fused to protect the device output
against overcurrent or short circuit conditions.
Figure 1.5
Sinking Output Example
DC Power
Supply
Field
Device
Field
Device
+V
-V
Bus
Common
Fuse
Fuse
10918-I
Block I/O
Common