Rockwell Automation 1791-I0VX BLOCK I/O - Manual (Page 10)

Introducing Block I/O
Chapter 1
1-4
In sinking inputs, the dc common is bussed on the block. and the current is
sourced from the field device. The sourcing field device switches the hot
side of the power supply bus causing current to flow through the sourcing
device to the sinking input on the block. Refer to Figure 1.2.
Figure 1.2
Sinking Input Example
DC Power
Supply
Field
Device
Field
Device
Sinking
Input
+V
-V
10826-I
Block I/O
Common
Bus
Sourcing outputs have the power bussed in the block. When the output is
on, current is supplied to the field control device, which sinks the current.
The field circuit and the equipment remain at ground potential until the
output is turned on. Refer to Figure 1.3.
Note: The outputs must be externally fused to protect the device output
against overcurrent or short circuit conditions.
Figure 1.3
Sourcing Output Example
DC Power
Supply
Field
Device
Field
Device
+V
-V
Bus
Common
Fuse
Fuse
10827-I
Block I/O
Common
The 1791-IOVX block uses sourcing inputs and sinking outputs.