Allen-Bradley 1756 Series, User Manual, Page: 58 / 136

58 Rockwell Automation Publication 1756-UM013B-EN-P - October 2019
Chapter 4 1756-OBV8S Output Module Features
Overview
The 1756-OBV8S is a safety output module that uses eight safety outputs. You
use the outputs in one of the following ways:
• Sourcing/sinking outputs in Bipolar Output mode
• Sourcing outputs in Sourcing Output mode.
• Solid-state outputs
• Single-channel mode uses one output signal, that is, data from an output
channel, to provide control.
• Dual-channel mode uses two output signals, that is, data from two output
channels to provide redundant control.
• Safety outputs can be pulse-tested to detect field wiring short-circuits to
24V DC.
• The 1756-OBV8S module follows the mode of the Safety Task, which can
be different than the mode of the controller.
When the safety task encounters a nonrecoverable safety fault, a standard
major recoverable fault is also logged, and the controller proceeds to
execute the controller fault handler, if one exists. If the controller fault
handler handles this fault, then the standard tasks continue to run, even
though the safety task remains faulted.
If a recoverable fault occurs in the safety application, the system can halt
the execution of the safety task, depending upon whether or not the fault is
handled by Program Fault Routines in the safety application. If the
recoverable safety fault is not handled, a standard major recoverable fault is
also logged, and the controller proceeds to execute the controller fault
handler, if one exists. If the controller fault handler handles this fault, then
the standard tasks continue to run, even though the safety task remains
faulted.
In these scenarios, the 1756-OBV8S module follows the Safety Task and
will be in Program Mode/Communications Fault mode even though the
controller is still in Run mode.
For information on Safety Faults, see the ControlLogix® 5580 and
GuardLogix® 5580 Controllers User Manual, publication 1756-UM543 .
IMPORTANT Single-channel mode is only certified for functional safety
applications with process safety times greater than or equal to
200 ms; or, applications with demand rates less than or equal to 3
demand per minute.
IMPORTANT If there is a fault on a separate safety output on the same module, the module
could switch off all outputs.