Allen-Bradley 1756 Series, User Manual, Page: 70 / 136

70 Rockwell Automation Publication 1756-UM013B-EN-P - October 2019
Chapter 4 1756-OBV8S Output Module Features
Output Recovery After Overload or Short Circuit to Ground Condition
Table 21
describes test output recovery after overload or short circuit to ground
conditions occur.
Thermal Shutoff
Thermal Shutoff helps prevent damage to the output that can result when an
output gets hotter than it can handle.
This feature is
directly related to Short Circuit Protection
feature. The
increased temperature at the output results from an excessive load at the output.
That is, a load with high current is applied to the output. The high current heats
the output beyond an acceptable temperature and the output turns off.
Table 22 describes what happens when a thermal shutoff
condition is detected
on a 1756-OBV8S module.
Table 23 describes what happens when the thermal shutoff
condition is
corrected
on a 1756-OBV8S module.
For more information on how to use the modules, see Appendix B, Module Tag
Definitions on page 113 .
Table 21 - Output Recovery - 1756-OBV8S Module
Cause of Fault Module Operating Conditions Correction Recovery Time
Overload Condition • Output Point Mode - Safety or Safety
Pulse Test.
• Output Data tag = 1.
• Overload current ≥1.5 A
(1)
Remove the load from the output point. See Safety Output Fault Reset on page 63 .
Short Circuit to Ground
Condition • Output Point Mode - Safety or Safety
Pulse Test.
• Output Data tag = 1.
• Output is connected directly to ground.
Remove the output connection to ground and
set the output to a safe state.
(1) Do not use the module beyond the rated the capacity of 1 A per channel for continuous operation. For ratings, see the 1756 ControlLogix I/O Specifications Technical Data pub 1756-TD002 .
Table 22 - Thermal Shutoff - 1756-OBV8S Module
Output Behavior Tag Value Diagnostic Value I/O Status Indicator State
• Faults
• Turns off
One of the following:
• If the output point is shorted to 24V DC when the thermal shutoff
condition occurred, the I.Ptxx.ShortCircuit tag = 1.
• If the output point is shorted to ground when the thermal shutoff
condition occurred, there is no change to the tags.
One of the following:
• If the output point is shorted to 24V DC when
the thermal shutoff condition occurred, there is
no change in the diagnostics.
• If the output point is shorted to ground when
the thermal shutoff condition occurred, the
ShortCircuitGround diagnostic = 1.
Steady red
Table 23 - Thermal Shutoff - 1756-OBV8S Module
Output Behavior Tag Value Diagnostic Value I/O Status Indicator State
Remains in the off state I.Ptxx.ShortCircuit tag = 0 One of the following:
• If the output point was shorted to 24V DC when the thermal shutoff
condition occurred, the Overload diagnostic = 0.
IMPORTANT : You must cycle power to the module to reset the diagnostic.
• If the output point was shorted to ground when the thermal shutoff
condition occurred, the ShortCircuitGround diagnostic = 0.
Turns off if there is no longer a load
that is connected to the output.