Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 56)

56 Rockwell Automation Publication 1756-UM540A-EN-P - May 2014
Chapter 3 1756-IF8I Isolated Analog Input Module
Wire Off Detection
The 1756-IF8I module alerts you when a wire is disconnected from a channel or
the RTB is removed from the module. The following events occur when a wire
off condition exists:
• Module Operating in Voltage Mode
–
Input data for that channel changes to a specific scaled value
corresponding to the Overrange value.
– The Overrange bit is set in the I:Ch[x].Overrange tag.
• Module Operating in Current Mode
–
Input data for that channel changes to a specific scaled value
corresponding to the Underrange value.
– The Underrange bit is set in the I:Ch[x].Underrange tag.
• A fault bit is set in the owner-controller that can indicate the presence of a
wire off condition.
Because the module can be used in voltage or current applications, differences
exist as to how a wire off condition is detected in voltage or current applications.
IMPORTANT Be aware that the Disable All Alarms feature, does not disable the wire off
detection feature. The Disable All Alarms feature disables all alarms on the
module.
The wire off detection feature is not an alarm. It is an indicator that a wire
has been disconnected from the channel but does not trigger an alarm.
To disable the wire off detection feature, you must disable the channel.
Table 6 - 1756-IF8I Module - Wire Off Conditions in Different Applications
Application Configuration Wire Off Condition Cause Resulting Module Behavior
Voltage Applications Either of the following:
• A wire is disconnected from
the module.
• The RTB is disconnected from
the module.
• Input data for that channel changes to the scaled value associated with the overrange signal value of the
selected operational range.
• The I.Ch[x].Overrange (x=channel number) tag is set to 1.
Current Applications • Input data for that channel changes to the scaled value associated with the underrange signal value of the
selected operational range.
• The I.Ch[x].Underrange (x=channel number) tag is set to 1.