Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 102)

102 Publication 1756-UM009C-EN-P - December 2010
Chapter 5 Sourcing Current Loop Input Module (1756-IF6CIS) and Isolated Analog Voltage/Current Input Module (1756-IF6I)
Wire Off Detection
The 1756-IF6CIS and 1756-IF6I modules will alert you when a wire has been
disconnected from one of its channels or the RTB has been removed from the
module. Two events occur when a wire off condition occurs for this module.
• Input data for that channel changes to a specific scaled value.
• A fault bit is set in the owner-controller that may indicate the presence
of a wire off condition.
Because the 1756-IF6I module can be used in voltage or current applications,
differences exist as to how a wire off condition is detected in each application.
The 1756-IF6CIS module can only be used in current mode.
The table lists the differences that occur when a wire off condition occurs in
various applications.
IMPORTANT
Be careful when ‘disabling all alarms’ on the channel because it
also disables the underrange/overrange detection feature. If
alarms are disabled, overrange/underrange is zero and the only
way you can discover a wire-off detection is from the input
value itself. If you need to detect a wire-off status, do not
‘disable all alarms’.
We recommend that you disable only unused channels so
extraneous alarm bits are not set.
Wire Off Conditions in Different Applications
Wire Off Condition Occurrence
Voltage Applications
1756-IF6I only
• Input data for that channel changes to the scaled value
associated with the overrange signal value of the selected
operational range in floating point mode (maximum possible
scaled value) or 32,767 counts in integer mode.
• The ChxOverrange (x=channel number) tag is set to 1.