Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules User Manual
Page 65
Publication 1756-UM009C-EN-P - December 2010
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Non-isolated Analog Voltage/Current Input Modules (1756-IF16, 1756-IF8) Chapter 4
Because the 1756-IF16 and 1756-IF8 modules can be applied in voltage or
current applications, differences exist as to how a wire-off condition is
detected in each application.
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
When the Wire-Off
condition occurs
These events occur
Single-ended Voltage
Applications
• Input data for odd numbered channels changes to the scaled
value associated with the underrange signal value of the
selected operational range in floating point mode (minimum
possible scaled value) or -32,767 counts in integer mode.
• The ChxUnderrange (x = channel number) tag is set to 1.
• Input data for even numbered channels 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
(1)
is set to 1.
Single-Ended Current
• Input data for that channel changes to the scaled value
associated with the underrange signal value of the selected
operational range in floating point mode (minimum possible
scaled value) or -32,768 counts in integer mode.
• The ChxUnderrange (x= channel number) tag is set to 1.
Differential Voltage
• 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 32,768 counts in integer mode.
• The ChxOverrange (x= channel number) tag is set to 1.