Wire off detection – Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules User Manual
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Publication 1756-UM009C-EN-P - December 2010
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Temperature-measuring Analog Modules (1756-IR6I, 1756-IT6I, and 1756-IT6I2) Chapter 6
Wire Off Detection
The ControlLogix temperature-measuring modules alert you when a wire has
been disconnected from one of their channels. When a wire off condition
occurs, two events occur:
• 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 these modules can each be used in various applications, differences
exist when 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
In this application
The following causes a wire off condition
And if the wire off condition is detected, this occurs
1756-IR6I Module in
Temperature
Applications
Either of the following:
1. When only the wire connected to terminal A
is lost.
2. When any other combination of wires are
disconnected from the module.
for a wiring diagram.
If possibility number 1 (in the previous column) is the cause:
• Input data for the channel changes to the highest scaled
temperature value associated with the selected RTD type.
• The ChxOverrrange (x=channel number) tag is set to 1.
If possibility number 2 (in the previous column) is the cause:
• Input data for the channel changes to the lowest scaled
temperature value associated with the selected RTD type.
• The ChxUnderrange (x=channel number) tag is set to 1.
1756-IR6I Module in
Ohms Applications
Either of the following:
1. When only the wire connected to terminal A
is lost.
2. When any other combination of wires are
disconnected from the module.
for a wiring diagram.
If possibility number 1 (in the previous column) is the cause:
• Input data for the channel changes to the highest scaled
ohm value associated with the selected ohms range.
• The ChxOverrange (x=channel number) tag is set to 1.
If possibility number 2 (in the previous column) is the cause:
• Input data for the channel changes to the lowest scaled
ohm value associated with the selected ohms range.
• The ChxUnderrange (x=channel number) tag is set to 1.