Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules - Manual (Page 59)

Rockwell Automation Publication 1756-UM533C-EN-P - February 2011 59
1756-IF8H HART Analog Input Module Chapter 4
Rate Alarm
The value for the Rate Alarm Limit is entered in scaled engineering units per
second. The rate alarm triggers if the rate of change between input samples for
each channel exceeds the specified rate-alarm trigger point for that channel. Rate
Alarm uses the signal value after filtering by the Module Filter and before the
Digital Filter is applied.
Wire-off Detection
The 1756-IF8H modules alert you when a signal wire is disconnected from one
of its channels or the RTB is removed from the module. When a wire-off
condition occurs for this module, two events occur:
• Input data for that channel changes to a specific scaled value.
• A fault bit is set in the input tag, which may indicate the presence of a
wire-off condition.
Because 1756-IF8H modules can be applied in voltage or current applications,
differences exist as to how a wire-off condition is detected in each application.
Table 5 identifies the conditions that are reported in the input tag when a wiring
anomaly is detected.
Table 5 - Wire-off Detection
Input Range Wiring Problem Condition Reported in Input Tag
Input Data changes to ChXOverrange ChXBrokenWire ChXUnderrange
Voltage -10 V…+ 10 V
0 V …+5 V
0 V…+10 V INx or INx removed Maximum scaled value
(overrange value) 1 1
Current 0 …20 mA RTB removed or INx and
I RTN-x jumper removed Maximum scaled value
(overrange value) 1 1
Only INx removed (jumper in
place) Minimum scaled value
(underrange value) 0 1
Only jumper removed Maximum scaled value
(overrange value) 1 1
4…20 mA RTB removed or INx and
I RTN-x jumper removed Maximum scaled value
(overrange value) 1 1
Only INx removed (jumper in
place) Minimum scaled value
(underrange value) 1 1
Only jumper removed Maximum scaled value
(overrange value) 1 1