Rockwell Automation 1794-OF8IH FLEX Isolated Input/Output HART Analog Modules - Manual (Page 58)

Publication 1794-UM065B-EN-E - September 2010
46 1794-IF8IH and 1794-OF8IH Configuration
Real Time Data (RTD)
Profile, Primary Status
Parameters Alarms
This module is capable of generating four different alarms; low, high, remote
and loop alarm. The diagram below graphically shows at what values these
alarms are generated for Data Format 5.
Alarm Operation
In this example the normal active data range is 4…20 mA. The alarms will be
generated in three overlapping bands. Looking at the high end of the range
first:
If the input signal exceeds the High Alarm Limit a High Alarm is generated.
This alarm stays active at any value above the High Alarm Limit. The High
Alarm Limit parameter allows you to program this threshold in 1
μ A steps at
any level from 0.0mA to 22 mA. For this data format this would indicate -25%
to 112.50% of range. In practice this is meant to be used as a High Alarm, set
from 20.001 mA to 22 mA (for this data format this is 100.0063% to 112.50%
of range), as example.
If the input signal exceeds the Remote High High Alarm Limit the Remote
Alarm is issued. This alarm stays active at any value above the Remote High
High Alarm Limit. The Remote High High Alarm Limit parameter allows you
to program this threshold in 1
μ A steps at any level from 0.0 mA to 22 mA.
For this data format this would indicate -25% to 112.50% of range. In practice
this is meant to be used as a High High Alarm, set from 20.001 mA to 22 mA
(for this data format this is 100.0063% to 112.50% of range), as example.
If the input continues to climb the Loop Alarm will be issued at 22 mA
(112.50% of range). Again, as with the High Alarm and Remote Alarm, when
the Loop Alarm is issued, it stays active at any value above 22 mA (112.50% of
range).
Similarly, looking at the low end of the range:
If the input signal falls below the Low Alarm Limit an Low Alarm is
generated. This alarm stays active at any value below the Low Alarm Limit.
The Low Alarm Limit parameter allows you to program this threshold in 1
μ A
steps at any level from 0.0 mA to 22 mA. For this data format this would
indicate -25% to 112.50% of range. In practice this is meant to be used as a
Low Alarm, set from 3.999 mA to 2 mA (for this data format this is -0.0063%
to -12.50% of range), as example.
If the input signal falls below the Remote Low Low Alarm Limit the Remote
Alarm is issued. This alarm stays active at any value below the Remote Low
Low Alarm Limit. The Remote Low Low Alarm Limit parameter allows you to
program this threshold in 1
μ A steps at any level from 0.0 mA to 22 mA. For
this data format this would indicate -25% to 112.50% of range. In practice this