Rockwell Automation 1794-OF8IH FLEX Isolated Input/Output HART Analog Modules - Manual (Page 59)

Publication 1794-UM065B-EN-E - September 2010
1794-IF8IH and 1794-OF8IH Configuration 47
is meant to be used as a Low Low Alarm, set from 3.999 mA to 2 mA (for this
data format this is -0.0063% to -12.50% of range), as an example.
If the input continues to fall the Loop Alarm is issued at 2 mA (-12.50%).
Again, as with the Low Alarm and Remote Alarm, when the Loop Alarm is
issued, it stays active at any value below 2 mA (-12.50% of range).
Data Format 5 Alarm Example, Series B
Data Formats 8…11 do not issue Low or Remote Alarms due to input low
conditions, since the normal input range includes 0 mA, and these Data
Formats have pre-programmed fault levels, see Data Formats and Error
Ranges on page 42.
The Remote and Loop Alarms are issued with the same bit whether the cause
is an under or overrange. Just looking at these bits will not indicate if the fault
is from a too low or too high input. The High Alarm and Low Alarm bits
should be monitored to determine which way the reading is moving. By
programmatically combining High, Low and Remote Alarm bits, Low Low,
Low, High and High High Alarms can be generated.
Another use of these alarms and thresholds is to accommodate transmitters
which sense faults in the remote loop and give a drastic under or overrange
indication to the local loop when the fault occurs. By appropriately setting the
Remote High High or Remote Low Low Alarm Limit parameters and
monitoring the Remote Alarm bit.
When active, these alarms trigger at set currents. Depending on Data Format,
these current values may indicate percent, mA or integer values.
The Remote Alarm and Loop Alarm may be disabled by the Fault Mode bit.
The High Alarm is active for Data Formats 0-7, unless disabled by a "0"
(default) value of High Alarm Limit. The High Alarm is always active for Data
0 mA
Loop
Alarm
-25.00 % -12.50 %
Remote Alarm
programmable
in 1
μ
A steps
by Remote
Low Low
Alarm Limit
parameter
programmable
in 1
μ
A steps by
Low Alarm
Limit parameter
0.00 %
Low Alarm
4 mA 20 mA
Normal Signal Range
100.00 %
programmable
in 1
μ
A steps by
High Alarm
Limit parameter
programmable
in 1
μ
A steps
by Remote
High High
Alarm Limit
parameter
112.50 %
High Alarm
Remote Alarm
Loop
Alarm
22 mA
PHYSICAL INPUT SIGNLA RANGE
45152
Format 5