Reference Manual
00809-0100-4021, Rev FB
August 2011
3-23
Rosemount 3144P
HART
Figure 3-7. Open
Sensor Response
Intermittent Sensor Detect (Advanced Feature)
The Intermittent Sensor Detect feature is designed to guard against process
temperature readings caused by intermittent open sensor conditions. An
intermittent sensor condition is an open sensor condition that lasts less than
one update. By default, the transmitter is shipped with the Intermittent Sensor
Detect feature switched ON and the threshold value set at 0.2% of sensor
limits. The Intermittent Sensor Detect feature can be switched ON or OFF and
the threshold value can be changed to any value between 0 and 100% of the
sensor limits with a Field Communicator.
Transmitter Behavior with Intermittent Sensor Detect ON
When the Intermittent Sensor Detect feature is switched ON, the transmitter
can eliminate the output pulse caused by intermittent open sensor conditions.
Process temperature changes (T) within the threshold value will be tracked
normally by the transmitter’s output. A T greater than the threshold value will
activate the intermittent sensor algorithm. True open sensor conditions will
cause the transmitter to go into alarm.
The threshold value of the 3144P should be set at a level that allows the
normal range of process temperature fluctuations; too high and the algorithm
will not be able to filter out intermittent conditions; too low and the algorithm
will be activated unnecessarily. The default threshold value is 0.2% of the
sensor limits.
Transmitter Behavior with Intermittent Sensor Detect OFF
When the Intermittent Sensor Detect feature is switched OFF, the transmitter
tracks all process temperature changes, even from an intermittent sensor.
(The transmitter in effect behaves as though the threshold value had been set
at 100%.) The output delay due to the intermittent sensor algorithm will
be eliminated.
0
0
5
10
15
20
25
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Transmitter Output (mA)
Time (seconds)
When Intermittent Sensor Detect is
OFF, a false temperature output is
possible when an open sensor
condition is detected. A false
temperature output in either direction
up to the threshold value (100 % of
sensor limits if Intermittent Sensor
Detect is OFF) is possible when an
open sensor condition is detected.
Normal open sensor responses
High Alarm
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