Rosemount 248 - Page 37

Reference Manual
00809-0100-4825, Rev BB
August 2005
3-13
Rosemount 248
Figure 3-2. Open
Sensor Response
Open Sensor Holdoff
The Open Sensor Holdoff option, at the normal setting, enables the
Rosemount 248 to best tolerate heavy EMI disturbances without producing
brief periods of alarm. This is accomplished through the software by having
the transmitter perform additional verification of the open sensor status prior
to activating the transmitter alarm. If the additional verification shows that the
open sensor condition is not valid, the transmitter will not go into alarm.
For users of the Rosemount 248 that desire a more immediate open sensor
detection, the Open Sensor Holdoff option can be changed to a fast setting.
With this setting, the transmitter will report an open sensor condition without
additional verification of the open condition.
Fast Key Sequence 1, 3, 5, 3
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
644-644_03