Emerson Rosemount 248 Reference Manual page 41

Reference Manual
00809-0100-4825
Transmitter behavior with intermittent sensor detect OFF
When the Intermittent Sensor Detect feature is switched OFF , the transmitter tracks all
process temperature changes, even if they are the result of an intermittent sensor. (The
transmitter behaves as though the threshold value had been set at 100 percent.)
The output delay because of the intermittent sensor algorithm will be eliminated.
Intermittent threshold
The threshold value can be changed from the default value of 0.2 percent. Turning the
Intermittent Sensor Detect feature OFF or leaving it ON and increasing the threshold value
above the default does not affect the time needed for the transmitter to output the
correct alarm signal after detecting a true open sensor condition. However, the
transmitter may briefly output a false temperature reading for up to one update in either
direction (see
Intermittent Sensor Detect is OFF). Unless rapid response rate is necessary, the suggested
setting of the Intermittent Sensor Detect mechanism is ON with 0.2 percent threshold.
Figure 3-2: Open Sensor Response
Open sensor holdoff
The Open Sensor Holdoff option, at the normal setting, enables the Rosemount 248 to
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. On this setting, the
transmitter reports an open sensor condition without additional verification of the open
condition.
Rosemount 248 Temperature Transmitter Reference Manual
Figure 3-3) up to the threshold value (100 percent of sensor limits if
Configuration
May 2019
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