Emerson Rosemount 644 Reference Manual page 43

Reference Manual
00809-0200-4728
2.10.3 Intermittent sensor detection
The intermittent sensor detection feature (also known as the transient filter) is designed to
guard against erratic 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
detection feature switched ON and the threshold value set at 0.2 percent 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 percent of the sensor limits with a Field
Communicator.
When the intermittent sensor detection 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 transmitter 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 percent of the sensor limits.
When the intermittent sensor detection feature is switched OFF, the transmitter tracks all
process temperature changes, even from an intermittent sensor. (The transmitter behaves
as though the threshold value had been set at 100 percent.) The output delay due to the
intermittent sensor algorithm will be eliminated.
Configure intermittent sensor detect using a Field
Communicator
The following steps indicate how to turn the intermittent sensor detect (or transient filter)
feature ON or OFF. When the transmitter is connected to a Field Communicator, use the
Fast Key sequence and choose ON (normal setting) or OFF.
From the HOME screen, enter the Fast Key sequence.
Device Dashboard Fast Keys
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 up to the threshold value (100 percent of sensor limits if Intermittent Sensor
Detect is OFF). Unless a rapid response rate is necessary, the suggested setting is ON with
0.2 percent threshold.
Configure intermittent sensor detect using AMS Device
Manager
Procedure
1. Right click on the device and select Configure.
Emerson.com/Rosemount
2, 2, 7, 4, 2
Configuration
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