Emerson Rosemount 644 Reference Manual page 45

Reference Manual
00809-0200-4728, Rev RA
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.
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 644 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.
When the Intermittent Sensor Detection 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.
Configure intermittent sensor detection with 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%. 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% of
sensor limits if Intermittent Sensor Detect is OFF). Unless a rapid response rate is necessary, the
suggested setting is ON with 0.2% threshold.
Configure intermittent sensor detection with AMS Device
Manager
1.
2.
3.
4.
Configuration
Right click on the device and select Configure.
In the left navigation pane select Manual Setup.
On the Device Tab there will be a group box called Noise Rejection, in the box
Transient Filter Threshold, enter the desired percent.
Select Apply when complete.
Section 2: Configuration
2, 2, 7, 4, 2
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