Emerson Rosemount 327T, Quick Start Manual

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Drift Monitoring
For Drift Monitoring Diagnostic, the temperature transmitter compares the temperature
deviation of sensor element 1 (NTC) and sensor element 2 (Pt 1000) to the average
temperature value. The parameters drW (warning threshold) and drA (alarm threshold)
define the permissible temperature deviation.
When values exceed these thresholds, the temperature transmitter triggers drift
monitoring and identifies a fault (see
Diagnostic cases ).
Figure 1-2: Drift monitoring example
Example: NTC sensor element (1) measures 149 °F and Pt 1000 sensor element (2)
measures 140 °F. The average value (3) is 144.5 °F, i.e. both elements deviate by 4.5 °F.
With setting drW = 4 °F and drA = 9 °F, the temperature transmitter provides a warning
message if drEd = OFF. In this case, the temperature transmitter would not send an alarm
message.
For more information about configuring drW and drA, see Setting range for drW and drA .
Note
Temperature difference of at most 0.18 °F (0.1 °C) can occur with sensor elements
because of standard manufacturing tolerances. This does not affect the drift monitoring
diagnostic.
Note
Large temperature changes in the medium might cause short-term differences between
the measured temperature values of both sensor elements. To avoid short-term drift
warnings, increase the drift warning delay time (ddr).
Sensor backup
If one of the two sensors in the transmitter fails, the temperature transmitter can use the
remaining sensor for temperature measurement.
For more information on operating the temperature transmitter in backup mode, see
Troubleshooting .
Introduction Quick Start Guide
January 2019 00825-0100-4329
8 Quick Start Guide