Emerson Rosemount 3144P Reference Manual page 110

HART Commissioning
April 2017
How it works:
The thermocouple degradation diagnostic measures the amount of resistance on a thermocouple
sensor path. Ideally a thermocouple would have zero resistance, but in reality it has some resistance
especially for long thermocouple extension wires. As the sensor loop degrades (including sensor
degradation and wire or junctions degradation), the resistance of the loop increases. First, the
transmitter is configured to a baseline by the user. Then, at least once per second, the degradation
diagnostic monitors the resistance in the loop by sending a pulsed current (in microamps) on the loop,
measuring the voltage induced and calculating the effective resistance. As the resistance increases, the
diagnostic can detect when the resistance exceeds the threshold set by the user at which the diagnostic
will provide a digital alert. This feature is not intended to be a precise measurement of thermocouple
status, but is a general indicator of thermocouple and thermocouple loop health by providing trending
over time. The thermocouple degradation diagnostic does not detect shorted thermocouple conditions.
Take away: "Thermocouple Diagnostic monitors the health of a thermocouple loop"
Target applications: Control loops, safety loops, "problem thermocouples"
Configure Thermocouple Degradation in guided setup
Enable Thermocouple Degradation in guided setup: Fast Keys 2-1-7-1
1. From the Home Screen, select 2 Configure.
2. Select 1 Guided Setup.
3. Select 7 Diagnostics Suite.
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Reference Manual
00809-0100-4021, Rev JA
HART Commissioning