Emerson Rosemount 3144P, Справочное руководство

Страница: 109 / 236

99
Reference Manual
00809-0100-4021, Rev JA
HART Commissioning
April 2017
HART Commissioning
Use these steps to set up the HART Tri-Loop to transmit sensor failure alerts.
1. Configure the dual-sensor Rosemount 3144P variable map as shown.
2. Configure Channel 1 of the HART Tri-Loop as TV (differential temperature). If either sensor should fail,
the differential temperature output will be +9999 or –9999 (high or low saturation), depending on
the position of the Failure Mode Switch (see
“Alarm switch (HART Protocol)” on page 12 ).
3. Select temperature units for Channel 1 that match the differential temperature units of the
transmitter.
4. Specify a range for the TV such as –100 to 100 °C. If the range is large, then a sensor drift of a few
degrees will represent only a small percent of range. If Sensor 1 or Sensor 2 fails, the TV will be +9999
(high saturation) or –9999 (low saturation). In this example, zero is the midpoint of the TV range. If a
Δ
T of zero is set as the lower range limit (4 mA), then the output could saturate low if the reading
from Sensor 2 exceeds the reading from Sensor 1. By placing a zero in the middle of the range, the
output will normally stay near 12 mA, and the problem will be avoided.
5. Configure the DCS so that TV
<
–100 °C or TV
>
100 °C indicates a sensor failure and, for example,
TV
≤
–3 °C or TV
≥
3 °C indicates a drift alert. See Figure 3-11 .
Figure 3-11. Tracking Sensor Drift and Sensor Failure with Differential Temperature
Advanced diagnostic
Thermocouple degradation
Problem description: Thermocouples can fail unexpectedly, potentially causing lost production and
increased maintenance costs when unplanned service is performed.
Our solution: Thermocouple Degradation Diagnostic acts as a gauge of general thermocouple health
and is indicative of any major changes in the status of the thermocouple or the thermocouple loop. The
transmitter monitors for increasing resistance of the thermocouple loop to detect drift conditions or
wiring condition changes. The degrading thermocouple can be caused by wire thinning, sensor
breakdown, moisture intrusion or corrosion and can be an indication of an eventual sensor failure.
Variable Mapping
PV Sensor 1 or Sensor Average
SV Sensor 2
TV Differential Temperature
QV As Desired
3 °C
0 °C
–3 °C
100 °C
Sensor drift
Sensor drift
Sensor failure
(failure mode switch HIGH)
D
iff
e
ren
ti
a
l t
e
mper
at
ure
Sensor failure
(Failure mode switch LOW)
–100 °C