Emerson Rosemount 644 with HART Protocol, Reference Manual

Page: 46 / 112

38
Reference Manual
00809-0200-4728, Rev SA
Configuration
July 2018
Configuration
1. Configure the dual-sensor Rosemount 644 Transmitter 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
“Set the alarm switch” on page 45 ).
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 2-24 .
Figure 2-24. Tracking Sensor Drift and Sensor Failure with Differential Temperature
2.14 Transmitter security
2.14.1 Available security options
There are three security methods to utilize with the Rosemount 644 Transmitter.

Software security switch (write protect)

HART lock

LOI password
The write protect feature allows you to protect the transmitter data from accidental or unwarranted
configuration changes. To enable the write protect feature, perform the following procedures.
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)
DIFF
ER
E
N
TI
AL
TE
M
P
E
R
A
T
U
R
E
Sensor failure
(Failure mode switch LOW)
–100 °C