Emerson Rosemount 644, Reference Manual

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5
Reference Manual
00809-0200-4728, Rev RA
Section 1: Introduction
April 2015
Introduction
Figure 1-1. 644 Head Mount Transmitter Connection Head Temperature Rise vs. Extension
Length
Example
The maximum permissible housing temperature rise (T) can be calculated by subtracting the
maximum ambient temperature (A) from the transmitter’s ambient temperature specification
limit (S). For instance, if A = 40 °C.
T = S - A
T = 85 °C – 40 °C
T = 45 °C
For a process temperature of 540 °C (1004 °F), an extension length of 3.6 inches (91.4 mm)
yields a housing temperature rise (R) of 22 °C (72 °F), providing a safety margin of 23 °C (73 °F). A
6.0 inch (152.4 mm) extension length (R = 10 °C [50 °F]) offers a higher safety margin (35 °C
[95 °F]) and reduces temperature-effect errors but would probably require extra transmitter
support. Gauge the requirements for individual applications along this scale. If a thermowell
with lagging is used, the extension length may be reduced by the length of the lagging.
1.4 Return of materials
To expedite the return process in North America, call the Emerson Process Management
National Response Center toll-free at 800-654-7768. This center, available 24 hours a day, will
assist you with any needed information or materials.
The center will ask for the following information:

Product model

Serial numbers

The last process material to which the product was exposed
60 (108)
50 (90)
40 (72)
30 (54)
20 (36)
10 (18)
0
3 4 5 6 7 8 9
815 C (1500 F)
Oven Te
mpe
rature
540 C (1000 F)
Ove
n Te
mpe
rature
250 C (482 F)
Oven Temperature
Housing Te
mpe
rature Rise Above Ambie
nt C ( F)
Extension Length (in.)
3.6
22