Considerations; General; Commissioning; Mechanical - Emerson Rosemount 644 Reference Manual

Section 1: Introduction
April 2015
1.3

Considerations

1.3.1

General

Electrical temperature sensors such as RTDs and thermocouples produce low-level signals
proportional to their sensed temperature. The 644 converts the low-level sensor signal to a
standard 4–20 mA DC or digital HART signal that is relatively insensitive to lead length and
electrical noise. This signal is then transmitted to the control room via two wires.
1.3.2

Commissioning

The transmitter can be commissioned before or after installation. It may be useful to
commission it on the bench, before installation, to ensure proper operation and to become
familiar with its functionality. Make sure the instruments in the loop are installed in accordance
with intrinsically safe, or non-incendive field wiring practices.
1.3.3

Mechanical

Location
When choosing an installation location and position, take into account the need for access to
the transmitter.
Special mounting
Special mounting hardware is available for mounting a 644 Head Mount Transmitter to a DIN rail
or assembling a new 644 Head Mount to an existing threaded sensor connection head (former
option code L1).
1.3.4

Electrical

Proper electrical installation is necessary to prevent errors due to sensor lead resistance and
electrical noise. For best results, shielded cable should be used in electrically noisy
environments.
Make wiring connections through the cable entry in the side of the housing. Be sure to provide
adequate clearance for cover removal.
1.3.5

Environmental

The transmitter electronics module is permanently sealed within a plastic enclosure, resisting
moisture and corrosive damage. Verify that the operating atmosphere of the transmitter is
consistent with the appropriate hazardous locations certifications.
Temperature effects
The transmitter will operate within specifications for ambient temperatures between –40 and
185 °F (–40 °C and 85 °C). Heat from the process is transferred from the thermowell to the
transmitter housing. If the expected process temperature is near or beyond specification limits,
consider the use of additional thermowell lagging, an extension nipple, or a remote mounting
configuration to isolate the transmitter from the process.
Figure 1-1
rise and extension length.
4
provides an example of the relationship between transmitter housing temperature
Reference Manual
00809-0200-4728, Rev RA
Introduction