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

Reference Manual
00809-0100-4728, Rev HA
December 2002

CONSIDERATIONS

General

Commissioning

Mechanical

Electrical

Environmental

Refer to the following literature for a full range of compatible connection
heads, sensors, and thermowells provided by Emerson Process
Management.
• Temperature Sensors and Assemblies Product Data Sheet, Volume 1
(document number 00813-0100-2654)
• Temperature Sensors and Assemblies Product Data Sheet, Volume 2
(document number 00813-0200-2654)
Electrical temperature sensors such as RTDs and thermocouples produce
low-level signals proportional to their sensed temperature. The Model 644
converts the low-level sensor signal to a standard 4–20 mA dc signal that is
relatively insensitive to lead length and electrical noise. This current signal is
then transmitted to the control room via two wires.
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 before connecting a HART communicator
in an explosive atmosphere.
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 Model 644H head
mount transmitter to a DIN rail, or assembling a new Model 644H to an
existing threaded sensor connection head (former option code L1).
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. A resistance between 250 and 1100
ohms must be present in the loop for communication with a Model 275 HART
Communicator.
Make wiring connections through the cable entry in the side of the connection
head. Be sure to provide adequate clearance for cover removal.
The transmitter electronics module is permanently sealed within the housing,
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 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, and extension nipple, or a remote mounting
configuration to isolate the transmitter from the process.
Models 644H and 644R
1-3