Emerson 644 manual Considerations

Reference Manual

00809-0400-4728, Rev AA June 2011

Rosemount 644

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)
CONSIDERATIONS
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 FOUNDATION
	fieldbus signal that is relatively insensitive to lead length and electrical noise.
	This signal is then transmitted to the control room via two wires.
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,
	FISCO, or non-incendive field wiring practices.
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).
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 connection
	head. Be sure to provide adequate clearance for cover removal.
Environmental	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.
	Figure 1-1provides an example of the relationship between transmitter
	housing temperature rise and extension length.

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