Information Variables - Emerson Rosemount 644H Reference Manual

Models 644H and 644R

Information Variables

3-8
2-Wire RTD Offset
Fast Key Sequence
The 2-Wire RTD Offset command allows the user to input the measured lead
wire resistance, which will result in the transmitter adjusting its temperature
measurement to correct the error caused by this resistance. Due to a lack of
lead wire compensation within the RTD, temperature measurement made
with a 2-wire RTD are often inaccurate. See "Sensor Lead Wire
Resistance Effect– RTD Input" on page 2-11 for more information.
To utilize this feature perform the following steps:
1. Measure the lead wire resistance of both RTD leads after installing
the 2-wire RTD and the Model 644H.
2. From the HOME screen, select 1 Device Setup, 3 Configuration,
2 Sensor Configuration, 1 Sensor 1, 2 Snsr 1 Setup, and 1 2-Wire
Offset.
3. Enter the total measured resistance of the two RTD leads at the
2-Wire Offset prompt. Enter this resistance as a negative (–) value to
ensure proper adjustment.The transmitter then adjusts its
temperature measurement to correct the error caused by lead wire
resistance.
Access the transmitter information variables on-line using the HART
Communicator or other suitable communications device. The following is a list
of transmitter information variables. These variables include device identifiers,
factory-set configuration variables, and other information. A description of
each variable, the corresponding fast key sequence, and a review of its
purposes are provided.
Tag
Fast Key Sequence
The Tag variable is the easiest way to identify and distinguish between
transmitters in multi-transmitter environments. Use it to label transmitters
electronically according to the requirements of the application. The tag
defined is automatically displayed when a Model 275 HART Communicator
establishes contact with the transmitter at power-up. The tag may be up to
eight characters long and has no impact on the primary variable readings of
the transmitter.
Date
Fast Key Sequence
The Date command is a user-defined variable that provides a place to save
the date of the last revision of configuration information. It has no impact on
the operation of the transmitter or the Model 275 HART Communicator.
Descriptor
Fast Key Sequence
The Descriptor variable provides a longer user-defined electronic label to
assist with more specific transmitter identification than is available with the tag
variable. The descriptor may be up to 16 characters long and has no impact
on the operation of the transmitter or the Model 275 HART Communicator.
1, 3, 2, 1, 2, 1
1, 3, 4, 1
1, 3, 4, 2
1, 3, 4, 3
Reference Manual
00809-0100-4728, Rev HA
December 2002