Trim The Analog Output - Emerson Rosemount 644 Reference Manual

Reference Manual
00809-0200-4728
EMF compensation allows the transmitter to provide sensor measurements that are
unaffected by unwanted voltages, typically due to thermal EMFs in the equipment
connected to the transmitter, or by some types of calibration equipment. If this
equipment also requires steady sensor current, the transmitter must be set to "Active
Calibrator Mode." However, the steady current does not allow the transmitter to perform
EMF compensation and as a result, a difference in readings between the Active Calibrator
and actual sensor may exist.
If a reading difference is experienced and is greater than the plant's accuracy specification
allows, perform a sensor trim with "Active Calibrator Mode" disabled. In this case, an
active calibrator capable of tolerating pulsating sensor current must be used or the actual
sensors must be connected to the transmitter. When the Field Communicator, AMS
Device Manager, or the LOI asks if an Active Calibrator is being used when the sensor trim
routine is entered, select No to leave the "Active Calibrator Mode" disabled.
5.5

Trim the analog output

5.5.1 Analog output trim or scaled analog output trim
Perform an output trim or a scaled output trim if the digital value for the primary variable
matches the plant's standards but the transmitter's analog output does not match the
reading on the output device. The output trim function calibrates the transmitter to a 4–
20 mA reference scale; the scaled output trim function calibrates to a user-selectable
reference scale. To determine the need for an output trim or a scaled output trim, perform
a loop test
Figure 5-4: Measurement Dynamics of Temperature Transmitter
5.5.2 Analog output trim
The analog output trim allows the transmitter's conversion of the input signal to a 4–20
mA output to be altered
to maintain measurement precision.
Emerson.com/Rosemount
(Perform a loop test).
Analog-to-Digital
Signal Conversion
Sensor and ohm/mV
Trim adjust the signal here
Analog Input
Field Communicator
(Figure
Microprocessor
HART
Output
5-4). Adjust the analog output signal at regular intervals
Operation and Maintenance
March 2021
Digital-to-Analog
Signal Conversion
Output and Scaled Output Trim
Trim adjust the signal here
Analog
Output
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