Emerson Rosemount 248 Reference Manual page 46

Operation and Maintenance
May 2019
• Sensor Input Trim: digitally alter the transmitter's interpretation of the input signal
• Transmitter-sensor matching: generates a special custom curve to match that specific
sensor curve, as derived from the Callendar-Van Dusen (CVD) constants
• Output Trim: calibrates the transmitter to a 4–20 mA reference scale
• Scaled Output Trim: calibrates the transmitter to a user-selectable reference scale.
4.2.1 Trim the transmitter
One or more of the trim functions may be used when calibrating. The trim functions are as
follows:
• Sensor input trim
• Transmitter-sensor matching
• Output trim
• Output scaled trim
Sensor input trim
Perform a sensor trim if the transmitters digital value for the primary variable does not
match the plant's standard calibration equipment. The sensor trim function calibrates the
sensor to the transmitter in temperature units or raw units. Unless your site-standard
input source is NIST-traceable, the trim functions will not maintain the NIST-traceability of
the system.
The Sensor Input Trim command allows the transmitter's interpretation of the input
signal to be digitally altered (see
combined sensor and transmitter system to a site standard using a known temperature
source. Sensor trimming is suitable for validation procedures or for applications that
require calibrating the sensor and transmitter together.
To perform a sensor trim with a Rosemount 248:
Procedure
1. Connect the calibration device or sensor to the transmitter. Refer to
2. Connect the communicator to the transmitter loop.
3. From the Home screen, select 1 Device Setup, 2 Diag/Service, 2 Calibration,
4. Set the control loop to manual and select OK .
5. Answer the Active Calibration question.
6. Select 1 Lower Only or 2 Lower and Upper at the Select SENSOR Trim Points
7. Adjust the calibration device to the desired trim value (must be within the selected
46
inside of the transmitter terminal side cover for sensor wiring diagrams. If using an
active calibrator, please see
1 Sensor 1 Trim, 1 Sensor 1 Input Trim to prepare to trim the sensor.
prompt.
sensor limits). If a combined sensor and transmitter system are being trimmed,
expose the sensor to a known temperature and allow the temperature reading to
Figure 4-1). The sensor input calibration trims the
Active calibrator.
Rosemount 248 Temperature Transmitter Reference Manual
Reference Manual
00809-0100-4825
Figure 2-10 or