Emerson Rosemount 248 Reference Manual page 53

Reference Manual
00809-0100-4825, Rev CB
To perform a sensor trim with a Rosemount 248:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Output trim or scaled 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 as shown
on page
Figure 4-1. Dynamics of Smart Temperature Measurement
Sensor and Ohm/mV
Trim adjust the signal here
Operation and Maintenance
Connect the calibration device or sensor to the transmitter. Refer to
page 16 or inside of the transmitter terminal side cover for sensor wiring diagrams. If
using an active calibrator, please see
Connect the communicator to the transmitter loop.
From the Home screen, select 1 Device Setup, 2 Diag/Service, 2 Calibration, 1 Sensor 1
Trim, 1 Sensor 1 Input Trim to prepare to trim the sensor.
Set the control loop to manual and select OK.
Answer the Active Calibration question.
Select 1 Lower Only or 2 Lower and Upper at the SELECT SENSOR TRIM POINTS prompt.
Adjust the calibration device to the desired trim value (must be within the selected
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 stabilize. Use
a bath, furnace or isothermal block, measured with a site-standard thermometer, as the
known temperature source.
Select OK when the temperature stabilizes. The communicator displays the output
value the transmitter associates with the input value provided by the calibration device.
Enter the lower or upper trim point, depending on the selection in Step 6.
34.
Transmitter Electronics Module
Analog-to-Digital
Microprocessor
Signal Conversion
Analog
Field
Input
Communicator
Section 4: Operation and Maintenance
"Active calibrator" on page
Digital-to-Analog
Signal Conversion
Output and Scaled Output
Trim adjust the signal here
HART
Analog
Output
Output
March 2014
Figure 2-6 on
35.
45