Reference Manual
00809-0100-4825, Rev BB
August 2005
4-3
Rosemount 248
Use the following procedure to perform a sensor trim with a Rosemount 248.
1.
Connect the calibration device or sensor to the transmitter. Refer to
Figure 2-6 on page 2-9 or inside of the transmitter terminal side cover
for sensor wiring diagrams. (If using an active calibrator, please see
“Active Calibrator” on page 3-10)
2.
Connect the communicator to the transmitter loop.
3.
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.
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
prompt.
7.
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.
8.
Select
OK
once the temperature stabilizes. The communicator
displays the output value the transmitter associates with the input
value provided by the calibration device.
9.
Enter the lower or upper trim point, depending on the selection in
Step 6.
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 (see “Loop Test” on page 3-9).
Figure 4-1. Dynamics of Smart
Temperature Measurement
Microprocessor
Digital-to-Analog
Signal Conversion
Analog-to-Digital
Signal Conversion
Transmitter Electronics Module
Analog
Input
Analog
Output
HART
Communicator
HART
Output
Sensor and Ohm/mV
Trim adjust the signal here
Output and Scaled Output
Trim adjust the signal here
Summary of Contents for 248
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