Active Calibrator And Emf Compensation - Emerson Rosemount 3144P Reference Manual

Reference Manual
00809-0100-4021, Rev AA
March 2002
7. Select 1 Lower Only, 2 Upper Only or 3 Lower and Upper at the SELECT
SENSOR TRIM POINTS prompt.
8. Adjust the calibration device to the desired trim value (must be within the
selected sensor limits). If trimming a combined sensor and transmitter
system, 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.
9. Select OK once the temperature stabilizes.
The communicator displays the output value the transmitter associates with
the input value provided by the calibration device.
10. Enter the lower or upper trim point, depending on your selection in
Step 7.
The trim functions should not be confused with the rerange functions.
Although the rerange command matches a sensor input to a 4–20 mA
output—as in conventional calibration—it does not affect the transmitter's
interpretation of the input.
To trim Sensor 2, repeat the same procedure, but in Step 1, disable Sensor 1
instead of Sensor 2.

Active Calibrator and EMF Compensation

HART Fast Keys 1, 2, 2, 1, 3
The transmitter operates with a pulsating sensor current to allow EMF
compensation and detection of open sensor conditions. Because some
calibration equipment requires a steady sensor current to function properly,
the "Active Calibrator Mode" feature is used during sensor trim. Enabling this
mode will temporarilly set the transmitter to provide steady current, and
disabling it will set the transmitter back to the default setting, pulsating
current. "Active Calibrator Mode" is volatile and will automatically be disabled
when a Master Reset is performed (via HART) or when power is cycled.
EMF compensation allows the transmitter to provide sensor measurements
that are not affected by unwanted voltages, which are 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" during sensor trim.
However, the steady current does not allow the transmitter to perform EMF
compensation. As a result, a difference in readings between the time when
performing a trim and those after exiting trim may exist.
If a reading difference is experienced and the difference is greater than the
plant's accuracy specification allows, perform a sensor trim with "Active
Calibrator Mode" disabled. When the Model 275 HART Communicaator asks
if an Active Calibrator is being used when the sensor trim routine is entered,
select No. This will leave the "Active Calibrator Mode" disabled. By selecting
Yes, the "Active Calibrator Mode" will be enabled.
Contact a Rosemount representative for more infomation.
Model 3144P
3-25