Choosing A Trim Procedure; Sensor Trim Overview - Emerson Rosemount 3051S Series Reference Manual

Reference Manual
00809-0100-4801, Rev CB
January 2007
Choosing a Trim
Procedure

Sensor Trim Overview

To decide which trim procedure to use, you must first determine whether the
analog-to-digital section or the digital-to-analog section of the transmitter
electronics needs trimming. Refer to Figure 4-1 and perform the following
procedure:
1. Connect a pressure source, a HART Communicator or AMS, and a
digital readout device to the transmitter.
2. Establish communication between the transmitter and the HART
Communicator.
3. Apply pressure equal to the upper range point pressure.
4. Compare the applied pressure to the pressure process variable value on
the Process Variables menu on the HART Communicator or the Process
Variables screen in AMS. For instructions on how to access process
variables, see page 3-7 of Section 3: Configuration.
a. If the pressure reading does not match the applied pressure (with
high-accuracy test equipment), perform a sensor trim. See "Sensor
Trim Overview" on page 4-5 to determine which trim to perform.
5. Compare the Analog Output (AO) line, on the HART Communicator or
AMS, to the digital readout device.
a. If the AO reading does not match the digital readout device (with
high-accuracy test equipment), perform an analog output trim. See
"Analog Output Trim" on page 4-7.
Trim the sensor using either sensor or zero trim functions. Trim functions vary
in complexity and are application-dependent. Both trim functions alter the
transmitter's interpretation of the input signal.
Zero trim is a single-point offset adjustment. It is useful for compensating for
mounting position effects and is most effective when performed with the
transmitter installed in its final mounting position. Since this correction
maintains the slope of the characterization curve, it should not be used in
place of a sensor trim over the full sensor range.
When performing a zero trim with a manifold, refer to Manifold Operation on
page 2-23.
NOTE
Do not perform a zero trim on 3051S Absolute pressure transmitters. Zero
trim is zero based, and absolute pressure transmitters reference absolute
zero. To correct mounting position effects on a 3051S Absolute Pressure
Transmitter, perform a low trim within the sensor trim function. The low trim
function provides an offset correction similar to the zero trim function, but it
does not require zero-based input.
Sensor trim is a two-point sensor calibration where two end-point pressures
are applied, and all output is linearized between them. Always adjust the low
trim value first to establish the correct offset. Adjustment of the high trim value
provides a slope correction to the characterization curve based on the low
trim value. The trim values allow you to optimize performance over your
specified measuring range at the calibration temperature.
Rosemount 3051S Series
4-5