Reference Manual
00809-0100-4360, Rev BA
August 2008
4-5
Rosemount 1151
The low trim value should be trimmed first. This provides a stable
reference for additional sensor trim adjustment. Adjustment of the low trim
value provides an offset correction to the factory-established characterization
curve. Adjustment of the high trim value provides a slope or gain correction to
the characterization curve based on the low trim value. In neither case is the
factory-established characterization curve changed by this procedure. The
trim values allow optimized performance over a specified measuring range at
the calibration temperature. See Figure 4-3 on page 4-6 for instrumentation
set up.
Zero Trim
A zero trim is a simpler, one-point adjustment. It must be zero-based (in other
words, within 3.0% of true zero) and it may be performed when an exact
pressure source is not available for the second pressure needed in a sensor
trim.
It is useful for compensating for mounting position effects or for zero shifts due
to static pressure in differential pressure applications. However, 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.
Zero trim is best performed with the transmitter installed in its final mounting
position with static pressure applied (or no pressure for a gage transmitter).
NOTE
Because a zero trim must be zero-based, it generally should not be used with
Rosemount 1151 Smart Absolute Pressure Transmitters. Absolute pressure
transmitters reference absolute zero. To correct mounting position effects on a
Rosemount 1151 Smart Absolute Pressure Transmitter, perform a low trim
within the full sensor trim function. The low trim function provides a “zero”
correction similar to the zero trim function but it does not require the input to
be zero based.
Sensor Trim
A sensor trim is a two-point sensor calibration where two end-point
pressures are applied, and all output is linearized between them. To start the
procedure, connect the communicator and a pressure input source of at least
three times greater accuracy than the Rosemount 1151 Smart Transmitter as
shown in Figure 4-3. Always let the variable stabilize for 10 seconds after
application of the pressure source before taking its reading.
HART Comm. Fast Key Sequence 1, 2, 3, 3, 1
HART Comm. Fast Key Sequence 1, 2, 3, 3
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