Reference Manual

29
Reference Manual
00809-0100-4045, Rev AB
Operation and Maintenance
March 2016
Operation and Maintenance
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 device 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, ensure that the equalizing valve is open and all wet legs are
filled to the correct levels. Line pressure should be applied to the device during a zero trim
to eliminate line pressure errors. Refer to “Manifold operation” on page 12.
Note
Do not perform a zero trim on the Rosemount Wireless Pressure Gauge with absolute
measurement type. Zero trim uses a zero reference against ambient air pressure for gage,
vacuum, and compound pressure devices. While absolute pressure devices reference
absolute zero. To correct mounting position effects on a Wireless Pressure Gauge with
absolute measurement type, 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 char-
acterization curve based on the low trim value. The trim values allow you to optimize
performance over your specified measuring range at the calibration temperature.
During a trim operation, the device is placed in high power refresh mode, which provides
frequent pressure measurement updates. This behavior allows for more accurate
calibration of the device. When the device is in high power refresh mode, the battery power
supply will be depleted more rapidly.
Figure 4-1. Sensor Trim Example
A. Before trim
B. After trim
A
B
B
A