CALIBRATION
Troxler calibrates the 3450 gauge at the factory. The operating
range of the gauge is from 1100 to 2700 kg/m
3
(70 to 170 pcf).
Troxler also calibrates the Model 3450 for thin layer measurements.
The thin layer factory calibration covers a thickness range of 2.5 to
10 cm (1.0 to 4.0 in.).
OFFSETS
The factory calibration provides accurate results for the majority of
materials found in the field. If the gauge is to be used to test
materials not covered by the factory calibration, the readings can be
adjusted using either an offset as described below or a special
calibration as described in Chapter 6.
Perform a wet density offset if the test material is outside the density
range for average soil or if the material composition varies from
average soil/asphalt. Perform a moisture offset if the test material
contains hydrogenous materials other than water or materials that
absorb neutrons. Materials such as cement, gypsum, coal, mica, and
lime are all hydrogenous. Material such as boron and cadmium are
neutron absorbers.
Vertical structures scatter neutrons and gamma photons back to the
gauge. This could result in inaccurate moisture and density readings.
To take readings in a trench or within 0.6 m (2 ft) of a large vertical
structure, perform a trench offset.
If the composition of the test material differs greatly from average
soil and an offset does not provide adequate measurement accuracy,
then the gauge may need to be calibrated. A special calibration
allows the operator to calculate new calibration constants. For more
information on the Special Calibration feature, see Chapter 6.
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