OFFSETS
The Model 3430 is factory-calibrated for soils, asphalt, and concrete
with an approximate density range of 1100 to 2700 kg/m
3
(70 to 170
pcf). With an offset, the operator can adjust the gauge readings to
correlate to traditional laboratory methods, such as core samples.
The 3430 gauge provides three offsets: density, moisture, and
trench.
NOTE
When an offset has been enabled, all future readings will
automatically be adjusted with the offset factor
regardless of the test site. It is very important that the
operator disable the offset function prior to taking
readings on materials that do not require an offset.
Offsets are disabled if the gauge is turned off for more
than 10 seconds.
Density offsets are common when the material being measured is
outside the range of 70 to 170 pcf (1121 to 2723 kg/m
3
) or if the
material composition varies from average soil/asphalt on which the
factory calibration is based.
Moisture offsets are required for accurate measurements if the
material to be measured contains elements that can cause the gauge
to yield erroneous results. A negative offset is required if the
material to be measured is high in hydrogenous components such as
cement, gypsum, coal, or lime. A positive offset is required if the
material is high in neutron-absorbing material such as boron or
cadmium.
The 3430 gauge requires an offset if measurements are to be taken
inside a trench or close to vertical structures. Vertical structures can
scatter neutrons and gamma photons back to the gauge, increasing
the possibility of moisture or density errors due to high counts.
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