7–2
A
A
b
b
o
o
u
u
t
t
O
O
f
f
f
f
s
s
e
e
t
t
s
s
The Model 3440 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, you can adjust the gauge
readings to correlate to traditional laboratory methods, such as
core samples. The Model 3440 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
you 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 Model 3440 gauge requires a trench 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.
NOTE
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