Model 3440-L 6–15
6. SPECIAL FUNCTIONS
NOMOGRAPH
In some cases, the 3440-L may be used to determine the density of thin
asphalt overlays. This measurement may be performed with the gauge in
backscatter mode and using the “Nomograph” method of density
measurement. It should be noted that this method is not as accurate as a
true thin-layer gauge. However, this method may produce satisfactory
results under many conditions.
When a nuclear gauge is used in backscatter mode on overlays under 3 in.
(7.5 cm), several effects must be overcome to produce an accurate reading.
With most gauges, the primary problem is the result of photons from the
source penetrating deeper than 3 in. (7.5 cm) and scattering back to the
gauge. These backscattered photons from the underlying material will
adversely influence the reading.
Obtaining an accurate overlay density with the Nomograph method
requires that the density of the bottom layer and the thickness of the top
layer be determined. The simplest method of determining the density of the
bottom layer is to take a nuclear gauge measurement prior to applying the
top layer or overlay. With the overlay applied and compacted, the depth of
the layer should be determined. At this time, the gauge may be used to
calculate the overlay layer density.
To access the Nomograph function, press 〈SHIFT〉 and 〈SPECIAL〉 for:
SPECIAL FUNCTION
YES- Next menu
1- STAT TEST
2- DRIFT TEST
Press 〈YES〉 two times for the display:
YES- Next menu
6-SPECIAL CALIB.
7- NOMOGRAPH
8- PRECISION
Press 〈7〉 for the display:
NOMOGRAPH - OFF
Press: 1- enable
2- disable
3- chg/view data
At this time, the operator may enable, disable, or change the Nomograph
function.
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