TAKING THE STANDARD COUNT
The front of the 3440-L gauge is closest to you when the gauge is placed
with the source rod to the left and the control panel to the right, as shown
in Figure 2–1. The handle contains the indexer trigger mechanism, used to
position the source rod on the notched index rod.
NOTE
The source rod should always be in the SAFE position
when the gauge is not in use.
NOTE
2. GETTING STARTED
All Troxler nuclear gauges use low-level radioactive
sources for taking measurements. The sources in the
3440-L gauge have a half-life of 30 years (cesium-137) and
432 years (americium 241:beryllium). In other words, the
amount of radioactivity from the cesium source will be
reduced by one-half (1/2) in 30 years. Because of this
continual decay, the standard count is taken to re-adjust
the gauge to compensate for the decay. This decay is a
known occurrence and will not compromise the accuracy
of the gauge as long as the standard counts are taken. It is
important to take the standard count when a gauge is
initially received from the factory and before taking
measurements at the worksite.
The gauge should be turned ON before leaving for the worksite. This
allows the gauge to complete its self-test routine while in transit. The
standard count set can then be taken upon arrival at the work site without
any delays. The gauge automatically compares the new density and
moisture standard counts to the average of the values from the last four
standard counts. The new standard count will “pass” if the density standard
count is within 1% of the density average and the moisture standard count
is within 2% of the moisture average. After taking the standard count, be
sure to enter it in the log.
To take a standard count, place the reference standard block on a flat
surface at least 6 ft (2 m) from any vehicle or structure, and a minimum of
30 ft (10 m) from any other radioactive source. The surface can be asphalt
or concrete pavement, compacted aggregate or a similar surface with
density not less than 100 pcf (1600 kg/m
3
). Do not use truck beds,
tailgates, tabletops, and so on.
Model 3440-L 2–13
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