5–10
OFFSETS – TRENCH
Vertical structures such as the walls of a building, trench, or ditch often
“echo” gamma photons and neutrons back to the gauge. This “echoing”
may adversely affect density and moisture measurements. Trench offsets
compensate for the influence of vertical structures on measurements.
Use a trench offset if taking a measurement inside a trench or within 2 ft
(0.6 m) of a large vertical structure. When used, the trench offset adjusts all
moisture measurements, but only the density measurements from
backscatter through 4 in. (10 cm).
To perform a trench offset:
As described on page 2–13, take the daily standard count outside the
trench and record the moisture and density count values.
Place the reference standard block and gauge in the trench. Position
the gauge on top of the reference standard block as in Figure 5–1.
Take a one-minute count using the Trench Offset mode as follows.
NOTE
During the one-minute count, the gauge must be the same
distance from the wall as it will be during the anticipated test
readings.
Press 〈3〉 from the display on page 5–3.
Trench Offset
DISABLED
Want to use
Trench Offset?
Press 〈YES〉 to perform the trench offset.
Trench Offset
M. constant=xxx
D. constant=xxx
Want to change?
Press 〈YES〉 to perform a new offset. Press 〈NO/CE〉 to use the
existing offset constants. If a new offset is to be performed, the display
will be:
Rod -> SAFE pos.
Press START for
1 min. STD cnt.
in Trench.
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