Troxler Application Brief - Troxler Electronic Laboratories

Troxler Electronic Laboratories, Inc.
PO Box 12057 • 3008 Cornwallis Rd. • Research Triangle Park, NC 27709
Tel: (919) 549-8661 • Fax: (919) 549-0761 • web:
Troxler Application Brief
An Instruction Guide for the
Trench Correction Procedure for Troxler 3400 Series Gauges
October, 1998
In order to perform moisture and density tests in a trench or against a large solid object it is necessary to
perform a trench offset to adjust the gauge. The gauge will often read a falsely high moisture content if this is
not done. Moisture present in the walls can thermalize neutrons which return to the gauge and are read as
moisture by the He3 detector in the gauge. If the trench wall is at least 0.6 meters (24 inches) from each side of
the gauge, the trench effect will not be significant. If the trench is at least 0.6 meter (24 inches) wide and the
gauge is used in direct transmission mode (at a 10 cm (4 inch) depth or greater) the density error will be
insignificant. Use the following procedure to avoid erroneous readings.
1. Models 3411 and 3401:
It is necessary to determine the increase in the moisture count due to the hydrogen bearing material in the trench
walls. This difference will be subtracted from the moisture measurement counts before the moisture ratio is
determined. Perform the daily standard count outside of the trench or away from the large vertical object on the
reference standard block as usual.
a.) Place the gauge in the trench or near the vertical object and take a count with the gauge set on the reference
standard at the desired test site. (3411 operators – do not take a standard count, take a measurement;
pressing the shift key will erase the daily standard count) The distance from the wall must be the same as
the area to be tested. Set the PWR/TIME switch at NORM for this count.
b.) Subtract the moisture standard count from the moisture count taken in the trench.
c.) 3401 – this moisture offset value will be subtracted from the moisture measurement count before you divide
by the daily moisture standard count.
e.) 3411 – this moisture offset value should be set on
the moisture correction switches. This value is
preset as a negative number by depressing and
holding the SHIFT key and depressing MC. The
value set on the moisture correction switches should
now appear on the display. This offset can be
removed by setting the switches back to “00” and
entering this value.
Be sure to return the moisture correction switches to “00” (or the correct factor if a moisture offset is
necessary) after entering the trench correction.
2. 3430:
It is necessary to determine the increase in the moisture count due to the hydrogen bearing material in the trench
walls or the “echo” effect from a vertical object. Take the daily standard count (outside the trench) and record
the moisture and density count values. (DS & MS)
a.) Place the gauge on the reference block in the trench the same distance from the wall as the anticipated
readings. Set the count time to 4 minutes. Press <ENTER> to start the count. Record these values (DCtrench
and MCtrench).
b.) Subtract the daily standard counts from the trench counts.
Dens. offset = (DCtrench ) - DS
Moist. offset = (MCtrench ) - MS
c.) Choose trench from the Offset options under the Special functions. The gauge will request the Density
const and Moist const; enter the above calculated values ignoring the +/- sign on the display.
3. 3440 and 3450
a.) Perform a daily standard count on the reference
standard block as usual.
b.) Press the OFFSET key to access the proper menu.
Choose the trench option from the menu.
c.) When enabled, the most current trench offset values will be displayed. If this is the offset desired, then do
not change or create a new one. If the environment (trench) has changed a new offset must be performed.
d.) Position the gauge on the reference standard block in the trench at the same position as the anticipated
measurements. The display prompts you to now press the START key to begin the 1 minute count.
3450 – accept the values if the count was performed properly.
e.) Disable trench offset when not in use.
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