Campbell Scientific DMM600 Duff Moisture Meter - Manual (Page 21)

DMM600 Duff Moisture Meter
sitting time will allow the water content to equilibrate throughout the
sample.
2. Load a portion of the sample into the chamber and take a measurement.
See Section 7.4.2, Duff Size and Water Content Heterogeneity, for
discussion of sample heterogeneity. Record the frequency in MHz that is
displayed as “Raw”.
3. Unscrew the compression knob counting the number of turns from the
position of measurement to fully out. Use the index on the compression
knob and the radial lines on the sample chamber cap for this. Record the
number of turns.
4. Remove the material from the sample chamber to a container of known
weight. Weigh the sample and container. Repeat steps 2 and 3 at least
three times using different portions of the sample.
5. Dry the samples and then weigh. See Section 7.7, Drying Samples and
Calculating Volumetric Water Content, for guidance on drying samples.
6. Using the dried samples repeat steps 2 through 4. The dried sample
measurements are zero water content values.
7. Use the following equation to calculate volume of sample at time of
measurement.
Volume rotations = − 157 97 7 25 . . *
8. Calculate the bulk density (g/cm 3 ) by dividing the dry weight of the
sample by the volume.
9. Estimate the amount of water to add to the dry samples to obtain 50%
volumetric water content using the following equation.
wet sample weight dry sample weight
bulk density
= +
⎛
⎝
⎜
⎞
⎠
⎟ *
*
50
100
1
The value 50 is the target volumetric water content.
10. Place the sample(s) in sealable plastic bag(s) and add water. Work water
into sample. Set aside for 8 hours to allow equilibration.
11. Repeat steps 2 through 8.
12. Repeat steps 9 through 11 for other target volumetric water contents to
provide a range of calibration water contents.
13. Derive the calibration equation using polynomial curve fitting such as the
trendline function of Microsoft Excel.
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