Campbell Scientific DMM600 Duff Moisture Meter - Manual (Page 17)

DMM600 Duff Moisture Meter
7.4.1.1 Determining Duff Sample Bulk Density
The bulk density of the sample at time of measurement is determined as
follows.
1. After the measurement is made, count the number of compression knob
rotations required to move compression piston from measurement position
to completely out.
2. Use following equation to calculate volume of sample at time of
measurement.
Volume rotations = − 157 97 7 25 . . *
3. Dry then weigh the sample used for the measurement.
4. The bulk density in g/cm 3 is the dry weight divided by the volume.
7.4.2 Duff Size and Water Content Heterogeneity
There is considerable variability in both the physical characteristic and water
content distribution in duff. Because this variability can be significant over a
small area or even within a handful-sized sample, several measurements of the
material are needed to obtain reliable estimates of the water content for the area
of interest.
Duff commonly varies in fragment size, and it may be necessary to grind or
chop the material to improve measurement accuracy and repeatability. A #4
sieve is included with the DMM600 for this purpose. Forcing the sample
material through the sieve will improve measurement accuracy and
repeatability.
The heterogeneity of material size can be characterized by making repeated
measurements of the same material. Place the duff in the sample chamber and
make a measurement. Remove the duff from the chamber and restore its
natural structure by working it by hand. Put the duff back in the sample
chamber and make another measurement. Repeat this process several times. If
the measurements vary by more than about 5% water content, this indicates
that the material should be sieved before measuring to reduce the effect of the
fragment size variation.
7.5 PCDMM Software
7.5.1 Introduction
PCDMM is PC software used to download user defined calibrations, retrieve
calibration coefficients from DMM600, reset DMM600 and monitor battery
voltage.
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