DMM600 Duff Moisture Meter
The DMM600 presents water content measurement results in volumetric terms
because that is what the DMM600 measures. Conversion to gravimetric
requires knowledge of the material bulk density. Bulk density of duff tends to
be similar for many forest types. If the bulk density of a particular material is
known or measured, the displayed volumetric water content value is easily
converted to gravimetric by adjusting the calibration coefficients.
As an example, consider that the bulk density of a lodgepole pine was
determined to be 0.25 g/cm
3
. The calibration equation to convert circuit output
frequency to volumetric water content is
VolumetricWater Content
freq
freq
=
+
−
5 288 5 905
0142
2
.
.
*
.
*
To convert to gravimetric water content, each calibration equation coefficient is
divided by the bulk density. Applying for this example gives
GravimetricWater Content
freq
freq
=
+
−
21152 23 620
0 568
2
.
.
*
.
*
This is not a general calibration equation but an example.
NOTE
PCDMM can be used to load the modified calibration equation (see FIGURE
7-1). When downloaded, the DMM600 will alternately display volumetric
water content using standard calibration and gravimetric water content using
the modified equation.
FIGURE 7-1. Downloading coefficients to convert to gravimetric water
content
10