
EN 7
moisture measuring device BM40
Measuring principle
The measuring device at hand serves for the rough
determination of the material or wood moisture content
according to the dielectric measuring principle. Fields of
application include the non-destructive moisture measurement
of sawn timber, lumber and firewood as well as of mineral
building materials.
The dielectric measuring method is an indirect measurement
method, since the moisture content of the measured material is
deduced from the changed dielectric permittivity.
Influencing variables suitable to change this parameter, e.g.
electrically conducting materials or dissolved salts, hence also
have a direct influence on the determined measured values.
Since the exact composition of building materials is generally
unknown before a moisture measurement, the displayed
measured values can only be regarded as an indicator of the
moisture content.
General notes on use
Calibration curves for measuring the moisture level in different
mineral building materials, hardwood, softwood and chipboard
are stored in the device. If precise material moisture values are
required, an additional control measurement applying the Darr
procedure is recommended. Especially for precise wood
moisture measurements for other wood temperatures or with
due regard to the type and bulk density of a certain timber it is
recommended to use a wood moisture measuring device with
temperature comparison function and selection option for the
specific wood type calibration.
• When selecting the measuring positions observe the
following:
– Always measure the material moisture at three different
positions in order to achieve a sufficient accuracy by
means of the arithmetic average.
– Do not measure the face, because there are mainly dry
areas.
– Preferably do not measure at cracks, branches or resin
pockets either.
• The measurement results are only to be used as reference
for a rough orientation.
• The height of the measured value can be calculated from
the determined dielectric constant of the measured
material. Dry air has a constant of 1, water 80. Hence, the
more humidity is contained in the material, the higher will
be the displayed measured value.
• Another important variable influencing the measured value
is the bulk density of the good to be measured. The higher
the bulk density, the higher the measured value.
Notes on use regarding the material moisture measurement
No further settings are required for the quick determination of
the material moisture at the device. Nevertheless, when
assessing the measurement results one has to bear in mind that
the results can be influenced by various factors.
• Performing the measurement
– The measurement's accuracy depends on the contact
pressure of the measuring electrodes. Ideally, they
should be applied with a steady contact pressure of
approx. 10N (this corresponds to approx. 1kg of
weight force), however not bent to the point of
overlapping.
• Measuring depth
– Depending on the material's bulk density and degree of
moisture penetration, the device's penetration depth
ranges up to 40mm. Conclusions regarding zones
located at a lower level cannot be drawn.
• Material characteristics
– Increased occurrences of soluble salts in the measured
material can distort the result of the measurement. The
more salts present, the higher the conductivity of the
material and the higher will be the displayed
measurement value.
– If possible, do not measure wood with a temperature
below -5 °C. Too low wood temperatures distort the
result of the measurement.
– Material aggregates and their concentration, e.g. in
screed or concrete, can also considerably influence the
height of the measured value.
– The material should be preferably homogenous and not
have any air pockets.