
5 EN
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.
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.
• 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 50mm. 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.
– The material should be preferably homogenous and not
have any air pockets.
• Electrically conducting materials or electrical fields
– If a construction material contains electrically
conducting substances, the dielectric constant is also
increased, which then simulates high moisture values.
Consequently, a too high measured value will be
displayed.
– From visual inspection it is not always apparent,
whether there are any electrically conducting
substances inside the construction material. Some of
the main error sources here are in particular
reinforcements, metal laminations and conducting
insulation such as slag in timber beam ceiling
constructions. Especially in case of insulation materials
with metal lamination, measured values are often
misinterpreted.
– Avoid static charge of the material to be measured due
to friction. Static charge distorts the measurement
result.
– With a wood moisture of less than 10%RH,
electrostatic forces may occur at the good to be
measured. This can falsify the result of the
measurement. Experience has shown that this occurs at
the outlet of veneer drying plants. Remove the static
charge by use of suitable grounding measures.
– For optimum conditions neither electrical fields nor
conducting materials should be present.