
5Operating manual – Moisture measuring device BM12 EN
The measuring device at hand serves for the rough determination
of the material or wood moisture content according to the
resistance measuring method. Fields of application are wood
moisture measurements of sawn timber and firewood. Moreover,
the measuring device can be used to detect the moisture in soft
building materials such as gypsum or plaster.
The resistance measuring method is an indirect measurement
method, since the moisture content of the measured material is
deduced from the its conductivity.
Influencing variables suitable to change the conductivity, e.g.
electrically conducting materials or dissolved salts, hence also
have a direct influence on the determined measured values.
Therefore, the displayed measured values can only be considered
as indicator of the moisture content.
Notes on use regarding the wood moisture measurement:
For wood moisture measurement a calibration curve is stored in
the device, which corresponds to the average of the relevant
kinds of wood in Europe based on a wood temperature of 20 °C.
Therefore, no further settings are required for a quick rough
determination of the wood moisture content. If precise wood
moisture values are required for other wood temperatures or with
due regard of the type and bulk density of a certain timber, an
additional control measurement applying the Darr procedure or
else using a wood moisture measuring device with temperature
comparison function and selection option for the specific wood
type calibration is recommended.
• Always insert the measuring tips transverse to the wood fibre
direction. The conductivity transverse to the wood fibre
direction is lower than that in line with it.
• 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.
• Oily and/or aqueous timber preservatives affect the
measurement result.
• If possible, do not measure wood with a temperature
below -5 °C. Too low wood temperatures distort the result of
the measurement.
• 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 %, electrostatic forces
can appear 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.
• The measurement's accuracy depends on the contact
pressure of the measuring tips. The measuring tips must be
connected to the wood in a way that the contact resistance is
small as compared to the measuring resistance.
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 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.
Further observe disruptive influences due to electrically
conducting substances:
If a construction material contains electrically conducting
substances, it also has a lower resistance value, which then
simulates high moisture values. Which means that a too high
measured value is 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 during the resistance
measurement. Quantitative conclusions about the moisture
content of the mineral material to be measured can only be drawn
by applying the Darr procedure or the CM method.
Measuring principle