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2. General Product Description
2.1 System Overview
The LabTouch-aw system has been specifi cally developed for determining the
water activity in a test sample like food, cosmetics or pharmaceuticals. Water
activity is defi ned as the current volume and availability of “free” water in a
sample and should not be directly compared with the water content (g water/
g sample). The water activity is given as the aw – value and ranges between
0 (absolute dryness) and 1 (100% relative humidity) and is a relative, sample-
mass independent measurement. Only this free water takes an active part in
the exchange of moisture with the ambient air and can possibly form the ideal
medium for microbiological growth on the surface and infl uences the biological
functions of microorganisms which has an impact on the microbiological stability
plus chemical and physical properties of a product.
Special laboratory equipment is required for water activity (aw -value)
determination which quantifi es the air humidity directly over a sample in a
closed chamber after reaching the humidity equilibrium between free water in
the sample and water in the surrounding air.
The measured air humidity is directly proportional to the aw -value. An accurate
and reproducible measurement is thereby only possible if the sample temperature
is kept constant (i.e. 25°C) and if the measurement is taken after reaching
the humidity equilibrium. Thus it is obvious that the measurement of water
activity always take some time, means is not fi nished within a few seconds.
The establishment of the equilibrium is sample-independent and can not be
shortened anyhow due to the fact that it is physics and chemistry.
An inevitable pre-requisite for determining water activity with extreme precision
is the use of an excellent moisture sensor that provides exact, reproducible
response over a very wide range (moisture from 0....100% rH), no hysteresis
and a good chemical robustness. Novasina has been developing special
electrolytic moisture sensors that stand out for such unique properties for more
than 50 years.
The integrated, resistive electrolytic LabTouch-aw sensor is based on the new
chemical substance of the Novasina „Novalyte Technology“, which achieves
the required accuracy and reproducibility for the daily sample measurement
in the lab.
The complete LabTouch-aw system comprises two software options and can
be optimally adapted to customer's needs.
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