AquaLab 2 ABOUT AQUALAB
water activity of a sample. The sensor is suspended in the headspace
of the chamber and uses a special polymide material sandwiched be-
tween two electrodes to sense humidity changes. The sensor converts
the humidity value into a specific capacitance, which is then mea-
sured electronically by the circuit. This signal is then translated by
the software and displayed as water activity on the instrument screen.
At equilibrium, the relative humidity of the air in the chamber is the
same as the water activity of the sample.
2.5 AquaLab and Temperature
Samples not read at room temperature during the read cycle equili-
brate with the AquaLab temperature before the water activity dis-
plays. Large temperature differences cause longer reading times,
since the Series 4 does not make a complete and accurate reading un-
til the sample and the instrument equilibrate to ±4
◦
C of each other.
There are several advantages in having a temperature-controlled wa-
ter activity meter. A few major reasons are:
1. Research purposes. Researchers can use temperature con-
trol to study the effects of temperature on the water activity of
a sample, make a comparison of the water activity of different
samples independent of temperature, and conduct accelerated
shelf-life studies or other water activity studies where temper-
ature control is critical. There are many shelf-life, packaging,
and isotherm studies in which temperature control would be
very beneficial. (see Section 14 for further resources)
2. Compliance with government or internal regulations for
specific products. Though the water activity of most products
varies by less than ±0.002 per
◦
C, some regulations require
measurement at a specific temperature. The most common
specification is 25
◦
C, though 20
◦
C is sometimes indicated.
3. Minimization of extreme ambient temperature fluctu-
ations. If the environmental and AquaLab temperatures fluc-
tuate by as much as ±5
◦
C daily, water activity readings vary
by ±0.01 a
w
. Temperature control eliminates variations due to
changes in ambient conditions.
7
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