Water activity
instrument
tests
Details for
portable instruments
EminTech
The instruments were kindly lent out by the Swedish suppliers.
The suppliers knew that the instruments were going to be
tested and that the tests would be published at this site.
The measurements were run at room temperature, 22 - 23 °C.
The tests were run during end of March, 2004.
Decagon PawKit
One single measurement using PawKit took about 5 minutes, after
which a
signal sounded.
During the first three measurement series the criterion was used,
that two
consecutive measurements should show the same result.
Normal total time
for the criterion to be fulfilled was 3-4
measurements,
giving a total analysis
time of about 20 minutes.
Note that PawKit only showed two figures in the
result.
In the fourth series, PawK4c, a stable value was defined as
three consecutive
equal results.
This method gave no significant increase in accuracy.
After completion of the first measurement series, PawK1c,
the instrument
was rested for about 2 days.
The next measurement series, PawK2c, gave about
0.02 aw higher
values. Calibration resulted in a decrease of read values
with
0.01 aw. After calibration the device appeared stable.
Rotronic HygroPalm AW1
HygroPalm AW1 was used in Quick Mode using factory defaults
for when a measurement
was finished.
The criterion was used, that two consecutive measurements
should
show the same result. One single measurement took about 5 minutes
and 5-7 measurements were required to fulfil the criterion.
A normal analysis
time was hence about 30 minutes.
Note that the result was given with three
figures.
After battery replacement it became obvious that the measurement
results
increased. The instrument was calibrated, resulting in a
decrease of
read values with 0.015 aw.
During one measurement reading, the fan in the sample cell
was not running.
No significant alteration of the measured
result was, however, noted.
Running HygroPalm in continuous mode (AwE) gave no significant
difference
in results. Each measurement was given about one hour.
Testo 650
Due to lack of information in the manual, Testo 650 was run in
continuous
mode only. The criterion was used, that two subsequent
readings should show
the same result. The time between readings
varied. Measurement time was
estimated to be about one hour.
The results show that the first measurement series, Testo1c, gave
very good
results for values lower than aw = 0.97. The following two
series showed
significantly increasing values for the NaCl sample.
The results for values above aw = 0.97 could not increase more than
in the
first measurement due to instrument cut-off at 0.999.
The battery was exchanged after the NaCl sample in series
Testo2c.
Hence does battery voltage not explain the increase between this
series and series Testo1c.