Water activity

Details for
portable instruments



  Portable instrument details

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.
Navigation: Water activity
  What is water activity
  Test Introduction
Test details
  Salt solutions used
  Calibration samples used
  Desktop instruments
    Portable instruments
  Desktop instruments
  Decagon AquaLab 3TE
  Novasina LabMASTER-aw
  Rotronic HygroLab 2
  Portable instruments
  Decagon PawKit
  Rotronic HygroPalm
  Testo 650
  Desktop instruments
  Portable instruments

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.

    Test of Decagon PawKit          
  Test of Rotronic HygroPalm AW1          
  Test of Testo Testo 650   aw instrument test introduction EminTech Start Page