28
aw value measurement
The aw value (water activity) plays a decisive role fot the pro-
duct quality and the growth of bacteria. Bacteria need high water
activity (salmonella min. aw = 0.95). The amount of water is not
important in this case, the degree of availability is more
important.
aw = 0
➪
anhydrous substances
aw = 1
➪
pure water
The reference temperature is always given because water activity
depends on temperature.
In order to measure the aw value you will need, in addition to the
testo 400/testo 650 measuring instrument, a highly accurate
humidity probe and a measuring device (accessories).
It consists of a pressure tight measuring chamber which is
filled with the goods to be measured. Fill the container half the
minimum. The time of adjustment takes approx. 30 minutes at
constant temperature depending on the goods to be measured.
Contact your Testo dealer and ask for the detailed scientific
paper.
A new function button is generated once a humidity probe is
connected. This can only be assigned or is only visible in the
display if exactly one humidity probe is connected (-Do not
connect any more than 1 probe!-). Start the aw-value
measurement by pressing this function button.
The aw value measurement is finished, if no changes occur
within a defined period of time. Enter these values in the main
menu under Special aw value.
Input limits: 1.0 to 10.0 %RH and 1 to 60 min.
Standard setting 1.0 %RH, 5 min.
Move the cursor with to the number to be changed and
change the number with / . Confirm the settings with
.
4400..11
%
2255..11
°C
aw value
aw value
0011..00
%
0055
min
to
Change
SSppeecciiaall
Memory
Meßpro
Probe
Special
Units
Printer
SSppeezziiaall
Parameter
Pitot factor
Corr. factor
VAC module
aw value
aw value
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