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ment, until you have no bigger shift once measurement is stable. That is your
stability observation time for the currently measured product type.
Note:
The logged data measurement data on the SD-Card can be displayed as
a graph within NovalogMC. This might simplify the finding of the best stability
observation time
4.2.4 Stable Indicator / Progress bar
For the ease of use, the progress of equilibrium establishment and stable condi-
tions achievement based on user‘s programming is visible on the measurement
screen, by a stable indicator (progress bar). In addition, other useful information
around stability is displayed as well.
The stable indicator has two colors:
•
Yellow indicates the remaining „time“ to complete the measurement
• Green indicates the progress of the measurement
In other words, the greener the bar, the closer the measurement is to it‘s end.
The selected stability mode or the programmed stability observation time is
listed below the progress bar.
Depending on the settings and condition of the aw meter, it can occur that the
progress bar is fully green but measurement is not considered as stable and
stability is retarded (delayed). Respective information is displayed directly below
the stable mode info in red color.
Retarded (gradient)
Progress bar is green, retarded (gradient) is displayed. In this case, the water
activity value is questionable due to a remarkable temperature difference bet-
ween sample surface (IR) and sensor. If message persists, open chamber, check,
if measurement table and outer metal ring of measurement head are clean and
free of dust and dirt and redo the measurement.
Retarded (temp)
Progress bar is green, retarded (temp) is displayed. It indicates that tempera-
ture control could not reach a stable target value. This delay and error message
can be avoided by setting „Stability check temperature“ to „OFF“ in „Chamber
Settings“. However, it can occur that measurement will not be finished at target
tempe/-0.05°C. If temperature control is switched off, retarded (temp) is
it as well.
4.2.5 Stability check temperature
This setting allows the user to distinguish between a measurement which is
exactly at target measurement temperature or if it is also ok if temperature is
just around it as by experience, some samples have a temperature coefficient of
0.002aw/°K, so even if current temperature is 2°C away from target, we speak
about a deviation of 0.004aw from the final value. Something which might be
neglectable, depending on the internal requirements in terms of water activity
value accuracy.
Stability check temperture „ON“
Stability is reached if aw value is stable plus once sample has reached target
measurement tempe/-0.05°C. This mode ensures accuracy and precisi-
on as well as high repeatability but it takes longer as sample temperature must
be exactly at target. Use this mode if you want to compare water activity values
from batch to batch (quality trending) or different products. It is mandatory to
record the values at the same temperature if you compare them!