Ohaus MB45 MOISTURE ANALYZER Manual - Manual (Page 55)

MB45 53
8.6 Analysis of the drying profile
In the first type, the drying profile is asymptotic. The amount of moisture lost assumes a constant value
and no longer changes after long drying times. With this drying profile, repeatable determinations of the
moisture content are always simple.
The measurement result then corresponds exactly to the constant value of the asymptote. It is also
correspondingly easy to find a suitable switch-off criterion.
In the second type, drying runs quickly at the start and then flattens out. The moisture content never
assumes a constant value. The causes of such a drying profile can be as follows:
The sample exhibits thermal
decomposition, the decomposition products
vaporize and the sample continuously
loses weight. Fats, oils, plasticizers or other
volatile components can lead to
superimposed profiles owing to their slower
vaporization than water. The difficult to
volatilize components lead to a slow,
continuous decrease in weight.
Measurement results of such a drying
profile can be optimized:
— Lowering the temperature can slow down the decomposition reaction.
— The selection of a suitable switch-off criterion can allow recognition of the end of the analysis at
the desired break point of the drying curve.
— The selection of a constant drying time often provides good measurement results.
— Keep the initial weight of the sample constant (+10%....+20%).