KERN & SOHN DBS 60-3 - Manual (Page 75)

DBS-BA-e-1311 75
12 General information concerning moisture analysis
12.1 Application
In all cases where moisture is added to or removed from products, a fast
determination of the moisture content is of enormous importance. For countless
products the moisture content is not only a quality feature but also an important cost
factor. Very often fixed limits for moisture content apply to the trade in industrial or
agricultural goods as well as chemical or food products which are defined by terms of
delivery and general standards.
12.2 Basics
Moisture does not only mean water but includes all substances that evaporate when
heated up. In addition to water this includes,
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Fats
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Oils
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Alcohol
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Solvent
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etc...
There are various methods to analyse moisture in a product.
KERN DBS uses a method called thermogravimetrics. In accord with this method,
the sample is weighed before and after heating, determining the material moisture by
looking at the difference.
The conventional drying chamber method follows the same principle, with the
exception that this method requires a considerably longer measuring period. . In
accord with the drying chamber method, the sample is heated from the outside to the
inside by a hot air current, so as to remove the moisture. The radiation applied in the
KERN DBS penetrates mainly the sample in order to be transformed inside it into
heat energy that is, warming from the inside to the outside. A minor amount of
radiation is reflected by the sample, a reflection that is less in dark samples than in
light-coloured ones. The depth of penetration of the radiation depends on the
permeability of the sample. In samples of low permeability the radiation only
penetrates the outer layers of the sample, possibly resulting in imperfect drying,
incrustation or burning. For that reason the preparation of a sample is of great
importance.
12.3 Adjustment to existing measuring method
Quite frequently the KERN DBS replaces a different drying method (such as a drying
chamber) as the KERN DBS achieves shorter measuring times during a simplified
operation. For that reason the conventional measuring method must be matched to
the KERN DBS in order to achieve comparable results.
• Carry out parallel measurement
Lower temperature setting for KERN DBS than drying chamber method
• Result of KERN DBS does not match reference
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Repeat measurement with changed temperature setting
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Vary switch-off criterion