KERN & SOHN DLB 160-3A - Manual (Page 49)

DLB_A-BA-e-1511 49
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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Solvents
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etc...
There are various methods to analyse moisture in a product.
KERN MLB 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 DLB
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 DLB replaces a different drying method (such as a drying
chamber) as the KERN DLB achieves shorter measuring times during a simplified
operation. For that reason the conventional measuring method must be matched to the
KERN DLB in order to achieve comparable results.
• Carry out parallel measurement
Lower temperature setting for KERN DLB than drying chamber method
• Result of KERN DLB does not match reference
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Repeat measurement with changed temperature setting
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Vary shutoff criterion