3.
To obtain the second reference value “dry glass beads”, set the probe vertically into the vessel of
dry glass beads up to the lower rim of the probe body. Make sure that the probe lead exerts no
noticeable load on the probe when doing so in order to prevent creating an air space between the
probe rods and glass beads. Tap the outside of the vessel lightly to ensure that the beads sit
tightly around the rods. The glass bead vessel and the probe themselves must not be in contact
with any metal objects (e.g. a metal table top).
Note: Use only the glass beads we supply with the “calibration set” as otherwise completely dif-
ferent results may be obtained if others are used. The glass beads must be dry and clean and at
room temperature (18-24°C).
The probe, too, must be at room temperature as otherwise condensation may form on the probe
rods and thereby serious distort the results.
The diameter of the vessel used must be at least 18-20 cm; where probe rods are immersed com-
pletely, at least 3-4 cm must remain between the tips of the rods and the bottom of the vessel.
Reason:
The single-point correction shifts the measurement value by only one offset, the slope remains un-
changed. In other words: the measurement value has been corrected only by a single additive con-
stant (positive or negative), the sensitivity remains unchanged so the scale of the deviation can differ
depending on the moisture range in which the measurement is being taken.
The main factor influencing the offset is a differing length of the probe lead. The main factor influenc-
ing the slope is a differing length of the probe rods. There are, however, other parameters as well that
can influence both.
The single-point offset correction is to be regarded as no more than a stopgap because – arising from
the dielectric constant of air compared to that of the other material – it is not carried out in the range of
the target moisture for the material to be dried (generally ~8-14%) , but with a theoretical moisture
value of -11% (air). Deviations in the slope (sensor sensitivity) therefore have a considerably greater
effect at approx. 20 % on either side of a given moisture range.
1. If the readings deviate excessively from the reference values (cf. table at the top of section 4.2.2
Reference values of the calibration media used for the basis calibration
must be repeated using the affected TRIME
®
-GW instruments.
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Summary of Contents for Trime-GW
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