GANN Hydromette RTU 600 Betriebsanleitung Seite 16

Species Correction
The electrical resistance of the different species of wood may vary considerably at the same moisture content. This
requires a correction of the readings according to the species of wood to be tested. With the Hydromette RTU
600 some 81 different meter calibrations can be set for automatic species correction of the readings. The
appropriate setting can be found in the table supplied with each meter, in which some 250 species of wood
have been classified according to their moisture dependent resistance curve.
Testing non-classified species of wood
As generally known, the accuracy of electrical wood moisture meters is affected by differences in species and
conditions of growth of the timber to be measured. However, even in these cases the unique device of the
Hydromette RTU 600 for automatic species correction of the readings permits a quick and smooth adaption
to altered conditions.
In order to determine the proper setting of the wood species selector switches »X« and »Y« ((4) and (5)) in
such cases or for species of wood not classified in the table of wood species, proceed as follows:
The exact moisture content, if not already known, should be determined from a very wet and a dry specimen
of the relevant species of wood by means of an oven test. For this purpose only a part of the wet specimen
should be used, whereas the remainder should be packed in an air-tight plastic foil and stored at 10 - 20 °C.
The test specimen should be weighed and then dried at 100 - 105 °C to constant weight. The moisture content in
percent is calculated according to the formula:
Loss in weight x 100
___________________
= wood moisture in % of dry weight
Dry weight
After obtaining the result of the oven test, the remaining part of the test specimen is to be measured with the
species selector switch »Y« (5) set to position »5«, whereas selector »X« (4) is successively switched to all
positions (1 to 9) and finally left at that position at which the reading displayed deviates least from the actual
moisture content obtained by the oven test.
Then proceed with the dry specimen in the same way, i.e. determine from a part of it the actual moisture content
by an oven test and measure the remaining part with the moisture meter by turning selector »Y« from position 1 to
9. In this case, too, the switch should be left at that setting at which the reading displayed deviates least from
the actual moisture content found by the oven test. If this should be the position »5«, the setting found for the
switch »X« can also be regarded as definitive.
If the slightest deviation is found with another setting of the switch »Y«, the wet specimen must be tested once
again to see whether the accuracy of the reading can be improved still further if the switch
»X« is set to one of the two neighbouring positions, e.g. if the greatest accuracy has been found at the first
measurement at position »4«, it should be checked if the accuracy can be improved at the positions »3« or
»5«. If this is not the case, the setting found for the switch »Y« may also be regarded as definitive, otherwi-
se the dry specimen should be checked once more to see whether an improvement in the accuracy of rea-
dings can be obtained at one of the two neighbouring positions.
The settings found in this way for the two switches can now be used for all future measurements of the rel-
evant species of wood.
Temperature Compensation
The built-in device for automatic temperature compensation of the readings permits also accurate measure-
ments on cold or hot timber, without the need for using correction tables.
For measurements at normal ambient temperatures, set selector switch (6) to 20 °C (68 °F). For temperatures
below or above 20 °C, e.g. during or immediately after kiln drying, set switch to actual wood temperature or
to temperature prevailing in the dry kiln. Frozen wood with moisture content in excess of 20 % cannot be
measured.
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15.11.2006 Hydromette RTU 600 #013629