Berthold LB 442, Operating Manual

Page: 74 / 158

7.3 Calibration
72
7.3.3 Preparation for Calibration Weighing
Required material quantity
At least 20% material of the maximum load is needed for one cali-
bration weighing.
Example: If the measuring range is 0-200 t, at least 40 t material
has to be available for this calibration weighing. For a four-point
calibration 4 times as much material, i.e. 160 t.
In general one can say: the longer a calibration weighing is run-
ning, the more accurate the result of the calibration will be. There-
fore, calibration weighings are often performed at maximum load,
in our example 200 t. Essentially, however, this is dependent upon
the situation on site.
Unforeseen
Since a calibration weighing is typically performed outside a regu-
lar production process, one has to expect that a calibration weigh-
ing may often fail for technical or other reasons. For this case,
more material should be prepared.
Comparative weigher
As mentioned above, calibration is a correlation of weight to count
rate. To get a comparative weight, the material has to be weighed
on another pair of scales, i.e. a comparative weigher. Which kind
of comparative weighings are performed is dependent on the situa-
tion on site.
-
Truck weigher
The material conveyed through the measuring frame is loaded onto
a truck and then moved onto a truck weigher. The truck weigher is
the comparative weigher. Another possibility is to weigh the mate-
rial prior to calibration and to have it ready for calibration.
-
Storage container with weighing cell
The material measured by the measuring frame is conveyed in a
storage container standing on weighing cells.
-
Calibration in kg/m
Another possibility is calibration in kg/m. With material that is
moved through the measuring frame as "endless plate", e.g. plates
of 1 m length can be cut out and weighed. While the material is
transported through the measuring frame, the LB 442 averages the
count rate, at the same time the reference samples have to be cut
out. The averaging time should be at least 5 minutes. The com-
parative weight is calculated from the average value of several
plates and entered in kg/m.
The unit kg/m has to be selected for this kind of calibration. See
also "Select unit" on page 51.
Prerequisite is that the plates always have the same width; other-
wise, the measurement has to be performed at different product
calibrations.