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Basic Weighing Function
Purpose
The basic weighing function is always
accessible and can be used alone or
in combination with an application pro-
gram (Toggle between Weight Units,
Counting, Weighing in Percent, etc.).
Features
– Taring the GPC65
– Assigning IDs to weights
– Printing weights
– Printing ID codes for weights
General Instructions
for "Analytical Weighing"
with Weigh Cells
Handling of Samples and Containers
Samples should be acclimatized to the
temperature of the weigh cell to avoid
negative effects on results, such as
measurement errors and fluctuations
caused by air buoyancy resulting from
convection currents across the surface
of the sample.
These negative effects increase as the
volume and/or surface area of the sam-
ple increases. For this reason, the size of
the container should be appropriate for
the sample.
Samples and containers should not be
touched by the operator's hands, as the
hygroscopic effect of fingerprints and
the effect of the hand's temperature
can influence the measurement results.
Samples must be applied very carefully,
whether manually (using a forceps) or
automatically (by a robot or filling
system).
When designing a draft shield device,
steps must be taken to keep the increase
in temperature within the weighing
chamber to a minimum (e.g., using
a bypass).
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Weighing Electrostatically Charged
Samples or Containers
If a sample or container is electrostatically
charged, significant errors may result
during weighing. Materials with low
conductivity, such as glass, plastic or
filters, are particularly susceptible to
static electricity (resulting, e.g., from
friction) because the weighing pan can
discharge the static electricity only very
slowly.
The result is a force action between the
charge on the sample and the perma-
nently installed parts of the weigh cell.
This causes the readout to fluctuate
constantly.
Ionization can be applied to make the
air around the sample conductive. This
allows the charge to be compensated
through the air, or discharged through
the ground (grounded).
Aside from purely mechanical solutions
(e.g., using a special weighing pan to
shield the system), bombarding the
sample with ions of opposing polarity
to neutralize the surface charge is one
of the most effective methods for
eliminating static electricity.
Sartorius can provide ionization devices
for installation in weighing systems.
The area around the weigh cell can also
contain charges that negatively affect
the accuracy of weighing results.
Appropriate steps taken in the design
of a draft shield device can counteract
such effects.
Weighing Magnetic or Magnetizable
Samples
The use of magnetizable materials in
the manufacture of weigh cells is
unavoidable, primarily because the
operating principle of high-resolution
weigh cells is based on compensation
of the load through magnetic forces.
When weighing magnetic or magnetiza-
ble samples or containers, interaction
between the sample or container and
certain parts inside the weigh cell may
distort weighing results.
To keep such distortion to a minimum,
we recommend increasing the distance
between the sample/container and the
weighing system using a non-magnetic
material. The force is reduced quadrati-
cally with the increase in distance.
Magnetizable or magnetized samples
and the weigh cell itself interact with
magnetic fields and magnetizable or
magnetized parts in the area surroun-
ding the weighing system. The system
can be shielded from external magnetic
fields to some extent using (soft mag-
netic) plates.
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