Operating The Balance; Basic Weighing Function; General Instructions For "Analytical Weighing - Sartorius ME415S Operating Instructions Manual

Operating the Balance

Basic Weighing Function

Purpose
The basic weighing function is always
accessible and can be used alone
or in combination with an application
program (Toggle between Weight Units,
Counting, Weighing in Percent, etc.).
Features
– Taring the balance
– Assigning IDs to weights
– Printing weights
– Printing ID codes for weights
Soft Key Functions
Cal
Start calibration/adjustment
isoCAL
Press when necessary to
start calibration and
adjustment
S ID
Stored ID entered
General Instructions
for "Analytical Weighing"
Handling Samples and Containers
The sample should be conditioned
to the temperature inside the balance.
This is the only way to avoid errors
caused by air buoyancy and deviations
caused by convection currents at the
surface of the sample.
Since these effects increase proportion-
ally to the volume and surface of the
sample, make sure that the size of the
tare vessel selected is appropriate for
the initial sample.
Never use your bare hands to touch
samples to be weighed. In addition to
the effect of the temperature, the
extremely hygroscopic behavior
of fingerprints left on the sample will
otherwise cause considerable inter-
ference during weight measurement.
Use forceps or a similar utensil that is
appropriate to place your sample care-
fully on the pan. Working with your
balance requires a steady hand and a
smooth, uninterrupted technique.
If the weighing chamber has not been
opened for a relatively long period,
it may have a temperature different
from that of the balance's surrounding
environment. When you open the
weighing chamber, a change in temp-
erature will inevitably occur, due to the
laws of physics, and may show up as
a change in the weight readout.
Therefore, we recommend that before
you begin the actual weighing series you
open and close the weighing chamber at
the same rate as you will be doing during
weighing. After the weighing chamber
has been closed, the weight readout will
usually stabilize after about 8 seconds.
The accuracy of the weight readouts will
increase as you continue weighing with
greater consistency.
Weighing Electrostatically Charged
Samples and Containers
Major measuring errors can occur when
electrostatically charged samples and
containers are weighed. This problem
particularly involves samples that have
extremely poor conductivity (glass, plastic,
filters) since they can discharge electro-
static – i.e., friction-induced – charges only
over a relatively long period of time. The
result is an interaction of forces among the
charges adhering to the sample and the
stationary components of the balance
(weighing chamber base plate, draft shield
construction, balance housing). This is
noticeable when the weight readout drifts.
At high humidity, this effect is not
very pronounced or may not occur at all,
due to the thin layer of water that
condenses on the sample and, through
conductive discharge, counteracts
interfering static electricity.
In addition to taking purely mechanical
counteractive measures (protecting the
sample using a special antistatic weighing
pan – see the "Accessories"), you can
neutralize the surface charges by
"bombarding" them with ions of the
opposite polarity (see page 45 for
instructions on activating the ionizer).
This is a highly effective procedure
for eliminating static electricity.
The balance's environment, including the
operator, can considerably interfere with
weighing results, due to static electricity.
The balances of the Genius Series have
been designed to counteract this phenom-
enon: the glass surfaces of the draft shield
have a special metallic coating.
The rear panel of the balance has a
terminal for connecting an equipotential
grounding conductor. It is used for
additional grounding of a peripheral
device (for example, a vibrating spatula).
This terminal is designed for single
grounding wires up to .25" standard
2
gauge or 6 mm stranded wires and for .18"
2
standard gauge or 4mm stranded wires.
Weighing Magnetic or Magnetizable
Samples
It is technically impossible to avoid the use
of magnetizable materials in the manufac-
ture of balances. Ultimately, the operating
principle of high-resolution balances is
based on electromagnetic force compensa-
tion of the load placed on the weighing
pan.
When magnetic or magnetizable samples
or containers (e.g., a beaker with a stirrer)
are weighed, interactions among the
above-mentioned components of the bal-
ance may occur, distorting weight
readouts.
Unlike deviations caused by electrostatic
charges, magnetic interference is usually
constant over time. However, it is sensitive
to and dependent on the position of the
sample container on the weighing pan and
is also characterized by poor repeatability.
To reduce the effect described above,
we recommend increasing the distance
between the sample and the weighing pan
by inserting a non-magnetizable material
between them (the reduction in force is
proportional to the quadrate of the distance).
In special cases, soft-magnetic plates
should be used to shield against interfering
magnetic effects.
In the presence of extremely strong mag-
netic fields – for instance, when measuring
the susceptibility of a sample in an electro-
magnet – you should use the below-bal-
ance weighing port, which comes standard
on your balance.
39