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Chemir Analytical Services conducted balance stability tests on the XPert Filtered
Balance System mounted on a Solid Epoxy Work Surface. No marble slab was
used. The enclosure was tested while operating at three face velocities – 0, 78 fpm
(factory setting), and 100 fpm. Samples of 5 mg, 50 mg and 100 mg were weighed
on an analytical balance located inside the enclosure. Test results were excellent
and confirm that the XPert Filtered Balance System, including its built-in blower
and the airflow through the enclosure, caused no detectable instability to the
balance. The weight of each sample was stable to five decimal places.
Listed next are some hints on balance stability.
1.
Balance is not calibrated (or at least not recently) – All balances should be
calibrated at least annually or after they have been shipped or moved
around frequently. If the balance has just been moved around the lab, it
probably will not require recalibration. Most new balances have an internal
mechanism that compensates for drift and vibration. If in doubt, schedule
recalibration.
2.
Shield is not tight on the balance – If the balance shield is loose, air can get
into the weighing chamber and cause fluctuation in sensitive weigh
applications. In other words, air can get into the balance and cause the
weigh plate to fluctuate. The best way to address the problem is to have
the balance servicer fix the balance shield.
3.
There is no shield on the balance – Sometimes open balances without
shields fluctuate. Try running the ventilated balance enclosure at slower
speeds such as 60-70 feet per minute, getting a shield placed around the
balance, or using a balance with a tight shield.
