The environment surrounding a balance is vital if
you are to maintain the manufacturer's stated
performance ratings. Really, the manufacturer doesn’t
matter in this regard, as a bad environment will
adversely affect any balance. There are many influences
to consider and to remove, as far as is possible, from
the area surrounding the balance.
The air currents and changes in temperature from direct
sunlight will play havoc with the performance of a
balance. Keep all balances out of an area that
will be covered by direct sunlight, yes, even in
Northern climes (for our Canadian friends).
The changes in air pressure and air movement caused by
the opening of doors, people passing by, air
conditioning etc. can all cause balances to give
unstable and incorrect weights. All these should be
avoided, even if the balance has a draft shield.
Even subtle vibration can affect the performance of
balances. The table wobbling or the table not
being strong enough can make the balance vibrate and the
weight displayed unstable. You must have a stable and
strong platform. Machinery vibration, people walking
past on a springy floor, trains going past the building
within 1000 yards, all these issues will be reflected in
poor balance performance.
To a sensitive balance such as a 4 place or above
(0.0001 g or higher sensitivity) the temperature change
caused by the radiated heat from your hand is enough to
upset the balance. This is one reason why people often
wear gloves when dealing with balances (not just balance
calibrators). With all balances, direct heat of
any sort should be avoided.
No this is not a joke! With the most sensitive of
balances, your breath is more powerful than you think.
Very often when we calibrate balances that are
analytical or above, we cover our mouths and
breathe in a shallow fashion, to make sure we do not
disturb the balance reading. Even though the doors are
closed on the weighing chamber, you will be amazed how a
little air current will disturb things.
Keeping the doors closed
It is always imperative to keep the doors open for the
shortest time possible on analytical balances,
especially if the balance has a conventional force
restoration mechanism that will generate heat and is
under the platter. The heat builds up in the weighing
chamber over time. If the doors are opened for long, the
warm air will escape and cold air will fill the chamber,
leading to air disturbance in the chamber, right over
the platter. Here is a good reason to consider
“crossover” doors, that allow for holding the sample in
one hand and opening the door with the opposing hand.
This dramatically cuts down the time the doors are open.
We, as human beings generate static every day. It
builds up in our bodies, our clothes and is also
generated by machinery in laboratories. Parts of most
balances have some ferrous material in them and as such
are affected by static. The electrical field set up by
static can radically affect results by attracting
balance parts to each other, the attraction causing a
force that the balance will see as weight (or lack of
it). Use of an Ionizer will help with this problem, as
it will dissipate the static that builds up in the
vicinity of the balance.
When all is said and done, the balance is one of the
most sensitive pieces of equipment that you will use in
the laboratory. Consider that a digital thermometer may
read in 0.1 °C, perhaps 1000 divisions of the scale.
(100 ÷ 0.1 = 1000) while the 200 g balance reads in
0.0001 g that is 2,000,000 divisions of the balance
range. It is no wonder that the balance needs to have a
safe and secure environment.