Labconco XPert Filtered Balance Stations 3962622 - Manual (Page 9)

Chapter 2: Prerequisites
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To correct or ensure against electrostatic issues, the following additional measures
may be prescribed to improve weighing operations.

Maintain a humidity level between 45 and 60%. The ability to sustain this
humidity range can be challenging depending upon the regional climate and
HVAC system.

Ionizers in various forms (guns, bars and blowers) are effective ways to flood
an area with ions and essentially “neutralize” electrostatic electricity.
Background on Electrostatics or Static Electricity
Electrostatic charges on a surface such as the wall of a balance enclosure are not
created by moving air. Gases do not cause the charge. Impurities within the air
impinging upon surfaces dictate the polarity and magnitude of the charge. The
process, triboelectrification, occurs when the dust particles contact the surface,
creating friction and electrons move across the interface.
The ability of a material to become polarized is a property known as permittivity.
On highly insulative materials like acrylic, ions or charged molecules are strongly
bound to the surface by polarization forces. The higher the force, the higher is the
permittivity value of the material. It is suggested by balance manufacturers that
the use of high permittivity materials, such as plastic be avoided.
Since static electricity is a surface phenomenon, materials can also be classified by
their surface resistivity measured in ohms per square. The table below lists the
surface resistivity of various classes of material.
Surface Resistivity Table
Material Surface Resistivity Example
Conductive 0

10 5 
per square Skin, Metals
Static dissipative 10 5 
10 9 
per square Glass
Antistatic 10 9 
10 12 
per square Polyethylene bag
Insulative 10 12 
per square
 Acrylic, Packing foam, Styrofoam
Location and Air Current Requirements
The XPert Filtered Enclosures have been designed to contain hazards by negating
typical cross drafts and turbulence within the opening. Air movement does not
affect most modern balances with draft shields. However, as a precautionary
safety measure and a higher level of quality management, it is recommended that
the enclosure be placed in an area to avoid:

High traffic areas where walking might cause an air disturbance or be a
nuisance to balance readings.

Overhead or wall HVAC diffusers, fans, radiators or other lab equipment
producing air currents.

Next to doorways or windows that may be opened.