Vari-Cab ] WPS ] NRC-300 & RSC-100 ] MTS-60 ] [ EMI FIELDS ]


Aerofeed Ltd.

Aerofeed Storage Cabinets


"The damaging effects of electrostatic discharge (ESD) are well known by people working with electronic components and devices. Less well known, however, is that certain devices can be damaged by static electricity without any static discharge ever taking place. Most of this damage is caused by exposure to electromagnetically induced (EMI) fields.

EMI fields are created by triboelectric effect any time two dissimilar materials are brought together, then separated. As one material strips loosely held surface electrons from the other, the two surfaces come apart carrying equal but opposite electrical charges. If a material is a good conductor, the magnitude of the surface charge is quickly reduced by redistribution of electrons throughout the material, and eliminated entirely if the material is grounded. If the material is neither a conductor nor static-dissipative, however, the charge remains intact on the surface until it is removed by external means.
While this surface charge exists it exhibits certain magnetic properties, specifically, the abilities to repel or attract particles of similar or opposite charge, and to generate an electric current in any conductor moving through the field (or remaining stationary while the field moves through it).

A "G" suffix cabinet has a front made with untreated acrylic which, being a non-conductor, may emit an EMI field ranging from a few volts (either positive or negative) to several thousand. When an item not enclosed in a static-dissipative container is moved into the cabinet it must pass through this field,

meaning that an electric current may be generated inside the item (due to relative motion), the magnitude of which will depend on the strength (voltage) of the field. Once the item is placed inside the cabinet, a second current may be
generated in the item as the door is closed (more relative motion). While inside the cabinet any free or loosely bound electrons in the device are likely to migrate either toward or away from the cabinet front (depending on the field's polarity), concentrating in one portion of the item. A third current will be generated as the item is removed
Whether or not these short-duration currents and/or localized electron concentrations have any degrading effects on the item involved depends entirely on what the item is and how it is engineered. Possible effects range from absolutely none through erratic operation to virtually total failure. If an item to be stored is suspected of being sensitive to EMI field exposure, it should be placed inside a static dissipative container before being exposed to the field or else stored inside a "TSD" cabinet, which, being constructed entirely of static-dissipative materials, has no EMI fields to guard against.

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Copyright 1998 BITA ELECTRONIQUE S.A. 
Last modified: 2017-11-22