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Insulating Yourself from the Effects of Static Electricity

(September 2008) posted on Tue Sep 16, 2008

Is static standing in the way of quality and productivity in your shop? This discussion will help you identify sources of static electricity as well as the types of systems available to eliminate it from your production process.

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By David Rogers

Passive eliminators Passive eliminators are useful for reducing high levels of static charge, from tens of kV down to levels of a few kV. However, by their very nature, they are not able to completely neutralize the surface charge. A charged object generates an electric field between itself and any surrounding earthed object (or any object of differing voltage). In the case of a passive eliminator, the field is between the surface and the tips of the carbon-fiber or stainless-steel earthed brush (Figure 2). The fine point at the end of the individual bristles causes the electric field to be highly concentrated at this point. Ionization of the air molecules surrounding the tip occurs when the strength of this electric field reaches a sufficient value. In (Figure 2), the positive charge on the surface of the material causes electrons from the tip of the brush to jump to surrounding air molecules that will then have a net negative charge and are thus negative ions.

Radioactive eliminators Radioactive eliminators employ polonium 210 or other low-level radioactive source. Alpha particles are emitted to the surrounding atmosphere in the process of radioactive decay. These high-speed particles collide with the air molecules and, in doing so, cause the air to become ionized. This ionized air then neutralizes nearby surfaces in similar fashion to the passive eliminators.

AC eliminators AC Eliminators operate at supply frequency. The main voltage (110, 240, etc.) is greatly increased using a ferro-resonating transformer to generate voltages of between 4.5-7 kV. This high voltage is fed to the ionizing pins, and the casing of the bar is connected to earth (Figure 3).

If we look at the positive cycle of the input waveform, we will see that the electrode pin is at a positive voltage compared to the casing. This generates a strong electric field between the two that is highly concentrated at the sharp point of the electrode pin. This, in similar fashion to the passive bar, generates positive ions at the pin point. These mo-lecules are then repelled from the pin due to their like charge. As the ionization at the bar is not dependent upon the surface charge and ions are produced regardless of the proximity of a surface charge, complete neutralization of a surface can be achieved. This is a significant advantage over the passive eliminators.


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