Static Electricity 2000 Edition

6.5.3 Active Electric Static Neutralizers.
6.5.3.1
Electric static neutralizers use a high voltage power
supply to produce corona from sharp electrodes. The charge
on any object near the device attracts charge from the corona
to achieve neutralization. The use of a high voltage power sup-
ply eliminates the limitation of inductive neutralizers in con-
trol of charges having fields below the corona onset threshold.
6.5.3.2
Electric static neutralizers suitable for hazardous (clas-
sified) locations use a high voltage power supply to energize
the corona electrodes at 50 Hz to 60 Hz. The use of an alter-
nating field stresses the electrodes to produce both positive
and negative ions for use in the neutralizing process. Current
from the power supply is capacitive-coupled to each or to sev-
eral of the sharp electrodes to limit spark energy in the event
of a short circuit. These alternating current (AC)–powered
static neutralizers must be approved for use in hazardous (clas-
sified) locations.
6.5.3.3
Electric static neutralizers that use pulsed or steady-
state double-polarity direct current (DC) use a pulsed or
steady field to stress the electrodes to produce ions for use in
the neutralizing process. The spark energy, in the event of a
short circuit, is controlled by current-limiting resistors. Pulsed
or double-polarity DC ionizers that are used in hazardous
(classified) locations should be listed for such use.
6.5.4 Active Radioactive Static Neutralizers.
Radioactive
(nuclear) ionizers use ionizing radiation to produce ions for
neutralization of static electric charges. The most common
radioactive ionizers depend on alpha particle generation from
the decay of Polonium-210 (
210
Po). Performance of radioactive
ionizers deteriorates with the decay of the radioactive material.
The neutralizers must be registered and installed in accordance
with the Nuclear Regulatory Commission regulations and
replaced periodically (at least annually) because ionization
capability diminishes with radioactive decay. Radioactive ioniz-
ers are often used in conjunction with inductive neutralizers to
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STATIC ELECTRICITY
2000 Edition
control high charge densities. Although cost and regulatory
compliance issues are associated with radioactive ionizers, they
are nonincendive, require no wiring, and can reduce static elec-
tric charges to the lowest levels.