Monroe Electronics Electrostatic Fieldmeter - Static Monitor - model 177A - Manual (Page 61)

APNE-0015 60
V. Continuous Static Control
Control of static is not something that occurs once and can then be forgotten. It requires the
implementation of continuous procedures such as charge neutralization using ionizers with
electric field monitoring using permanent fieldmeters and probes to verify that the ionizers
are working effectively.
Passive Ionizers
Passive ionizers connected to ground (e.g. tinsel, conductive brushes) rely on the electric
field produced by the charge on the web to produce positive and negative ions by corona
discharge. Passive ionizers feature points that concentrate the electric field to produce field
strengths that, when they exceed the dielectric breakdown strength of air (30,000 volts per
centimeter, V/cm), produce positive and negative air ions at the points. Passive ionizers rely
on the electric field from the web to pull these air ions to the web to partially neutralize the
charges on the web. Since passive ionizers rely on the electric field from the web to
produce ionization, they are not very effective at field strengths below 1000 V/cm, but
become very effective at higher field strengths. The effectiveness of passive ionizers also
depends on point cleanliness and sharpness, number of points per unit area, distance from
the web, web span length, and proximity to other conductors.
Electric Powered Active Ionizers
Electric powered active ionizers produce corona discharge ionization by applying a high
voltage to geometrically arranged emitter elements. Ionizers made for reducing web charge
use AC voltage, producing large amounts of both negative and positive air ions, or DC
voltage producing only one polarity of air ion.
Various designs are used, depending upon the ionizer's purpose, but the high voltage
emitter elements are usually needle points or thin wires. Operating details vary with
different designs, but, as with passive ionizers, they rely on the electric field from the web to
pull opposite polarity air ions from the emitter elements to the web for charge neutralization.
Since they do not rely on the electric field from the web to produce ionization, they are
effective at all but the highest field strengths. Some models use blowers or compressed air
assistance to drive ions further distances toward the web. The effectiveness of active
ionizers also depends greatly upon their design, their operating voltage, the web speed,
point cleanliness and sharpness, web span length, distance from the web, and proximity to
conductors.
Some electronic ionizers claim to be able to monitor the charge on the web. These ionizers
monitor their own ion current. They provide an indication of the performance of the ionizer.
They are not true monitors of the charges on web materials, and are not a replacement for
electrostatic fieldmeters that are placed downstream of the ionizers to monitor web
charging.
Radioactive (Nuclear) Powered Active Ionizers
Nuclear ionizers use radiation ( or  particles) that strip electrons from air molecules to
make both positive and negative air ions. The air ions are attracted to the web by the
electric field produced from the charge on the web. These ionizers usually can’t produce as
many ions per unit time as do electric powered ionizers. Since there is a specific amount of
radioactive material in each device and radioactive decay occurs independent of process
variables, the rate of ion production is not controllable and is independent of the amount of
charge on the web. For example, Polonium 210, a Beta emitter, has a half life of 138 days,
at which time its ion production is reduced by half.
Nuclear ionizers do not employ the use of high voltage to create air ions. Therefore, they do