Equivalent circuits for air ionizers used in static control

Abstract

Air ionization systems can be described by an equivalent electrical circuit connecting a charged object to ground. This suggests an alternate characterization technique to the traditional charged-plate method that relies on measurements of charge decay time and balance voltages. The equivalent circuits for a variety of ionizers were obtained by measuring the current from a biased plate over a range of voltage, and then fitting these results to a circuit consisting of a resistance, a voltage source, and a saturation current. The ionizer is most effective when the resistance dominates, so that the decay of charge from the object follows an exponential decay law. The voltage source represents the offset voltage that an ungrounded object will acquire when exposed to the ionization system and the current represents the maximum ion output that can be extracted from the ionizer. The equivalent-circuit model has been incorporated into a technique called the biased-plate monitor (BPM) to provide an new way to describe air ionizer systems. The BPM is faster and more descriptive than the charged-plate method, and can also be made much smaller if the region of interest is confined. It also gives a better description of charge control effectiveness for very small (hard-disk heads) or very large (LCD) devices.