Balanced static elimination in variable ion mobility environments

Electrical ionizers with point-to-point and point-to-plane electrode arrangements were evaluated for use in static elimination systems. Elevated temperature tests to 433 K were done in air, while reduced temperature tests to 213 K were done in liquid nitrogen vapors. Balanced static elimination was obtained throughout the temperature range by controlling the ratio of the potentials on the positive and negative emitters, and allowing large free-electron currents from the negative emitters in the nitrogen environment. The charge-decay times were continuous through the nitrogen-to-air transition and dependent upon temperature as exp(const/kT). Under balanced conditions, the ratio of charge-decay times for negatively-charged and positively-charged targets increased from about 1.1 at 213 K to 1.4 at 323 K, and returned to about 1.0 at 433 K. In air, the charge-decay times at constant negative emitter current decreased and their ratio approached unity with increasing superficial flow in the chamber. Nitrogen injection about the emitters primarily influenced static elimination when gas circulation in the chamber was otherwise small. Separate control of positive and negative carrier generation is essential to achieve balanced static elimination in industrial applications.