The Measurement of Net Space Charge Density Using Air Filtration Methods

The efficiency of a high efficiency particulate air (HEPA) or absolute filter for removing charge from an air stream has been measured for a variety of space charge and air flow conditions. Ion densities ranged from lOs to 10
6
/cm
3
and were for positive and negative space charge as well as mixtures. The space charge was made up predominantly of ions with mobilities greater than 0.1 x 10
-4
m
2
/Vs. For all conditions studied, the transmission of the filter was less than 0.1%. For space charge consisting of ions of one polarity, space charge density measurements made using HEPA filters and ion counters may be compared directly. The filter is well suited for accurate measurements of net space charge density.