| 摘要 |
Air filtration apparatus comprises an inlet 14, an outlet 16, a fan 18, a corona discharge cell 20 and an electret filter 22 e.g. polypropylene. In another embodiment, Figure 3, two discharge cells (40, 44) are provided in sequence, and two electret filters (42, 46) the first being thicker than the second. The return current from the filter element (54 Figure 4) can be measured to give an indication of levels of pollutant particles present, the indication being used to control the speed of the fan and show when the filter needs to be replaced. |
