| 摘要 |
A filter cartridge comprising a coarse filter stage 24 in which dust and other contaminants are removed and a fine filter stage 30 for producing substantially clean air. Outlets 28, 34 remove air both before and after the fine filtering stage. The coarse filter stage may be an open cell foam, and the fine filter stage ultra-fine cloth or paper. The cartridge is used in a smoke detection system, such as one based on detecting light scattered by smoke particles, which uses a substantially clean flow of air from outlet 34 to prevent air being measured (from outlet 28) from contaminating the detection system. |
