| 摘要 |
A sample chamber has a gas sample flow 30 from a flue or stack, with light (70, Fig 1) being directed non-parallel, such as orthogonal, through the sample flow, the light scattered (80, Fig 1) from particles being detected, and a curtain of gas 120 thermally isolates the sample flow from the sample chamber walls. The gas curtain may be an air sheath annular and concentric with the sample flow. The temperature or flow rate of the gas curtain may be adjusted to either prevent condensation, or deliberately condense material known to be present in the chimney. A second gas stream 130, of a different temperature, parallel with the light may flow transversely relative to and be entrained 140 by the gas skirt, guided by a conical conduit 47, 57 that prevents the unwanted scattering of stray light. The cone may accelerate the second gas stream to keep the walls of the conduit free from condensation and particulate accumulation. |
