| 摘要 |
<p>A gas sampling device (10) includes a dilution tunnel (12) of particularly effective construction that reduces contamination or soiling of the ducting leading to a filter assembly (66) and improves the accuracy of the results. The gas sampling device (10) has a sampling probe (56) disposable in the gas stream (64) of an engine (95) or the like, and a controlled source of clean and pressurized diluent air (36). The dilution tunnel (12) includes an air distribution tube (14) defining a plurality of distribution holes (18) therethrough, a collar (30) defining a first annular chamber (28) about the air distribution tube (14) that is connected to the air source (36), and a porous center tube (48) having a plurality of micron-sized pores (50) connected between the sampling probe (56) and the filter assembly (66). A second annular chamber (47) is defined between both tubes (14, 48), and the diluent air supplied thereto is uniformly passed through the porous center tube (48) to effect good mixing of the exhaust gas and diluent air while providing a boundary layer of diluent air that keeps the center tube (48) clean. An alternate embodiment gas sampling device (10') employing master and slave mass flow controllers (80, 82) is also disclosed.</p> |
