| 摘要 |
<p>Device comprises a sampling tube having a mouthpiece, at one end and a suction blower at the other end. The mouthpiece is equipped with a closure valve, which is closed at least once during each dust-removal period, the blower being kept in operation during this time. Pref. the valve is opened and closed at the start and end of a removal (sampling) period and, more specifically, may be closed and then reopened rapidly just before the final closure at the end of the period. As a variant, a cycle of repeated short closure and short opening may be carried out during or throughout the sampling period. Used in particular for monitoring discharges to atmosphere. The use of a rapidly closing and opening valve ensures that shock waves travel along the sampling tube, thus dislodging any dust which might adhere to the inner face of the tube, causing accumulation of dust and distortion to the results of the test.</p> |
