| 摘要 |
<p>An opening end face of a frame is closed by a transparent thin film, a vent is formed in the frame, and a filter having a filtration area larger than the sectional area of the vent is mounted to the frame to cover the vent. The filtration area of the filter an effective area where allows the passage of gas in the filter. Then, the filter is mounted to the frame so that there is a certain space between the frame and the filter. In the convent,ional device, since the filter is directly mounted to the frame without space between the filter and the frame, the filtration area of the filter is substantially the same as the sectional area of the vent. In case of mounting the filter apart from the frame, however, the filtration area of the filter can be lager than the sectional area of the vent so that the quantity of gas flow is greater than that of the conventional one. Therefore, its adaptability to the changes in atmospheric pressure and in temperature is also improved. <MATH></p> |
