| 摘要 |
<p>PURPOSE:To suppress the occurrence of measurement errors owing to the insertion of the automatic opening and closing valve to the minimum degree, by setting the total area of the cross section of openings of a valve seat and a variable restriction to be 6-9 times the area of the cross section of a flow path between a measuring nozzle and a material to be measured. CONSTITUTION:When the measurement is not performed, the back pressure of a measuring head 5 is small. Therefore, the back pressure Po acting on a valve body 13 in a back pressure chamber 3 is smaller than an energyzing force fo caused by a spring 14. The valve body 13 is contacted with the valve seat 12 and closes the seat 12. Therefore the amount of an air flow flowing the measuring head 5 is a minute amount of a flow flowing the variable restriction 10 in a secondary path. When the measuring nozzle 5 is approached to the material to be measured 16 and a gap x is measured, the back pressure of the measuring head 13 is increased, and the back pressure Po acting on the valve body 13 become larger than fo. Then the valve body 13 is lifted, the valve seat 12 is opened, and the air flows. Since the total area of the cross section of the openings of the valve seat 12 and the variable restriction 10 is larger than the area of the cross section of the flow in the gap x by 6-9 times, the occurrence of the measurement errors owing to the insertion of the automatic opening and closing valve 13 is suppressed to the minimum.</p> |
