| 摘要 |
<p>A measured amt. of liq., esp. a clinical specimen, is taken from a container and transferred by a piston communicating with a vertically mobile cannula whose end dips into the liq. to a depth controlled by a level sensor. This operates with compressed air delivered down the outer of a double tube concentrically surrounding and shorter than the cannula. Air after travelling down this space is reflected from the liq. surface back up the inner space where its pressure is sensed and actuates a drive to move the cannula vertically. The outer tube is pref. longer than the inner tube, and their ends are shaped to facilitate air movement from the outer to the inner space. Level detection involves no physical contact between sensing means and liq., and the cannula need only dip about 1 mm below the surface. The device is compact, e.g. the unit entering the container may be 3 mm dia. including the 1 mm dia. cannula.</p> |
