| 摘要 |
A regulator is provided for maintaining a preset air velocity through the work chamber of a fume hood. The regulator compares a measured air velocity at the inlet into the chamber with a preset air velocity and adjusts air velocity in response to differences in measured and preset values. Air velocity is measured with a high sensitivity pitot with an exterior end to be positioned outside the fume hood, and an interior end to be positioned inside the fume hood. The pitot includes spaced parallel plates with front and rear ends, an exterior air pressure sensor positioned at the front end of the plates, and an interior air pressure sensor positioned at the rear end of the plates. The interior air pressure sensor includes openings substantially equidistant between the plates that are toward the rear of the pitot when the pitot is mounted on a fume hood. The exterior end of the pitot preferably curves below horizontal to minimize the effect of transient air currents. Face velocities as low as five linear feet per minute can be measured.
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