| 摘要 |
PROBLEM TO BE SOLVED: To suppress energy cost by generating a signal indicative of the presence of a working object in a gas hood and controlling the quantity of the air being purged from the gas hood in response to that signal thereby optimizing the flow rate of the gas hood. SOLUTION: A gas hood 60 is provided, at one inner end thereof, with a plurality of light emitting devices 142 each facing a photodetection device 146 disposed the other end thereof in order to detect presence of an object along the optical path. A gas hood controller controls the air flow in the gas hood as a function of the absence of an object or the position of an object present in the gas hood. The controller sets a minimum allowable gas flow when an object is not present in the gas hood. When all objects are present within about 2 inch from the back face of the gas hood, the current velocity is decreased down to about 50% of the nominal mean surface velocity. When the objects are present within about 6 inch from the front face of the gas hood, the nominal mean surface velocity is sustained. When the objects are present between 6 inch from the front face and 2 inch from the back face of the gas hood, the current velocity is controlled in proportion to the distance. |
