Fume hood controller

In a fume hood installation having:

• a plurality of fume hoods each including a sash which moves to provide an opening for access to the fume hood interior;
• an exhaust blower driven by a blower motor;
• and exhaust ducting connecting each of the fume hoods to the blower;
• a fume hood controller, comprising;
• a plurality of transducer means, equal in number to the number of fume hoods and each transducer being associated with a respective one of the fume hoods, for providing sash opening signals representative of the amount by which the sash of the associated fume hood is open;
• means for combining the sash opening signals from the plurality of transducers to provide an intermediate signal representative of the combined areas of the openings into the plurality of fume hoods;
• speed control means, responsive to the intermediate signal, for producing a speed control signal representative of blower motor speed, the speed control signal being a function of the intermediate signal;
• and
• motor drive means, responsive to the speed control signal, for applying signals to the blower motor to cause the motor to rotate at the speed represented by the speed control signal.

A fume hood, comprising:

• an enclosure;
• means for providing access into the interior of the enclosure, including a movable sash which moves over a travel range from a minimum opening to a maximum opening to provide an opening into the hood of variable area;
• a by-pass opening which provides an opening through which air can enter the enclosure;
• means for closing the by-pass opening so that it is closed by the sash while the sash position is above a predetermined height in its travel range;
• means for opening the by-pass opening when the sash position is below the predetermined height so that the area of the by-pass opening increases by substantially the same amount as the area of the sash opening decreases as the sash moves below the predetermined height, whereby the combined area of the by-pass opening and the sash opening is constant when the sash is below the predetermined height;
• a blower driven by a blower motor;
• exhaust duct means for connecting the enclosure and the blower so that the blower can exhaust air from the enclosure;
• transducer means responsive to the position of the fume hood sash for producing a sash opening signal the value of which varies as a function of the sash opening;
• means, responsive to the sash opening signal, for providing an intermediate signal which is substantially proportional to the area of the sash opening when the sash is above said predetermined height and which is substantially constant when the sash is below said predetermined height;
• speed control means, responsive to the intermediate signal, for producing a speed control signal representative of blower speed, the speed control signal being a linear function of the intermediate signal over at least a portion of the range of the intermediate signal;
• and
• blower drive means, responsive to the speed control signal, for causing the blower to rotate at the speed represented by the intermediate signal.

A fume hood, comprising:

• an enclosure;
• means for providing access into the interior of the enclosure, including a movable sash which moves to provide an opening of variable area;
• a blower driven by a blower motor;
• an exhaust duct connecting the enclosure and the blower so that the blower can exhaust air from the enclosure;
• sensor means for measuring the volume of the air flow in the exhaust duct and for providing an air flow signal representative thereof;
• transducer means responsive to the position of the fume hood sash for producing a sash opening signal the value of which varies as a function of the area of the sash opening;
• speed control means, responsive to the sash opening signal and to the air flow signal, for producing a speed control signal representative of a motor speed which will cause an exhaust air flow volume proportional to the area of the sash opening;
• and
• motor drive means, responsive to the speed control signal, for applying signals to the blower motor to cause the motor to rotate at the speed represented by the speed control signal.