Fume hood controller

Claim 2

A fumed hood controller for controlling the air flow through a fume hood to maintain a relatively constant face velocity through a fume hood opening as the fume hood sash is moved, comprising: transducer means responsive to the position of the fume hood sash for producing a sash opening signal the value of which is a substantially continuous and monotonic function of the sash opening; air flow control means, responsive to an air flow signal, for varying the air flow through the fume hood in accordance with the air flow signal; flow control means, responsive to the sash opening signal, for producing the air flow signal, including: means for setting a first air flow at a first sash position; means for setting a second air flow at a second sash position; and means for providing, to the air flow means, an air flow control signal having a value so as to maintain the air flow through the hood substantially proportional to the sash opening area as the sash is moved between the first and second sash positions, said means for providing including means for maintaining a linear relationship between the air flow signal and the air flow through the hood.

Claim 3

The fume hood controller of claim 1 wherein the transducer means includes a variable resistor connected to the sash so that the resistance varies as the sash is moved.

Claim 4

The controller of claim 2 wherein the transducer means comprises: a cable having one end connected to the fume hood sash; and a constant-tension, spring-return, cable-driven potentiomenter, including a reel to which is attached the cable so that the potentiometer is varied by the cable unwinding and winding on the reel as the sash moves.

Claim 5

The controller of claim 1 wherein the air flow control means includes a damper.

Claim 6

The controller of claim 1 wherein the air flow control means includes: means, responsive to the air flow signal, for providing a variable resistance to air flow as a function of the air flow signal; and means, responsive to the air flow signal, for maintaining a constant air flow through the air flow means for a constant air flow signal, independent of pressure changes across the means for providing a variable resistance.

Claim 7

The fume hood controller of claim 1 wherein the flow control means further includes: turndown means for selecting a sash position as said first sash position wherein the sash is less than fully closed; means for setting a minimum air flow at the first sash position; and means for setting a maximum air flow at a second sash position; said means for producing the air flow signal further including: means for changing the air flow signal as a substantially linear function of the sash opening signal as the sash moves between the first position and the second position; and means for maintaining the air flow signal at said minimum air flow when the sash is below the position first.

Claim 8

The controller of claim 1 wherein the air flow signal providing means includes means for sensing the air flow volume through the hood.

Claim 9

The controller of claim 1, wherein the air flow control means further includes. an exhaust blower driven by a blower motor and connected to the fume hood via exhaust ducting; and means responsive to the air flow signal, for varying the speed of the blower motor; wherein the controller further includes sensor means, located in the air flow between the fume hood and the exhaust blower, for providing a second signal representative of the air flow through the hood; and wherein the flow control means further includes means responsive to the second signal for increasing the blower motor speed when the second signal drops below a predetermined minimum level.

Claim 10

The controller of claim 8 wherein the sensor means includes a sensor located in the exhaust ducting for measuring the pressure differential between interior of the ducting and the exterior of the fume hood and for providing a signal representative thereof.

Claim 11

The controller of claim 9 wherein the means for increasing the blower motor speed includes: means for setting a reference signal representative of a minimum air flow; means for comparing the reference signal with the second signal and for providing a difference signal representative of the difference therebetween; and means for increasing the motor speed when the difference signal indicates that the air flow is less than the minimum air flow level.

Claim 12

The controller of claim 2 wherein the air flow control means includes a damper.

Claim 13

The controller of claim 3 wherein the air flow control means includes a damper.

Claim 14

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; and 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, each for producing a respective sash opening signal the value of which is a substantially continuous and monotonic function of the associated sash opening; a plurality of flow control means, each associated with a respective one of the transducer means and responsive to the sash opening signal therefrom, for producing an air flow signal representative of a desired air flow through the associated hood, the air flow signal being a function of the sash opening signal; and a plurality of air flow control means, each associated with a respective one of the fume hoods and responsive to the air flow signal, for controlling the air flow through the associated fume hood so that it varies in accordance with the air flow signal; each flow control means further including: means for setting a first air flow at the first sash position; means for setting a second air flow at the second sash position; and means for providing, to the air flow control means, an air flow signal having a value so as to maintain the air flow through the hood substantially proportional to the sash opening area as the sash is moved between the first and second sash positions, said means for providing including means for maintaining a linear relationship between the air flow signal and the air flow through the hood.

Claim 15

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; and 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, each for producing a respective sash opening signal the value of which is a substantially continuous and monotonic function of the associated sash opening; a plurality of flow control means, each associated with a respective one of the transducer means and responsive to the sash opening signal therefrom, for producing an air flow signal representative of a desired air flow through the associated hood, the air flow signal being a function of the sash opening signal; and a plurality of air flow control means, each associated with a respective one of the fume hoods and responsive to the air flow signal, for controlling the air flow through the associated fume hood so that it varies in accordance with the air flow signal; each flow control means further including: means for setting a first air flow at the first sash position; means for setting a second air flow at the second sash position; and means for providing, to the air flow control means, an air flow signal having a value so as to maintain the air flow through the hood substantially proportional to the sash opening area as the sash is moved between the first and second sash positions, said means for providing including means for maintaining a linear relationship between the air flow signal and the air flow through the hood.

Claim 16

The controller of claim 13 wherein each of the air flow control means includes means, located in the ducting between the associated hood and the blower for providing a variable resistance to the air flow through the hood.

Claim 17

The controller of claim 13 wherein the means for providing a variable resistance includes a damper.

Claim 18

The controller of claim 14 wherein the means for providing a variable resistance includes: means, responsive to the air flow signal, for providing a variable resistance to air flow as a function of the air flow signal; and means, responsive to the air flow signal, for maintaining a constant air flow control through the air flow means for a constant air flow signal, independent of pressure changes across the means for providing a resistance.

Claim 19

The controller of claim 14 further including: means, responsive to the sash opening signals from each of the transducer means, for providing a combined sash signal; and means responsive to the combined sash signal for controlling the total air flow provided by the exhaust blower.

Claim 20

The controller of claim 17 wherein the means for providing a combined sash signal includes means, responsive to the sash opening signals from each transducer, for providing a combined sash signal which is proportional to the sum of the sash opening signals.

Claim 21

The controller of claim 18 wherein the means for combining further includes means for scaling each of the sash opening signals by a scale factor reflecting the proportionality of the air flow through the associated hood to the total air flow through the exhaust blower.

Claim 22

The controller of claim 19 wherein the means for controlling the total air flow includes means for controlling the speed of the blower motor as a function of the combined sash signal.

Claim 23

The controller of claim 19 wherein the means for controlling the total air flow includes means for providing a variable resistance to the total air flow through the exhaust blower.

Claim 24

The controller of claim 21 wherein the means for providing a variable resistance to the air flow through the blower includes a damper in series with the exhaust blower.

Claim 25

The controller of claim 14 further including: a pressure sensor, located in the air flow between the blower and the fume hoods and upstream of the fume hood whose connection to the ducting is closest to the blower, for measuring pressure and providing a pressure signal representative thereof; means for providing a reference signal representative of a reference pressure level; and means, responsive to the reference signal and to the pressure signal, for controlling the air flow provided by the exhaust blower so as to maintain a relatively constant pressure at the the pressure sensor.

Claim 26

The controller of claim 23 wherein the means for controlling the exhaust blower air flow includes means for varying the speed of the blower motor.

Claim 27

The controller of claim 23 wherein the means for controlling the exhaust blower air flow includes a damper in series with the total airflow through the exhaust blower.

Claim 28

The controller of claim 13 wherein each of the transducer means comprises: a cable having one end connected to the associated fume hood sash; and a constant-tension, spring-return, cable-driven potentiometer, including a reel to which is attached the cable so that the potentiometer is varied by the cable unwinding and winding on the reel as the associated sash moves.