US20130337737A1

US20130337737A1 - Compressed gas cylinder cabinet with regulated exhaust control

Info

Publication number: US20130337737A1
Application number: US13/517,799
Authority: US
Inventors: Craig N. DeVarney; Janice M. Edler; Gregory S. Nelson; Patrick Zachary
Original assignee: International Business Machines Corp
Current assignee: GlobalFoundries Inc
Priority date: 2012-06-14
Filing date: 2012-06-14
Publication date: 2013-12-19

Abstract

A gas cabinet and a method of controlling air flow through said gas cabinet. The gas cabinet includes an enclosure; a damper having at least two flow rate positions; an exhaust outlet; a set of sensors; and a programmable logic controller configured to change a flow rate position of the damper from a first flow rate position to a second flow rate position based on the state of the sensors. The method includes using the damper to lower the amount of exhausted air required under normal operating conditions and using the damper to increase the amount of exhausted air when a possible gas leak is detected.

Description

FIELD OF THE INVENTION

The present invention relates to the field of industrial gas supply systems; more specifically, it relates to a compressed gas cylinder cabinet with regulated exhaust control and a method of regulating exhaust of a compressed gas cylinder cabinet.

BACKGROUND

The extensive use of compressed and highly toxic gases in the fabrication of electronic semiconductor devices has led to the use of gas cabinets for containment of the compressed gas cylinders. In order to protect personnel in the case of a toxic gas leak from a cylinder in the cabinet, the cabinets are exhausted. Typically, a gas cabinet will exhaust several hundred cubic feet per minute of temperature and humidity conditioned air at all times. Because of the amount of energy required to condition the air and run the exhaust fans continuously, the cost in energy consumption is very high. Accordingly, there exists a need in the art to mitigate the deficiencies and limitations described hereinabove.

SUMMARY

A first aspect of the present invention is a gas cabinet, comprising: an enclosure; a damper having at least two flow rate positions; an exhaust outlet; a set of sensors; and a programmable logic controller configured to change a flow rate position of the damper from a first flow rate position to a second flow rate position based on the state of the sensors.
A second aspect of the present invention is a method, comprising: providing a gas cabinet, comprising: an enclosure; a damper having at least two flow rate positions; an exhaust outlet; a set of sensors; and a programmable logic controller configured to change the flow rate position of the damper from a first flow rate position to a second flow rate position based on the state of the sensors; and if the exhaust static pressure within the cabinet is lower than a preset minimum pressure then changing the damper from the first flow rate position to the second flow rate position if one or more sensors of the set of sensors indicates a gas leak within the enclosure, the second flow rate position having a higher flow rate than the first flow rate position.
These and other aspects of the invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is an isometric view of a compressed gas cabinet according to the embodiments of present invention;

FIG. 2 is a schematic diagram of an exhaust system for the compressed gas cabinet of FIG. 1;

FIG. 3A is a front view, FIG. 3B is a sectional view through line 3B-3B of FIG. 3A, and FIG. 3C is a top view of the damper assembly of FIG. 1;

FIGS. 4A, 4B and 4C illustrate various positions of the damper of FIG. 1.

FIG. 5 is a top view of a first alternative damper assembly according to embodiments of the present invention;

FIG. 6 is a front view of a second alternative damper assembly according to embodiments of the present invention;

FIG. 7 is a side view of a third alternative damper assembly according to embodiments of the present invention;

FIG. 8 is a schematic diagram of a control system for the compressed gas cabinet of FIG. 1;

FIGS. 9A, 9B and 9C are flowcharts illustrating the logic of the programmable logic controller of FIG. 8; and

FIG. 10 is a schematic block diagram of an exemplary programmable logic controller.

DETAILED DESCRIPTION

The embodiments of the present invention include a compressed gas cylinder cabinet that includes an array of sensors and a programmable logic controller (PLC) that automatically controls the quantity of air flow drawn into the cabinet based on the sensor data using an electromechanical damper to increase or decrease the flow of air into the cabinet and the speed of the exhaust fan and thus the amount of air flowing into the cabinet and ultimately exhausted from the cabinet. The damper will be controlled by the PLC, wherein exhaust requirements are determined. The exhaust requirements are determined by sensors inside the cabinet, a gas detector in the cabinet and sensors in the exhaust ducting. Reducing the need for continuously high flow amounts of air through the cabinet increases the sensitivity of the gas detector. The sensors measure gas delivery pressure, gas cylinder pressure, gas flow, exhaust velocity, exhaust static pressure, cylinder weight and whether the gas cabinet is in normal or maintenance mode.
Under normal operating conditions, the damper will be closed and the cabinet interior will be held at a pressure that is negative to the cabinet exterior so there will be none to very little air flow and attendant waste of energy. The PLC will monitor several sensors and automatically open the damper to provide necessary exhaust flow when needed. The PLC monitors for a possible gas leak in the cabinet and if a request for access to the interior of the cabinet has been initiated. The parameters of the exhaust flow determination logic are configured based on cylinder pressures, gas delivery pressures, gas flow rates and gas hazard classification. Each sensor has a programmable set point and acceptable range that the PLC uses to determine the damper setting.
The damper setting is based on, for example, one or more of (1) detection of the gas inside the cabinet; (2) is the air pressure inside the cabinet negative relative to the to air pressure outside the cabinet within a specified range; (3) is the gas flow within a specified range; (4) is the gas cylinder pressure within a specified range; (5) is the gas delivery pressure within a specified range; (6) have there been dynamic changes in gas cylinder pressure or delivery pressure; (7) have there been dynamic changes in gas cylinder weight; (8) is there a need for personnel to access the interior of the cabinet; and (9) when the damper is open, is the exhaust pressure within a specified range. A dynamic change is defined in a time rate of change in the parameter that exceeds the time rate of change of that parameter under normal gas usage which is programmed into the PLC.
FIG. 1 is an isometric view of a compressed gas cabinet according to the embodiments of present invention. In FIG. 1, a compressed gas cabinet 100 for holding a compressed gas cylinder 105 includes an exhaust duct 110 open to the interior of the cabinet, a fixed left side 115A, a fixed right side 115B, a fixed top 120, a fixed bottom 125, a fixed back wall 130 and a cabinet door 135 attached to left side 115A by a hinge 140. It is preferred that exhaust duct 110, sides 115A and 115B, top 120, bottom 125 and back 130 be joined in an airtight manner. Door 135 includes a damper 145 which comprises an array of openings 150 and a positional actuator 155. Door 135 also includes a window 160 connected to the door by a hinge 165 and including a window open/closed sensor 170. Window 170 is fitted with a latch (not shown) on the outside of the door. In one example, window 160 is sealed air-tight in the closed and latched position. Door 135 is also fitted with a door latch 175. In one example, door 135 is sealed air-tight in the closed and latched position. The window and door latch 175 are under the control of the PLC but may be fitted with manual overrides.
Right side 115A includes a door open/closed sensor 180 and is penetrated by a purge line 185. Purge line 185 is sealed air-tight to sidewall 115B. Top 120 is penetrated by a gas supply line 190 in order to supply gas from gas cylinder 105 to a fabrication line tool (e.g., plasma etch or deposition tool, chemical vapor deposition tool. etc.) not shown. Gas supply line 190 is sealed air-tight to top 120. In one example, there are no openings in sides 115A and 115B, top 120, bottom 125 and back 130 that allow outside air to enter cabinet 100. A gas sensor 195 is fitted to exhaust duct 110 so as to be able to detect the presence of gas from cylinder 105 in the exhaust stream. Alternatively, gas sensor 195 may be mounted inside cabinet 100.
Cabinet 100 includes a cylinder weight sensor 200 (e.g., a scale) upon which gas cylinder 105 sits and a strap 205 for securing the gas cylinder to back wall 130 of the cabinet. Cabinet 100 further includes a pneumatic cylinder valve 210, a gas flow sensor 215 (e.g., a mass flow meter), a high pressure sensor 220, a high pressure isolation valve 225, a gas pressure regulator 230, a low pressure sensor 235, a low pressure isolation valve 240, a purge valve 245 and a vent valve 250. Pneumatic cylinder valve 210 allows connection of gas cylinder 105 to the gas delivery and vent lines inside cabinet 100. Gas flow sensor 215 measures the rate of gas flow from cylinder 105 to the gas delivery lines. High pressure sensor 220 monitors the pressure within the cylinder when pneumatic cylinder valve 210 is open. High pressure isolation valve 225 controls gas flow to pressure regulator 230 (which lowers the pressure of the gas supplied to the tool). Pressure regulator 230 sets the tool supply gas pressure and low pressure sensor 235 monitors the gas pressure supplied to the tool. Low pressure isolation valve 240 isolates the gas delivery and vent lines from the tool. Purge valve 245 and vent valve 250 allow purging and venting of toxic gas to exhaust duct 110.
Pneumatic cylinder valve 210, high pressure isolation valve 225, gas pressure regulator 230, low pressure isolation valve 240, purge valve 245 and vent valve 250 may be manually operated when the cabinet door 135 or access window 160 is open or remotely operated when the access door and/or window is closed or open. Door latch 175 and the window latch (not shown) are normally unlatched remotely, but may include a manual (e.g., key) override. With cabinet door 135, window 160 and damper 145 closed, gas cabinet 100 is hermetically sealed.
FIG. 2 is a schematic diagram of an exhaust system for the compressed gas cabinet of FIG. 1. In FIG. 2, an exhaust plenum 255 is connected to exhaust duct 110 of gas cabinet 100. Two exhaust fans 260A and 260 B having motors 265A and 265B are connected to exhaust plenum 255 by ducts 270A and 270B respectively. Motors 265A and 265B are controlled by variable frequency drive (VFD) controls 275A and 275B respectively. Contained within cabinet 100 (or alternatively, within exhaust duct 110) is an exhaust static pressure sensor 280 which indicates the pressure within the cabinet or exhaust duct relative to the pressure outside of the cabinet. Contained within exhaust plenum 255 is an exhaust flow sensor 285 which measures the cubic feet per minute (CFM) being drawn by fans 260A and 260B. While two exhaust fans are illustrated for redundancy and added safety, a single fan may be used.
FIG. 3A is a front view, FIG. 3B is a sectional view through line 3B-3B of FIG. 3A, and FIG. 3C is a top view of the damper assembly of FIG. 1. In FIG. 3A a grate 290 having openings 295 is positioned over openings 150 of door 135 and held moveably in position by a frame 300. Positional actuator 155 is connected to grate 290 by an actuator arm 292. In the example of FIG. 3A and 3B, openings 295 circular are larger in diameter than openings 150 which are also circular. It should be understood, that openings 150 and 295 may have shapes other than circular (e.g., square, rectangular, oval, or polygonal) and that openings 150 may be larger than openings 295 as long as grate 290 can completely block openings 150 in the fully closed position. Actuator 155 may be configured to move grate 290 between first and second positions, so damper 145 is fully open (see FIG. 4A), or fully closed (see FIG. 4C) or configured to move grate 290 in any position (see FIG. 4B) between the first and second position so the damper may be fully open, partially open, partially closed or fully closed. The default (e.g., no power) position of damper 145 is fully closed. While actuator 155 has an internal spring and gear assembly that would close grate 290 in the event of a power failure, an optional spring 307 (or other closing assist means) is provided. In FIG. 3C, seals/slides 305 are fitted between grate 290 and door 135 and frame 300.
FIGS. 4A, 4B and 4C illustrate various positions of the damper of FIG. 1. In FIG. 4A, grate 290 is in the fully open position (i.e., grate 290 does not block any regions of openings 150). In FIG. 4B, grate 290 is in a partially open (or closed) position (i.e., grate 290 blocks regions of openings 150). In FIG. 4C, grate 290 is in the fully closed position (i.e., grate 290 blocks all regions of openings 150). In the fully closed position, negative pressure (relative to the ambient pressure outside of the cabinet) inside cabinet 100 compresses grate 290 against cabinet door 135 to seal the damper. In one example, a normal operating position of damper 145 is fully closed position to totally stop air flow into the gas cabinet or a partially opened position so as to reduce the air flow to about 10% or less of the air flow into the gas cabinet when damper 145 is in the fully opened position. In one example, an emergency position of damper 145 is a fully open position. In one example, a maintenance position of damper 145 is a partially open position, which is more opened than the normal operating position but not completely open. In one example, a maintenance position of damper 145 is the fully open position. For example, given a maximum flow of about 300 CFM with the damper in the fully open position, the flow in the normal operating position is between about 0 CFM and about 10 CFM and in the maintenance position s between about 150 CFM and about 250 CFM. These CFM values are converted into grate positions and are adjustable and programmable.
FIG. 5 is a top view of a first alternative damper assembly according to embodiments of the present invention. In FIG. 5, a damper 145A includes a grate 290A (similar to grate 290 of FIG. 3C) that is held in place over a single large opening in door 135 by a frame 300A. Positional actuator 155 (see FIG. 1) connected to grate 290A by actuator arm 292A. A region 308 of frame 300A includes an array of openings (not shown) similar to openings 150 of FIGS. 3A and 3B. Positional actuator 155 (see FIG. 1) is connected grate 290A. Damper assembly 145A is mounted to the outside of door 135. Operation of damper 145A is similar to damper 145 of FIGS. 4A, 4B and 4C.
FIG. 6 is a front view of a second alternative damper assembly according to embodiments of the present invention. In FIG. 6, a damper assembly 145B includes a set of wedge shape openings 310 in door 135 and a rotatable plate 315 having wedge shaped openings 320. Openings 310 in door 135 are arranged in a ring array about a center 325. Openings 320 in plate 315 are also arranged in a ring array about center 325. Plate 315 is rotatable about center 325 by means of an actuator arm 292B offset horizontally from center 325. Actuator arm is connected to positional actuator 155 (see FIG. 1) and is configured to rotate plate 315 to completely block, partially block or not block openings 310. Damper assembly 145B is illustrated in the fully open position. Damper assembly 145B is mounted to the outside of door 135. The default (e.g., no power) position of damper 145B is fully closed. An optional spring 307B (or other closing assist means) assists closing damper 145B in the event of a power failure. Seals (not shown) may be provided between plate 320 and door 135. While illustrated as integral with door 135, a damper assembly incorporating openings 310 in a second plate may be fabricated for placement in a single large opening in door 135. Operation of damper 145B as to normal, maintenance and emergency CFM flow is similar to damper 145 of FIG. 3A. Optionally, an off center weight may be attached to plate 315 to assist in closing damper 145B.
FIG. 7 is a side view of a third alternative damper assembly according to embodiments of the present invention. In FIG. 7, a damper assembly 145C comprises louvers 330 mounted on a frame 335 which is mounted to door 135 over an opening 340 in door 135. Positional actuator 155 (see FIG. 1) connected to louvers 330 by actuator arm 292C and may be adapted to completely open louvers 330, partially close louvers 330 or completely close louvers 330 thereby blocking openings 340. Damper assembly 145C is illustrated in the full open position. An optional spring 307C (or other closing assist means) assists closing damper 145B in the event of a power failure. Seals (not shown) may be provides between adjacent louvers 330 and between louvers 330 and door 135. Optionally, a weight may be attached to plate the lower end of to assist in closing damper 145B. Operation of damper 145C as to normal, maintenance and emergency CFM flow is similar to damper 145 of FIG. 3A.
FIG. 8 is a schematic diagram of a control system for the compressed gas cabinet of FIG. 1. In FIG. 8, a PLC 345 is connected to receive input from door open sensor 180, window open sensor 170, high pressure sensor 220, low pressure sensor 235, cylinder weight sensor 200, gas sensor 195, flow sensor 215, exhaust static pressure sensor 280 and exhaust flow sensor 285. PLC 345 is connected to send control signals to cabinet door latch 175, pneumatic cylinder valve 210, low pressure isolation valve 235 and high pressure isolation valve 225. PLC 345 is connected to receive from and send signals to VFD 275. PLC 345 may include human interface devices such as a display, keyboard, and means for entering data (e.g., parameter set points and control ranges) into and programming the logic of the PLC. In one example, PLC 345 may comprise a general-purpose computer.
FIGS. 9A, 9B and 9C are flow charts illustrating the logic of PLC 345 of FIG. 8. FIG. 9A describes the control logic for normal/emergency operation of the gas cabinet. In step 400, PLC 345 of FIG. 8 is initialized by loading a control program (which sets up a state machine) and entering parameter set points specified control ranges for the various sensors into memory or resetting the logic state machine previously defined by the control program. In step 405, the damper (e.g., damper 145 of FIG. 3) is set to the normal operating position by control signals sent to the actuator (e.g., actuator 155 of FIG. 3) and exhaust fans 260A and 260B of FIG. 2 are ramped up to the corresponding pressure and flow rate for the normal operating position of the damper by control signals sent by PLC 345 to VFDs 275 of FIG. 2. In step 410, gas flow sensor 215, gas sensor 195, cylinder weight sensor 200, low pressure sensor 235, high pressure sensor 220 of FIGS. 1 and 8 are monitored, checking if each sensor is reading within the specified control range. In step 415, the sensors are polled to determine if a fault has been detected. If a fault is detected then step 420 is performed, else the loop of step 410 and 415 is repeated.
The sensors polled are:
(1) gas flow sensor 215 of FIGS. 1 and 8 to determine if the gas flow exceeds a specified value in case the PLC generates a gas flow fault signal;
(2) low pressure sensor 235 of FIGS. 1 and 8 to determine if a dynamic change in gas pressure over a specified amount of time exceeds a specified value in which case the PLC generates a low pressure fault signal;
(3) cylinder weight sensor 200 of FIGS. 1 and 8 to determine if there has been dynamic change in cylinder weight over a specified amount of time exceeds a specified value (which could indicate a gas leak) in which case the PLC generates a cylinder weight fault;
(4) high pressure sensor 220 of FIGS. 1 and 8 to determine if a dynamic change in gas pressure over a specified amount of time exceeds a specified value in which case the PLC generates a high pressure fault signal; and
(5) gas sensor 195 of FIGS. 1 and 8 to determine if gas has been detected in the exhaust stack in which case the PLC generates a gas leak fault signal.
In step 420, the fault type is displayed (if the PLC is so equipped) and exhaust fans 260A and 260B of FIG. 2 are ramped up to a fan speed that corresponds to a preset exhaust pressure and exhaust flow rate for the emergency (e.g. an open) damper position. Note the damper is not yet in the emergency position. This is accomplished by control signals sent by PLC 345 to VFDs 275 of FIG. 2. The fault type may also be indicated by colored lights and/or audible tones. The fault type may be networked to remote monitoring stations. Note, the PLC itself may be remote from the gas cabinet and connected to a network interface that is connected to the various sensors and control valves of the gas cabinet and also connected an additional network interface connected to the VFDs and exhaust sensors. Additionally, high pressure isolation valve 225, low pressure valve isolation valve 240, and pneumatic cylinder valve 210 of FIGS. 1 and 8 are closed by a control signals sent by PLC 345 to those valves. Next, in step 425, exhaust static pressure sensor 280 of FIGS. 2 and 8 is polled to determine if the pressure is lower than a specified maximum pressure. This is a check that the cabinet is at a negative pressure compared to the ambient air pressure outside the cabinet. If the pressure is above the maximum pressure then in step 430, PLC 345 initiates an exhaust pressure alarm and no further action is taken automatically. If in step 425, the pressure is lower than the specified maximum pressure, step 435 is performed. In step 435, the damper (e.g., damper 145 of FIG.3) is set to the emergency position by control signals sent to the actuator (e.g., actuator 155 of FIG. 3) and step 440 is then performed. In step 440, exhaust flow sensor 285 of FIGS. 2 and 8 is polled to determine if the flow is higher than a specified minimum flow. This is a check that the amount of air flow is sufficient to ensure no escape of gas from the cabinet into the room. If the flow is below a minimum flow then in step 445, PLC 345 initiates an exhaust flow alarm and no further action is taken automatically; otherwise the sub-routine of FIG. 9C is initiated through connector “A.”
Exhaust flow does not exert any control over the damper (e.g., damper 145 of FIG. 3). That is, no control signals are sent to damper by PLC 345 of FIG. 8 in response to exhaust flow sensor signals and the position of damper is not affected by exhaust flow volume or changes in exhaust flow volume.
FIG. 9B describes the control logic for maintenance operation of the gas cabinet. In step 450, PLC 345 of FIG. 8 receives a request for maintenance access to cabinet 100 via window 160 or door 135 (see FIG. 1). In step 455, exhaust fans 260A and 260B of FIG. 2 are ramped up to the corresponding pressure and flow rate for the maintenance position of the damper by control signals sent by PLC 345 to VFDs 275 of FIG. 2. Next, in step 460, exhaust static pressure sensor 280 of FIGS. 2 and 8 is polled to determine if the pressure is lower than a specified maximum pressure. This is a check that the cabinet is at a negative pressure compared to the ambient air pressure outside the cabinet. If the pressure is above the maximum pressure then in step 465, PLC 345 of FIG. 8 initiates an exhaust pressure alarm and no further action is taken automatically. If in step 460, the pressure is lower than the specified maximum pressure, step 470 is performed. In step 470, the damper (e.g., damper 145 of FIG. 3) is set to the maintenance position (e.g., an open position) by control signals sent to the actuator (e.g., actuator 155 of FIG. 3) and step 475 is then performed. In step 475, exhaust flow sensor 285 of FIGS. 2 and 8 is polled to determine if the flow is higher than a specified minimum flow. If the flow is below the minimum flow then in step 480, PLC 345 initiates an exhaust flow alarm and no further action is taken automatically and no access is granted. If the flow is above the minimum flow then in step 485 PLC 345 of FIG. 8 unlatches door 135 or window 160 of FIG. 1. Next, the sub-routine of FIG. 9C is initiated through connector “A.”
FIG. 9C describes the control logic for an exhaust monitoring sub-routine. In step 490, exhaust flow sensor 285 of FIGS. 2 and 8 is polled to determine if the flow is higher than a specified minimum flow. If the flow is higher than the minimum flow then the loop 490 and 495 is repeated. If in step 490, the flow is lower than the minimum flow then in step 500, high pressure isolation valve 225, low pressure valve isolation valve 240, and pneumatic cylinder valve 210 of FIGS. 1 and 8 are closed by a control signals sent by PLC 345 to those valves (if not already closed) and PLC 345 of FIG. 8 initiates an exhaust flow alarm.
FIG. 10 is a schematic block diagram of an exemplary programmable logic controller. In FIG. 10, a general purpose computer system 600 is used as programmable logic controller 310 (see FIG. 5), but alternatively, a purpose built logic controller may be used which would have similar components to computer 600. In FIG. 10, computer system 600 has at least one microprocessor or central processing unit (CPU) 605. CPU 605 is interconnected via a system bus 610 to a random access memory (RAM) 615, a read-only memory (ROM) 620, an input/output (I/O) adapter 625 for connecting a removable data and/or program storage device 630 and a mass data and/or program storage device 635, a user interface adapter 640 for connecting a keyboard 645 and a mouse 650, a port adapter 655 for connecting a data port 660 and a display adapter 665 for connecting a display device 670.
ROM 620 contains the basic operating system for computer system 600. The operating system may alternatively reside in RAM 615 or elsewhere as is known in the art. Examples of removable data and/or program storage device 630 include magnetic media such as floppy drives and tape drives and optical media such as CD ROM drives. Examples of mass data and/or program storage device 635 include electronic, magnetic, optical, electromagnetic, infrared, and semiconductor devices. Examples of a computer-readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD. In addition to keyboard 645 and mouse 650, other user input devices such as trackballs, writing tablets, pressure pads, microphones, light pens and position-sensing screen displays may be connected to user interface 640. Examples of display devices include cathode-ray tubes (CRT) and liquid crystal displays (LCD).
A computer program with an appropriate application interface may be created by one of skill in the art and stored on the system or a data and/or program storage device to simplify the practicing of this invention. In operation, information for the computer program created to run the present invention is loaded on the appropriate removable data and/or program storage device 630, fed through data port 660 or typed in using keyboard 645.
Generally, the method described herein with respect to the flow diagrams of FIGS.9A, 9B and 9C may be coded as a set of instructions on removable or hard media for use by programmable logic controller 310 (see FIG. 5) or general-purpose computer 600 (see FIG. 10) and stored as code 675 on RAM 615.
Thus the embodiments of the present invention provide a compressed gas cylinder cabinet with regulated exhaust control and a method of regulating exhaust of a compressed gas cylinder cabinet that is energy efficient.
The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

What is claimed is:

1. A gas cabinet, comprising:

an enclosure;

a damper having at least two flow rate positions;

an exhaust outlet;

a set of sensors; and

a programmable logic controller configured to change a flow rate position of said damper from a first flow rate position to a second flow rate position based on the state of said sensors.

2. The gas cabinet of claim 1, wherein said set of sensors includes one or more sensors selected comprising a gas flow sensor, a gas sensor, a gas cylinder weight sensor, a low pressure sensor, or a high pressure sensor.

3. The gas cabinet of claim 1, wherein said programmable logic controller is configured to change said damper from said first flow rate position to said second flow rate position if one or more sensors of said set of sensors indicates a gas leak within said enclosure, said second flow rate position having a higher flow rate than said first flow rate position.

4. The gas cabinet of claim 3, wherein (i) said first flow rate position is a fully closed position and said second flow position is a fully open position or (ii) said first flow rate position is a partially closed position and said second flow rate position is a more open position than said first position.

5. The gas cabinet of claim 1, wherein said damper includes:

a first set of fixed openings;

a moveable plate having a second set of openings;

means for moving said second plate relative to said first set of openings; and

wherein in a first position of said plate corresponding to said first flow rate position, said plate blocks each of said fixed openings and in a second position of said plate corresponding to said second flow rate position, each opening of said second set of openings aligns with a respective opening of said fixed openings.

6. The gas cabinet of claim 1, wherein said damper includes:

a first set of fixed openings;

a moveable plate having a second set of openings;

means for moving said second plate relative to said first set of openings; and

wherein in a first position of said plate corresponding to said first flow rate position, said plate blocks more of each opening of said fixed openings then are blocked by said plate in a second position corresponding to said second flow rate position.

7. The gas cabinet of claim 1, wherein said damper includes:

a set of moveable louvers and means for opening and closing said louvers.

8. The gas cabinet of claim 1, further including:

a set of valves configured to control a flow of gas from a gas cylinder mounted in said cabinet to a gas supply line exiting from said cabinet; and

wherein said programmable logic controller is configured to close said set of valves if one or more sensors of said set of sensors indicates an out of specification condition.

9. The gas cabinet of claim 8, wherein said exhaust outlet is connected to an exhaust fan through an exhaust duct and said programmable logic controller is connected to an exhaust static pressure sensor in said exhaust duct; and

said programmable logic controller is configured to (i) increase the fan speed of said exhaust fan if one or more sensors of said set of sensors indicates a gas leak and (ii) not change the flow rate position of said damper if said exhaust static pressure sensor indicates that the pressure in said exhaust duct is greater than a preset minimum pressure.

10. The gas cabinet of claim 8, wherein said exhaust outlet is connected to an exhaust fan through an exhaust duct and said programmable logic controller is connected to an exhaust flow sensor in said exhaust duct; and

said programmable logic controller is configured to (i) increase the fan speed of said exhaust fan if one or more sensors of said set of sensors indicates a gas leak and (ii) to close said set of valves if said exhaust flow sensor indicates that the air flow rate is less than a preset minimum flow rate.

11. The gas cabinet of claim 1, wherein said enclosure is fitted with a door.

12. The gas cabinet of claim 11, wherein said damper is the only means for air entry into said cabinet when said door is closed and latched.

13. The gas cabinet of claim 11, wherein said damper is contained with said door.

14. A method, comprising:

providing a gas cabinet, comprising:

an enclosure;

a damper having at least two flow rate positions;

an exhaust outlet;

a set of sensors; and

a programmable logic controller configured to change the flow rate position of said damper from a first flow rate position to a second flow rate position based on the state of said sensors; and

if the exhaust static pressure within said cabinet is lower than a preset minimum pressure then changing said damper from said first flow rate position to said second flow rate position if one or more sensors of said set of sensors indicates a gas leak within said enclosure, said second flow rate position having a higher flow rate than said first flow rate position.

15. The method of claim 14, wherein (i) said first flow rate position is a fully closed position and said second flow rate position is a fully open position or (ii) said first flow rate position is a partially closed position and said second flow rate position is a more open position than said first position.

16. The method of claim 14, said gas cabinet further including:

closing said set of valves if one or more sensors of said set of sensors indicates an out of specification condition.

17. The method of claim 16, wherein said exhaust outlet is connected to an exhaust fan through an exhaust duct and said programmable logic controller is connected to an exhaust static pressure sensor in said exhaust duct;

increasing the fan speed of said exhaust fan if one or more sensors of said set of sensors indicates a gas leak; and

not changing said flow rate position of said damper if said exhaust static pressure sensor indicates that the pressure in said exhaust duct is greater than said preset minimum pressure.

18. The method of claim 16, wherein said exhaust outlet is connected to an exhaust fan through an exhaust duct and said programmable logic controller is connected to an exhaust flow sensor in said exhaust duct;

closing said set of valves if said exhaust flow sensor indicates that the air flow rate is less than a preset minimum flow rate.

19. The method of claim 14, wherein said set of sensors includes one or more sensors selected from the group consisting of a gas flow sensor, a gas sensor, a gas cylinder weight sensor, a low pressure sensor, and a high pressure sensor.

20. The method of claim 14, wherein said damper includes a first set of fixed openings and a moveable plate having a second set of openings; and

changing said damper from a first position corresponding to said first flow rate position to a second position corresponding to said second flow rate position includes moving said moveable plate relative to said first set of openings wherein in said first position, said plate blocks more of each opening if said fixed openings then are blocked by said plate in a second flow rate position.

21. The method of claim 14, wherein said damper includes a first set of fixed openings and a moveable plate having a second set of openings; and

changing said damper from a first position corresponding to said first flow rate position to a second position corresponding to said second flow rate position includes moving said moveable plate relative to said first set of openings wherein in said first position said plate, said plate blocks each of said fixed openings and in said second position of said plate each opening of said second set of openings align with respective openings of said fixed openings.

22. The method of claim 14, further including:

monitoring the state of said sensors and if said sensors indicate a gas leak, first increasing the speed of exhaust fans connected to said exhaust outlet followed by closing gas delivery valves within said cabinet followed by determining if an exhaust pressure of said cabinet is less than a preset minimum pressure; and

performing said changing said damper from said first flow rate position to said second flow rate position only if said exhaust pressure is less than said preset minimum pressure.

23. The method of claim 22, further including:

determining if an exhaust flow rate of said cabinet is greater than a preset exhaust flow rate and if said exhaust flow rate of said cabinet is not greater than a preset exhaust flow rate then closing said gas delivery valves if said gas delivery valves are not already closed.

24. The gas cabinet of claim 14, wherein said enclosure is fitted with a door.

25. The gas cabinet of claim 24, wherein said damper is the only means for air entry into said cabinet when said door is closed and latched.

26. The gas cabinet of claim 24, wherein said damper is contained with said door.