CA2055147C - Method and apparatus for determining the uncovered size of an opening adapted to be covered by multiple moveable doors - Google Patents

Abstract

Fume hood controller apparatus includes a computing means, together with associated memory, which can be configured fox horizontally and/or vertically moveable sash doors by inputting the necessary dimensions of the sash doors and other structural features, such as the upper lip height, frame widths and the like. The apparatus rapidly calculates the size of the uncovered area of the fume hood as a function of the position of the sash doors.

Description

-1- ~ 205514

2 THE UNCOVERED
SIZE OF AN OPENING
ADAPTED

3 TO BE COVERED BY MULTIPLE MOVEABLE DOORS
_

4 6 Cross Reference to Related Canadian Applications 8 1. Title: Apparatus for Determining the Position of a 9 Moveable Structure Along a Track Inventors: David Egbers and Steve Jacob 11 Serial No.: 2,055,258 12 Filed: November 12, 1991 14 2. Title: A System for Controlling the Differential Pressure of a Room Having Laboratory Fume Hoods 16 Inventors: Osman Ahmed and Steve Bradley 17 Serial No.: 2,055,101 18 Filed: November 7, 1991 3. Title: Apparatus for Controlling the Ventilation of 21 Laboratory Fume Hoods 22 Inventors: Osman Ahmed, Steve Bradley, Steve Fritsche and 23 Steve Jacob 24 Serial No.: 2,055,126 Filed: November 7, 1991 27 4. Title: Laboratory Fume Hood Control Apparatus Having 28 Improved Safety Considerations 29 Inventors: Osman Ahmed Serial No.: 2,055,100 31 Filed: November 7, 1991 The present invention relates generally to the 36 control of th e ventilation of laboratory fume hoods, and more 37 particularly to a method and apparatus for calculating the 38 area of an opening of a fume hood that is not covered by one 39 or more sash doors.

Fume hoods are utilized in various laboratory 41 environments for providing a work place where potentially 42 dangerous chemicals are used, with the hoods comprising an 43 enclosure having moveable doors at the front portion 2Q55~~~~

1 thereof which can be opened in various amounts to permit a 2 person to gain access to the interior of the enclosure for 3 the purpose of conducting experiments and the like. The 4 enclosure is typically connected to an exhaust system for removing any noxious fumes so that the person will not be 6 exposed to them while performing work in the hood.
7 Fume hood controllers which control the flow of 8 air through the enclosure have become more sophisticated in 9 recent years, and are now able to more accurately maintain the desired flow characteristics to efficiently exhaust the 11 fumes from the enclosure as a function of the desired 12 average face velocity of the opening of the fume hood. The 13 average face velocity is generally defined as the flow of 14 air into the fume hood per square foot of open face area of the fume hood, with the size of the open face area being 16 dependent upon the position of one or more moveable doors 17 that are provided on the front of the enclosure or fume 18 hood, and in most types of enclosures, the amount of bypass 19 opening that is provided when the door or doors are closed.
The fume hoods are exhausted by an exhaust system 21 that includes a blower that is capable of being driven at 22 variable speeds to increase or decrease the flow of air 23 from the fume hood to compensate for the varying size of 24 the opening or face. Alternatively, there may be a single blower connected to the exhaust manifold that is in turn 26 connected to the individual ducts of multiple fume hoods, 27 and dampers may be provided in the individual ducts to 28 control the flow from the individual ducts to thereby 29 modulate the flow to maintain the desired average face velocity.
31 The doors of such fume hoods can be opened by 32 raising them vertically, often referred to as the sash 33 position, or some fume hoods have a number of doors that 34 are mounted for sliding movement in typically two sets of vertical tracks. There are even doors that can be moved 36 horizontally and vertically, with the tracks being mounted 37 in a frame assembly that is vertically movable.
38 Prior art fume hood controllers have included 29551~'~

1 sensing means for measuring the position of a vertically 2 moveable sash door and then producing a signal proportional 3 to the sensed position to thereby vary the speed of the 4 blowers or the position of the dampers. While sensing means for determining the position of a single vertically 6 moveable sash door are known and are relatively simple to 7 implement, a more difficult situation exists when several 8 sash doors are present in the fume hood.
9 Accordingly, it is a primary object of the pres-ent invention to provide an improved fume hood controller 11 which is adapted to determine the uncovered area of the 12 opening of the fume hood, even when the fume hood is of the 13 type which has several sash doors.
14 It is another object of the present invention to provide such an improved fume hood controller that is 16 easily adaptable for use in controlling most commercially 17 available fume hoods, and accurately calculates the effec-18 tive area of uncovered opening to the fume hood, taking 19 into consideration the number of sash doors, the sizes of the sash doors, any bypass area, in addition to other 21 structural features, such as the upper lip height.
22 A related object of the present invention is to 23 provide an improved fume hood controller which includes a 24 computing means and is adapted to accurately calculate the uncovered area of the opening of a fume hood which has a 26 plurality of sash doors, and which can be easily configured 27 for most commercial fume hoods by simply inputting various 28 structural dimensions for the fume hood.
29 Still another object of the present invention is to provide an improved fume hood controller which provides 31 extremely rapid response to changes in the position of one 32 or more sash doors by virtue of its capability of calculat-33 ing the uncovered area of the opening of the fume hood 34 every few hundred milliseconds.
These and other objects will become apparent upon 36 reading the following detailed description of the present 37 invention, while referring to the attached drawings, in 38 which:

2g551~~

1 FIGURE 1 is a schematic block diagram of appa-2 ratus of the present invention shown integrated with a room 3 controller of a heating, ventilating and air conditioning 4 monitoring and control system of a building:
FIG. 2 is a block diagram of a fume hood control-6 ler, shown connected to an operator panel, the latter being 7 shown in front elevation:
8 FIG. 3 is a diagrammatic elevation of the front 9 of a representative fume hood having vertically operable sash doors;
11 FIG. 4 is a diagrammatic elevation of the front 12 of a representative fume hood having horizontally operable 13 sash doors;
14 FIG. 5 is a cross section taken generally along the line 5-5 of FIG. 4;
16 FIG. 6 is a diagrammatic elevation of the front 17 of a representative combination sash fume hood having 18 horizontally and vertically operable sash doors:
19 FIG. 7 is an electrical schematic diagram of a plurality of door sash position indicating switching means;
21 FIG. 8 is a cross section of the door sash posi-22 tion switching means;
23 FIG. 9 is a schematic diagram of electrical cir-24 cuitry for determining the position of sash doors of a fume 2 5 hood 26 FIG. 10 is a block diagram illustrating the rela-27 tive positions of FIGS. 10a, lOb, lOc, lOd and l0e to one 28 another, and which together comprise a schematic diagram of 29 the electrical circuitry for the fume hood controller means embodying the present invention:
31 FIGS. 10a, lOb, lOc, 10d and 10e, which if con-32 nected together, comprise the schematic diagram of the 33 electrical circuitry for the fume hood controller means 34 embodying the present invention;
FIG. 11 is a flow chart of the general operation 36 of the fume hood controller;
37 FIG. 12 is a flow chart of a portion of the 3~3 operation of the fume hood controller, particularly ~a5514'~

-5-1 illustrating the operation of the feed forward control 2 scheme, which may be employed;
3 FIG. 13 is a flow chart of a portion of the 4 operation of the fume hood controller, particularly illustrating the operation of the proportional gain,

6 integral gain and derivative gain control schemes;

7 FIG. 14 is a flow chart of a portion of the

8 operation of the fume hood controller, particularly

9 illustrating the operation of the calibration of the feed forward control scheme;
11 FIG. 15 is a flow chart of a portion of the 12 operation of the fume hood controller embodying the present 13 invention, particularly illustrating the operation of the 14 calculation of the uncovered opening for a number of hori-zontally moveable sash doors; and, 16 FIG. 16 is a flow chart of a portion of the 17 operation of the fume hood controller embodying the present 18 invention, particularly illustrating the operation of the 19 calculation of the uncovered opening for a number of hori-zontally and vertically moveable sash doors.
21 Detailed Description 22 It should be generally understood that a fume 23 hood controller controls the flow of air through the fume 24 hood in a manner whereby the effective size of the total opening to the fume hood, including the portion of the 26 opening that is not covered by one or more sash doors will 27 have a relatively constant average face velocity of air 28 moving into the fume hood. This means that regardless of 29 the area of the uncovered opening, an average volume of air per unit of surface area of the uncovered portion will be 31 moved into the fume hood. This protects the persons in the 32 laboratory from being exposed to noxious fumes or the like 33 because air is always flowing into the fume hood, and out 34 of the exhaust duct, and the flow is preferably controlled at a predetermined rate of approximately 75 to 150 cubic 36 feet per minute per square feet of effective surface area 37 of the uncovered opening. In other words, if the sash door 2~5514~
' -6-1 or doors are moved to the maximum open position whereby an 2 operator has the maximum access to the inside of the fume 3 hood for conducting experiments or the like, then the flow 4 of air will most likely have to be increased to maintain the average face velocity at the predetermined desired 6 level.
7 Broadly stated, the present invention is directed 8 to an improved fume hood controlling apparatus that is 9 adapted to provide many desirable operational advantages for persons who use the fume hoods to perform experiments 11 or other work, and also for the operator of the facility in 12 which the fume hoods are located. The apparatus embodying 13 the present invention provides extremely rapid and effec-14 tive control of the average face velocity of the fume hood, and achieves and maintains the desired average face 16 velocity within a few seconds after one or more doors which 17 cover the front opening of the fume hood have been moved.
18 This is achieved, at least in part, by the rapid calcula-19 tion of the uncovered area of the opening of the fume hood, i.e., that area not covered by sash doors, frames, lips and 21 the like, which calculation is repeated several times per 22 second. The fume hood controller apparatus of the present 23 invention includes a computing means, together with asso-24 ciated memory, which can be configured for horizontally and/or vertically moveable sash doors by inputting the 26 necessary dimensions of the sash doors and other structural 27 features, such as the upper lip height, frame widths and 28 the like, as will be described.
29 Turning now to the drawings, and particularly FIG. 1, a block diagram is shown of several fume hood 31 controllers 20 embodying the present invention inter-32 connected with a room controller 22, an exhaust controller 33 24 and a main control console 26. The fume hood con-34 trollers 20 are interconnected with the room controller 22 and with the exhaust controller 24 and the main control 36 console 26 in a local area network illustrated by line 28 37 which may be a multiconductor cable or the like. The room 38 controller the exhaust controller 24 and the main control . . 2x55147 1 console 26 are typically part of the building main HVAC
2 system in which the laboratory rooms containing the fume 3 hoods are located. The fume hood controllers 20 are pro-4 vided with power through line 30, which is at the proper voltage via a transformer 32 or the like.
6 The room controller 22 preferably is of the type 7 which is at least capable of providing a variable air 8 volume to the room, and may be a Landis & Gyr Powers System 9 600 SCU controller. The room controller 22 is capable of communicating over the LAN lines 28. The room controller 11 preferably is a System 600 SCU controller and is a commer-12 cially available controller for which extensive documenta-13 tion exists. The User Reference Manual, Part No. 125-1753 14 for the System 600 SCU controller is specifically incor-porated by reference herein.
16 The room controller 22 receives signals via lines 17 81 from each of the fume hood controllers 20 that provides 18 an analog input signal indicating the volume of air that is 19 being exhausted by each of the fume hood controllers 20 and a comparable signal from the exhaust flow sensor that 21 provides an indication of the volume of air that is being 22 exhausted through the main exhaust system apart from the 23 fume hood exhausts. These signals coupled with signals 24 that are supplied by a differential pressure sensor 29 which indicates the pressure within the room relative to 26 the reference space enable the room controller to control 27 the supply of air that is necessary to maintain the dif-28 ferential pressure within the room at a slightly lower 29 pressure than the reference space, i.e., preferably within the range of about 0.05 to about 0.1 inches of water, which 31 results in the desirable lower pressure of the room rela-32 tive to the reference space. However, it is not so low 33 that it prevents persons inside the laboratory room from 34 opening the doors to escape in the event of an emergency, particularly if the doors open outwardly from the room.
36 Also, in the event the doors open inwardly, the differen-37 tial pressure will not be so great that it will pull the 38 door open due to excessive force being applied dug to such 2~5~14?
_8_ 1 pressure.
2 The sensor 29 is preferably positioned in a suit-3 able hole or opening in the wall between the room and the 4 reference space and measures the pressure on one side rela-y tive to the other. Alternatively, a velocity sensor may be 6 provided which measures the velocity of air moving through 7 the opening which is directly proportional to the pressure 8 difference between the two spaces. Of course, a lower 9 pressure in the room relative to the reference space would mean that air would be moving into the room which is also 11 capable of being detected. Referring to FIG. 2, a fume 12 hood controller 20 is illustrated with its input and output 13 connector ports being identified, and the fume hood con-14 troller 20 is connected to an operator panel 34. It should be understood that each fume hood will have a fume hood 16 controller 20 and that an operator panel will be provided 17 with each fume hood controller. The operator panel 34 is 18 provided for each of the fume hoods and it is intercon-19 nected with the fume hood controller 20 by a line 36 which preferably comprises a multi-conductor cable having eight 21 conductors. The operator panel has a connector 38, such as 22 a 6 wire RJ11 type telephone jack for example, into which 23 a lap top personal computer or the like may be connected 24 for the purpose of inputting information relating to the configuration or operation of the fume hood during initial 26 installation, or to change certain operating parameters if 27 necessary. The operator panel 34 is preferably mounted to 28 the fume hood in a convenient location adapted to be easily 29 observed by a person who is working with the fume hood.
The fume hood controller operator panel 34 in-31 eludes a liquid crystal display 40 which when selectively 32 activated provides the visual indication of various aspects 33 of the operation of the fume hood, including three digits 34 42 which provide the average face velocity. The display 40 illustrates other conditions such as low face velocity, 36 high face velocity and emergency condition and an indi-37 cation of controller failure. The operator panel may have ~8 an alarm 44 and an emergency purge switch 46 ~~hirh an 20~~14~' -g-1 operator can press to purge the fume hood in the event of 2 an accident. The operator panel has two auxiliary switches 3 48 which can be used for various customer needs, including 4 day/night modes of operation. It is contemplated that night time mode of operation would have a different and 6 preferably reduced average face velocity, presumably 7 because no one would be working in the area and such a 8 lower average face velocity would conserve energy. An 9 alarm silence switch 50 is also preferably provided to extinguish an alarm.
11 Fume hoods come in many different styles, sizes 12 and configurations, including those which have a single 13 sash door or a number of sash doors, with the sash doors 14 being moveable vertically, horizontally or in both direc-tions. Additionally, various fume hoods have different 16 amounts of by-pass flow, i.e., the amount of flow permit-17 ting opening that exists even when all of the sash doors 18 are as completely closed as their design permits. Other 19 design considerations involve whether there is some kind of filtering means included in the fume hood for confining 21 fumes within the hood during operation. While many of 22 these design considerations must be taken into account in 23 providing efficient and effective control of the fume 24 hoods, the apparatus of the present invention can be configured to account for virtually all of the above 26 described design variables, and effective and extremely 27 fast control of the fume hood ventilation is provided.
28 Referring to FIG. 3, there is shown a fume hood, 29 indicated generally at 60, which has a vertically operated sash door 62 which can be moved to gain access to the fume 31 hood and which can be moved to the substantially closed 32 position as shown. Fume hoods are generally designed so 33 that even when a door sash such as door sash 62 is com-34 pletely closed, there is still some amount of opening into the fume hood through which air can pass. This opening is 36 generally referred to as the bypass area and it can be 37 determined so that its effect can be taken into considera-38 tion in controlling the flow of air into the fume hood.

-10-1 Some types of fume hoods have a bypass opening that is 2 located above the door sash while others are below the 3 same. In some fume hoods, the first amount of movement of 4 a sash door will increase the opening at the bottom of the door shown in FIG. 3, for example, but as the door is 6 raised, it will merely cut off the bypass opening so that 7 the effective size of the total opening of the fume hood is 8 maintained relatively constant for perhaps the first one-9 fourth amount of movement of the sash door 62 through its course of travel.

11 Other types of fume hoods may include several

12 horizontally moveable sash doors 66 such as shown in FIGS.

13 4 and 5, with the doors being movable in upper and lower

14 pairs of adjacent tracks 68. When the doors are positioned as shown in FIGS. 4 and 5, the fume hood opening is com-16 pletely closed and an operator may move the doors in the 17 horizontal direction to gain access to the fume hood. Both 18 of the fumes hoods 60 and 64 have an exhaust duct 70 which 19 generally extends to an exhaust system which may be that of the HVAC apparatus previously described. The fume hood 64 21 also includes a filtering structure shown diagrammatically 22 at 72 which filtering structure is intended to keep noxious 23 fumes and other contaminants from exiting the fume hood 24 into the exhaust system. Referring to FIG. 6, there is shown a combination fume hood which has horizontally mov-26 able doors 76 which are similar to the doors 66, with the 27 fume hood 74 having a frame structure 78 which carries the 28 doors 76 in suitable tracks and the frame structure 78 is 29 also vertically movable in the opening of the fume hood.
The illustration of FIG. 6 has portions removed as shown by 31 the break lines 73 which is intended to illustrate that the 32 height of the fume hood may be greater than is otherwise 33 shown so that the frame structure 78 may be raised suffi-34 ciently to permit adequate access to the interior of the fume hood by a person. There is generally a by-pass area 36 which is identified as the vertical area 75, and there is 37 typically a top lip portion 77 which may be approximately 38 2 inches wide. This dimension is preferably defined so 2Q551~'~
1 that its effect on the calculation of the open face area 2 can be taken into consideration.
3 While not specifically illustrated, other combin-4 ations are also possible, including multiple sets of ver-y tically moveable sash doors positioned adjacent one another 6 along the width of the fume hood opening, with two or more 7 sash doors being vertically moveable in adjacent tracks, 8 much the same as residential casement windows.
9 In accordance with an important aspect of the present invention, the fume hood controller 20 is adapted 11 to operate the fume hoods of various sizes and configura-12 tions as has been described, and it is also adapted to be 13 incorporated into a laboratory room where several fume 14 hoods may be located and which may have exhaust ducts which merge into a common exhaust manifold which may be a part of 16 the building HVAC system. A fume hood may be a single 17 self-contained installation and may have its own separate 18 exhaust duct. In the event that a single fume hood is 19 installed, it is typical that such an installation would have a variable speed motor driven blower associated with 21 the exhaust duct whereby the speed of the motor and blower 22 can be variably controlled to thereby adjust the flow of 23 air through the fume hood. Alternatively, and most 24 typically for multiple fume hoods in a single area, the exhaust ducts of each fume hood are merged into one or more 26 larger exhaust manifolds and a single large blower may be 27 provided in the manifold system. In such types of instal-28 lations, control of each fume hood is achieved by means of 29 separate dampers located in the exhaust duct of each fume hood, so that variation in the flow can be controlled by 31 appropriately positioning the damper associated with each 32 fume hood.
33 The fume hood controller is adapted to control 34 virtually any of the various kinds and styles of fume hoods that are commercially available, and to this end, it has a 36 number of input and output ports (lines, connectors or 37 connections, all considered to be equivalent for the 38 purposes of describing the present invention) that can be .. 2055147 1 connected to various sensors that may be used with the 2 controller. As shown in FIG. 2, it has digital output or 3 DO ports which interface with a digital signal/analog 4 pressure transducer with an exhaust damper as previously described, but it also has an analog voltage output port 6 for controlling a variable speed fan drive if it is to be 7 installed in that manner. There are five sash position 8 sensor ports for use in sensing the position of both 9 horizontally and vertically moveable sashes and there is l0 also an analog input port provided for connection to an 11 exhaust air flow sensor 49. A digital input port for the 12 emergency switch is provided and digital output ports for 13 outputting an alarm horn signal as well as an auxiliary 14 signal is provided. An analog voltage output port is also provided for providing a volume of flow signal to the room 16 controller 22. In certain applications where the exhaust 17 air flow sensor is not provided, a wall velocity sensor 18 indicative of face velocity may be utilized and an input 19 port for such a signal is provided, but the use of such sensors is generally considered to be less accurate and is 21 not the preferred embodiment. With these various input and 22 output ports, virtually any type of fume hood can be con-23 trolled in an effective and efficient manner.
24 From the foregoing discussion, it should be appreciated that if the desired average face velocity is 26 desired to be maintained and the sash position is changed, 27 the size of the opening can be dramatically changed which 28 may then require a dramatic change in the volume of air to 29 maintain the average face velocity. While it is known to control a variable air volume blower as a function of the 31 sash position, the fume hood controller apparatus of the 32 present invention improves on that known method by incor-33 porating additional control schemes which dramatically 34 improve the capabilities of the control system in terms of maintaining relatively constant average face velocity in a 36 manner whereby reactions to perturbations in the system are 37 quickly made.
38 To determine the position of the sash doors, a M ~0551~7 1 sash position sensor is provided adjacent each movable sash 2 door and it is generally illustrated in FIGS. 7, 8 and 9.
3 Referring to FIG. 8, the door sash position indicator 4 comprises an elongated switch mechanism 80 of relatively simple mechanical design which preferably consists of a 6 relatively thin polyester base layer 82 upon which is 7 printed a strip of electrically resistive ink 84 of a known 8 constant resistance per unit length. Another polyester 9 base layer 86 is provided and it has a strip of elec-trically conductive ink 88 printed on it. The two base 11 layers 82 and 86 are adhesively bonded to one another by 12 two beads of adhesive 90 located on opposite sides of the 13 strip. The base layers are preferably approximately five-14 thousandths of an inch thick and the beads are approxi-mately two-thousandths of an inch thick, with the beads 16 providing a spaced area between the conductive and resis-17 tive layers 88 and 84. The switching mechanism 80 is 18 preferably applied to the fume hood by a layer of adhesive 19 92.
The polyester material is sufficiently flexible 21 to enable one layer to be moved toward the other so that 22 contact is made in response to a preferably spring biased 23 actuator 94 carried by the appropriate sash door to which 24 the strip is placed adjacent to so that when the sash door is moved, the actuator 94 moves along the switching 26 mechanism 80 and provides contact between the resistive and 27 conductive layers which are then sensed by electrical 28 circuitry to be described which provides a voltage output 29 that is indicative of the position of the actuator 94 along the length of the switching means. Stated in other words, 31 the actuator 94 is carried by the door and therefore 32 provides an electrical voltage that is indicative of the 33 position of the sash door.
34 The actuator 94 is preferably spring biased toward the switching mechanism 80 so that as the door is 36 moved, sufficient pressure is applied to the switching 37 means to bring the two base layers together so that the 38 resistive and conductive layers make electrical contact zo~5~ ~ ~

1 with one another and if this is done, the voltage level is 2 provided. By having the switching means 80 of sufficient 3 length so that the full extent of the travel of the sash 4 door is provided as shown in FIG. 3, then an accurate determination of the sash position can be made.
6 It should be understood that the illustration of 7 the switching mechanism 80 in FIGS. 3 and 5 is intended to 8 be diagrammatic, in that the switching mechanism is 9 preferably actually located within the sash frame itself and accordingly would not be visible as shown. The width 11 and thickness dimensions of the switching mechanism are so 12 small that interference with the operation of the sash door 13 is virtually no problem. The actuator 94 can also be 14 placed in a small hole that may be drilled in the sash door or it may be attached externally at one end thereof so that 16 it can be in position to operate the switch 80. In the 17 vertical moveable sash doors shown in FIGS. 3 and 6, a 18 switching mechanism 80 is preferably provided in one or the 19 other of the sides of the sash frame, whereas in the fume hoods having horizontally movable doors, it is preferred 21 that the switching mechanism 80 be placed in the top of the 22 tracks 68 so that the weight of the movable doors do not 23 operate the switching mechanism 80 or otherwise damage the 24 same.
Turning to FIG. 9, the preferred electrical 26 circuitry which generates the position indicating voltage 27 is illustrated, and this circuitry is adapted to provide 28 two separate voltages indicating the position of two sash 29 doors in a single track. With respect to the cross-section shown in FIG. 5, there are two horizontal tracks, each of 31 which carries two sash doors and a switching mechanism 80 32 is provided for each of the tracks as is a circuit as shown 33 in FIG. 9, thereby providing a distinct voltage for each of 34 the four sash doors as shown.
The switching means is preferably applied to the 36 fume hood with a layer of adhesive 92 and the actuator 94 37 is adapted to bear upon the switching means at locations 38 along the length thereof. Referring to FIG. 7, a 2455~~~

-15-1 diagrammatic illustration of a pair of switching means is 2 illustrated such as may occur with respect to the two 3 tracks shown in FIG. 5. A switching mechanism 80 is 4 provided with each track and the four arrows illustrated represent the point of contact created by the actuators 94 6 which result in a signal being applied on each of the ends 7 of each switching means, with the magnitude of the signal 8 representing a voltage that is proportional to the distance 9 between the end and the nearest arrow. Thus, a single switching mechanism 80 is adapted to provide position li indicating signals for two doors located in each track.
12 The circuitry that is used to accomplish the voltage 13 generation is shown in FIG. 9 and includes one of these 14 circuits for each track. The resistive element is shown at 84 and the conductive element 88 is also illustrated being

16 connected to ground with two arrows being illustrated, and

17 represented the point of contact between the resistive and

18 conductive elements caused by each of the actuators 94

19 associated with the two separate doors. The circuitry includes an operational amplifier 100 which has its output 21 connected to the base of a PNP transistor 102, the emitter 22 of which is connected to a source of positive voltage 23 through resistor 104 into the negative input of the opera-24 tional amplifier, the positive input of which is also con-nected to a source of positive voltage of preferably 26 approximately five volts. The collector of the transistor 27 102 is connected to one end of the resistive element 84 and 28 has an output line 106 on which the voltage is produced 29 that is indicative of the position of the door.
The circuit operates to provide a constant cur-31 rent directed into the resistive element 84 and this cur-32 rent results in a voltage on line 106 that is proportional 33 to the resistance value between the collector and ground 34 which changes as the nearest point of contact along the resistance changes. The operational amplifier operates to 36 attempt to drive the negative input to equal the voltage 37 level on the positive input and this results in the current 38 applied at the output of the operational amplifier varying 2055~4~

1 in direct proportion to the effective length of the resis-t tance strip 84. The lower portion of the circuitry 3 operates the same way as that which has been described and 4 it similarly produces a voltage on an output line 108 that is proportional to the distance between the connected end 6 of the resistance element 84 and the point of contact that 7 is made by the actuator 94 associated with the other sash 8 door in the track.
9 Referring to the composite electrical schematic diagram of the circuitry of the fume hood controller, if 11 the separate drawings FIGS. 10a, lOb, lOc, 10d and l0e are 12 placed adjacent one another in the manner shown in FIG. 10, 13 the total electrical schematic diagram of the fume hood 14 controller 20 is illustrated. The operation of the cir-cuitry of FIGS. l0a through l0e will not be described in 16 detail. The circuitry is driven by a microprocessor and 17 the important algorithms that carry out the control func-18 tions of the controller will be hereinafter described.
19 Referring to FIG. lOc, the circuitry includes a Motorola MC
68HC11 microprocessor 120 which is clocked at 8 MHz by a 21 crystal 122. The microprocessor 120 has a databus 124 that 22 is connected to a tri-state buffer 126 (FIG. lOd) which in 23 turn is connected to an electrically programmable read only 24 memory 128 that is also connected to the databus 124. The EPROM 128 has address lines AO through A7 connected to the 26 tri-state buffer 126 and also has address lines A8 through 27 A14 connected to the microprocessor 120.
28 The circuitry includes a 3 to 8-bit multiplexer 29 130, a data latch 132 (see FIG. lOd), a digital-to-analog converter 134, which is adapted to provide the analog out-31 puts indicative of the volume of air being exhausted by the 32 fume hood, which information is provided to room controller 33 22 as has been previously described with respect to FIG. 2.
34 Referring to FIG. lOb, an RS232 driver 136 is provided for transmitting and receiving information through the hand 36 held terminal. The circuitry illustrated in FIG. 9 is also 37 shown in the overall schematic diagrams and is in FIGS. 10a 38 and lOb. The other components are well known and therefore 205514' 1 need not be otherwise described.
2 As previously mentioned, the apparatus of the 3 present invention utilizes a flow sensor preferably located 4 in the exhaust duct 70 to measure the air volume that is being drawn through the fume hood. The volume flow rate 6 may be calculated by measuring the differential pressure 7 across a multi-point pitot tube or the like. The preferred 8 embodiment utilizes a differential pressure sensor for 9 measuring the flow through the exhaust duct and the appa-ratus of the present invention utilizes control schemes to 11 either maintain the flow through the hood at a predeter-12 mined average face velocity, or at a minimum velocity in 13 the event the fume hood is closed or has a very small 14 bypass area.
The fume hood controller of the present invention 16 can be configured for almost all known types of fume hoods, 17 including fume hoods having horizontally movable sash 18 doors, vertically movable sash doors or a combination of 19 the two. As can be seen from the illustrations of FIGS. 2 and 10, the fume hood controller is adapted to control an 21 exhaust damper or a variable speed fan drive, the con-22 troller being adapted to output signals that are compatible 23 with either type of control. The controller is also 24 adapted to receive information defining the physical and operating characteristics of the fume hood and other ini-26 tializing information. This can be input into the fume 27 hood controller by means of the hand held terminal which is 28 preferably a lap top computer that can be connected to the 29 operator panel 34. It should be appreciated that the day/night operation may be provided, but is not the pre-31 ferred embodiment of the system; if it is provided, the 32 information relating to such day/night operation should be 33 included.
34 Operational information:
1. Time of day:
36 2. Set day and night values for the average 37 face velocity (SVEL), feet per minute or 38 meters per second;

205514fi 1 3. Set day and night values for the minimum 2 flow, (MINFLO), in cubic feet per minute;
3 4. Set day and night values for high velocity 4 limit (HVEL), F/m or M/sec;
5. Set day and night values for low velocity 6 limit (LVEL), F/m or M/sec;
7 6. Set day and night values for intermediate 8 high velocity limit (MVEL), F/m or M/sec;
9 7. Set day and night values for intermediate low velocity limit (IVEL), F/m or M/sec;
11 8. Set the proportional gain factor (KP), 12 analog output per error in percent;
13 9. Set the integral gain factor (KI), analog 14 output multiplied by time in minutes per error in percent;
16 10. Set derivative gain factor (KD), analog 17 output multiplied by time in minutes per 18 error in percent:
19 11. Set feed forward gain factor (KF) if a variable speed drive is used as the control 21 equipment instead of a damper, analog output 22 per CFM:
23 12. Set time in seconds (DELTIME) the user 24 prefers to have the full exhaust flow in case the emergency button is activated:
26 13. Set a preset percent of last exhaust flow 27 (SAFLOQ) the user wishes to have once the 28 emergency switch is activated and DELTIME is 29 expired.
The above information is used to control the mode 31 of operation and to control the limits of flow during the 32 day or night modes of operation. The controller includes 33 programmed instructions to calculate the steps in para-34 graphs 3 through 7 in the event such information is not provided by the user. To this end, once the day and night 36 values for the average face velocity are set, the con-37 troller 20 will calculate high velocity limit at 120% of '~8 the ~-.~~~~ ~ fare velocity, the low ~~~Zc~city limit at 80%

.. ~o~~~~~

1 and the intermediate limit at 90%. It should be understood 2 that these percentage values may be adjusted, as desired.
3 Other information that should be input include the follow-4 ing information which relates to the physical construction of the fume hood. It should be understood that some of the 6 infonaation may not be required for only vertically or 7 horizontally moveable sash doors, but all of the informa-8 tion may be required for a combination of the same. The 9 information required includes vertical segments, which is defined to be a height and width dimension that may be 11 covered by one or more sash doors. If more than one sash 12 door is provided for each segment, those doors are intended 13 to be vertically moveable sash doors, analogous to a double 14 sash residential window. The information to be provided includes the following:
16 14. Input the number of vertical segments;
17 15. Input the height of each segment, in inches;
18 16. Input the width of each segment, in inches;
19 17. Input the number of tracks per segment;
18. Input the number of horizontal sashes per 21 track;
22 19. Input the maximum sash height, in inches:
23 20. Input the sash width, in inches;
24 21. Input the location of the sash sensor from left edge of sash, in inches;
26 22. Input the by-pass area per segment, in 27 square inches;
28 23. Input the minimum face area per segment, in 29 square inches;
24. Input the top lip height above the 31 horizontal sash, in inches:
32 The fume hood controller 20 is programmed to 33 control the flow of air through the fume hood by carrying 34 out a series of instructions, an overview of which is contained in the flow chart of FIG. li. After start-up and 36 outputting information to the display and determining the 37 time of day, the controller 20 reads the initial sash 38 positions of all doors (block 150), and this information is 2Q55.~4~

-20-1 then used to compute the open face area (block 152). If 2 not previously done, the operator can set the average face 3 velocity set point (block 154) and this information is then 4 used together with the open face area to compute the ex-haust flow set point (SFLOW) (block 156) that is necessary 6 to provide the predetermined average face velocity given 7 the open area of the fume hood that has been previously 8 measured and calculated. The computed fume hood exhaust 9 set point is then compared (block 158) with a preset or required minimum flow, and if computed set point is less 11 than the minimum flow, the controller sets the set point 12 flow at the preset minimum flow (block 160). If it is more 13 than the minimum flow, then it is retained (block 162) and 14 it is provided to both of the control loops.
If there is a variable speed fan drive for the 16 fume controller, i.e., several fume hoods are not connected 17 to a common exhaust duct and controlled by a damper, then 18 the controller will run a feed-forward control loop (block 19 164) which provides a control signal that is sent to a summing junction 166 which control signal represents an

21 open loop type of control action. In this control action,

22 a predicted value of the speed of the blower is generated

23 based upon the calculated opening of the fume hood, and the

24 average face velocity set point. The predicted value of the speed of the blower generated will cause the blower 26 motor to rapidly change speed to maintain the average face 27 velocity. It should be understood that the feed forward 28 aspect of the control is only invoked when the sash 29 position has been changed and after it has been changed, then a second control loop performs the dominant control 31 action for maintaining the average face velocity constant 32 in the event that a variable speed blower is used to 33 control the volume of air through the fume hood.
34 After the sash position has been changed and the feed forward loop has established the new air volume, then 36 the control loop switches to a proportional integral 37 derivative control loop and this is accomplished by the set 38 flow signal being provided to block 168 which indicates 2fl~514'~

1 that the controller computes the error by determining the 2 absolute value of the difference between the set flow 3 signal and the flow signal as measured by the exhaust air 4 flow sensor in the exhaust duct. Any error that is com-puted is applied to the control loop identified as the 6 proportional-integral-derivative control loop (PID) to 7 determine an error signal (block 170) and this error signal 8 is compared with the prior error signal from the previous 9 sample to determine if that error is less than a deadband error (block 172). If it is, then the prior error signal 11 is maintained as shown by block 174, but if it is not, then 12 the new error signal is provided to output mode 176 and it 13 is applied to the summing junction 166. That summed error 14 is also compared with the last output signal and a deter-urination is made if this is within a deadband range (block 16 180) which, if it is, results in the last or previous 17 output being retained (block 182). If it is outside of the 18 deadband, then a new output signal is provided to the 19 damper control or the blower (block 184). In the event that the last output is the output as shown in block 182, 21 the controller then reads the measured flow (MFLOW) (block 22 186) and the sash positions are then read (block 188) and 23 the net open face area is recomputed (block 190) and a 24 determination made as to whether the new computed area less the old computed area is less than a deadband (block 192) 26 and if it is, then the old area is maintained (block 194) 27 and the error is then computed again (block 168). If the 28 new area less the old area is not within the deadband, then 29 the controller computes a new exhaust flow set point as shown in block 156.
31 One of the significant advantages of the present 32 invention is that the controller is adapted to execute the 33 control scheme in a repetitive and extremely rapid manner.
34 The exhaust sensor provides flow signal information that is inputted to the microprocessor at a speed of approximately 36 one sample per 100 milliseconds and the control action 37 described in connection with FIG. 11 is completed appro-38 ximately every 100 milliseconds. The sash door position i signals are sampled by the microprocessor every 200 milli-2 seconds. The result of such rapid repetitive sampling and 3 executing of the control actions results in extremely rapid 4 operation of the controller. It has been found that movement of the sash will result in adjustment of the air 6 flow so that the average face velocity is achieved within 7 a time period of only approximately 3-4 seconds after the 8 sash door reposition has been stopped. This represents a 9 dramatic improvement over existing fume hood controllers.
In the event that the feed forward control loop 11 is utilized, the sequence of instructions that are carried 12 out to accomplish running of this loop is shown in the flow 13 chart of FIG. 12, which has the controller using the 14 exhaust flow set point (SFLOW) to compute the control output to a fan drive (block 200), which is identified as 16 signal AO that is computed as an intercept point plus the 17 set flow multiplied by a slope value. The intercept is the 18 value which is a fixed output voltage to a fan drive and 19 the slope in the equation correlates exhaust flow rate and output voltage to the fan drive. The controller then reads 21 the duct velocity (DV) (block 202), takes the last duct 22 velocity sample (block 204) and equates that as the duct 23 velocity value and starts the timing of the maximum and 24 minimum delay times (block 206) which the controller uses to insure whether the duct velocity has reached steady 26 state or not. The controller determines whether the 27 maximum delay time has expired (block 208), and if it has, 28 provides the output signal at output 210. If the max delay 29 has not expired, the controller determines if the absolute value of the difference between the last duct velocity 31 sample and the current duct velocity sample is less than or 32 equal to a dead band value (block 212). If it is not less 33 than the dead band value, the controller then sets the last 34 duct value as equal to the present duct value sample (block 214) and the controller then restarts the minimum delay 36 timing function (block 216). Once this is accomplished, 37 the controller again determines whether the max delay has 38 expired (block 208). If the absolute value of the ~~55~4~~

1 difference between the last duct velocity and the present 2 duct velocity sample is less than the dead band, the 3 controller determines whether the minimum delay time has 4 expired which, if it has as shown from block 218, the output is provided at 210. If it has not, then it deter-6 mines if the max delay has expired.
7 Turning to the proportional-integral-derivative 8 or PID control loop, the controller runs the PID loop by 9 carrying out the instructions shown in the flow chart of FIG. 13. The controller uses the error that is computed by 11 block 168 (see FIG. 11) in three separate paths. With 12 respect to the upper path, the controller uses the pre-13 selected proportional gain factor (block 220) and that 14 proportional gain factor is used together with the error to calculate the proportional gain (block 222) and the propor-16 tional gain is output to a summing junction 224.
17 The controller also uses the error signal and 18 calculates an integral term (block 226) with the integral 19 term being equal to the prior integral sum (ISUM) plus the product of loop time and any error and this calculation is 21 compared to limits to provide limits on the term. The term 22 is then used together with the previously defined integral 23 gain constant (block 230) and the controller than calcu-24 lates the integral gain (block 232) which is the integral gain constant multiplied by the integration sum term. The 26 output is then applied to the summing junction 224.
27 The input error is also used by the controller to 28 calculate a derivative gain factor which is done by the 29 controller using the previously defined derivative gain factor from block 234 which is used together with the error 31 to calculate the derivative gain (block 236) which is the 32 reciprocal of the time in which it is required to execute 33 the PID loop multiplied by the derivative gain factor 34 multiplied by the current sample error minus the previous sample error with this result being provided to the summing 36 junction 224.
37 The control action performed by the controller 20 38 as illustrated in FIG. 13 provides three separate gain 2~55~4?' 1 factors which provide steady state correction of the air 2 flow through the fume hood in a very fast acting manner.
3 The formation of the output signal from the PID control 4 loop takes into consideration not only the magnitude of the error, but as a result of the derivative gain segment of 6 control, the rate of change of the error is considered and 7 the change in the value of the gain is proportional to the 8 rate of change. Thus, the derivative gain can see how fast 9 the actual condition is changing and works as an "antici-pator" in order to minimize error between the actual and 11 desired condition. The integral gain develops a correction 12 signal that is a function of the error integrated over a 13 period of time, and therefore provides any necessary cor-14 rection on a continuous basis to bring the actual condition to the desired condition. The proper combinations of pro-16 portional, integral and derivative gains will make the loop 17 faster and reach the desired conditions without any over-18 shoot.
19 A significant advantage of the PID control action is that it will compensate for perturbations that may be 21 experienced in the laboratory in which the fume hood may be 22 located in a manner in which other controllers do not. A
23 common occurrence in laboratory rooms which have a number 24 of fume hoods that are connected to a common exhaust manifold, involves the change in the pressure in a fume 26 hood exhaust duct that was caused by the sash doors being 27 moved in another of the fume hoods that is connected to the 28 common exhaust manifold. Such pressure variations will 29 affect the average face velocity of those fume hoods which had no change in their sash doors. However, the PID con-31 trol action may adjust the air flow if the exhaust duct 32 sensor determines a change in the pressure. To a lesser 33 degree, there may be pressure variations produced in the 34 laboratory caused by opening of doors to the laboratory itself, particularly if the differential pressure of the 36 laboratory room is maintained at a lesser pressure than a 37 reference space such as the corridor outside the room, for 38 example.

~fl5514~

-25-1 It is necessary to calibrate the feed forward 2 control loop and to this end, the instructions illustrated 3 in the flow chart of FIG. 14 are carried out. When the 4 initial calibration is accomplished, it is preferably done through the hand held terminal that may be connected to the 6 operator panel via connector 38, for example. The control-? ler then determines if the feed forward calibration is on 8 (block 242) and if it is, then the controller sets the 9 analog output of the fan drive to a value of 20 percent of the maximum value, which is identified as value A01 (block 11 244). The controller then sets the last sample duct 12 velocity (LSDV) as the current duct velocity (CDV) (block 13 246) and starts the maximum and minimum timers (block 248).
14 The controller ensures the steady state duct velocity in the following way. First by checking whether the max timer 16 has expired, and then, if the max timer has not expired, 17 the controller determines if the absolute value of the last 18 sample duct velocity minus the current duct velocity is 19 less than or equal to a dead band (block 270), and if it is, the controller determines if the min timer has expired 21 (block 272). If it has not, the controller reads the 22 current duct velocity (block 274). If the absolute value 23 of the last sample duct velocity minus the current duct 24 velocity is not less than or equal to a dead band (block 270), then the last sample duct velocity is set as the

26 current duct velocity (block 276) and the mintimer is

27 restarted (block 278) and the current duct velocity is

28 again read (block 274). In case either the max timer or

29 min timer has expired, the controller then checks the last analog output value to the fan drive (252) and inquires 31 whether the last analog output value was 70 percent of the 32 maximum output value (block 254). If it is not, then it 33 sets the analog output value to the fan drive at 70 percent 34 of the max value A02 (block 256) and the steady state duct velocity corresponding to A01. The controller then repeats 36 the procedure of ensuring steady state duct velocity when 37 analog output is A02 (block 258). If it is at the 70 38 percent of max value, then the duct velocity corresponds to 1 steady state velocity of A02 (block 258). Finally, the 2 controller (block 262) calculates the slope and intercept 3 values.
4 The result of the calibration process is to determine the duct flow at 20% and at 70% of the analog 6 output values, and the measured flow enables the slope and 7 intercept values to be determined so that the feed forward 8 control action will accurately predict the necessary fan 9 speed when sash door positions are changed.
The apparatus of the present invention is adapted 11 to rapidly calculate on a periodic basis several times per 12 second, the uncovered or open area of a fume hood access 13 opening that is capable of being covered by one or more 14 sash doors as previously described. As is shown in FIG. 6, the actuator 94 is preferably located at the righthand end 16 of each of the horizontally movable doors of which there 17 are four in number as illustrated. The position indicating 18 capability of the switching mechanism 80 provides a signal 19 having a voltage level for each of the four doors which is indicative of the position of the particular sash door 21 along its associated track. While the actuators 94 are 22 shown at the righthand portion of the sash doors, it should 23 be understood that they may be alternatively located on the 24 lefthand portion, or they could be located at virtually any location on each door, provided that the relationship 26 between the width of the door and the position of the 27 actuator is determined and is input into the fume hood con-28 trolley. It should be appreciated that having the location 29 of the actuators 94 at a common position, such as the right end, simplifies the calculation of the uncovered opening.
31 While the fume hood shown in FIG. 6 is of the 32 type which has four horizontally movable doors 76 that are 33 housed within a frame structure 78 that itself is vertical-34 ly movable, the fume hood controller apparatus of the pres-ent invention is adapted to be used with up to four movable 36 sash doors in a single direction, i.e., horizontally, and 37 a perpendicularly movable sash door frame. However, there 38 are five analog input ports in the controller for inputting 20~5~4~

1 position information regardless of whether it is horizontal 2 or vertical and the controller can be configured to accom-3 modate any combination of horizontally and vertically mov-4 able doors up to a total of five. To this end, it should be appreciated that there are vertically movable double 6 sash doors in certain commercially available fume hoods, 7 which configuration is not specifically shown in the 8 drawings, with the double sash configuration being housed 9 in a single frame structure that itself may be horizontally movable. The fume hood controller of the present invention 11 may treat the double sash door configuration in the ver-12 tical direction much the same as it operates with the 13 horizontally movable sash doors that operate in two tracks 14 as shown in FIG. 6.
Turning now to FIG. 15, the flow chart for the 16 fume hood controller operation as it calculates the 17 uncovered portion of the opening of the fume hood as 18 illustrated for the embodiment of FIG. 6 with respect to 19 the four horizontally movable doors. The flow chart operation would also be applicable for determining the 21 uncovered area for the embodiment of FIG. 4 as well. The 22 initial step is to read each sash door position (block 23 300). The next step is to sort the sash doors to determine 24 the sash door positions relative to the left edge of the opening (block 302). It should be understood that the 26 determination could be made from the right edge just as 27 easily, but the left edge has conveniently been chosen.
28 The apparatus then initializes the open area 304 as being 29 equal to zero and then the apparatus computes the distance between the right edge of the sash door nearest the left 31 edge of the opening and the right edge of the next sash 32 door that is adjacent to it (block 306).
33 If the difference between the edges, as deter-34 mined by the actuator location, is greater than the width of the sash (block 308), then the net open area is set to 36 be equal to the net open area plus the difference minus the 37 sash door width (block 310) and this value is stored in 38 memory. If the difference is less than the sash door ~0~5147 1 width, then the program proceeds to repeat for the next two 2 pair of sash doors (block 312) as shown. In either event, 3 then the program similarly repeats for the next two pair of 4 sash doors. After the controller performs its repetitions to calculate any open area between all of the sash doors, 6 then the controller checks the distance between the right 7 edge of the nearest sash door and the left track edge which 8 is comparable to the left opening (block 314) and if the 9 left difference is less than the sash door width (block 316) the controller then checks the distances between the 11 left edge of the furthest sash door and the right edge of 12 the track, i.e., the right opening 318. If the left dif-13 ference is not less than the sash door width, then the net 14 open area is determined to be equal to the net open area plus any left difference (block 320). The controller then 16 determines if the right difference is less than the sash 17 width (block 322) which, if it is, results in the net face 18 area being equal to the net open area plus the fixed area 19 (block 324) with the fixed area being the preprogrammed bypass area, if any. If the right difference is not less 21 than the sash width, then the controller determines that 22 the net open area equals the net open area plus the right 23 difference (block 326). In this way, the net open area is 24 determined to be the addition between any open areas between sash doors and between the rightward sash door and 26 the right edge of the opening and the difference between 27 the left edge of the leftmost sash door and the left edge 28 of the opening.
29 Turning now to FIG. 16, a flow chart of operation of the apparatus for determining the uncovered area of the 31 opening for a fume hood which has multiple vertically 32 moveable sash doors is shown. The controller, when ini-33 tially configured, requires the input of the width of each 34 segment, the number of such segments, the minimum face area, i.e., the bypass area, plus any other residual open 36 area with the sash doors closed, and the number of sash 37 doors per segment (block 330). The controller then sets 38 the area equal to zero (block 332) and begins the zo5~~~~

1 calculation for the first segment (block 334) and sets the 2 old height equal to zero (block 336). It then begins with 3 the first sash door (block 338) and reads the sash position 4 (block 340), inputs the slope and intercept (block 342) from the prior calibration routine, and calculates the 6 height for that sash door and segment (block 344). The 7 apparatus then determines if it is sash door number 1, 8 which if it is, forwards the height of the segment (block 9 348), obtains the width of the segment (block 350) and calculates the area by multiplying the height times the 11 width (block 358). If the sash door was not the number 1 12 sash, then the controller determines if the height of the 13 segment and sash was less than the old height, which if it 14 is, then the height of the segment is set as the height (block 352) and the next sash door is made the subject of 16 inquiry (block 354) and the old height is retrieved (block 17 356) and the controller returns to block 338 to repeat the 18 calculations for the other segments and sash doors. After 19 the sash doors for a segment have been considered, and the area of the segment determined (block 358), the controller 21 determines if the area for the segment is less than the 22 minimum flow area, and if it is, then the area is set to 23 the minimum flow area (block 362). If it is greater than 24 the minimum flow area, then the area for the segment is determined to be equal to the bypass area plus the cal-26 culated area for the segment (block 364). The area is then 27 calculated as the prior calculated area plus the area of 28 the segment under consideration (block 366), and the 29 controller then proceeds to consider the next segment (block 368). After all segments have been considered, the 31 total area is obtained (block 370).
32 In accordance with an important aspect of the 33 present invention, the apparatus is also adapted to deter-34 mine the uncovered area of a combination of vertically and horizontally moveable sash doors, such as the fume hood 36 illustrated in FIG. 6, which has four horizontally moveable 37 sash doors that are contained in two sets of tracks, with 38 the sets of tracks being contained in a frame structure 20~~14'~

-30-1 which is itself vertically moveable. As previously men-2 tinned, there is an upper lip 77 having a front thickness 3 of about 2 inches, the exact dimension of which can vary 4 with the manufacturer's design, a lower portion 79 of the frame 78, and a bypass area 75. As may be appreciated, 6 when the frame 78 is in its lowermost position, the entire 7 bypass area is "open" and air may be moved through it. As 8 the frame is raised, the portion of the sash doors 76 which 9 cover the opening will increasingly cover the bypass area as shown. In the particular illustration of FIG. 6, the 11 horizontally moveable doors overlap and are completely 12 closed, but the frame is shown being slightly raised.
13 To determine the uncovered area of the combina-14 tion sash door fume hood, the following specific steps are performed. The net open area, i.e., the uncovered area, is 16 the sum of the vertical (hereinafter "V" in the equations) 17 area and the horizontal (hereinafter "H") area:
18 Net Open Area = V area + H area 19 with the horizontal area being determined as follows:
H area = H width * minimum of (panel Ht; Max of 21 (panel Ht + top lip Ht + min. face Ht -22 sash Ht; 0)}
23 with the H width comprising the previously described opera-24 tion being performed with respect to the horizontally mov-able sash doors. The vertical area (V area) is determined 26 by the following equation:
27 V area = Max of (Sash Ht * V width; minimum face 28 area) 29 To complete the determination, the Net Face Area is then equal to the sum of the Net Open Area and the Fixed

31 or bypass Area:

32 Net Face Area = Net Open Area + Fixed Area

33 From the foregoing detailed description, it

34 should be appreciated that a fume hood controller has been shown and described that has superior capabilities in being 36 able to determine the effective uncovered area through 2~5514f~

1 which air may pass into most fume hoods that are commer-2 cially available. Moreover, this capability exists even 3 when there are multiple sash doors, as well as combination 4 sash door configurations which have both horizontal and vertical movement. With such capability, and the fact that 6 the fume hood controller calculates the open area several 7 times per second, the volume of air being drawn through the 8 fume hood can be very rapidly adjusted to maintain the 9 average face velocity at the desired value even when sash door positions are changed.
11 While various embodiments of the present inven-12 tion have been shown and described, it should be understood 13 that various alternatives, substitutions and equivalents 14 can be used, and the present invention should only be limited by the claims and equivalents thereof.
16 Various features of the present invention are set 17 forth in the following claims.

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of determining the uncovered area of an opening of predetermined size in a fume hood structure which has at least two doors of known dimensions which are adapted to be selectively positioned to at least partially cover the opening, the doors being horizontally moveable in at least two sets of tracks, the structure having means for determining the position of each door along the length of the set of tracks in which the respective door is moveable, the determining means providing electrical signals that are indicative of the position of a predetermined location on each door along the length of the set of tracks in which the respective door is moveable, comprising the steps of:
determining the location of each end of the opening and generating values indicative thereof and storing said values in a processing means;
determining said predetermined location on each door and the size of each door and generating values indicative thereof and storing said values in a processing means;
providing an electrical signal that is indicative of the position of the door nearest a first end of the opening to the processing means, and storing a value corresponding thereto in the processing means;
applying electrical signals that are respectively indicative of the position of each of the other doors in the opening to the processing means, and storing respective values corresponding thereto in the processing means:
operating the processing means to determine the amount of any overlap between adjacent doors and any space between adjacent doors utilizing said electrical signals and said stored values of the sizes of the doors and the predetermined location on the doors;
operating the processing means to determine the amount of any space between the nearest door to each end of the opening utilizing said electrical signals and said stored values of the sizes of the doors and the predetermined location on the door and the stored values indicative of the location of the end; and, operating the processing means to determine the amounts of any spaces that exist between adjacent doors and between the door nearest each end and the nearest end of the opening to obtain a value that is indicative of the total uncovered area of the opening.

2. A method as defined in claim 1 wherein said predetermined location on the doors is at a common location at one end thereof, the operation of the processing means to determine the amount of any overlap and any space between adjacent doors being accomplished by determining values that are indicative of the locations of said positions of predetermined locations along the length of the respective tracks relative to values that are indicative of one end of the tracks, subtracting values of one from another and subtracting values that are indicative of the width of a door from the difference, a positive value determining the amount of space and a negative value determining the amount of an overlap.

3. A method of determining the size of an uncovered area of an opening of predetermined size in a structure which has a plurality of doors of known height and width which are adapted to be selectively positioned to at least partially cover the opening, the doors being horizontally moveable along at least two sets of tracks, the structure having means for determining the horizontal position of a specified location on each door relative to at least one end of the set of tracks in which the respective door is moveable, the determining means providing electrical signals that are indicative of the position of each door along the length of the set of tracks in which the respective door is moveable, comprising the steps of:
determining the location of each end of the opening and generating values indicative thereof and storing said values in a processing means;

determining the size of each door and generating values indicative thereof and storing said values in a processing means;
providing an electrical signal that is indicative of the position of specified location of the door nearest a first end of the opening to the processing means, and storing a value corresponding thereto in the processing means;
determining the positions of the specified locations of next adjacent doors relative to the first end and providing an electrical signal that is indicative of each such position and generating values indicative thereof and storing said values in a processing means;
subtracting the value that is indicative of the position of the specified location of each door starting at said first end from the value that is indicative of the position of the specified location of the next adjacent door and obtaining a value that is indicative of the value from which the value that is indicative of the width of a door is subtracted to determine a value that is indicative of the any overlap between adjacent doors and any space between adjacent doors;
determining a value that is indicative of the amount of any space between the door nearest each end of the opening utilizing said value; and, summing the values that are indicative of the spaces that exist between adjacent doors and between any door and the nearest end of the opening to determine the total width of uncovered area of the opening;
multiplying a value that is indicative of the size of the total summed spaces by a value that is indicative of the height of the opening to determine the size of the uncovered area of the opening.

4. A method as defined in claim 3 wherein said step of determining the position of the specified location of the next closest door to the door nearest the first end further comprises examining the value indicative of the positions of the specified locations of all remaining doors and determining which of the remaining doors are adjacent one another.

5. Apparatus for determining the size of an uncovered portion of an opening of predetermined size in a fume hood of the type which has a plurality of doors of known height and width adapted to be selectively positioned to at least partially cover the opening, wherein the doors are at least horizontally moveable along at least two sets of tracks, the fume hood having switching means for determining the location of a specified reference location of each door relative to at least one end of the set of tracks in which the respective door is moveable, said switching means providing electrical signals that are indicative of the position of each door relative to at least one end of the switching means and being capable of providing signals that are indicative of any position across the entire width of the opening, said apparatus comprising:
processing means for calculating the uncovered portion of the opening, said processing means including a memory means, said memory means including information identifying the horizontal location of each end of the opening of the fume hood, the height of the opening and of the width of the doors;
said processing means receiving the electrical signals and determining the position of the specific reference location of the door nearest a first end of the opening;
said processing means receiving the electrical signals and determining the positions of the specific reference locations of next adjacent doors relative to the first end;
said processing means successively subtracting the position of the specified location of each door starting at one end from the position of the specified location of the next adjacent door and obtaining a value upon each subtraction from which the width of each door is also subtracted to obtain a positive or negative value that is indicative of the magnitude of any overlap and any space between adjacent doors, a positive value being indicative of a space between adjacent doors;
said processing means receiving the electrical signals and determining the value of any space between the door nearest each end of the opening;
said processing means summing the spaces that exist between adjacent doors and between each end of the opening and an immediately adjacent door; and, said processing means multiplying the summed values of the total spaces by the height of the opening to determine the size of the uncovered area of the opening.

6. Apparatus for determining the covered area of an opening of a fume hood that can be at least partially covered by the selective positioning of a plurality of doors of known height and width along at least two sets of tracks, the fume hood having means for determining the location of a specified reference location of each door relative to at least one end of the set of tracks in which the respective door is moveable, said location determining means providing electrical signals that are indicative of the position of each door relative to at least one end of the location determining means and being capable of providing signals that are indicative of any position extending across the entire opening, said apparatus comprising:
processing means for calculating the uncovered portion of the opening, said processing means including a memory means, said memory means including information identifying the location of each end of the opening in the direction of movement of the doors of the fume hood and of the size and number of the doors;
said processing means receiving the electrical signals for determining the position of the specific reference location of the door nearest a first end of the opening;
said processing means receiving the electrical signals for determining the positions of the specific reference locations of next adjacent doors relative to the first end;

said processing means receiving successively subtracting the position of the specified location of each door starting at one end from the position of the specified location of the next adjacent door and obtaining a value upon each subtraction from which the width of each door is also subtracted to obtain a positive or negative value that is indicative of the magnitude of any overlap and any space between adjacent doors, a positive value being indicative of a space between adjacent doors; and, said processing means summing the sizes of the doors and subtracting the value of the total overlap of adjacent doors to thereby obtain the value of the covered area of the opening.

7. Apparatus as defined in claim 6 wherein said doors are horizontally moveable relative to the opening.

8. Apparatus as defined in claim 6 wherein said doors are vertically moveable relative to the opening.

9. Apparatus as defined in claim 6 wherein said processing means is adapted to determine the value of the uncovered area of the opening by subtracting the value of the covered area of the opening from the total size of the opening.