CA2055126C - Apparatus for controlling the ventilation of laboratory fume hoods - Google Patents

Abstract

Apparatus for controlling the air flow through a fume hood to maintain a predetermined average face velocity through an uncovered portion of an opening of a fume hood of the type which has at least one moveable sash door adapted to cover the opening as the fume hood sash door is moved. The apparatus detects the position of each moveable sash door and calculates the size of the uncovered portion of the opening, measures the actual flow of air through the exhaust duct, and varies the flow of air through the exhaust duct responsive to door position signals and the actual flow signal for controlling a flow modulating means to maintain the predetermined average face velocity through the uncovered portion of the opening.

Description

5 1 2 ~

2 VENTILATION OF LABORATORY FUME HOODS

3 Cross Reference To Related Applications

4 1. Title: Apparatus for Determining the Position of a

- 5 Moveable Structure Along a Track

6 Inventors: David Egbers and Steve Jacob

7 Serial No.: 2~055~258

8 2. Title: A System for Controlling the Differential

9 Pressure of a Room Having Laboratory Fume Hoods 11 Inventors: Osman Ahmed and Steve Bradley 12 Serial No.: 2,055,101 13 3. Title: A Method and Apparatus for Determining the 14 Uncovered Size of an Opening Adapted to be Covered by Multiple Moveable Doors 16 Inventors: Osman Ahmed, Steve Bradley and Steve 17 Fritsche 18 Serial No.: 2,055,147 19 4. Title: Laboratory Fume Hood Control Apparatus Having Improved Safety Considerations 21 Inventors: Osman Ahmed 22 Serial No.: 2,~55,100 23 The present invention relates generally to the 24 control of the ventilation of laboratory fume hoods, and more particularly to an improved method and apparatus for 26 controlling the ventilation of fumes from one or more fume 27 hoods that are typically located in a laboratory 28 environment.
~' A

2 ~ 2 b~

1 Fume hoods are utilized in various laboratory 2 environments for providing a work place where potentially 3 dangerous chemicals are used, with the hoods comprising an 4 enclosure having moveable doors at the front portion thereof which can be opened in various amounts to permit a 6 person to gain access to the interior of the enclosure for 7 the purpose of conducting experiments and the like. The 8 enclosure is typically connected to an exhaust system for 9 removing any noxious fumes so that the person will not be exposed to them while performing work in the hood.
11 Fume hood controllers which control the flow of 12 air through the enclosure have experience increased 13 sophistication in recent years, and are now able to more 14 accurately maintain the desired flow characteristics to efficiently exhaust the fumes from the enclosure as a 16 function of the desired average face velocity of the 17 opening of the fume hood.
18 The average face velocity is generally defined as 19 the flow of air into the fume hood per square foot of open face area of the fume hood, with the size of the open face 21 area being dependent upon the position of one or more 22 moveable doors that are provided on the front of the 23 enclosure or fume hood, and in most types of enclosures, 24 the amount of bypass opening that is provided when the door or doors are closed.
26 The fume hoods are exhausted by an exhaust system 27 that includes one or more blowers that are capable of being 28 driven at variable speeds to increase or decrease the flow 29 of air from the fume hood to compensate for the varying size of the opening or face. Alternatively, there may be 31 a single blower connected to the exhaust manifold that is 32 in turn connected to the individual ducts of multiple fume 33 hoods, and dampers may be provided in the individual ducts 34 to control the flow from the individual ducts to thereby modulate the flow to maintain the desired average face 36 velocity.
37 The doors of such fume hoods can be opened by 38 ra~sing them vertically, often referre~ to as the sash i 2 ~

1 position, or some fume hoods have a number of doors that 2 are mounted for sliding movement in typically two sets of 3 tracks. There are even doors that can be moved 4 horizontally and ve.rtically, with the tracks being mounted in a frame assembly that is vertically moveable.
6 Prior art fume hood controllers have included 7 sensing means for measuring the position of the doors and 8 then using a signal proportional to the sensed position to 9 thereby vary the speed of the blowers or dampers. While such control has represented an improvement in the control 11 of fume hoods, there are circumstances that arise that 12 require further adjustment of the exhausting of such hoods 13 that such a controller cannot perform. This is in part due 14 to the fact that such position sensing of the doors results in essentially a prediction of the required blower speed or 16 damper position which should result in the required flow to 17 maintain a desired face velocity over the entire open area 18 of the hood for a given position of the doors without 19 actually measuring the resultant flow. This type of control is known as an open loop type of control scheme.
21 Accordingly, it is one of the primary objects of 22 the present invention to provide an improved fume hood 23 controller apparatus, as well as an improved method, which 24 overcomes many of the disadvantages of existing controllers.
26 Another one of the primary objects of the present 27 invention is to provide such an improved apparatus and 28 method which provides for very accurate control to thereby 29 maintain the desired average face velocity of air across the open areas of the fume hood, which by virtue of 31 apparatus' design, also exhibits a very fast response time 32 in maintaining such control when the door positions are 33 changed or other balance upsetting circumstances change.
34 Still another object of the present invention is to provide such an improved method and apparatus which 36 utilizes a closed loop type of control, which during its 37 operation, employs three distinct types of gain to measure ?~ 2n-ol in the d~sired ~ac~ veloci~y, with the co~trol sche~e 1 operating to reduce the error to zero in a rapid manner.
2 A more detailed object of the present invention 3 is to provide an improved method and apparatus, which in 4 all of its embodiments, employs proportional gain, integral gain and derivative gain in achieving the desired average 6 face velocity of air inwardly through the open areas to the 7 fume hood, i.e., the areas not covered by one or more 8 doors.
9 Yet another object of the present invention is to provide an improved method and apparatus, which in certain 11 of its embodiments, employs the above mentioned 12 proportional gain, integral gain and derivative gain, but 13 in addition, employs a feed-forward type of control which 14 occurs when one or more of the doors is moved to alter the open area of the hood.
16 Still another object of the present invention is 17 to provide such an improved fume hood controller apparatus 18 and method which is susceptible of being integrated with 19 the heating, ventilating and air conditioning control system of a laboratory room in which the fume hoods are 21 located.
22 Yet another object of the present invention is to 23 provide such an improved fume hood controller apparatus and 24 method, which apparatus includes a small, convenient and effective operator panel that is located on the fume hood 26 itself at a location easily observed and convenient for 27 manipulation by a person, which operator panel is adapted 28 to monitor and control the fume hood controller at any 29 time.
A closely related object lies in the provision of 31 providing a connector on said operator panels which is 32 adapted to receive a hand held terminal that can be used to 33 change various critical parameters relating to the 34 operation of the fume hood controllers.
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:

2 ~ 6 1 FIGURE 1 is a schematic block diagram of 2 apparatus of the present invention shown integrated with a 3 room controller of a heating, ventilating and air 4 conditioning monitoring and control system of a building;
FIG. 2 is a block diagram of a fume hood 6 controller, shown connected to an operator panel, the 7 latter being 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 22 position switching means;
23 FIG. 9 is a schematic diagram of electrical 24 circuitry for determining the position of sash doors of a fume hood;
26 FIG. 10 is a block diagram illustrating the 27 relative positions of FIGS. lOa, lOb, lOc, lOd and lOe to 28 one another, and which together comprise a schematic 29 diagram of the electrical circuitry for the fume hood controller means embodying the present invention;
31 FIGS. lOa, lOb, lOc, lOd and lOe, which if 32 connected 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 of the present invention;
37 FIG. 12 is a flow chart of a portion of the 3~ o~er~tion of the fume hood controller of the present ~ û S ~

1 invention, particularly illustrating the operation of the 2 feed forward control scheme, which is included in one of 3 the preferred embodiments of the present invention;
4 FIG. 13 is a flow chart of a portion of the operation of the fume hood controller of the present 6 invention, particularly illustrating the operation of the 7 proportional gain, -integral gain and derivative gain 8 control scheme, which embodies the present invention; and, 9 FIG. 14 is a flow chart of a portion of the operation of the fume hood controller of the present 11 invention, particularly illustrating the operation of the 12 calibration of the feed forward control scheme;
13 FIG. 15 is a flow chart of a portion of the 14 operation of the fume hood controller embodying the present invention, particularly illustrating the operation of the 16 calculation of the uncovered opening for a number of 17 horizontally moveable sash doors; and, 18 FIG. 16 is a flow chart of a portion of the 19 operation of the fume hood controller embodying the present invention, particularly illustrating the operation of the 21 calculation of the uncovered opening for a number of 22 horizontally and vertically moveable sash doors.
23 Detailed Description 24 It should be generally understood that a fume hood controller controls the flow of air through the fume 26 hood in a manner whereby the effective size of the total 27 opening to the fume hood, including the portion of the 28 opening that is not covered by one or more sash doors will 29 have a relatively constant average face velocity of air moving into the fume hood. This means that regardless of 31 the area of the uncovered opening, an average volume of air 32 per unit of surface area of the uncovered portion will be 33 moved into the fume hood. This protects the persons in the 34 laboratory from being exposed to noxious fumes or the like because air is always flowing into the fume hood, and out 36 of the exhaust duct, and the flow is preferably controlled 37 at a predetermined rate of approximately 75 to 125 cubic 38 feet per minute per square feet of effective surface area 1 of the uncovered opening. In other words, if the sash door 2 or doors are moved to the maximum open position whereby an 3 operator has the maximum access to the inside of the fume 4 hood for conducting experiments or the like, then the flow of air will most likely have to be increased to maintain 6 the average face velocity at the predetermined desired 7 level. The capabilities and effectiveness of various 8 controllers of the prior art varies considerably.
9 Broadly stated, the present invention is directed to an improved fume hood controlling apparatus that is 11 adapted to provide many desirable operational advantages 12 for person which use the fume hoods to perform experiments 13 or other work, and also for the operator of the facility in 14 which the fume hoods are located. The apparatus embodying the present invention provides extremely rapid and 16 effective control of the average face velocity of the fume 17 hood, and achieves and maintains the desired average face 18 velocity within a few seconds after one or more doors which 19 cover the front opening of the fume hood have been moved.
Also, if other perturbations occur within the laboratory 21 environment where one or more fume hoods are located, the 22 control apparatus of the present invention is adapted to 23 quickly react and stabilize to maintain the desired flow 24 conditions.
Turning now to the drawings, and particularly 26 FIG. 1, a block diagram is shown of several fume hood 27 controllers 20 embodying the present invention 28 interconnected with a room controller 22, an exhaust 29 controller 24 and a main control console 26. The fume hood controllers 20 are interconnected with the room controller 31 22 and with the exhaust controller 24 and the main control 32 console 26 in a local area network illustrated by line 28 33 which may be a multiconductor cable or the like. The room 34 controller, the exhaust controller 24 and the main control console 26 are typically part of the building main HVAC
36 system in which the laboratory rooms containing the fume 37 hoods are located.
38 The room controller 22 preferably is of ~he type -8- 2~126 1 which is at least capable of providing a variable air 2 volume to the room, and may be a Landis & Gyr Powers System 3 600 SCU controller. The room controller 22 is capable of 4 communicatin~ over the LAN lines 28. The room controller preferably is a System 600 SCU controller and is a 6 commercially available controller for which extensive 7 documentation exists.

n The room controller 22 may also receive signals ~ via lines 81 from each of the fume hood controllers 20 that provides an analog input signal indicating the volume of 11 air that is being exhausted by each of the fume hood ~2 controllers 20 and a comparable signal from the exhaust 13 flow sensor that provides an indication of the volume of 1~ air that is being exhausted through the main exhaust system apart from the fume hood exhausts. These signals coupled 16 with signals that are supplied by a differential pressure 17 sensor 29 which indicates the pressure within the room 1~ relative to the reference space enable the room controller 1~ to control the supply of air that is necessary to maintain the differential pressure within the room at a slightly 21 lower pressure than the reference space. Such a system is ~2 disclosed in cross referenced application, assigned to the same assignee as the present application, entitled A system ~4 for controlling the differential pressure of a room having laboratory fume hoods, by Ahmed, et al., Serial No.:
2~, 2,055,101.
27 The fume hood controllers 20 are provided with 2~ power through line 30, which is at the proper voltage via 29 a transformer 32 or the like.
Referring to FIG. 2, a fume hood controller 20 is 3~ illustrated with its input and output connector ports being 32 identified, and the fume hood controller 20 is connected to 33 an operator panel 34. It should be understood that each 34 fume hood will have a fume hood controller 20 and that an operator panel will be provided with each fume hood 36 controller. The operator panel 34 is provided for each of 1 the fume hoods and it is interconnected with the fume hood 2 controller 20 by a line 36 which preferably comprises a 3 multi-conductor cable having eight conductors. The 4 operator panel has a connector 38, such as a 6 wire RJll type telephone jack, for example, into which a lap top 6 personal computer or the like may be connected for the 7 purpose of inputting information relating to the 8 configuration or operation of the fume hood during initial 9 installation, or to change certain operating parameters if necessary. The operator panel 34 is preferably mounted to 11 the fume hood in a convenient location adapted to be easily 12 observed by a person who is working with the fume hood.
13 The fume hood controller operator panel 34 14 includes a liquid crystal display 40 which when selectively activated provides the visual indication of various aspects 16 of the operation of the fume hood, including three digits 17 42 which provide the average face velocity. The display 40 18 illustrates other conditions such as low face velocity, 19 high face velocity and emergency condition and an indication of controller failure. The operator panel may 21 have an alarm 44, an emergency purge pushbutton 46 which an 22 operator can press to purge the fume hood in the event of 23 an accident. The operator panel has two auxiliary switches 24 48 which can be used for various customer needs, including day/night modes of operation. It is contemplated that 26 night time mode of operation would have a different and 27 preferably reduced average face velocity, presumably 28 because no one would be working in the area and such a 29 lower average face velocity would conserve energy. An alarm silence switch 50 is also preferably provided.
31 Fume hoods come in many different styles, sizes 32 and configurations, including those which have a single 33 sash door or a number of sash doors, with the sash doors 34 being moveable vertically, horizontally or in both direction. Additionally, various fume hoods have different 36 amounts of by-pass flow, i.e., the amount of flow 37 permitting opening that exists even when all of the sash 38 doors are as completely closed as their design permits.

-lo- 2d~ 512~

1 Other design considerations involve whether there is some 2 kind of filtering means included in the fume hood for 3 confining fumes within the hood during operation. While 4 many of these design considerations must be taken into account in providing efficient and effective control of the 6 fume hoods, the apparatus of the present invention can be 7 configured to account for virtually all of the above 8 described design variables, and effective and extremely 9 fast control of the fume hood ventilation is provided.
Referring to FIG. 3, there is shown a fume hood, 11 indicated generally at 60, which has a vertically operated 12 sash door 62 which can be moved to gain access to the fume 13 hood and which can be moved to the substantially closed 14 position as shown. Fume hoods are generally designed so that even when a door sash such as door sash 62 is 16 completely closed, there is still some amount of opening 17 into the fume hood through which air can pass. This 18 opening is generally referred to as the bypass area and it 19 can be determined so that its effect can be taken into consideration in controlling the flow of air into the fume 21 hood. Some types of fume hoods have a bypass opening that 22 is located above the door sash while others are below the 23 same. In some fume hoods, the first amount of movement of 24 a sash door will increase the opening at the bottom of the door shown in FIG. 3 for example, but as the door is 26 raised, it will merely cut off the bypass opening so that 27 the effective size of the total opening of the fume hood is 28 maintained relatively constant for perhaps the first one-29 fourth amount of movement of the sash door 62 through its course of travel.
31 Other types of fume hoods may include several 32 horizontally moveable sash doors 66 such as shown in FIGS.
33 4 and 5, with the doors being movable in upper and lower 34 pairs of adjacent tracks 68. When the doors are positioned as shown in FIGS. 4 and 5, the fume hood opening is com-36 pletely closed and an operator may move the doors in the 37 horizontal direction to gain access to the fume hood. Both 38 of the fumes hoods 60 and 64 have an exhaus~ duct 70 which 1 2 ~

1 generally extends to an exhaust system which may be that of 2 the HVAC apparatus previously described. The fume hood 64 3 also includes a filtering structure shown diagrammatically 4 at 72 which filtering structure is intended to keep noxious S fumes and other contaminants from exiting the fume hood 6 into the exhaust system. Referring to FIG. 6, there is 7 shown a combination fume hood which has horizontally 8 movable doors 76 which are similar to the doors 66, with 9 the fume hood 74 having a frame structure 78 which carries the doors 76 in suitable tracks and the frame structure 78 11 is also vertically movable in the opening of the fume hood.
12 The illustration of FIG. 6 has portions removed 13 as shown by the break lines 73 which is intended to 14 illustrate that the height of the fume hood may be greater than is otherwise shown so that the frame structure 78 may 16 be raised sufficiently to permit adequate access to the 17 interior of the fume hood by a person. There is generally 18 a by-pass area which is identified as the vertical area 75, 19 and there is typically a top lip portion 77 which may be approximately 2 inches wide. This dimension is preferably 21 defined so that its effect on the calculation of the open 22 face area can be taken into consideration.
23 While not specifically illustrated, other com-24 binations are also possible, including multiple sets of vertically moveable sash doors positioned adjacent one 26 another along the width of the fume hood opening, with two 27 or more sash doors being vertically moveable in adjacent 28 tracks, much the same as residential casement windows.
29 In accordance with an important aspect of the present invention, the fume hood controller 20 is adapted 31 to operate the fume hoods of various sizes and configura-32 tions as has been described, and it is also adapted to be 33 incorporated into a laboratory room where several fume 34 hoods may be located and which may have exhaust ducts which merge into a common exhaust manifold which may be a part of 36 the building HVAC system. A fume hood may be a single 37 self-contained installation and may have its own separate 38 exhaust duct. In the event that a single fume hood is -12- ~ 1 2 ~

1 installed, it is typical that such an installation would 2 have a variable speed motor driven blower associated with 3 the exhaust duct whereby the speed of the motor and blower 4 can be variably controlled to thereby adjust the flow of S air through the fume hood. Alternatively, and most typical 6 for multiple fume hoods in a single area, the exhaust ducts 7 of each fume hood are merged into one or more larger 8 exhaust manifolds and a single large blower may be provided 9 in the manifold system. In such types of installations, control of each fume hood is achieved by means of separate 11 dampers located in the exhaust duct of each fume hood, so 12 that variation in the flow can be controlled by 13 appropriately positioning the damper associated with each 14 fume hood.
The fume hood controller is adapted to control 16 virtually any of the various kinds and styles of fume hoods 17 that are commercially available, and to this end, it has a 18 number of input and output ports (lines, connectors or 19 connections, all considered to be equivalent for the purposes of describing the present invention) that can be 21 connected to various sensors that may be used with the 22 controller. As shown in FIG. 2, it has digital output or 23 DO ports which interface with a digital signal/analog 24 pressure transducer with an exhaust damper as previously described, but it also has an analog voltage output port 26 for controlling a variable speed fan drive if it is to be 27 installed in that manner. There are five sash position 28 sensor ports for use in sensing the position of both 29 horizontally and vertically moveable sashes and there is also an analog input port provided for connection to an 31 exhaust air flow sensor 49. A digital input port for the 32 emergency switch is provided and digital output ports for 33 outputting an alarm horn signal as well as an auxiliary 34 signal is provided. An analog voltage output port is also provided for providing a volume of flow signal to the room 36 controller 22. In certain applications where the exhaust 37 air flow sensor is not provided, a wall velocity sensor J~ indic~ve ~f fac~ ~/eloc~ty r~y he utili~d and ~ ~np~t -13- ~a-J512 6 1 port for such a signal is provided, but the use of such 2 sensors is generally considered to be less accurate and is 3 not the preferred embodiment. With these various input and 4 output ports, virtually any type of fume hood can be controlled in an effective and efficient manner.
6 From the foregoing discussion, it should be 7 appreciated that if the desired average face velocity is to 8 be maintained and the sash position is changed, the size of 9 the opening can be dramatically changed which may then require a dramatic change in the volume of air to maintain 11 the average face velocity. While it is known to control a 12 variable air volume blower as a function of the sash 13 position, the fume hood controller apparatus of the present 14 invention improves on that known method by incorporating additional control schemes which dramatically improve the 16 capabilities of the control system in terms of maintaining 17 relatively constant average face velocity in a manner 18 whereby reactions to perturbations in the system are 19 quickly made.
To determine the position of the sash doors, a 21 sash position sensor is provided adjacent each movable sash 22 door and it is generally illustrated in FIGS. 7, 8 and 9.
23 Referring to FIG. 8, the door sash position indicator 24 comprises an elongated switch mechanism 80 of relatively simple mechanical design which preferably consists of a 26 relatively thin polyester base layer 82 upon which is 27 printed a strip of electrically resistive ink 84 of a known 28 constant resistance per unit length. Another polyester 29 base layer 86 is provided and it has a strip of electrically conductive ink 88 printed on it. The two base 31 layers 82 and 86 are adhesively bonded to one another by 32 two beads of adhesive 90 located on opposite sides of the 33 strip. The base layers are preferably approximately five-34 thousandths of an inch thick and the beads are approximately two-thousandths of an inch thick, with the 36 beads providing a spaced area between the conductive and 37 resistive layers 88 and 84. The switching mechanism 80 is 38 preferably applied to the fume hood by a layer of adhesive -14- XO.~512~

1 92.
2 The polyester material is sufficiently flexible 3 to enable one layer to be moved toward the other in 4 response to an actuator 94 carried by the appropriate door sash to which the strip is placed adjacent to so that when 6 the door sash is moved, the actuator 94 moves along the 7 switching mechanism 80 and provides contact between the 8 resistive and conductive layers which are then sensed by 9 electrical circuitry to be described which provides a voltage output that is indicative of the absolute position 11 of the actuator 94 along the length of the switching means.
12 Stated in other words, the actuator 94 is carried by the 13 door and therefore provides an electrical voltage that is 14 indicative of the absolute position of the door sash.
The actuator 94 is preferably spring biased 16 toward the switching mechanism 80 so that as the door is 17 moved, sufficient pressure is applied to the switching 18 means to bring the two base layers together so that the 19 resistive and conductive layers make electrical contact with one another and if this is done, the voltage level is 21 provided. By having the switching means 80 of sufficient 22 length so that the full extent of the travel of the sash 23 door is provided as shown in FIG. 3, then an accurate 24 determination of the sash position can be made. It should be understood that the illustration of the switching 26 mechanism 80 in FIGS. 3 and 5 is intended to be 27 diagrammatic, in that the switching mechanism is preferably 28 actually located within the sash frame itself and 29 accordingly would not be visible as shown. The width and thickness dimensions of the switching mechanism are so 31 small that interference with the operation of the sash door 32 is virtually no problem. The actuator 94 can also be 33 placed in a small whole that may be drilled in the door or 34 it may be attached externally at one end thereof so that it can be in position to operate the switch 80. In the 36 vertical moveable sash doors shown in FIGS. 3 and 6, a 37 switching mechanism 80 is preferably provided in one or the 38 other of the sides of the sash frame, whereas in the fume ~0~5126 1 hoods having horizontally movable doors, it is preferred 2 that the switching mechanism 80 be placed in the top of the 3 tracks 68 so that the weight of the movable doors do not 4 operate the switching mechanism 80 or otherwise damage the same. It is also preferred that the actuator 94 is located 6 at one end of each of the doors for reasons that are 7 described in the cross-referenced application entitled 8 Apparatus for determining the position of a moveable 9 structure along a track, by Egbers et al., Serial No.:
2,055,258-11 Turning to FIG. 9, the preferred electrical12 circuitry which generates the position indicating voltage 13 is illustrated, and this circuitry is adapted to provide 14 two separate voltages indicating the absolute position of two door sashes in a single track. With respect to the 16 cross-section shown in FIG. 5, there are two horizontal 17 tracks, each of which carries two door sashes and a 18 switching mechanism 80 is provided for each of the tracks l9 as is a circuit as shown in FIG. 9, thereby providing a distinct voltage for each of the four sash doors as shown.
21 The switching means is preferably applied to the 22 fume hood with a layer of adhesive 92 and the actuator 94 23 is adapted to bear upon the switching means at locations 24 along the length thereof. Referring to FIG. 7, a diagrammatic illustration of a pair of switching means is 26 illustrated such as may occur with respect to the two 27 tracks shown in FIG. 5. A switching mechanism 80 is 28 provided with each track and the four arrows illustrated 29 represent the point of contact created by the actuators 94 which result in a signal being applied on each of the ends 31 of each switching means, with the magnitude of the signal 32 representing a voltage that is proportional to the distance 33 between the end and the nearest arrow. Thus, a single 34 switching mechanism 80 is adapted to provide absolute position indicating signals for two doors located in each 36 track. The circuitry that is used to accomplish the 37 voltage generation is shown in FIG. 9 and includes one of 38 th~se circuits for each track. The resistive element is A

-16- ~ 0~

1 shown at 84 and the conductive element 88 is also 2 illustrated being connected to ground with two arrows being 3 illustrated, and represented the point of contact between 4 the resistive and conductive elements caused by each of the actuators 94 associated with the two separate doors. The 6 circuitry includes an operational amplifier 100 which has 7 its output connected to the base of a PNP transistor 102, 8 the emitter of which is connected to a source of positive 9 voltage through resistor 104 into the negative input of the operational amplifier, the positive input of which is also 11 connected to a source of positive voltage of preferably 12 approximately five volts. The collector of the transistor 13 102 is connected to one end of the resistive element 84 and 14 has an output line 106 on which the voltage is produced that is indicative of the absolute position of the door.
16 The circuit operates to provide a constant 17 current directed into the resistive element 84 and this 18 current results in a voltage on line 106 that is propor-19 tional to the resistance value between the collector and ground which changes as the nearest point of contact along 21 the resistance changes. The operational amplifier operates 22 to attempt to drive the negative input to equal the voltage 23 level on the positive input and this results in the current 24 applied at the output of the operational amplifier varying in direct proportion to the effective length of the 26 resistance strip 84. The lower portion of the circuitry 27 operates the same way as that which has been described and 28 it similarly produces a voltage on an output line 108 that 29 is proportional to the distance between the connected end of the resistance element 84 and the point of contact that 31 is made by the actuator 94 associated with the other sash 32 door in the track.
33 Referring to the composite electrical schematic 34 diagram of the circuitry of the fume hood controller, if the separate drawings FIGS. lOa, lOb, lOc, lOd and lOe are 36 placed adjacent one another in the manner shown in FIG. 10, 37 the total electrical schematic diagram of the fume hood 38 controller 20 is illustrated. The operation of the -17- ~ 512~

1 circuitry of FIGS. 10a through 10e will not be described in 2 detail. The circuitry is driven by a microprocessor and 3 the important algorithms that carry out the control 4 functions of the controller will be hereinafter described.
Referring to FIG. 10c, the circuitry includes a Motorola MC
6 68HCll microprocessor 120 which is clocked at 8 MHz by a 7 crystal 122. The microprocessor 120 has a databus 124 that 8 is connected to a tri-state buffer 126 (FIG. 10d) which in 9 turn is connected to an electrically programmable read only memory 128 that is also connected to the databus 124. The 11 EPROM 128 has address lines A0 through A7 connected to the 12 tri-state buffer 126 and also has address lines A8 through 13 A14 connected to the microprocessor 120.
14 The circuitry includes a 3 to 8-bit multiplexer 130, a data latch 132 (see FIG. 10d), a digital-to-analog 16 converter 134, which is adapted to provide the analog 17 outputs indicative of the volume of air being exhausted by 18 the fume hood, which information is provided to room 19 controller 22 as has been previously described with respect to FIG. 2. Referring to FIG. 10b, an RS232 driver 136 is 21 provided for transmitting and receiving information through 22 the hand held terminal. The circuitry illustrated in FIG.
23 9 is also shown in the overall schematic diagrams and is in 24 FIGS. 10a and 10b. The other components are well known and therefore need not be otherwise described.
26 As previously mentioned, the apparatus of the 27 present invention utilizes a flow sensor preferably located 28 in the exhaust duct 70 to measure the air volume that is 29 being drawn through the fume hood. The volume flow rate may be calculated by measuring the differential pressure 31 across a multi-point pitot tube or the like. The preferred 32 embodiment utilizes a differential pressure sensor for 33 measuring the flow through the exhaust duct and the 34 apparatus of the present invention utilizes control schemes to either maintain the flow through the hood at a predeter-36 mined average face velocity, or at a minimum velocity in 37 the event the fume hood is closed or has a very small 38 byp3~s area.

Xi~512~

1 The fume hood controller of the present invention 2 can be configured for almost all known types of fume hoods, 3 including fume hoods having horizontally movable sash 4 doors, vertically movable sash doors or a combination of the two. As can be seen from the illustrations of FIGS. 2 6 and 10, the fume hood controller is adapted to control an 7 exhaust damper or a variable speed fan drive, the 8 controller being adapted to output signals that are 9 compatible with either type of control. The controller is also adapted to receive information defining the physical 11 and operating characteristics of the fume hood and other 12 initializing information. This can be input into the fume 13 hood controller by means of the hand held terminal which is 14 preferably a lap top computer that can be connected to the operator panel 34. The information that should be provided 16 to the controller include the following, and the dimensions 17 for the information are also shown. It should be appre-18 ciated that the day/night operation may be provided, but is 19 not the preferred embodiment of the system; if it is pro-vided, the information relating to such day/night operation 21 should be included.
22 Operational information:
23 5. Time of day;
24 6. Set day and night values for the average face velocity (SVEL), feet per minute or 26 meters per second;
27 7. Set day and night values for the minimum 28 flow, (MINFLO), in cubic feet per minute;
29 8. Set day and night values for high velocity limit (HVEL), F/m or M/sec;
31 9. Set day and night values for low velocity 32 limit (LVEL), F/m or M/sec;
33 10. Set day and night values for intermediate 34 high velocity limit (MVEL), F/m or M/sec;
11. Set day and night values for intermediate 36 low velocity limit (IVEL), F/m or M/sec;
37 12. Set the proportional gain factor (KP), 38 analog output per error in percent;

2~.5~12~

1 13. Set the integral gain factor (KI), analog 2 output multiplied by time in minutes per 3 error in percent;
4 14. Set derivative gain factor (KD), analog output multiplied by time in minutes per 6 error in percent;
7 15. Set feed forward gain factor (KF) if a 8 variable speed drive is used as the control 9 equipment instead of a damper, analog output per CFM;
11 16. Set time in seconds (DELTIME) the user 12 prefers to have the full exhaust flow in 13 case the emergency button is activated;
14 17. Set a preset percent of last exhaust flow (SAFLOQ) the user wishes to have once the 16 emergency switch is activated and DELTIME is 17 expired.
18 The above information is used to control the mode 19 of operation and to control the limits of flow during the day or night modes of operation. The controller includes 21 programmed instructions to calculate the steps in para-22 graphs 3 through 7 in the event such information is not 23 provided by the user. To this end, once the day and night 24 values for the average face velocity are set, the con-troller 20 will calculate high velocity limit at 120% of 26 the average face velocity, the low velocity limit at 80%
27 and the intermediate limit at 90%. It should be understood 28 that these percentage values may be adjusted, as desired.
29 Other information that should be input include the following information which relates to the physical con-31 struction of the fume hood. It should be understood that 32 some of the information may not be required for only 33 vertically or horizontally moveable sash doors, but all of 34 the information may be required for a combination of the same. The information required includes vertical segments, 36 which is defined to be a height and width dimension that 37 may be covered by one or more sash doors. If more than one ~^~ s~sh d~or is provi~ed for ea~h se~mer~ ~h~ r~

1 intended to be vertically moveable sash doors, analogous to 2 a double sash residential window. The information to be 3 provided includes the following:
4 18. Input the number of vertical segments;
S 19. Input the height of each segment, in inches;
6 20. Input the width of each segment, in inches;
7 21. Input the number of tracks per segment;
8 22. Input the number of horizontal sashes per 9 track;
23. Input the maximum sash height, in inches;
11 24. Input the sash width, in inches;
12 25. Input the location of the sash sensor from 13 left edge of sash, in inches;
14 26. Input the by-pass area per segment, in square inches;
16 27. Input the minimum face area per segment, in 17 square inches;
18 28. Input the top lip height above the 19 horizontal sash, in inches;
The fume hood controller 20 is programmed to 21 control the flow of air through the fume hood by carrying 22 out a series of instructions, an overview of which is 23 contained in the flow chart of FIG. 11. After start-up and 24 outputting information to the display and determining the time of day, the controller 20 reads the initial sash 26 positions of all doors (block 150), and this information is 27 then used to compute the open face area (block 152). If 28 not previously done, the operator can set the average face 29 velocity set point (block 154) and this information is then used together with the open face area to compute the 31 exhaust flow set point (SFLOW) (block 156) that is 32 necessary to provide the predetermined average face 33 velocity given the open area of the fume hood that has been 34 previously measured and calculated. The computed fume hood exhaust set point is then compared (block 158) with a 36 preset or required minimum flow, and if computed set point 37 is less than the minimum flow, the controller sets the set ~8 point flow at the preset minimum flow ~block 160). Tf it -21- ~ 51~

1 is more than the minimum flow, then it is retained (block 2 162) and it is provided to both of the control loops.
3 If there is a variable speed fan drive for the 4 fume controller, i.e., several fume hoods are not connected to a common exhaust duct and controlled by a damper, then 6 the controller will run a feed-forward control loop (block 7 164) which provides a control signal that is sent to a 8 summing junction 166 which control signal represents an 9 open loop type of control action. In this control action, a predicted value of the speed of the blower is generated 11 based upon the calculated opening of the fume hood, and the 12 average face velocity set point. The predicted value of 13 the speed of the blower generated will cause the blower 14 motor to rapidly change speed to maintain the average face velocity. It should be understood that the feed forward 16 aspect of the control is only invoked when the sash 17 position has been changed and after it has been changed, 18 then a second control loop performs the dominant control 19 action for maintaining the average face velocity constant in the event that a variable speed blower is used to 21 control the volume of air through the fume hood.
22 After the sash position has been changed and the 23 feed forward loop has established the new air volume, then 24 the control loop switches to a proportional integral derivative control loop and this is accomplished by the set 26 flow signal being provided to block 168 which indicates 27 that the controller computes the error by determining the 28 absolute value of the difference between the set flow 29 signal and the flow signal as measured by the exhaust air flow sensor in the exhaust duct. Any error that is 31 computed is applied to the control loop identified as the 32 proportional-integral-derivative control loop (PID) to 33 determine an error signal (block 170) and this error signal 34 is compared with the prior error signal from the previous sample to determine if that error is less than a deadband 36 error (block 172). If it is, then the prior error signal 37 is maintained as shown by block 174, but if it is not, then 3~ the new errcr signal is provided to outpvt mode 176 and it 5 1 2 ~

1 is applied to the summing junction 166. That summed error 2 is also compared with the last output signal and a 3 determination is made if this is within a deadband range 4 (block 180) which, if it is, results in the last or previous output being retained (block 182). If it is 6 outside of the deadband, then a new output signal is 7 provided to the damper control or the blower (block 184).
8 In the event that the last output is the output 9 as shown in block 182, the controller then reads the measured flow (MFLOW) (block 186) and the sash positions 11 are then read (block 188) and the net open face area is 12 recomputed (block 190) and a determination made as to 13 whether the new computed area less the old computed area is 14 less than a deadband (block 192) and if it is, then the old area is maintained (block 194) and the error is then 16 computed again (block 168). If the new area less the old 17 area is not within the deadband, then the controller 18 computes a new exhaust flow set point as shown in block 19 156.
One of the significant advantages of the present 21 invention is that the controller is adapted to execute the 22 control scheme in a repetitive and extremely rapid manner.
23 The exhaust sensor provides flow signal information that is 24 inputted to the microprocessor at a speed of approximately one sample per 100 milliseconds and the control action 26 described in connection with FIG. 11 is completed appro-27 ximately every 100 milliseconds. The sash door position 28 signals are sampled by the microprocessor every 200 29 milliseconds. The result of such rapid repetitive sampling and executing of the control actions results in extremely 31 rapid operation of the controller. It has been found that 32 movement of the sash will result in adjustment of the air 33 flow so that the average face velocity is achieved within 34 a time period of only approximately 3-4 seconds after the sash door reposition has been stopped. This represents a 36 dramatic improvement over existing fume hood controllers.
37 In the event that the feed forward control loop ?Q is ut~ d! the se~e~e of instr~ctions that are ca-r;ed ~5512~

1 out to accomplish running of this loop is shown in the flow 2 chart of FIG. 12, which has the controller using the 3 exhaust flow set point (SFLOW) to compute the control 4 output to a fan drive (block 200), which is identified as signal AO that is computed as an intercept point plus the 6 set flow multiplied by a slope value. The intercept is the 7 value which is a fixed output voltage to a fan drive and 8 the slope in the equation correlates exhaust flow rate and 9 output voltage to the fan drive. The controller then reads the duct velocity (DV) (block 202), takes the last duct 11 velocity sample (block 204) and equates that as the duct 12 velocity value and starts the timing of the maximum and 13 minimum delay times (block 206) which the controller uses 14 to insure whether the duct velocity has reached steady state or not. The controller determines whether the 16 maximum delay time has expired (block 208), and if it has, 17 provides the output signal at output 210. If the max delay 18 has not expired, the controller determines if the absolute 19 value of the difference between the last duct velocity sample and the current duct velocity sample is less than or 21 equal to a dead band value (block 212). If it is not less 22 than the dead band value, the controller then sets the last 23 duct value as equal to the present duct value sample (block 24 214) and the controller then restarts the minimum delay timing function (block 216). Once this is accomplished, 26 the controller again determines whether the max delay has 27 expired (block 208). If the absolute value of the 28 difference between the last duct velocity and the present 29 duct velocity sample is less than the dead band, the controller determines whether the minimum delay time has 31 expired. If it has as shown from block 218, the output is 32 provided at 210. If it has not, then it determines if the 33 max delay has expired.
34 Turning to the proportional-integral-derivative or PID control loop, the controller runs the PID loop by 36 carrying out the instructions shown in the flow chart of 37 FIG. 13. The controller uses the error that is computed by 38 block 168 (see FIG. 11) in three separate paths. wit~A

'~0~12~

1 respect to the upper path, the controller uses the 2 preselected proportional gain factor (block 220) and that 3 proportional gain factor is used together with the error to 4 calculate the proportional gain (block 222) and the proportional gain is output to a summing junction 224.
6 The controller also uses the error signal and 7 calculates an integral term (block 226) with the integral 8 term being equal to the prior integral sum (ISUM) plus the 9 product of loop time and any error and this calculation is compared to limits to provide limits on the term. The term 11 is then used together with the previously defined integral 12 gain constant (block 230) and the controller then 13 calculates the integral gain (block 232) which is the 14 integral gain constant multiplied by the integration sum term. The output is then applied to the summing junction 16 224.
17 The input error is also used by the controller to 18 calculate a derivative gain factor which is done by the 19 controller using the previously defined derivative gain factor from block 234 which is used together with the error 21 to calculate the derivative gain (block 236) which is the 22 reciprocal of the time in which it is required to execute 23 the PID loop multiplied by the derivative gain factor 24 multiplied by the current sample error minus the previous sample error with this result being provided to the summing 26 junction 224.
27 The control action performed by the controller 20 28 as illustrated in FIG. 13 provides three separate gain 29 factors which provide steady state correction of the air flow through the fume hood in a very fast acting manner.
31 The formation of the output signal from the PID control 32 loop takes into consideration not only the magnitude of the 33 error, but as a result of the derivative gain segment of 34 control, the rate of change of the error is considered and the change in the value of the gain is proportional to the 36 rate of change. Thus, the derivative gain can see how fast 37 the actual condition is changing and works as an 38 "anticipator" in order to minimize error between the ac~aJ

~0~512~

1 and desired condition. The integral gain develops a cor-2 rection signal that is a function of the error integrated 3 over a period of time, and therefore provides any necessary 4 correction on a continuous basis to bring the actual condition to the desired condition. The proper combina-6 tions of proportional, integral and derivative gains will 7 make the loop faster and reach the desired conditions 8 without any overshoot.
9 A significant advantage of the PID control action is that it will compensate for perturbations that may be 11 experienced in the laboratory in which the fume hood may be 12 located in a manner in which other controllers do not. A
13 common occurrence in laboratory rooms which have a number 14 of fume hoods that are connected to a common exhaust manifold, involves the change in the pressure in a fume 16 hood exhaust duct that was caused by the sash doors being 17 moved in another of the fume hoods that is connected to the 18 common exhaust manifold. Such pressure variations will 19 affect the average face velocity of those fume hoods which had no change in their sash doors. However, the PID
21 control action may adjust the air flow if the exhaust duct 22 sensor determines a change in the pressure. To a lesser 23 degree, there may be pressure variations produced in the 24 laboratory caused by opening of doors to the laboratory itself, particularly if the differential pressure of the 26 laboratory room is maintained at a lesser pressure than a 27 reference space such as the corridor outside the room, for 28 example.
29 It is necessary to calibrate the feed forward control loop and to this end, the instructions illustrated 31 in the flow chart of FIG. 14 are carried out. When the 32 initial calibration is accomplished, it is preferably done 33 through the hand held terminal that may be connected to the 34 operator panel via connector 38, for example. The controller then determines if the feed forward calibration 36 is on (block 242) and if it is, then the controller sets 37 the analog output of the fan drive to a value of 20 percent 38 of the maximum value, which is identified as value AOl -26- ~J~512~

1 (block 244). The controller then sets the last sample duct 2 velocity (LSDV) as the current duct velocity (CDV) (block 3 246) and starts the maximum and minimum timers (block 248).
4 The controller ensures the steady state duct velocity in the following way. First by checking whether the max timer 6 has expired, and then, if the max timer has not expired, 7 the controller determines if the absolute value of the last 8 sample duct velocity minus the current duct velocity is 9 less than or equal to a dead band (block 270), and if it is, the controller determines if the min timer has expired 11 (block 272). If it has not, the controller reads the 12 current duct velocity (block 274). If the absolute value 13 of the last sample duct velocity minus the current duct 14 velocity is not less than or equal to a dead band (block 270), then the last sample duct velocity is set as the 16 current duct velocity (block 276) and the mintimer is 17 restarted (block 278) and the current duct velocity is 18 again read (block 274). In case either the max timer or 19 min timer has expired, the controller then checks the last analog output value to the fan drive (252) and inquires 21 whether the last analog output value was 70 percent of the 22 maximum output value (block 254). If it is not, then it 23 sets the analog output value to the fan drive at 70 percent 24 of the max value A02 (block 256) and the steady state duct velocity corresponding to A01. The controller then repeats 26 the procedure of ensuring steady state duct velocity when 27 analog output is A02 (block 258). If it is at the 70 28 percent of max value, then the duct velocity corresponds to 29 steady state velocity of A02 (block 258). Finally, the controller (block 262) calculates the slope and intercept 31 values.
32 The result of the calibration process is to 33 determine the duct flow at 20% and at 70% of the analog 34 output values, and the measured flow enables the slope and intercept values to be determined so that the feed forward 36 control action will accurately predict the necessary fan 37 speed when sash door positions are changed.
38 The fume hood controller is adapted to rapidly .5 1 ~ ~

1 calculate on a periodic basis several times per second, the 2 uncovered or open area of a fume hood access opening that 3 is capable of being covered by one or more sash doors as 4 previously described. As is shown in FIG. 6, the actuator 94 is preferably located at the righthand end of each of 6 the horizontally movable doors of which there are four in 7 number as illustrated. The position indicating capability 8 of the switching mechanism 80 provides a signal having a 9 voltage level for each of the four doors which is indicative of the position of the particular sash door 11 along its associated track. While the actuators 94 are 12 shown at the righthand portion of the sash doors, it should 13 be understood that they may be alternatively located on the 14 lefthand portion, or they could be located at virtually any location on each door, provided that the relationship 16 between the width of the door and the position of the 17 actuator is determined and is input into the fume hood 18 controller. It should be appreciated that having the 19 location of the actuators 94 at a common position, such as the right end, simplifies the calculation of the uncovered 21 opening.
22 While the fume hood shown in FIG. 6 is of the 23 type which has four horizontally movable doors 76 that are 24 housed within a frame structure 78 that itself is vertically movable, the fume hood controller apparatus of 26 the present invention is adapted to be used with up to four 27 movable sash doors in a single direction, i.e., 28 horizontally, and a perpendicularly movable sash door 29 frame. However, there are five analog input ports in the controller for inputting position information regardless of 31 whether it is horizontal or vertical and the controller can 32 be configured to accommodate any combination of 33 horizontally and vertically movable doors up to a total of 34 five. To this end, it should be appreciated that there are vertically movable double sash doors in certain 36 commercially available fume hoods, which configuration is 37 not specifically shown in the drawings, with the double 38 sash confi~uration being housed in a single frame structure Z~5126 1 that itself may be horizontally movable. The fume hood 2 controller of the present invention may treat the double 3 sash door configuration in the vertical direction much the 4 same as it operates with the horizontally movable sash doors that operate in two tracks as shown in FIG. 6.
6 Turning now to FIG. 15, the flow chart for the 7 fume hood controller operation as it calculates the 8 uncovered portion of the opening of the fume hood as 9 illustrated for the embodiment of FIG. 6 with respect to the four horizontally movable doors. The flow chart 11 operation would also be applicable for determining the 12 uncovered area for the embodiment of FIG. 4 as well. The 13 initial step is to read each sash door position (block 300) 14 and this is done by sorting the sash doors to determine the sash door positions relative to the left edge of the 16 opening (block 302). It should be understood that the 17 determination could be made from the right edge just as 18 easily, but the left edge has conveniently been chosen.
19 The apparatus then initializes the open area 304 as being equal to zero and then the apparatus computes the distance 21 between the right edge of the sash door nearest the left 22 edge of the opening and the right edge of the next sash 23 door that is adjacent to it (block 306).
24 If the difference between the edges, as determined by the actuator location, is greater than the 26 width of the sash (block 308), then the net open area is 27 set to be equal to the net open area plus the difference 28 minus the sash door width (block 310) and this value is 29 stored in memory. If the difference is less than the sash door width, then the program proceeds to repeat for the 31 next two pair of sash doors (block 312) as shown. In 32 either event, then the program similarly repeats for the 33 next two pair of sash doors. After the controller performs 34 its repetitions to calculate any open area between all of the sash doors, then the controller checks the distance 36 between the right edge of the nearest sash door and the 37 left track edge which is comparable to the left opening 3~ (block 314) and if the left difference is less than the ~Q~512~

1 sash door width (block 316) the controller then checks the 2 distances between the left edge of the furthest sash door 3 and the right edge of the track, i.e., the right opening 4 318. If the left difference is not less than the sash door width, then the net open area is determined to be equal to 6 the net open area plus any left difference (block 320).
7 The controller then determines if the right 8 difference is less than the sash width (block 322) which, 9 if it is, results in the net face area being equal to the net open area plus the fixed area (block 324) with the 11 fixed area being the preprogrammed bypass area, if any. If 12 the right difference is not less than the sash width, then 13 the controller determines that the net open area equals the 14 net open area plus the right difference (block 326). In this way, the net open area is determined to be the 16 addition between any open areas between sash doors and 17 between the rightward sash door and the right edge of the 18 opening and the difference between the left edge of the 19 leftmost sash door and the left edge of the opening.
Turning now to FIG. 16, a flow chart of operation 21 of the apparatus for determining the uncovered area of the 22 opening for a fume hood which has multiple vertically 23 moveable sash doors is shown. The controller, when 24 initially configured, requires the input of the width of each segment, the number of such segments, the minimum face 26 area, i.e., the bypass area, plus any other residual open 27 area with the sash doors closed, and the number of sash 28 doors per segment (block 330). The controller then sets 29 the area equal to zero (block 332) and begins the calculation for the first segment (block 334) and sets the 31 old height equal to zero (block 336). It then begins with 32 the first sash door (block 338) and reads the sash position 33 (block 340), inputs the slope and intercept (block 342) 34 from the prior calibration routine, and calculates the height for that sash door and segment (block 344). The 36 apparatus then determines if it is sash door number 1, 37 which if it is, forwards the height of the segment (block 3~ ob~ ~ins t~e w~th of the segment ~b~eck 3sn! <~

~f~5126 1 calculates the area by multiplying the height times the 2 width (block 358). If the sash door was not the number 1 3 sash, then the controller determines if the height of the 4 segment and sash was less than the old height, which if it is, then the height of the segment is set as the height 6 (block 352) and the next sash door is made the subject of 7 inquiry (block 354) and the old height is retrieved (block 8 356) and the controller returns to block 338 to repeat the 9 calculations for the other segments and sash doors. After the sash doors for a segment have been considered, and the 11 area of the segment determined (block 358), the controller 12 determines if the area for the segment is less than the 13 minimum flow area, and if it is, then the area is set to 14 the minimum flow area (block 362). If it is greater than the minimum flow area, then the area for the segment is 16 determined to be equal to the bypass area plus the 17 calculated area for the segment (block 364). The area is 18 then calculated as the prior calculated area plus the area 19 of the segment under consideration (block 366), and the controller then proceeds to consider the next segment 21 (block 368). After all segments have been considered, the 22 total area is obtained (block 370).
23 In accordance with an important aspect of the 24 present invention, the apparatus is also adapted to determine the uncovered area of a combination of vertically 26 and horizontally moveable sash doors, such as the fume hood 27 illustrated in FIG. 6, which has four horizontally moveable 28 sash doors that are contained in two sets of tracks, with 29 the sets of tracks being contained in a frame structure which is itself vertically moveable. As previously 31 mentioned, there is an upper lip 77 having a front 32 thickness of about 2 inches, the exact dimension of which 33 can vary with the manufacturer's design, a lower portion 79 34 of the frame 78, and a bypass area 75. As may be appreciated, when the frame 78 is in its lowermost 36 position, the entire bypass area is "open" and air may be 37 moved through it. As the frame is raised, the portion of 38 the sash doors 76 which cover the opening will increasingly Z~ j~l26 1 cover the bypass area as shown. In the particular 2 illustration of FIG. 6, the horizontally moveable doors 3 overlap and are completely closed, but the frame is shown 4 being slightly raised.
To determine the uncovered area of the 6 combination sash door fume hood, the following specific 7 steps are performed. The net open area, i.e., the 8 uncovered area, is the sum of the vertical (hereinafter "V"
9 in the equations) area and the horizontal (hereinafter "H") area:
11 Net Open Area = V area + H area 12 with the horizontal area being determined as follows:
13 H area = H width * minimum of {panel Ht; Max of 14 (panel Ht + top lip Ht + min. face Ht -sash Ht; 0)) 16 with the H width comprising the previously described 17 operation being performed with respect to the horizontally 18 moveable sash doors. The vertical area (V area) is 19 determined by the following equation:
V area = Max of (Sash Ht * V width; minimum face 21 area) 22 To complete the determination, the Net Face Area 23 is then equal to the sum of the Net Open Area and the Fixed 24 or bypass Area:
Net Face Area = Net Open Area + Fixed Area 26 From the foregoing detailed description, it 27 should be appreciated that an extremely effective and 28 efficient fume hood controller has been shown and described 29 that offers significant advantages over the current prior art controllers. The fume hood controller has a design 31 that permits it to be configured to control virtually any 32 type of fume hood that is now available, and it has the 33 capability to very rapidly adjust the flow of air through 34 the fume hood to maintain the average face velocity at the desired value even when sash positions are changed or other 36 perturbations occur, and such adjustment results in steady ~0~5126 1 state operation within approximately 3 to 4 seconds.
2 While various embodiments of the present 3 invention have been shown and described, it should be 4 understood that various alternatives, substitutions and equivalents can be used, and the present invention should 6 only be limited by the claims and equivalents thereof.
7 Various features of the present invention are set forth in 8 the following claims.

Claims (31)

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

1. Apparatus for controlling the air flow through a fume hood to maintain a predetermined average face velocity through an uncovered portion of an opening of a fume hood of the type which has at least one moveable sash door adapted to cover the opening as the fume hood sash door is moved, the fume hood being in communication with an exhaust duct for expelling air and fumes from the fume hood, said apparatus comprising:
means for detecting the position of each moveable sash door and generating a position signal that is indicative of the sash door position;
means responsive to said position signals for calculating the size of the uncovered portion of the opening;
means for measuring the actual flow of air through the exhaust duct and generating an actual flow signal that is indicative of the actual flow of air through the exhaust duct;
modulating means for varying the flow of air through the exhaust duct responsive to a control signal being received from a controller means; and controller means responsive to said position signals and said actual flow signal for controlling the flow modulating means to generate the greater of a predetermined minimum flow rate signal value or a desired flow rate signal value as a function of the calculated size of the uncovered portion, said desired flow rate signal corresponding to a flow rate that is sufficient to maintain the predetermined average face velocity through the uncovered portion of the opening, said controller means comparing said desired flow rate signal and said actual flow rate signal and generating an error signal indicative of any error that exists by taking a plurality of successive measurement samples of said actual flow rate, determining at least two distinct factors of said error signal from said successive samples and summing the said factors to generate said error signal, said controller means generating and outputting a control signal to said modulating means for selectively reducing said error signal to a predetermined minimum value when said actual flow rate signal exceeds said predetermined minimum flow rate signal value or providing a predetermined minimum flow rate.

2. Apparatus as defined in claim 1 wherein the fume hood has one sash door that is moveable in a vertical direction to selectively cover and uncover the opening, said detecting means comprising an elongated resistance means located adjacent the sash door adapted to be contacted at different positions along its length by actuator means associated with said sash door as the door is moved vertically, said position signal being generated by said detecting means comprising a voltage level that is indicative of the position of said sash door.

3. Apparatus as defined in claim 1 wherein the fume hood has a plurality of sash doors that are moveable in at least a horizontal direction to selectively cover and uncover the opening, said detecting means comprising an elongated resistance means located adjacent the sash doors adapted to be contacted at different positions along its length by actuator means associated with each sash door as each sash door is horizontally moved, said position signals being generated by said detecting means comprising voltage levels that are indicative of the horizontal positions of each sash door.

4. Apparatus as defined in claim 3 wherein said plurality of sash doors are mounted in a frame means that is moveable in a vertical direction, said detecting means further comprising a second elongated resistance means located adjacent the frame means adapted to be contacted at different positions along its length by actuator means associated with said frame means as said frame means is vertically moved said position signals being generated by said detecting means also comprising voltage levels that are indicative of the vertical position of each sash door.

5. Apparatus as defined in claim 1 wherein said modulating means comprises a motor driven blower means wherein said motor is controlled by a motor controller adapted to vary the speed of the motor in order to vary the exhaust air flow in the duct.

6. Apparatus as defined in claim 1 wherein said modulating means comprises a damper means located in the exhaust duct and actuating means for varying the position of the damper means to thereby vary the flow of air through the exhaust duct.

7. Apparatus as defined in claim 1 wherein said air flow measuring means comprises a flow sensor.

8. Apparatus as defined in claim 1 wherein said controller means determines three distinct factors of said error signal from said successive samples and sums the said factors to generate said error signal, said factors comprising a proportional action factor, an integral action factor and a derivative action factor.

9. Apparatus as defined in claim 8 wherein said integral action factor at any given time is directly proportional to the integral action factor calculated from the immediately prior sample multiplied by a loop cycle time, plus any error measured by the present sample.

10. Apparatus as defined in claim 8 wherein said derivative action factor at any given time is directly proportional to the difference between any error determined from the immediately prior sample and the current sample divided by a loop cycle time.

11. Apparatus as defined in claim 8 wherein said proportional action factor at any given time is directly proportional to any error determined from the current sample.

12. Apparatus as defined in claim 8 wherein said modulating means comprises a motor driven blower means wherein said motor is controlled by a motor controller adapted to vary the speed of the motor, said controller means generating a feed forward control signal for said modulating means and inhibiting any error signal generation in response to a sash door being moved, said feed forward control signal predicting the actual flow rate of air through the exhaust duct as a function of the calculated size of the uncovered portion, said controller means thereafter ceasing the inhibiting of any error signal generation.

13. Apparatus as defined in claim 12 wherein said feed forward control signal at any given time comprises an intercept value plus a slope value multiplied by a predetermined set flow value.

14. Apparatus as defined in claim 1 further including an operator panel adapted to be mounted on the fume hood in position to be observed by a person, said operator panel being connected to said controller means, said operator panel including display means for displaying the average face velocity being calculated for the associated fume hood, and for displaying other status information relative to the operation of the apparatus.

15. Apparatus as defined in claim 14 wherein said operator panel includes means for placing said controller in one of two modes of operation, one mode being a day mode and the other a night mode, said controller means including memory means for storing information relative to the operation of said apparatus, said controller means being adapted to receive separate predetermined average face velocity values for each of said day and night modes.

16. Apparatus as defined in claim 15 wherein said operator panel includes connector means adapted to be connected to a computer means of the type which has a keyboard, the computer means being capable, when connected to the operator panel, of defining parameters and operating values of the fume hood to which the apparatus is to control.

17. Apparatus as defined in claim 16 wherein said parameters and operating values include the number of sash doors and the possible movement of such sash doors, the physical dimensions of the sash doors and of the opening of the fume hood, the average face velocity for day and night modes.

18. Apparatus as defined in claim 1 wherein said means for calculating the size of the uncovered portion of the opening comprises computing means located within said controller means.

19. Apparatus for controlling the air flow through a plurality of fume hoods to maintain a predetermined average face velocity through an uncovered portion of an opening of each fume hood, each fume hood being of the type which has at least one moveable sash door adapted to selectively cover the opening as the fume hood sash door is moved, each fume hood in communication with an exhaust duct for expelling air and fumes from each fume hood, the exhaust ducts for each fume hood being in communication with an exhaust system, said apparatus comprising:
means associated with each fume hood for detecting the position of each moveable sash door and generating a position signal that is indicative of the position of such sash door;
means responsive to said position signals for calculating the size of the uncovered portion of the opening of each fume hood;
means for measuring the actual flow of air through the exhaust duct in communication with each fume hood and generating an actual flow signal that is indicative of the actual flow of air through the exhaust duct;

modulating means associated with each fume hood for varying the flow of air through the exhaust duct that is in communication with the respective fume hood responsive to a control signal being received from a controller means; and controller means responsive to said position signals and said actual flow signal for controlling the flow modulating means associated with each respective fume hood to generate a desired flow rate signal as a function of the calculated size of the uncovered portion, said desired flow rate signal corresponding to a flow rate that is sufficient to maintain the predetermined average face velocity through the uncovered portion of the opening of each fume hood, said controller means comparing said desired flow rate signal and said actual flow rate signal for each fume hood and generating an error signal indicative of any errors that exist by taking a plurality of successive measurement samples of said actual flow rate, determining at least two distinct factors of said error signal from said successive samples and summing the said factors to generate said error signal, said controller means outputting a control signal to said modulating means associated with each fume hood for selectively reducing said error signal to a predetermined minimum value or maintaining a predetermined minimum actual flow.

20. Apparatus as defined in claim 19 wherein said controller means determines three distinct factors of said error signal from said successive samples and sums the said factors to generate said error signal, said factors comprising a proportional action factor, an integral action factor and a derivative action factor.

21. Apparatus as defined in claim 19 wherein said integral action factor at any given time is directly proportional to the integral action factor calculated from the immediately prior sample multiplied by a loop cycle time, plus any error measured by the present sample.

22. Apparatus as defined in claim 19 wherein said derivative action factor at any given time is directly proportional to the difference between any error determined from the immediately prior sample and the current sample divided by a loop cycle time.

23. Apparatus as defined in claim 19 wherein said proportional action factor at any given time is directly proportional to any error determined from the current sample.

24. Apparatus as defined in claim 19 wherein said modulating means comprises a damper means located in the exhaust duct and actuating means for varying the position of the damper means to thereby vary the flow of air through the exhaust duct.

25. Apparatus as defined in claim 20 wherein said measurement samples are taken generally every 100 milliseconds.

26. Apparatus as defined in claim 20 wherein position detecting means operates to generate a position signals generally every 200 milliseconds.

27. Apparatus as defined in claim 20 wherein said controller means generates said control signal generally every 100 milliseconds.

28. Apparatus for controlling the air flow through a fume hood to maintain a predetermined average face velocity through an uncovered portion of an opening of a fume hood of the type which has at least one moveable sash door adapted to cover the opening as the fume hood sash door is moved, the fume hood being in communication with an exhaust duct for expelling air and fumes from the fume hood, said apparatus comprising:
means for detecting the position of each moveable sash door and successively generating a position signal that is indicative of the position of each sash door;
means responsive to said position signals for calculating the size of the uncovered portion of the opening;
means for successively generating an actual flow signal that is indicative of the actual flow of air through the exhaust duct;
modulating means for varying the flow of air through the exhaust duct responsive to a control signal being received from a controller means; and controller means responsive to said position signals and said actual flow signal for controlling the flow modulating means, said controller means either generating a control signal value that maintains a predetermined minimum flow rate or generating a desired flow rate signal as a function of the calculated size of the uncovered portion, said desired flow rate signal corresponding to a flow rate that is sufficient to maintain the predetermined average face velocity through the uncovered portion of the opening, said controller means generally continuously comparing said desired flow rate signal with successive instantaneous sample values of said actual flow signal and generating an error signal having a magnitude that is directly proportional to the sum of any calculated integration error, any calculated derivative error and any calculated proportional error, said controller means successively generating and outputting a control signal to said modulating means for reducing said error signal to a predetermined minimum value or maintaining said predetermined minimum actual flow.

29. Apparatus as defined in claim 28 wherein said measurement samples are taken generally every 100 milliseconds.

30. Apparatus as defined in claim 28 wherein position detecting means operates to generate a position signals generally every 200 milliseconds.

31. Apparatus as defined in claim 28 wherein said controller means generates said control signal generally every 100 milliseconds.