JPH05165529A - Apparatus for controlling ventilation of haze hood - Google Patents

Abstract

PURPOSE: To accurately and quickly control and average speed of air flowing through the non-covered part of the opening of a fume hood at the time of maintaining the average air speed passing by changing the flow rate of air flowing through an exhaust duct in accordance with a door position signal and an actual flow rate signal by controlling a flow rate changing means. CONSTITUTION: The fume hood controller 20 measures the actual flow rate of air flowing through the non-covered part of the opening of a fume hood by detecting the position of each mobile sashed door 76. The controller 20 also maintains a prescribed average air speed at the non-covered part by changing the actual flow rate of air flowing through an exhaust duct 70 in accordance with a door position signal and an actual flow rate signal. Therefore, the control which is performed for maintaining the average air speed at the non-covered part can be performed accurately as the sashed door 76 move. When the position of one door 76 is changed or another state change which loses the balance occurs, the control can be performed at an extremely fast response speed. Moreover, all types of fume hoods which are available at present can be controlled.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates generally to laboratory fume hood ventilation control, and more particularly to an improved method and apparatus for controlling fume ventilation from one or more fume hoods typically located in a laboratory environment.

[0002]

Fume hoods are used in a variety of laboratory environments that provide a work location where potentially dangerous chemicals are used, and these hoods allow workers access to the interior of the enclosure for experiments. Where possible, it has an enclosure with a movable door in the front that can be opened in different amounts. Typically, the enclosure is connected to an exhaust system that removes harmful fumes to prevent personnel from being exposed to harmful fumes while working in the hood.

[0003] Fume hood controllers that control the flow rate of air through an enclosure have become increasingly sophisticated in recent years and now accurately maintain the desired flow characteristics and are a function of the desired average face velocity of the fume hood opening. As a result, the smoke can be efficiently exhausted from the enclosure.

Average face velocity is generally defined as the amount of air flowing into the fume hood per square foot of the open face area of the fume hood, the size of the open face area provided on the front of the enclosure or fume hood. The position of one or more movable doors, and even most types of enclosures, depends on the amount of bypass openings provided when one or more doors are closed.

A fume hood includes an exhaust containing one or more blowers that can be driven at variable speeds to increase or decrease the flow rate of air from the fume hood to compensate for the varying size of the openings or open surfaces. Exhausted by the system. Alternatively, one blower is connected to the exhaust manifold connected to each duct of multiple fume hoods, and a damper is installed in each duct to control the flow rate from each duct to maintain a desired average surface velocity. Alternatively, the flow rate may be modulated.

The door of such a fume hood can be opened by raising it vertically to a position often referred to as the sash position, and some fume hoods are usually slidable along two sets of tracks. It has a plurality of mounted doors. In addition, some doors have multiple tracks mounted in a vertically movable frame assembly and are movable in both horizontal and vertical directions.

[0007]

A conventional fume hood controller includes a detection means for measuring the position of each door and changing the speed of the blower or the position of the damper using a signal proportional to the detected position. .. While such control represents an improvement in the control of the fume hood, situations have arisen that require further adjustment of the exhaust air from the fume hood, which cannot be done with such controllers. This is in part due to the fact that sensing the position of such doors results in a prediction of the blower speed or damper position that is substantially required, without having to actually measure the resulting flow rate of the fume hood for a given position on each door. It is based on the fact that one obtains the flow rate necessary to maintain the desired face velocity over the open area. This type of control is known as an open loop control method.

Accordingly, one of the main objects of the present invention is to provide an improved fume hood controller device and improved method which overcomes many of the drawbacks of existing controllers.

Another of the main objects of the present invention is to provide very precise control to maintain the desired average surface velocity of the air passing through the open area of the fume hood, while changing the door position, or It is an object of the present invention to provide an improved apparatus and method designed to exhibit an extremely fast response time for performing the above-mentioned control when a situation change that causes other imbalances occurs.

Yet another object of the present invention is to employ closed loop control, in which the desired face velocity error is measured using three different types of gain, and then the difference is determined in a rapid manner. It is to provide an improved method and apparatus in which the control scheme operates to reduce to zero.

A further object of the invention, in all of its embodiments, is to determine the desired mean surface velocity of the air entering through the open area of the fume hood, ie the area not covered by the one or more doors. To achieve
It is an object of the present invention to provide an improved method and apparatus using proportional gain, integral gain and derivative gain.

Another object of the invention is, in some of its embodiments, in addition to using the proportional gain, integral gain and derivative gain as described above, one or more for changing the open area of the fume hood. It is an object of the present invention to provide an improved method and apparatus using a feedforward type control that is performed when more doors are moved.

Yet another object of the present invention is to provide an improved fume hood control system and method which is easy to incorporate into a heating, ventilation and air conditioning control system of a laboratory room having a fume hood disposed therein.

Another object of the present invention includes a small, easy to use, effective operator panel located at a location within the fume hood itself that is easily observed by operators and convenient for operation. It is an object of the present invention to provide an improved fume hood control apparatus and method in which an operator panel constantly monitors and controls the fume hood controller.

An object closely related to the present invention is to provide a connector on the operator panel suitable for receiving a handheld terminal that can be used to alter various important parameters associated with the operation of a fume hood controller. It is in.

The above and other objects will become apparent from the following detailed description of the invention with reference to the accompanying drawings.

[0017]

In order to achieve the above object, the device according to the invention comprises a predetermined passage through an uncovered part of an opening of a fume hood having at least one movable sash door which covers the opening as it is moved. A device for controlling the air flow rate through the fume hood to maintain an average face velocity, wherein the fume hood is in communication with an exhaust duct through which air and fume are discharged, the position of each movable sash door Means for detecting and generating a position signal indicative of the position of the sash door; means for calculating the size of the uncovered portion of the opening in response to the position signal; measuring the actual air flow rate through the exhaust duct; Means for generating an actual flow rate signal indicative of the actual flow rate of air through the air flow; flow rate of air through the exhaust duct in response to a control signal received from the controller means Modulating means for changing; controlling the flow rate modulating means in response to the position signal and the actual flow rate signal, among a desired flow rate signal value as a function of a predetermined minimum flow rate signal value or the calculated size of the uncovered portion. In the controller means generating the larger one, the desired flow signal corresponds to a flow rate sufficient to maintain a predetermined average surface velocity through the uncovered portion of the opening, the controller means providing the desired flow rate. A signal is compared with the actual flow signal to generate an error signal indicating an error existing between the signals, and when the actual flow signal exceeds the predetermined minimum flow signal, the error signal is set to a predetermined minimum value. It is characterized by comprising controller means for selectively generating a control signal for reducing or for giving a predetermined minimum flow rate and outputting it to the modulating means.

[0018]

To begin with, as a general rule, the fume hood controller controls the flow of air through the fume hood and the effective size of all openings to the fume hood, including those openings not covered by one or more sash doors, is It should be understood that it is intended to provide a relatively constant average surface velocity of the air moving into the hood. This means that regardless of the area of the uncovered opening, the average amount of air per unit surface area of the uncovered part is
Means moving into the fume hood. As a result,
Air constantly flows into the fume hood and out of the exhaust duct, protecting workers in the laboratory from exposure to harmful fumes and air flow.
It is preferably controlled at a predetermined rate of approximately 75-125 cubic feet per minute per square foot of effective surface area of uncovered openings. In other words, if one or more sash doors are moved to the maximum open position and workers gain maximum access to the interior of the fume hood for experiments, etc. The flow of must be increased. There are significant differences in the capabilities and effectiveness of various prior art controllers.

Generally speaking, an improved fume hood that provides many desirable operational benefits to workers performing experiments and other tasks using the fume hood, as well as operators of the facility in which the fume hood is located. A controller device is obtained according to the invention. The apparatus embodying the present invention provides very fast and effective control of the average face velocity of the fume hood, with the desired average face velocity within seconds after the movement of one or more doors covering the front opening of the fume hood. Achieve and maintain. Also, as other variations occur in the laboratory environment in which one or more fume hoods are located, the controller of the present invention reacts quickly and stabilizes to maintain the desired flow conditions.

In the apparatus of the present invention, the fume hood maintains a predetermined average surface velocity through the uncovered portion of the fume hood opening having at least one movable sash door that covers the opening as the fume hood sash door moves. Controls the air flow rate through the. In other words, this device detects the position of each movable sash door, calculates the size of the uncovered part of the opening, measures the actual air flow rate through the exhaust duct, and measures the exhaust duct according to the door position signal and the actual flow signal. The flow rate modulation means is controlled so as to change the air flow rate through the opening and maintain a predetermined average surface velocity through the uncovered portion of the opening.

[0021]

1 is a block diagram of several fume hood controllers 20 interconnected with a room controller 22, an exhaust controller 24, and a main control console 26 and embodying the present invention. .. The fume hood controller 20 is interconnected with a room controller 22, an exhaust controller 24 and a main control console 26 by a local area network (LAN) indicated by line 28 which may be formed of a multi-conductor cable or the like. Room controller 22, exhaust controller 24
And the main control console 26 is typically part of the main HVAC system of the building in which the laboratory room containing the fume hood is located.

The room controller 22 is preferably such that at least a variable amount of air can be given to the room.
It can be a System 600 SCU controller from ndis & Gyr Powers. Room controller 22 is LAN line 2
8 can be used for communication. The room controller is preferably a System 600 SCU controller, which is a commercially available controller for which extensive documentation exists. In particular, the System 600 SCU Controller User Reference Manual, Part Nos. 125-1753, is hereby incorporated by reference.

Room controller 22 receives a signal from each fume hood controller 20 via line 81 that provides an analog input signal indicating the amount of air being exhausted by each fume hood, and the fume hood exhaust. And a comparison signal from an exhaust flow sensor that provides an indication of the amount of air being exhausted through another main exhaust system. These signals are combined with the signal provided by the differential pressure sensor 29, which indicates the pressure in the room compared to the standard space, so that the room controller can maintain the differential pressure in the room just below the standard space. The required air supply can be controlled. Such a system
Ahmet et al., Assigned to the same applicant as this application and included in the aforementioned cross-referenced application, entitled "Differential Pressure Control System for Chambers with Laboratory Fume Hoods", Serial No. 52497.
Is disclosed in.

Power is supplied to the fume hood controller 20 via a transformer 32 or the like through line 30 at an appropriate voltage.

Referring to FIG. 2, the fume hood controller 20 is shown explicitly showing the functions of its input and output connector ports, which are connected to an operator panel 34. It should be understood that each fume hood has a fume hood controller 20 and an operator panel is provided for each fume hood controller 20. That is, an operator panel 34 is provided for each fume hood and is interconnected with the fume hood controller 20 by a line 36 which preferably comprises a multi-conductor cable having eight conductors. The operator panel 34 is, for example, a 6-line RJ
It has a connector 38 such as a 11-inch phone jack, and a laptop personal computer or the like can be connected to the connector 38 in order to input information regarding the configuration and operation of the fume hood at the time of initial setting, or to change some operation parameters if necessary. Can be connected. Also, the operator panel 34
Is preferably attached to the fume hood in a convenient location for easy observation by an operator working in the fume hood.

The fume hood controller operator panel 34 includes a liquid crystal display 40 which is selectively energized to provide a visual indication of various aspects of the fume hood, including a three digit 42 which provides an average face velocity. Display 4
0 also indicates low face velocities, high face velocities, emergency conditions, and other conditions such as an indication of controller failure. The operator panel 34 may also have an alarm 44 and an emergency purge switch 46 that the operator can press to purge the fume hood in the event of an accident. The operator panel also has two auxiliary switches 48 that can be used for various customer needs, including day / night mode of operation. It is conceivable that the nighttime mode of operation will have a different, preferably lower, average surface velocity than the daytime mode of operation. This is because it is assumed that no one will work indoors late at night and such a low average surface velocity will save energy. An alarm silence switch 50 is also preferably provided.

The fume hood can be of many different styles, sizes and shapes, including those with one or multiple sash doors, with the sash doors being movable vertically, horizontally or in both directions. Also, various fume hoods have different bypass flow rates, i.e., different flow rates through the openings that are present even when all sash doors are closed as far as possible by design. Other design factors also include whether there is any type of filtering means in the fume hood that traps the fume in the hood during operation. Although many such design factors must be taken into account to provide efficient and effective control of the fume hood, the apparatus of the present invention can be configured to take into account almost all of the design variables described above and fume hood ventilation. Effective and extremely quick control of is obtained.

Referring to FIG. 3, there is shown a fume hood, generally indicated at 60, which is movable to provide access to the fume hood and is in a generally closed position as shown. It has a vertically actuable sash door 62 movable to. The fume hood is generally designed so that there is a certain amount of openings through which air can pass through the fume hood, even when the door sash, such as the door sash 62, is completely closed. This opening is commonly referred to as the bypass region and can be chosen so that its effect can be taken into account when controlling the flow of air into the fume hood. Some fume hoods have a bypass opening located above the door sash, while others are located below. In some of the fume hoods, the initial movement of the sash door increases the opening at the bottom of the door shown in FIG. 3, for example, but the door blocks the bypass opening as it rises, and the total opening of the fume hood increases. The effective size is kept relatively constant during the first approximately 1/4 of the travel along the path of movement of the sash door 62.

Another type of fume hood includes several horizontally movable sash doors 66, as shown in FIGS. 4 and 5, and upper and lower pairs of adjacent tracks 68.
Each door may be movable along. When the door is positioned as shown in FIGS. 4 and 5, the opening of the fume hood is completely closed and the operator can move the door horizontally to gain access to the inside of the fume hood. Smoke hood 6
Both 0 and 64 have an exhaust duct 70 that typically extends to an exhaust system that may be for an HVAC device as described above. Fume hood 64 includes a filtering structure, shown generally at 72, which prevents harmful fumes and other contaminants from flowing out of the fume hood into the exhaust system.
Referring to FIG. 6, there is shown a combined fume hood 74 having a horizontally movable door 76 similar to the door 66, which fume hood 74 supports a frame structure 78 supporting the door 76 along a suitable track. And the frame structure 78 is vertically movable within the fume hood opening.

In FIG. 6 there is an abbreviated portion, indicated by dashed line 73, which allows the fume to be raised sufficiently to allow proper access to the interior of the fume hood by personnel. It is intended to show that the height of the hood can be made larger than shown. Generally, there is a bypass area shown as vertical area 75,
There is also typically a top lip 77, which can be about 2 inches wide. This dimension is preferably determined so that its influence on the calculation of the open surface area can be taken into account.

Although not specifically shown, substantially the same as a fenestration for a dwelling, one to the other along the width of the fume hood opening, such as two or more vertically movable sash doors along adjacent tracks. Other combinations are possible, including multiple sets of vertically movable sash doors located adjacent to each other.

In accordance with an important feature of the present invention, the fume hood controller 20 operates fume hoods of various sizes and configurations as described above, and may have several fume hoods arranged, and the building. It is mounted in a laboratory room that may include an exhaust duct that joins a common exhaust manifold that may be part of the HVAC system. The fume hood may be a single independent fume hood or may have its own separate exhaust duct. If one fume hood is installed, such an installation would have a blower driven by a variable speed motor and attached to the exhaust duct, with the motor and blower to regulate the air flow through the fume hood. Generally, the speed can be variably controlled. Alternatively, in the most common case where there are multiple fume hoods within a region, each fume hood has one exhaust duct.
There may be one large blower in the manifold system, merged with one or more larger exhaust manifolds. In such equipment, since the control of each fume hood is performed by the separate damper arranged in each fume hood, it is possible to control the change in the flow by appropriately positioning the damper attached to each fume hood. ..

The fume hood controller can control virtually any of the various types and styles of fume hoods that are commercially available, and as such, has a large number of input / output ports (connectable to the various sensors used in the controller). Line, connector or connection, which are all considered equivalent for purposes of describing the invention). As shown in FIG. 2, the fume hood controller has a digital output or DO port for interfacing with the digital signal / analog pressure conversion element provided in the exhaust damper as described above, and the variable speed fan drive is provided in an analog manner. If so, it also has an analog voltage output port for controlling its drive. Used to detect the position of a sash that can move both horizontally and vertically 5
There are also two sash position sensor ports and an analog input port connected to the exhaust air flow rate sensor. Further, a digital input port for an emergency switch is provided, and each digital output port for outputting an alarm horn signal and an auxiliary signal is also provided. Further, an analog voltage output port for providing a flow rate signal to the room controller 22 is also provided. In some applications where an exhaust air flow rate sensor is not provided, a wall velocity sensor that indicates the surface velocity may be used, in which case an input port for that signal is provided, but such a sensor is generally less accurate. It is considered and its use is not a preferred embodiment. With the various ports mentioned above, almost any type of fume hood can be controlled in an effective and efficient manner.

From the above description, when it is attempted to maintain the desired average surface velocity while changing the sash position, the size of the opening changes greatly, so that a large change in the air amount is required to maintain the average surface velocity. It should be understood that there is a need. While it is known to control a variable air blower as a function of sash position, the fume hood controller of the present invention makes the control system's capability relatively constant so that it can react quickly to variations in the system. The known method is improved by incorporating an additional control scheme that provides a significant improvement in maintaining the average face velocity of the.

To determine the position of the sash door, a sash position sensor is provided adjacent to each moveable sash door, which is schematically illustrated in FIGS. 7, 8 and 9. Referring to FIG. 8, the door sash position indicator preferably comprises a relatively thin polyester base layer 82, an elongated switching mechanism 8 of relatively simple mechanical design.
0 is printed on the base layer 82 in the form of a strip of electric resistance ink 84 having a known constant resistance per unit length. Another polyester base layer 86 is provided, on which conductive ink 88 is also printed in strips. The two base layers 82 and 86 are adhesively bonded to each other by two beads of adhesive 90 located on opposite sides of the strip. Both base layers are preferred to be approximately five thousandths of an inch thick and both beads are approximately two thousandths.
At a thickness of inches, these beads provide a space between conductive layer 88 and resistive layer 84. Switching mechanism 8
The zeros are preferably attached to the fume hood by a layer of adhesive 92.

The polyester material is flexible enough to allow one layer to move toward and contact the other layer in response to an actuator 94 carried by the corresponding sash doors in which the strips are placed side by side. Upon movement, the actuator 94 moves along the switching mechanism 80 to create a contact between the resistive layer and the conductive layer, which is sensed by an electrical circuit, described below, and the actuator 94 along the length of the switching mechanism 80.
Gives a voltage output that indicates the absolute position of. That is, by supporting the actuator 94 on the sash door,
Provides a voltage that indicates the absolute position of the sash door.

The actuator 94 receives sufficient pressure on the switching mechanism 80 as the sash door moves, and
The two base layers are abutted, and the resistive layer and the conductive layer are preferably spring biased toward the switching mechanism 80 so as to make an electrical contact with each other and to provide a voltage level in response to the electrical contact. .. The sash position can be accurately determined by making the switching mechanism 80 long enough to cover the entire range of movement of the sash door as shown in FIG. It should be noted that the switching mechanism 80 shown in FIGS. 3 and 5 is only an outline, and it is preferable that the switching mechanism 80 is actually disposed inside the sash frame itself, and is not visible from the outside as illustrated. Due to the small width and thickness dimensions of the switching mechanism 80, interference with the operation of the sash door is virtually non-issue. The actuator 94 may be placed in a small hole drilled in the sash door, or mounted outside one end of the sash door so that the switching mechanism 80 is in a position to operate. In the vertically movable sash door shown in FIGS. 3 and 6, it is preferable to provide the switching mechanism 80 on one side or the other side of the sash frame, while in the fume hood having the horizontally movable door, the movable door is used. It is preferable to place the switching mechanism 80 on top of the track 68 so that the weight thereof does not affect or damage the switching mechanism 80. Also,
Among the above-mentioned cross-referenced applications, the application of Egberth et al., "Device for determining the position of a movable structure along a track",
For the reasons described in Serial No. 52496, the actuator 94 is preferably located at one end of each door.

Referring to FIG. 9, there is shown a preferred electrical circuit for producing the position indicating voltage, which electrical circuit is suitable for providing two separate voltages indicative of the absolute position of two sash doors within a truck. .. Referring to the cross-sectional view shown in FIG. 5, there are two horizontal tracks each supporting two sash doors, and each track is provided with the same circuit as shown in FIG. 9 including the switching mechanism 80, Separate voltages are provided for each of the four sash doors shown.

The switching mechanism 80 is preferably attached to the fume hood with a layer of adhesive 92, with actuators 94 abutting it at each location along the length of the switching mechanism 80. Referring to FIG. 7, 2 shown in FIG.
A schematic diagram of a pair of switching mechanisms 80, as used in one truck, is shown. The switching mechanism 80 is provided in each track, and the four arrows in the figure represent the contact points formed by the actuators 94. As a result, a signal is given to each end of each switching mechanism, and the magnitude of this signal is It represents the voltage proportional to the distance between each end and the closest arrow. Thus one switching mechanism 80 provides absolute position indication signals for the two doors located on each truck. The circuitry used to implement the above voltage generation is shown in FIG. 9, with one circuit for each track. The resistive element (layer) is shown at 84, and the conductive element (layer) 88 is shown with one end connected to ground, and two arrows at the other end are shown for each actuator 9 attached to two separate doors.
4 represents the contact point between the resistive element and the conductive element formed by 4. The circuit shown includes an operational amplifier 100 having an output connected to the base of a PNP transistor 102, the emitter of PNP transistor 102 via resistor 104 to a positive voltage source and directly to operational amplifier 100. Connected to the negative input of the operational amplifier 100
The positive input of is also connected to a positive voltage source, preferably about 5 volts. The collector of the transistor 102 is the resistance element 8
4, which has an output line 106, at which a voltage is generated which is indicative of the absolute position of the door.

The circuit operates to provide a constant current to the resistive element 84, which produces a voltage proportional to the resistance between the collector and ground which changes as the closest contact point along the resistance changes. Occurs on output line 106. Operational amplifier 100 operates to drive the negative input to equalize the voltage level of the positive input, resulting in a current at the output of the operational amplifier that varies in direct proportion to the effective length of resistive element 84. The lower part of the circuit operates in the same manner as described above, providing a voltage proportional to the distance between the connecting end of the resistive element 84 and the point of contact by the actuator 94 attached to the other sash door in the track.
8 occurs similarly.

Referring to the synthetic electrical schematic of the circuit of the fume hood controller, FIGS. 10a, 10b, 10c, 10
If the drawings of d and 10e are arranged side by side as shown in FIG. 10, an electrical schematic diagram of the entire fume hood controller 20 is obtained. The operation of the circuits of Figures 10a to 10e will not be described in detail. The circuit is driven by a microprocessor and the key algorithms that implement the control functions of the fume hood controller are described below. Figure 10
Referring to FIG. 3c, the circuit shown in FIG.
Motorola MC68 to which MHz clock input is applied
It includes an HC11 microprocessor 120. Microprocessor 120 has a data bus 124 connected to a tri-state buffer 126 (FIG. 10d), which is connected to an electrically programmable read only memory (EPROM) 128 which is also connected to data bus 124. ing. EPROM 128 is a 3-state buffer 12
6 has address lines A0-A7 connected to it and also has address lines A8-A14 connected to the microprocessor 120.

The circuit also includes a 3 to 8-bit multiplexer 130, a data latch 132 (see FIG. 10d), and a digital-to-analog converter 1 that provides an analog output indicating the amount of air being exhausted by the fume hood.
34, the information of which is provided to the room controller 22 described above with reference to FIG. Referring to FIG. 10b, R for sending and receiving information via a handheld terminal.
An S232 driver 136 is provided. The circuit shown in FIG. 9 is also shown as a general schematic in FIGS. 10a and 10b. The other parts are well known and need not be described at all.

As mentioned above, the apparatus of the present invention uses an air flow sensor, which is preferably located in the exhaust duct 70 to measure the amount of air being drawn through the fume hood. The air flow rate can be calculated by measuring the differential pressure between both sides, such as a multi-point Pitot tube. In the preferred embodiment, a differential pressure sensor is used to measure the flow through the exhaust duct so that the device of the present invention maintains the flow through the fume hood at a predetermined average surface velocity, or the fume hood is closed or A control method that keeps the minimum speed when a small bypass area is used is used.

The fume hood controller of the present invention is applicable to almost any type of known fume hood, including horizontally movable sash doors, vertically movable sash doors, or a combination of both.
As is clear from FIGS. 2 and 10, the fume hood controller controls the exhaust damper or the variable speed fan drive, and outputs a signal compatible with any type of control. The fume hood controller also receives information that determines the physical and operational characteristics of the fume hood and other initialization information. This type of information can be input to the fume hood controller by a handheld terminal, which is preferably a laptop computer connectable to the operator panel 34. The information to be provided to the controller includes the following, together with the dimensions of the information. It should be noted that a day / night operation mode may be provided, but this is not the preferred embodiment of the system and, if provided, information regarding day / night operation should be included.

Operation information: 5. Time; 6. 6. Average surface velocity (SVEL) day / night setting, feet per minute or meters per second; 7. Minimum flow (MINFLO) day / night setting, cubic feet per minute; High-speed limit (HVEL) day / night setting, F / m or M / sec; Day / night value setting of low speed limit (LVEL), F / m or M / sec; 10. 10. Mid-high speed limit (MVEL) day / night value setting, F / m or M / sec; 12. Mid-low speed limit (IVEL) day / night setting, F / m or M / sec; 13. Set proportional gain factor (KP), analog output per error, percent; 13. Setting of integral gain coefficient (KI), product of analog output and minute-hour per error, percent; 14. Setting of differential gain coefficient (KD), product of analog output and minute per error, percentage; 15. Feedforward gain coefficient (K when a variable speed drive is used instead of a damper as a control device)
F) setting, analog output per CFM.

16. Time when the user wants to maintain the full exhaust flow rate when the emergency switch is operated (DELTIME)
Set in seconds.

17. The emergency switch is operated and the DELT
When IME expires, set the preset percentage (SAFLOQ) of the final exhaust flow rate that the user wants to keep.

The above information is used to control the mode of operation and also the flow limit during the day or night mode of operation. The controller 20 includes programmed instructions for calculating the steps in paragraphs 3-7 above if the relevant information is not provided by the user. Therefore, when the day and night value of the average surface speed is set, the controller 20 sets the high surface speed limit of 120% of the average surface speed to 80%.
And a medium speed limit of 90%, respectively. It should be understood that these percentage values may be adjusted as desired. Other information to enter includes the following information related to the physical structure of the fume hood. Some of the following information may be unnecessary for sash doors that can only be moved vertically or horizontally, but both combinations require all information. The required information includes a vertical section defined by height and width dimensions covered by one or more sash doors. If more than one sash door is provided in each section, those doors will be vertically movable sash doors, as will double sash residential windows.
The information to be provided includes: 18. Enter the number of vertical divisions; Enter the height of each section, inches; 20. Enter the width of each section, inches; 21. Enter the number of tracks for each category; 22. Enter the number of horizontal sashes per track; 23. Enter the maximum sash height, inches; 24. Enter the sash width, inches; 25. Enter the position of the sash sensor from the left edge of the sash, inches; 26. Enter the bypass area per section, square inches; 27. Enter the minimum surface area per section, square inches; 28. Enter top lip height above horizontal sash, inches; Fume hood controller 20 is programmed to control the flow of air through the fume hood by performing a series of instructions, a schematic of which is shown in FIG. Included in the flow chart. After start-up, the information is output to the display to determine the time, and then the controller 20 reads the initial sash positions of all doors (block 15).
0), and then this information is used to calculate the open surface area (block 152). If not previously done, the operator can now set the average face velocity set point (block 154) and this information will later be given along with the open face area, given the previously measured and calculated open area of the fume hood. , Is used to calculate the exhaust flow rate set point (SFLOW) required to give a given average surface velocity (block 1
56). The calculated fume hood exhaust flow setpoint is then compared to a preset or required minimum flow (block 158) and if the calculated setpoint is less than the minimum flow, the controller presets the setpoint flow. And set the minimum flow rate (block 160). If the computation set point is greater than the minimum flow rate, then it is retained (block 16
2), provided to both control loops.

If a variable speed fan drive is present in the fume hood controller, that is, if some fume hoods are not connected to a common exhaust duct and are not controlled by dampers, the controller executes a feedforward control loop (block 164) represents a control operation of the open loop type and gives a control signal to be sent to the addition junction 166. In this control operation, a blower speed estimate is generated based on the calculated opening of the fume hood and the average face speed set point. The predicted value of the blower speed thus generated causes the blower motor to quickly change the speed so as to maintain the average surface speed.
It should be noted that the control of the feedforward mode is called only when the sash position is changed and after that,
When a variable speed blower is used to control the amount of air passing through the fume hood, it should be understood that another control loop performs the predominant control action to keep the average face velocity constant. Is.

After the sash position has changed and the feedforward loop has established a new air quantity, the control loop switches to a proportional-integral-derivative control loop, which provides the set flow signal to block 168. Performed by block 168, the controller computes the error by determining the absolute value of the difference between the set flow signal and the flow signal measured by the exhaust air flow sensor in the exhaust duct. The calculated error is applied to a control loop called a proportional-integral-derivative control loop (PID) to obtain an error signal (block 170), which error signal is compared with the previous error signal from the previous sample, It is determined whether the error is less than a dead band (block 172). If it is smaller, the previous error signal is block 1
A new error signal is provided at output node 176, and then to summing junction 166, if maintained as shown at 74 but not small. The error after addition is also compared to the previous output signal to determine if it is within the dead zone (block 180) and if so, the previous or previous output is retained (block 182). If outside the dead zone, a new output signal is provided to the damper controller or blower (block 184).

If the previous output is an output, as shown in block 182, the controller determines the measured flow rate (MFLO
W) is read (block 186), then the sash position is read (block 188), the net open surface area is recalculated (block 190), and the new calculated area minus the old calculated area is less than the dead zone. It is determined whether or not (block 192), if smaller, the old area is maintained (block 194), and the error is calculated again (block 168). If the new area minus the old area is not within the dead zone, the controller computes a new exhaust flow rate set point, as shown in block 156.

One of the important advantages of the present invention is that the fume hood controller is suitable for implementing the control strategy very quickly in an iterative manner. The exhaust air flow sensor provides flow signal information that is input to the microprocessor at a rate of about 1 sample every 100 ms, and the control operation described in connection with FIG. 11 is completed about every 100 ms. .. The sash door position signal is sampled by the microprocessor every 200 milliseconds. This iterative sampling and execution of rapid control actions results in a very rapid operation of the controller.
It has thus been found that the movement of the sash door results in an adjustment of the air flow rate and that the average surface velocity is achieved within only about 3-4 seconds after the sash door is repositioned and stopped. This represents a significant improvement over existing fume hood controllers.

If a feedforward control loop is used, the sequence of instructions used to execute this loop is shown in the flow chart of FIG. 12, where the controller uses the exhaust flow set point (SFLOW) to drive the fan drive. The control output of the is calculated (block 200). This control output is shown as signal AO and is calculated as the product of the set flow rate and the slope value plus the intercept point. The intercept point is the value of the fixed output voltage to the fan drive, and the slope in the equation correlates the exhaust flow rate with the output voltage to the fan drive. The controller then reads the duct velocity (DV) (block 202) and takes the previous duct velocity sample (block 204).
Set it as the duct velocity value and start the maximum and minimum delay time timing functions (block 206), which the controller uses to determine if the duct velocity has reached a steady state. That is, the controller determines whether the maximum delay time has elapsed (block 20).
8) If yes, give an output signal at output 210. If the maximum delay time has not elapsed, the controller determines if the absolute difference between the previous duct velocity sample and the current duct velocity sample is less than or equal to the deadband value (block 212). If not less than the deadband value, the controller sets the previous duct value equal to the current duct value sample (block 214) and then restarts the minimum delay timing function (block 216). At the end of this process, the controller again determines if the maximum delay has elapsed (block 208). If the absolute value of the difference between the previous duct velocity sample and the current duct velocity sample is less than the dead zone value, the controller determines whether the minimum delay time has elapsed, and if it has, as shown in block 218. , The output is provided to 210. If not, it is determined again whether the maximum delay time has elapsed.

Looking at the proportional-integral-derivative or PID control loop, the controller implements the PID loop by executing the instructions shown in the flow chart of FIG. The controller uses the error calculated in block 168 (see FIG. 11) in three separate paths.
In the upper path, the controller uses a preselected proportional gain factor (block 220), which is used with the error to calculate the proportional (P) gain (block 222), and the calculated proportional gain is It is output to the addition junction 224.

The controller also uses the error signal to calculate an integral term (block 226), which is equal to the product of loop time and error plus the previous sum of integrals (ISUM), and the resulting calculation. The value is compared to the limit to give a limit to the integral term. This integral term is then used with the previously defined integral gain constant (block 230) from which the controller calculates the integral (I) gain (block 232). The obtained integral gain is obtained by multiplying the constant of the integral gain by the term of the integral sum. The output is then provided to summing junction 224.

The input error is also used by the controller to calculate the differential gain factor. Therefore, the controller inputs the previously defined differential gain factor at block 234 and uses it with the error to differentiate (D).
The gain is calculated (block 236). This differential gain is obtained by multiplying the reciprocal of the time required to execute the PID loop by the differential gain coefficient and multiplying this by the difference obtained by subtracting the previous sample error from the current sample error, and the result is the addition junction. 224.

The control action performed by the controller 20 as shown in FIG. 13 provides three separate gain factors, which provide a very quick way to effect a steady state correction of the air volume through the fume hood. Such PID
The formation of the output signal based on the control loop takes into account not only the magnitude of the error but also the result of the differential gain part of the control, so the change speed of the error is also taken into consideration, and the change in the gain value changes. It is proportional to speed. In other words, the differential gain makes it possible to grasp how fast the actual state is changing, and acts as a "predictor" for minimizing the error between the actual state and the desired state. The integral gain produces a correction signal that is a function of the error integrated over a period of time, thus providing on a continuous basis the correction necessary to bring the actual state closer to the desired state. With a proper combination of proportional, integral, and derivative gains, the processing speed of the loop is increased, and a desired state can be reached without overshooting.

An important advantage of PID control operation is that it compensates for possible variations in the laboratory in which the fume hood is located in a manner not available with other controllers. In a laboratory room with multiple fume hoods connected to a common exhaust manifold, moving the sash door with a separate fume hood connected to a common exhaust manifold typically causes pressure changes in the fume hood exhaust duct. To do. These pressure changes affect the average face velocity of the fume hood that did not move the sash door. However, in the PID control operation, the air flow rate can be adjusted by obtaining the pressure change by the exhaust duct sensor. Opening and closing of the laboratory doors may cause pressure changes within the laboratory, but to a lesser extent, especially if the differential pressure inside the laboratory is maintained below a standard space, such as an outdoor corridor. ..

It is also necessary to calibrate the feedforward control loop, and for this purpose the instructions shown in the flow chart of FIG. 14 are implemented. When performing the initial calibration,
This is preferably done, for example, via a handheld terminal connectable to the operator panel via connector 38. The controller then determines if feedforward calibration is on (block 242) and if so, sets the fan drive analog output to a value of 20% of maximum value,
This is set to the value AO1 (block 244). The controller then sets the previous sample duct velocity (LSDV) as the current duct velocity (CDV) (block 2
46), start both maximum and minimum timers (block 248). The controller verifies steady-state duct velocity as follows. First, it checks whether the maximum timer has expired, and if not, the controller determines whether the absolute value of the difference between the previous sample duct speed and the current duct speed is less than the dead zone (block 20), and if less then the controller determines (block 272) whether the minimum timer has expired. If not, the controller reads the current duct speed (block 274).
If the absolute value of the difference obtained by subtracting the current duct speed from the previous sample duct speed is greater than the dead zone, the previous sample duct speed is set as the current duct speed (block 276), and the minimum timer is restarted (block 278) and the current duct velocity is read again (block 274). If either the maximum timer or the minimum timer has expired, the controller checks the previous analog output value to the fan drive (block 252) and the previous analog output value is 70% of the maximum output value.
(Block 254).
If it is not 70%, set the analog output value to the fan drive to 70% of the maximum value AO2 (block 256).
Set a stable duct speed corresponding to O1. The controller then repeats the procedure for ascertaining steady-state duct velocity when the analog output is AO2 (block 258). If it is 70% of the maximum value, then the duct velocity corresponds to the steady state velocity of AO2 (block 258). Finally, the controller calculates both slope and intercept values (block 262).

As a result of the calibration process, 20% of the analog output value
The duct flow rate at 70% and 70% is determined, and both slope and intercept values can be determined from the measured flow rate so that the feedforward control operation can accurately predict the required fan speed when the sash door is repositioned.

The fume hood controller quickly calculates the uncovered or open area of the fume hood access openings that can be covered by one or more sash doors as described above on a periodic basis of several times per second. Suitable for The actuator 94 is preferably located at the right end of each of the four horizontally moveable doors as shown in FIG. The position pointing capability of switching mechanism 80 provides, for each of the four doors, a voltage level indicative of the position of the corresponding sash door along the associated track. Although each actuator 94 is shown at the right end of the sash door, it could alternatively be located at the left end, or if the relationship between the door width and the actuator is desired and input to the fume hood controller, then substantially each door 94 is shown. It can be placed in any position. However, the actuator 94
It should be understood that a common location, such as the right edge, can simplify the calculation of uncovered openings.

The fume hood shown in FIG. 6 has four horizontally moveable doors 76 housed within a vertically movable frame structure 78, and the fume hood of the present invention. The hood controller is suitable for use with up to four sash doors that are movable in one direction or the horizontal direction and for sash door frames that are movable in the vertical direction. However, the controller has a total of 5 since there are 5 analog input ports in the controller, regardless of whether it is horizontal or vertical.
It can be configured to fit any combination of up to two horizontally and vertically movable doors. For this reason, although not specifically shown in the drawings, it is a vertically movable double sash door, such as found in some commercial fume hoods, and this double sash configuration is itself a horizontally movable single frame structure. It can also be applied to items stored in the body. The fume hood controller of the present invention can handle a vertical double sash door configuration, much like operation for a horizontally movable sash door along two tracks as shown in FIG.

Referring now to FIG. 15, the operation of calculating the uncovered opening of a fume hood with four horizontally movable doors as shown in the embodiment of FIG. 6 in a fume hood controller. A flow chart is shown.
The operation of this flow chart can also be applied to obtain the non-covering area in the embodiment of FIG. The first step is to read the position of each sash door (block 300), which is done by sorting the sash doors and determining the sash door position relative to the left edge of the opening (block 302). It should be noted that the position measurement from the right edge can be easily performed as well, but the left edge is selected here for convenience. The controller then initializes the open area equal to zero (block 304) and then computes the distance between the right edge of the sash door closest to the left edge of the opening and the right edge of the next sash door adjacent to the sash door. (Block 306).

If the difference between the two edges determined by the position of the actuator is greater than the width of the sash door (block 3
08), the net open area is set equal to the net open area + difference−sash door width (block 310) and this value is stored in memory. If the difference is less than the width of the sash door, the program repeats the process for the next two pairs of sash doors (block 3).
12). In any case, the program similarly repeats the processing for the next two pairs of sash doors. After iterating to calculate the open area between all sash doors, the controller checks the distance between the right edge of the closest sash door that corresponds to the left opening and the left edge of the truck (block 314) and determines this left difference. If is less than the width of the sash door (block 316), then the controller checks the distance between the left edge of the furthest sash door and the right edge of the truck, the right difference (block 318). If the left difference is not less than the width of the sash door, the net open area is set equal to the net open area plus the left difference (block 320).

The controller then determines if the right difference is less than the width of the sash door (block 32).
2) If smaller, if there is a fixed area, then the net open area is set equal to the net open area + fixed area (block 324). Here, the fixed area is a bypass area preset by a program. If the right difference is not less than the width of the sash door, the controller
The net open area is determined to be equal to the net open area plus the right difference (block 326). Thus the net open area is
It is defined as the sum of the open areas between each sash door, between the right edge of the rightmost sash door and the right edge of the opening, and between the left edge of the leftmost sash door and the left edge of the opening.

Referring now to FIG. 16, there is shown a flow chart of the operation of the apparatus for determining the uncovered area of the opening of a fume hood having a plurality of vertically movable sash doors. When initially configuring the controller, you need to enter the width of each section, the number of sections, the minimum surface area, that is, the sum of the bypass area and the remaining open area remaining with the sash door closed, and the number of sash doors per section. (Block 330). The controller then sets the area equal to zero (block 332), begins the calculation for the first partition (block 334), and sets the old height equal to zero (block 336). Then, the calculation for the first sash door is started (block 338), the sash position (AI) is read (block 340), and the slope and intercept are entered from the calibration routine described above (block 342) to determine the height of the sash door and section. Is calculated (block 344). The controller then determines if it is the first sash door, and if so, the height of the segment (block 348), then obtains the width of the segment (block 350) and multiplies the height and width. The area is calculated (block 358). If the sash door is not the first sash door, the controller determines whether the height of the compartment and sash is less than the old height, and if less, the height of the compartment is set as the height (block 352) and the next sash door is queried. Targeted (block 35)
4). The old height is then retrieved (block 356) and the controller returns to block 338 to repeat the calculation for another segment and sash door. After considering each sash door of a segment and determining the area of the segment (block 358), the controller determines if the segment area is less than the minimum flow area and if so, sets the area to the minimum flow area. (Block 362). If the section area is greater than the minimum flow area, then the section area is defined equal to the bypass product + the calculated section area (block 364). The area is then calculated as the previous calculated area plus the section area under consideration (block 366) and the controller proceeds to consider the next section (block 368). After considering all partitions, the total area is obtained (block 370).

In accordance with an important feature of the present invention, the device has four sash doors horizontally movable along two sets of trucks, such as the fume hood shown in FIG. It can also be applied to determine the uncovered area of a combination of both vertically and horizontally movable sash doors, where the truck itself is housed in a vertically movable frame structure. As mentioned above, there is also an upper lip 77, a lower lip 79 of the frame 78, and a bypass area 75 having a forward thickness of about 2 inches and the exact dimensions varying depending on the manufacturer's design. As can be seen from the above description, when the frame 78 is in its lowest position, the entire bypass area is "open" and air moves through it. As the frame rises, the portion of the sash door 76 that covers the opening as shown gradually covers the bypass area. In the particular illustrated state of FIG. 6, the horizontally moveable doors overlap each other and are completely closed, but the frame is shown slightly elevated.

To determine the uncovered area of the combined sash door fume hood, the following predetermined steps are performed. The net open area, or uncovered area, is the sum of the vertical (hereinafter "V" in the equation) and horizontal (hereinafter "H" in the equation) areas: net open area = V area + H area where the horizontal area is defined as: H area = H width * {panel height; panel height + top lip height + minimum surface height-sash height; 0) minimum The minimum value of the value} Here, the H width is obtained from the above-described processing operation performed on the sash door that is movable in the horizontal direction. Vertical area (V
Area) is calculated from the following formula: V area = maximum value of (sash height * V width; minimum surface area) Finally, the net surface area is equal to the sum of the net open area and the fixed or bypass area: net Surface area = net open area + fixed area

[0069]

As will be appreciated from the foregoing detailed description, the highly effective and efficient fume hood controller shown in the drawings and described above provides significant advantages over conventional existing controllers. Fume hood controller
It can be configured to control almost any type of fume hood available at the moment and very quickly adjusts the flow rate of air through the fume hood in the event of sash position changes or other fluctuations. With the ability to maintain the average face velocity at the desired value, such adjustment results in steady state operation within about 3-4 seconds.

While various embodiments of the present invention have been shown and described,
It should be understood that various alternatives, substitutions and equivalents can be used, and the present invention should be limited only by the description of the claims and equivalents thereof.

Various features of the invention are set forth in the appended claims.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of the apparatus of the present invention shown together with a room controller for a monitor and control system for heating, ventilation and air conditioning of a building.

FIG. 2 is a block diagram of a fume hood controller, shown connected to an operator panel shown in a front view.

FIG. 3 is a front schematic view of an exemplary fume hood having a vertically actuatable sash door.

FIG. 4 is a front schematic view of an exemplary fume hood having a horizontally actuatable sash door.

5 is a cross-sectional view substantially taken along line 5-5 of FIG.

FIG. 6 is a schematic front view of an exemplary combined sash fume hood having sash doors operable in both horizontal and vertical directions.

FIG. 7 is an electrical schematic diagram of a plurality of door sash positions showing switching means.

FIG. 8 is a sectional view of door sash position switching means.

FIG. 9 is a schematic diagram of an electric circuit for determining the position of the sash door of the fume hood.

FIG. 10 is a block diagram showing a relative positional relationship between FIGS. 11, 12, 13, 14 and 15, and also constitutes a schematic diagram of an electric circuit for a fume hood controller embodying the present invention.

11 is connected to FIGS. 12, 13, 14 and 15,
1 is a schematic diagram of an electric circuit for a fume hood controller embodying the present invention.

12 is connected to FIGS. 11, 13, 14 and 15;
1 is a schematic diagram of an electric circuit for a fume hood controller embodying the present invention.

FIG. 13 is connected to FIGS. 11, 12, 14 and 15.
1 is a schematic diagram of an electric circuit for a fume hood controller embodying the present invention.

14 is connected to FIGS. 11, 12, 13 and 15;
1 is a schematic diagram of an electric circuit for a fume hood controller embodying the present invention.

FIG. 15 is connected to FIGS. 11, 12, 13 and 14.
1 is a schematic diagram of an electric circuit for a fume hood controller embodying the present invention.

FIG. 16 is a flowchart of the overall operation of the fume hood controller of the present invention.

FIG. 17 is a partial flowchart of the operation of the fume hood controller of the present invention, specifically showing the operation of the feedforward control scheme included in one of the preferred embodiments of the present invention.

FIG. 18 is a partial flow chart of the operation of the fume hood controller of the present invention, showing a proportional gain implementing the present invention,
The operation of the integral gain and differential gain control methods will be particularly shown.

FIG. 19 is a partial flowchart of the operation of the fume hood controller of the present invention, specifically showing the operation of a feedforward control type calibration.

FIG. 20 is a partial flowchart of the operation of a fume hood controller embodying the present invention, particularly showing the operation of calculating the uncovered opening of multiple horizontally movable sash doors.

FIG. 21 is a partial flowchart of the operation of a fume hood controller embodying the present invention, particularly showing the operation of calculating a number of horizontally and vertically movable sash doors uncovered openings.

[Explanation of symbols]

 20 Fume Hood Controller 22 Room Controller 24 Exhaust Controller 34 Operator Panel 40 Display Means (Display) 49 Actual Air Flow Rate Measuring Means (Exhaust Air Flow Rate Sensor) 60, 64, 74 Fume Hood 62, 66, 76 Sash Door 68 Truck 70 Exhaust Duct 78 frame means 80 door position measuring means (switching means, mechanism) 84 resistance means 94 actuator means

Front Page Continuation (72) Inventors Stephen, Arthur, Bradley, West 74 Street, Prairie Village 66208, Kansas, USA 3811 (72) Inventors Stephen, Elle, Frice, Illinois, USA 60060, Mandeline, Cardinal Court 425 (72) Inventor Steven, Dee, Jacob, Hampstead Court, Roselle, 60172, Illinois, USA 344

Claims (32)

[Claims] 1. To control an air flow rate through a fume hood to maintain a predetermined average surface velocity through an uncovered portion of the fume hood having at least one moveable sash door that covers the opening as it is moved. Device in which the fume hood is in communication with an exhaust duct through which air and fumes are exhausted: means for detecting the position of each movable sash door and generating a position signal indicative of the position of the sash door; Means for calculating the size of the uncovered portion of the opening according to the above; means for measuring the actual air flow rate through the exhaust duct and generating an actual flow rate signal indicative of the actual air flow rate through the exhaust duct; controller means Modulating means for varying the flow rate of air through the exhaust duct in response to a control signal received from the; flow rate in response to the position signal and the actual flow rate signal Controller means for controlling the adjusting means to generate the greater of the desired minimum flow signal value or the desired flow signal value as a function of the calculated size of the uncovered portion, wherein the desired flow signal is the opening. Corresponding to a flow rate sufficient to maintain a predetermined average surface velocity through the uncovered portion of the controller and the controller means compares the desired flow rate signal with the actual flow rate signal and is present between both signals. An error signal indicating an error is generated, and further, when the actual flow rate signal exceeds the predetermined minimum flow rate signal, the error signal is reduced to a predetermined minimum value or a control signal for giving a predetermined minimum flow rate is selectively generated. And a controller means for outputting to the modulating means. 2. The fume hood has one sash door that is vertically movable and selectively covers or opens the opening, and the detection means is attached to the sash door as the sash door moves vertically. Elongate resistance means disposed adjacent to the sash door for making contact at different positions along the length by actuator means, the position signal being generated from the detection means as a voltage level indicative of the position of the sash door. The device according to claim 1, wherein 3. The fume hood has a plurality of sash doors that are movable in at least a horizontal direction and selectively cover or open the opening, and the detecting means is provided on each sash door as the sash door moves in the horizontal direction. An elongated resistance means arranged adjacent to the sash door so as to make contact at different positions along the length by means of an associated actuator means, the position signal from the detection means indicating the horizontal position of each sash door The apparatus of claim 1 generated as a voltage level. 4. The plurality of sash doors are mounted on a vertically movable frame means, and the detection means is along its length by actuator means attached to the frame means as the frame means moves vertically. Further elongate resistance means arranged adjacent the frame means for making contact at different locations, the position signal being also generated from the detection means as a voltage level indicative of the vertical position of each sash door. The device according to claim 3. 5. The apparatus of claim 1 wherein said modulating means comprises a motor driven blower means, said motor being controlled by a motor controller which varies the speed of the motor to vary the exhaust air flow rate in said exhaust duct. 6. The apparatus according to claim 1, wherein said modulation means comprises damper means arranged in the exhaust duct, and operating means for changing the position of said damper means to change the flow rate of air passing through the exhaust duct. 7. An apparatus according to claim 1, wherein said air flow rate measuring means comprises a flow rate sensor. 8. The apparatus of claim 1 wherein said air flow measuring means comprises means for measuring the differential pressure across a tube having a series of orifices located within the exhaust duct. 9. The controller means generates the error signal by taking a series of continuous measurement samples of the actual flow rate, wherein the series of samples determines three different coefficients of the error signal. 2. The apparatus according to claim 1, wherein the coefficient components are added to generate the error signal, and the three coefficients are a proportional operation coefficient, an integral operation coefficient, and a differential operation coefficient. 10. The coefficient of integration at any given time is directly proportional to the coefficient of integration calculated by multiplying the immediately preceding sample by the period time of the loop and adding the error measured from the current sample. Item 9. The apparatus according to Item 9. 11. The apparatus of claim 9, wherein the derivative coefficient of motion at any given time is directly proportional to the difference between the error determined from the immediately preceding sample and the current sample divided by the cycle time of the loop. 12. The apparatus of claim 9, wherein the proportional coefficient of motion at any given time is directly proportional to the error determined from the current sample. 13. The modulating means comprises a motor driven blower means, the motor being controlled by a motor controller for varying the speed of the motor, the controller means generating a feedforward control signal for the modulating means, Prohibiting the generation of an error signal during movement of the sash door, the feedforward control signal predicting the actual flow rate of air through the exhaust duct as a function of the calculated size of the cover, after which the controller means 10. The apparatus according to claim 9, wherein the prohibition of occurrence of is removed. 14. The apparatus of claim 13, wherein the feedforward control signal at any given time comprises a slope value multiplied by a predetermined set flow rate value, plus an intercept value. 15. An operator panel attached to said fume hood in a position observable by a worker, said operator panel being connected to said controller means, said operator panel being further calculated for the corresponding fume hood. The average surface velocity is displayed and
The apparatus of claim 1 including display means for displaying other status information regarding the operation of the apparatus. 16. The operator panel includes means for setting the controller means in one of two operating modes, one of the operating modes being a day mode and the other being a night mode, wherein the controller means is of the device. 16. The apparatus of claim 15 including memory means for storing information regarding motion and receiving a separate predetermined average surface velocity value for each of the day and night modes. 17. The operator panel includes connector means connectable to computer means such as having a keyboard, the computer means, when connected to the operator panel, for indicating the parameters and operating values of the fume hood to be controlled by the device. 17. The device of claim 16, which can be defined. 18. The apparatus of claim 17, wherein the parameters and operating values include the number of sash doors, possible movements of the sash doors, physical dimensions of sash doors and fume hood openings, and average face velocity for day and night mode. 19. The apparatus of claim 1 wherein said means for calculating the size of the uncovered portion of said opening comprises computing means located within said controller means. 20. A device for controlling the air flow rate through a plurality of fume hoods to maintain a predetermined average surface velocity through the uncovered portion of each fume hood, the openings being selectively moved as they are moved. Each of the fume hoods has at least one movable sash door that covers, and each of the fume hoods is in communication with an exhaust duct through which air and fumes are discharged, and an exhaust duct for each fume hood is connected to an exhaust system. In communication with each other: means attached to each of the fume hoods for detecting the position of each movable sash door and generating a position signal indicating the position of the sash door; Means for calculating the size of the non-covered portion; actual flow which indicates the actual air flow rate through the exhaust duct by measuring the actual air flow rate through the exhaust duct communicating with each of the fume hoods A means for generating a signal; a modulation means attached to each of the fume hoods for changing the flow rate of air through the exhaust duct in communication with the respective fume hood in response to a control signal received from the controller means; The controller means for controlling the flow rate modulation means attached to each fume hood according to the actual flow rate signal and generating a desired flow rate signal as a function of the calculated size of the uncovered portion, the desired flow rate. A signal corresponding to a flow rate sufficient to maintain a predetermined average surface velocity through the uncovered portion of each fume hood opening, said controller means providing said desired flow rate signal and said actual flow rate signal to each fume hood. An error signal indicating an error existing between the two signals is generated, and the error signal is further reduced to a predetermined minimum value or a predetermined minimum flow rate is maintained. Alternatively the control signal, the controller means for outputting to said modulating means attached to each fume hood; device equipped with. 21. The controller means generates the error signal by taking a continuous series of measured samples of the actual flow rate, wherein three different coefficients of the error signal are determined from the continuous samples. 21. The apparatus according to claim 20, wherein the coefficient components are added to generate the error signal, and the three coefficients are a proportional operation coefficient, an integral operation coefficient, and a differential operation coefficient. 22. The integral coefficient of motion at any given time is directly proportional to the integral coefficient of motion calculated by multiplying the immediately preceding sample by the period time of the loop and adding the error measured from the current sample. Item 21. The device according to item 20. 23. The apparatus of claim 20 wherein the derivative coefficient of motion at any given time is directly proportional to the difference between the error determined from the immediately preceding sample and the current sample divided by the cycle time of the loop. 24. The apparatus of claim 20, wherein the proportional coefficient of motion at any given time is directly proportional to the error determined from the current sample. 25. An apparatus according to claim 20, wherein said modulation means comprises damper means arranged in the exhaust duct and operating means for changing the position of said damper means to change the flow rate of air passing through the exhaust duct. 26. The apparatus of claim 21, wherein the measurement samples are taken approximately every 100 milliseconds. 27. The apparatus of claim 21 wherein said position sensing means is operative to generate a position signal approximately every 200 milliseconds. 28. The apparatus of claim 21 wherein said controller means produces said control signal approximately every 100 milliseconds. 29. To control the air flow rate through the fume hood to maintain a predetermined average surface velocity through the uncovered portion of the fume hood having at least one moveable sash door that covers the opening as it is moved. Device in which the fume hood is in communication with an exhaust duct through which air and fumes are discharged: means for detecting the position of each movable sash door and continuously generating a position signal indicative of the position of each sash door. Means for calculating the size of the uncovered portion of the opening in response to the position signal; means for continuously generating an actual flow signal indicative of the actual air flow rate through the exhaust duct; control received from controller means Modulating means for changing the flow rate of air passing through the exhaust duct according to a signal; controlling the flow rate modulating means according to the position signal and the actual flow rate signal; Controller means for generating a control signal value that maintains a minimum flow rate of, or for generating a desired flow signal value as a function of the calculated size of the uncovered portion, wherein the desired flow signal uncovers the opening. Corresponding to a flow rate sufficient to maintain a predetermined average surface velocity through the section, the controller means comparing the desired flow rate signal and successive instantaneous sampled values of the actual flow rate signal substantially continuously. Generating an error signal having a magnitude directly proportional to the sum of the calculated integral error, the calculated differential error and the calculated proportional error, and further reducing said error signal to a predetermined minimum value or said predetermined signal. An apparatus comprising controller means for continuously generating a control signal for maintaining a minimum flow rate and outputting the control signal to the modulating means. 30. The apparatus of claim 29, wherein the measurement samples are taken approximately every 100 milliseconds. 31. An apparatus according to claim 29, wherein said position detecting means is operative to generate a position signal approximately every 200 milliseconds. 32. The apparatus of claim 21 wherein said controller means produces said control signal approximately every 100 milliseconds.