JP2715023B2 - Device to control the ventilation of the fume hood - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to 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]

BACKGROUND OF THE INVENTION Fume hoods are used in a variety of laboratory environments that provide workplaces where potentially hazardous chemicals are used, and these hoods allow workers to access the interior of the enclosure for experiments and the like. Where possible, it has an enclosure with a movable door at the front that can be opened in various amounts. Typically, the enclosure is connected to an exhaust system that removes harmful fumes so that personnel are not exposed to harmful fumes while working in the hood.

[0003] Fume hood controllers for controlling the flow of air through the enclosure have become increasingly sophisticated in recent years and now maintain precisely the desired flow characteristics and are a function of the desired average surface velocity of the fume hood opening. As a result, fumes can be efficiently exhausted from the enclosure.

[0004] Average surface velocity is generally defined as the flow rate of air entering the fume hood per square foot of open area of the fume hood, the size of the open area being provided in front of the enclosure or fume hood. It depends on the location of one or more movable doors and, for most types of enclosures, on the amount of bypass opening provided when one or more doors are closed.

[0005] Fume hoods include an exhaust that includes one or more blowers that can be driven at a variable speed to increase or decrease the flow of air from the fume hood to compensate for the varying size of the opening or open surface. Exhausted by the system. Alternatively, one blower is connected to an exhaust manifold connected to each duct of a plurality of fume hoods, and a damper is provided in each duct to control the flow rate from each duct to maintain a desired average surface velocity. The flow rate may be modulated.

[0006] The doors of such fume hoods can be opened by raising them vertically to a position often referred to as the sash position, and some fume hoods are typically slidable along two sets of trucks. It has a plurality of doors mounted. In addition, some doors have multiple trucks mounted in a vertically movable frame assembly and are movable both horizontally and vertically.

[0007]

The conventional fume hood controller includes a detecting means for measuring the position of each door and changing the speed of the blower or the position of the damper by using a signal proportional to the detected position. . Although such control represents an improvement in the control of the fume hood, situations have arisen that require further adjustment of the exhaust from the fume hood that cannot be achieved with such a controller. This is in part because such door position sensing results in a prediction of the substantially required blower speed or damper position, and thus the fume hood for each door at a given position without actually measuring the resulting flow rate. It is based on the fact that the required flow rate is maintained to maintain the desired surface velocity over the open area. This type of control is known as an open-loop control method.

It is, therefore, one of the main objects of the present invention to provide an improved fume hood controller and an improved method that eliminate many of the disadvantages of existing controllers.

Another one of the main objects of the present invention is to provide very precise control to maintain the desired average surface velocity of air through the opening area of the fume hood, and to change the position of the door, or It is an object of the present invention to provide an improved apparatus and method designed to provide an extremely fast response time for performing the above control when a situation change that causes a loss of balance occurs.

It is a further object of the present invention to employ a closed loop type of control in which three different types of gains are used to measure the desired surface velocity error, 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.

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

Another object of the present invention is to provide, in some of its embodiments, one or more of the above-described proportional, integral, and derivative gains, in addition to using one of the above to change the open area of the fume hood. It is an object of the present invention to provide an improved method and apparatus using a feed-forward control that is performed when more doors are moved.

It is yet another object of the present invention to provide an improved fume hood control apparatus and method which is easy to incorporate into a heating, ventilation and air conditioning control system of a laboratory room in which the fume hood is located.

Another object of the present invention is to include a small, easy-to-use and effective operator panel located in the fume hood itself, which is easily observed by an operator and convenient for operation. It is an object of the present invention to provide an improved fume hood control device 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 an operator panel with a connector suitable for receiving a hand-held terminal that can be used to change various important parameters related to the operation of the fume hood controller. It is in.

These and other objects will become apparent from the following detailed description of the invention which refers to the accompanying drawings.

[0017]

SUMMARY OF THE INVENTION To achieve the above object, an apparatus according to the present invention is provided which passes through an uncovered portion 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 a fume hood to maintain an average surface velocity, wherein the fume hood is in communication with an exhaust duct through which air and fumes are discharged, wherein the position of each movable sash door is determined. 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 through the exhaust duct, Means for generating an actual flow signal indicative of the actual air flow rate through the exhaust duct; the flow rate of air through the exhaust duct in response to a control signal received from the controller means A modulating means for controlling the flow rate modulating means according to the position signal and the actual flow rate signal, and a desired minimum flow rate signal value or a desired flow rate signal value as a function of the calculated size of the uncovered portion; Controller means for generating a greater one, wherein the desired flow rate signal corresponds to a flow rate sufficient to maintain a predetermined average surface velocity through the uncovered portion of the opening, and wherein the controller means determines that the desired flow rate The signal and the actual flow signal are compared to generate an error signal indicating an error existing between the two signals, and further, when the actual flow signal exceeds the predetermined minimum flow signal, the error signal is reduced to a predetermined minimum value. Controller means for selectively generating a control signal for decreasing or providing a predetermined minimum flow rate and outputting the control signal to the modulating means is provided.

[0018]

In general, the fume hood controller controls the flow of air through the fume hood and determines the effective size of the full opening to the fume hood, including the openings not covered by one or more sash doors. It should be understood that this is to provide a relatively constant average surface velocity of the air traveling 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,
It means moving into the fume hood. As a result,
Since air constantly flows into the fume hood and out of the exhaust duct, workers in the laboratory are protected from exposure to harmful fumes, etc.
Preferably, the predetermined speed is controlled at approximately 75-125 cubic feet per minute per square foot of effective surface area of the uncovered opening. In other words, if one or more sash doors are moved to the maximum open position and the operator gains maximum access to the interior of the fume hood to perform an experiment or the like, the air is maintained to maintain the average surface velocity at a predetermined desired level. Flow must be increased. There are significant differences between the capabilities and effectiveness of various prior art controllers.

Briefly, an improved fume hood that provides many desirable operational benefits to workers performing experiments and other operations using the fume hood, as well as to operators of facilities where the fume hood is located. A controller device is obtained according to the invention. An apparatus embodying the present invention provides very fast and effective control of the average surface velocity of the fume hood, and within a few seconds after movement of one or more doors covering the front opening of the fume hood, the desired average surface velocity Achieve and maintain. Also, when other fluctuations occur in the laboratory environment where one or more fume hoods are located, the controller of the present invention reacts quickly to stabilize to maintain the desired flow conditions.

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

[0021]

1, there is shown 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 by multi-conductor cables 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 including the fume hood is located.

The room controller 22 is preferably one capable of supplying at least a variable amount of air to the room.
It can be an ndis & Gyr Powers system 600 SCU controller. Room controller 22 is LAN line 2
8 can be communicated. The room controller is preferably a system 600 SCU controller, which is a commercially available controller for which extensive documentation exists. In particular, the User's Reference Manual for the System 600 SCU Controller, Part Nos. 125-1753, is hereby incorporated by reference.

The room controller 22 receives via line 81 a signal from each fume hood controller 20, which provides an analog input signal indicating the amount of air being exhausted by each fume hood, and exhausts the fume hood. And a comparison signal from an exhaust flow sensor which gives an indication of the amount of air being exhausted through another main exhaust system. By combining these signals with the signal provided by the differential pressure sensor 29 indicating the pressure in the room relative to the standard space, the room controller can maintain the differential pressure in the room at a slightly lower pressure than the standard space. The supply of necessary air can be controlled. Such a system,
No. 52497, assigned to Ahmed et al., Assigned to the same assignee as the present application and included in the aforementioned cross-referenced application, entitled "System for controlling differential pressure in a room having a fume hood for a laboratory".
Is disclosed.

The fume hood controller 20 is supplied with power through a line 30 at an appropriate voltage, such as via a transformer 32.

Referring to FIG. 2, the fume hood controller 20 is shown with the functions of its input and output connector ports explicitly shown, and the fume hood controller 20 is 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 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-wire RJ
It has a connector 38 such as an 11-inch telephone jack, and a laptop personal computer or the like is connected to the connector 38 in order to input information about the configuration and operation of the fume hood at the time of initial setting or to change some operation parameters if necessary. Connectable. The operator panel 34
Is preferably attached to the fume hood at a convenient location that is easy to observe by workers working in the fume hood.

The operator panel 34 of the fume hood controller includes a liquid crystal display 40, which is selectively energized to provide visual indication of various aspects of the fume hood, including a three digit 42 for providing average surface speed. Display 4
0 also indicates other conditions such as low surface speed, high surface speed, emergency status, and indication of controller failure. The operator panel 34 may also have an alarm 44 and an emergency purge switch 46 that can be pressed by an operator 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 modes of operation. In the night time mode of operation, it is conceivable to have a different, preferably lower, average surface velocity than the day time mode. Nobody is working indoors late at night, and such a low average surface speed is expected to save energy. Preferably, an alarm silence switch 50 is also provided.

The fume hood can be of many different styles, sizes and shapes, including those having one or multiple sash doors, and those in which the sash doors can move vertically, horizontally or in both directions. Also, the various fume hoods have different bypass flow rates, i.e. different flow rates through the openings that are also present when all sash doors are closed as completely as possible by design. Other design factors also include whether there is any type of filtering means in the fume hood that traps the fumes 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 the ventilation of the fume hood Effective and extremely quick control of the vehicle.

Referring to FIG. 3, there is shown a fume hood, generally indicated at 60, wherein the fume hood 60 is movable to provide access to the fume hood and is in a substantially closed position as shown. And has a vertically operated sash door 62 that is movable to The fume hood is generally designed so that even when a door sash, such as door sash 62, is completely closed, there is a certain amount of opening through which air can pass through the fume hood. This opening is commonly referred to as a bypass region, and can be determined such 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. Also, in some fume hoods, the initial displacement of the sash door increases, for example, the opening at the bottom of the door shown in FIG. 3, but as it rises, the door blocks the bypass opening, and the total opening of the fume hood increases. The effective size is kept relatively constant during the first approximately one-quarter travel of the sash door 62 along the travel path.

Another type of fume hood includes several horizontally movable sash doors 66 as shown in FIGS.
Each door may be movable along. When the door is located as shown in FIGS. 4 and 5, the opening of the fume hood is completely closed and the worker can move the door horizontally to gain access into the fume hood. Fume hood 6
Both 0 and 64 have an exhaust duct 70 that typically extends to the exhaust system, which may be for an HVAC device as described above. The fume hood 64 includes a filter filtration structure, indicated generally at 72, which prevents harmful fumes and other contaminants from exiting 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, the fume hood 74 having a frame structure 78 supporting the door 76 along a suitable truck. And the frame structure 78 is vertically movable within the fume hood opening.

FIG. 6 includes an omission, indicated by dashed line 73, which is used to raise the frame structure 78 sufficiently to allow personnel to properly access the interior of the fume hood. It is intended to indicate that the height of the hood can be greater than shown. Generally, there is a bypass region, shown as vertical region 75,
There is also typically a top lip 77 that can be about 2 inches wide. This dimension is preferably determined such that its influence on the calculation of the open surface area can be taken into account.

Although not specifically shown, two or more sash doors, such as two or more sash doors that are vertically movable along adjacent tracks, are similar to each other in a fence hood opening. Other combinations are also possible, including a plurality 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 the fume hoods of various sizes and configurations as described above, and may include several fume hoods, as well as a building. It is mounted in a laboratory room that may have an exhaust duct that joins a common exhaust manifold that may be part of the HVAC system. The fume hood can be one independent or have its own separate exhaust duct. If one fume hood is installed, such equipment has a blower driven by a variable speed motor and attached to an exhaust duct, and the motor and blower are arranged to regulate the flow of air through the fume hood. Generally, the speed can be variably controlled. Alternatively, in the most common case where there are multiple fume hoods in one area, the exhaust duct of each fume hood may be one
One or more larger exhaust manifolds may be merged and one large blower may be provided in the manifold system. In such equipment, since the control of each fume hood is performed by a separate damper disposed in each fume hood, it is possible to control the flow change by appropriately positioning the damper attached to each fume hood. .

The fume hood controller is capable of controlling virtually any of various types and styles of fume hoods on the market, and therefore has a large number of input / output ports () that can be connected to various sensors used in the controller. Lines, connectors or connections, all of which are considered equivalent for purposes of describing the present 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 a variable speed fan drive is provided in an analog system. If so, it also has an analog voltage output port for controlling the drive. Used to detect the position of a sash that can be moved both horizontally and vertically 5
There are also two sash position sensor ports and an analog input port connected to the exhaust air flow 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 signal to the room controller 22 is also provided. In some applications where an exhaust air flow sensor is not provided, a wall speed sensor that indicates the surface speed may be used, in which case an input port for the signal is provided, but such a sensor generally loses accuracy. It is considered, and its use is not a preferred embodiment. With the various ports described above, virtually any type of fume hood can be controlled in an effective and efficient manner.

From the above description, if the desired average surface velocity is to be maintained while changing the sash position, the size of the opening changes greatly. Therefore, a large change in the amount of air is required to maintain the average surface velocity. It should be understood that it is necessary. Although 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 responds quickly to changes in the system. The known method is improved by incorporating an additional control scheme which greatly improves in maintaining the average surface speed of the control.

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

The polyester material is sufficiently flexible so that one layer can move toward and contact the other layer in response to the actuator 94 supported by the corresponding sash door with the strips arranged next to each other. 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 along the length of the switching mechanism 80.
Voltage output indicating the absolute position of That is, by the actuator 94 being supported by the sash door,
Provide a voltage indicating the absolute position of the sash door.

Actuator 94 applies sufficient pressure to switching mechanism 80 as the sash door moves,
Preferably, the two base layers abut and the resistive and conductive layers make electrical contact with each other and are spring biased toward the switching mechanism 80 such that a voltage level is provided in response to the electrical contact. . By making the switching mechanism 80 long enough to cover the entire range of movement of the sash door as shown in FIG. 3, the sash position can be determined accurately. It should be noted that the switching mechanism 80 shown in FIGS. 3 and 5 is only an outline, and in practice, the switching mechanism 80 is preferably arranged in the sash frame itself, and cannot be seen from the outside as shown. Since the width and thickness dimensions of the switching mechanism 80 are small, interference with the operation of the sash door is practically not a problem. The actuator 94 may be placed in a small hole drilled in the sash door, or attached to the outside of one end of the sash door, so that the switching mechanism 80 is operated. 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 Preferably, the switching mechanism 80 is located on top of the track 68 so that the weight of the switching mechanism 80 does not affect or damage the switching mechanism 80. Also,
Among the cross-referenced applications mentioned above, the application of Egbers et al., Titled "Device for finding the position of the movable structure along the 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 generating a position indicating voltage which is suitable for providing two separate voltages indicative of the absolute position of two sash doors within one track. . Referring to the cross-sectional view shown in FIG. 5, there are two horizontal tracks each supporting two sash doors, and the same circuit as that shown in FIG. 9 is provided for each track, including the switching mechanism 80, A separate voltage is 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 and an actuator 94 abuts 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 track, is shown. The switching mechanism 80 is provided on each track, and four arrows in the figure represent 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 reduced. It represents a voltage proportional to the distance between each end and the closest arrow. Thus, one switching mechanism 80 provides an absolute position indicating signal for the two doors arranged on each track. The circuit used to implement the above voltage generation is shown in FIG. 9, where one circuit is provided 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 the two arrows at the other end point to the respective actuator 9 attached to two separate doors.
4 represents the point of contact 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 which is directly connected to a positive voltage source via a resistor 104 to the operational amplifier 100. Connected to the negative input of the
Is also connected to a positive voltage source, preferably about 5 volts. The collector of the transistor 102 is a resistance element 8
4 has an output line 106 at which a voltage indicative of the absolute position of the door is generated.

The circuit operates to provide a constant current toward the resistive element 84 which produces a voltage proportional to the resistance between the collector and ground, which varies as the closest contact point along the resistor changes. Occurs on output line 106. Operational amplifier 100 operates to drive the negative input to equal the voltage level of the positive input, so that the output of the operational amplifier is provided with a current 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, and outputs a voltage proportional to the distance between the connection end of the resistive element 84 and the point of contact by the actuator 94 attached to the other sash door in the track on the output line 10.
8 occurs similarly.

Referring to the composite electrical schematic of the fume hood controller circuit, FIG.
When the respective drawings d and 10e are arranged side by side as shown in FIG. 10, an electric schematic diagram of the entire fume hood controller 20 is obtained. The operation of the circuits of FIGS. 10a to 10e will not be described in detail. The circuitry is driven by a microprocessor and the key algorithms that implement the control functions of the fume hood controller will be described later. FIG.
Referring to FIG. 3C, the circuit shown in FIG.
Motorola MC68 to which MHz clock input is applied
HC11 microprocessor 120 is included. Microprocessor 120 has a data bus 124 connected to a three-state buffer 126 (FIG. 10d), and buffer 126 is connected to an electrically programmable read-only memory (EPROM) 128 also connected to data bus 124. ing. EPROM 128 is a three-state buffer 12
6 and 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 that transmits and receives information via a hand-held terminal
An S232 driver 136 is provided. The circuit shown in FIG. 9 is also shown as a comprehensive schematic in FIGS. 10a and 10b. The other components are well known and need not be described in particular.

As mentioned above, the apparatus of the present invention employs an air flow sensor which is preferably located within the exhaust duct 70 to measure the amount of air being drawn through the fume hood. Air flow may be calculated by measuring the differential pressure between both sides, such as a multi-point pitot tube. In a preferred embodiment, a differential pressure sensor that measures the flow through the exhaust duct is used, and the device of the present invention maintains the flow through the fume hood at a predetermined average surface velocity, or when the fume hood is closed, When a small bypass region is used, a control method for maintaining the minimum speed is used.

The fume hood controller of the present invention is applicable to almost any type of known fume hood, including a horizontally movable sash door, a vertically movable sash door, or a combination of both.
As apparent 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 operating characteristics of the fume hood and other initialization information. Such information can be input to the fume hood controller by a hand-held terminal, 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 mode of operation may be provided, but this is not a preferred embodiment of the system, and if provided, information regarding day / night operation should be included.

Operation information: 5. Time; 6. Day and night setting of average surface velocity (SVEL), feet per minute or meters per second; 7. Day and night setting of minimum flow (MINFLO), cubic feet per minute; 8. High speed limit (HVEL) day / night value setting, F / m or M / sec; 9. Day / night setting of low speed limit (LVEL), F / m or M / sec; 10. Mid-high speed limit (MVEL) day / night value setting, F / m or M / sec; 11. Mid / low speed limit (IVEL) day / night setting, F / m or M / sec; 12. Proportional gain coefficient (KP) setting, analog output per error, percent; 13. setting of integral gain factor (KI), product of analog output and minute time per error, percent; 14. setting of differential gain coefficient (KD), product of analog output and minute time per error, percent; The 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 continue full exhaust flow when the emergency switch is operated (DELTIME)
Set in seconds.

17. Emergency switch operated, DELT
When the IME expires, set a preset percentage (SAFLOQ) of the final exhaust flow that the user wants to keep.

The above information controls the mode of operation and is used to control the flow limit during the day or night mode of operation. The controller 20 includes programmed instructions for calculating each of the steps 3-7 if the relevant information is not provided by the user. Therefore, when the day / night value of the average surface speed is set, the controller 20 sets the high speed limit, which is 120% of the average surface speed, to 80%.
Is calculated, and a medium speed limit of 90% is calculated. It should be understood that these percentages can 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 not be necessary for a sash door that can be moved only vertically or horizontally, but all information is required for a combination of both. The required information includes a vertical section with defined height and width dimensions that are covered by one or more sash doors. If more than one sash door is provided in each section, the doors will be vertically movable sash doors, similar to a double sash residential window.
The information to be provided includes: Enter the number of segments in the vertical direction; 20. Enter the height of each section, inches; 21. Enter the width of each section, inches; 21. Enter the number of tracks for each section; 22. Enter the number of horizontal sashes per track; Enter the maximum sash height, inches; Enter sash width, inches; 25. Enter sash sensor position from left edge of sash, inches; 26. Enter bypass area per section, square inches; 28. Enter minimum surface area per section, square inches; Enter the top lip height above the horizontal sash, in inches; the fume hood controller 20 is programmed to control the flow of air through the fume hood by performing a series of commands, schematically shown in FIG. It is included in the flowchart. After starting, the information is output to the display and the time is obtained, and then the controller 20 reads the initial sash positions of all the doors (block 15).
0), then this information is used to calculate the open area (block 152). If not previously done, the operator can now set the average surface velocity set point (block 154), and this information is later taken together with the open surface area, given the previously measured and calculated fume hood open area. , Used to calculate the required exhaust flow set point (SFLOW) to provide a predetermined average surface velocity (block 1)
56). The calculated fume hood exhaust flow set point is then compared to a preset or required minimum flow (block 158), and if the calculated set point is less than the minimum flow, the controller presets the set point flow. The minimum flow rate is set (block 160). If the operation set point is larger than the minimum flow rate, it is kept as it is (block 16).
2), given to both control loops.

If there is a variable speed fan drive in the fume hood controller, ie if some fume hoods are not connected to a common exhaust duct and are not controlled by a damper, the controller executes a feedforward control loop (block 164), which represents a control operation of the open-loop type, and provides a control signal sent to the addition junction 166. In this control operation, a predicted value of the blower speed is generated based on the calculated opening of the fume hood and the average surface speed set point. The predicted value of the generated blower speed causes the blower motor to change its speed quickly so as to maintain the average surface speed.
Note that the control of the feed forward mode is called only when the sash position is changed and after it is changed,
If 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 dominant control action to keep the average surface velocity constant. It is.

After the sash position has changed and the feedforward loop has established a new air volume, the control loop switches to a proportional-integral-differential control loop, in which the set flow signal is provided to block 168. In block 168, the controller calculates 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 provided to a control loop called a proportional-integral-differential control loop (PID) to determine an error signal (block 170), which is compared to a previous error signal from a previous sample, It is determined whether the error is less than a dead band (block 172). If smaller, the previous error signal is block 1
Maintained as shown at 74, but if not small, a new error signal is provided at output node 176 and further to summing junction 166. 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 not, 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) (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 smaller than the dead zone. A determination is made (block 192), if so, 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 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 a control strategy very quickly in an iterative manner. An exhaust air flow sensor provides flow signal information, which is input to the microprocessor at a rate of about one sample every 100 milliseconds, and the control operations described in connection with FIG. 11 are completed approximately every 100 milliseconds. . The sash door position signal is sampled by the microprocessor every 200 milliseconds. This rapid repetitive sampling and execution of control actions results in a very quick action of the controller.
Thus, it has been found that movement of the sash door results in adjustment of the air flow rate and achieves an average surface velocity 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 feed-forward 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. 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 speed (DV) (block 202) and retrieves the previous duct speed sample (block 204).
It sets the duct speed value and starts the maximum and minimum delay timing functions (block 206), which the controller uses to determine if the duct speed has reached a steady state. That is, the controller determines whether the maximum delay time has elapsed (block 20).
8) If the time has elapsed, give an output signal to the output 210. If the maximum delay has not elapsed, the controller determines whether the absolute value of the difference between the previous duct speed sample and the current duct speed sample is less than or equal to the deadband value (block 212). If not, 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 conclusion of this process, the controller again determines whether the maximum delay has elapsed (block 208). If the absolute value of the difference between the previous duct speed sample and the current duct speed sample is less than the dead zone value, the controller determines whether the minimum delay time has elapsed and, if so, as shown in block 218. , The output is provided to 210. If not, it is determined again whether the maximum delay time has elapsed.

Referring to the proportional-integral-differential or PID control loop, the controller executes the PID loop by executing the commands shown in the flowchart 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 error to calculate a proportional (P) gain (block 222), and the calculated proportional gain is The signal 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 the loop time and the error plus the previous integral sum (ISUM), resulting in a calculated result. The value is compared to the limit to place a limit on the integral term. This integral term is then used with the previously defined integral gain constant (block 230), and the controller calculates the integral (I) gain therefrom (block 232). The obtained integral gain is obtained by multiplying the integral gain constant by the integral sum term. Thereafter, the output is provided to summing junction 224.

The input error is also used by the controller to calculate the derivative gain factor. To this end, the controller inputs the previously defined derivative gain coefficient at block 234 and uses this together 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 the difference by subtracting the previous sample error from the current sample error. 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 of modifying the steady state 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. 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 "prediction factor" 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 time, thus providing the necessary corrections to bring the actual state closer to the desired state on a continuous basis. With an appropriate combination of the 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 the PID control operation is that it compensates for variations that may occur in the laboratory where 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 the common exhaust manifold typically causes pressure changes in the fume hood exhaust duct. I do. These pressure changes affect the average surface 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 determining a change in pressure using an exhaust duct sensor. To a lesser extent, the opening and closing of the laboratory's own doors can cause pressure changes in the laboratory, especially if the differential pressure in the laboratory room is maintained at a pressure lower than the standard space, for example, 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 initial calibration,
Preferably, for example, via a hand-held terminal that can be connected to the operator panel via connector 38. The controller then determines whether feedforward calibration is on (block 242), and if so, sets the analog output of the fan drive to a value of 20% of the maximum value;
This is set to the value AO1 (block 244). Thereafter, the controller sets the previous sample duct speed (LSDV) as the current duct speed (CDV) (block 2).
46) Start both the maximum and minimum timers (block 248). The controller determines the steady state duct speed as follows. First, the controller checks whether the maximum timer has expired. If not, the controller determines whether the absolute value of the difference between the previous sample duct speed minus the current duct speed is equal to or less than the dead zone (block 20) If so, the controller determines whether the minimum timer has expired (block 272). 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 larger 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 276). 278), the current duct speed 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.
It is inquired as to whether or not (block 254).
If it is not 70%, the analog output value to the fan drive is set to 70% of the maximum value AO2 (block 256).
A stable state duct speed corresponding to O1 is set. The controller then repeats the procedure for determining a steady state duct speed when the analog output is AO2 (block 258). If it is 70% of the maximum, the duct speed corresponds to the steady state speed 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
And 70% duct flow is determined, and both slope and intercept can be determined from the measured flow so that the required fan speed can be accurately predicted by the feedforward control operation when the position of the sash door is changed.

The fume hood controller quickly calculates the uncovered or open area of the fume hood access opening, which can be covered by one or more sash doors as described above, on a periodic basis several times per second. Suitable for The actuator 94 is preferably arranged at the right end of each of the four horizontally movable doors as shown in FIG. The position indicating capability of the 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 may alternatively be located at the left end, or if the relationship between the door width and the actuator is determined and input to a fume hood controller, then substantially each door is substantially It can be placed at any position. However, the actuator 94
It is to be understood that the placement of the common position, such as the right end, can simplify the calculation of uncovered openings.

The fume hood shown in FIG. 6 has four horizontally movable doors 76 which are housed within a vertically movable frame structure 78, and the fume hood of the present invention. The food controller is suitable for use with up to four sash doors that can be moved in one direction, i.e., horizontally, and sash door frames that can be moved in a vertical direction. However, the controller has a total of 5 analog input ports, regardless of whether it is horizontal or vertical, for inputting position information, since the controller has 5 analog input ports.
Configurable to fit any combination of up to three horizontally and vertically movable doors. For this reason, although not specifically shown in the drawings, a vertically movable double sash door such as that found in some commercial fume hoods, the double sash configuration being itself a single horizontally movable frame structure It can also be applied to those stored inside the body. The fume hood controller of the present invention can handle a vertical double sash door configuration in much the same way as operating on a sash door that can move horizontally along two tracks as shown in FIG.

Referring now to FIG. 15, the fume hood controller calculates the uncovered portion of the fume hood opening with four horizontally movable doors as shown in the embodiment of FIG. A flowchart is shown.
The operation of this flowchart can be applied to obtain the uncovered area in the embodiment of FIG. The first step is to read the position of each sash door (block 300), which is done by classifying the sash doors and determining the sash door position relative to the left edge of the opening (block 302). Although the position measurement from the right edge can be easily performed, 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 that sash door. (Block 306).

If the difference between the two edges determined by the position of the actuator is larger than the width of the sash door (block 3)
08), net open area is set equal to 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 as shown (block 3).
12). In any case, the program repeats the same process for the next two pairs of sash doors. After performing an iteration to calculate the open area between all sash doors, the controller checks the distance between the right edge of the nearest sash door and the left edge of the truck, which corresponds to the left opening (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 determined equal to the net open area plus the left difference (block 320).

The controller then determines whether the right difference is less than the width of the sash door (block 32).
2) If less, if there is a fixed area, the net open area is set equal to the net open area plus the fixed area (block 324). Here, the fixed area refers to a bypass area preset in a program. If the right difference is not less than the width of the sash door, the controller:
A determination is made that the net open area is 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 the fume hood having a plurality of vertically movable sash doors. When configuring the controller for the first time, it is necessary to enter the width of each section, the number of sections, the minimum surface area, i.e., the sum of the bypass area and other remaining open areas when the sash door is closed, and the number of sash doors per section. There is (block 330). The controller then sets the area equal to zero (block 332), begins the calculation for the first section (block 334), and sets the old height equal to zero (block 336). Thereafter, the calculations for the first sash door begin (block 338), the sash position (AI) is read (block 340), and the slope and intercept from the calibration routine described above are entered (block 342), and the height of the corresponding sash door and section is reached. Is calculated (block 344). Next, the controller determines whether it is the first sash door, and if so, the section height (block 348), then obtains the section width (block 350) and multiplies the height by the width. The area is calculated (block 358). If the sash door is not the first sash door, the controller determines whether the section and sash heights are less than the old height; if so, the section height 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 calculations for another section and sash door. After considering each sash door in a section and determining the area of the section (block 358), the controller determines whether the section 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, the section area is determined equal to the bypass product plus the calculated section area (block 364). The area is then calculated as the previous calculated area plus the partition area to be considered (block 366), and the controller proceeds to consider the next partition (block 368). After considering all partitions, the total area is obtained (block 370).

In accordance with an important feature of the present invention, the apparatus has four sash doors that can be moved horizontally 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 vertically and horizontally movable sash doors in which 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 front thickness of about 2 inches, the exact dimensions of which depend on the design of the manufacturer. As will be appreciated from the foregoing description, when the frame 78 is in its lowest position, the entire bypass area is "open" and air moves therethrough. 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 movable doors are completely closed one above the other, but the frame is shown slightly elevated.

To determine the uncovered area of the combined sash door type fume hood, the following predetermined steps are performed. The net open area, or uncovered area, is the sum of the vertical (hereinafter referred to as "V") area and the horizontal (hereinafter referred to as "H") area: Net open area = V area + H area Here, the horizontal area is defined as follows: H area = H width * ｛panel height; panel height + top lip height + minimum surface height−sash height; minimum of 0) Here, the H width is obtained from the above-described processing operation performed on the sash door movable in the horizontal direction. Vertical area (V
The area is determined from the following equation: 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 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. The fume hood controller is
It can be configured to control almost any type of fume hood available at the moment, and adjusts the flow rate of air through the fume hood very quickly, even if the sash position is changed or otherwise fluctuated. With the ability to maintain the average surface speed at the desired value, such adjustment will result 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 may be used, and the present invention is limited only by the following claims and equivalents thereof.

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

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of the apparatus of the present invention shown in conjunction with a room controller for monitoring and controlling heating, ventilation and air conditioning of a building.

FIG. 2 is a block diagram of the fume hood controller, shown connected to an operator panel showing 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 schematic front view of an exemplary fume hood having a horizontally actuatable sash door.

FIG. 5 is a sectional view taken substantially along the line 5-5 in FIG. 4;

FIG. 6 is a front schematic view of an exemplary combination sash fume hood having a sash door 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 a door sash position switching means.

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

FIG. 10 is a block diagram showing a relative positional relationship among 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 view of an electric circuit for a fume hood controller embodying the present invention.

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

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

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

FIG. 15 is linked to FIGS. 11, 12, 13 and 14;
1 is a schematic view 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 flowchart of a part of the operation of the fume hood controller of the present invention, particularly illustrating the operation of the feedforward control method included in one of the preferred embodiments of the present invention.

FIG. 18 is a partial flowchart of the operation of the fume hood controller of the present invention, showing a proportional gain embodying the present invention;
In particular, the operation of the integral gain and differential gain control schemes is shown.

FIG. 19 is a flow chart of a part of the operation of the fume hood controller of the present invention, specifically illustrating the operation of the feedforward control type calibration.

FIG. 20 is a flow chart of a portion of the operation of a fume hood controller embodying the present invention, specifically illustrating the operation of calculating the uncovered openings of a number of horizontally movable sash doors.

FIG. 21 is a flow chart of a portion of the operation of a fume hood controller embodying the present invention, specifically illustrating the operation of calculating the uncovered openings of a number of horizontally and vertically movable sash doors.

[Explanation of symbols]

 Reference Signs List 20 fume hood controller 22 room controller 24 exhaust controller 34 operator panel 40 display means (display) 49 actual air flow measuring means (exhaust air flow 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

Continuing the front page (72) Inventor Stephen, El, Fritche, United States, 60060, Illinois, Mandelain, Cardinal Court 425 (72) Inventor Steven, Dee, Jacob United States, Illinois 60172, Roselle, Hampstead Court 344

Claims (32)

(57) [Claims] 1. A method for controlling air flow through a fume hood so as to maintain a predetermined average surface velocity through an uncovered portion of the fume hood opening having at least one movable sash door covering the opening as it is moved. Means for detecting the position of each movable sash door and generating a position signal indicating the position of the sash door, wherein the fume hood is in communication with an exhaust duct for discharging air and fumes therefrom; Means for calculating the size of the uncovered portion of the opening in response to the signal; means for measuring the actual air flow rate through the exhaust duct and generating an actual flow signal indicative of the actual air flow rate through the exhaust duct; Modulating means for changing a flow rate of air passing through the exhaust duct in response to a control signal received from the controller means; Controller means for controlling the flow rate modulating means to generate the larger of a predetermined minimum flow signal value or a desired flow signal value as a function of the calculated size of the uncovered portion, Corresponds to a flow rate sufficient to maintain a predetermined average surface velocity through the uncovered portion of the opening, and the controller means compares the desired flow rate signal with the actual flow rate signal and determines between the two signals. Generating an error signal indicating an error existing in the control signal, and further selecting a control signal that reduces the error signal to a predetermined minimum value or provides a predetermined minimum flow rate when the actual flow rate signal exceeds the predetermined minimum flow rate signal. A controller means for controlling the ventilation of the fume hood. 2. The fume hood has one sash door movable vertically and selectively covering or opening the opening, and the detecting means is attached to the sash door as the sash door moves vertically. Elongate resistance means positioned adjacent to the sash door so as to make contact at different locations along the length by the actuator means, wherein the position signal is generated from the detection means as a voltage level indicative of the position of the sash door. The apparatus for controlling ventilation of a fume hood according to claim 1, wherein: 3. The fume hood has a plurality of sash doors which are movable at least in a horizontal direction and selectively cover or open the opening, and wherein the detecting means is provided on each sash door as the sash doors move in a horizontal direction. Elongate resistance means disposed adjacent to the sash door so as to make contact at different locations along the length by associated actuator means, the position signal indicating from the detection means the horizontal position of each of the sash doors. 2. The device for controlling ventilation of a fume hood according to claim 1, wherein the device is generated as a voltage level. 4. A plurality of sash doors are mounted on vertically movable frame means, and said detecting means is moved along a length by actuator means attached to said frame means as said frame means moves in a vertical direction. A further elongated resistance means arranged adjacent to the frame means to make contact at different positions, wherein the position signal is also generated from the detection means as a voltage level indicative of a vertical position of each of the sash doors. The apparatus for controlling ventilation of a fume hood according to claim 3, wherein: 5. The apparatus according to claim 1, wherein said modulating means comprises a blower means driven by a motor, and said motor is controlled by a motor controller which changes a speed of a motor to change a flow rate of exhaust air in said exhaust duct. An apparatus for controlling ventilation of a fume hood according to claim 1. 6. The apparatus according to claim 1, wherein said modulating means comprises damper means disposed in the exhaust duct, and operating means for changing a position of the damper means to change a flow rate of air passing through the exhaust duct. An apparatus for controlling ventilation of a fume hood according to claim 1. 7. An apparatus for controlling ventilation of a fume hood according to claim 1, wherein said air flow measuring means comprises a flow sensor. 8. The ventilation of a fume hood according to claim 1, wherein said means for measuring air flow comprises means for measuring the differential pressure across a tube located in an exhaust duct and having a series of orifices. Device to control the. 9. The controller means for generating the error signal by taking a continuous series of measurement samples of the actual flow rate, wherein three different coefficients of the error signal are determined from the continuous samples. 2. The apparatus for controlling ventilation of a fume hood according to claim 1, wherein the error signal is generated by adding the coefficient components of the above-mentioned equation (1), and the three coefficients comprise a proportional operation coefficient, an integral operation coefficient, and a differential operation coefficient. . 10. The integral operating coefficient at any given point in time is directly proportional to the integral operating coefficient calculated by multiplying the immediately preceding sample by the period time of the loop and adding the error measured from the current sample. The apparatus for controlling ventilation of a fume hood according to claim 9, characterized in that: 11. The method according to claim 1, wherein the differential operating coefficient at any given point in time is directly proportional to the difference between the error obtained from the previous sample and the current sample divided by the cycle time of the loop. An apparatus for controlling ventilation of a fume hood according to claim 9. 12. The apparatus for controlling ventilation of a fume hood according to claim 9, wherein said proportional coefficient of operation at any given time is directly proportional to the error determined from the current sample. 13. The modulating means comprises a blower means driven by a motor, the motor being controlled by a motor controller for changing a speed of the motor, wherein the controller means generates a feedforward control signal for the modulating means, Prohibiting the generation of an error signal during the 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, and then the controller means 10. The apparatus for controlling ventilation of a fume hood according to claim 9, wherein the prohibition of the generation of the smoke is released. 14. The fume hood of claim 13, wherein said feedforward control signal at any given point in time comprises a slope value multiplied by a predetermined set flow rate value plus an intercept value. A device that controls the ventilation of the house. 15. An operator panel attached to the fume hood at a position observable by an operator, the operator panel being connected to the controller means, wherein the operator panel is calculated for a corresponding fume hood. Average surface velocity
2. The apparatus for controlling ventilation of a fume hood according to claim 1, further comprising display means for displaying other status information on the operation of the apparatus. 16. The operator panel includes means for setting the controller means to one of two operation modes, one of the operation modes being a day mode and the other being a night mode, and wherein the controller means is for operating the apparatus. 16. Apparatus for controlling ventilation of a fume hood according to claim 15, including memory means for storing information relating to operation and receiving a separate predetermined average surface velocity value for each of said day and night modes. 17. The operator panel includes connector means connectable to computer means such as having a keyboard, and when connected to the operator panel, the computer means sets parameters and operating values of a fume hood to be controlled by the device. 17. The device for controlling ventilation of a fume hood according to claim 16, wherein the device can be defined. 18. The system according to claim 17, wherein said parameters and operating values include the number of sash doors, possible movements of the sash doors, physical dimensions of the sash doors and fume hood openings, and average surface speed for day and night modes. A device to control the ventilation of the fume hood. 19. The apparatus for controlling ventilation of a fume hood according to claim 1, wherein said means for calculating the size of the uncovered portion of said opening comprises arithmetic means disposed in said controller means. . 20. An apparatus for controlling air flow through a plurality of fume hoods to maintain a predetermined average surface velocity through the uncovered portion of each fume hood opening, wherein the openings are selectively moved as they are moved. Each fume hood has at least one movable sash door covering the fume hood, and each of the fume hoods is connected to an exhaust duct for discharging air and fumes therefrom; and an exhaust duct for each fume hood is connected to an exhaust system. In communication with the fume hood, means for detecting the position of each movable sash door and generating a position signal indicating the position of the sash door, and opening the respective fume hoods in response to the position signal Means for calculating the size of the uncovered portion of the airbag, and measuring the actual airflow through the exhaust duct communicating with each of the fume hoods and indicating the actual airflow through the exhaust duct. Means for generating an actual flow rate signal, a modulation means attached to each of the fume hoods, and modulating a flow rate of air passing through the exhaust duct in communication with the respective fume hoods, in accordance with a control signal received from the controller means. Controller means for controlling the flow rate modulation means attached to each fume hood according to the position signal and the actual flow rate signal, and generating a desired flow rate signal as a function of the calculated size of the non-covered portion, The desired flow rate signal corresponds to a flow rate sufficient to maintain a predetermined average surface velocity through the uncovered portion of each of the fume hood openings, and the controller means controls the desired flow rate signal and the actual flow rate signal. Is compared for each fume hood to generate an error signal indicating an error existing between the two signals, and the error signal is further reduced to a predetermined minimum value or a predetermined minimum Controller means for selectively outputting a control signal for maintaining the quantity to said modulating means associated with each fume hood. 21. The controller means for generating the error signal by taking a continuous series of measurement samples of the actual flow rate, wherein three different coefficients of the error signal are determined from the continuous samples. 21. The apparatus for controlling ventilation of a fume hood according to claim 20, wherein the error signal is generated by adding the coefficient components of the following formulas, and the three coefficients include a proportional operation coefficient, an integral operation coefficient, and a differential operation coefficient. . 22. The integral operating coefficient at any given point in time is directly proportional to the integral operating coefficient calculated by multiplying the immediately preceding sample by the period time of the loop and adding the error measured from the current sample. 21. The method according to claim 20, wherein
A device for controlling the ventilation of the fume hood described. 23. The differential operating coefficient at any given point in time is directly proportional to the difference between the error obtained from the previous sample and the current sample divided by the cycle time of the loop. 20. An apparatus for controlling ventilation of a fume hood according to claim 20. 24. The apparatus for controlling fume hood ventilation according to claim 20, wherein said proportional operating coefficient at any given time is directly proportional to the error determined from the current sample. 25. The apparatus as claimed in claim 25, wherein said modulating means comprises damper means disposed in the exhaust duct, and operating means for changing a position of the damper means to change a flow rate of air passing through the exhaust duct. 20. An apparatus for controlling ventilation of a fume hood according to claim 20. 26. The apparatus for controlling ventilation of a fume hood according to claim 21, wherein said measurement sample is taken approximately every 100 milliseconds. 27. An apparatus for controlling ventilation of a fume hood according to claim 21, wherein said position detecting means is operative to generate a position signal approximately every 200 milliseconds. 28. An apparatus for controlling ventilation of a fume hood according to claim 21, wherein said controller means generates said control signal approximately every 100 milliseconds. 29. To control the air flow through the fume hood to maintain 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 it is moved. Means for detecting the position of each movable sash door and continuously generating a position signal indicating the position of each sash door, wherein the fume hood is connected to an exhaust duct for discharging air and fumes therefrom. 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 indicating the actual air flow through the exhaust duct; and receiving from the controller means. Modulating means for changing a flow rate of air passing through the exhaust duct according to a control signal to be supplied; and the flow rate modulating means according to the position signal and the actual flow rate signal. Control and generate a control signal value to maintain a predetermined minimum flow rate or generate a desired flow signal as a function of the calculated size of the uncovered portion or of the uncovered portion. Controller means for generating a value, wherein said desired flow signal corresponds to a flow rate sufficient to maintain a predetermined average surface velocity through the uncovered portion of said opening, said controller means providing said desired flow signal. And the continuous instantaneous sample values of the actual flow signal are substantially continuously compared to generate an error signal having a magnitude directly proportional to the sum of the calculated integration error, the calculated differential error, and the calculated proportional error. Controller means for reducing the error signal to a predetermined minimum value or continuously generating a control signal for maintaining the predetermined minimum flow rate and outputting the control signal to the modulation means. A device for controlling ventilation of a fume hood. 30. The apparatus for controlling ventilation of a fume hood according to claim 29, wherein said measurement sample is taken approximately every 100 milliseconds. 31. Apparatus for controlling ventilation of a fume hood according to claim 29, wherein said position detecting means is operative to generate a position signal approximately every 200 milliseconds. 32. Apparatus for controlling ventilation of a fume hood according to claim 29, wherein said controller means generates said control signal approximately every 100 milliseconds.