SYSTEM AND METHOD FOR CONTROLLING AIRFLOW IN A LABORATORY OR FUME HOOD

Abstract: The present invention pertains to a system for directing air flow in a fume hood (46) having a sash (14). The system comprises means or a mechanism (16) for producing an output control signal corresponding to a desired flow of air through the sash of the fume hood. The producing mechanism comprises a producing CPU (24) which actively produces the output control signal. The producing mechanism is to be disposed in fluid communication with the fume hood. The system also comprises means or a mechanism (18) for controlling air flow through the sash of the fume hood corresponding to the output control signal. The controlling mechanism is connected to the producing mechanism to receive the output control signal. The controlling mechanism comprises a controlling CPU (24) which actively produces a drive signal for operating the controlling mechanism corresponding to the output control signal.

Description: SYSTEM AND METHOD FOR CONTROLLING AIRFLOW IN A LABORATORY OR FUME HOOD FIELD OF THE INVENTION The present invention is related to the control of air in a laboratory or a fume hood. More specifically, the present invention is related to the control of air in a laboratory or a fume hood using a distributed architecture of intelligent non-hierarchical input and output devices. BACKGROUND OF THE INVENTION With the primary industry emphasis on autonomous fume hood controllers and the operation of the laboratory control loop in response to their causal laboratory airflow perturbations with the resultant non-optimum laboratory loop control lag, there exists a need for a more holistic approach. Current fume nood based controllers invoke perceived control actions without any concept or regard for laboratory or neighboring fume hood(s) flow history or perceived future demands. This approach and its resultant lag has m essence rendered laboratory controllers virtually impossible to setup and tune for any reasonably wide turndown range for any but the simplest (and mostly inaccurate) opening size based analog positioning systems. If the laboratory is assumed to be the primary control loop and the individual hoods/sashes and exhaust dampers are assumed to be just a varied group of controllable exhaust vents, with make-up air loops on individual hoods (if applicable) and supply fans/dampers nust another varied group of input vents, and laboratory differential pressure (inside lab/outside lab) an indication of room door(s) flow direction then perhaps a more straightforward and effective control strategy will result. With a neuron-based approach, the generated network vanaoles to/from all neurons will appear on the network with the resultant binding cf certain variables for localized mαiv dual mput/exhaust vent control and the binding of (laboratory) glooal variables for whole system control will result m a flatter, more timely architecture than wnat currently exists. Witr. tne Binding of all local hood desired flow variables into a lac total exhaust demand variable at tne same time as the local hood exhaust intelligent actuators are receiving the same desired flow variable will allow the lab control neuron (possibly the same product with a different superset application as the hood differential airflow sensor neuron since it too will measure differential pressure withm/witnout tne lac) to determine and effect the remaining damper/vents in con unction with uncontrolled openings (doors et . al . ) at essentially the same time. In essence the command to the lab systems supply and auxiliary exhaust vents intelligent actuators will occur simultaneously with the command to the individual intelligent actuators bound to individual (hood) exhaust dampers. All the laboratory actuators will slew in concert with each other. The laboratory will truly be just one system with some local damper actuators (hoods) having certain minimums and maximums that must be maintained (actually no different than just about any flow controlling damper anyway) . In addition, the automatic sash closure strategy is best handled at the laboratory level m a non-autonomous fashion. Since the laboratory is the main application with localized subset applications, the inclusion of a meaningful/integral smoke/fire control strategy is as straightforward as the inclusion of tne laboratory into tne building HVAC/ligh ing control strategy. In essence, the present invention is a fully distπouted architecture. Tne concept of a fully distributed architecture of intelligent non-hierarchical input (sensors) and output (actuation) devices is predicated on the existence of a 'flat architecture' in which intelligent devices act as peers communicating the sensible status of a process and implementing resultant controlling adjustments in response without the intervention of a superior hierarchical controller. In this architecture, inputs such as sash position sensors, air flow sensors, human presence sensors each has its own mtelliαence and communications capabilities in order to exist on a network with similarly intelligent and communication capable output devices such as intelligent dampers, intelligent VEntuπ valves, intelligent actuators or intelligent sash closure devices such that complete process control actions can be implemented without the intervention or independent coordination of a controlling element' which occupies a superior position m networking or calculation. In this 'flat architecture' intelligent inputs and intelligent outputs act as peers m a non-hierarchial network and exchange sensed and controlling information m a configuraple network which envisions single process loop control (such as a fume hood) and multiple process loop control (such as laboratories with multiple hoods) or arbitrarily configurable process loops to create 'virtual applications'. In this approach, the elements of input and output have the means of calculation or communication resident on them and integral to them. This method using distributed elements necessary to a process application where those elements can share a non-hierarchial high speed network in which a single control loop including one or more input or output, or more than one control loop which incorporates inputs and/or outputs which may be simultaneously used by more than one loop or calculation or application, allows the global sharing of sensed elements and the fuller, faster implementation of final control actions. Other approaches envision inputs and outputs that are digital or analog which are connected to a hierarchically superior 'controller' which manages the inputs and outputs using their values as elements in calculations or electronics which determine final control actions. Subsequently, the 'controller' may communicate with other 'controllers' m a network of 'controllers' which may share sensed or calculated values m order to accomplish global control strategies In that approach, the inputs and output have no inherent or integral intelligence or communications capabilities. Tn s new approach increases the speed of communications, improves access to shared inputs and values, and removes significant cost elements required m hierarchical networks or global control applications SUMMARY OF THE INVENTION The present invention pertains to a system for directing air flow in a fume hood having a sash. The system comprises means or a mechanism for producing an output control signal corresponding to a desired flow of air through the sash of the fume hood. The producing mechanism comprises a producing CPU which actively produces the output control signal . Tne producing mechanism is to be disposed in fluid communication with the fume hood. The system also comprises means or a mechanism for controlling air flow through tne sash of the fume hood corresponding to the output control signal. The controlling mechanism is connected to the producing mechanism to receive the output control signal . The controlling mechanism comprises a controlling CPU which actively produces a drive signal for operating the controlling mechanism corresponding to the output control signal . Tne present invention pertains to a method for controlling air flow in a fume hood. The method comprises the steps of measuring air flow in a fume hood to identify a measured air flow. Then, there is the step of producing a network variable corresponding to a desired flow of air through tne fume hood based on the measured air flow witn a producing processor. Next, there is the step of transmitting the network variable over a network. Then, there is the step of receiving the network variable at a device with a controlling processor which controls air flow through tne fume hood. Next, there is the step of controlling the air flow through the fume hood with the device based on the network variable which has been processed by the controlling processor. The present invention pertains to a system for maintaining a desired relationship regarding air. The system comprises a first room. The system also comprises a second room separated from but connected to the first room by a wall with an interface through which air could pass when the interface is m an open state. The first room has means or a mechanism for producing a network variable corresponding to a desired condition of air in the first room so air will only flow from the second room into the first room. The first room also has means or a mechanism for controlling the condition of the air in the first room based on the network variable received from the producing means or mechanism The system comprises a network to which the producing means or mecnanism and the controlling means or mechanism are connected to communicate with eacn other BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, tne preferred embodiment of the invention and preferred methods of practicing the invention are illustrated m which Figure 1 is a schematic of an information flow diagram for a distributed architecture of intelligent non-hierarchical input and output devices. Figure 2 is a schematic representation of the major software components of a face velocity sensor. Figure 3 is a schematic representation of the circuit for the intelligent actuator Figure 4 is a schematic representation of the major components of a differential pressure face velocity sensor. Figure 5 is a schematic representation of a system of the present invention. Figure 6 is a schematic representation of a system of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein like reference numerals refer to similar or identical parts throughout the several views, and more specifically to figure 1 tnereof, there is shown a schematic representation of a system 10 for directing air flow m a fume hood 12 having a sash 14. The system 10 comprises means or a mechanism for producing an output control signal corresponding to a desired flow of air through the sash 14 of the fume hood 12. The producing means or mechanism 16 comprises a producing CPU 24 which actively produces the output control signal. The producing means or mechanism 16 is to be disposed in fluid communication with the fume hood 12. The system 10 also comprises means or a mechanism for controlling air flow through the sash 14 of the fume hood 12 corresponding to the output control signal. The controlling means or mechanism 18 is connected to the producing means or mechanism 16 to receive the output control signal. The controlling means or mechanism 18 comprises a controlling CPU 24 which actively produces a drive signal for operating the controlling means or mechanism 18 corresponding to the output control signal. The producing means preferably comprises means or a mechanism for creating an air flow signal corresponding to the air flow through the fume hood 12. The air flow signal is provided to the producing CPU 24. The producing CPU 24 is connected to the creating means or mechanism 20. The creating means or mechanism 20 preferably comprises an air foil pitot 26 in contact with the fume hood 12 and in communication with the producing CPU 2 . The air foil pitot 26 detects the air pressure in regard to the fume hood 12. See U.S. Patent No. 5,415,583, incorporated oy reference nerem, for a full description of an air foil pitot and a fume nood. The air foil pitot 26 is in communication with the producing CPU 24. Besides an air fo l pitot 26, other sensors which identify air flow through the fume hood 12 can be used. Examples of such sensors are sash 14 position sensors or flow sensors which produce a signal corresponding to the flow of air through the fume hood 12, as is well known in the art. Additionally, the creating means or mechanism 20 preferably comprises an ultra-low differential pressure sensor 28 connected to the air foil pitot 26 and the producing CPU 24 which creates the air flow signal. The controlling means or mechanism 18 preferably comprises an actuator 30 in which the controlling CPU 24 is disposed and is operated by the drive signal. Moreover, the controlling means or mechanism 18 comprises a damper 34 connected to the actuator 30 which is operated by the actuator 30. The position of the damper 34 controls flow of air through a duct, as is well known in the art. Alternatively, a blower instead of a clamper can be used to control the flow of air through a duct connected to the fume hood. Referring to figure 4, the producing means or mechanism 16 preferably comprises a differential face velocity sensor 32. The producing CPU 24 is disposed in the producing means or mechanism 16. Preferably, the differential face velocity sensor 32 comprises a dual-slope integrating A/D converter 36 for converting analog signals to digital signals. Additionally, the differential face velocity sensor 32 comprises a neuron circuit 38 which produces a network variable which corresponds to a flow of air. The neuron circuit 38 is connected to the dual-slope integrating A/D converter 36. There is a memory circuit 38 for storing code which the neuron circuit 38 processes. The memory circuit 38 is connected to the neuron circuit 38. Moreover, the differential face velocity sensor 32 comprises a power circuit 40 for providing power to the neuron circuit 38 and is connected to the neuron circuit 38. Also, the differential face velocity sensor 32 comprises a network circuit 42 for communicating with a network and to provide the network variable to the network. The network circuit 42 is m connection with the neuron circuit 38. The present invention pertains to a method for controlling air flow n a fume hood 12. The method comprises the steps of measuring air flow m a fume hood 12 to identify a measured air flow. Then, there is the step of producing a network variable corresponding to a desired flow of air through tne fume hood 12 based on the measured air flow with a producing processor. Next, there is the step of transmitting the networκ variable over a network Then, there is tne step of receiving the network variable at a device witn a controlling processor which controls air flow through tne fume hood 12. Next, there is the step of controlling the air flow through the fume hood 12 with the device based on the network variable which nas been processed by the controlling processor. The present invention pertains to a system 10 for maintaining a desired relationship regarding air, as shown in figure 6. The system 10 comprises a first room 44. The system 10 also comprises a second room 46 separated from but connected to the first room 44 by a wall 48 with an interface 50 througn which air could pass when the interface 50 is m an open state. The interface 50 can be a door, window or preferably a fume hood 12 sash 14. The first room 44 has means or a mechanism for producing a network variable corresponding to a desired condition of air m the first room 44 so, preferably, air will only flow from the second room 46 into the first room 44. The condition can be humidity, for instance, or preferably pressure. The first room 44 also has means or a mechanism for controlling the condition of the air m the first room 44 based on the network variable received from the producing means or mechanism 160. The system 10 comprises a network 52 to which the producing means or mechanism 160 and the controlling means or mechanism 180 are connected to communicate with each other The system 10 can preferably also include a sensor 45, such as a pressure sensor m communication and preferably disposed in the second room The sensor can be a pressure sensor connected to the controlling means or mechanism. The controlling means or mechanism can use the pressure of the second room as a reference and cause the pressure m the first room to be less than the pressure in the second room by controlling the flow of air through, for instance, a duct with a damper out of the second room. Alternatively, the controlling means or mechanism can use the sensor in the second room to make sure the pressure is always greater in the first room than the second room in the same manner as previously described. In the operation of the invention, the Intelligent Differential Pressure Face Velocity Sensor calculates the face velocity at the sash. The face velocity sensor must be used with an ultra-low differential pressure transmitter, which is responsible for converting the high and low port pressures to a 4-20 mA analog signal. An example of the typical configuration used with the Face Velocity Sensor is shown m Figure 1. A 3150 Neuron Processor is the basis of the face velocity sensor. A dual -slope integrating converter converts the 4-20 mA analog differential pressure to a digital value. The converter interface software is simplified, since tne Neuron Processor has a pre-defined software object for the dual-slope integrating converter. A program converts the differential pressure value to face velocity througn a formula. Another program uses this face velocity and a PID loop to calculate a actuator response network variable. See the Appendix for the application program which operates the face velocity sensor. See the Neuron C Reference Guide and the Neuron C Programmer's Guide, both of which are incorporated by reference herein, by Echelon Corp. 4015 Miranda Avenue, Palo Alto, California 94304, for a complete explanation of the operation of the 3150 Neuron Processor, programming, networking, protocols, etc. As Figure 1 illustrates, there are 5 major components to the Intelligent Differential Pressure Face Velocity Sensor, the 3150 Neuron Processor Circuit, Memory Circuit, Power Circuit, Network Circuit, and the Dual -Slope Integrating A/D. Each of these components are discussed in the following sub-sections. The 3150 Neuron Processor Circuit is composed of the 3150 Neuron Processor and support for the clock, service pm, and reset. The 3150 Neuron Processor is the major component of the face velocity sensor. The 3150 Neuron Processor is composed cf three separate logical units, the Media Access Control (MAC) Processor, Network Processor, and tne Application Processor. The MAC Processor handles layers one and two of tne seven- layer network protocol stack This includes driving the communications subsystem hardware as well as executing the collision avoidance algorithm. The MAC Processor works in conjunction with the Network Processor and they communicate using network buffers located in the onboard shared memory. The Network Processor implements layers three through six of the network protocol stack. It handles network variable processing, addressing, transaction processing, authentication, background diagnostics, software timers, network management, and routing functions. The Network Processor works m conjunction with the Application Processor and they communicate using application buffers located m the onboard shared memory. The Application Processor implements layer seven of the network protocol stack and executes the operating system and the application code. The operating system consists of a built -m multitasking scheduler which allows for parallel events . The clock support is a simple circuit which provides a clock input to the 3150 Neuron Processor and the FTT-10 Free Topology Transceiver. The clock support circuit consists of a 10 MHZ crystal, capacitors, and two resistors. This circuit is recommended by the Echelon Corporation. The service support is a circuit which provides an indicator of the service status and a means for generating a service request across the network. A service request is necessary for configuring the LONTalk network with an "off the self" network management tool. The service pin support consists of a LED, resistor, and a push button. The reset circuit is a standard Low Voltage Indication (LVI) Circuit using a MC33164-5 LVI part, capacitor, and a 74AC00 NAND Logic Gate. The LVI provides a clean reset and under voltage protection to the Neuron Processor, Memory, and Network Transceiver. The NAND gate is used to prevent bus contention between the Neuron Processor and the Memory by delaying the reset signal to the memory. The memory circuit is composed of a MCM606C 32K x 8 SRAM part, a 29C257-120 64K x 8 FLASH part, a 74AC00 NAND Logic Gate, and a 74AC32 AND Logic Gate. The SRAM provides additional RAM to the Neuron Processor and it is mapped into memory at OxDFFF to 0x8000. The FLASH provides code space for the Application and System Images. The application image is the user program and any additional standard Neuron Processor library functions and is executed by the Application Processor. The System image is the code which is executed by the MAC and Network Processors . Tne Logic Gates provide the logic used to decode the memory space, control the select lines, and control the output enables. The Power Circuit is composed of a LM2574M-5V Switching Regulator, capacitors, a Zener Diode, a Diode, and an Inductor. This circuit is a common power supply circuit. The Network Circuit is composed of a FTT-10 Free Topology Transceiver, capacitors, and surge protectors. The Dual-Slope Integrating A/D is composed of OP Amps, resistors, capacitors, and an CD4016 Analog Switch. This circuit is recommended by the Echelon Corporation for supporting the Dual-Slope Integrating A/D object. The 3150 Neuron simplifies software development, since many device drivers are pre-written as I/O objects. Figure 2 illustrates the major components of the application program for the Face Velocity Sensor. Tne Initialization Task is automatically run after the Face Velocity Sensor is reset or powered on. The Initialization Task allocates memory and sets default values for Network Variables, Input/Output Objects, Timer Objects, Global Variables, Network Buffers, and Application Buffers. After tne Initialization Task executes it passes control over to the eve t scheduler. Network Variables are similar to Global Variables in ' C , but Network Variables can be sent or received by other LONWorks controllers on the LONTalk network. The Neuron Processor takes care of sending and receiving Network Variables, but a Network Configuration Tool is necessary to link network variables between controllers. There are two basic type of network variables, input and output. Input network variables receive their values from other controllers on the network. Output network variables send their values to other controllers on the network. The Face Velocity Sensor has the following system network variables : Name Direction Type Description nviDateTune input SNVT_t_me_stamp System Date and Time nvoAlarmStatus output SNVT_alarm Face Velocity Alarm Status nviEmergency input SNVT_swιtch Emergency Status nviEmerPosition output SNVT_le\_cont_f Damper Emergency Position πviName input SNVT str asc Controller Name Ip. nviDateTime network variable is used for receiving me current αate ana time. Tne Face Velocity Sensor does not have a real time clock, so t is dependent on anotner ccr.troller to Broadcast the date and time on the network. Tne face velocity sensor uses the date and time to time stamp face velocity alarms. Tne nviAlarmStatus network variable is used for reporting the high and low face velocity alarms. The alarm status is very robust and it includes a date and time stamp when the alarm occurred, the face velocity value, the alarm limit, type of the alarm (high limit, high limit return, low limit, low limit return, no alarm condition), and the name of the controller. The nviEmergency and nviEmerPosition network variables are used to control the damper actuator when there is an emergency condition is broadcast on the network. The nviEmergency variable receives the emergency status. When there is an emergency, nviEmerPosition is the position for the PID loop's output. The nviName network variable is the name of the controller and its default is "Hood_l". The Face Velocity Sensor has the following network variables for converting the raw voltage representing the differential pressure to a face velocity m engineering units: Description Update Rate for A/D Convener Low Scaling Value for Diff Pressure High Scaling Value for Diff. Pressure Face Velocity Low Alarm Limit Face Velocity High Alarm Limit Face Velocity Value The nviFVReadRate network variable is the scan rate for the A/D converter. The scan rate should never be less than 20 which is 20 milliseconds. The scan rate has the units of milliseconds. The nviDPLowScale and nviDPHighScale network variables are the high and low scaling values for converting the raw counts (0 to 65535) to a differential pressure. The Face Velocity sensor is assuming a 0 to 5 Volt linear differential pressure transmitter. If a different differential pressure transmitter wants to be used, the LOW_COUNTS and HIGH_COUNTS defines m the application code must be changed. The LOW_COUNTS (0) define corresponds to the low scaling value and the HIGH_COUNTS (65535) corresponds to the mgn scaling value. The differential pressure s calculated from the raw counts using tne following ecruaticr.. D;-_βr__:-A. Prβsscre - Cann es - LOV COUHTSi x l nTiDPHip Sctl e _ιτ_.--_>_.o»Sca_.» l =: . — -nvxDPLo*Sca. . e ( HIGH COUNTS LOW Co tTS) Tne nviFVLowLimt and nviFVHignLimit network vanacles define the face velocity's low and hign alarm limits, respectively. When the face velocity is below tr.e low alarm, limit, a low limit alarm is generated. When tne face velocity returns to a value above the low alarm limit, a low limit return is generated. When the face velocity is above tne high alarm limit, a high limit alarm is generated. When the face velocity returns to a value below the hign alarm limit, a high limit return is generated. The nvoFaceVelocity network variable is the calculated face velocity. The face velocity is calculated from the differential pressure using the following equation: .037 V /Di__ferencial Pressure The Face Velocity Sensor has a built in PID control routine which has the following network variables for controlling the damper actuator: The nviPIDSetpoint network variable is the control setpoint for the PID loop. The PID loop controls the face velocity through the nvoPIDOut network variable. The PID loop's output is broadcast on the network and the damper actuator controller receives this value and uses it to modulate ts damper. The PID output is a percentage from 0 to 100%. The nviPIDEnable network variable is used for disabling and enabling PID control. The nviPIDSign network variable controls if the PID loop is forward or reverse acting. The control sign is an integer value and it can have a value of -1 or +1. The control sign's default is +1, forward acting. The nviPIDDeadband network variable helps to eliminate toggling the damper actuator when the face velocity is around the setpomt When the face velocity is within the αeadband around the setpomt, the PID loop does not change ts output Doing this nelpε to reduce wear on the damper actuator Tne nviPIDProp network variable is the proportional ga for tne PID control loop Tne nviPIDIntegral network variable is the integral ga for tne PID control loop. The nviPIDDeπvative network variable is the derivative ga for the PID control loop. The Neuron processor has built -in Input/Output objects which simplify the development of controllers since the device drivers are pre-written The Face Velocity sensor is using a dual slope A/D converter I/O object called ADCONVERTOR. This A/D converter performs measurements with 16-bits of resolution for as little as a 13 ms integration period. The ADCONVERTOR requires a millisecond timer to provide continuous A/D conversion. The ConvertTimer millisecond timer object is provided for continuous reading of the A/D converter at the rate determined by the network variable nviFVReadRate . The face velocity sensor defines the following constants : Same Type Description LOW_COU\TS unsigned long Raw counts which correspond to the low scaling value HIGH COUNTS unsigned lona Raw counts which correspond to the high scaling value CONTROL VALUE unsisned long Integrating peπod for the dual slope A/D converter The face velocity sensor uses the following global variables: Name Type Description nviPIDSetpoint SNVT_speed_f Control Setpomt RawCounts unsigned long Differential pressure in raw unsealed counts DiffPressure float_type Calculated differential pressure Error float_type PID Error (Setpomt - Face Velocity) PrevError float type PID Error from the previous PED loop's calculation PPart float_type Proporaonal component of the PID loop's output IPart float_type Integral component of the PID loop's output DPart float_type Differenπal component of the PID loop ' s output AIR_COEF float type Coefficient of Air for face velocity calculation PID_MAX_OLT float_type PID loop's maximum output in percent PID_MIN_OUT float_type PID loop's minimum output m percent ZERO float type Zero in represented as a floating point number The Event Scheduler allocates processor time to the application tasks. The Event Scheduler decides when it is time to run a task, and the higher priority tasks run first such as t e Reset Task. The Event Scheduler passes control to a task and the completed task relinquishes control to the Event Scheduler. The Event Scheduler is responsible for updating me Watchdog timer. Tne Reset Task is responsible for setting up the variables and I/O objects to a know state. The timer object ConvertTirrer is set to the network variable nviFVRe dRate . This causes the A/D I/O object, ADCONVERTOR to be updated at the desired rate. Neuron C does not support floating point numbers. All floating point calculations are accomplished by using Echelon's floating point library. The global variables AIRJCOEF, PID_MAX_OUT, PID_MIN_OUT, and ZERO are really used as defined constants and the Reset Task must initialize them to their proper values. The timer object ConvertTimer is a repeating timer which expires at the set nviFVReadRate. The A/D Timer Expires Task is responsible for starting the A/D conversion by writing the CONTROL_VALUE constant to ADCONVERTOR I/O Ob ect . The A/D Update Task occurs when the A/D converter has completed its conversion of the unsealed differential pressure. This raw value must be converted to differential pressure that has engineering unit using the following formula : D i -.*„._.,. , ( Ha ir Conn.-- LOV_COUHτS ) x (nτιDPM.<?hSc*le - __τ.EFlo»'S_._._.βl (Hiσκ_cotwτs ioi. comrsi - n _ p ι. r _ cιit The face velocity must Pe calculated using tne differential pressure Tne following formula is used. . Oπ Dift -_rβπt_.-_l Pressure After calculating the face velocity, it is checking to make sure it is within the alarm limits . This alarm checking is done by the function Alarm ( ) . If there is a face velocity alarm condition, it is reported by the network variable nvoAlarmStatus . If the network variable nviEmergency indicates that there is an emergency condition, the PID loop' s output is to the emergency position indicated cv the network variable nviEmerPosition . If there is no emergency condition and the PID loop is enabled by the network variable nviPIDEnable, the face velocity sensor will control the damper actuator through the function PID() . The PID loop's, setpoint, deadband, gains, and control sign are all controllable through their respective network variables. The PID loop's output is broadcast by the network variable nvoPIDOu . Tne Neuron Processor has tasks that are handled by the Event Scheduler. These task are event based. To complemεr. and provide more modularity, tasks can call functions. Functions resemble tasks, but they must be invoked py a task or another function and not the Event Scheduler. The face velocity sensor has the following functions : Function Description Alarm () Checks and reports face velocity alarms CheckFor larm ( ) Looks for face velocity alarms ReportAlarmO Reports alarm conditions PI O Performs PID control DeadBandO Determines if the face velocity is within the deadband around the setpoint FillArray () Copies a SNVT_speed_f type value to an arrav of four unsigned integers Alarm() Function void Alarm () Remarks ι The Alarm () function reports alarm and return from alarm conditions. This function uses the high and low alarm limit network variables, nviFVLowLimit and nviFVHighLimit . Alarms are reported through the nvoAlarmStatus network variable . Return Value (s) None CheckForAlar O Function int CheckForAlarm ( ] Remarks : The CheckForAlarmO function checks the face velocity network variable, nvoFaceVelocity against the high and low alarm limit network variables, nviFVLowLimit and nviFVHighLimit . Return Value (s) HIGH_LIMIT_ALARM if the face velocity is above the high alarm limit. LOW_LIMIT_ALARM if the face velocity is below the low alarm limit. NO_ALARM if the face velocity is between the high and low alarm limits. ReportAlarm( ) Function void eportAlar ι unsigned long ObjectID alarm_type__t AlarmType pnorιty_level_t PriorityLevel unsigned long IndexToSNVT unsigned Value [4] unsigned AlarmLimit [4] ObjectID Face velocity sensor object number AlarmType Type of alarm PriorityLevel Priority Level for this alarm IndexToSNVT Standard Network Variable Type Index for alarm value and limit Value [4] Value which caused the alarm AlarmLimit [4] Alarm limit Remarks : The ReportAlarm 0 function takes the passed parameters and fills in the alarm status network variable, nvoAlarmStatus . Along with the passed parameters, this function fills in the date and time and the face velocity sensor's name. Return Value (s) None PID ( ) Function void PID Remarks : Tne PID() function uses a PID algorithm to control the face velocity by modulating the PID loop's output. The output from the PID loop is broadcast as a control signal to tne damper actuator controller. The loop must be enabled by setting the PID loop enable to "ON". If tne PID loop enable is "OFF" the PID loop's output is not updated. If the face velocity is within the deadband around the setpoint, no control action is taken and the loop's output is not changed. The PID loop can be selected to operate one of two ways, forward acting or reverse acting, by the control sign. The control sign is configurable tnrough the nviPIDSign network variable When the PID loop is controlling, its output is a summation of the Proportion, Integral, and Derivative components. The Proportional component is calculated 5 by the following formula: Ppart = Error * nviPIDProp The Integral component is calculated by the following formula: Ipart = Ipart + (nviPIDIncegral * Error) 10 The derivative component is calculated by the following formula: Dpart = (Error - Previous Error) * nviPIDDerivative The PID Loops output is broadcast to 15 other damper actuator controllers on the network though the nviPIDOut network variable. Most of the time, the PID loop's output is just a summation of the all three components, Proportional, 20 Inteσral, and Derivative. But, the control loop can suffer from anti-windup reset. Anti-windup reset is an over accumulation of the Integral component, since the integral component is used in its own formula. To combat this, a special check is made to ensure that the PID loop's output is clamped to the minimum or maximum output value. If the PID loop's output value is outside these limits, the Integral component is adjusted so that the total of all components equals the maximum or minimum output values. The PID loop's output is calculated by the following formulas: nvoPIDOut = Ppart + Ipart + Dpart if nvoPIDOut > PID_MAX_OUT then IPart = IPart + PID_MAX_OUT - nvoPIDOut nvoPIDOut = PID_MAX_OUT else if nvoPIDOut < PID_MIN_OUT then IPart = IPart + PID_MIN_OUT - nvoPIDOut nvoPIDOut = PID MIN OUT Return Value (s) None DeadBand P Function boolean DeadBand ( ) Remarks : The DeadBand function determines if the face velocity is within the deadband around the setpoint. The deadband is defined by the nviPIDDeadband network variable . Return Value ( s ) TRUE, the face velocity is outside the deadband FALSE, the face velocity is inside the deadband FillArrayO Function void FillArray ( SNVT_speed_f * value_f, unsigned int * value) value Pointer to the speed variable which is a floating point number to be copied. value Pointer to the unsigned four byte array to be filled by the floating point number. Remarks . The FillArrayO function copies a variable which is defined as a floating point speed into a four byte unsigned array . Return Value (s): None The Air Pitot Tube is placed in the moving air stream, usually mounted under the fume hood's bypass airfoil. The bypass airfoil is a metal plate which directs the airflow across the fume hood's work surface. The Airfoil Pitot Tube provides two different pressure components, total pressure and static pressure. The static pressure is the pressure which impacts all surfaces of the probe. The total pressure is the combination of the impact pressure of the airstream hitting the part of the probe facing into the airstream and the static pressure. The total pressure is measured by the sensing ports parallel to airstream and the static pressure is measured by the sensing ports perpendicular to the airstream. These two pressures are transmitted to an ultra- low differential pressure transmitter through pneumatic air lines . The two pressures, total and static are transmitted from the Airfoil Pitot Tube to the ultra-low differential pressure transmitter. The pressure transmitter subtracts the static pressure from the total pressure to produce a differential pressure. This differential pressure is actually the velocity pressure, which is proportional to the face velocity by the following equation: Fβcβ The velocity pressure is in the units millimeters of water and the face velocity is in the units meters per second. The differential pressure transmitted converts the differential pressure to a linear analog signal 0 to 5 Volt signal. A 250 Ohm resistor can be used with pressure transmitters whose output is 4 to 20 mA. This voltage signal is transmitter through signal wire to the A/D Converter's terminals on the face velocity sensor. The analog velocity pressure signal is received by the Dαal-Slope Integrating A/D circuit. This circuit performs A/D measurements with 16 bits of resolution at a sample rate of 13 ms . Control of this A/D converter is quite simple, because the Dual Slope A/D Converter I/O object is provided by the Neuron Circuit . This A/D converter is discussed in detail in the Neuron C Reference Guide mentioned above. The A/D Timer Expires Task and the A/D Update Task the application program handles the A/D conversion. The A/D Update Task reads the raw count velocity pressure and converts it to a floating point number. The scaling values are adjustable through the network to provide flexibility with choosing the differential pressure transmitters. The following formula is used to convert the velocity pressure's raw count value to floating point value with engineering units . ( -I*-- CooJJta - LOW COUNTS! xlaτlDPKlσhScM.le - aι __3P__orSc»-_β) Velocity Pret nre- = - * nrlDPLorScele IB1GB COtWTS - LOV COtWTS) The network variables and defines are discussed in the Differential Pressure Face Velocity Sensor's design document, Hardware and Software Design. The A/D Update Task uses the differential pressure value to calculate the face velocity by using the following equation: The Alarm 0 function is called by the A/D Update Task to perform face velocity alarming. This function will broadcast high limit, high limit return, low limit, and low limit return alarms. The face velocity low and high limit alarm values are programmable through the network. The face velocity sensor is capable of receiving emergency broadcasts on the network. This operation is done in the A/D Update Task The sensor has no provisions for detecting emergency conditions itself. If there is an emergency condition, the PID control loop will be suspended, and the emergency position value will be the PID loop's output. The emergency position value is programmable through the network. The calculated face velocity is used by the PID() function to control the damper actuator. This function is invoked by the A/D Update Task. PID loop control can be disabled through the network. The PID loop uses Proportional, Integral, and Derivative Control to modulate its output. The ga s associated with the PID loop are programmable through the network. To help alleviate oscillation around the setpoint, there is a deadband. If the face velocity is with the deadband around the setpomt, the PID loops output remains the same. If the face velocity is outside the deadband, the PID loop calculates the output. To prevent the integral component from becoming too large, there is anti-wind up reset protection. This protection clamps the integral value when all of the components add up to more than 100% or less than 0%. The output from the PID loop is broadcast on the network for the damper actuator controller to receive. The following equations are used for PID control : Error = Setpomt - Face Velocity Proper:lonal Component = Error * Proportional Gain Integral Component = Integral Component + (Integral Gain * Error) Derivative Component = (Error - Previous Errcri * Derivative Component FID Output = Propcrticr. Co-rpσner.t + Integral Component + Derivative Component Referring to figure 3, the intelligent actuator comprises the same essential circuitry as the differential airflow transducer with the exception of using the dual -slope input object to measuring actuator position feedback via a potentiometer (if needed) , and the generation of a pulse- width (duty-cycle) modulated wave via a pulse-width output object which is filtered to produce an analog voltage which is a position command to the actuator. The actuator and the damper are standard, whose operation is well known, once the actuator receives the analog voltage. Note that the analog voltage does not have to be precise, just monotonic, if feedback is used. The analog voltage actuator command could just as well be replaced by a 2 bit up and down command to directional power switches which could control the actuator motor directly, again relying on the feedback for actual position control. Additionally, the analog input used for feedback could be replaced with the quadrature-detect input object used m conjμnction with an optical (or mechanical) encoder to determine position (if needed) . With this encoder, not only position but velocity as well can be inferred for minimal overshoot within the intelligent actuator via its own PI (D with voltage command) loop and an inner velocity loop for top speed (slew rate) regulation. The PID loop the differential pressure sensor bound to the actuator modifies the network variable for desired airflow (consistent with closed loop control) to achieve the desired airflow through the airflow vent (sash) regardless of actuator position error anyway. During operation, the intelligent actuator receives the desired position network variable that is bound to this neuron and produces an output command which is a function of its known response transfer function of tne attached damper. This command is the interpolation of the command value as a function of tne minimum and maximum of the αa pers ' position, possibly modified by the use of a lookup taole Verification of the position is read pac via either tne dual-slope object or the quadrature object, if needed. Tne use of "means" herein is pursuant to 35 U.S.C. §112, while tne use of "mechanism" herein is not subject to 35 U.S.C. §112. Although the invention has been described m detail in the foregoing embodiments for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled m the art without departing from the spirit and scope of tne invention except as it may be described by the followin g claims. APPENΏIX // — 10 . ir.p t t aisiope ted tiocxiO) ΛECtr.vertt: // // Tiaers II- mc tier tepeatr.g ConvertTiaer; // Defines / / // Glob l vanasie Deciarati: / // Regular ".'ar acies •jr.___.gr.et long awCour.tΞ ; //: __-ϊ 2-Tsnt_. _. Pressure __— -.aw 5 D Pressura; //: -.f f Ξ sn i ?rΞSS " n :_oa //_ ___ιιr — *-_ //. noa PPart; 11\ float IPart; II float 3?art; * !■ Deπviat ve Cct_tonet // Floating ?=: ,.-.: Defines f!oat_typ //Coefficient of float_f.- //PID Loop MaxitK- ,— rwu.t_•t_.,u,—t float f- / I1ZZ Loop Min__.__t- Output float ' tv- I In floatmσ ooir.t zero // Fur.citor. Prototypes // : vα c t(void) ; int dec<ςForAlara(void) ; void ReportAlarπf unsigned long object_id, ala_-_a_type_t alar-a_type, priαrity_level_t priorϊty_leveI unsigned long index_to_SNV , unsigned value { 4 ] 7 unsigned alar_a_Li__-it .4 ] ) ; void PID (void); boolean DeadBand (void) ; void "ϋlArrayf S_τvτ_speed_ Speed_ , unsigned Value ) ; // // Reset // when (reset) { // Setup the Read Rate for the analog input CαnvertTi er - {unsigned long) nviFVReadRa t e; // Evaluate the Coefficient of Air define fl_from_ascn("4.037" / iAIR COEF) ; // Evaluate the PID Loop's Maxarua Cuttu t αefine fro_--_ascι ."100", &PID MAX OUT.; // Evaluate the PID Loop's Kiaa Cutau t αefir.e l_frcr_._ascι CO", «?ID MIN_0UT) ; Evai ats r.a Zero '"a__:= tafme / ZZZZL.ZZZZZZZZZZ-Z ZZ-.ZZ.ZZ~ " wnen ! tι_aer_e-_p ras (Cor.vertT rer: ) //Start the first mtecrat cn oe- — a ' — -■.«. - /-. - //(9ms g lOMHt: _" " e " /D ==" v =--" i=_ π_req-.-est;ADCcr.vertor. C0NTR0L_VALUϊ ) ,- // The A/D ctnvertor has a new value wner. ( o_upo_ate_occ rs (ADCcr.vertor: ) floa t _ t ype wrO Z ; //Teapory Floa t V ariable ' • floa t _ t ype ri_f ; //Tesaory π oat v r ' Ini! ' uns i gned long wrO.ul ; „ r J ^S^ 1 ^ . *!. // The differential pressure incut value <s b - _*« . .- . . ^ - π __ // of the control value usec. Correct J ' J bv :ϊ r} β h nβ ? atlve vaiue aawcaunrs - m?ut_value - CO.JTRO ^-; V " "*" // Scale zr.e Raw Counts to a Differen t ia' °— ssu-e ' nv i DPLowScale // Perfom ti.-e above equation using the floating point library wrO u = RawCounts - LOW COUNTS; fl_frs-_-_uioπg( wr0_ui, δwrO_f) ; fl_sus( (const float_type » T inviDPKignScale. ( const fioat~type *) inviDPLowScaie, 4wtl_ ) ; fl___-ui ! iwrO i , &wri f, SDif Pressure! ; vrO_ i - HIGK_C0U1TTΞ _ - LO _COUNTS; l_ rc.n_uiong ( wrO_ul, &wrO_ . ; fl sui (~ " &wrO_f, SDΪf Pressure, fiwri f ) fl_acd ( iwrl_f, ( const float_type "7 inviDPLowScaie, SDif Pressure) // Convert the Differential Pressure to a Face Veioctcv // nv FaceVeiocity - 4.037 sςr(DiffPressure) fl_sςrt( &D ffPressure, iwrO f) ; fl_3ui ( -_wrO_ , 4AIRJ-.OE", fiwr0_ ! ; nvoFaceVelocity = * " (SNVT_speed~f » j &wr0 f; //Perfom the Alaming Tasic Alamo ; // Per cm the PID Control Loop // Do PID control if ts enaniec f (nv PIDEnarie. state — ON) ( // Only Perfom PID Control If were are not m Eaerσencv f (nviEmergency.state — ON) ( nvoPIDOut - πviEaerPosition; // Only Perfom PID Control If the face veloci t y is ou t side // tne DeadBand else if (DeadBand) ( PIDO ; i // Chec. 1 : for Hign or Low Liai Alaras / / // __.~v • * — — a*ra • c A _»• * •■• ica veiocitv aiam c —ons β : float_type invoFacsVelocity, icons: : oat Oe iπviFVϋicn isit: ) .(KIGH_-__MIT_ALAHM) ; // Cϊi cx. if there is a low face velocity aiam else f ( fi_lt ( (const float_type *) snvoFacaVelocity, ( const fioat~type *) sπviFVLowLiniti ) I return (LOW LIMIT ALABM) ; return (MC ALARM) ; // Alarm Check tor Kigr. ant Low Lit- t Aiams ant Clears / / void Aiam; ', Al art-Status; /' urrent Alam Sta t us ~T speec_f wr0_sceen; / ' "Terr.p Varianie o t Ξpeec Ty p e -opy o: tr.e racs velocity T ll tr.s Ur.s gr.ec race Veiocitv Arrav -..i t . wrC stee ■ nvoFaceVelocity; Fill-Array' iwr _speec, i nsigned ") iSpeed) ; // Sat t.-.e aiam status to our previous aiam con d i t ion switrr ; nvcAlamS tatus . aiam_type < // Previous aiam was a low iim clear case AL LOW LMT CΛ_1: case AL~-iIGH_LMT d_R 1: case AL_NO_CONDITION7 // Set Z a aiam status accordingly switch (AlamS tatus ) ( // There is a low liait alarπs case LO _LIMIT_ALΛRM: // Fill the Alam Liπit w th the Low Liait value FillArray( iπviFVLowLtiit, ( unsigned • ) iLiπit ) ,- // Report the Alarm ReportAlara( OB ECT_π., AL_L0W LMT ALM_1, PR LΞVEL 37 SPEED_SNVT_-_NDEX, Speed, ~ Liait ) ; break; // There is a high limit alarms case HIGH_LHiIT_ALARM: // Fill the AJ_am Limit with tne Hign Limit value FiliArra ( inviFVHignLiπit, (unsignec » ) iLimit ); // Report the alarm ReportAlam( OBJE TED, AL HIGH LMT ALM 1. traax; // Oeϊacit or.uition ce≤auit: / I ~- i - ' - tne Alarm Limit with a tero value FiliArray ( ( SNVT_speeα_f *) iZΞP.C, (unsigned » ) sLi it ) ; //.Report the alarm ReportAiarmt OBJECT ID, AL NO CONDITION. ?R~LΪVEL 3, S?EΞD_SNVT INDEX, Speed, ~ Limit ) ,- ) areaJc; // Previous alarm was a low limit alarm case AL_LCW_LMT_ALM_1 : // Set the alarm status accordingly switc (Alarmstatus i i // If there is a high limit alarm or r.o alarm // clear the low limit alarm case HIGK_LIX r ALARM: case NO_ALA?.M: // Fill the Alarm Limit with tne low Limit value FiliArray ( .nviFVLowLimit, .unsignec - iLmit ; // Report the alarm Reportλlarm( OBJECT ID, AL_LOW~LMT CLR 1, ??._LEVEL 37 S_=ΞΞD_SNVT_INDE , Speed, ~ brea ; // If there is still a low limit alarm do nothing case LOW_LmiT_ALARM: όreaκ; // Default Condition default: // Fill the Alarm Limit with zero FiliArray ( (SNVT_speed_f *! SZERO, (unsigned *) SLi it ); // Report the alarm ReportAlarm( OBJECT ID, AL_N0_C3NDITI0N , PR_LΞVEL_ , S?ΞED_SNVT_INDEX , Speed7 ~ creak; // Previous alarm was a h gn limit alarm case AL_HIGK_L T_AL _i: // Set tne alarm status accordingly switc ! AlamStatus ) i // If there is a low imit aiam or no aiam ~' ea - // tne hign limit aiam "" ~ case L0W_LIKIT_ALΛIU1: case N0_ALARM:~ FiliArray ; inv FVHignLi it. (unsignea " i imit // Report the aiam P.eportλiam. 03 ECT_ID, AL HIGH LMT CLR ' PR~^2 EΪ_3,~ ~ S?EΞD_SNVT_rNDEX , Speed, ~ Limit ); break; // If there is still a high limit alarm, do nothing case HIGH_LIMIT_ALARM: break " // Default Condition default: // Fill the Alarm Limit with zero FiliArray ( (SNVT_speed_f *) SZERO, (unsigned '7 sLimit ) ; // Report the alarm ReportAlamf OBJECT ID, AL NO CONDITION, ?R_LE7ΞL_3 , S?EE2_SNVT_INDEX , Speec, / / P.eport Alarms -/cm =.spc".-_ar___ ! uns gnsc long ObjectID, ala_____type_t AlarmType , prιoπty_levei_t PriorityLevel , unsigned long ~ IncexToSNVT, unsigned Value £ 4 ] , • unsigned AlarmLimit [ 4 ] ) / / Fill the in the passed alarm information srrmy t ( char * ) invoAlar S tatus . location, (cha: sπviNa e! nvo Alarms tatus . on j e t_id - ObjectID; nvoAlarmS tatus . aiarm_type - AlarmType; nvoAlarmS tatus . priori ty_levei » PriorityLevel; nvoAlarmS tatus . index_to~SNVT » IndexToSNVT; // Fill the Current Face Velocity Value nvoAlarmS tatus . value CO] - Value CO] , nvo Alarms tatus . value Cl] » Value [1] , nvoAlarmS tatus . value { 2 ] - Value [ 2 j . nvoAlarmS tatus . value j 3 j « Value { 3 ] , // Fill the Alarm Limit Value nvoAlarmStatus.alarm_lιmit[0] ■ Aleu_ml_ j __it[0] nvoAlarmStatus.alarm_liit {1j - Al rπr, , τπi,t {l] nvoAlarmStatus .alarm~l__J-.it.2j ■ Alaxal_iait[2] oAlarmStatus.alam_li__.it[3j - AlarmLimi [3] // Fill in the current Hm» and ^^ nvoAlarmStatus. year - nviDateTime. year; nvoAlarmStatus. onth - nviDateTime. onth; nvoAlarmStatus. day - nviDateTime. ay; nvoAlarmStatus.hour - nviDateTime.hour; nvoAlarmSta t us. inute - nviDateTime.minute; nvoAlarmSta t us.second » nviDateTime.second; sceec vεriacis ar** z: s ar. / / ;.. - sceec _- vai ε isisned * value; // Set up some temp pointers .atir.g paint numaer t o the unsiςnec arrav till -Jeacianc ', ;: ™ Ξ-r - ? *« V , iac "ϊ ^ °u t Slaβ t e deadbanα //_::::::_:: ~ ::_::_: * :!_:!!L!: 0 r -- ' s ~' slae c - e ae «k»nα )eac=anc : . / / Tampory Floating Poin t Var acie 1 // Teπnory floating Point Varianie 2 *-*e ta_t or tne OeacSanc ιeι____0 _! * tl nal_Ξ* - 3£I - ' - ' ? e '! i nviSiDDeadhanc, stance, f. !l f) ---- a 5? : '■ "~-~ z floa t rype ' ) inviPlDSetnomt, i t a al - :, &temρ0_fϊ; t -..__-.. , ( cons t - oat_type *) invoFaceVeicci t v, " ste ϊm t p0_f) j return ( L Xl • // ChecK tne lower limit fi_sun( (const fioat_type *) inviPlDSetpomt, ste sl f, stemn0_f) . f (fi it! (ccnst float type » ) SnvoFaceVelocitv, itemaO f) " ) ( return (TP.CT. ; / / The face velocity is mside the deadhand return ( Fai-SΞ! ; // ?1Z Central loop void PIDO ( float_type tempO // TeaiDory rioating Point Variable 1 float type ta__-pi_ // empory Floating Point Variable 2 - EvoFaceVeiocity r ) iπv PIDSetno nr ') invoFacsVeioci- e_se , P.everse Control Sign /, __rrtr , a_c _at= tne ?r=ρ=rtιsn omsor.ent / PPart - Ξrror * nviPIΞProp (const fioat_type τ ) inviPIDProp, ϊPPart. ; // Calculate the Integral ComDonent // IPart » IPart - nv PIDIntegral * Error i_ ul ! (const fioat_type » ! inviPIDIntecral, ite=_?0_ ) ; fi_acd! i Part, ites_?0_f. ._IPart " ; // Calculate the Derivative Component // DPar - (Error - PrevError. * aviPIODerivative fi_su_-> ( άError, ά revErrcr, itεmp0_ ! ,- fl_=ul( άtemnO^f, (const float_ ype » ) mv PlDDerivative, -.DPart: ; // -_cc a_l t e PID components :ccst_ιer . -' I sτsz:rvCut ■ PPart ÷ IPart - IPart fl ace: iPPaπ. ilPart. itamp _f : ; fl ice itamoC_f, i Part. s.tampC_;: ; ■ / Water. f;r positive anti-reset winc s f TsmncryCut > ~Z2 ΑX_Cϋτ then IPart = IPart - ?ID_M X_OϋT - lemporyC-t Tem cryCur = PI_:_MAX_0U fl_rt. «tem?C_f, i?Z JΑX_CV:', : fl_acc.iIP3.rt. s?I_._MAX_OUT. ;templ_f : ,- fl_sun ; atεmpi_f, ites_p0~f, ilPart; ; temnO f - PIS MA OUT; . ' / Water, for r.eσative anti-reset incup Cy ; // Save the PID Output // nvoPIDOut » TemporyOut nvoPIDOut » * (SNVT_lev_cont_f » ) itempO // update the Previous Error PrevError - Error;

Claims: WHAT 15 CLAIMED IS: 1. A system for directing air flow m a fume hood having a sash comprising: a mechanism for producing an output control signal corresponding to a desired flow of air through the sash of the fume hood, said producing mechanism comprising a producing CPU which actively produces the output control signal, said producing mechanism to De disposed in fluid communication w th the fume hood; and a mecnanism for controlling a r flow through the sash of tne fume nood corresponding to the output control signal, sa d controlling mechanism connected to the producing mechanism to receive the output control signal, said controlling mecnanism comprising a controlling CPU whicn actively produces a drive signal for operating the controlling mechanism corresponding to the output control signal . 2. A system as described in Claim 1 wherein the producing mechanism comprises a mechanism for creating an air flow signal corresponding through the air flow to the fume hood, said air flow signal provided to the producing CPU, said producing mechanism connected to the creating mechanism. 3. A system as described m Claim 2 wherein the creating mechanism comprises an air foil pitot in contact with the fume hood and in communication with the producing CPU, said air foil pitot detects the air pressure in regard to the fume hood, said air foil pitot in communication with the producing CPU. 4. A system as described in Claim 3 wherein the creating mechanism comprises an ultra-low differential pressure sensor connected to the air foil pitot and the producing CPU which creates the air flow signal. 5. A system as described m Claim 4 wherein the controlling mechanism comprises an actuator m which the controlling CPU is disposed and is operated by the drive signal . 6. A system as described in Claim 5 wherein the controlling mechanism comprises a damper connected to the actuator which is operated by the actuator. 7. A system as described in Claim 6 wherein the producing mechanism comprises a differential face velocity sensor, said producing CPU disposed in the producing mechanism. 8. A differential face velocity sensor comprising: a dual -slope integrating A/D converter for converting analog signals to digital signals; a neuron circuit which produces a network variable which corresponds to a flow of air, said neuron circuit connected to the dual-slope integrating A/D converter; a memory circuit for storing code which the neuron circuit processes, said memory circuit connected to the neurcr. circuit; a power circuit for providing power to the neuron circuit and connected to the neuron circuit; and a network circuit for communicating with a network and to provide the network variable to the network, said network circuit in connection with said neuron circuit. 9. A method for controlling air flow in a fume hood comprising the steps of: measuring air flow m a fume hood to identify a measured air flow; producing a network variable corresponding to a desired flow of air through the fume hood based on the measured air flow with a producing processor; transmitting the network variable over a network; receiving the network variable at a device with a controlling processor which controls air flow through the fume hood; and controlling the air flow through the fume hood with the device based on the network variable which has been processed by the controlling processor. 10. A system for maintaining a desired relationship regarding air comprising: a first room; a second room separated from but connected to the first room by a wall with an interface through which air could pass when the interface is in an open state, said first room having means or a mechanism for producing a network variable corresponding to a desired condition of air in the first room so air will only flow from the second room into the first room, said first room having means or a mechanism for controlling the condition of the air in the first room based on the network variable received from the producing means or mechanism; and a network to which the producing means or mechanism and tne controlling means or mechanism are connected to communicate with each other. 11. A system for directing air flow m a fume hood having a sash comprising: means for producing an output control signal corresponding to a desired flow of air through the sash of the fume nood, said producing means comprising a producing CPU wπicn actively produces tne output control signal, said producing means to be disposed in fluid communication with the fume nood; and means for controlling air flow through the sash of the fume hood corresponding to the output control signal, said controlling means connected to the producing means to receive the output control signal, said controlling means comprising a controlling CPU which actively produces a drive signal for operating the controlling means corresponding to the output control signal .

Inventors: HEFFEREN PETER J, KIKTA CHRISTOPHER E, WIEDMANN JOHN F, HEFFEREN, PETER, J., KIKTA, CHRISTOPHER, E., WIEDMANN, JOHN, F.
Applicants: HEFFEREN PETER J, INNOVEX TECHNOLOGIES INC, KIKTA CHRISTOPHER E, WIEDMANN JOHN F, HEFFEREN, PETER, J., INNOVEX TECHNOLOGIES, INC., KIKTA, CHRISTOPHER, E., WIEDMANN, JOHN, F.
Application year: 1997
Main classification: B08B15
IPC codes: B08B15, G05D7, G05D27