JP4544992B2 - Apparatus and method for mass flow control insensitive to pressure fluctuations - Google Patents

Description

Related applications

  It is assigned to the same assignee as this patent application, has the name `` APPARATUS AND METHOD FOR CALIBRATION OF MASS FLOW CONTROLLER '' filed on the same day as this patent application, and the inventor is in Nicholas Kottenstette and Jesse Ambrosina. A patent application with the name "APPARATUS AND METHOD FOR SELF-CALIBRATION OF MASS FLOW CONTROLLER" and the inventors are Nicholas Kottenstette, Donald Smith, and Jesse Ambrosina. (The docket number of the agent is MKS-108) and the patent application (the agent docket of the agent) with the name "APPARATUS AND METHOD FOR MASS FLOW CONTROLLER WITH NETWORK ACCESS TO DIAGNOSTICS" and the inventors are Nicholas Kottenstette and Jesse Ambrosina The number is MKS-109), and the patent application with the name "APPARATUS AND METHOD FOR DISPLAYING MASS FLOW CONTROLLER PRESSURE" and the inventor is Nicholas Kottenstette and Jesse Ambrosina. The patent number is MKS-110) and the patent application with the name "APPARATUS AND METHOD FOR DUAL PROCESSOR MASS FLOW CONTROLLER", the inventors are Nicholas Kottenstette and Jesse Ambrosina (the agent's docket number is MKS-111) and , "APPARATUS AND METHOD FOR MASS FLOW CONTROLLER WITH EMBEDDED WEB SERVER", the inventor is Nicholas Kottenstette and Jesse Ambrosina patent application (attorney's docket number is MKS-112) and "APPARATUS AND METHOD FOR MASS FLOW CONTROLLER WITH ON-LINE DIAGNOSTICS ", the inventor is Nicholas Kottenstette and Jesse Ambrosina patent application (attorney's docket number is MKS-113) and" APPARATUS AND METHOD FOR MASS FLOW CONTROLLER WITH A " A patent application with the name `` PLURALITY OF CLOSED LOOP CONTROL CODE SETS '' and inventors Nicholas Kottenstette and Jesse Ambrosina (the agent's docket number is MKS-114) Incorporated Te.

  The present invention relates to mass flow sensing and control systems.

  Capillary thermal mass flow sensors have a heat transfer from the wall of the tube to the fluid flowing through the layered tube as a function of the mass flow rate of the fluid, the difference between the fluid temperature and the wall temperature, and the specific heat of the fluid. Take advantage of the fact that there is. Mass flow controllers use various mass flow sensor configurations. For example, one type of configuration includes a stainless steel flow sensor tube having one and more typically two or more resistive elements in thermal conductive contact with the sensor tube. The resistance element is typically composed of a material having a high temperature resistance coefficient. Each element can act as a heater, a detector, or both. One or more of the elements are energized using an electric current, and the mass flow rate of the fluid passing through the tube can be derived from the temperature difference in the element. The fluid mass flow rate can also be derived by varying the current through the heater to maintain a constant temperature profile.

  Such a thermal mass flow sensor can be attached as part of the mass flow controller, and fluid is supplied to the capillary (also referred to herein as the sensor tube) from the main channel of the controller. The portion of the main channel that is associated with the sensor tube inlet and outlet is often referred to as the “bypass” of the flow sensor. In many applications, multiple mass flow controllers are used to regulate the supply of fluid through the supply line, and the multiple supply lines are “split” from the main fluid supply line. When the flow to one of the controllers suddenly changes, pressure fluctuations occur at the inlet to one or more of the other controllers that are separated from the main supply line. Such pressure fluctuations cause a difference between the flow rates at the inlet and outlet of the affected mass flow controller. A thermal mass flow sensor measures the flow at the inlet of a mass flow controller, but since the outlet flow from the controller is an important parameter for process control, such a flow discrepancy between the inlet and outlet can cause serious problems. Process control errors can occur.

  In semiconductor processing applications, the process tool includes a plurality of chambers, each chamber having a plurality of mass flow controllers that control the flow of constituent gases into itself. Each mass flow controller is typically recalibrated every two weeks. This recalibration process is described in US Pat. No. 6,332,348, issued December 25, 2001 to Yelverton et al. This US patent is incorporated in this application. During such “in-situ” calibration, the conventional method involves a technician connecting a mass flow meter to each of the mass flow controllers with a wire and passing the gas through the mass flow meter and the mass flow controller. It is necessary to compare the mass flow controller reading with the mass flow meter reading and adjust the calibration constants as necessary. Such cumbersome operation is very time consuming and expensive due to the human expense and the lack of process tools with which the mass flow controller operates.

  A mass flow sensor that substantially eliminates sensitivity to pressure fluctuations is therefore highly desirable. A convenient calibration method and apparatus for a mass flow controller is also highly desirable. A more flexible access to the mass flow controller is also highly desirable. Devices and methods that improve the control performance of mass flow controllers are also highly desirable.

  In one embodiment, a mass flow controller in accordance with the principles of the present invention includes a combination of a thermal mass flow sensor and a pressure sensor that provides a mass flow controller that is relatively insensitive to input pressure fluctuations. This new controller is relatively inexpensive, i.e. it does not require a pair of expensive and accurate pressure sensors, nor does it require a differential sensor with a surface wetted by total stainless steel. However, this new controller can control fluid flow over a wide range of fluid pressures. The new mass flow controller includes a thermal mass flow sensor, a pressure sensor, and an electronic controller. The thermal mass flow sensor is configured to measure the inlet flow of the controller. The pressure sensor senses the pressure in the volume in the channel between the flow sensor bypass and the outlet control valve. This volume is referred to in this application as a “dead volume” and the pressure sensor and thermal mass flow sensor each provide a signal indicating the measured inlet flow rate and the pressure in the dead volume. Provide to the controller. The temperature sensor is used to sense the temperature of the fluid in the dead volume. In one embodiment, the temperature sensor senses the temperature of the controller wall as an approximation of the temperature of the fluid in the dead volume. The volume of the dead volume is determined or stored or downloaded for use by the electronic controller, for example, during the manufacturing or calibration process.

  The controller uses the measured pressure in the dead volume to compensate for the numerical value of the inlet flow rate and compensates for the outlet flow rate as a function of the measured pressure and the measured inlet flow rate. Yields a measure. This compensated measure of outlet flow rate is used to operate the control valve of the mass flow controller. By reading the pressure sensor output over a period of time, the electronic controller determines the rate of time change in pressure within the dead volume. Given the dead volume, the temperature of the fluid in the dead volume, and the inlet flow rate sensed by the thermal mass flow sensor, the electronic controller determines the fluid flow rate at the outlet of the mass flow controller. As a function of the variable. The electronic controller uses this calculated outlet fluid flow rate in the closed loop control system to control the opening of the mass flow controller outlet control valve. In certain embodiments, the pressure sensed by the pressure sensor is displayed locally (ie, at the pressure sensor) and / or remotely (eg, at the control panel or via a network interface).

  According to another aspect of the principles of the present invention, a mass flow controller can be calibrated using a variable flow fluid source, a known volume receptacle (= vessel), and a pressure differentiator. The variable flow fluid source supplies gas at a variable rate to a calibrated mass flow controller and at a proportional rate to a known volume receptacle. The pressure differentiator calculates the time derivative of the gas flow into a known volume receptacle, and then calculates the actual flow into the receptacle. Given the actual flow, the proportional flow into the mass flow controller is determined and the flow signal from the mass flow controller is actual float correlated. In one embodiment, the mass flow controller closes the outlet valve to form a known volume (dead volume) receptacle. A pressure sensor located in the dead volume produces a signal representative of the pressure in the dead volume. When the outlet valve is closed, the flow into the dead volume decreases exponentially, while the pressure is until the pressure in the dead volume is equal to the pressure at the inlet to the mass flow controller. ,To rise. The electronic controller of the mass flow controller calculates the time derivative of the pressure at multiple times. Given the dead volume / receptacle volume, the time derivative of the pressure in the dead volume, and the temperature of the gas, the controller calculates the flow rate at these sample times. The electronic controller also calibrates the mass flow controller by correlating the flow rate so calculated with the flow reading produced by the thermal mass flow sensor of the mass flow controller. This operation is self-contained in that it does not require an external mass flow meter or other calibration device. Various techniques and mechanisms can be used to extend the time period during which the flow continues into the dead volume, thereby allowing the calculation of a larger number of correlations or calibration points. For example, the outlet valve can be fully released before it is closed at the beginning of the calibration process, otherwise, for example, means for restricting the flow are inserted at various positions in the gas flow path. The

  According to another aspect of the principles of the present invention, the mass flow controller includes an interface that allows an operator, such as a technician, to make a diagnosis over a network. Such a diagnosis may be “active”, “passive”, “online”, “offline”, “manual” or “automatic”, or any combination of the above. By “active” diagnosis is meant a diagnosis that allows the operator to change the drive signal in addition to or instead of the monitor signal. By enabling the use of the drive signal, the technician can change the setting of the test point and thus, for example, change the current flowing through the resistor. The engineer monitors the corresponding signal from the current sensor, for example. Alternatively, the technician can directly apply the drive signal to the valve actuator rather than relying on the mass flow controller's electronic controller to set the flow set point and adjust the valve drive signal in the desired manner. You can choose to change. Since such changes potentially cause flow control errors, access to such controls is limited, for example, by the use of passwords and other security measures at the network level. The term “passive” diagnosis means, for example, a diagnosis that includes a monitoring function. The term “on-line” diagnostic means, for example, a diagnostic that is real-time and operates concurrently with the process control operation of the mass flow controller. The term “offline” diagnostic refers to a diagnostic that is real-time but not operating during the process control operation of the mass flow controller. The term “automatic” diagnosis refers to a diagnosis that includes multiple diagnostic steps, each of which can be active or passive. The term “manual” diagnosis refers to a diagnosis that is responsive to operator input at each step.

  A mass flow controller according to another aspect of the principles of the present invention allows an operator, such as a technician, to connect an interconnect network, such as the Internet, from a web-viewable device such as a workstation, laptop computer, or personal digital assistant. A web server that allows to interact with the mass flow controller via The mass flow controller web server includes a web page that provides, for example, the manufacturer's part number, specifications, location, and performance information. In addition, diagnosis is performed from a web-viewable device via the interconnect network.

  According to yet another aspect of the principles of the present invention, the mass flow controller includes a pressure display that displays the pressure in the mass flow controller. The display may be local, i.e. in direct contact with and supported by the mass flow controller, or remote, e.g., in a gas box control panel. In one embodiment, the pressure sensor is arranged to measure the pressure in the mass flow controller dead volume, which is the displayed pressure.

  A dual processor mass flow controller in accordance with yet another aspect of the principles of the present invention includes a decision processor that performs control operations for the mass flow controller and a non-decision processor that handles tasks such as providing a user interface. . In one embodiment, the decision processor is a digital signal processor (DSP).

  According to yet another principle of the principles of the present invention, multiple executable code sets are uploaded by the electronic controller of the mass flow controller. In one embodiment, a non-decision processor of a dual processor flow controller uploads multiple executable code sets for the decision processor and makes a selection within this code set for execution by the decision processor Like that. Such a selection by a non-deterministic processor allows some form of customization.

  These and other advantages of this disclosure will be apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment illustrated in the accompanying drawings. . For convenience of illustration, the elements in the figure are not drawn to scale.

  A mass flow sensor in accordance with certain aspects of the present invention uses a thermal mass flow sensor to sense and provide a measure of fluid flow to the inlet of a fluid flow device, such as a mass flow controller. . In one embodiment, the mass flow sensor uses a pressure sensor to compensate for the inlet flow measure provided by the thermal mass flow sensor to more accurately reflect the fluid flow at the outlet of the associated mass flow controller. Provide an indicator to do. A system 100 utilizing and utilizing a mass flow sensor according to the principles of the present invention is illustrated in the schematic block diagram of FIG.

  The plurality of mass flow controllers MFC1, MFC2,..., MFCn receive gas from the main gas supply lines 102 and 103. The mass flow controllers MFC1, MFC2,..., MFCn are respectively connected to the main gas supply lines 102, 103 via the inlet supply lines 104, 106,. , 115 are connected to chambers C1, C2,..., Cn. In this example, the term “chamber” is used in a broad sense, and each chamber is not limited to enumeration, but as any of a variety of applications including reactions related to the manufacture of semiconductor components. It is used. In general, the chamber user is interested in knowing and controlling the amount of each gas supplied to each of the chambers C1, C2,..., Cn. Each chamber C1, C2,..., Cn also includes one or more additional inlet lines for the supply of another type of gas. The output flow from the chamber is routed through a line (not shown) for recycling or disposal.

  The mass flow controllers MFC1, MFC2,..., MFCn are mass flow sensors MFS1, MFS2,..., MFSn, electronic controllers EC1, EC2,. -Including OCVn. It is assumed that at least one of the mass flow sensors, and for ease of explanation, all are compensated mass flow sensors according to the principles of the present invention. Each mass flow sensor senses the mass of gas flowing into the mass flow controller and provides a signal indicative of the sensed value to the corresponding electronic controller. The electronic controller compares the mass flow indication indicated by the sensed value provided by the mass flow sensor with the set point and calculates the difference between the set point and the sensed value provided by the mass flow sensor. Operate the outlet control valve to minimize any difference. Typically, the set point can be entered manually at the mass flow controller or it can be downloaded to the mass flow controller. The set point can be adjusted to be justified by human operator intervention or by an automatic control system. The inlet supply lines 104, 106,..., 109 have different gauges and / or can be processed at any of the various flow rates to the mass flow controller. In accordance with one aspect of the principles of the present invention, a single electronic controller, such as electronic controller EC1, can be linked to multiple mass flow sensor and outlet control valve combinations to operate the combination. That is, for example, any number of the illustrated electronic controllers EC2 to ECn can be removed and the corresponding mass flow sensor and outlet control valve linked to the electronic controller EC1 for operation.

  For example, a rapid change in flow rate to any mass flow controller due to a change in set point is reflected as a rapid pressure change at one or more inlets in the other mass flow controllers. If an abrupt change occurs in a mass flow controller with a high flow rate, such undesirable side effects occur more clearly in a mass flow controller with a relatively low flow rate. Since the mass flow sensor of this embodiment is a thermal mass flow sensor positioned to sense the flow to the mass flow controller at the entrance to the mass flow controller, the mass flow sensed by the thermal mass flow sensor is , May not accurately reflect the flow at the controller exit. To compensate for this disadvantage, a mass flow sensor according to one aspect of the principles of the present invention is a pressure arranged to provide an indication of the pressure in the volume between the inlet and outlet of the mass flow controller. Includes sensors. In one embodiment, the pressure sensor is located in a “dead volume” between the thermal mass flow sensor bypass and the outlet control valve. The electronic controller uses the pressure indication provided by the pressure sensor to compensate the measure of mass flow provided by the thermal mass flow sensor. The resulting compensated mass flow reading reflects more accurately the flow at the outlet of the mass flow controller, and as a result, this reading is effective for the operation of the outlet control valve by the mass flow controller. Used. A display for displaying the sensed pressure may be included. This display may be attached to and supported by the mass flow controller, or if it is remote, for example, at the location of a gas box control panel connected to the mass flow controller via a data link There is also.

  In semiconductor processing applications, the process tool includes a plurality of chambers, each chamber having a plurality of mass flow controllers that control the flow of constituent gases into itself. Each mass flow controller is typically recalibrated every two weeks. This recalibration process is described in US Pat. No. 6,332,348, issued December 25, 2001 to Yelverton et al. This US patent is incorporated in this application. During such “in-situ” calibration, the conventional method involves a technician connecting a mass flow meter to each of the mass flow controllers with a wire and passing the gas through the mass flow meter and the mass flow controller. It is necessary to compare the mass flow controller reading with the mass flow meter reading and adjust the calibration constants as necessary. Such cumbersome operation is very time consuming and expensive due to the human expense and the lack of process tools with which the mass flow controller operates. In the embodiment detailed in the discussion relating to FIG. 7, a mass flow controller in accordance with the principles of the present invention includes a self-calibration mechanism that substantially eliminates such cumbersome and expensive operations.

  The cross-sectional view of FIG. 2 provides an illustration of a mass flow controller 200 using a mass flow sensor 202 according to one aspect of the principles of the present invention. The mass flow sensor 202 includes a thermal mass flow sensor 204, a pressure sensor 206, a temperature sensor 208, and an electronic controller 210. The laminar flow element 212 establishes a pressure drop across the capillary of the thermal mass flow sensor 204, which is described in more detail in the discussion relating to FIG. In operation, fluid that is directed to the mass flow controller 200 through the inlet 214 travels through a bypass channel 216 that includes a laminar flow element 212. A relatively small amount of fluid is diverted through the thermal mass flow sensor 204 and re-enters the bypass channel 216 downstream of the laminar flow element 212. The electronic controller 210 operates the outlet control valve 220 to provide a controlled fluid mass flow rate to the outlet 222 by providing a signal to the control valve actuator 218. The pressure sensor 206 senses the pressure in the volume in the bypass channel 216 between the laminar flow element 212 and the outlet control valve 220. This volume is referred to as “dead volume 216a” in this application. As will be described in detail later in the discussion relating to FIG. 5, the electronic controller 210 uses the pressure sensed by the sensor 206 in the dead volume 216a to use the inlet flow rate sensed by the thermal mass flow sensor 204. To compensate. This compensated inlet flow rate value more accurately reflects the flow rate at the outlet, which is the ultimate target of control. In particular, a mass flow sensor according to one aspect of the principles of the present invention provides an accurate measure of mass flow during a pressure transient using a time rate of change of pressure in a known volume 216a; In combination with a thermal mass flow sensor that is “corrected” using pressure driven mass flow measurements. The temperature sensor 208 senses the temperature of the fluid in the dead volume. In one embodiment, the temperature sensor 208 senses the temperature of the controller wall as an approximation of the temperature of the fluid in the dead volume 216a.

  The dead volume volume 216a is determined, for example, during the manufacturing or calibration process and stored or downloaded for use by the electronic controller 210. By obtaining sequential readings from the pressure sensor output 206 and acting on the data, the electronic controller 210 determines the rate of time change in pressure within the dead volume 216. Given the dead volume, the temperature of the fluid in the dead volume, the flow rate at the inlet sensed by the thermal mass flow sensor 204, and the time rate of change in pressure in the dead volume, the electronic controller 210 approximates the fluid flow rate at the output 222 of the mass flow controller 200. As mentioned earlier, this approximation can also be viewed as a compensation for the numerical value of the mass flow rate produced by the thermal mass flow sensor 204. The electronic controller 210 uses this calculated output fluid flow rate in a closed loop control system to control the opening of the outlet flow control valve 220 of the mass flow controller. In certain embodiments, the pressure value sensed by pressure sensor 206 is displayed locally (ie, at the pressure sensor) and / or remotely (eg, at the control panel or via a network interface). be able to. In the self-calibrating process described below in the discussion with respect to FIG. 7, the electronic controller 210 implements the actual flow into the mass flow controller by calculating the time derivative of the pressure signal when the flow rate varies in the mass flow controller. Leading the flow rate. This actual flow rate can be used to construct a mass flow controller.

  The cross-sectional view of FIG. 3 provides a more detailed view of the thermal mass flow sensor 204, but this sensor can be used with a pressure sensor to compensate for a compensated mass flow indication, i.e., in a digital implementation. Produces a multi-bit digital value. This multi-bit digital value is closer to the actual mass flow at the outlet of the mass flow controller than the value that an uncompensated mass flow sensor would give, especially during pressure transients at the inlet line of the mass flow controller Provide an approximation. The thermal mass flow sensor 204 includes a laminar flow element 212 that is in the bypass channel 216 and provides a pressure drop across the bypass channel 216 relative to the thermal mass flow sensor 204. Provide to drive a portion of the gas that passes through the sensor capillary 320 of the thermal mass flow sensor 204. The mass flow sensor 202 senses the flow rate of gas passing through the controller 200 and controls the operation of the control valve 220 accordingly. The thermal mass flow sensor assembly 204 is attached to the wall 322 of the mass flow controller 200 that forms the boundary of the bypass channel 216. Input 324 and output 326 apertures in wall 322 provide access to thermal mass flow sensor assembly 204 for gas moving through the thermal mass flow controller, which is typically bypassed. • The portion of the path between the input and output that defines the channel. In this example, mass flow sensor assembly 204 includes a base plate 328 for attachment to wall 322. Base plate 328 is attached to the wall and the rest of the sensor assembly using, for example, a combination of a threaded hole and a bolt that engages it. The legs of the sensor tube 320 with the input 330 and the output 332 extend through the respective apertures 334 and 336 of the base plate 328 and the apertures 324 and 326 of the mass flow controller wall 322. .

  The mass flow sensor assembly preferably includes portions of an upper portion 338 and a lower portion 340 that, when combined, are coupled to the active area of the sensor tube 320 (ie, by the opposite ends of the resistive element in thermal contact with the sensor tube). A thermal clamp 341 is formed that maintains both ends of the defined region) at substantially the same temperature. This thermal clamp also forms a chamber 342 around the active area of the sensor tube 320. That is, the portion of the mass flow sensor tube in the chamber 342 is in thermal communication with two or more resistive elements 344, 346 that each function as a heater, a detector, or both. One or more of these elements are energized by an electrical current to provide heat to the fluid as it flows through the tube 320. The thermal clamp 341 is typically manufactured from a material characterized by a higher thermal conductivity compared to the thermal conductivity of the sensor tube, but the sensor tube slightly downstream of the resistive element 344. And a portion of the sensor tube slightly upstream of the resistive element 344 has a good thermal conductivity contact relationship. Thus, the thermal clamp surrounds and protects the resistive elements 344 and 346 and the sensor tube 320. Furthermore, the thermal clamp 341 thermally “fixes” the portion of the sensor tube that is in contact to or near ambient temperature. In order to remove even the slightest errors due to temperature differences, the sensor tube is moved inside the thermal clamp and any difference between the resistances of the two coils is due to the fluid flow through the sensor tube. It is ensured that it is not due to a temperature gradient applied to the coil from the environment.

  In this embodiment, resistive elements 344 and 346 each include a heat sensitive resistive conductor that is wrapped around a corresponding portion of sensor tube 320. The resistive elements each extend along a corresponding portion of the sensor tube 320 along an axis defined by the working portion of the sensor tube 320. The downstream resistance element 346 is disposed downstream of the resistance element 344. The elements are preferably in contact with each other or separated by a small gap for manufacturing convenience and electrically connected in the middle of the tube. Each resistive element 344, 346 provides an electrical resistance that varies as a function of its temperature. The temperature of each resistive element varies as a function of the current flowing through the resistive element and the mass flow rate in the sensor tube 320. In this way, each resistive element operates as both a heater and a sensor. That is, these elements operate as a heater that generates heat as a function of the current flowing through the element, and at the same time operate as a sensor that allows the temperature of the element to be measured as a function of its electrical resistance. . The thermal mass flow setup 204 uses any of a variety of electronic circuits, typically having a Wheatstone bridge configuration, to provide energy to the resistive elements 346 and 344 in the temperature dependent element. The change in resistance is measured, and thus the mass flow rate of the fluid passing through the sensor tube 320 is measured. Circuits used for this purpose are disclosed, for example, in US Pat. No. 5,461,913 to Hinkle et al. And US Pat. No. 5,410,912 to Suzuki. These US patents are hereby incorporated by reference in their entirety.

  In operation, fluid flows from the inlet 214 to the outlet 222 and a portion of the fluid flows through the resistive laminar flow element 212. The remaining and proportional portion of fluid flows through sensor tube 320. A circuit (not shown) causes current to flow through the resistive elements 344 and 346, whereby the resistive elements 344 and 346 generate heat and provide it to the sensor tube 320, thus passing through the sensor tube 320. Give to flowing fluid. The upstream resistive element 346 transfers heat to the fluid before it reaches the portion of the sensor tube 320 that is surrounded by the downstream resistive element 344 so that the fluid flows from the downstream resistive element 344. Rather, it conducts more heat from the upstream resistive element 346. The difference in the amount of heat taken away by conduction from the two resistive elements is proportional to the mass flow rate of the fluid in the sensor tube and, by extension, the total mass passing through the mass flow rate controller 200 from the input port 214 to the output port 222. Proportional to flow rate.

  The conceptual block diagram of FIG. 4 illustrates the architecture of an electronic controller 400 as may be used with a mass flow sensor according to the principles of the present invention. In this embodiment, controller 400 includes an interface between sensor 402 and actuator 404. Between sensor interfaces 402, a flow sensor interface 408 operates in conjunction with the mass flow sensor to produce a digital representation of the mass flow rate in the associated mass flow controller. The controller 400 may include various other sensor interfaces such as a pressure sensor interface 410 and a temperature sensor interface 411. One or more actuator drivers 412 are used by the controller 400 to control, for example, the opening of the output control valve of the associated mass flow controller. The actuator may be any type of actuator, such as a current driven solenoid or a voltage driven piezoelectric actuator.

  The controller 400 operates in conjunction with the mass flow controller to produce a digital representation of the mass flow rate in the associated mass flow controller. A thermal mass flow controller as discussed in the discussion relating to FIG. 3 may be used to produce a mass flow measurement. The controller 400 may monitor the pressure of the fluid in the associated mass flow controller using the pressure sensor interface 410. In some embodiments, a pressure sensor, such as pressure sensor 206 of FIG. 2, provides a measure of pressure in the mass flow controller. More specifically, in this embodiment, the sensor measures the pressure inside the dead volume of the mass flow controller. In one embodiment, the mass flow controller pressure measured in this way is displayed, for example, at the pressure sensor 206 or controller housing, or elsewhere.

  The controller 400 converts this pressure measurement into a digital format that can be used in analysis or other functions. For example, if the mass flow controller uses a thermal mass flow sensor, the controller 400 can use the pressure measurement of the mass flow controller to compensate for an inlet pressure transient. For example, a temperature sensor interface can be used to obtain temperature readings from temperature sensors attached to the mass flow controller wall, but a separate temperature sensor is required for each mass flow controller There is nothing. For example, as discussed in more detail in the discussion relating to FIG. 1, a mass flow controller is used with a semiconductor processing tool that includes a number of mass flow controllers and other devices that are all linked to the controller, such as a workstation. There are many. The processing tool is operated in a carefully controlled environment characterized by a relatively stable temperature. The temperature of the fluid in the mass flow controller is approximately equal to the temperature of the enclosure wall, and the enclosure wall is approximately equal to the temperature of the room in which the tool is located, for example, the workstation controlling the tool The temperature measurement from can provide a sufficiently accurate estimate of the gas temperature in the mass flow controller. As a result, in addition to or instead of using a separate temperature sensor at each mass flow controller, the temperature was placed on another sensor in the same environment as the mass flow controller, for example, a workstation. It is possible to get from things.

  The controller 400 is used with one or more input devices such as a keypad, keyboard, mouse, trackball, joystick, buttons, touch screen, dual in-line package (DIP) or thumbwheel switch, for example, It includes a local user interface 416 that receives input from a user such as a technician operating the controller. The local user interface 416 also includes one or more outputs suitable for driving one or more devices such as a display, which is used to communicate information from the mass flow controller to the user. For example, an indicator light or audio output device such as a character, alphanumeric or graphic display. The communication interface 416 allows the mass flow controller to communicate with one or more other devices and / or a local controller, such as a workstation that controls a tool that uses multiple mass flow controllers, and / or an integrated circuit, for example. It is possible to communicate with other devices for manufacturing the device.

  In this embodiment, the communication interface 414 includes a DeviceNet interface. Device nets are known and are discussed in US Pat. No. 6,343,617 issued to Tinsley et al. On Feb. 5, 2002. This US patent is incorporated in this application. The controller 400 may also be in the form of an electrically erasable programmable read only memory (EEPROM) used to store, for example, calibration data, mass flow controller IDs or codes for operating the mass flow controller. Storage 418 having Various other types of storage such as random access memory (RAM) can also be used. Storage can take many forms and, for example, some are physically located on the controller's “chip” (integrated circuit) while others are It can also be given off-chip. The controller 400 uses a data processor 420 which, for example, takes the form of an arithmetic logic unit (ALU) in a general purpose microprocessor to reduce data. For example, the data processor 420 averages the readings received at the sensor input to determine the number of times the sensor reading has exceeded one or more threshold values, and the sensor reading remains within the threshold value range. Record time or perform other forms of data logging.

  Pressure transients in the inlet supply line to the mass flow controller 200 using the thermal mass flow sensor 204 result in mass flow readings that contain errors. Mass flow readings with errors can cause improper control of the mass flow controller outlet valve, which can damage objects being processed with gas under the control of the mass flow controller. Or there is a possibility of destruction. The digital representation of the mass flow rate has one or more data value formats and causes fluctuations due to pressure transients in the mass flow sensor inlet line. In one embodiment, the controller 400 uses data obtained at the pressure sensor interface 410 to compensate for fluctuations that occur in the thermal mass flow sensor 204 due to pressure transients in the mass flow sensor inlet line 214. In this embodiment, the controller 400 acquires temperature information via the temperature interface 411. The controller 400 uses the temperature, pressure and mass flow readings obtained from the corresponding interface to more accurately determine the mass flow at the outlet of the mass flow sensor than if readings from the thermal mass flow sensor alone provide. Produces a compensated mass flow reading that reflects. The controller 400 also provides control to the sensors as needed via the flow sensor interface, pressure sensor interface and temperature interfaces 408, 410 and 411, respectively.

  Controller 400 includes a valve actuator interface 404 that is used to control the position of a valve, such as valve 220 of FIG. 2, through a mass flow controller, such as mass flow controller 200, in a closed loop control process. To control the fluid flow rate. The valve actuator is, for example, a solenoid-driven actuator or a piezoelectric actuator. The controller 400 has the ability to read various sensor outputs with sufficient speed and to operate to compensate and adjust the mass flow controller outlet control valve 200 as necessary to produce a predetermined flow rate. There must be. The flow rate is predetermined in the sense that it is “desired” in a certain sense. However, in the sense that it must be a static setting, it is not predetermined. That is, the predetermined flow rate can be set by an operator using mechanical means such as dial settings, or can be downloaded from another controller, such as a workstation, and updated.

  In one embodiment, the controller 400 uses flow readings obtained at the mass flow interface 408 from a thermal mass flow sensor 204 that senses the mass flow at the inlet 214 to the mass flow controller 200 using readings from the pressure interface 410. Compensate the measured value. The compensated flow measurement more accurately represents the flow at the outlet 222 of the mass flow controller 200. This outlet flow is a flow that is directly controlled by the mass flow controller 200 and is typically a flow of interest to the end user. Flow measurements that are pressure compensated according to the principles of the present invention improve the accuracy of the outlet flow reading of the mass flow sensor, thereby allowing the mass flow controller to more accurately control the flow of fluid. That is, at equilibrium, the mass flow rate at the inlet of the mass flow controller is equal to the mass flow rate at the outlet of the same mass flow controller, but the flow rate is sometimes significant while the inlet or outlet pressure is in a transient state. Different. As a result, a mass flow controller that provides closed loop control that uses its inlet flow to control its outlet flow may be making substantial control errors.

The steady state mass flow in the sensor capillary 320 of the thermal mass flow sensor as described in the discussion relating to FIG. 3 is described by the following equation:
^{_{Qc = (d C 2 / 32μ}} ) (P i / P R) (P i -P) / L C
However,
dC = capillary inner diameter;
LC = capillary length;
ρi = gas density at the inlet;
ρR = density of gas at standard temperature and pressure;
μ = gas viscosity;
Pi = pressure at the inlet of the mass flow controller Po = pressure at the outlet of the mass flow controller;
P = pressure in the dead volume of the mass flow controller.

  The overall flow through the mass flow controller is related to the overall flow through the sensor capillary 320 via a separation ratio (split ratio) α≡QBP / Qc. Here, QBP is a flow that passes through the bypass channel 216, and Qc is a flow that passes through the capillary 320. The overall flow Qi at the mass flow controller inlet 214 is Qi = QBP + Qc = (1 + α) Qc.

If the flow continues to be stratified in both the bypass and the capillary, the separation rate will remain constant. When the inlet pressure varies with time, the transient nature of the inlet pressure and dead volume pressurization dominate the flow at the inlet. Assuming that the thermodynamic event in the dead volume occurs at a constant temperature equal to the temperature of the enclosure that forms a partial receptacle around the dead volume, mass conservation in the dead volume is qo ₌ I described by _{Qi- (T R V / T W} P R) (dP / dt).
However,
P _R = pressure at standard temperature and pressure (760 Torr);
T _R = temperature at standard temperature and pressure (273K);
T _W = wall temperature (mass flow controller wall temperature);
V = volume of dead volume;
Qi = inlet flow to the mass flow controller;
Qo = outlet flow from the mass flow controller.

  The mass flow sensor according to the principles of the present invention substantially compensates for the mass flow signal of the thermal mass flow sensor using the relationship of equation (2), thereby substantially reducing the mass flow reading error during pressure transients. Decrease.

  The flow diagram of FIG. 5 illustrates a process by which a thermal mass flow sensor reading can be processed according to the principles of the present invention. The process begins at step 500 and then proceeds to step 502 where a mass flow sensor controller such as the controller content acquisition server 400 of FIG. 4 obtains a mass flow reading. This reading is obtained from a thermal mass flow sensor via a flow interface, such as interface 408 of FIG. This flow measurement reflects the mass flow rate at the inlet of the mass flow controller and, as described above, does not adequately represent the mass flow rate at the outlet of the mass flow controller. The mass flow rate at the outlet of the mass flow controller is generally the ratio of interest used in control applications. As a result, the mass flow controller according to the principles of the present invention compensates for the inaccuracies inherent in assuming that the inlet flow rate to the mass flow controller is equal to the outlet flow rate from the mass flow controller. From step 502, the process proceeds to step 504, where the sensor controller 400 obtains the temperature of the flow in the bypass channel. This temperature can be obtained via a temperature interface, such as interface 412 of FIG. 4, or can be downloaded to a compensated mass flow sensor. The compensation process can safely assume that the gas temperature is equal to the temperature of the mass flow controller enclosure. Furthermore, in most applications, the temperature remains relatively stable over time, so that the stored temperature value can be used while updating as needed.

After obtaining the gas temperature at step 504, the process proceeds to step 506 where the sensor controller obtains the volume of the dead volume. This value is stored, for example, during manufacture. From step 506, the process proceeds to step 508 where the pressure in the dead volume is acquired over a period of time. The number of measurements and the time at which the measurements are made depend on the speed and duration of the transient at the mass flow controller inlet. In step 510, the processor uses the pressure measurement obtained in step 508 to calculate the time rate of change of pressure in the dead volume. After calculating the time rate of change of pressure in the dead volume, the process proceeds to step 512 where the compensated outlet flow value is calculated according to equation (2). In the calculation process, simplifications can be made. For example, dead volume volume, standard temperature, and standard pressure are all used together with inlet flow measurements and the time rate of change of pressure in the dead volume to calculate an approximate value for the compensated outlet flow. Can be combined into one constant. This simplification yields equation (3) of the form
Qo = Qi-C1 (V / T) (dP / dt)
However,
Qo = compensated sensed outlet flow rate;
Qi = sensed inlet flow rate;
C1 = normalization constant relating temperature and pressure to standard temperature and pressure;
V = volume between sensor bypass and outlet flow control valve T = temperature of fluid in this volume;
dP / dt = time change rate of pressure in volume.

  As described above, the volume V can be incorporated into the constant C1. From step 512, the process proceeds to step 514 where the flow sensor controller obtains pressure, temperature and flow readings and calculates an estimate of the compensated outlet flow as described. . The process proceeds from step 514 to step 516 and ends when the mass flow sensor is stopped.

  Returning to the block diagram of FIG. 4, in this example, the controller 400 allows an operator, such as a technician, to not only initialize the mass flow controller but also perform diagnostic tests on the mass flow controller. A diagnostic interface 422 is included. In addition, the interface 422 allows the operator to perform diagnostics so that it does not require input from a local system controller that normally controls the mass flow controller, such as a workstation. Become. Such diagnostics are transparent to the local system controller, which may not know about the diagnostics that are being executed, and consequently continues its operation unchanged. You can also. The diagnostic interface provides access to mass flow controller sensor measurements, control outputs, and mass flow controller diagnostic inputs and outputs. These various inputs and outputs are implemented and measured through the diagnostic interface with almost little delay. In the dual processor embodiment detailed in the discussion relating to FIG. 9, the decision processor modifies the output from, for example, a sensor or test point and / or monitors the input. During online diagnostics, the controller continues unimpeded to perform its process control functions, while at the same time, the controller interacts with the technician in real time (i.e., to a human operator). Provides an interaction such that no delay is perceivable), either locally or via a communication connection.

  Using the diagnostic interface 422, an operator can adjust control values such as set points used to determine the operation of the mass flow controller. Further, the operator can modify the sensor output value to test the mass flow controller response to the specified sensor reading. That is, the operator can operate the controller for diagnostic purposes by modifying the sensor reading that the mass flow controller uses to control the flow of gas through the outlet valve. The operator reads not only the information stored about the control (stored by the decision controller in the dual processor embodiment), but also all sensor and test point inputs, reads all sensor values, And control information such as a desired set point can be read. In addition, the operator can write to control the output and test points, and overwrite the stored values, such as sensor readings or set point information, to fully test the controller via the diagnostic port.

  In one embodiment, a mass flow controller according to the principles of the present invention includes a web server. Such a web server is included, for example, in a diagnostic interface. In this example, the diagnostic interface includes a web server that allows a mass flow controller to be used in a system such as that illustrated in the block diagram of FIG. In this system, a user such as a technician operates a web browser (eg, Netscape or Explorer) to communicate with a server 602 embedded in the mass flow controller 604, a personal digital assistant or A web browsing device 600 such as a cellular phone is used. Server 602 includes a web page that provides a user with an interface to mass flow controller 604 in accordance with the principles of the present invention. The discussion relating to FIGS. 13A through 13E provides further details regarding web server capabilities embedded in an exemplary embodiment of a mass flow controller in accordance with the principles of the present invention.

  Mass flow sensors are typically calibrated during their manufacturing process. Although the mass flow sensor is typically integrated into a mass flow controller, this discussion is with respect to a mass flow controller, but the methods and apparatus discussed herein are based on a “stand-alone” mass flow sensor. Can be applied as well. For the calibration process, the technician is required to supply gas to the mass flow controller at a known flow rate and to correlate the flow signal of the mass flow sensor with that known flow rate. For example, in the case of a mass flow sensor that provides a voltage output corresponding to the flow, the technician maps the voltage output from the sensor into the actual flow rate. This process is repeated for multiple flows, resulting in a voltage / flow correlation set. For example, a 4 volt output indicates a flow of 40 standard cubic centimeters per minute (sccm), a 5 volt output indicates a flow of 50 sccm, and so on.

  The flow rate that falls between the calibration points can be interpolated using, for example, linear or polynomial interpolation. This process can be repeated for multiple gases. Correlation tables relating signals (eg, voltages) from mass flow sensors for various gases to flow rates are thus created and stored. Such a table can be downloaded to the mass flow controller for use "in the field" or stored inside the mass flow controller. Often, a technician calibrates the mass flow controller with a relatively innocuous gas, such as N2, and provides a calibration factor that is used to correlate the flow of other gases to the calibration gas. These calibration factors are used in the field when a known gas “flows” through the mass flow controller to calculate the actual flow from the apparent flow. That is, the apparent flow is a flow correlated to N2, and when the arsine gas is sent through the mass flow controller, the mass flow controller multiplies the apparent flow by the arsine gas calibration factor. And get the actual flow. In addition, once in the field, the mass flow controller is regularly used to accommodate “drift”, direction, moisture content of the gas whose flow is being controlled, or to ensure other factors. Recalibration is done. US Pat. No. 6,332,348, issued to Yelverton et al. On Dec. 25, 2001, incorporated herein by reference, describes these factors and the tedious process necessary to perform these field calibrations. Are discussed in detail.

A calibration method and apparatus according to the principles of the present invention are described in the discussion relating to the conceptual block diagram of FIG. The calibration system and method may be used during manufacturing or, in some embodiments, incorporated into a self-calibrating mass flow controller. The mass flow controller 700 includes a mass flow sensor 702 and an electronic controller 704 that receives flow signals from the mass flow sensor 702. The calibrator 706 includes a variable flow gas source 708, a predetermined volume receptacle 710, and a pressure differentiator 712. It should be noted that the lines separating different functional blocks are somewhat fluid. That is, in different embodiments, functions associated with a block may be incorporated into one or more blocks. For example, in one embodiment, the pressure differentiator 712 is implemented in whole or in part by executing code in the electronic controller 704. Variable flow gas source 708 provides gas in proportion to both a predetermined volume receptacle and a mass flow sensor. The flow rate to the mass flow sensor 702 can be equal to the flow rate to the predetermined volume receptacle 710. That is, for example, the proportionality constant may be 1. The mass flow sensor 702 is configured to generate a mass flow signal that is indicative of the flow that it senses, and in this example, this signal is sent to the electronic controller 704. The pressure differentiator 712 generates a signal correlated to the flow from the variable flow gas source 708 to the predetermined volume of the receptacle 710 according to the relationship of Equation 4 below.
Qo = Qi-C1 (V / T) (dP / dt)
However,
Qo = outlet flow in units of standard cubic centimeters / minute;
Qi = inlet flow in units of standard cubic centimeters / minute;
C1 = normalization constant relating temperature and pressure to standard temperature and pressure;
V = predetermined volume of receptacle in liters;
T = Kelvin temperature of the fluid in the receptacle;
dP / dt = Time change rate of pressure in the receptacle in units of Torr / sec.

In one embodiment, the receptacle is closed and gas flows into the receptacle until the pressure in the receptacle is equal to the pressure of the gas supplied by variable flow source 708. In such an embodiment, the variable flow source is a constant pressure gas source that will supply gas at a flow rate that decreases exponentially as the pressure in the receptacle increases. In such a case, the outlet flow Qo = 0, and the inlet flow Qi is given by the following equation (5).
Qi = C1 (V / T) (dP / dt)
The pressure differentiator 712 calculates the time derivative of the pressure in the receptacle 710 and given the normalization constant C1, the predetermined volume V, and the gas temperature in the receptacle, this pressure differentiator (and The electronic controller 704) can determine the actual flow into the receptacle 710. Since the flow in the receptacle is proportional to the flow into the thermal mass flow sensor 702, the actual flow into the thermal mass flow sensor 702 is proportional to the actual flow into the receptacle (eg, these Can be determined by multiplying the number of negative cases is 1). The signal from the mass flow sensor is then correlated, for example by electronic controller 704, with the actual flow determined as described above. This correlation relates one or more signal levels from the mass flow sensor to the actual flow. The pressure differentiator 712 includes, for example, an analog differentiator circuit that calculates the time derivative of the pressure signal. The signal representing the time derivative dP / dt of the pressure in the receptacle, which is the output signal of this subcircuit, is sampled by an analog-to-digital converter (not shown), for example a microprocessor, DSP chip or dual processor Allows an electronic controller 704 to act on the time derivative signal. Alternatively, the pressure differentiator 712 may convert the pressure signal into a digital format for processing by the electronic controller 704. The electronic controller 704 calculates the time derivative of the pressure signal. In such an embodiment, the electronic controller operates as a differentiator with a differentiator code. The controller calculates the derivative using at least two pressure differences divided by the corresponding time interval. The gas is supplied in parallel to the receptacle and the mass flow sensor, or is supplied in series. This will be explained in more detail in the discussion below regarding the self-calibrating mass flow controller.

  In operation, the mass flow controller can be calibrated as described above using a plurality of gases and using correlation values (mapping sensor output to actual flow) stored in a table. A calibration factor relating one gas flow measurement to another gas can be generated and stored. This table and / or coefficients can be downloaded to an on-site mass flow controller, which can be used by the controller in controlling the gas flow. Various known interpolation methods, such as linear or polynomial interpolation, can be used with the calibration table and / or coefficients. Furthermore, the calibration table and / or coefficients so stored can be used as default values in a self-calibrating mass flow controller according to the principles of the present invention. A self-calibrating mass flow controller according to the principles of the present invention includes a calibrator 706 and a mass flow sensor 702 and can be used to calibrate the mass flow controller as described above. However, in the case of a self-calibrating mass flow controller, the calibration can be performed in situ, i.e. in the field, as easily as manual setting.

  For example, as in the system 100 of FIG. 1, once installed on-site in a semiconductor processing tool, the mass flow controller can itself calibrate with the gases used during semiconductor processing. By using the gas used in the process, the mass flow controller can provide more accurate flow measurements because the mass flow controller automatically changes, for example, moisture content. Because it can. In addition, a new process gas can be used just as easily as a conventional gas because the self-calibrating mass flow controller is a standard other gas such as N2. Because it can itself be calibrated (i.e., correlate the mass flow signal level with the actual flow level determined by the pressure differentiator). Since the mass flow controller is calibrated in the direction it will be used, the disadvantages caused by the redirection of the mass flow controller in the field in relation to the calibrated position during manufacturing are virtually eliminated. The All mass flow controllers in a system, such as the system 100 of FIG. 1, can be calibrated automatically and simultaneously for a short period of time. This is in contrast to the cumbersome and difficult process used in conventional mass flow controllers. In the conventional process, one technician performs a calibration operation individually using a plurality of mass flow meters while jumping from one mass flow controller to another. As will be explained in more detail later when discussing FIG. 8, a mass flow controller including a thermal mass flow sensor and a pressure transducer is required to produce a fluctuating gas flow into its dead volume. Close its outlet valve. By calculating the time derivative of pressure, the actual flow into the dead volume receptacle can be determined. The correlation of the actual flow value by the mass flow controller to the thermal mass flow sensor signal acts as a calibration of the mass flow controller.

  FIG. 8 is a conceptual block diagram of a self-calibrating mass flow controller 800 in accordance with the principles of the present invention. In this exemplary serial flow embodiment, gas flows through thermal sensor 802 into a predetermined volume of receptacle 804 and passes through outlet valve 806. The exit flow Qo is typically a controlled flow into a chamber, such as a chamber in an integrated circuit processing tool. In this embodiment, an electronic controller 808 that executes the code that performs the differentiation required to obtain the actual flow as described in the discussion with respect to FIG. 7 includes a thermal sensor 802, a pressure sensor 805, and an outlet valve 806. Has a communication relationship. In one exemplary process, electronic controller 808 operates with outlet valve 806 to form a variable flow gas supply. That is, the electronic controller reduces the flow exponentially by closing the outlet valve. The pressure in the dead volume increases and the electronic controller differentiates this signal multiple times to obtain the actual flow reading and correlates to the mass flow sensor signal value over a relatively wide range of flows. In addition, the electronic controller is fully opened before the outlet valve is closed to expand the time period during which the flow fluctuates and to obtain the actual flow value used to correlate with the thermal mass flow signal value over a wide range. Release to the desired position.

An overview of the pressure and flow associated with such a process is conceptually illustrated in FIG. At start time t _0, the pressure difference between the pressure P _R in the downstream gas pressure Pin and receptacle 804 at the inlet to the mass flow controller, the gas is forced to flow at a rate Qin through the mass flow controller. In this example, the inlet pressure Pin, the pressure P _R of within the receptacle, the flow Qin passing inlet of a mass flow controller, a constant. At time t _SO , the controller closes the outlet valve, thereby reducing the outlet flow Q _O to zero. As long as there is a pressure difference between the receptacle and the inlet, the gas will continue to flow into the receptacle. As the pressure P _R in the receptacle exponentially increases toward the equal equilibrium with the inlet pressure Pin, the inlet flow Qin decreases. By calculating the derivative of the pressure change in the receptacle (also referred to as “dead volume” in the context of the embodiment of the invention), the electronic controller, as described above, The actual flow to can be determined.

The electronic controller can calibrate the mass flow sensor by correlating multiple simultaneous readings arising from the thermal mass flow sensor. That is, once this process is complete for a particular gas, the flow reading from the thermal mass flow sensor can be correlated to the actual flow rate. This result can be used by the electronic controller 808 to control the opening of the valve 806 in the closed loop control system to produce the selected flow downstream. In order to increase the time period t _SO from when the controller closes the valve to when the flow becomes undetectable, ie, to increase the number of pressure measurements that can be taken and improve accuracy, before closing at time t _SO, it is possible to open the valve. In addition, one or more flow restriction means may be disposed in the flow path between the inlet to the thermal mass flow sensor and the inlet to the receptacle 804.

  The conceptual block diagram of FIG. 10 illustrates the architecture of a dual processor embodiment of electronic controller 100 that can be used in a mass flow sensor according to the principles of the present invention. In this embodiment, the controller includes two processors 1002, 1004. One processor 1002 is dedicated to “real-time” processes and the other processor 1004 is dedicated to non-real-time processes. Here, “real time” means a process that requests a specific level of service during a limited response time. In this sense, such a process is decisive and the processor 1002 will be referred to herein as a decision processor. The purpose of the dual processor architecture is to manage asynchronous event responses in a predictable manner with a reduced number of interrupts. The non-decision processor 1004 is to handle event-driven interrupts such as responses to input from the user. The decision processor 1002 processes only frame-driven interrupts, i.e. regularly timed interrupts. In one embodiment, the non-deterministic processor is not a special purpose coprocessor such as a mathematical or communications coprocessor, but a general purpose processor 1004 suitable for various tasks such as a user interface and various other tasks. . In particular, a TMS320VC5471 available from Texas Instruments can be used in a dual processor embodiment that follows this principle. This TMS320VC5471 is described in the data manual available at http://www-s.ti.com/sc/ds/tms320vc5471.pdf. This is incorporated in this application.

  The processor interface 1006 provides communication between processors. Decision processor 1002 includes a sensor and actuator interface. Within the sensor interface, the flow sensor interface 1005 operates in conjunction with a mass flow sensor to produce a digital representation of the mass flow rate at the associated mass flow controller. One or more actuator interfaces 1010 are used, for example, by decision processor 1002 to control the opening of the output control valve of the associated mass flow controller or to drive a diagnostic test point. The actuator is, for example, a current-driven solenoid or a voltage-driven piezoelectric actuator. As described in detail below in the discussion of the flow diagram of FIG. 9, after initialization, the decision processor 1002 loops through the control sequence, collects sensor data, and sets configuration information (eg, desired mass). Collect flow rate settings), provide status information, and control the status of the outlet valve. Since non-deterministic tasks are offloaded to non-determining processor 1004, the decision processor control loop can be very compact. As a result, the control task can be executed during a minimum time period, and the control readings and drive signals will provide time for non-deterministic tasks in advance. Can be updated more often than is possible.

  The controller 1000 operates in conjunction with the thermal mass flow sensor described in general terms in the discussion regarding FIG. 3 to produce a digital representation of the mass flow rate into the associated mass flow controller. This digital representation has the form of one or more data values and is subject to fluctuations due to pressure transients at the input of the mass flow sensor. More specifically, the controller 1000 uses the data acquired at the pressure sensor interface 1006 to compensate for fluctuations induced in the thermal mass flow sensor due to pressure transients in the mass flow sensor inlet line. . In this example, decision processor 1002 uses temperature, pressure, and mass flow readings obtained from interfaces 1008, 1007, and 1005, respectively, at the outlet of the mass flow sensor rather than readings from thermal mass flow alone. Produces a compensated mass flow reading that more accurately reflects the mass flow. The decision processor 1002 also provides control to the sensors as needed through the heat flow 1005, pressure 1007 and temperature 1008 sensor interfaces. The compensation process is described in more detail below in the discussion relating to FIG. The decision processor 1002 also includes a valve actuator interface 1010, which controls the position of a valve, such as the valve 220 of FIG. Used to control the flow rate of fluid through a mass flow controller.

  The decision processor 1002 is dedicated to the closed-loop valve control process, so that it reads various sensor outputs with sufficient speed and compensates and adjusts the valves as necessary to produce a predetermined flow rate. The action can be performed. The flow rate is predetermined in the sense that it is “desired” in a certain sense, and no static setting is required. That is, the predetermined flow rate can be set by the operator using mechanical means such as dialing, or downloaded from another controller, such as a frequently updated workstation. Is possible. Typically, relatively high speed operations are required for gas flow control, and in this case for compensated gas flow control. Various types of processors such as reduced instruction set (RISC), mathematical coprocessor, digital signal processor (DSP) are suitable for such high speed operation. The DSP's computational performance regarding signal conditioning and interface is particularly suitable for operations such as decision processor 1002. As discussed in detail later in the description of the control process associated with the discussion of FIG. 9, the functions performed by decision processor 1002 are controlled by certain operations being completed in a timely and regular manner. It is crucial in that it can eliminate the possibility of errors and instability in the process. The decision 1002 and non-decision 1004 processors communicate via the interprocess interface 1006 in a manner that does not interfere with the critical operation of the decision processor 1002. The communication between processors will be described later in detail in the discussion regarding FIG.

  Non-decision processor 1004 is used with one or more input devices such as, for example, a keypad, keyboard, mouse, trackball, joystick, button, touch screen, dual in-line package (DIP) or thumbwheel switch, Input from a user such as a technician operating a mass flow controller associated with the non-determining processor 1004 is received. The local user interface 1016 also includes one or more outputs suitable for driving one or more devices such as a display, which is used to communicate information from the mass flow controller to the user. For example, an indicator light or audio output device such as a character, alphanumeric or graphic display. The communication interface 1018 allows the mass flow controller to communicate with one or more other devices and / or a local controller, such as a workstation that controls a tool that uses multiple mass flow controllers, and / or an integrated circuit, for example. It is possible to communicate with other devices for manufacturing the device. In this embodiment, the communication interface 1018 includes a DeviceNet interface. A diagnostic interface 1020 is provided for a technician to perform a diagnosis as described above in connection with the diagnostic interface 422 of FIG. In one embodiment, the diagnostic interface includes an Ethernet interface and a web server.

  The compact code for decision processor 1002 allows the decision processor to respond appropriately to input changes and to quickly modify actuator signals in response to such changes. is there. Also, this division of operation between the decision processor and the non-decision processor facilitates initial development of code for both the decision processor and the non-decision processor. For example, the decision code need not respond to unscheduled events such as "mirroring" the user's request on the display at the user interface, and the non-decision code can be set to control the outlet valve every 50 bus cycles. There is no need to leave the user feedback to adjust. Also, revision and update are relatively easy due to the division between decision and non-decision. If the code for one processor has to be revised or updated, the code for the other processor needs no revision or only a few revisions. In particular, the code for the decision processor is more “mature” or fixed than the code for the non-decision processor. That is, user interfaces, communications or other similar functions tend to be updated more frequently than critical mass flow controls and functions.

  With this exemplary dual processor embodiment, the user interface can be updated, for example, without any impact on the control function code. Revision and maintenance of mixed-mode code (decision and non-determination code) is much more complex and expensive than code divided in a manner according to the principles of the present invention. In one embodiment, the dual processor controller 1000 may be a hybrid processor with two processors mounted on a single integrated circuit. An integrated circuit such as the TMS320C5471 hybrid processor available from Texas Instruments can be used as a dual processor in accordance with the principles of the present invention. The digital signal processing (DSP) subsystem of this chip is more suitable as a decision processor in such applications due to its mathematical capabilities. The IC's dual-port memory can be used as an interface between processors, in which case the processor that writes to and reads from the memory location contains information including data, commands, and command responses. It has a role of functioning as a “mail box” for transferring the mail.

  Such an inter-processor interface allows the decision processor to continue to operate in a frame driven mode while simultaneously playing a diagnostic and calibration role. Any request for sensor data from a non-decision processor can be picked up from the mailbox on one pass through the decision processor's control loop, and the reading will be placed in the mailbox on the next pass through that loop. Can be put. The diagnostic output can be modified in the same way. The decision processor can also operate in other non-process oriented modes. For example, during the self-calibration process as described above, the decision processor no longer operates to maintain a set flow that passes through the mass flow controller. In such a mode, the decision processor closes the mass flow controller outlet valve, calculates multiple time derivatives of pressure in the dead volume, calculates the corresponding actual flow in the mass flow controller, It is occupied by correlating that actual flow with the flow signal from the thermal mass flow sensor.

  The flow diagram of FIG. 11 is an overview of a process for sensing and controlling gas flow through a dual processor mass flow controller in accordance with the principles of the present invention. The process begins at step 1100 and then proceeds to step 1102 where the controller is initialized. This initialization step may include uploading calibration values or the calibration sequence itself. Further, operational codes for both decision processor 1002 and non-decision processor 1004 may be uploaded at this point. In one embodiment, non-decision processor 1004 uploads its own code and begins operation, and then uploads code for decision processor 1002. In the process of uploading code for decision processor 1002, non-decision processor 1004 coordinates the operation of decision processor 1002 by making a choice between multiple executable code sets that are uploaded to decision processor 1002. Non-decision processor 1004 makes this selection based on, for example, switch settings, commands from a local controller (eg, a workstation that controls the operation of a semiconductor process tool) or settings stored in non-volatile storage. . Such selection allows the mass flow controller to be adapted to different flow control operations. For example, an engineer can make the controller to operate in “pressure controller” mode rather than “mass flow controller” mode by making a choice between code sets, Or remotely (i.e., via a communication link).

  In step 1104, the non-decision processor 1004 sends the action code and initial control settings to the decision processor 1002, which operates in a manner generally as described in the flow charts of FIGS. Start. From step 1104, the process proceeds to step 1106, where the non-determining processor 1004 services the local input / output impedance. Providing this service includes reading various inputs including keyboard, switch or mouse inputs and displaying information locally via LEDs, alphanumeric displays or graphical displays. From step 1106, the process proceeds to step 1108, where the non-decision processor 1004 provides services for the communication interface. This service provision includes uploading control and sensor data to a workstation operating as a local controller of, for example, a semiconductor process tool. Further, the non-decision processor 1004 can also download updated settings from the local controller.

  The process proceeds from step 1108 to step 1110, where the non-decision processor 1004 services the diagnostic interface. Various diagnostic operations may be performed as described in the discussion relating to FIG. In one embodiment, the mass flow controller includes a web server that allows an operator to perform diagnostics over a network such as the “world wide web”. Following step 1110, the process proceeds to step 1112 where the non-decision processor 1004 provides service to the interprocess interface 1006. During “normal” non-decision operations, the non-decision processor 1004 obtains readings from the decision processor 1002 and sends control information such as flow settings obtained via the communication interface to the decision processor. From step 1112, the process proceeds to end step 1116 where, for example, the mass flow controller is turned off.

  As mentioned above, the steps given in this flow chart and other flow charts in this application need not be sequential; in fact, many functions performed by the non-decision processor 1004 are event interrupt driven. There is no predictable sequence in the operation of this non-deterministic processor. Other processes such as data logging may be performed at regular intervals. Non-decision processors provide a relatively direct connection between a remote user and a decision processor, for example, by supporting a two-way socket connection to the decision processor via an Ethernet network interface can do.

  The flowcharts of FIGS. 12A-12B illustrate the operation of the decision processor of a dual processor mass flow controller in accordance with the principles of the present invention. In the context of this flowchart, it is assumed that an initialization process has already occurred and the decision processor is cycling through its control loop. The process begins at step 1200 of FIG. 12A and then proceeds to step 1202, where the decision processor should operate with its “normal” control capability, eg, manual diagnostic mode or automatic Judge whether to operate in other modes such as diagnostic mode. The decision processor makes this decision based on information obtained from the processor-to-processor interface 1006. The decision processor operates in a claims-driven manner rather than an event-driven interrupt, and as a result, periodically polls the processor-to-processor interface to obtain such information.

  If the decision processor operates in its normal mode, the process proceeds from step 1202 to 1204, where the decision processor obtains information regarding the desired control settings from the interprocessor interface. This information may be in the form of a desired flow rate received, for example, from a local controller, from a front panel user interface, or from a diagnostic port. The decision processor may also transfer information, such as sensor data, to the non-decision processor via the processor-to-processor interface during this step. From step 1204, the process proceeds to step 1206, where the decision processor collects data from, for example, various sensors. Sensors from which the decision processor collects data include, for example, mass flow sensors (thermal or other types), temperature sensors, or pressure sensors.

  From step 1206, the process proceeds to step 1208, where the decision processor calculates the flow rate of material through the mass flow controller. In one embodiment, the mass flow controller includes a thermal mass flow sensor and a pressure sensor that measures the pressure in a dead volume between the thermal mass flow sensor bypass and the mass flow controller outlet valve in step 1212. And are included. In this embodiment, the decision processor uses the method described above in connection with the discussion of FIG. 5 to compensate for the flow rate measured by the thermal mass flow sensor at the controller inlet to obtain the flow rate at the controller outlet. Approximate more accurately. In embodiments where the flow rate obtained from the sensor is not compensated, the process skips the calculation process of step 1208 and proceeds directly from step 1206 to step 1210.

  In step 1210, the decision processor indicates the flow rate calculated in step 1208 (or read in step 1206) by setting information obtained from the non-determining processor via the processor-to-processor interface in step 1204. Determine if it is equal to the desired flow rate. If these values are equal, the decision processor continues operation as indicated by the “Continue” block 1214 as described above (ie, the decision processor returns to step 1202 and enters the loop). Continue the cycle). If these values are not equal, the decision processor calculates an error signal and uses this error signal to adjust the drive signal to the outlet valve of the mass flow controller. From step 1212, the process proceeds to continue at step 1214. The process then proceeds from step 1214 to step 1216, where the mass flow controller is terminated or reset, for example.

  If in step 1202 concludes that the decision processor should not operate in normal mode, the process proceeds to step 1218 of FIG. 12B via connection box A, where the decision processor should operate in diagnostic mode. Judge whether or not. The decision processor can obtain this information from the processor-processor interface. If the decision processor is to operate in diagnostic mode, the process proceeds to step 1220. In step 1220, the decision processor determines in which diagnostic mode to operate. Again, this information can be sent to the decision processor via the processor-to-processor interface. In the “automatic” mode, the decision processor obtains a series of diagnostic values from the interprocessor interface. The decision processor can obtain this set of values at this interface. The diagnostic value is a value that sets the opening of the outlet valve of the mass flow controller or a value that sets the test point drive value. A reading may be indicated. This diagnostic value may also indicate, for example, a sequence in which this value is used to set the test point drive value and read the test point output. In manual mode, diagnostic values are made available to the decision processor one at a time via the processor-to-processor interface. In an embodiment where the mass flow controller includes a web server, a technician connects to the server in the mass flow controller using a workstation that can browse to the web. Once the link to the server is established, the technician can enter a valve setting command, for example, by typing, selecting from a pull-down menu, or clicking on an icon. This single configuration command is received by the non-decision processor via its decision port and sent to the decision processor via the processor-to-processor interface.

  In manual diagnostic mode, the decision processor executes any diagnostic value available at the processor-to-processor interface via the diagnostic value and returns to its normal control loop. For example, if a single diagnostic value, such as a test point drive value, is provided to the decision processor, this “overrides” a single control loop cycle and a series of diagnostic values is determined. When given to the processor, it takes precedence over multiple control loop cycles. In the automatic diagnostic mode, a large number of diagnostic values are exchanged via the processor-to-processor interface during a period corresponding to several control loop cycles, and at least 10 times a significant number of control loops in many orders. The cycle intervenes during the automatic diagnostic exchange. The diagnostic modes may be combined, for example, to produce an automatic active online diagnostic mode. In one embodiment, a mass flow controller according to the principles of the present invention operates in a 1 millisecond control loop cycle and provides 1 percent of full scale accuracy during that cycle.

  Keeping in mind these various diagnostic modes, and further keeping in mind that the process illustrated using the flow diagram is not a strictly linear process, and that other flow diagrams are possible within the scope of the present invention. However, the diagnostic process is generally described in relation to steps 1220 to 1226. In step 1220, the decision processor obtains a diagnostic value from the processor-processor interface. As described above, these values are for use by the decision processor as a control output, or represent data that the decision processor obtains from, for example, a sensor. From step 1220, the process proceeds to step 1222, where the decision processor, for example, by changing the actuator drive signal of the outlet valve or transferring the sensor reading to the interprocessor interface, step 1220. Process the value obtained in.

  From step 1222, the process proceeds to step 1224, where the decision processor determines whether it has finished its diagnostic task. If the diagnostic task has not been completed, for example, if the process is still operating in automatic mode and there are multiple values in the set of values to be retrieved from the interprocessor interface, the process Returning to step 1222, the subsequent steps are as described above. If in step 1224 the conclusion is reached that the decision processor has finished its diagnostic task, the process returns via connection box B to step 1214 in FIG. If the decision processor determines that it is not operating in diagnostic mode, the process proceeds from step 1218 where the processor performs functions such as routine background operations, returns to step 1214 through connection box B, and thereafter. Is as described above.

  The screen shots of FIGS. 13A through 13E illustrate a user interface that can be utilized for access to a mass flow controller in accordance with the principles of the present invention, including a web server interface such as interface 608 of FIG. In one embodiment, the mass flow controller includes a web server, such as server 602 in FIG. The user can use the server locally via a local controller, or it can be used remotely from a device capable of web browsing, such as the device 600 of FIG. In this way, the same user interface can be used for both remote and local interaction with the mass flow controller. Detailed information regarding the mass flow controller, such as model number, range, and manufacturing setting parameters, is displayed to the user, and setting parameters that can be changed by the user are also displayed. Different display technologies can also be used. If there is only a limited number of acceptable values, they can be displayed and selected from a pull-down menu, for example. As described above, a user such as an engineer can change, for example, a set point value, valve opening / closing, flow output monitoring, and the like through this interface. Furthermore, while the mass flow controller is operating under a process control application, the user can have the server plot and record the parameter values obtained from the mass flow controller.

  The screen shot of FIG. 13A is an illustration of a display that a user will see upon first accessing a mass flow controller according to the principles of the present invention on the web. This display prompts the user to select a communication protocol using a pull-down window 1300. A “query device” link 1302 allows the user to start the process and find all devices that their browser can recognize.

  Basic information can be downloaded from the server. Information about the mass flow controller is displayed on the screen of FIG. 13B. This screen can be expanded or reduced. The user can also choose to view information about a portion of the displayed mass flow controller. Based on the model number, serial number and internally stored code, the product specifications for this mass flow controller can be displayed, for example as a list, along with user selectable parameters. The user can use this screen to download calibration data to and from the mass flow controller and enter a calibration table. The user can also change the set point through this interface and monitor the reported flow passing through the corresponding mass flow controller. In addition, the user can change settings and open or close the outlet control valve of the mass flow controller. The specifications for each mass flow controller can be seen as illustrated in the screen of FIG. 13C. The screen shot of FIG. 13D displays graphical user-selectable parameters, and calibration data that the user can download from the mass flow controller is illustrated in the screen shot of FIG. 13E.

  The software implementation of the above-described embodiments is fixed to or via a tangible medium such as a computer-readable medium such as a diskette, CD-ROM, ROM, or fixed disk. It consists of a series of computer instructions that can be transmitted to a computer system via a modem or other interface device such as a communication adapter connected to the network. The latter medium includes, but is not limited to, optical or analog communication lines, or may also be realized by wireless technologies including, but not limited to, microwave, infrared, or other transmission technologies. The series of computer instructions here implements all or part of the functions described in this application in relation to the present invention. Those skilled in the art will appreciate that such computer instructions can be written in many programming languages for use with many computer architectures or operating systems. Further, such instructions may be stored using any memory technology including, but not limited to, current or future semiconductor, magnetic, optical, or other memory devices, and again limited list. However, it is possible to transmit using current, future, optical, infrared, microwave or other transmission technologies. Such a computer program can be distributed as a removable medium, for example printed as shrink-wrapped software or with electronic documents, or can be distributed to a computer system, for example on a system ROM or fixed disk. It can be provided in a pre-loaded state or can be distributed from a server or electronic bulletin board on a network such as the Internet or the World Wide Web.

  While various exemplary embodiments of the present invention have been disclosed above, it will be apparent to those skilled in the art that some of the advantages of the present invention may be made without departing from the spirit and scope of the invention. Various changes and modifications that can realize the above are possible. As will also be apparent to those skilled in the art, other components that perform the same function can alternatively be used. In addition, the method of the present invention can be implemented by all software implementations using appropriate objects or processor instructions, or by hybrid implementations that achieve the same result using a combination of hardware logic, software logic and / or firmware. It is also possible to do. The process illustrated using the flow diagram need not be a strictly linear process and can be implemented using other flows within the scope of the present invention. The particular arrangement of logic and / or instructions used to accomplish a particular function is intended to be within the scope of the appended claims, as well as other modifications to the inventive concepts.

  The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. Accordingly, it is not intended to be exhaustive or to limit the invention to the precise form disclosed, and many modifications and variations are possible in accordance with the above teachings. The above examples best illustrate the principles of the invention and its practical application, and are therefore selected to enable those skilled in the art to use the invention in its best mode. It is described. It is intended that the scope of the invention be defined only by the claims that follow.

1 is a block diagram of a system including a mass flow sensor according to the principles of the present invention. 1 is a cross-sectional view of a mass flow controller using a mass flow sensor according to the principles of the present invention. FIG. 3 is a cross-sectional view of an exemplary thermal mass flow sensor used with a pressure sensor to produce a compensated indication of mass flow through a mass flow controller. 2 is a block diagram of a control electronics used by an embodiment of a mass flow sensor according to the principles of the present invention. FIG. 4 is a flow diagram of a process for compensating a thermal mass flow sensor signal in accordance with the principles of the present invention. 1 is a conceptual block diagram of a web-based mass flow controller in accordance with the principles of the present invention. 1 is a conceptual block diagram of a compensator used with a mass flow controller in accordance with the principles of the present invention. 1 is a block diagram of a self-calibrating mass flow controller in accordance with the principles of the present invention. FIG. 4 is a graphical representation of flow and pressure curves corresponding to a process for compensating a mass flow controller in accordance with the principles of the present invention. 2 is a conceptual block diagram of a dual processor configuration used in a mass flow controller according to the principles of the present invention. FIG. 4 is a flow diagram of the general operation of a non-deterministic processor of a mass flow controller according to the principles of the present invention. 2 is a flow diagram of the general operation of a decision processor of a mass flow controller in accordance with the principles of the present invention. 2 is a flow diagram of the general operation of a decision processor of a mass flow controller in accordance with the principles of the present invention. 4 is a screen shot of a web page used by a web server embedded in a mass flow controller according to the principles of the present invention. 4 is a screen shot of a web page used by a web server embedded in a mass flow controller according to the principles of the present invention. 4 is a screen shot of a web page used by a web server embedded in a mass flow controller according to the principles of the present invention. 4 is a screen shot of a web page used by a web server embedded in a mass flow controller according to the principles of the present invention. 4 is a screen shot of a web page used by a web server embedded in a mass flow controller according to the principles of the present invention.

Claims (33)

A mass flow sensor operating with a mass flow controller including an outlet control valve that controls fluid flow through the mass flow controller itself,
A thermal mass flow sensor including a sensor bypass and sensing fluid flow into the inlet of the mass flow controller;
A pressure sensor for sensing fluid pressure in a volume between the sensor bypass and the outlet control valve;
An electronic controller that monitors the pressure sensed by the pressure sensor and compensates for the inlet flow rate sensed by the mass flow sensor, thus producing a measure of the compensated fluid flow rate out of the controller;
A temperature sensor that senses the temperature of the fluid in the volume between the sensor bypass and the outlet control valve and provides a signal indicative of the sensed temperature;
The electronic controller uses a signal indicative of the sensed temperature in producing the compensated fluid flow rate, and a pressure in a volume between the sensor bypass and the outlet control valve. A mass flow sensor that calculates a rate of time change and uses the time rate of change of pressure to produce a compensated measure of the flow rate of fluid exiting the controller .   The mass flow sensor of claim 1, wherein the temperature sensor senses the temperature of a wall that defines a portion of the volume between the sensor bypass and the outlet control valve and uses the sensed temperature. A mass flow sensor for producing the temperature signal.   2. The mass flow sensor of claim 1, further comprising a display for displaying the pressure in the volume between the sensor bypass and the outlet control valve.   2. The mass flow sensor of claim 1, wherein the electronic controller compares a compensated measure of fluid flow rate out of the controller with a set value, adjusts the outlet control valve, and A mass flow sensor that minimizes the difference between a set value and a compensated measure of fluid flow rate out of the controller.   5. The mass flow sensor of claim 4, wherein the electronic controller is configured to determine from the sensed inlet flow rate a normalized rate of change of pressure in the volume between the sensor bypass and the outlet control valve. Compensate the sensed inlet flow rate of the controller by subtracting the product of the normalized temperature of the fluid in the volume and the volume between the sensor bypass and the outlet control valve A mass flow sensor characterized by the above.   5. The mass flow sensor of claim 4, wherein the electronic controller determines a constant, a volume between the sensor bypass and the outlet control valve, and a sensor bypass from a sensed inlet flow rate of the controller. Compensate the perceived inlet flow rate of the controller by subtracting the product of the time rate of change in pressure in the volume between the outlet control valve and the temperature of the fluid in the volume. A mass flow sensor. 5. The mass flow sensor of claim 4, wherein the electronic controller includes a compensated value of Q ₀ sensed inlet flow rate, Q _i sensed inlet flow rate, C 1 as a normalization constant, and V as a sensor value. After compensation of the sensed inlet flow rate, where T is the volume between the bypass and the outlet flow control valve, T is the temperature of the fluid in the volume, and (dP / dt) is the time rate of change in pressure in the volume. The mass Q ₀ is compensated for the sensed inlet flow rate Q _i of the controller by calculating the value Q _{0 according} to the formula Q ₀ = Q _i −C 1 (V / T) (dP / dt) Flow sensor.   8. The mass flow sensor according to claim 7, wherein the constant C1 is a result of dividing the temperature at the standard temperature and the pressure by the pressure at the standard temperature and the pressure. A method for determining an outlet flow rate of fluid from a mass flow controller including an outlet control valve, comprising:
A) sensing a fluid flow to the inlet of the controller using a thermal mass flow sensor including a sensor bypass to provide an indication;
B) sensing fluid pressure in a volume between the sensor bypass and the control valve to provide an indication;
C) the electronic controller monitoring the pressure reading sensed in step B for a period of time to obtain at least two pressure readings;
D) the electronic controller compensates the flow rate reading sensed in step A based on the pressure monitored in step C;
E) sensing the temperature of the fluid in the volume of step B and providing a signal indicative of the sensed temperature;
F) In compensating the flow rate reading in step D, the electronic controller uses a signal indicating the sensed temperature of step E;
The compensation step D comprises: D1) the electronic controller calculates the rate of change of pressure in the volume between the sensor bypass and the outlet control valve, and using the result, the controller Generating a compensated measure of the flow rate of the fluid exiting from the chamber . The method of claim 9, wherein
Sensing the temperature of the fluid in the volume to provide an indication,
E1) sensing the temperature of a wall defining a portion of the volume between the sensor bypass and the outlet control valve. The method of claim 9, wherein
G) The method further comprising the step of displaying the pressure sensed in step B. The method of claim 11 wherein the step G of displaying pressure comprises:
G1) A method comprising displaying the pressure locally. The method of claim 11 wherein the step G of displaying pressure comprises:
G2) A method comprising remotely displaying the pressure. 12. The method of claim 11, wherein the electronic controller is
H) comparing a compensated measure of fluid flow rate out of the controller with a set value;
I) adjusting the outlet control valve to minimize the difference between the set value and a compensated measure of fluid flow rate out of the controller;
The method of further comprising. The method of claim 9, wherein the step F of compensating for an indication by the controller of a sensed inlet flow rate comprises:
F1) The electronic controller determines, from the sensed inlet flow rate reading, a normalized rate of change in pressure in the volume between the sensor bypass and the outlet control valve, and in the volume Subtracting the product of the normalized temperature of the fluid and the volume between the sensor bypass and the outlet control valve. The method of claim 9, wherein the step F of compensating for an indication by the controller of a sensed inlet flow rate comprises:
F2) The electronic controller determines from the sensed inlet flow rate a constant, a volume between the sensor bypass and the outlet control valve, and a volume between the sensor bypass and the outlet control valve. Subtracting the product of the product of the pressure and the time rate of change divided by the temperature of the fluid in the volume. The method of claim 9, wherein the step F of compensating for an indication by the controller of a sensed inlet flow rate comprises:
F3) The electronic controller includes a compensated value of Q ₀ sensed inlet flow rate, Q _i sensed inlet flow rate, C 1 a normalization constant, V a sensor bypass and an outlet flow control valve The compensated value Q ₀ of the sensed inlet flow rate is given by the equation Q, where T is the volume of the fluid, T is the temperature of the fluid in the volume, and (dP / dt) is the time rate of change in pressure in the volume. A method further comprising the step of calculating according to ₀ = Q _i −C1 (V / T) (dP / dt).   18. The method of claim 17, wherein the constant C1 is the result of dividing the standard temperature (273.15 K) by the standard pressure (760 Torr). A mass flow controller comprising:
An outlet control valve;
A thermal mass flow sensor including a sensor bypass and sensing fluid flow into the inlet of the controller;
A pressure sensor for sensing fluid pressure in a volume between the sensor bypass and the outlet control valve;
An electronic controller that monitors the pressure sensed by the pressure sensor and compensates for the inlet flow rate sensed by the mass flow sensor, thus producing a compensated measure of the fluid flow rate out of the controller. An electronic controller that generates a closed loop control signal for the outlet control valve using a compensated measure of fluid flow out of the controller;
A temperature sensor that senses the temperature of the fluid in the volume between the sensor bypass and the outlet control valve and provides a signal indicative of the sensed temperature;
The electronic controller uses a signal indicative of the sensed temperature in producing the compensated fluid flow rate, and a time of pressure in the volume between the sensor bypass and the outlet control valve A mass flow controller that calculates a rate of change and uses the time rate of change of this pressure to produce a compensated measure of the flow rate of fluid exiting the controller.   20. The mass flow controller of claim 19, wherein the mass flow controller is linked to a plurality of mass flow sensors and an outlet control valve and provides a closed loop control signal to the plurality of outlet control valves. A mass flow sensor operating with a mass flow controller, wherein the mass flow controller includes an outlet control valve that controls fluid flow through the controller.
A thermal mass flow sensor including a sensor bypass, sensing a flow of fluid to the inlet of the controller and producing a mass flow signal representative of the flow;
A pressure sensor for sensing fluid pressure in a volume between the thermal mass flow sensor bypass and the control valve;
An electronic controller for providing a closed loop control signal for the outlet control valve based on the mass flow signal;
A display for displaying the pressure sensed by the pressure sensor;
A temperature sensor that senses the temperature of the fluid in the volume between the sensor bypass and the outlet control valve and provides a signal indicative of the sensed temperature;
The electronic controller uses a signal indicative of the sensed temperature in producing the compensated fluid flow rate, and a time of pressure in the volume between the sensor bypass and the outlet control valve the change rate was calculated, the mass flow sensor with the time rate of change of this pressure, characterized Rukoto produce compensated measure of flow rate of the fluid exits from the controller.   24. The mass flow controller of claim 21, wherein the mass flow controller includes a housing that surrounds the mass flow sensor, and the display is supported by the housing.   The mass flow controller of claim 21, wherein the display is connected to the mass flow controller via a serial data link.   The mass flow controller of claim 21, wherein the display is connected to the mass flow controller via a parallel data link. 24. The mass flow controller of claim 21, wherein the electronic controller provides a network interface that allows active diagnosis of the mass flow controller from devices connected to the network.   26. The mass flow controller of claim 25, wherein the active diagnostic code for operation with the electronic controller of the mass flow controller includes a code that enables operation of operational signals from devices connected to the network. Mass flow controller.   26. The mass flow controller of claim 25, wherein the active diagnostic code for operation with the electronic controller of the mass flow controller includes a code that enables operation of diagnostic signals from devices connected to the network. Mass flow controller.   26. The mass flow controller of claim 25, wherein the active diagnostic code for operation with the electronic controller of the mass flow controller includes a code that enables monitoring of operational signals from devices connected to the network. Mass flow controller.   26. The mass flow controller of claim 25, wherein the active diagnostic code for operation with the electronic controller of the mass flow controller includes a code that enables monitoring of diagnostic signals from devices connected to the network. Mass flow controller. The mass flow controller of claim 25,
The mass flow controller further comprising an on-line diagnostic code that operates in conjunction with the electronic controller of the mass flow controller and enables on-line monitoring of operating signals from devices connected to the network. The mass flow controller of claim 25,
A mass flow controller further comprising an online diagnostic code that operates with the electronic controller of the mass flow controller and enables online monitoring of diagnostic signals from devices connected to the network. The mass flow controller of claim 25,
The mass flow controller further comprising an online diagnostic code that operates with the electronic controller of the mass flow controller and enables online operation of diagnostic signals from devices connected to the network. The mass flow controller of claim 25,
The mass flow controller further comprising an online diagnostic code that operates with the electronic controller of the mass flow controller and enables on-line manipulation of operating signals from devices connected to the network.

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