GB2419422A - Mass flow controller configured to upload closed-loop code sets - Google Patents

Abstract

A mass flow controller (200) comprises: a mass flow sensor (202) configured to produce a mass flow signal representative of a gas flow through the mass flow controller (200); and an electronic controller (210) configured to produce a closed loop control signal for an outlet control valve(220), based on the mass flow signal. The electronic controller (210) is also configured to upload a plurality of executable closed-loop code sets, which may include code for executing a diagnostic or calibration mode of operation. The electronic controller (210) may comprise a dual processor arrangement consisting of a deterministic 1002 and a non-deterministic 1004 processor, where the non-deterministic processor 1004 is configured to upload a plurality of executable code sets, select one of the code sets and pass the selected code to the deterministic processor 1002 for execution.

Description

241 9422 i

MASS FLOW CONTROLLER

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

Capillary tube tllerinal mass flow sensors exploit Lle fact Flat lint transfer to a fluid flowing in a larniar tube front the tube walls is a function of mass flow rate of else fluid, tle difference between the fluid temperature and the wall Lerngerature, and the specific heat of the fluid. Mass flow controllers employ a varicLy of Class flow sensor configurations. For example, one type oTconstructio involutes a stainless steel flow sensor tube Title one, arid snore tyliccally two or Injure, resistive clenieits in thermally conductive coLacL Title tle sensor tulle.

Tle rec,isLive e]eents are typically composed oL a material 1lavirg a lii, ,l f.eml:,eraLure coefLiciert of -esisLace. ticicl of Else elernel.s call act,rs a locater, a clcLecLo; or bolls Ogle or galore of the eleelLs is enegizt d wield electrical current Lo supply lineal lo tle fluid sLrea LhroLgl Like tube. If the leaves are supplied Evilly coolant ctrret, tile to l.e ol'luid mass flow Llu-ough L.lle Lube Gait be derived Lio Leleral. ui-e dif'reces in the elemeLs. fluid Harass flow rates can also be clerivel 11 var,N/in,' Llae current Lloul LIIG heaters Lo llainLai a coisLant LelperaLure profile.

SUC11 t11eriMaI IlaSS [10NV sensors may be aLtacled as a part of a Gnats loom' 0 controller, wills Iluid froth the conLrollers aid cllarel l-'eedin, tile capillary tube (also rei-rccl to herein as the sensor tube). The portion of the main channel Lo which bloc inlet and outlet of tile sensor Lube are attached is often referred to as the "bypass" of the flow sensor. many applications employ a plurality of nuns ilONV Gotrolles to regulate tile supply offluid through a supply line, and a plurality of the supply lines relay be "tapped off" a mails fluid supply line. A sudden change in flow to vile of the comptrollers may create pressure fluctuaLioils at tle inlet to one or Galore of the otlier controllers tapped off else main supply line. Such pressure fluctuations create differences between the flow rate at tle inlet arid outlet of an affected mass flow controller Because therinal mass flow sensors measure ilov - 2 at the inlet of a mass icons controller, but outlet Dow from the controller is the critical parameter for process control, such inlet/outlet flow discrepancies can lead to significant process control errors.

In a semiconductor processing application, a process too] may include a plurality of chambers with each clamber having one or more mass flow controllers controlling the flow of gas into the clamber. Each of the mass flow controllers is typically re-calibrated every two weeks. The recalibration process is described, for example, in U.S. I,atenL 6,332,348 B1, issued Lo Yelverton et al. December 2S, 2001, which is hereby incorporated by reference. In the cow-se of such an ''In Situ" calibration, coventioral netlods require a technician to connect a mass flow meter in line Title each of the mass Dow controllers7 flow gas Lhrougl the mass flow Uniter anal snags [low controller, compare the mass flow carols reading Lo that of the mass slow meter and adjust calibration constants, as necessary. Such painstaking operations can require a great:leal of time arid, due to labor costs aud the urravaiPability of process tools, with which to mass Dow co,Lrullers operate, can be very costly.

A mass flow sensor that substaLially eliminates sensitivity to pressure v; rriaLions would therefore be highly desirable. A convenient calibration lnel.llod amid apparatus for mass flow controllers would also be highly desirable. More 2() flexible access Lo a mass Bow controller would also be highly desirable.

Apparatus and n1etllod for increasing the control performance of a mass flow controller would also be highly desirable.

Summary of the Illvelltioll

According to the present invention there is provided a n1ass flow controller and a system, defining a flow path between a gas inlet and an outlet of the system as set forth in rl1e appended claims.

Brief Description of Drawings

Figure 1 is a block diagram of a system that includes a mass flow sensor; Figure 2 is a sectional view of a mass flow controller that employs a mass flow sensor.

Figure 3 is a sectional view of an illustrative thermal mass flow sensor as used in conjunction with a pressure sensor to produce a compensated indication of mass flow through a mass flow controller; Figure 4 is a block diagram of the control electronics employed by an illustrative enbodUnerlt of a mass flow sensor.

Figure 5 Is a How chart of the process of compensating a "hernial mass flow sensor sill.

lugure 6 is a conceptual block diagr-an of a web-enabled mass Dow controller.

Figure 7 is a conceptual block diagram of calibrator such as nay be employed with a mass flow controller.

Figure 8 is a block diagram of a self-calibrating mass flow controller.

Figure Y is a graphical representation of flow and pressure curves corresponding to the process of calibrating a mass flow controller.

Figure 1() is a conceptual block diagram ol a dual processor configuration such as may be used in a mass flow controller.

Figure 11 is a flow chart of the general operation of a mass flow controller's non deterministic processor.

Figures 12A and 12B are flow charts of the general operation of a mass flow controller's deterministic processor, and Figures] 3A through 1 3E are screen shots of web pages such as may be employed by a web settler embedded within a mass flow controller.

Detailed Description of Disclosure

A mass flow sensor employs a thermal mass flow sensor to sense and provide a measure of the flow of fluid into an inlet of a fluid flow device, such as a mass flow controller. The mass flow sensor uses a pressure sensor to compensate the inlet flow measure provided by the thermal mass flow sensor to thereby provide an indicator that more accurately reflects the Quid flow at the outlet of the associated mass flow controller.

A system 100 that benefits frown and includes Ihe use of a mass flow sensor is shown in Ille illustrative block diagram of Figure 1.

A plurality of mass flow controllers MFC1, MFC2, ... MFCn receive gas from main gas supply lines 102, 103. Tile mass Dow controllers, MFCI, MFC2, MFCn are respectively connected through inlet supply lines 104, 106, ...109 to a main gas supply lisle 102, 1()3 arid tlrougl respective outlet supply lines 110, 112, ...115 to chambers Cl, C2, Cn. In this illustrative enbodiment, the term "chamber" is used ill a broad sense, and each ol Ihc chambers nay be used lor any of a variety of applications, including, but not liniIed to, reactions involved i', the production of semiconductor components. Generally, users of Ihe clambers are interested in knowing and controlling the amount of each gas supplied to each of the chambers C1, C2, ...Cn. Each chamber C1, C2, ... Cn may also include one or more additional inlet lines for the supply of another type of gas. Outflow frolic Ihe chambers may be routed through lines (not shown) for recycling or disposal.

the mass floNv controllers, MFC1, MFC2, MFCn, include respective mass flow sensors MFS1, MFS2, ...MFSn, electronic controllers EC1, EC2, ...Ecn and outlet control valves OCV1, OCV2, ...OCVn. At least one of the mass flow sensors is, and, for ease of description, assume all are, compensated mass flow sensors. Each mass flow sensor senses the mass of gas flowing into the mass flow controller and provides a signal indicative of Ihe sersecl value to a corresponding elccIronic controller. Tile electronic controller compares the indication of mass flow as indicated by the sensed value provided by the mass flow sensor to a set point and operates the outlet control valve to minimize any difference between the set point and the sensed value provided by the mass flow sensor.

Typically, the set point may be entered manually, at the mass flow controller, or downloaded to the mass flow controller. The set point may be adjusted, as warranted, tluough the intervention of a human operator or automatic control system. Each of the inlet supply Ihles 104, 106, ... 109 may be of a different gauge, and/or may handle any of a variety of flow rates into the mass flow controller. A single electronic controller, such as electronic controller EC1, may be linked to arid operate a plurality of mass flow sensoloutlct control valve combhlations. That is, for example, any number of the illustrated electronic controllers EC2 through LIcn may be eliminated with the corresponding mass flow sensors arid outlet control valves linkett lo the electronic control for EC I lor operalion.

An abr'pl chaotic of flow rate, due lo a change in set point for example, into any of the mass flow controllers may be reflected as an abrupt pressure change at the inlet of one or more of the other mass flow controllers. This unwanted side effect may be more pronounced in a relatively low flow rate mass flow controller if the abrupt change occurs in a high flow-rate mass flow controller. Because the mass flow sensors in this illustrative embodiment are thermal mass flow sensors positioned to sense flow in the mass flow controller at the inlet to the mass flow controller, the mass How sensed by the thermal mass flow sensor may not accurately reflect the flow at the outlet of the controller. In order to compensate for this discrepancy, a mass flow sensor includes a pressure sensor positioned to provide an indication of the pressure within the volume between the inlet and outlet of the mass flow controller. In an illustrative embodiment, the pressure sensor is located in lice "clead voluble'' between lee lhennal mass flow sensor's bypass anti the gullet control valve. An electronic controller employs the indication of pressure provided by the pressure sensor lo compensate the measure of mass Dow provided by the thermal mass flow sensor.

Tle resultant, a compensated mass flow indication, snore accurately reflects the flow at the outlet of the mass flow controller and, consequently, this indication may be employed to advantage by a mass flow controller in the operation of its outlet control valve. A display may be included to display the sensed pressure. The display may be local, attached to or supported by the mass flow controller, or it may be remote, at a gas box control panel, for example, connected to the mass flow controller through a data link.

in a semiconductor processing application, a process fool may include a plurality of chambers with each chamber having a plurality of mass flow controllers respectively controlling the flow of constituent gases into the chamber. Each of the mass flow comptrollers is typically recalibraled every two weeks. The re-calibration process is described, for example, in US Patent 6,332,348 Bl, issued to Yelverton et al. December 25, 2001, which is hereby incorporated by reference. In the course of such an "In Situ" calibration, conventional methods require a technician to con'ecl a mass flow meter in line with each of the news flow controllers, flow gas through the mass flow meter and mass flow controller, compare the mass flow controller reading to that of the mass flow meter and adjust calibration constants, as necessary. Such painstaking operations can require a great deal of tine and, due to labour costs and the unavailability of process tools with which the mass flow controllers operate, can be very costly. In an Illustrative enbodnent described in greater detail in the discussion related to Figure 7, a mass flow controller includes a self-calibrating mechanism that substantially eliminates such tedious and costly chores.

The sectional view of Figure 2 provides an illustration of a mass flow controller 2()() that employs a mass flow sensor 202. 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. A laninar flow element 212 establishes a pressure drop across the capillary tube of the thermal mass flow sensor 204, as will be described in greater detail in the discussion related to Figure 3. In operation, a fluid that is introduced to the mass flow controller 200 tl-ough the inlet 214 proceeds through the bypass channel 216 containing the laminar flow clement 212. A relatively small amount of the fluid is diverted through the thermal mass flow sensor 204 anti re-enters the bypass channel 216 downstream of the lumbar flow element 212. The electronic controller 210 provides a signal lo the control valve actuator 218 to thereby operate the outlet control valve 220 in a way that provides a controllcLI mass flow of fluid to the outlet 222. The pressure sensor 206 senses the pressure within the volume within the bypass chamlel 216 between the lani'ar flow element 212 and the outlet control valve 220, referred to herein as the "dead volume 216a".

As will be Llescribed in greater dcIail in the discussion related to Figure 5, the electronic controller 210 employs the pressure sensed within the dead volume 216a by the sensor 206 to compensate tile inlet How rate sensed by the thcnnal mass flow sensor 204. Ellis compensated inlet flow rate figure snore closely reflects the outlet flow rate, which is the ultimate target of control. In particular, a mass flow sensor is a combination sensor that employs the tine rate of change of pressure within a known volcano 21Ga to provide a precise measure of mass flow during pressure transients and a thennal mass flow sensor that may be "corrected" using the pressure-derived mass flow measurement. Both the themlally-sensed and pressure derived mass flow measurements are available for processing. The temperature sensor 208 senses the temperature of the fluid within the dead volume. In an illustrative embodiment, the temperature sensor 208 senses the temperature of a wall of the controller, as an approximation of the temperature of the fluid within the LleaLI volcano 21 a.

The volume 216a of the dead volume is determined, during manufacturing or a calibration process, for example, and may be stored or downloaded for use by the electronic controller 210. By taking sequential readings fionn the pressure sensor output 2()6 and operating on that data, the electronic controller 210 detennines the time rate of change of pressure within the dead volume 216a. Given the dead volume, the temperature of the fluid within the dead volume, the input flow rate sensed by the thermal mass flow sensor 204, and the time rate of change of pressure within the dead volume, the electronic controller 21() approximates the fluid flow rate at the output 222 of the mass flow controller 200. As previously noted, this approximation may also be viewed as 1 0 compensathg the mass flow rate figure produced by the Ihennal mass flow sensor 204.

The electronic controller 210 employs this computed output land flow rate in a closed loop control system to control the opening of the mass flow controller gullet control valve 220.

In an Ihstratvc embodimct, the value of the pressure sensed by the pressure sensor 206 Delay also be displayed locally, (that is, at the pressure sensor) ar.d/or remotely (at a control panel or through a network interface for example). In a self-calibratig process described hereinafter in the discussion related to Figure 7 the electronic controller 210 may take the time derivative of the pressure signal When the floivrate varies in the mass flow controlled and thereby derive the actual flow rate into the mass flow controller.

The actual flow rate may then be used to calibrate the mass flow controller.

The sectional view of Figure 3 provides a more detailed view of a Floral mass:tlow sensor 204 such as may be employed in conjunction with a pressure sensor to produce a compensated mass flow indication that is in a digital innplementation a multi-bit digital value. The multi-bit digital value provides a closer approximation to the actual mass [low at the outlet of a mass flow controller tl1arl an unconpensaLed mass flow sensor would particularly during pressure transients ore the mass flout controller inlet lines. The thermal mass flow sensor 204 includes lanirar flow element 212 which rests witli the bypass channel 21G arid provides a pressure drop across the bypass channel 216 lair the Lhernal mass flow sensor 204 and drives a portions ol flee gas tlrough the sensor capillary Lube 320 ol the Lhernal mass flow sensor 204. The mass flow sensor 202 includes circuitry trial senses Lle rate of flow of gas through the controller 00 aurJ coLrols operation of the control valve 220 accordingly. The thermal snaps flow sensor assembly 204 is attached to a wall 322 of the mass flow c.onlrolle!- 900 that forms a boundary of the bypass chapel 016 layout 31 and output 326 a.perLures in the wall 322 provide access to the thermal In ass flow sensor assembly 204 for a gas travailing through the thermal mass flow controller and it is the portion of this passageway between the input and output that typically defines the bypass channel. In this illustrative embodiment the mass flow sensor assembly 204 includes a baseplate 38 for attachment to the wall 322. The baseplate 308 may de attached to the wall and to the remainder of the sensor assembly using threaded hole and mating bolt combinations, for example.

Input 330 and output 332 legs of the sensor tube 320 extend through respective input 334 arid output 336 apertures of the baseplate 398 and, through apertures 324 and 326, the mass DOW controller wall 3Q2.

The mass flow sensor assembly preferably includes top 338 arid bottom 340 sections that, plan jointed, form a thermal clamp 341 that holds both ends of tl-e sensor tube 320 active area (tlat is, the area defined by Llie extremes of resistive elements in thermal contact with the sensor Lube) at substantially the salve temperature. The thermal clamp also forms a chamber 342 around the active area of the sensor tube 320 Thai is, Lhe segment of the mass flow sensor tube witli the chamber 342 is in thermal communication Title Lasso or mole resistive elects 344, 346, each of wlich may act as a hcaLer, a detector, or polio. One or more of the elene'ts is energized wills electrical current to supply loot to Lhe fluid as iL streams lln-ough Lhe Lube 320. The thermal clamp 3z11, which is typically fabricated l.roin a material claracLerized by a hilly ller, al coducLivity relative to Lhe thermal cocLucLiviLy of L-e sensor Lube, snakes good 1.S therally conductive contact with Else portion of Else sensor Lube just downstream lion Lee resistive element 314 arid with Lhe,uorLion of the sensor tube just upsLrea'l lion tle resistive eleneut 3 '6. I'le Llciina.l clamp thereby closes arid protects Like resistive element 344 and 346 and the sensor tube 370. Additionally, flee vernal clamp 341 vernally "actors" t-lose portions oFLhe sensor tube with which it males contact at, or near, Ll1e ambient Lcnperature. In order to elininaie event nil errors due lo teniperature clil.-erentia.ls, Lle sensor tube may be moved sviLhin Lhe Lhernal clamp to insure that any dilrecc between the resistance of tile two coils is due to fluid flow thorough the sensor tube, not to temperature gradients imposed upon the coils lrom the environment.

In this illustrative enhodinent, each of the resistive elements 344 and 346 includes a thermally sensitive resistive conductor that is wound around a respective portion of the sensor tube 320. Each of the resistive elements extends along respective portions of the sensor tube 320 along an axis defined by the operational segrneit of the sensor tube 320. Downstream resistive element 346 is disposed downsLrean of the r esistive element 344. Tl1e elements abut one another or are separated by a small gap for manufacturing convenience and are preferably electrically connected at the center 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 electrical current Cowing through its resistive conductor aucl tile mass flow rate within the sensor tube 320. L1 tl1is way, each of else resistive elements operates as both a heater and a sensor. That is, the elene1t acts as a heater that generates lost as a function of the current througl the elernet and, at the satire time, the element acts as a sensor, allowing the temperature of the element to be measured as a function of I O its electrical resistance The Llie-lcl mass.Llow sensor 004 may Cloy arty of a variety of electronic ci cults, t.ylically irk a Wl1eatstoe bridge arranr,emer1t, to apples energy to the resistive elenenLs 346 and 344, to measure the temperature depede1L resistance chan; ,es in else eleleuL and, Hereby, flee mass Dov rate of T]uicl p-ssig Lln ougl1 else sensor Lube 320. Circuits employed for this purpose are disclosed, Lor example, ifs U.S. Patent 5,461,913, issued Lo 1-Iinlcle et al and U.S PaLcnL 5,41O,912 issued Lo Suzulci, hotly of which ale leery i1corporaLed by reLcre'ce ilk their entirely.

Ln operation, fluid 110WS from tle inlet 214 to the outlet 222 arid a portion of [lie fluid f10ws tln-ougl the restrictive laninar flow element 212. I've -enaiing and proportional amount of Quill flows tlrougl1 the sensor tube 320.

Tle circuit (not shown leered causes an electrical current to flow Llu-vu, l the resistive elenents 344 and 346 so Ll1at tile resistive elements 344 and 346 generate and apply heat to tle sensor tube 320 and, thereby, to the fluid flowing tl-ough the sensor tube 320 Because the upstream resistive element 346 transfers lost Lo the fluid before the fluid reaches the uorLion of flee sensor tulle 320 enclosed by the downstream resistive element 344, the fluid conducts snore lost away from the upstream resistive element 346 chard it does from the dowsLrean resistive elenent 344. The difference in the an1ou1t of heat conducted away from the two resistive elements is proportional to the mass flow rate of fluid within the sensor tube and, by extension, the total mass flow rate through the mass flow rate controller 200 from the input pout 214 tll. lough tile output port 222. The circuit measures this difference by sensing the respective electrical resistances of resistive elenenLs 344, 346 and generates an output signal that is representative of the mass flow rate throu=,l1 the sensor tube 320.

The conceptual block dia-an1 of Figure 4 illustrates the architecture of an electronic controller 400 such as may be usual in a mass flow sensor. In this illustrative embodiment, the controller 400 includes sensor 402 and actuator 404 interface. Among the sensor interfaces 402, a flow sensor interface 408 operates in conjunction with a mass flow sensor to produce a digital representation of the rate of mass flow into an associated mass flow controller. The controller 400 may include various other sensor interfaces, such as a pressure sensor interface 410 or a temperature sensor interface 411. One or more actuator drivers 412 are employed by tl1e controller 400 lo control, lor cxanplc, the opening of an associated mass Dow controller's outlast control valve. The actuator may be any type of actuator, such as, 1 5 for example, a cun-ent-lriven solenoid or a vo]Lage-driven piezoelcctric actuator.

Tle conLl-oller 400 operates ire conjunctions with a mass 11rJW controller Lo produce a digital repr-eseltation of tl-e rate of mass 110NV into an associated mass flow controller A lher-nal mass flow controller, such as described in tle discussion related to Figu-e 3, may be employed to produce the mass 110NY neasui-enellL. flee comptroller 400 may employ a pressure sensor interface 410 to nolliLur Lle pressure of fluid within an associated mass flow controller. In an illustrative embodiment, a pressure sensor, such as the pressure sensor 206 ol: figure 7, provides a measure of the pressure within the mass flow controller.

More specifically, in this illustrative embodiment, the sensor measures tile pressure within dead volume of the mass flow controller. D1 an illustrative embodiment, the mass flow controller pressure thus measured may be displayed, at the pressure sensor 206 or at the controller housing, for example, or some other locations.

The controller 400 may convert the pressure measurement to digital form and employ it in ar.alysis or other fuctiors. For example, if the mass flow controller employs a thermal mass flow sensor, the controller 400 may use the mass floNN, controller pressure Measurement to compensate for inlet pressure transients. Although a temperature sensor interface nnay be used to obtain a temperature reading from a temperature sensor attached, for example, to the Nvall of a mass flow controller, a separate ternperatui-e sensor may not be required for each mass flow controller. For example, mass flow controllers are often employed, as described in greater detail in the discussion related to Figure 1, ifs cojunctiol wills a semiconducLorpiocessi1g tool Lhat includes a number of na.ss flow controllers and Oliver devices that are all linked to a controller, such as a workstation. The processing tool is operated within a carefully controlled environment that features a relatively stable tenlerature. Because the tcni.'ei-ature of Ale fluid wiLIin Else mass flow controller is very nearly eclual Lo Blat of else wall of Else enclosure and the wall of the enclosure is very nearly the l.en-pera ur e of Lye oon1 within Nvhic]l the tool is loused a LcnperaLure Ineasul-elu.enL fi one, for example, the workstation Lhat controls Else tool, may confide a suflcienL] y accurate estimate of the gas Lernperature within the Ross flow controller. Consequently, ill addition Lo, or instead of, employing a separate tenperatu-e scissor oat each mass flow controller, the temperature may be obtained 1i-on another scissor within Lle same environment as the mass flow coltrrller: one located at a workstation, for example.

the controller 400 includes a local user interface 416 that may be used with one or more input devices, such as a keypacl, I.eyboard, mouse, traclchall, joy stick, buttons, touch screens, dual inline packaged (DIP) or tl1unlb-wheel swiLcl1es, for example, to accept input from users, sucl, as technicians wlo operate a mass flout controller. The local user interface 414 may also include one or more outputs suitable for driving one or more devices, such as a display, which may be an indicator light, a character, alphanumeric, or graphic display, or an audio Output device used to communicate ird'orlation front a mass flow controller to a user, for example. A communications interface 416 permits a mass iron controller to communicate with orre or more other instruments, and/or Title a local controller, sulk as a workstation Blat controls a tool that employs a plurality of mass flow controllers and/or other devices in tle production of integrated circuits, for example.

In Allis illustrative example, the cornmunicatioils interface 414 includes a DeviceNet interface. DeviceNet is lcuown and discussed, lor exannple, in U.S. Patent No. 6,343,617 B1 issued to Tinsley et al. February 5, 200?, Rich is hereby incorporated by reference. The controller 400 also includes storage 418 ill tile lorry, for example, of electrically erasable programrfable read only memory (E111'ROM) that may be used to store calibration data, mass flow controller iclenLil-cat.ion, or code for operating flee news flow controller, for exan'le.

Various roller forms of sLora.ge, sucl as random access rnenor-y (RAM), may lie employed. Tile storage call talce many forms, and, for example, may be disLribuLed, Will portions plysically located on a controller "clip" (iLegraLed circuit) anal oLler porLioi1s 1ocaLed off:clip. The controller 4U() employs a data processor 420, Lick iigliL Lake LhC for of an ardlrleLic logic trail (GNU) in a general purpose nicrolJrocessor, for example, to replace data. For example, the data processor 49:0 may average readings received at tle sensor inputs, determine the nurtber at Limes a sensor readily leas exceeded one or ignore tlueslold values, record the time a sensor readiiL; remains beyond a Lhi-eslold value, or 1erturi oilier forms of data logging. lJ-essure transients on else inlet supply line Lo a mass flow controller

200 t:haL einploys a tlerinal mass flow sensor 204 may create erroneous mass flow readings. Erroneous mass flow readings may lead, ire turn, t.o improper control of a inass flow controller's outlet valve, which could damage or destroy articles being processed Title gasses under control of tile mass flow controller. The digital representation of mass flow may tale tile forni of one or more data values and is subject to fluctuations due to pressure Lralsients Oil the inlet line of tle mass flow sensor. D an illustrative embodiment, the conLioller 400 employs data obtained at the pressure sensor interface 410 to compensate for fluctuations induced in a thermal mass flow sensor 204 by pressure transients on the mass flow sensor inlet line 214. In this illustrative embodiment, the controller 400 obtains temperature inf-ornation through a temperature interface 411. The conLioller 400 employs the temperature, pressure, and mass flow readings obtained from the respective interfaces, to produce a compensated mass flout reading Flat more closely reflects the mass flow at tile outlet of the mass flow sensor thank a reading from the Lhernal mass flow sensor alone provides. The controller 400 also provides control to sensors, as necessary, through [low sensor interface, pressure sensor interface, and Lenleratu-e interfaces, ADS, 410, and 41 l, respectively.

The controller 400 also includes a valve actuator interface 404, which the cort-oller 4-00 employs to control the position of a valve, such as the valve 220 of Figure 2, to thereby coLrol Ll1e rate of fluid flow Ll- ougl a mass f-lov controller, sucll as the mass flow corrLroller COO, in a closed -loop control process. Tle valve act:uaLor may be a solenoiddriven actuator or peizo-electric actuator, for exanple. Tle conL'oller 400 must be capable of operating wild sufficient speed Lo lead tile various sensor oulluLs, comlJe'sal.e as necessary, arid adjust: the mass flow coLrol]er outlet control valve 220 l:o produce a predetermined flow rate.

Elite flow late is predeternined in flue sense Llat it is "desired" in some sense. It is not predetermined in the souse that it must be a static settings. That is, the prcdctcrllicd flow rate may be act by act operator using a ncclianical means, such as a dial settirg, or nay be dovloacled from another controller, such as a workstation, for example, and may be updated.

In an illustrative enbodinenL, flee conLrDller 400 employs reaclirgs Lion the prcssu-e interface 410 to compensate flow measurements obtained at tl1c mass flow interface 408 from "hernial news flow sensor 204 that senses nass flow at the inlet 214 to mass flow controller o00 The compensated flow 1leasuremeiit more accurately depicts the flow at the outlet 222 of the mass flow controller 200.

This outlet flow is the flow beirig directly controlled by the mass flow controller 200 and typically is the flow of interest to end users. Employing a pressure 1G compensated flow neasurenent in accordance with the principles of tle present inflection improves the accuracy of a mass flout sensor's outlet flow reading and thereby permits a mass flow controller to more accurately control the flow of fluids. That is, at equilibrium, mass flout at a mass flow cot roller's inlet is equal to the mass flow at the outlet of the mass flow controller, but during inlet or outlet pressure transients, the flow rates differ, sonelines significantly. As a result, a mass flow comptroller that provides closed loop control using its inlet flo to control its outlet flow may con nit substantial control errors.

The steady state mass flow hl the capillary sensor tube 320 of a tlermal mass flow sensor such as described in the discussion related to Figure 3 is generally described by Lhe following equation: )='i' ti \VI1oJ'C: do = capillary Lube inside diameter tic--- capillary tube length pi = Lhe density of ills gas aL [lie inlet ply = Lhe clesit:y of Lhe gas aL standard 1 ernperature and pressure = tLe,g-as viscosity l-'i = Lhe pressure aL Lhe inlet of tile mass Llov controller SO Po = The pressure at the outlet ofthe mass flow controller P = the pressure e in the dead volume of the mass flow controller The total flow through tle repass flow cor.troller is related to that through tile capillary sensor tube 320 tl-ough a split ratio: 2 5 a- QBP/Qc where QBP is Lhe flow lrougl1 the bypass channel 216 and Qc is the flow through the capillary tube 320. The total flow Qi at the mass flow Qcontroller inlet 214 is: Qi = QBP -rQc = (1+ ol)Qc If ilov remains laminar in both the bypass and capillary, Lhe split ratio Will remain constant. Wl1en Lle inlet pressure varies with tin1e, the stature of the inlet pressure transient and the pressurization of Lhe dead volume govern tile flow at the inlet. Assuining that all tlernodynanic events within the dead volume occur at a constant temperature that is equal to flee teu1l:>erahre of the enclosure that Borings a partial receptacle around the deacl volume, flee snags cosc-rvaLion violin the dead volume may be described by: l.,,PR tit Where: Pit = pressure aL sLandc-d t.enpei-alure and pressure (700 l'orr.) Tic = Len-perature aL sLa1dard LerperaLu-e anti pressure (73 lo) row = wall Lengera.ure (Len1peraLurc of Else wall of the mass flow comptroller) V = volume ol the dead volume Qj = inlet flow Lo the mass flow comptroller (0 - outlet l1OW ii om the mass flow controller A mass How sensor employs the relationship of equation (2) to compensate a then1al mass flow sensor's mass flow signal and to thereby substantially reduce errors in mass flow readings during pressure transients.

The How chart of Figure 5 depicts the process of compensating a thermal mass flow sensor reading.

The process begins in step 500 and proceeds from there to step 502 where a mass flow sensor's controller, such as the controller 400 of Figure 4, obtains a mass flow reading. This reading may be obtained from a thermal mass flow sensor through a flow interface, such as interface 408 of Figure 4, for example.

This flow measurement reflects the rate of mass flow at the inlet of a mass flow controller and, as previously described, may not adequately represent the mass flow rate at the outlet of the mass flow controller. The mass flow rate at the outlet of a mass flow controller is generally the rate of interest for use in control applications. Consequently, a mass flow controller compensates for the inaccuracy inherent in assuming that the inlet flow rate Lo a mass flow controller is equal to the outlet flow rate from the mass flow controller. From step 502 the process proceeds Lo step 504 where the sensor controller 40() obtains the temperature of Lhe flow within the bypass channel. The temperature could be obtained through a temperature interface such as interface 412 of Figure 4, or it inky be downloaded to the conpcnsated mass flow sensor. The compensation Process allay safely assume that the gas temperature is equal the tenpcrature of the encksure of tile mass flow comptroller. Additionally, in most applications, Tic ten1pcraturc will remain relatively stable over a long period of tine, so that a sloretl temperature value may be employed, with updates as necessary.

Alter obLainitlg the gas Lempcratulc ill stop 504 tile process proceeds to step 506 vlere the sensor coLroller obtains the volume of Lhe dead volume. Tllis value inay have been stored during manufacturing, for example. From step 506 Lhe process proceeds Lo step 508 where the pressure within the dead Alone is cbLaiied over a period of Lime. Tile number of neasurenents arid the time over which tile neasuremerts are made depend upon the speed and duration of transients at tile inlet of flee mass flow controller. In step 510 the processor employs the pressure measurements made in step 508 to compute the tithe rate of change of pressure within the dead volume. After computing the time rate of cleanse of pressure within talc dead volume, tile process proceeds to step 512 where a compensated outlet flow value is computed according to equation (a).

Simplifications may be made in the computational process. For example, the volume of the dead volume, standard temperature, and stadarcf pressure may all be combined into a single constant for use with the inlet flow measurenacut arid tline rate of change of pressure Within the dead volume to compute a compensated outlet flow approxination. This simplification would yield an equation of the Boron: Qo = Qi - Cl(V/T) (dP/dt) (3) wlere: Qo = the compensaled sensed outlet floss, rate, Qi = flee sensed inlet flow rate, C1 = a noralizin:', consLaut relati'r Lhe tenperaLure arid Pressure Lo standard temperature and pressure V = the volume between Lhe sensor bypass and Lhe Outlet flow control valve, rl = Lhe tenperaLure of' the fluid within tle volume, dl'/cit = time rate of clal,e olpressure whir the volume.

As pre.iousl; noted, the volume could be folded into the constant (31.

Strom step 512 the process proceeds to step 514 where IL continues, with the flow sesor's controller obtaining pressure, temperature, arid flow readings and computing a corpesated outlet flow estimate, as described. The process proceeds from step 514 to end ifs step 516, for examples when the mass flow sensor is slant down.

Returning to the block diagran of Figure 4, in this illustrative embodiment, tile controller 400 includes a diagnostic interface 422 that permits an operator, sucl1 as a tactician for example, to not only initiate, but conduct diagnostic tests on tile mass flow controller. Furtllerore, the interface 422 permits the operator to conduct the diagnostics in a manner that requires no input from the local system controller, vehicle may be a vorkstatio, Blat othenvise normally controls else mass [low controller. Such diagnostics are transparent to the local system controller, which may not even be made aware of the diagnostics being performed arid may, consequently, continue its operations unabated. The diagnostic interface provides access to mass flow controller sensor neasurenerts, control outputs and mass flow controller diagnostic inputs and outputs. These various inputs and outputs may be exercised and measured through Else diagnostic interface Title fiery little delay. In an illustrative dual I O processor enbodirnent described ill greater detail in the description related to Else cliscussio of Figure9, a deterministic processor Inky moodily outputs and/or monitor inputs, frown sensors or test points, for example. During the execution of online dia. gnQstics, the controller continues to execute its process control furcl. ions, uinpeded, while, at tle saline Line, Lle controller may provide real tinkle int.eracLion wilily r t.eclnician (i.e. iL-eractios wlerei the delays are iperceJ:'tib]e Lo a loan operator) either locally or Lhrougl a telecommunications comectior.

Using the diagnostic interface 422, an operator can adjust control values, sole as tile set point, used to detente the mass flow coLrol]ers operations AcldiLionally, Else operator niay nodif: sensor untpuL values ifs order to test the na.ss flow corLroller's response to pecifed tensor readings. Tlat is, an upeiclLul call rloclifr the sensor readings a mass flow comptroller employs to control the Ilow of gasses tIu-ougl its outlet valve and, thereby, exercise the controller for diagnostic purposes. \] operator may read all sensor and test point inputs as well as information stored regarding control (stored by the dete-niisLic controller in the dual processor embodiment), read all sensor values, read test point values, read control information, sucl as the desired set point. Additionally, the operator may write to control oLtputs and test points and over-write stored values, such as sensor readings or set polut iforination in order to Filly test tile controller through the diagnostic post.

In an illustrative embodiment, a mass flow controller may include a web server. Such a web server may be included within the diagnostic interface, for example. In such an embodiment, the diagnostic interface includes a web-serrer that permits the mass flow controller to be used in a system such as illustrated in the block diagram of Figure 6. In such a system, a user, such as a teclmicial, may employ a web-enabled device 600 such as a personal computer, personal digital assistant, or cellular telephone that runs a web Browser (e.g. Netscape (RTM) or Explorer (RIM) to communicate with a server 602 embedded in the mass flow controller 604. The server 602 includes web pages that provide an interface for the user to the mass flow controller 604. The discussion related to Figures 13A tl-ough 13E provide greater detail related lo the web server capability embedded ifs an illustrative embodiment of a Glass flow controller.

Mass flow sensors are typically calibrated fluting their manufa.cLuring process. Because a mass flow sensor is usually incorporated into a mass l. lov controller, this discussion avid center on mass floral corLrollers, but Lhe methods arid apparatus discussed 1lerein are applicable to "sLandalol:le" mass flow sensors as well. The calioratior process requires a Leelllicia to supply a gas at a known flow rate lo the mass flow controller and correlate Lhe mass flow sensor's flow sign,1 to Lhe lno:!n flow rate For cxanple, in the case of a Class f.lov sensor that provides a voltage output corresponding to flow, Lhe technician maps the voltage output frolic tile sensor into the actual flow rate. Allis process may be repeated For a plurality of flows in order to develop a set of voltage/flow correlations: fUr example, a 457olt output indicates a 40 standard cubic centimeter per niuLe (scowl) flow, a 5 Volt output indicates a 50 scorn flow, etc. Plow rates that fall between calibration points may be interpolated using linear or polynomial interpi-etation techniques, for example. This process may be repeated for several gases. Correlation tables Blat relate the signal fro rn the mass flow sensor (chicle may be a voltage) to flow rates for v:. rious gases may thus be developed and stored. Such tables may be downloaded to a mass flow controller for use "in the field", or may be stored within a mass flow controller. Often, technicians calibrate a mass flow controller using a relatively innocuous gas, such as N2, and provide calibration coefficients that may be used to correlate the flow of another gas to the calibration gas. Sliest calibration coefficients may then be used in tile field when a known gas is "flowed" though the mass flow controller to compute the actual flow frown the apparent flow. float is, the apparent flow may be a {low correlated to N2 and, if Arsire gas is sent through the mass flow controller, the Grass flow controller multiplies tile apparent flow by an Arsine,gas ccalibraLion coelficieL to obtain the actual flow. Additionally, once in the field, mass flow controllers nay be re-calibraLcd on a regular basis to accorninodaLe "drill", orieLLion, water cogent of a gas else flow of which is being controlled, or Lo comlesaLc for ogler factors. U.S. i'atent 6,332 348 B1, issued on December 25, 20)1 Lo Yelvertor el al, which is hereby incorporated by reference, discusses tliesc factors, avail blue unwieldy processes arid equipnie't r ecluircd Lo carry out these in-Lle-field calibrations in greater derail.

A calibration metro and apparatus will be lescrberl in the discussion related Lo the conceylual block diagram of Figure 7. This cabbraLioil system arid netted Nay be employed in a manufacturing selling, or, in an illustrative enbodin1enl, may be incorporated into a self-calibrating mass flow controller. The mass flow controller 7()0 includes a mass flow sensor 7()2 and an electronic controller 7()4 that receives a flow signal fi orn the mass flow sensor 702. A calibrator 706 Includes a variable flow gas source 7()8, a receptacle of predetermined volume 710, and a pressure differentialor 712. It should be noted that the lines separating different functional blocks are somewhat fluid. That is, in different cmbodh1enls, the function associated with one block may be subsumed by one or more other blocks. For example, in an illustrative embodiment, the pressure differentiator 712 is implemented all, or in past, by the execution of code within the electronic controller 704. The variable flow gas source 708 provides a gas at proportional rates to both the receptacle of predetertniecl volume and the mass flow sensor.

The flow rate Lo the mass flow sensor 702 may be equal to the flow rate to the receptacle of predetermined volume 710: i e., a proportionality constant of 1, for example. I'he mass flow sensor 702 is configured to produce a mass flower signal indicative of tale flow that it senses and, in tlis illustrative en1bodinent, this signal is sent to the electronic controller 704. The pressure differetiator 712 produces a signal correlated to Else flow Groin Like variable flow source 708 into the receptacle of predetermined volume 710 according to the relationship of equation 4: Qo = Qi - Cl(V/T)('dP/dt) (4) He-e: Qo = Else outlet flow rate ill sLdard cubic centimeters per nominate, Qi = the inlet l:lov rate in standard cubic cenLirnete-s per minute, Cl = a nornalizig constant relating: Lee Leperature arid pressure to sktldard Lenperature arid pressure V = the predetermined volume of the receptacle in liters, I = Lle Melvin temperature of tle fluid within Lle r ecel:,Lacle, dl'/dt = time r.l.e of change of pressure within tle receptacle ill Torr/second.

In act illustrative embodiment, the receptacle is closed and gas flows into the receptacle until the pressure within the receptacle equals [ltat of gas supplied by the variable flow source 708. In such an illustrative embodiment, the variable flow source may be a constant-pressure source that, as pressure Within Else receptacle builds, supplies gas at act exponentially decreasing flow rate. In sulk a case, the outlet flow Qo = 0, and the inlet flo:v, Qiis given by: Qi = C 1 (/T)(dP/dt) (5) Tile pressure differentiator 712 takes the time derivative of the pressure within the receptacle 710 arid, givers the normalizing constant C1, the predetermined volume V, and the gas temperature within the receptacle, the differentia.tor (and/or the electronic controller 704) may determine the actual flow into the receptacle 710. Because the flow idle the receptacle is proportional to the flow into the tle-ma] mass flow sensor 70:, the actual flow into the thermal mass flow sensor 702 may also be determined by a multiplying the actual flow into the receptacle by a yropotionality constant (c.g, tle proportionality constant is I if the flows are equal). The signal from the mass flow sensor is then correlated, by Lllc clecLroic controller 704 for es.anple, to flee acLua1 flow, determined as just clescribed. Sucl correlation relates ogle or refire signal levels from Lhe mass flow sensor to tle actual flows. The pressure diL'L'erentiator 712 Inky include analog differentiaLor circuitry, for example, that takes Lhe tinge derivative ot'the pressure signal. 'I'le cliL'ferenLiaLor output signal, a signal rcpreseutative of Lye Little derivative of Lhe pressure within the receptacle dp/lt, may be sampled by an analog-Lo-digital conveyer (not shown) Lo permit Lhe electronic controller 704, wlicl may include a nicrolrocessor, DSI. chip, or dual processors, for example Lo operate on the Lime derivative signal Alternatively, the pressure differentiator 712 nary curvcrL the pressure signal Lo digital boron for processing by the clecL-oilic controller 704, vlicl takes tl-e Line derivative of Lhe pressure signal.

In such an enbodinent, tle elects optic controller, in conbina.tion with difIcrcnLiaLor code, operaLcs Is Llc dil'fereltiator. flee comptroller employs at least l.vo pressure differences divided by corresponding time intervals to compute the derivative. I'lle gas may be supplied in parallel to tile receptacle and mass flow serisor, or it may be supplied in series, as will be described in greater detail in the following discussion related to a self-calibrating mass flow controller.

In operation, a mass flow controller inay be calibrated as just described, using a plurality, of gases, wills tile correlation values (mappings of sensor output to actual flow) stored in tables. Calibration coefficients, relating flow rrleasui-einents of one gas to another may also be developed and stored. The tables and/or coefficients may be downloaded to a mass flow controller in the field for use by the controller in controlling tile flow of a gas. Various known interpolation techniques, such as linear or polynomial ir.terpolation may be employed in conjunction with the calibrations tables and/or coefficients. Additionally, such stored calibration tables ad/or coefficients may be used as default values in a self-calibrating mass flow controller in accordance with tile principles of the present invention. A self-calibra. ting repass flow controller in accordance with the principles of the present invention includes a calibrator 706 arid a repass flow sensor 702 which marl be employed to calibrate the mass Bow controller in a inner as just described. In the case of a self calibrating mass flow controller, trouble, the calibration call be perLormecl, In him, in Late field just as readily as in a aulacturig setline.

Once inst.Alled ifs ills l.ield, Ott a se;.icorducLor processing tool as in flee system 100 of Figure 1, lor example, Lhe mass Bow controller can calibrate itself using Lhe gas that is Lo be used during Else seicorcluclor processing By us, Else leas tlaL is to lee used in processing, t.lle mass flow comptroller Inlay provide a more accurate flow nt-asurenent, because it will auLt'aLically acct'rnodate variations, such as moisture corLent, for example. Additionally,, a flew processing gas nay lNe used just as readily as a conventiolal gas, since the self- calibraLin rho class [low controller gab' calibrate itself (tllaL is, correlate mass flow signal levels Lo acl..'a.l flovv levels tlcLcrrliined by Llie pressure difieretiaLoj, on the gas to be used, not in relation to another, standard gas, such as No. Because Lhe mass flow conLruller is calibrated in tile orientation in which it will be used, discrepancies due to re-orientation of the mass flow controller- ifs the field relative to the position in which it Divas calibrated during manufacturing will be substantially elininaLed. All the mass flow controllers within a system surly as system 100 of Figure I may be calibrated automatically and simultaneously, within monuments.

This is ill contrast to the cun1bersone, painstaking process employed for conventional mass flow controllers, which are typically individually calibrated by a tactician employing multiple mass flow ineters, going from mass flow controller to mass flow controller. As will be described in greater detail ire the description related to the discussion of Figure 8, a mass flow controller that includes a thermal mass flow sensor and a pressure transducer nay shut its outlet valve to create a varying gas flow into it's dead volume. By taking the time derivative of the pressure tle actual flow into the dead volume receptacle rna.y be determined The mass flow controllers correlations of the actual value of the flow to tle thermal mass flow sensor signal acts as the nnass flow controller's calibration.

Figure 8 is a conceptual block diagram of a self-calibrating mass flow controller 800. In this illustrative, series-flow, embodiment, a gas flows through a thermal sensor 802 into a receptacle of predetermined volume 804, then through an outlet valve 806.

Lyle outlet [low Qo would nornally be a controlled flow into a clamber, such as a clamber viLhin an inle,raLed circuit processing tool. Am electronic controller 808, wlicll, in this illustrative enbodi:nent, executes code to parlor the differenLiaLion ecluirecl Lo obtain actual flow, as descibetl in Llie discussion relaLetl Lo inure 7, is in con1nunicaLion wiLI tile Llernal sensor 802, pressure setsur of 805 and tle outlet valve S06. In an illustrative process, tl1e e]ecLronie controller 808 operates in conjunction with Else outlet valve SOG Lo form a variable-LIoNv gas supply. ThaL is, the electronic controller shuts the outlet valve, N, l1ich causes Lle flow to clecease exl:'oleLially. Tle pressure within the dead voluine increases, and the electronic controller dilferenLiaLes this signal a number of times in order to obtain actual flow readings to correlate to the mass flow sensor signal values over a relatively broad range of flows. Additionally, in order to extend the period of Lime during, whicl1 Else flow is varying and to obtain actual flow values for correlation Title tle thermal mass flow signal values over a broad range, tile electronic controller inay open the outlet valve to a fillly open position before closing it.

The pressure and flow profiles associated with such a process are illustrated conceptually in tl1e graph of Figure 9 At an initial tickle to the pressure difference between gas at the inlet to the mass flow controller Pitt arid the pressure Pr downstream in the receptacle 804 forces gas to flow tlrough the mass flow controller at a rate Qi. Ire this example, Lhe inlet pressure Pil,, pressure within the receptacle Pit, arid L103N! lrougl, tle input of the mass flow comptroller Qin are constant At time tSo the controller shuts the outlet valve, thereby reducing outlet lion Qo to zero. Gas continues to flow info the receptacle as long as there is a pressure difference between the receptacle and the inlet. As the pressure PR within the receptacle rises exponentially toward an equilibrium state of equality with il1e inlet pressure Pi,,, Ll1e inlet flow Q.,, decreases. By taking the derivative of 1() Lhe pressure cl1ange iLhir the recepLa.cle (also referred to herein as "dead voluble" ill associaLio,; with an illusLi-ative, embodineL of Lhe iveLio), tile elecl:rolic couLroller may cdeLernine [he actual flow into Lhe receptacle, as previously described.

The elecLroic controller may correlate a,pluraliLy of sinulLaneous re. rdigs lroclucecl by Ll1e Local class flow sensor, to thereby calibrate the harass flow SGnSOr 'l'lat is, once LhiS process is completed for a speciL;c gas, l10 readings li-011 Ll1e tlernal crease flow sensor inky be currelaLcd Lo actual loose rates. The results may be Cloyed by Lhe electronic controller 808 to control the opening of tile valve SOG in a closed loop control system in order to deliver a o0 selocLeLI flow dov1strean. In order Lo increase Lhe period of thee So from Allen Else controller shuts Else valve, to Lhe time at which tile flov becone.s un:letectable, an:l to thereby increase the number and precision of pressure measurements that nitty be made, the controller may open the valve conpleLe]y before shutting it at time too. Additionally, one or more flow resLrictors may be placed in the 10w path between the inlet to the thermal mass flow sensor and the inlet to tl1e r eceptacle S04.

The conceptual block diagram of Figure 10 illustrates the architecture of a clual-processor embodiment of an electronic controller 1000 such as may be used in a mass flow sensor in a.ccordace with Ike principles of the present invention.

In this illustrative embodiinent, the controller includes two processors 1002, 1004. One of the processors 1002 is dedicated to "real time" processes and the other processor 1004 is dedicated to non-real time processes. By ''real time" we mean processes that require a specified level of service within a bounded response tine. In this sense, the processes are deterministic and the processor 1009 will be referred to herein as the deterministic processor. The objective of the dual processor architecture is to reduce the nuinber of interrupts and manage asyncb-onous event responses in a predictable way. The non-deterninistic processor 1004 may handle event-driven interrupts, such as responding to input front a user. The deterministic processor 1002 handles only frame-driven, that is, regularly scleduled, interrupts. In an illustrative embodirneilt, the non deterniinistic processor is a general purpose processor 1004, suited for a variety of Laslcs, such as user-interface, and other, miscellaneous tasks, rather than a specializedco-processor, such as a math- or cominunicaLions - coprocessor In particular, a TMS320VC5471, available from Texas lusLunents, Inc., may be ended in a dual-processor enbodiinent in accordance with tle prirciples. Tlie 1'MS39()VC5471 is described in a data manual, available at 1Ltp://ww s i. i.cou/sc/ds/Lilis320vc547l pal, which is Merely incoi-poraLed by reference.

A processor interface l00G provides for inter-processor cominunicaLions.

I'lre deterministic processo' 1002, includes sensoi- and actuator interfaces. Amoig LO sensor inlerOces, a BOv sensor hlLc-face 1005 operates in conjunction with a Illt,SS i]U\ bISL)I' Lo pL,Lluce digiLaI esLLio of Ll,e i-aLe of bass ho w in ail associated mass flow controller One or more actuator interfaces I O 10 are employed by the deterministic processor 1002 to control the opening of au associated mass flow controlleris output control valve or drive a diagnostic test point, for example. The aL;tuaLur nay be a current-driven solenoid or a voltage driven piezo-electric actuator, for example. As will be described in greater detail in the discussion related to the flow chart of Figure 9, after initialization, the deterministic processor 1002 loops through a control sequence, gathering sensor data, gathering setting information (for example, a desired mass flow setting), 30}providing status inforilaation, and controlling the sLaLe of the outlet valve Because non-deteministic tasks are offloaded to the On- deterministic processor 1004, the deterministic processor's control loop may be very compact.

Consequently, control tussles nary be executed Within a minimal period of time and control readings and drive signals nary be updated more frequently than possible if lime Revere set aside for servicing nondeternninistic tasks.

The controller 1000 operates in conjunction levity a thermal mass flow sensor as generally described in Else discussion related to Figure 3 to produce a digital representation of the rate of mass flow into an associated Bass flow controller. Tle digital representation may take the form of one or more dada values and is subject to fluctuations due to pressure transients at the input of the mass infold sensor. The controller 1000, find more specifically, the deterministic processor 1002 near; employ data obtained at the pressure sensor interface 1006 to conpensaLc for 11uctuaLions induced in the thermal news flow sensor by pressure transieLs on LO mass Low sensor inlet line. In this illustrative enlodinenL, clue deterninisLic processor 1002 employs the LeperaLure, pressure, awl mass flow readings oL,t.ained front the especLive 1008, 1007, arid 1005 hLerfaces, Lo produce a conlcsated Harass flow reacting that more closely reflects the mass flow at the outlet of tire mass flow sensor than a reading from the Llerna.l flldSS flow sensor alone. Tile deLerninistic processor 1002 also provides control to sensors, as necessary, tl-rougl Llerral flow 1005, pressure 1007, arid tcl1peraLure 100, sensoi- interfaces. TO unpersatio1 process ill be desc;riL'ed ill greater detail in tile discussion related to Figure 11. The deLernilistic processor 1002 also includes a valve actuator interface 1010, which the deterministic processor employs to control the position of a valve, sulk as tle valve 220 of Figure 9, to thereby control tile rate of fluid flow tlu-Qug,l a class flow controller, such as tile mass flow controller 200, in a closed -loop control process.

The deterministic processor 1000 is devoted to the closed-loop valve control process, and, coilsequeritly, must be capable of operating Will sufficient speed to read the various sensor outputs, compensate as necessary, and adjust the valve to produce a predetermined flow rate. Tile flow rate is predeterrniled in the sense that it is "desired" in solve sense, and it need not be a static setting. That is, the predetermined flow rate may be set by an operator using a mechanical mear. s, sucl: as a dial setting, or may be downloaded from another controller, such as a workstation, for example, and updated frequently. Typically, gas'flow control, and in this case, corripensated gas flow control, requires relatively high-speed operation. Various types of processors, such as reduced instruction set (RISC), math coprocessor, or digital signal processors (DSPs) may be suitable for such Lightspeed operations The conpulational' signal conditioning, and interfacing capabilities of a DSP make it particularly suitable for operation as tile delcninisLic processor 1002. As will be described ifs greater derail in the description of Lle control process related to ilie discussion of [Figure 9, tile luctio periorrl:led by Lhe deLenilisLic processor 1002 is deLerni. istic ire Lhe sense tlat certain operations are completed in a timely and regular namer in orUcr Lo..VUiCi errors, awl possible instabilities, ifs else control process. AL lie deterministic lO02 and non-deLerrninisLic 1004 processors comnunicale via the iter-l:'rocessur iLerface 1006 in a arranger LhaL does not inlede tle deterininisLic operation of tile deterministic processor 1002. Int.er-processor colunicatios are cliscussed in greater detail in tle discussions related Lo Figure 9 Tile ioil-delerninistic processor 1004 includes a local user interface 101 6 1.hal may be used with one or snore input devices, such as a lce,pad, licyboard, nose, Lrackball, joy stick, ]uLtons, touch screens, dual inline pacla,ed (DL[) or Ll-unb-wlleel switcllcs, for example, lo accept input from users, sulk as teclmicians who operate a mass flow comptroller associated with the no- detcrninistic processor 1004. The local user interface 1016 also includes one or more outputs suitable for driving one or snore devices, sucl as a display, wlicl may Ire a character, alphanumeric, or graphic display, for example, indicator light, or audio output device used to communicate information 1:ion a mass flow controller to a user. A communications inteiface lOlS permits a mass flow controller to communicate with one or snore other instruments, and/or with a local controller, such as a workstation that controls a tool that employs a plurality of mass Bloat Controllers ad/or other devices in.the production of integrated circuits, for example. In this illustrative example, the communications interface IOlvq ineindes a DeviceNet interface. A diagnostic interface 1090 provides an interface for a teelmician to run diagnostics, as previously described in relation to Else diagnostic interface 422 of Figure 4. In all illustrative en1bodirnent, the diagnostic interface includes an Ethernet interface and a web server.

The corrpaetness of code for the deterrninisLie processor lOO? permits the deLerrinistic processor to be loathly responsive to input changes and to quickly modify actuator signals ifs response to those changes. This patiLioru1g of operations between deLern1inistic arid non-cleter1linisLie processors also eases the initial develop net of eocle, for both the deterninistie and non-deLermiistie processors. For exannple, the cleterninisLic code reedn't respond Lo unscl1ecluled events, sulk as "n1irrorigl" a user's recluests on a display cat a user iLerface, awl the non-dc=Lerlliistie code 1eedn'L lreak away from providing such user feedback IS ifs order to adjust au outlet valve control setting every lilty bus cycles. The partil.ioninO beLwven deLerniristie and nondeterministic also pencils relatively simple Jevisions anal upgrades Lle cocde for one processor oust be revised or upgraded, Lle c ode for- the other may require no revisions or only minor revisions.

In pa.r-Licu]ar, the code for tire deterministic processor may lie more "nature", or fixed than that for the non-deterministic processor; user interfaces, c.onnnunicarions arid other sin-iilar fuctius Lend Lo be upgraded more frecuent1y Lhar1 the deterministic, mass flow control, Junctions.

Using tlls illustrative:lual-processor cnbodirenL, a user iLerface may be updated without ally impact ore the control functions code, tor example. Revision and n1ainteai1Ge of: n1ixed-:node code (clete-ninisLic and nondeterministic code) would be a nucl more complicated and costly proposition than code partitioned in a maimer ire accordance with the principles of the present invention. In act illustrative embodiment the dual-processor controller lOOO may by a hybrid processor that incorporates two processors on OiC integrates circuit. An integrated circuit such as the TMS320C5471 hybrid processor available Worn Texas Instruments (RTM) may be eployecl as the dual processors in accordance with the principles of the present invention. The digital signal processing (DSP) subsystem of the chip, due to its math capabilities would be more suitable as the deterministic processor in sully an application. The IC's dual-ported memoi y ma), be employed as the ilter- processor interface, Title the processors writing to arid reading from memory locations set aside to act as "mail boxes" for the transfer of information, including data, coinmands, and coranand responses.

Such an iter-processor interface pennits the deterrniistic processor to continue operating in a frame-driven mode awhile, at the same tine, allowing the delern-inisLic processor Lo play a role in diagnostics and calibration. Any request for sensor data front tle non-deterministic processor may be picked up from Else mailbox on one pass of the deLerrninisLic processor's control loop, with the readings deposited in the mailbox Lye very next time througl the loop. DiagosLic outputs lacy be modiiie:l similarly. The deterministic processor may also operate I5 in other, non-process oriented triodes. For exarl'L'le, during a selfcalibratio process such as previously described, the deteniistic processor would no longer operate Lo 1ailLain a set Dow Llrough flee repass Dow controller. h such a mode the clcLerminislic processor would be occupied by shutting tle mass flow controller's outlet valve, taking a plurality of time derivatives of the pressure within tile deacl volume, coinsuring the corresponlig actual flow in the mass flow controller, and correlating the ac:lal flow to Ll1e flow signal produced by a Llenal mass flow sensor.

The flow chart of Figure l l outlines the process of sensing and controlling the flow of gas tln-ough a dual processor mass flow controller.

The process degas in step 110() and proceeds frown there to step 1102 where the controller is initialized. This initialization step may include the uploading of calibration values or a calibration sequence itself. Additionally, operating code for both the deterministic and nondetenninistc processors 1004 may be uploaded at this point. In an illustrative embodiment, the non-deterministic processor 1()04 may upload its own code and begin operating, then upload code for the deterministic processor 1002. In the process of uploading code for the deterministic processor 1002, the non-deterministic processor 1004 may select among a plurality of executable code sets to upload to the deterministic processor 1002, thereby tailoring the operation of the deterministic processor 1002. Tle non-deterr.ninistic processor 1004 may base this selection of switch settings, coinnands from a local controller (e=,., a workstation controlling the operation of a semiconductor process tool), or settings stored in non-volatile storage, for example. Such a selection permits a mass flout comptroller to be tailored to different flow control operations. For example, a l.eclnicia. n relay, by selecting among code sets, choose Lo operate the controller in a "pressure corLro.[ler" anode rattler than a "mass [low coiLroller'' mode, ally Ellis selections nay be made locally or remotely (i.e., though a telecommuicaLions Link).

In step 1104 the non-deLerninistic IJrooessor 1004 passes operatir.g code arid initial control seLLing,s to the deLerniisLic processor 1002 which then Aegis operating in a manner Described generally in connection with the 110W chart of Figure 12. Front slop 1104, Else process proceeds Lo sLep 1106 where the nan 1eLerninistic processor 1004 services the local inluL/out interface. Such servicing may include r eading various inputs, including keyboard, switch, or mouse inputs, o0 Lund clisplaying inforratioL1 locally, Llrougl WEDS, alphanumeric displays, or graphical displays. From step 11uo the process proceeds to step llUS wllele tile non-deLernillisLic processor 1004 services the coirllunications interface. This servicing may include Else steps of uploading control and sensor data to a :vorlcstatio that operates as the local controller of a semiconductor process tool' for example. Additiolaily, else non-deterministic processor 1002 may download updated settings from tile local controller.

From step l 108 the process proceeds to step l 110 where the non deleri:inistic processor 1004 services the diagnostic interface. Various diagnostic operations, sucl1 as set forth in the description related to tile discussions of Figure 4, may be performed ifs this step. In an illustrative embodiment the mass flow controller includes a web server which permits an operator to run diagnostics tlrrough a network such as the "world wide web. " Frorn step 1110 the process proceeds to step 1112 where the non-deterministic processor 1004 services the inter-processor interface 1006. During "normal" non-diag:nostia operation the noHdeterininistic processor 1004 obtains readings from the deterministic processor 1002 and passes control il.dorrratioll such as a flow setting obtained tlIrougll the communications interface Lo the deterministic processor. From step 1112 tle process proceeds to continue the processes just set forth in step 1114. The process proceeds to end in step 1116 when the mass flow controller is turned off for example.

As previously noted the steps set forth in this and other flow chains herein need not be sequential and in fact a number of functions performed by the non- deterniistic processor 1004 may be event-interrupt-iven and Rio predictable sequence may be ascribed to the non-deLer1linistic processor's operation. Other processes such EtS data-logging nosy be perfonned at regular intervals. The on- (leLerninistic pi ocessor can support a L\vo-way socket connection Lo the clelernlinisLic processolL1-ouyl all ELlernet network inl.erface for example Lo provide a relatively direct collection between a renoLe user and the deterministic processor.

The flow chart of Figure 12A-12B depicts the operation of the delemlinisLic processor of a dual processor mass flow controller. In the context of this flow chart it is assuaged that all initialization process has taken place and that the deterministic processor is cycling through its control loop. The process begins in step 1200 Figurc 12A and proceeds limos there to step 1202 where the deterministic processor detennines whether it is to operate in its "normal" control capacity or whether it is to operate in an alternative mode such as a manual diagnostic mode or an automatic diagnostic mode for example.

The deterministic processor bases this decision on infonnation it obtains from the inter processor interface 1006. The deterministic processor services fi-ame-driven rather than even-driven interrupts consequently it regularly polls the inter-processor interface to obtain information such as this. l

If tl1e deterministic Processor is to operate in its normal mode, the process proceeds from step 1202 to step 1204, where the deterministic processor obtains information Mom the inter-processor interface regarding the desired control settings. This information may be ilk the form of a desired flow rate received from a local controller, from a front panel user interface, or to ough the diagnostic port ]090 lor example. The deterministic processor may also transfer infornatiort, such as sensor data, for example, to the non-deterministic processor through tl:e inter-processor interface during this step. From step 1204 the process proceeds to stop 1206 where the deterministic processor gathers data, Groin a variety or sensors Dor example. The sensors fi om which the deterministic processor obtains gala may include a mass BOW sensor (Llernal or other type), a Lerngerature sensor, or a pressure sensor, or example.

] 5 Front step 1206 Else process proceeds Lo step 1208, where the clever uinisLic processor corpuLes the now rate of material tlu-ough the mass flow comptroller. In an illustrative embodineut, the mass floes controller includes a thermal mass flow sensor and a pressure sensor c; orfigured to measw-e the pressure within the dead volume beLNveen Lle Llrer-mal nrass flow sensor's bypass arid Lice mass flow controller outlet valve, step 1212. In this en-bodinet, the Jeterninisl.ic processor may employ the rneLlud described in relation to tile discussion of Figure S to conpersaLe a flow rate measured by a thermal Nash flout sensor at tire inlet of Lhe controller to snore closely approximate tle flow rate at tile outlet of the controller. In an ernbodinelL ifs wlich the flow rate obtained frown tle sensor is not compensated, the process would proceed directly front step lQ06 to step 1210, skipping the computational process of step 1208.

In step 1210 the deterministic processor determines whether the ONV rate computed in step 1208 (or read in step 1206) is equal to the desired flow rate indicated by the setting information obtained from- Lhe nodeterministic processor via the inter-processor interface in step 1204. If Else values are equal the deterministic processor continues tl.e operation as just described, as indicated by the "continue" block 1214 (i. e., the deterministic processor returns to step 1202 and continues to cycle tlr-ough the loop). If the values a're not equal, the deterministic processor computes an error signal arid employs the error signal to adjust the drive signal to the nass flop, controller's outlet valve. From step 1212 the process proceeds to corltiue in step 1214. The process proceeds from step 1214 to end ifs step 1716 Men the mass flow controller is shut down or reset, for

example.

LO If, in step 1202 the deterministic processor concludes that it is not to operate in tle normal mode, tile process proceeds through coiectig box A Lo step 1218, leisure 12B, blare the deterninistic processor deLerrmies whether it is to operate ill a diagnostic node. flee deLerrninislic processor may obtain this inlorncLiu loom the inLer-pocessor itefirce. If the deLernilistic processor is Lo operate in r diagnostic node, the process proceeds to step 1220. In step 1270 tile deLerninisLic processor deLernines chicle diagosLic mode it is to operate irk.

Once again, Ellis inloraLiou may be passed Lo Lhe deterinisLic pros essor through tile inter-processor interlace. Ilk an "autonaLic" noodle, Lhe deterministic processor acquires a sequence of diaguosLic values fi-o' the iter-processor interface. The sequence ol values is available at the interface for acquisition by the deterministic processor Tile diagnostic plucks may be conLro] outputs, far settings Clue opening of Lhe inass flow controller outlet valve or for setting test point drive values, for example, or the diagnostic values may indicate desired sensor readings or leadings loom test prints, for example. The diagnostic values may also indicate the sequence in which the values are to be employed, in order to set test point driver values, tleu read test point outputs, for example. lu a manual node, diagnostic values are made assailable to the deterministic processor through the inter-processor interface one at a time. In an embodiment in which tile mass flow controller includes a web server, a tecllniciau may use a web enabled worl.station to contact the server in tile repass flow controller. Once linked in.

to the server, the technician may enter a valve setting command, by typing, selecting from a pull down menu of clicking on icon, for example. This single, setting, command would be received by the non-deterministic processor through its diagnostic port and passed to the deterministic processor through the iter processor interface.

In the manual diagnostic mode the deterministic processor executes through whatever diagnostic values are available at the inter-processor interface, then returns to it's coronal control loop. This could "override" a single control loop cycle if, for example, a single diagnostic value, such as a test point drive value, is presented to the deterministic processor or, if a sequence of diagnostic values is presented to tle deterministic processor, a umber of control loop cycles may be overridden. In the autonaLic diagnostic mode a number of diagnostic values may be exchanged tlHough the iter-processor iLerface in a period corresponding l.o a few control loop cycles, with a substantial umber, oil the or(lci- of lit lest ten times as mariy, control loop cycles intervening between auLoatic diagnostic exchanges. Diagnostic modes may be combined, for exanple, to produce an automatic active online diagnostic mode, for example. Tic all illustrative embodiment, a mass llov controller in accordance wiLI1 Lle lrirciples ol tlc present invention operates on a one-nillisecod control loop cycle, during wlicl1 it pr ovicles one percent ol bull-scale accuracy.

Keeping, Lle various diagnostic nodes in nailed, and kcephg ilk naiad Llv. t processes illustrated throu,h the use of 11ov charts nay not be strictly linear processes and alLeraLive horns may be inplenented within the scope of the invention, the diagnostic process will be described generally ilk elaLio to steps 1220 tl-ough 1226. In step 1220 the deterministic processor accluires diagnostic revalues frown the inter-processor interface. As previously noted, these values may be for the deterministic processor to use as control outputs or they inay indicate data that is to be acquired by the deterministic processor, from a sensor, for examples From step 1220 the process proceeds to step 1292 where the deterministic processor processes the values acquired in step 1220, by clanging an outlet valve actuator drive signal or transferring a sensor reading to tle inter processor inLerfiace, for example.

Frown step 1222 the process proceeds Loo step 1224 where the deterministic processor determines whether it has completed its diagnostic tasks. If it leas not completed its diagnostic tasks, for entangle if it is operating in the automatic diagnostic node and there are snore values in a sequence of values to be retrieved froth the inter-- processor interface, the process returns to step 1272 and front there as previously described. If, in step 1274 the detertr.inistic processor concludes tl-at it leas completed its diagnostic task, the process returns tlroup,h connecting boxy Lo step l 714ofPiStire 12A. If the deLerministicl:'rocessordetermines that it is not to operate in a diagnostic ode, the process proceeds from step 1718 vlere processcJr persons functions sucl, as routine background operations, then pocecds to return throuLrl conectig block B to step 1214 arid fi-om there as previously described.

Tle screens slims of I;igures 13A Llv-ougl 13E illustrate a user interface such as n1ay be made available 10r access to a mass low controller ill accordance wills Else principles of Else present invenLiu that includes a web server inLefa.ce, such as Lyle interface 608 of Figure 6. In an illustrative enbodimenL Else nass flow coLroller rclulcs a web server; sulk as tle server 602 of Figure 6. A user may employ the scaler locally, Lloug;l a local controller, or remotely, frown a web erab] ed device, such as the device 6()0 of Figure 6 In this nearer, the same user interface allay be employed for bolls remote and local inactions with the mass floor controller. Detailed information reg,aiding a nass Dow controller, such as model number, range, and rmanufacLuri=, setup parameters, may be displayed to a 2S user and user-cllalgeable setup parameters may be displayed as well. Different display techniques nary be employed. If there are only a limited Bunker of acceptable values, they may be displayed and Chopin front a pulldown nenu, for entangle. As previously described, a user, such as a technician can change set point values, open or close a valve, or monitor flow output, for exanple, through this interface. Additionally, while the mass flow controller is operating under a \ process control application, a user play induce the server to plot arid log parameter values obtained from the mass flow controller.

The screen shot of Fig,ure 13A illustrates the display a user may encounter when first accessing a mass flow controller in accordance with the principles of the present invention over the web. The display prompts the user to choose a cornnunications protocol Ll-ough use of the pulldown window 1300. The "query devices" Lilly 1302 allows the user to initiate a process Hereby his browser attempts to locate all devices that it recognizes.

Basic information play be downloaded tl-ou,h the server. Infornation related to the mass flow coLroller are displayed in the screen of figure 13B. Such screens may be expanded or collapsed. A user may choose lo view irformatio related to a subset of Lle displayed mass flow controllers. Basecl on tle model number, serial slumber and iLerally stored cocles, product specifictLions for flee mass flow controller are displayed along with user-selectable paranel.ers, which lS may be displayed ill a list, for example. user army employ this screen to download calil: rations data to or drool a nrass l1ow controller and to enter calibration tables. A user may also alter set points through this interface and monitor Ale repo-tecl flow rl-ough else corresponding repass flow controller.

Adciitioially, a user Inky ovenide selLi-s and >pen or close a mass flout conLro]ler's outlet control valve. Each mass flow controller's specifications may be viewed, as illustrated by the screen of Fi Sure 13C. IllusLr-ative user-selectable parameters are displayed in the screens shot of Figure 13D arid calibration data such as a user nay download iron, a news flow co'Lroller is illuslaLetl ilk the sL;-een shot of Figure 13E.

A software impleinentation of Ll1e above described enbodinent(s) may comprise a series of computer instructions either fixed on a tangible medium, such as a computer readable media, e.g. diskette, CD-ROM, ROM, or fixed disc, or transmittable to a computer system, via a modem or other interface device, such as conrnui1icatios adapter corulected to flee network over a medium.

Medium can be either a tangible medium, including but not limited to, optical or analog communications lines, or may be implemented With wireless techniques, including but not limited to microwave, infrared or otlaer transmission techniques.

The series of computer instructions embodies all or part of the functionality previously described herein Title respect to the invention. Those skilled in the art will appreciate that such computer instructions can be written in a number of programming languages for use Evils many computer architectures or operating systems Furller, such instructions may be stored using any memory technology, present or future, including, but riot limited Lo, semiconductor, magnetic, optical or Caller nerory devices, or LransmiLLed using any commuicaLions tecl:ology, preset. or future, including but not liniLed Lo optical, ilfi-ared, microwave, or oilier Lrarsrrissio- techoloy,ies. It is contemplated that sucl a co:puLer program product may be distributed as a removable media with accompanying printed or elecLroic:lucurenLaLio, e.g., sl-i vrpped software, preloaded Will a conpuLcr system, e g., Ott systemic MOM or fixed disc, or distributed from a server or electronic lulleti Lloyd over a eLworl, e g, Else 1nLeret or World Wide Web.

AILl-,ougl various exemplary clo:liile'Ls of Ale invention have been disclosed, it will be apparent to close skilled in the art that various changes and modifications can be Snide which will achieve some of tile advantages of the invention without departing from the scope of the invention. It will be apparent to those reasonably skilled in the art that other conponenLs perSorning the same functions nay be suitably substituted Further, the methods of the invention may be achieved in either all software implementations, using the appropriate object or processorinstructions, or in hybrid implementations that utilize a combination of hardware logic, software logic and/or firmware to achieve tle same results. Processes illustrated through the use of flow charts may not be strictly linear processes and alternative flows may be implemented within the scope of the inveiltio. The specific configuration of logic and/or instructions utilized to achieve a particular function, as well as other modifications to the iivenLive concept are intended to be covered by the appended clahlls.

The foregoing description of specific enbodinents of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise Porno disclosed, and many inodifications and variations are possible ifs light of the above teachings. The enbodinents were chosen and described to best explains the principles of else invention and its practical application, and to thereby enable others skilled in the art to best utilize the invention. It is intended that the scope of the invention be limited only by the claims appended hereto.

Claims (25)

1. A mass flow controller comprising: a mass flow sensor configured to produce a mass flow signal representative of a gas flow through the mass flow controller; and an electronic controller configured to produce a closed loop control signal for an outlet valve, based on said mass flow signal, wherein said electronic controller is also configured to upload a plurality of executable closed-loop code sets.

2. The mass flow controller of claim 1, wherein one or more executable code sets includes code for executing a diagnostic mode of operation.

3. The mass flow controller of claim 1, wherein one or more executable code sets includes code for executing a calibration mode of operation.

4. The mass flow controller of claim 1, wherein said electronic controller comprises a dual-processor controller.

5. The mass flow controller of claim 4, wherein said dual processors include a processor configured to operate in a deterministic mode and a processor configured to operate in a non-deterministic mode.

6. The mass flow controller of claim 5, wherein the deterministic processor is configured to produce said closed loop control signal for an outlet valve.

7. The mass flow controller of claim 6, wherein the non-deterministic processor is configured to upload said plurality of executable code sets, to select one of said executable code sets and to pass the selected code set to the deterministic processor for the processor to execute.

8. The mass flow controller of claim 7, wherein the mass flow sensor is a thermal mass flow sensor, including a sensor bypass, configured to sense the flow of fluid into the inlet of the controller.

9. The mass flow sensor of claim 8, further comprising: a pressure sensor configured to sense the fluid pressure in the volume between the thermal mass flow sensor bypass and the control valve.

10. The mass flow controller of claim 9, wherein Said deterministic processor is configured to acquire a pressure signal produced by said pressure sensor and to compensate the sensed inlet flow rate sensed by said mass flow sensor using the pressure signal to thereby produce a compensated measure of the rate of fluid flow out of the controller.

11. The mass flow controller of claim 10, wherein the deterministic processor is configured to compute the time rate of change of pressure within the volume between the sensor bypass and the outlet control valve, and to use this tine rate of change of pressure to produce the compensated measure of the rate of fluid flow out of the controller.

12. The mass flow controller of claim 11, wherein the deterministic processor is configured to compare the compensated measure of the rate of fluid flow out of the controller to a set value and to adjust the outlet control valve to minimize the difference between the set value and the compensated measure of the rate of fluid flow out of the controller.

13. The mass flow controller of claim 12, wherein the deterministic processor is configured to compensate the controller's sensed inlet flow rate, Qi, by calculating the compensated sensed inlet flow rate, Qo, according to: Qo = Qi - C1 (V/T)(dP/dt), whcrc: Qo = the compensated sensed inlet flow rate, Qi = the sensed inlet flow rate, Cl = a normalizing constant, V = the volume between the sensor bypass and the outlet flow control valve, T - the temperature of the fluid within the volume, C1 is the resultant of the temperature at standard temperature and pressure divided by the pressure at standard temperature and pressure, and (dP/dt) = time rate of change of pressure within the volume.

14. The mass flow controller of claim 7, wherein the deterministic processor is a digital signal processor (DSP).

15. The mass flow controller of claim 14, further comprising an interprocessor interface configured for communication between said deterministic and non-deterministic processors.

16. The mass flow controller of claim 15, wherein the inter-processor interface is a dual-ported memory with one or more locations arranged as mailboxes for the processors.

17. The mass flow controller of claim 16, wherein the non-deterministic processor is configured to provide a user interface to the mass flow controller.

18. The mass flow controller of claim 17, wherein the non-deterministic processor includes a network interface.

19. The mass flow controller of claim 18, wherein the network interface includes a web server.

20. The mass flow controller of claim 19, wherein the non-deterministic controller is configured to set up diagnostics through the network interfaces and exchange diagnostic information with the deterministic processor through the inter-processor interface and the deterministic processor is responsive to commands from the non-deterministic processor to perform diagnostic operations.

21. The mass flow controller of claim 20 wherein the deterministic processor is configured to run on-line diagnostics.

22. The mass flow controller of claim 20, wherein the network interface includes a web server and the web server is configured to set up said diagnostics.

23. The mass flow controller of claim 1, wherein the mass flow sensor is a thermal mass flow sensor, including a sensor bypass, configured to sense the flow of fluid into the inlet of the controller and further comprising: a mass flow calibrator operative to produce an electronic signal representative of mass flow in the mass flow controller independent of the mass flow sensor flow signal, and an electronic controller configured to correlate the mass flow signal from the thermal mass flow sensor to that of the mass flow calibrator.

24. A mass flow controller as in claim 23, wherein the mass flow calibrator comprises: a variable flow gas source; a receptacle of predetermined volume configured to receive gas from the variable flow gas source, the variable flow gas source configured to provide proportionate flow to the mass flow sensor and to the receptacle; and a pressure differentiator configured to produce an electronic signal representative of the time derivative of gas pressure within the receptacle of predetermined volume, said time derivative signal being proportional to the mass flow signal of the mass flow calibrator.

25. The mass flow controller of claim 24, wherein the differentiator includes: a pressure transducer configured to produce an electronic signal representative of the pressure within the receptacle; analog differentiator circuitry configured to produce an electronic signal that is representative of the time derivative of said electronic signal representative of the pressure within the receptacle; and an analog to digital converter configured to convert one or more values of the analog time derivative signal to digital samples of the time derivative.