CA2202293C

CA2202293C - Thermal mass flowmeter and mass flow controller, flowmetering system and method

Info

Publication number: CA2202293C
Application number: CA002202293A
Authority: CA
Inventors: Joseph C. Dille; Scott S. Bump; Gary P. Campbell
Original assignee: Emerson Electric Co
Current assignee: Emerson Electric Co
Priority date: 1996-10-04
Filing date: 1997-04-09
Publication date: 2000-05-23
Anticipated expiration: 2017-04-09
Also published as: US5911238A; CA2202293A1; JPH10111152A; EP0834723A1

Abstract

A flowmeter (100) or mass flow controller (101) used in a manufacturing process with toxic and reactive process fluids. A fluid flow sensor (114) sensesfluid flow. A set point is established based upon predetermined temperature and pressure conditions at which the fluid will be utilized in the process. A valve drive (124) operates a fluid flow valve (126) to the resulting fluid flow rate, this being based upon the sensed flow rate and the set point. A control unit (122) controls the valve drive. The control unit accesses a calibration data set to determine the amount of fluid to be delivered by the fluid flow valve based uponthe sensed flow rate and the set point. This calibration data set is created for the controller over its operational range using a calibration fluid having similar thermodynamic transport properties to a process fluid. The instrument is calibrated using the calibration fluid and the data set is produced by converting the calibration data using process fluid data stored in a data base (200). Accessing the data set stored in the instrument together with routing signals over a communication network (300) permits the instrument to precisely control process fluids without having to introduce external correction factors or other adjustments to the process.

Description

I

TTIFRMAT MAS~ FLOWMFTFR AND MAS~ FLOW CONTROLT FR, FLOWMFTFRTNG SYSTFM AND MFTHOD

BACK('TROUNI ) OF TTTF INVFNTION
5This invention relates to mass rate of Ille~ fluid flowmeters and flow controllers, and more particularly, to an analog or digital flowmeter employed in ", r 1.., ;"g processes such as the ", , r ~.- r of chips in which highly toxic and highly reactive fluids are used, and because of which, such flowmeters are not calibrated using the fluid they will be controlling 10 during a process.
Tn the r ~ _ of - ' integrated circuit (IC) chips and the like, it is necessary to use a variety of fluids (gases) which are highly toxic and/or reactive. A reactive fluid is a gas which is corrosive, flammable, or pyrophoric, among other things. Proper control of these fluids, for example"li~
15 (SiH2CI2), is therefore mandatory. The same is true in other r, .
processes as well; although these will not be discussed. Process control in the critical process steps where these fluids are used is _ . ' ' '. by monitoring the mass flow rate of the gas and controlling appropriate valving to adjust the flow to a desired rate for the process condition. Measuring mass flow rates is old in the 20 art. Essentially it is done using either an analog measuring system, or a digital based system. Regardless of which technique is used, there has been, and until now, continues to be, substantial control problems which must be overcome in order to maintain a process capable of producing quality chips.
There are a number of problems which currently effect flowmeter 25 calibration and p~. r... ". --.. e While these are discussed in more detail below, these problems are:
a) calibrating a flowmeter using an mert gas produces ;.. ~- ..,,...;1 .~
b) calibrating the flowmeter with a gas that is dangerous for one of a variety of reasons and which can potentially damage the instrument, if the 30 instrument is exposed to air or moisture at any time subsequent to calibration and before 1l ' , and, c) calibratu g the inslnDnent with a gas (freon, for exam,ple) tbat is ~, . . "~ unsound and wbich also causes oue or both of the other t vo problerns noted above.
Because of thermal transport properties in gases such as those used in ' ' , for example, the accuracy of current rnass flo v cordrollers (whether analog or digital) cannot be gualanteed to a level desirable both by the instrument maker and the end user. Ideally, flo~v controllers would be tested with the acblal gases they cordrol in a process so as to properly cah~atetheir r ~ for actual use. However, process capable cahl~tiorl data generally cu~ntly does not exist because the toxic and corrosive natnre of cerlain of these gases require speciel facilities be used to obtain the necessary To perform an instrument cshblation in a facility which rnay be suitable for use with a toxic or reaclive fluid is cunendy veîy expensive. Ihis is 1~ so where a cor~oller may be used with one of many such gases and the controller must be calibrated for use with each C out instnnnent calibration to an available facility is also expensive. It is not unusual for a calibration to cost well over a thousand doll~s per instrumer~ This procedure issimply not cost efficient. Rather, current practice is to calibrate the inslnDnent with an inert gas such as nitrogen (N~ rather tban any of the gases with which the controller will be used. The output of the instrument is then scated using a conversion factor to estirnate the I ' of the instrument with the process gas. Or, the instrument can be calibrated using a ~surrogate" gas. A surrogate gas is one which has specific heat propelties which are ~ "~ close to a process gas with which the controller is used. Using a surrogate gas reduces the mag ~itude of the conversion factor required to adapt the instrument's to the process gas.
Another problem mvolved with instrument calibration does not involve either the gases with which the controller will be used or the calibration facilities.
Radher it involves certain calibration fluids currendy used and dhe residual effects such gases may have on dhe instrument. For example, if a calibration is performed with a gas such as chlorine, unless sub~quent purging of the ins~nent effectively removes all traces of the gas, future exposure of the instrument to moisture, as when the in?~rument is exposed to air, will result in h, ~ ' ' acid(HCI) being formed. Damage to the instrument caused by the acid will ruin the S ins~ument, requinng a costly , ' Yet another problem is simply that some gases are expensive to use and calibrating a flowmeter with such gases is cost prohibitive.
The result of all of tbis is that process engineers responsible for controlling a ' ~ . . process and for using mass flow controllers, have devised valious 10 techniques to insure the accuracy of the inslruments they employ. Each rnass flow controller is dehvered to its end user with a complete set of calibration data, tbis data being based upon the inert gas with which the calibration was performed Tbis data is expressed, for example, as a curve of flow versus set point, and the curve covers the entire operating range of the instrument. The process engineer,15 using his knowledge of the process and the behavior of the gas used in the process, is able to adapt the calibration curve for the inert gas to the actual prccess gas using his prior experience. He rnay employ a "black book" or the like containing conversion factors he will use to interpret instrument readings for the process gas and meter fluid flow " ,1~ . This "Iweaking" however? comes at 20 a price. Certain processes, such as the '' of ' devices, require very precise process cordrols~ If in n occur, useless product results. It will be understood for example, that a conversion factor typically is accurate only at a single point, and the further readings are away from that pomt, the greater the divergence from a "true" value and the converted25 reading. Trial and error ~A~ ' ' " to determine what the adjustment factors for a particular instrument can cause delays and also result in lost production, increased down times, increased product costs, etc. Alleviation of problems concerning instrument calibration can have an immediate beneficial impact on many industries.

Another area of concem is the error that arises because of the v~ mvolved in signal handling and processing. All controllers, whether analog or digital controllers, use analog signals at one point or another throughout the processing and control fimctions performed by a controller. A
5 control system may include a central control computer which commands analog (1/0) cards of a process controller. The UO card converts digital signals from the computer to analog set point signals, and analog flow ~ r . -signals to digital signals supplied to the computer. The system includes thefollowing sources of potential signal error: wire and conmector losses, noise pick-10 up, and analog-to-digital and digital-to-analog conversion errors. Use of completely digital, between a central computer and mass flow controllers will eliminate various system errors.
SUMMARY OF T~F. INVF.l~TION
Among the several objects of the present invention may be noted the 15 provision of improved flowmeters and mass flow controllers having ~ ~r '~!1 greater accuracy than either existing digital or analog flowmeters and mass flowcontrollers. The illl~lU.~ in digital mass flow controller accuracy, for example, is partially the result of improved signal processing techniques, and partially a result of improved digital ~ within the controller.
20 Further, flowmeters and flow controllers can now be individually customized for the process gases with which they are used.
An important object of the present invention is the illll~lU.~ in IlI~,a:llJlCIII~ accuracy which results from the flowmeter's or flow controller's calibration for a customer's process gas or gases. The calibration process now 25 eliminates the need for "tweaking" by the user's technical personnel and the "cut and try" techniques previously used by such personmel to ~ ' a calibrated flowmeter or flow controller to the particular process. The aKendant costs and wastes arising from these techniques are now also eliminated, and process dcvclu,ulll~ time is shortened since these steps need no longer be 30 performed.

Another important object of the invention is the capability of the improved flowmeter or flow controller to be used in a variety of processes in which highly toxic, highly corrosive, or expensive gases, or some ~ ' thereof are normally used. Even though flowmeter or flow controller calibration is performedS on "safe" gases, the calibration is now such that the i' l~ , transport properties of such gases are taken into account as part of the calibration process.
A further object of the invention is the provision of an improved flowmeter or flow controller in which either is ' . ' 'y calibrated for a number of gases with which they are used and the calibration r " for each 10 gas is stored within the instrument and is readily accessible by a user. The personnel using the controller now no longer need to maintain separate "little black books" containing relevant ~ -~n necessary to adjust the instrument's operation, depending upon the gas currently being used in a process.
An additional object of the invention is the creation and usage of a 15 database which contains inf~ n relating ~, r~."., --, e of a flowmeter or flow controller with a gas used in a process as well as tbat of the instrument with acalibration gas or gases. rhe database enables the instrument to be readily usedwith process gases over the entire operating range of the instrument; that is, the instrument is readily used with any of the number of gases for which the 20 instrument is calibrated, and for the entire range of flow rates of these gases in a particular process.
A further object of the invention is to provide a flowmeter or mass flow controller having the capability to remotely zero the flow sensor used with the instrument. Other instrument capabilities include a digitally adjustable setpoint 25 and ramprate, and t~ a~ monitoring for indicating the i r ' ~ outside the instrument's flow rate sensor. Also, direct indications can be provided of asensor's raw output signals and a valve drive signal from the instrument so clogging or restriction of the sensor can be detected. Where a number of are used in a process, the ~ , can be hlt~,ll ' so, for~0 example, their setpoints can be " '~ adjusted.

It is also a provision of the improved processor of the flowmeter or flow controller to have sufficient data storage capability so all relevant r ~-relating to a calibration is stored in the mstrument and is readily accessible by theuser. Tbis enables a l~ldliu~ J between datd collected for a process gas and S l~,UI~ ., instrument calibration curves using a calibration gas (N2 for example) to be derived. From their 1, ' ', a calibration curve for the process gas can be determined and stored in the instrument, or in an external datdbase accessible by the instrument so this process gas calibration curve can be used during the process.
A fulther object of the invention is to provide an instrument having stored datd sets for various system operating pressures. The controller of the instrument is responsive to a pressure sensor reading or pressure input r " from a process control to interpolate between datd sets where the sensed pressure is hlt~l ' the pressure values for which the datd sets were produced.
Yet another object of the invention is the l J,~ h .,. .,1 of a system of fluid flowmeters or flow controllers each of which i. ,(1. ~ ly functions withinsome part of a v process. The system includes a .
network by which each flowmeter or flow controller can separately, quickly access a datdbase containing relevant r ~ for use by the instrument. Tbis 20 enables each instrument to have the r ~ readily available by which the instrument can readily and precisely monitor and/or control the fluid flow portion of the process with which it is associated.
Finally, it is a particular object of the invention to provide a flowmeter and mass flow controller which can be calibrated quickly, efficiently, and at a 25 reasonable cost, yet provide the necessary precision required when used in a r ' ' V process. Further, it is also an object to reduce the complexity of the monitoring and control system in which the mstrument is used. Tbis is achieved by an improved . ~ system that minimi~s wiring. In so doing, the overall reliability of the monitoring and control system is siv. fl.,a.~ly enhanced, resulting in substantial savings in process costs for the luollufa4~ of devices, for example.
In accordance with the mvention, generally stated, a flowmeter or mass flow controller is used in a r ' ' g process such as for the r ~ of ' chips. The flowmeter or mass flow controller meters, or meters and controls the flow of one of a variety of fluids used in the process, and a number of meters amd/or controllers may be used with the same or different fluids.
The process fluid is used in the process under a variety of t~ and pressure conditions. And, the fluids may be toxic, corrosive, or otherwise reactive. The mass flow meter comprises a fluid flow sensor for sensing fluid flow through a passage by which the fluid is directed to a portion of the process where it is used. The flow meter provides an output signal to the user that accurately represents the flow passing through the instrument at a given time. To do this, the instrument includes a processor which accesses stored calibration r ' derived for one or more process fluids the mass flowmeter measures and covers the operating ramge of the instrument. The signal from the flow sensor is processed by the instrument's processor using the calibration curve, i and pressure r ' ~ to give am accurate indication of the flow rate.
The mass flow controller compri~s the same sensing and signal processing elements as the mass flowmeter with the addition of a valve drive that operates a fluid flow valve to control the mass flow rate of fluid into the process and a control unit. A set point is established by an external input supplied by the user to establish a desired flow rate for a process fluid. The control unit of the instrument operates the valve drive. To do this, the control unit includes a processor which accesses stored calibration r " derived for one or more process fluids the mass flow controller controls and which covers the operating range of the instrument. From this calibration curve, the fluid flow rate for the process fluid to be delivered by the valve is ~' ' The calibration stored in the instrument is derived from calibration data for a calibration fluid which is not the process fluid whose flow is now being controlled, but which has similar Ih~lllOd~ lllc transport properties. The calibration r " is stored m a data base and the instrument's calibration is established for a particular process fluid by adapting the instrument's calibration curve for a calibration gas at certain set point conditions over the operating range 5 of the instrument using the process fluid data stored in the data base. As a ... c even though the instrument is calibrated with an inert gas, for example, the instrument can now accurately meter mass flow of a process fluid itis monitoring without external ~vl~, This, even though the process fluid is a toxic, reactive fluid. A system of process control employing multiple mass flowmeters and/or mass flow controllers in which set point ~ is supplied to each instrument, and a method of calibrating a flowmeter or mass flow controller with an inert fluid and adapting the resulting calibration curve so the instrument can be used for toxic, reactive process fluids are also disclosed. Other objects and features will be m part apparent and in part pointed out hereinafter.
BRTFF DF~CRTPTION OF TITF DRAWINGS
In the drawings, Fig. I is a block diagram IC~JII ' " of a prior art analog device for use in mass flow control;
Fig. 2 represents a .1.~ I;r. flow curve for the analog mass flow controller;
Fig. 3 is a block diagram l. ~IC:)clltdtiu.l of a prior art digital device for use in mass flow control;
Fig. 4 represents a ~ 1;. flow curve for the digital mass flow controller;
Fig. S is a block diagram IC~ CllldliVll of a digital mass flow controller of the present invention used in a system of mass flow controllers for controlling process fluids at different locations in a ~ ~ process;
Fig. 6 is a flow chart illustrating the creation and use of a process fluid data base for calibration of mass flow controllers;
Fig. 7 is a flow chart illustrating how a data base for a particular process fluid is created;

g Figs. 8A and 8B are calibration curves illustrating a 1~ ... method for calibrating a digital mass flow meter;
Figs. 9A and 9B are similar calibration curves to those in Figs. 8A and 8B
but reflect the calibration method ofthe present invention;
S Figs. 10A and 10B are curves illustrating data set generation for use in calibrating digital flowmeters in accordance with the present invention; and, Fig. I l is a curve or data set generation for use in calibrating an analog flowmeter.
Cu.... ' v reference characters indicate Cul~ ,~ ' V parts 10 throughout the drawings.
DF~CRIPTION OF T~F PRFFFRRED FMRODIMF~T
Referring to the drawings, Fig. I represents a prior art analog mass flow controller (MFC) 10. In an analog MFC, the functional , of the controller are i",~ using resistors, l~ut .,l;,..". ~. .~, capacitors, amplifiers, 15 etc. In this device, a flow rate sensor 12 is a thermal sensor which, as is well-known in the art, converts the flow rate of a gas into an electrical voltage signal.
In a flow controller r _d by the assignee of the present arplir~ n, the amplitude of this signal is a function of the thermal gradient (t~ ~.a~
difference) between an upstream and du...l~ monitoring location, and hence measured flow rate. A thermistor 14 is connected in series with windings (not shown) of the sensor to provide ~ for shifts in the sensor calibration resulting from tvlll~ effects on a , Use of the thermistor typically provides a linear or frrst order ~ , The full scale output voltage of sensor 12 is on the order of 50 mVDC.
The sensor output is provided to a gain and linr~ri7!ltion module 16 in which the analog output signal from the sensor is amplified, lineari7ed, and then supplied to a junction point 18. Module 16 employs feedback to produce a linear output to the summing point and controller, filtering to eliminate noise effects on the output signal, and adjustable , (~ ) for controller calibration. The output signal from module 16 is, for example, variable from 0-SVDC, and a setpoint input to the controller also varies between 0-SVDC. These signals are summed at junction point 18 and their difference is provided to a controller 20 which uses the difference value to determine the position of a fluid flow control valve V. The valve position is controlled by a valve drive 22 to S which outputs from controller module 20 are provided. The controller module takes into account factors such as the established operating setpoint, and overshoot, undershoot, and steady-state operating conditions to determine the valve V position.
Calibration of analog device 10 is performed by ~' ~ and adjusting 10 the flow of a calibration fluid at three points within the metering range of the instrument. These points reflect 0%, 50%, and 100% of the instfument's scale range. Based upon the instrument's p~ r ~ the l~ut ,1;...". f~ within module 16 are adjusted so the resulting calibration curve is essentially as by the dashed line in Fig. 2. That is, they are adjusted to control the IS instrument's zero, span, and linearity. As can be seen in the Fig., the ideal curve is a straight line (the solid line) extending between the 0,0 and 100,100 co-ordinates on the curve. However, the calibration curve may have a positive or negative offset at the respective ends of the curve; i.e., at the higher and lower flow rates. It will be understood that the dashed line ICi~ A~liUII in the Fig. is ; v~ ' for purposes of L ~ ' ~ v the ~ r capabilities of the instrument. The acttlal worst case error of a calibrated instrument is on the order of+l% full scale.
Referring to Fig. 3, a prior art digital mass rate flow controller 30 includes a flow sensor 32 amd a i r ci sensor 34. Here, an analog output signal from each sensor is separately provided to an analog-to-digital converter (ADC) 36, 38 . ADC 36 is, for example, a twenty-four bit converter, as is ADC 38.
The digital output from each converter is applied as a separate 1 " ~ input to a llfi~lu~Jluc~ ul 40. Mi~,lu,ulu~ ul 40 , three elements. First is a III;~IU~ ' 11l 42, second is a 64K by 8 erasable ~ read-only-memory or EPROM 44, and third is a 4K by 8 EEPROM 46. Operating software for runr~ing controller 30 is stored in EPROM 44, and product ~ r " and calibration tables are stored in EEPROM 46. ~he software ~, ' ' in the ~ r performs the ' and filtering functions performed in module 16 of the analog contrlla 10, as v,~ell as the controller 20 functions of the 5 analog inshument. In addition, the ~ . has enhanced I ' capabilities in tbese areas as vell as the capability to provide ~ r outputs to the user on a timely basis.
The contrl output frm the ~ , is a digital signal supplied to a di~, ' tv ' g converter (l)AC) 48 which produces an analog signal for valve 10 drive ~ to open and close valve V.
For putposes of this ~,, ' it will be understood that the distinction bet veen an arralog and a digital flowmeter is that in an analog unit, the basicsignal " ~ ~ and control functions are perfomned using an operational amplifia (op-amp). In a digital unit, a ~ . performs these functions.
15 It will further be understood that im a fL. ~ _ system, a digital flowmeter, for example, may be used with an arralog ~ ~ system. Other variations are also possible depending upon the user's system in which a flowmeter or flow contrller is inslalled~
Calibration of a digital flow contrller differs ~ from the 20 calibration of an analog flow controller. Now using variable digital values, a full scale flow rate having an accuracy on the orda of i 2% is produced. Next, the flow controller is operated at a number of different set points (ten, for example) over the operating range of the instrument. r~ ~ data is ~~ ' ' for each set point. An equation is now generated using the resulting test data. The 25 equation represents the calibration curve for the instrument over the entire operating range of the inslrument. Using the equation, a table of calibration points (twenty-five, for example) is created and stored in memory 46 of the controller. A
plot of the fiow rate vs. set point curve is illustrated in Fig. 4. The values displayed on the curve of Fig. 4 are corrected using t~ alul~ infi~mnsltion firom sensor 34. The - ' of the information firom the curve, and the correc60n, result in a worst case flow rate error on the order of iO.2%
full scale. Memory 46 of controller 30 is capable of storing mul6ple calibra60n curves so the conlroller can be sepa~ calibrated for mul6ple gases and mul6ple 90w rates.
As previously men60ned, it has heretofore been imprac6cal to always calibrate a controller with the process gas with which the controlla is used.
Rather, an inert calibra60n gas, or a su~rogate gas having similar fluid i' '.~ proper6es to the process gas have been used for calibra60n. The subsequent user of the cor~ller tben applies a conversion factor between measured flow rate data, and the calibra60n a~rve data, to generate a desired flow rate value for a parlicular set point. ~his conversion factor is based upon the rela6ve i- ~ proper6es of the cabbra60n fluid and a process fluid with which the controller is used. As noted, users of the flow con~roller have separately determined a conversion factor for use with a par6cular process fluidunder given set pomt condi60ns. This leads to process ' ~ , as well as errors m ~ ~
Referring now to Fig. 5, a flowmeter of the present invention is indicated generaUy 100 and a flow contmller 101. The flowlneter or flow controllff can be used ' ~ ~ ~ ~',~, or, as shown m Fig. 5, in a system having a plurality of other 20 flowmeters and flow controllers indicated MFC2MFCn. When used in a sysb~n, respec6ve flowmeters and flow controllers are in; with a process control 102 used to monitor the process and to establish set point conditions for each In Fig. 5, flowmeter 100, which is shown to be a digital flowmeter, is connected to a fluid flow cor~rol porlion of a prooess 104. The por60n of the prooess with which flowmeter 100 is associated mcludes a fluid flow passage 106, an inlet 108 to the passagS an outlet 110 from the passage, and a bypass 112 tbrough which a por60n of the prooess fluid flows. In common parlance, bypass 112 is also referred to as a restrictor, flow shunt, or flow splitter.
Fluid flow through bypass 112 is monitored by a flow sensor 114 of the flowmeter, and by a t~ U~ sensor 116. A pressure sensor 117 may also be used by the instrument. The fluid flow ;"r~"" ..;,~., gathered by sensor 114 is an analog signal output to an A/D converter 118. Similarly, the output of c sensor 116 (or pressure sensor 117) is an analog output which is provided as an input to an A/D converter 120. The digital signal outputs of the S A/D converters are supplied to a ~ ,lu~lu~ aOl 122 of the flowmeter. Stored within a memory portion of the Illl~,lU,UlU~.e~ UI are a series of data sets l~"Ul~ llti..g calibration curves developed for the instrument using data developed specifically for the process fluids with which the flowmeter or flow controller is used and for specific fluid pressure and fluid flow conditions. The UJ~lU.~ UI, utilizing the data set or fluid calibration curve for established set point conditions for the process, and the process fluid flow data, is now able to generate a fluid flow signal by which accurate flow rates are achieved. The result is the production of a control signal for a valve drive 124 by which the valve drive can open or close a flow control valve 126 and precisely control process fluid flow 15 through the passage. The control signal from UUIU~ UI 122 is a digital signal supplied to a D/A converter 128 to produce an analog signal used by valvedrive 124.
Referring to Figs. 6 and 7, the flow charts of the Figs. set forth how a ,1 is made as whether or not a flowmeter 100 or mass flow controller 20 101 is to be used with a process fluid for which flow control data exists, whether or not flow data for a particular process fluid is already stored in a data base; and, if not, how flow control data for the process fluid is developed, stored in the data base, and used to create a data set stored in a memory portion of III;~,IUIJIU~.I.,.l.~Ul 122 of the instrument. When an order for a flow controller is received as 25 indicated at step S1, the order typically includes a set of operating criteria in which the instrument will be used to control flow rate of a process fluid. This criteria includes the process fluids with which the controller will be used, as well as the flow range, and i r ' C and pressure conditions. A .1, is therefore first made as to whether flow control inf~ n for the fluid or fluids 30 and the range of operating conditions are currently in the data base. This is step S2 in Fig. 6. If so, the next d( ~ is whether the flowmeter or mass flow cont~ller will be an analog or digital instrument. This occurs at step S3.
If the instrument is an analog instrument, then the instrument is ~ ' and a calibration is performed on the instrument using nitrogen gas, 5 for example. This calibrdion is then matched to a companion curve generated from the stored flow data for the process fluid. This is step S4. At step S5, a quality cordrol check is perfonned to verify that the companion curve does matchIf there is ~ ' then the instrument is sbipped as indicated at step S6.
If the instrument is to be a digital flowmeter or mass flow controller, then 10 at step S7, the instrument is constmcted and calibrated. Again, nitrogen gas is the calibration fluid. Now, a scahng or conversion factor is used to deternune full scale flow of nitrogen and a conversion factor equation is developed based on the calibration results. Generation of the scaling factor is discussed hereaRer. Theconversion factor equation is stored m the . memoq of the 15 instrumerL At step S8, the equation is used to produce a calibration for the inslrument for the process gas with which the controller is used, and the given set of operating conditions. Next, a quality confrol check is made of the instrumentThis is step S9. If succes~l, the digital mass flow controller is shipped.
Retunung to step S2, if there is currently no ~ r '- m the data base 20 for a particular process fluid or set of operating conditions for a process fluid, then we proceed to step S10. At step S10, it is deternuned if there is any flow data for a particular process fluid; and if so, what are the "bounding" conditions for the data. That is, what are the l . and pressure conditions ~for which flow data was obtained, and how closely do these bounding conditions ~~
25 those under which the instrument will be used with the fluid. If there is no relevant ~ r " , then data base ' will be developed at step S l l and as discussed with reference to Fig. 7. If there is bounding r '- for the process gas as imdicated at step S12, a conversion factor is developed by whch acompanion curve can be generated for use in the instrument's calibration. This is the conversion factor used at step S8 in the calibration of a digital mass flow controller.
Referring to Fig. 7, step Sll involves generation of process fluid for inclusion in a data base. The data is ~I~A ' ' for a variety of 5 process fluids for a range of operating conditions. At step S13, the thresholdquestion to be asked is what data to collect. There are two sets of such data asindicated by steps S14 and S15. Step S14 is the r '~n requested by the customer for the process gases and sets of conditions under which the gas will be used. Step S14 includes the calibration r " normally generated by the 10 instrument r ' 1;~1. That is, the r ' ~ will have a standard calibration procedure (or procedures) which is normally performed on each instrument. From the r " gathered at steps S14 and S15, an overall calibration plan for the instrument is defined at step S16. This r " now includes all of the process fluids with which the instrument will possibly be used, 15 full scale flow values, and the range of i . c and pressure conditions for the various process fluids.
Next, the r ' C;l builds a number of hl~ as indicated at step S17. By building a minimum number of h~Lll , statistical validity of the ~ 11~".~' calibration can be ~' ' As indicated at step S18, the 20 i~ ts are then calibrated. Part of this procedure includes ranging the full scale output for a calibration gas equivalent of the actual (process) gas for given sets of conditions. That is, obtaining data for the defmed range of conditions using a gas having Ihc;llll(Jd,~ll~lliC transport properties which closely match those of the process fluid. After testing is complete, the hl~ are transported 25 (step Sl9) to a calibration installation which has facilities to develop the flow data for the process fluids with which the ill ,l.l are used.
At the test facility, and as indicated at step S20, the instruments are separated into analog and digital groupings. For an analog instrument, an actualgas calibration is performed using a process fluid at each of a set of pressure and 30 i . c, conditions (i.e., Pl-TI, P2-T2,...Pn-Tn). This is step S21. At step S22, a calibration check procedure is performed using a calibration gas at the same pressure conditions as the process gas and the calibration gas calibration data is compared against that obtained for the process fluids. The ~~ lts are then returned to the r ' ~1 (step S23) where calibration tests are made at 5 the various pressure conditions using the calibration gas (step S24). The resulting calibration data is now checked (step S25) and if the results correlate with those from the testing facility, the flow data for the process fluid for the given sets of conditions are entered into a data base 200 established for this purpose. If theresults do not correlate, then the process set out in steps S20-S24 is repeated.For a digital flowmeter, as indicated at step S26, data for the actual gas is collected at specific set point (i , G and pressure) conditions. If additional testing is desired, in order to obtain bounding conditions for p~ rf( predictions, then further actual gas testing is performed for additional conditions (step S27). If no additional testing is done, then a calibration check (similar to that performed at step S22 for analog controllers) is performed (step S29).
Thereafter, the i~ are returned to the r ' _1 (step S30) for the r ' ~I to perform a calibration check at his facility (step S31). Again, if the calibrations check out, the data is , ' in data base 200. If not, steps S25-S31 are repeated.
It will be understood that now, unlike with previous ill,ll, and calibration systems, one or more data sets can be created for each flowmeter or mass flow controller, not only for each process fluid with which the instrument is used, but for the range of flow conditions which will be ~ in carrying out the process with which the fluid is used. These data sets are represented bystored calibration curves. Now, when a set point is ~ ehP~1, the control means of the instrument can access the appropriate data set to provide the appropriateflow control signal to the valve means for sensed t.."l .,.~ and/or pressure conditions. This capability eliminates the need for external ~ ~.n of process t~ and pressure data, to provide flow control inputs into the 30 process. Further, once the data base 200 is established, it can be updated, amended, etc. as addi60nal process fluid ~ is collected. This not only irnproves the quality of instnnnent calibra6orL but reduces the time and cost involved inperformirlg acalibratiorL
Refernng now to Figs. 8A and gB, there is presented a simphfied S ~ ' ' rnethod for a digital flowmeter or rnass flow cor~ller.
Table 1 Set ~oint and Measur~d (~urve fit nksirednh~ired S4~ S4gnal F~wSignal Elow,N2 N2Flow llow,N2 N2asgEs iu E~lgr.
U~b, 0.000 0 0 0 0.000 0 0.625 160 125 0.488 125 1.250 320 320 250 0.977 250 1.875 470 375 1.496 375 2.500 600 600 500 2.083 500 3.125 700 625 2.790 625 3.750 800 800 750 3.516 750 4375 900 875 4.253 875 5.000 1000 1000 1000 5.000 1000 Using the data from the above table 1, the curve shown in Fig. 8A is plotted for flow volume in sbndard cubic cen6meters per rninute as the abscissa and a set point and raw signal value as the ordinate. The range for the set point is from 0.0 to 5.0, and five points are plotted to generate the curve. The set point values are listed in colurnn I of the chart, the five plotted points in colurnn 2.
Once the curve has been created, the curve fit flow values listed in colunm 3 are taken direc'dy from the plot Fig. 8B illustrates a calibra60n culve for a digital flowmeter or flow controller in which the ordinate is the same as in Fig. 8A. Now, the abscissa is for a desired signal and represents a modified set point value. These values are derived from tbe measured flow data for a set point as follows:
A desired flow is listed im column 4 of the chart. The desired signal ~ this flow is equal to the desired flow value of column 4, divided by the curve fit flow value of column 3, and with the result of the division multiplied by the raw signal value of colurnn I . That is, Desired signal =(desired flow/curve fit flow)*raw signal As an example of how the curve of Fig. 8B is generated, for a raw signal value of 0.625 (point X in Fig. 8B), the desired flow value m colunm 4 is 125, and the curve fit flow value in column 3 is 160. Using the above equation, the desired signal value is desired signal = (125/160)~0.625 = 0.488 which is the value entered in column 5. In column 6, the desired signal is expressed in rllL,; ..;"g units. The values in this column are arrived at by ,hlg the desired signal value in column 5 by a gas scaling f~tor. The values calculated for colunms 5 amd 6 now represent stored calibration data.
With respect to the curve shown m Fig. 8B, once all of the desired signal values have been calculated, the calibration is linear fit between adjacent points.
The table of data pomts for this curve are stored in the memory portion of the ~ "1"~~:':''" for the instrument. Now, when a set pomt is; ' ' ' 1, the desired signal Ic~ lthlg measured flow of the process fluid for that set point can be found in a look up table m the memory. Thus, as illustrated in Fig. 8B, for a set point of 4.000, the desired signal can be readily established. Here, it is 3.850.
Referring to the table 2 set out below and the Figs. 9A and 9B, a calibration performed on a digital flowmeter first comprises performing the steps involved in collecting the measured flow data set out in column 2 of the table, using nitrogen gas, for the set point conditions listed in column I of the table. As in the previously described calibration, a curve fit is made using the measured flow data. The resulting fitted curve is mdicated Cl in Fig. 9A. Next, similar data is gathered for a process gas, the actual gas (AG), with which the digital flow meter would be used, and a calculated AG curve is generated as indicated by curve C2 in Fig. 9A.
Table 2 Set point and Measnred Curve ft Data set Theoretical Desired 30 Raw SignalFlow, N2 N2 FlowC.F. eqn Actnal Flow Flow AG
AG
0 000 0 0 1.000 0.000 0 0.625 160 1.000 160.000 100 , 1.250 310 310 0.938 290.62s 200 1.875 455 0.872 396.915 300 2.500 575 575 0.850 488.750 400 3.125 690 0.843 581.571 500 3.750 790 790 0.838 661.625 600 4.375 895 0.822 735.889 700 5.000 looo looo 0.800 800.000 800 I 0 Desired SignaiSignal in Engr.
AG as gas units, AG
o.ooo o 0.391 loo 0.860 200 1.417 300 2.046 400 2.687 500 3.401 600 4.162 700 5.000 800 From these two curves, a ratio of values between the respective data values used in generating the curves can be created. The respective ratios for each set point are tabulated in column 4 above. Using this inf~ n, theoretical 25 actual flow values for the actual gas can be calculated using the equation:
theoretical actual flow = curve fit equation value (column 4)~curve fit N2 flow (column 3) Using this equation, the values listed in column 5 are tabulated.
Referring to table 3, and Figs. IOA and IOB, the data set equation 30 correction factors tabulated in column 4 of table 2, are arrived at as follows.
Table 3 A B C D E F
Set point and Average Average Average Average Ratio of Raw Signal Measnred Measured Curve Fit Curve Fit Average Fbw, AG Flow, N2 Ag nOw N2 Flow Curve Fits 0.000 o o o o 0.625 160 160 l.ooO
1.250 300 320 300 320 0.938 1.875 410 470 0.872 2.500 500 600 slo 600 0.850 3.125 590 700 0.843 3.750 680 800 670 800 0.838 4.375 740 soo 0.822 5.000 800 looo 800 looo 0.800 In Fig. lOA, curve X1 is a plot of the measured flow data for the actual gas, and curve X2 the measured flow data for the N2 gas. These plots are measured on the average measured flow values listed in columns B and C of table 3. The values ~ listed in columns D and E are the flow values for tbe set point values of colunm A, as taken from curves X1 and X2. The ratio values listed in column F of the table are arrived at by dividing the value for actual gas flow listed in column D by the N2 flow value in column E. Thus for the set pointvalue 0.125, the actual gas flow value 300 divided by the ~~UII~ , value 320 for N2 gas yields a ratio of 0.938. A curve X3 shown in Fig. IOB is a plot of the calculated ratios shown in column F. In accordance with the teachings of the invention, the actual gas and nitrogen or calibration gas values listed in table 3, and the calculated ratio values, are stored in the data base now used for mass flow controller calibration.
In colunm 6 of table 2, desired flow values for the actual gas are listed.
For each desired flow level, a CUI~ )ul.d;llg desired signal level can be determined from the equation:
desired signal = (desired flow/curve fit flow)*(raw signal) Thus for example, for a desired actual gas flow of lOû, the desired signal is calculated as desired flow = (100 (column 6 value)/160 (column 2 value))~0.625 (colunm 1 value) The resultant value is entered in colunm 7. After these values are produced, the curve C3 shown in Fig. 9B is generated. Also, and as listed in column 8 of the table, the signal in ~ units for the actual gas can be created by "i '.~illg the desired signal values of column 7 by a gas scaling factor.
For flowmeter 100 or flow controller 101 of Fig. 5, the ~ ~ ol 122 has stored therein data sets of process fluid calibration r which effectively comprises a series of curves C3. These curves are for all the process gases with which the controller is used and allows the instrument to provide accurate flow control for each of the process gases for the entire range of set point conditions which may be, cd by the instrument as part of the prooess. Each ofthe other digital mass flow controllers MFC2-MFCn is similarly calibrated for the process 9uids with which they are used. The process control 5 102 to which each of the rnass flow controllers is connected, provides updated set point and other relevant ~ ~ to each of the ur~its. The process control canpoll each separate instr~nent to obtain status and other pertinent " used to control the process.
An important advantage of such an iostrument calibrated in accordance 10 with the method of the invention, is that the flow control curve C3 developed by each controller for each process fluid, elirninates the need for ~tweaking' or otherwise having to refine flow process ~ developed by a flow controller to a fluid flow rate for a process fluid. As previously mentioned, it is not only desirable to calibrate digital flowmeters and mass flow controllers using the method of the invention, but analog insttuments as well. ~ ,, table 4 includes calibration gas data and process fluid or actual gas data Table 4 Set point and Avenge Average Average Average RawSignal Measured Linearized Me sured Cun~eFit Flow, AG Flow, AG Flow N2 N2 Flow o.ooo o o o o 0.625 140 1.250 300 220 270 270 1.875 375 2.500 510 400 480 480 3.125 590 3.750 680 580 720 720 4.375 850 5.000 800 800 looo 1000 The data in colurnn 2 of table 4 represents average measured flow data for the actual process gas. After 1 the data is plotted as shown by curve C4 in Fig. I 1, and listed in colurnn 3 of the table. After data has been similarly 35 acquired for the calibration gas, the process steps previously described withrespect to digital instrument calibrations are performed. The result is the curve C5 in Fig. I I and the data points listed in column 5 of the table.

The digital flow meters MFCI-MFCn shown in Fig. 5, could be aralog flow meters with the same process control capability being reali~able. Again, the flow controllers could be connected in a system with a process control whereby the process control is able to provide set point and other relevant 5 ~ r " to each controller and receive current process fluid flow ;, .r."., -;....
in retarn.
A further advantage of the invention is the . ~ h.. ,1 of an improved, digitd system 300 for routing r " to and from the process control and individual ...~,..t~. This digitd system eliminates signd 10 errors resulting from noise and other effects. Fl of such errors increases the precision with which the process is controlled thereby increasing the quality of the product produced by the process.
What has been described is an improved flowmeter or mass flow controller having s;~---fl~ lly greater accuracy than c~ lld digitd or~5 andog units. The instrument has both improved signd processing and digital capabilities, and can be specifically calibrated for the ' ~, process in which it will be used. It is a particular advantage of the method of the invention to quickly and efficiently cdibrate digital and andog flowmeters and mass flow controllers, and to do so at a reasonable cost while 20 providing a high precision instrament such as is needed in certain processes. Additiondly, the complexity of signdmg and controlling a process is reduced because of the improved system's . ~ Overdl, monitoring and control capabilities are increased which produces savings in process costs for the r ' C~ of articles such as ~ ... devices. Calibration is based 25 upon a particular customer's process gas or gases and eliminates the "tweaking"
and "cut and try" tech~iques now used to ---------- ' an instrument to a particular spplir.~irn Although calibration is done using "safe" gases, instead of the highly toxic and highly reactive gases with which an instrument is actually used, the C '~ ~ transport properties of such gases are readily taken into 30 account during calibration. Rc~ ~.~live units are i".l.l,..."L .aly calibrated for each of a number of gases with which it is used, with the calibration of each gas stored within a memory of a flowmeter or flow controller, the instrument having sufficient data storage capability so all relevant instrument and calibration data is stored in the instrument and is readily accessible by the user.
5 To facilitate instrument r~lihrAfionr~, a database is created containing r ~n relating to a unit's operation with a gas as well to that of the calibration gases.
The database enables calibration accuracy to be consistent over the unit's entire operating range, regardless of which gas with which the instrument is used, and the entire range of gas flow rates. The improved instrument also has a remote 10 capability, a digitally adjustable setpoint and ramprate, and t~ l,u~ tUI~
monitoring for indicating the i . ~ outside the instrument's flow rate sensor. A direct indication is also provided of the raw sensor signal and valve drive signal to detect sensor clogging or restriction. Multiple flow controllers can be . ~ into a flu.. ~ system for facilitatmg process control wherein each flowmeter is able to access the database to obtain r ~-pertinent to just that flowmeter to enable each flowmeter to separately regulatefluid flow in respective areas of the process.
In view of the foregoing, it will be seen that the several objects of the invention are achieved and other adv ~ results are obtained.
As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the , .~hlg drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A flowmeter for use in a manufacturing process for controlling the flow of one of a variety of fluids used in the process, a process fluid being used in the process under a variety of temperature and pressure conditions, the process fluid flowing through a valve controlled in response to a flow rate sensed by the flowmeter and said process fluid being a toxic, reactive, expensive, or difficult to dispose of fluid, or a combination thereof, the flowmeter comprising means for sensing fluid flow through a passage by which the process fluid is directed to aprocess location at which it is used; and processing means producing an output signal representative of the sensed flow rate of the process fluid, said processing means including means for accessing a calibration curve for the flowmeter to determine the amount of process fluid to be delivered by said fluid flow valve based upon said sensed flow rate and a set point externally established by an operator of the process, said calibration curve being derived from a calibrationdata set accumulated for the flowmeter over the operational range thereof and using a calibration fluid which is not the process fluid now being controlled bysaid flowmeter, accessing said data set for said process fluid permitting said flowmeter to condition an output signal generated by the flowmeter so the outputsignal accurately represents the sensed flow rate of the process fluid so the valve through which the process fluid flows can be accurately controlled to meet the set point requirements of the process even though said process fluid is not the fluid with which the flowmeter is calibrated.

2. The flowmeter of claim 1 further including means for sensing the temperature of the fluid, said processing means being further responsive to the sensed fluid temperature to determine the fluid flow rate for the fluid at the established set point conditions.

3. The flowmeter of claim 2 further including means for sensing the pressure of said fluid, said processing means being further responsive to said sensed pressure to determine the fluid flow rate.

4. The flowmeter of claim 3 wherein said processing means includes memory means in which is stored said data set defining said calibration curve and for said process fluid.

5. The flowmeter of claim 4 which is am analog flowmeter.

6. The flowmeter of claim 4 which is a digital flowmeter.

7. The flowmeter of claim 6 wherein said fluid flow sensing means and said temperature sensing means are analog sensors and said flowmeter further includesanalog to digital conversion means for converting the respective analog output of each sensing means to a digital signal.

8. The flowmeter of claim 7 wherein said processor means includes means for processing said digital signal inputs from said respective sensing means andfor supplying a digital signal output to a mass flow controller which operates said valve.

9. The flowmeter of claim 8 further including digital communication means for routing said digital signals within said flowmeter and to said mass flow controller.

10. The flowmeter of claim 4 wherein said processor means is a microprocessor and calibration of said flowmeter includes a data base established externally of said flowmeter and in which flow data for said process fluid is maintained for transference to a memory means of said microprocessor for use by said microprocessor in controlling flow of said process fluid.

11. The flowmeter of claim 10 wherein said external data base is capable of storing flow data for a plurality of process fluids, and said microprocessor memory means is capable of storing data sets for more than one process fluid with which said flowmeter can be used.

12. The flowmeter of claim 1 further including a plurality of flowmeters each of which includes a processor means, and communication means for routing digital signals within the flowmeter.

13. A mass flow control system for use in an industrial process in which at least one process fluid is used in producing a product, said process fluids being toxic, reactive, or both, the flow of each process fluid being controlled by a mass flow controller with the process fluids being used under a variety of temperature and pressure conditions, each mass flow controller comprising means for sensing fluid flow through a passage by which a process fluid is directed to a process location at which it is used; valve drive means for operating a fluid flow valve to control the mass flow rate of process fluid into the process based upon the sensed fluid flow rate and the established set point; and control means for controlling said valve drive means and including processor means for accessing a calibration curve for its associated mass flow controller to determine the amount of process fluid to be delivered by said fluid flow valve based upon said sensed flow rate and said set point, said calibration curve being derived from a calibration data set accumulated for the respective mass flow controller over the operational range thereof and using a calibration fluid which is not the process fluid with which said mass flow controller is used in performing the process, said control means accessing said data set for said process fluid and from which said calibration curve for a process fluid is created; and said system including process controlled means for establishing a set point for each process fluid controlled by a mass flow controller and based upon process temperature and pressure conditions for each respective process fluid.

14. The system of claim 13 wherein each mass flow controller further includes means for sensing the temperature of the fluid with which the mass flow controller is used, said control means for each mass flow controller further being responsive to the sensed fluid temperature to determine the fluid flow rate for the fluid at the established set point conditions.

15. The system of claim 14 wherein each mass flow controller further includes means for sensing the pressure of the fluid with which the mass flow controller is used

16. The system of claim 15 wherein each mass flow controller is a digital mass flow controller.

17. The system of claim 15 wherein each mass flow controller is an analog mass flow controller;

18. The system of claim 13 further including communication means for connecting said processor means of each mass flow controller to said process control means.

19. An analog mass flow controller for use in a manufacturing process to control the flow of a process fluid used in the process, the process fluid being used under a variety of temperature and pressure conditions and said process fluid being toxic, reactive, or both, and the analog mass flow controller comprising means for sensing fluid flow through a passage by which said process fluid is directed to a process location at which it is used and for producing an analog signal representative thereof; valve drive means for operating a fluid flow valve to control the mass flow rate of said process fluid based upon the sensed fluid flow rate and an established set point for said process fluid; and, control means forcontrolling said valve drive means, said control means including means for accessing a calibration curve for the mass flow controller to determine the amount of process fluid to be delivered by said fluid flow valve based upon said sensedflow rate and said set point, said calibration curve being derived from a calibration data set accumulated for a representative mass flow controller over the operational range thereof and using a calibration fluid which is not the process fluid now being controlled by said mass flow controller, said control means accessing saiddata set for said process fluid and from which said calibration curve for the process fluid is created.

20. The analog mass flow controller of claim 19 further including means for sensing the temperature of the process fluid and for producing an analog signal representative thereof, said control means further being responsive to the sensed fluid temperature to determine the fluid flow rate for the process fluid at the established set point conditions.

21. The analog mass flow controller of claim 19 further including means for sensing the pressure of the process fluid, said control means further being responsive to said sensed fluid pressure to determine the fluid flow rate of theprocess fluid.

22. The analog mass flow controller of claim 21 wherein said control means includes processor means within the mass flow controller for processing fluid flow, fluid temperature and pressure information from the respective sensing means, said processor means including memory means in which is stored said calibration curve and said data set, said data set including a range of flow condition information for the full operating range of the controller.

23. A digital mass flow controller for use in a manufacturing process to control the flow of a fluid used m the process, the process fluid being used under a variety of temperature and pressure conditions and said process fluid being toxic, reactive, or both, and the digital mass flow controller comprising means for sensing fluid flow through a passage by which process fluid is directed to a process location at which it is used and for producing an analog signal representative thereof; means for converting said analog signal from said sensing means to a digital signal; valve drive means for operating a fluid flow valve tocontrol the flow rate of process fluid into the process based upon the sensed fluid flow rate and an established set point for said process fluid; and, control means responsive to said digital signal from said sensing means for controlling said valve drive means, said control means including means for accessing a calibration curve for the mass flow controller to determine the amount of process fluid to be delivered by said fluid flow valve based upon said sensed flow rate and said setpoint, said calibration curve being derived from a calibration data set accumulated for the mass flow controller over the operational range thereof and using a calibration fluid which is not the process fluid now being controlled by said mass flow controller, said control means accessing said data set for said process fluid and from which said calibration curve for the process fluid is created.

24. The digital mass flow meter of claim 23 further including means for sensing the temperature of the fluid with which the mass flow controller is usedand for producing an analog signal representative thereof; and, means for converting said analog signal from said temperature sensing means to a digital signal, said control means being further responsive to the sensed fluid temperature to determine the flow rate for the process fluid at the established set point conditions.

25. The digital mass flow meter of claim 23 further including means for sensing the pressure of the fluid with which the mass flow controller is used and for producing an analog signal representative thereof; and, means for convertingsaid analog signal from said pressure sensing means to a digital signal, said control means being further responsive to the sensed fluid pressure to determinethe flow rate for the process fluid at the established set point conditions

26. The digital mass flow controller of claim 25 wherein said control means includes processor means for processing fluid flow, fluid temperature and pressure from the respective sensing means, said processor means including memory means in which is stored said calibration curve and said data set, said data set including a range of flow condition information for the full operating range of the controller.

27. The digital mass flow controller of claim 26 wherein said valve drive means is responsive to an analog input to open and close said fluid flow valve, and said mass flow controller further includes digital to analog conversion means for converting a digital output signal from said processor means to an analog input signal to said valve drive means.

28. A method of controlling the flow of a fluid used in a manufacturing process, the process fluid being used under a variety of temperature and pressure conditions, and the process fluid being a toxic, reactive or corrosive fluid and the method comprising sensing by a flowmetering means of fluid flow through a passage by which process fluid is directed to a process location at which it is used;
a set point, based upon predetermined process temperature and pressure conditions, for process fluid flow; determining the mass flow rate for the process fluid based upon a calibration curve for the flow controller means, saidcalibration curve being derived from a calibration data set accumulated for the flow controller means over the operational range thereof using a calibration fluid which is not the process fluid with which the flow controller means is used, determining the mass flow rate based upon the calibration curve including accessing said data set for the process fluid; and, operating a fluid flow valve by the flow controller means to control the flow rate of process fluid into the process, the flow rate being determined from said calibration curve, whereby the calibration fluid with which the flow controller means is calibrated is an inertfluid.

29. The method of claim 28 wherein a plurality of flow controller means are used in the process each of which separately controls flow of a process fluid in a different part of the process, and the method further include: accessing each flow controller means to establish a set point for the particular process fluid with which the flow controller means is used, said set point conditions being a function of the pressure and temperature conditions at the location in the process where the flow controller means operates.

30. The method of claim 29 further including sensing the process fluid temperature in addition to the fluid's flow rate and using the temperature to determine the flow rate of the process fluid through the flow control valve.

31. The method of claim 29 further including sensing the process fluid pressure in addition to the fluid's flow rate and using the pressure information to determine the flow rate of the process fluid through the flow control valve.

32. A method of calibrating a flowmeter or mass flow controller instrument used in a manufacturing process to control the flow of a fluid used in the process, the process fluid controlled by the instrument being used in the process under avariety of conditions, said process fluids being toxic, corrosive or reactive, and the method comprising performing a calibration procedure with the instrument using a calibration fluid which is not the process fluid with which the instrument will be involved when in use, performance of the calibration procedure generating calibration test data; separately performing a series of tests on said process fluid, said tests being performed on the process fluid under different temperature and pressure conditions which the process fluid may experience when used in a process, performance of said tests generating fluid flow data on the process fluid;
establishing a data base in which said fluid flow data for said process fluid isstored; manipulating the calibration test data with the process fluid data in the data base to generate a calibration data set for the instrument for the process fluid with which the instrument is used; storing said calibration data set in a memory of the instrument for a processor means of said instrument to access said calibration data set to determine the amount of process fluid to be delivered by a fluid flow valve based upon a sensed flow rate of the process fluid and a set point established for use of the process fluid.

33. The method of claim 32 wherein said calibration fluid is an inert gas.

34. The method of claim 33 wherein said instrument is usable with a plurality of process fluids and said method further includes separately performing a series of tests on each of said process fluids, each series of said tests being performed on the respective process fluids under different temperature and pressure conditions which said respective process fluids may experience when used in a process, performance of each of said series of tests generating fluid flow data for each of said process fluids; storing in said external data base fluid flow data for each of said process fluids; and, creating separate data sets for each process fluid andstoring said data sets in said memory of said instrument.

35. A mass flow controller for use in a manufacturing process for controllingthe flow of one of a variety of fluids used in the process, the process fluid controlled by the controller being used in the process under a variety of temperature and pressure conditions and said process fluids possibly being toxic, reactive, expensive, difficult to dispose of, or a combination thereof, the mass flow controller comprising means for sensing fluid flow through a passage by which a process fluid is directed to a process location at which it is used; valve drive means for operating a fluid flow valve to control the mass flow rate of process fluid into the process based upon the sensed fluid flow rate and an established set point for the process fluid; and, control means for controlling said valve drive means, said control means including means for accessing a calibration curve for the mass flow controller to determine the amount of process fluid to be delivered by said fluid flow valve based upon said sensed flow rate and said setpoint, said calibration curve being derived from a calibration data set accumulated for the mass flow controller over the operational range thereof and using a calibration fluid which is not the process fluid now being controlled by said mass flow controller, said control means accessing said data set for said process fluid and from which the calibration curve for the process fluid is created.

36. The mass flow controller of claim 35 further including means for sensing the temperature of the fluid, said control means being further responsive to thesensed fluid temperature to determine the fluid flow rate for the fluid at the established set point conditions.

37. The mass flow controller of claim 35 further including means for sensing the pressure of the fluid, said control means being further responsive to the sensed fluid pressure to determine the fluid flow rate for the fluid at the established set point conditions.

38. The mass flow controller of claim 37 wherein said control means includes processor means within the mass flow controller for processing fluid flow and fluid temperature and pressure information from the respective sensing means, said processor means including memory means in which is stored said calibration data set for a range of operating conditions.

39. The mass flow controller of claim 38 wherein said mass flow controller is an analog controller.

40. The mass flow controller of claim 38 wherein said mass flow controller is a digital controller.

41. The mass flow controller of claim 40 wherein said fluid flow sensing means and said temperature sensing means are analog sensors and said mass flow controller further includes analog to digital conversion means for converting the respective analog output of each sensing means to a digital signal.

42. The mass flow controller of claim 41 wherein said processor means includes means for processing said digital signal inputs from said respective sensing means and for supplying a digital output to said valve drive means.

43. The mass flow controller of claim 42 wherein said valve drive means is responsive to an analog input to operate said fluid flow valve, and said mass flow controller further includes digital to analog conversion means for converting said digital output signal from said processor means to an analog input signal to said valve drive means.

44. The mass flow controller of claim 38 wherein said processor means is a microprocessor and calibration of said mass flow controller includes a data baseestablished externally of said mass flow controller and in which flow data for said process fluid is maintained.

45. The mass flow controller of claim 44 wherein said external data base is capable of storing flow data for a plurality of process fluids, and said microprocessor memory means is capable of storing data sets for more than one process fluid with which said mass flow controller can be used.

46. The mass flow controller of claim 35 further including.
means routing digital signals within said mass flow controller.