CA1169561A - Apparatus for correcting measured gas flow - Google Patents
Apparatus for correcting measured gas flowInfo
- Publication number
- CA1169561A CA1169561A CA000394508A CA394508A CA1169561A CA 1169561 A CA1169561 A CA 1169561A CA 000394508 A CA000394508 A CA 000394508A CA 394508 A CA394508 A CA 394508A CA 1169561 A CA1169561 A CA 1169561A
- Authority
- CA
- Canada
- Prior art keywords
- display
- volume
- pressure
- switching element
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F15/00—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus
- G01F15/07—Integration to give total flow, e.g. using mechanically-operated integrating mechanism
- G01F15/075—Integration to give total flow, e.g. using mechanically-operated integrating mechanism using electrically-operated integrating means
- G01F15/0755—Integration to give total flow, e.g. using mechanically-operated integrating mechanism using electrically-operated integrating means involving digital counting
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F15/00—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus
- G01F15/02—Compensating or correcting for variations in pressure, density or temperature
- G01F15/04—Compensating or correcting for variations in pressure, density or temperature of gases to be measured
- G01F15/043—Compensating or correcting for variations in pressure, density or temperature of gases to be measured using electrical means
- G01F15/046—Compensating or correcting for variations in pressure, density or temperature of gases to be measured using electrical means involving digital counting
Abstract
APPARATUS FOR CORRECTING MEASURED GAS FLOW
ABSTRACT
A gas flow volume corrector mounted on a flow meter is provided with a microprocessor which calculates a corrected volume each time the meter measures a unit volume of flowing gas. Customer supplied data as to base conditions, specific gravity and gas composition are utilized to calculate super-compressibility values. These values are then processed to provide a plurality of constants which define calculation equations. The constants are stored in the corrector on a diode matrix card or PROM and are utilized each time the meter measures a unit volume of flowing gas for calculating the corrected volume. To conserve memory space, integer arithmetic, rather than floating point arithmetic, is util-ized in the calculations.
ABSTRACT
A gas flow volume corrector mounted on a flow meter is provided with a microprocessor which calculates a corrected volume each time the meter measures a unit volume of flowing gas. Customer supplied data as to base conditions, specific gravity and gas composition are utilized to calculate super-compressibility values. These values are then processed to provide a plurality of constants which define calculation equations. The constants are stored in the corrector on a diode matrix card or PROM and are utilized each time the meter measures a unit volume of flowing gas for calculating the corrected volume. To conserve memory space, integer arithmetic, rather than floating point arithmetic, is util-ized in the calculations.
Description
0lAM021~3 DL,~:jd 35~i~
DESCRIPTION
APPARATUS FOR C~RRECTING MEASURED GAS FLOW
BACKGROUND OF THE INVENTION
_ This invention relates to gas flow measurements and, more particularly, to the correction oE a measured unit volume of gas .flowing through a conduit -to a base volume S at given base conditions of base pressure and base tempera-ture.
Gas is a compressible item, the volume of which changes as a function of temperature and pressure, in accordance with well known physi.cal laws. Because gas is a compressible com-modity, the buyer and seller of this commodity must agreeupon the same conditions. Thus, to distribute and sell gas that is exposed to varying conditions of temperature and pressure, calculations must be made -to convert the measured gas flow volume Vf in terms of cubic feet at varying condi-tions of temperature Tf and pressure Pf, to a standard cubicfeet volume Vb at specified, previously agreed upon base temperature Tb and base pressure Pb.
:I ~ t;~3~t;-l The bas.ic gas law cqua tiOII of S tate is PV = WRTZ (1) where:
P is pressure V is volume W is mass R is gas constan-t T is tempera-ture Z is compressibility.
When dealing with a simple gas, such as N2 or 2' the classic gas laws serve very well, and Z may not be needed. However, when there are mixtures of gases and complex hydrocarbons, it has been found that Boyle's and Charles' laws are in error. Fuel gases -tend to be easier to compress, up to around 2000 psig, -than these laws would sugges-t. Ahove this pressure, the trend is reversed. The exact values are unc-tions of the pressure, temperatuxe and the gas composition.
The diffexence between the classic gas laws and the complex gas compression i.s called compressibili-ty, or Z.
From equation (l), the following relationship between base and flowing conditions may be derived:
Vb = Vf f Pa b pv (2) b Tf where: Vb is base volume : Vf is the measured uncorrected volume Pf is the flowing gas gage pressure Pa is atmospheric pressure Pb is base pressure T~ is base temperature in degrees Rankine Tf is the temperature of the flowing gas in R
Fpv is the supercompressibility factor which is equal to ¦~ base '.
J~ flowing l .ll ti~5tj.~
The cti~icult part of ca:Lculatillg base volume in accordance with equation ~2) is to determine the supercompressibility factor which is a function of the flowing temperatwre and pressure as well as the speciEic gravity and the composi--tion of the gas being measured. One way oE determining the supercompressibility fac-tor is to utilize tables such as those set Eorth in -the "Manual for the Determination of Supercompressibility Factors for Natura:L Gas", PAR Research Projects NX-19, published by the American Gas ~ssociation.
~owever, if i-t is desired to automate the correction of measured gas flow, it is difficult and expensive to utilize tables. Alternatively, it is possible to utilize a series of equations to calculate the supercompressibility factor.
U.S. Patent No. 4,173,891 discloses such an automated sys-tem including a microprocessor for repetitively calculating-the supercompressibili-ty Eactor. The method employed by the patented system includes a plurali-ty of compu-ting steps Eor each calculation of the base na-tural gas flow. Duriny each computing step, an initially appro~imated value oE the super-compressibili-ty factor or -the previously calculated value is used to calculate an indication of the base natural gas Elow, each computing step beiny insufficient -to recalculate -the supercompressibilit~ factor, this calculation taking a plu-rality of steps. Therefore, the disclosed system has the disadvan-tage that a relatively large amoun-t of time is required each time the supercompressibility factor is to be calculated. In fact, it requires five input meter pulses for a complete calculation to be performed. Another dis-advantage of the system disclosed in this patent is that the calculations are performed utilizing floating point arithmetic, which requires a larye amount of memory capacity, increasing the cost of the system hardware.
It is therefore an object of this invention to provide apparatus for measuring gas flow.
;4~
I-t is a .Eur-ther object oE this invention to provide such a~paratus which automatically corrects the measured gas flow to predetermined base conditions of temperature and pressure.
It is another objec-t of -this inven-tion to provide such apparatus wherein the corrected values`are e:Eficiently calcu-lated.
I-t is yet another object of this invention to provide such appara-tus wherein it is .relatively easy to make aclapta-tions for different base conditions and gas composition.
lQ It is still another object of this invention to provide such apparatus which can be utilized at remote meter locations without the necessity for connection to an external source of power.
SUM~5ARY OF T~E~ INVENTION
The foregoing and additional objects are attained in accordance with the principles oE this invention by providing apparatus for correcting a measured unit volume of gas flow-ing through a conduit -to a base volume at given base concli-tions oE base pressure and base temperature. The apparatus includes tempera-ture and pressure transducers which provide signals corresponding to their measurements of the -tempera-ture and pressure, respectively, of the flowing gas. A meter connected in -tlle condui-t measures the uncorrec-ted volume of the flowing gas and provides -to the appara-tus a volume pulse in response to measuring a unit volume of the gas. A set oE
constants derived from customer supplied data as to base con-ditions and gas content are stored in the apparatus on a diode matrix card. In response to the occurrence of a volume pulse, the stored constants and the measured temperature and pressure values are utilized for performing a series of cal-culations to derive the supercompressibility factor and in turn a correc-ted volume. All calculations are performed utilizing integer arithmetic, rather than floating point arithmetic, in order to efficiently utilize memory and achieve a cost savillg. The outpu-t of the apparatus is a first counter which indicates the uncorrected volume and a second counter which indicates the corrected volume.
In accordance with an aspect oE this invention, a -test unit is provided whicll may be plugged into the apparatus and is powered thereby. This test uni-t does not interfere with the operation of the apparatus or the meter. The test unit can be activated to display flowing pressure and temperature, to cancel out of limit indications, to verify system opera-tion and also may be utilized to test the apparatus counter.
DESCRIPTION OF THE DRAWINGS
The foregoing will be more readily apparent upon readingthe following description in conjunction with the drawings wherein:
FIG. 1 illustrates the moun-ting of volume corrector apparatus constructed in accordance with the principles of this invention and its relationsh.ip -to a meter connected in a conduit;
FIG. 2 illustrates a -test unit, constructed in accord-ance with -the principles of this invention, which may be plugged into the volume corrector apparatus shown in FIG. l;
FIG. 3 illustrates a diode matrix board which forms a part of the volume corrector apparatus and is used for stor-ing constants derived from customer supplied data;
FIG. 4 is a block diagram of the illustrative volume corrector apparatus and test unit of FIGS. 1, 2 and 3;
FIG. 5 is a flow diagram illustrating the overall sys-tem operation of the volume corrector apparatus constructed in accordance with the principles of this invention; and FIGS. 6 through 11 are flow diagrams of subroutines which form a part of the system operation shown in FIG. 5.
DL`rL'~IL~D DESCRIPTION
Referring now to the drawings, wherein like elemen-ts in different figures thereo~ have tlle same reference character applied -thereto, FIG. 1 illustrates volume corrector appara-tus, designated generally by the reference character 20,mounted on a me-ter 22 connected in a conduit 24 through which yas flows. The meter 22 does not :Eorm a part of the present invention and may be any -type of meter so long as it satisfies the requirement that the corrector 20 needs a low speed input derived from the output register drive shaft of the meter 22.
Alternatively, the corrector 20 may be mounted remotely from the meter 22 and in this case, the input to the corrector 20 will be an electrical switch closure derived from the output register drive shaft of the meter 22, in a manner well known lS in the art. The corrector 20 also derives input signals from a temperature -transducer 26 and a pressure transducer 28 which e~tend into the conduit 24. The temperature transducer 26 is illustratively a model ~C2626~ tempera-ture transducer manufactured by ~nalog Devices and is an integrated circuit housed in a stainless steel tubular probe which produces an output current linearly proportional to absolute temperature.
The pressure transducer 28 is illustra-tively a model ITQH-24 pressure transducer manufactured by Kulite Semiconductor Products and includes a solid state sensing element which is a monolithic integrated circuit Wheatstone bridge directly formed on a silicon diaphragm, and is available in different ranges, depending upon the desired application. The output of the pressure transducer 28 is a voltage which is related, over the range, to the pressure of the gas flowing through the conduit 24.
Since the corrector apparatus 20 is designed for use at - remote locations, such as in a desert area, where commercially available power may not be available, the apparatus 20 is designed to be battery operated. Further, a solar battery charger 27 may be provided mounted above the apparatus 20.
5~
, If the enclosed corrector apparatus 20 were to be exposed to direct sw~ ht, its interior temperature would rise to an unacceptable level. There~ore, a sunshade 29 is also pro-vided -to shield the apparatus 20 from the direct rays of the sun.
The corrector apparatus 20 has as i-ts output two count-ers. ~ first counter 30 is a mechanical coun-ter which dis-plays the uncorrected volume. The counter 30 is incremented by rotation of -the output register drive shaft of the meter 22. If the corrector 20 is not mounted on the meter 22, the uncorrected counter 30 is replaced by the original meter register. The second counter 32 is the corrected counter and is an electromechanical or electronic counter which dis-plays the corrected volume. It is incremen-ted by signals genera-ted within the corrector 20 in response to inp~ts from the meter 22 and calculations based UpOIl measured temp~rature and pressure, in a manner to be described in detail herein-after. The corrector apparatus also includes a low battery indica-tor 33.
FIG. 2 illustrates a test unit, denoted generally by the reference numeral 34, which is a portable instrument used in the shop and field to check the operation of the corrector 20. The test unit 34 includes a cable and connector assembly 36 which plugs into a suitable receptacle, not shown, in the corrector 20. Power for the test unit 34 is obtained from the corrector 20. The test unit 34 includes a numerical dis-play 38 and a plurality of test buttons 40, 42, 44, 46 and 48. When the test unit 34 is coupled to the corrector 20 via connector assembly 36, -the counter 32 may be checked by depressing the button 40. When the button 40 is depressed, the counter 32 is advanced one count. The flowing pressure may be read directly on the display 38 by depressing the but-ton 42. The flowing temperature may be read directly in C or F on the display 38 by depressing the button 44. When the button 46 is depressed, the display 38 will display a l,~.tit~
number which has been detersnined to be the "si~nature" of the corrector 20 when it is operating correctly. If the display 3~ displayed colons along with numbers when any of tlle buttons ~2, 44 or 46 was depressed, -th:Ls indicates that some time after the last check was made either the pressure or temperature was out of specified limits. The display of colons will not indicate wnich parameter was out of limit or if the high or low limi-t was exceeded. Depressing the button 48 will remove the colons from the display 38 and reset the corrector 20. When the but-tons 46 and 43 are depressed simultaneously, the display 38 will display a num-ber indicating the correction multiplier for the presently flowing conditions of pressure and temperature.
When a cus-tomer places an order for a correc-tor 20 to be used at a particular location, -the customer also speci-fies certain condi-tions at that location. Tlle customer must specify the type of flowing gas which is to be measured, its composition, -the range of pressures at which the gac; will Elow, and the base tempera-ture and press~lre -to wllich the fl~w volume is to be corrected. These values are utilized to cal-culate a series of constants which are stored in -the correc-tor 20 for subsequent utilization in making correction cal-culations. sefore the operation of the corrector 20 is described in further detail, at this point a description of -the mathematical basis for its operation is in order.
An examination of the compressibility tables for any gas within the range for which the corrector apparatus 20 - is designed for use, will provide the supercompressibility factor which is proportional to pressure divided by tempera-ture. It can be assumed that the following relationship nolds:
P
Fpv ~ 1 = f . (3) QTf i,!35~ ~
.~ ~
Then, Q = Pf . (4) ~Fpv ~ l)TE
Examining a table of values of Q indicates that in the ran~e of temperatures being considered, i.e. Tf = 520 + 80, a linear fit of Q as a function of Tf is possible. In fact, two fits are actually required, one for Tf below a ~iven value and one for Tf above that given value. Therefore, let:
Q = S + CTf . (5) In addition, C and S can be expressed as linear equations which are functions of the pressure Pf. Then, a form as shown below can be derived:
S = Ki+1 + ICi f (6) and C = Ki+3 + Ki-~2 ----lS where i = 1 when Tf is less than a given value and i = 5 when Ifis greater than or equal that given value.
Thus, based upon customer supplied data, the K constants are calculated. These constants Kl - K8 are stored within the corrector 20 on a diode matrix card 50 as shown in FIG.
3. Additionally, a constant Kg which equals 256 (utilized in e~uations (6) and (7) is stored on the card 50. The card S0 stores these values in binary coded decimal (sCD) and when voltages are applied to the appropriate leads 52, the leads - 54 are selectively energized in a manner well known in the art. Addi-tionally, i}le matrix card 50 stores the base pres-sure factor B which e~uals the atmospheric pressure divided 5~1 l~) by the base p,ressure, the maximum gage pressure for which readings are accurate, the range factor R of the pressure transducer 28 which equals the maximum gage pressure divided by the base pressure, the counter multiplier and -the base tem~erature Tb. These values are stored on the diode matrix card 50 by selectively connecting diodes be-tween the leads 52 and the leads 54, as is well known in the art, in a BCD
format. Alterna-tively, -the diode matrix card 50 may be replaced by a programmable ROM.
The mathematics utilized in calculating the supercompres-sibility factor and, accordingly, the corrected volume, utll-izing the measured pressure and temperature and the constants stored on the diode matrix card 50, in response to an input meter pulse, will now be described. Utilizing the stored constant values and the measured pressure and temperature, -the following calculations are performed:
Xl = RP t8) X 1000 Tb (9) - Tf X3 = Xl + B (10) X4 = X2X3 (11) where:
R is the range factor of the pressure transducer 28, which is stored on the diode matrix card 50 P is the measured pressure and varies from 0 to 1000 as a linear proportion of the range of the pressure trans-ducer 28 :~1. ~ t~:1 Tb is the base -temperature in degrees Rankine, and is stored on the diode matrix card 50 TE is -the Elowing temperature in degrees Rankine and equals the tempe.rature measured by -the temperature -transducer 26 (in degrees Fahrenheit) plus 460 B is the base factor and equals the atmos-pheric pressure divided by the base pressure, this cons-tant being stored on the diode matrix card 50.
Next, S and C are calculated from equations (6) and (7), utilizing the constants stored on the diode matrix card 50 (depending upon the measured temperature) and the measured pressure. Utilizing the calculated values of S and C, and the measured temperature and pressure, the following equa-tions (12~ - (16) are utilized to calculate -the supercom-pressibility factor Fpv.
CT
l ~ (12) . C2 =Cl + S (13) C3 = TfC2 (14) :
~: C = loooop ( 15) : C3 FpV = lO000 + C~ (16) where Pg is the gage pressure and equals the measured pres-25 sure P times the maximum gage pressure.
l l t '`~
The followincJ e-luations (17) and (18) are then utilized to calculate the corrected volume Vc:
Fz = _ _v)_ (17) Vc -4 Z ' (18) To increment the counter 32, the following equation (19) is utilized -to get a corrected count Vc, where M is the counter multiplier stored on the diode matrix card 50:
Vc c . (19) In the volume corrector apparatus 20, -the forego.incJ calcula-tiolls are performed each -time a pulse is received from the meter 22. These calculatiolls are perormed util:izing integ~r arithmetic to avoid the cost of floatincJ point arithmetic.
It has been determined that -the accuracy of the above calcu-lations is to within + 0.1~.
Referring now to FIG. 4, shown therein is an overall block diagram of volume corrector apparatus operating with accordance with the present invention, as described above.
All the functions of the volume corrector apparatus shown in FIG. 4 are controlled by a microprocessor 100, illustratively a type 1802 microprocessor manufactured by RCA Corporation.
The corrector apparatus is battery powered, by battery 102, and in order to reduce quiescent battery drain, the tempera-ture transducer 26 and the pressure transducer 28 are only energized through the power switch 103 when the microproces-sor 100 requires inputs therefrom. An illustrative arrange-ment for reducing quiescent battery drain is disclosed in U.S. Patent No. 4,0,6,717, and the reader is referred thereto ~ i;3~ 3 _~
if f~rther cletails are clesired. Whellever there is a siynal at the ou-tpu-t of the latch 104, through the control switch 106 to the microprocessor 100, the microprocessor 100 will start its internal program. An output Erom the latch 10 will occur ln response to either a request from the test unit 34 or a meter input switch pulse over the lead 108.
The meter input switch pulse is generated in response to rotation of the ou-tput recJister drive shaft oE the meter 22.
Illustratively, that shaft has mounted t'nereon a small per-manent magnet. A switching device located in close proximityto the magnet will provide two pulses over the lead 110 for every complete rotation of the output register drive shaft.
Each rotation of the output register drive shaft will also mecnanically increment the uncorrected counter 30, in a man-ner well known in the art. The pulses over the lead 110 pass through a Schmi-tt trigger circuit 112 which ~unctions as a squaring and debounce circuit, and then passes to the divide-by-two or divide-by-twen-ty circult 114, so that only every other or every twen-tie-th pulse will -trigger the one shot circui-t 116 -to se-t the l.atch 104. The reason that a divide-by-twenty opera-tion would be required is that if a large capacity meter with a ten foot drive is utilized, it is desirable -to reduce the number of input pulses to the corrector apparatus in order to conserve the batteries.
The latch 104 is also set by depression of any of the but-tons 42, 44 or 46 when the test unit 34 is connected to the corrector 20.
The microprocessor 100 is controlled by a fixed program contained in the ROM 120. The RAM 122 is used for the temp-orary storage of variables and calculations. Whenever thereis a signal at the output of the. latch 104, the microproces-sor 100 will start its program. An input meter pulse always has top priority and is always serviced regardless of inform-ation being requested by the test unit 34. The data bus 124 is a bidirectional signal highway from the ROM 120, the RAM
122, the output por-t 130 and the input port 123, to the micro-processor 100. The port select circuit 126 receives an out-put from the microprocessor 100 and direc-ts signals to the input port 128 or the outpu-t port 130. When the inpu-t port 128 is selected, the data from the tempera-ture -transducer 26, the pressure transducer 28 and the diode matrix 50 i5 Illade available -ta the microprocessor 100 via the analog-to-digi-tal conver-ter 132. The output port 130 directs data to the test unit display 38, the corrected counter 32, and strobes the analog-to-digital converter 132 to convert the information on pressure and temperaturej as will be described. The pressure transducer 28, through the instrument amplifier 134, or the temperature transducer 26, are coupled to the analog-to-digital converter 132 through the multiplexer 136. The multi-plexer 136 outputs either -temperature or pressure analog information to the analog-to-digital converter 132 which be-gins conversion upon receiving a star-t conversion signal from ou-tput port 130. The ou-tput :Erom the analog-to-digital converter 132 is in sequential ~CD, as con-trolled by the strobing :Erom the output po~t 130 upon receiving a conver-sion complete signal from converter 132.
The "signature" of the corrector apparatus is the cor-. rection factor obtainecl by using 50.5~ of the full scale value of maximum gage pressure, a temperature of 505R, and all the values supplied by the customer and converted into the cons-tants on -the diode matrix card 50. This signa-ture is calculated and displayed on the display 38 when the test unit 34 is connected to the corrector 20 and -the button 46 is depressed. If either the button 42 or the button 44 is depressed, this will cause the microprocessor 100 to be held in either the pressure or temperature mode and display on the display 38 updated information as to the pressure and temperature for as long as either of the buttons 42 or 44 is depressed, unless a meter input pulse occurs. In the event that either the pressure or temperature is outside the i'3~
operating limits set by the program in ROM 120, the limit de-tect and hold circuit 140 will be set which will cause the display 38 to display colons. If the cancel limit button 48 is depressed, this will reset -the limit detect and hold cir-cuit 140, cancelling the display of colons. However, shouldthe over ran~e condition still exis-t, the limit detect and hold circuit 140 will be reset immediately upon release of the cancel limi-t bu-tton 48 and the display of colons will return. Depressing but-tons 46 and 48 simultaneously simu-lates a meter input pulse. The correction factor is displayedon the tes-t unit display 38 but an output to the corrected counter 32 is inhibited.
FIG~ 5 is a flow diagram illustrating the overall opera-tion of the system described above. This operation is con-trolled by the microprocessor 100 operatin~ in accordance with a program s-tored in ROM 120. AS shown in F~G. 5, when power is first applied to the corrector apparatus, an initiclL-ization rou-tine is performed. The microprocessor 100 tllen goes into its ~START (warm start) state where it awaits a 20 signal ~rom the control swi-tch 106 that the latch 10~ has been set. When such a signal is recognized the battery con-dition is checked. If the battery condition is okay then -the program continues. If the battery condition is low then the program returns to WSTART and no calculations are performed.
As described above, -the first priority is an input meter pulse. In the event that the latch 104 was set in response to an input meter pulse, the microprocessor 100 must then collect all the data it requires for a correction calculation.
This data is from the temperature transducer 26, the pressure transducer 28 and the constants stored on the diode matrix card 50. This data, which i~ in Binary Coded Decimal form, is converted to hexadecimal form for calculation purposes.
This data is stored in the RAM 122.
5ti~
The correction calculations are nex-t performed. First, the PTCALC subroutine shown in EIG. 6 is performed. In that subroutine, blocks 202, 204 and 206 calculate Xl utilizing equation (8). Blocks 208 and 210 calculate X3 utilizing equation (10~. Blocks 212, 214 and 216 calculate X2 utiliz-ing equa-tion (9). Finally, blocks 218 and 220 calculate X4 utilizing equation (11). The results o:E -this calculation are then stored for later use, as shown by block 222. The program then returns to the main program where the nex-t s-tep is to do the supercompressibility calculation utilizing the FPVCLC-subroutine shown in FIG. 7. In this subroutine, it is first determined whether the measured temperature is less than or greate.r than a given value so that the proper value of i is utilized for equations (6) and (7). First, the CPGAG~ subroutine as shown in FIG. 8 is u-tilized -to calcu-late the gage pressure. Next, -the TYPCLC subrout:Lne is utilized -to calcula-te S, according to equation (6), clS 9hOWn in FIG. 9. Then, a~ain utiliæing the T~PCLC subroutine, C
is calculated ~ltilizin~ eq~lation (7)~ Nex-k, as shown in 20 block 224, Cl is calculated u-tiliæing equa-tion (12). Then, as shown in block 226, C2 and C3 are calculated utilizing equations (13) and (14). Utilizing equation (15), C4 is calculated as shown in block 228. Then, u-tilizing equation (16), Fpv is calculated as shown in block 230. Fz is then 25 calculated utilizing equation (17), as shown in block 232.
~Finally, as shown in block 234, the corrected volume is cal-culated utilizing equation (18). Control is then returned to the main program.
After the corrected volume has been calculated, the COUNT subroutine (FIG. 10) is called to update the corrected counter 32. As shown in FIG. 10, tne corrected volume which was calculated is added to a remainder value from a previous calculation. This sum is then divided by the counter multi-plier which results in an integral number of counts plus a new remainder, both of which are stored in the RAM 122. The i';3'-iti~
integral number of counts is then u-tilized to increment the corrected counter 32. Control is then returned to the main program which remains in the WSTART state awaiting another input pulse from the controL switch 106.
In the event that the latch 104 is set in response to an input Erom the tes-t unit 34, and not as a result of a meter input pulsel -the microprocessor 100 checks -to see whe-ther the pressure button 42, the tempera-ture button 44, or the system test button 46 was depressed, as shown in FIG. 5.
FIG. ll illustrates the subroutines for responding to depression of the buttons 42, 44 and 46. In -the event the pressure button 42 is depressed, the TPR~SS subroutine is performed First, the appropriate data is retrieved from the pressure transducer 28 and the diode matrix card 50 and converted -to hexadecimal. The pressure data is then examined to see if it is within the appropriate limi-ts. IE so, the CPGAGE subroutine (FIG. 8) is called to calculate the c3a~e pressure. The calculated ~age pressure in hexadecimal is then converted to binary coded decimal and displayed on the display 38 of the te~-t uni-t 34. This is used for calibration and check purposes. The program then returns to -the WSTART
state.
In the event that the temperature button 42 is depressed, the TTEMP subroutine (FIG. ll) is performed. First, the temperature data from tiie temperature transducer 26 is obtained, converted -to hexadecimal, and checked to see whe-ther it is within prescribed limits. Next, the temperature is conver-ted to degrees Fahrenheit and then converted to Binary Coded Decimal, in which form it is displayed on -the display 38. This is used for calibration and check purposes.
The program then returns to the WSTART state.
In -the event that the system test button 46 was depressed, the program causes the TTEST subroutine (FIG. ll) to be performed. First, data is retrieved from the diode matrix card 50 and in place of temperature and pressure 3~
readings, the Eixed constant 0505 is placed on data bus 124 via input port 123. Next, the calculations set forth in the calculation block of FIG. 5 are performed. This should result in a particular "signature" for -the volume corrector apparatus. This signa-ture is converted to Binary Coded Decimal and displayed on the display 33. The program then returns -to -the WSTART s-ta-te.
In -the event -tha-t bo-th the system test bu-tton 46 and the cancel limit button 4~ are depressed simultaneously, the pro-gram causes the TTEST. subroutine ~FIG. 11) to be executed.However, detection of simultaneous button pushes causes the program to read the pressure 28 and temperature 26 trans-duce`rs instead of presenting the fixed number 0505 to the in-put port 123, and the resulting calculation proceeds accord-ing to the calculation block of FIG. 5.
All of the calculations which have been described are performed utilizing integer arithmetic, rather than float-ing point arithmetic. Rccordingly, a large amoul~t of memory in tl~e RO~l 120 i.s saved, resulting in a cost saving. In integer arithmetic, 3 ' 2 = 1 (the 0.5 is lost). However, if somewhexe in -the procedure there is a multiplication by 10, one may say instead that 30 T 2 - 15. Accordingly, in the calculations described above, there are many multiplica-tions and divisions by powers of 10. ~owever, the overall truncation errors are not severe and the calculations are within + 0.1~ up -to 1000 psi for all Tf. From 1000 to 1500 psi and flowing temperatures above 0F the calculations are with +0.1~. All accuracies are over an ambient temperature range of -40F to +140F.
Accordingly, there has been disclosed a method and appa-ratus for correcting a measurea unit volume of flowing gas - to a base volume at given base conditions of base pressure and base temperature. It is understood that the above-described embodiment is merely illustrative of the applica-tion of the principles of this invention. Numerous other ~;,t~
embocliments may be devised by those skillecl in the art with-out depar-ting from the spirit and scope of -this inven-tion as defined by the appended claims.
.
DESCRIPTION
APPARATUS FOR C~RRECTING MEASURED GAS FLOW
BACKGROUND OF THE INVENTION
_ This invention relates to gas flow measurements and, more particularly, to the correction oE a measured unit volume of gas .flowing through a conduit -to a base volume S at given base conditions of base pressure and base tempera-ture.
Gas is a compressible item, the volume of which changes as a function of temperature and pressure, in accordance with well known physi.cal laws. Because gas is a compressible com-modity, the buyer and seller of this commodity must agreeupon the same conditions. Thus, to distribute and sell gas that is exposed to varying conditions of temperature and pressure, calculations must be made -to convert the measured gas flow volume Vf in terms of cubic feet at varying condi-tions of temperature Tf and pressure Pf, to a standard cubicfeet volume Vb at specified, previously agreed upon base temperature Tb and base pressure Pb.
:I ~ t;~3~t;-l The bas.ic gas law cqua tiOII of S tate is PV = WRTZ (1) where:
P is pressure V is volume W is mass R is gas constan-t T is tempera-ture Z is compressibility.
When dealing with a simple gas, such as N2 or 2' the classic gas laws serve very well, and Z may not be needed. However, when there are mixtures of gases and complex hydrocarbons, it has been found that Boyle's and Charles' laws are in error. Fuel gases -tend to be easier to compress, up to around 2000 psig, -than these laws would sugges-t. Ahove this pressure, the trend is reversed. The exact values are unc-tions of the pressure, temperatuxe and the gas composition.
The diffexence between the classic gas laws and the complex gas compression i.s called compressibili-ty, or Z.
From equation (l), the following relationship between base and flowing conditions may be derived:
Vb = Vf f Pa b pv (2) b Tf where: Vb is base volume : Vf is the measured uncorrected volume Pf is the flowing gas gage pressure Pa is atmospheric pressure Pb is base pressure T~ is base temperature in degrees Rankine Tf is the temperature of the flowing gas in R
Fpv is the supercompressibility factor which is equal to ¦~ base '.
J~ flowing l .ll ti~5tj.~
The cti~icult part of ca:Lculatillg base volume in accordance with equation ~2) is to determine the supercompressibility factor which is a function of the flowing temperatwre and pressure as well as the speciEic gravity and the composi--tion of the gas being measured. One way oE determining the supercompressibility fac-tor is to utilize tables such as those set Eorth in -the "Manual for the Determination of Supercompressibility Factors for Natura:L Gas", PAR Research Projects NX-19, published by the American Gas ~ssociation.
~owever, if i-t is desired to automate the correction of measured gas flow, it is difficult and expensive to utilize tables. Alternatively, it is possible to utilize a series of equations to calculate the supercompressibility factor.
U.S. Patent No. 4,173,891 discloses such an automated sys-tem including a microprocessor for repetitively calculating-the supercompressibili-ty Eactor. The method employed by the patented system includes a plurali-ty of compu-ting steps Eor each calculation of the base na-tural gas flow. Duriny each computing step, an initially appro~imated value oE the super-compressibili-ty factor or -the previously calculated value is used to calculate an indication of the base natural gas Elow, each computing step beiny insufficient -to recalculate -the supercompressibilit~ factor, this calculation taking a plu-rality of steps. Therefore, the disclosed system has the disadvan-tage that a relatively large amoun-t of time is required each time the supercompressibility factor is to be calculated. In fact, it requires five input meter pulses for a complete calculation to be performed. Another dis-advantage of the system disclosed in this patent is that the calculations are performed utilizing floating point arithmetic, which requires a larye amount of memory capacity, increasing the cost of the system hardware.
It is therefore an object of this invention to provide apparatus for measuring gas flow.
;4~
I-t is a .Eur-ther object oE this invention to provide such a~paratus which automatically corrects the measured gas flow to predetermined base conditions of temperature and pressure.
It is another objec-t of -this inven-tion to provide such apparatus wherein the corrected values`are e:Eficiently calcu-lated.
I-t is yet another object of this invention to provide such appara-tus wherein it is .relatively easy to make aclapta-tions for different base conditions and gas composition.
lQ It is still another object of this invention to provide such apparatus which can be utilized at remote meter locations without the necessity for connection to an external source of power.
SUM~5ARY OF T~E~ INVENTION
The foregoing and additional objects are attained in accordance with the principles oE this invention by providing apparatus for correcting a measured unit volume of gas flow-ing through a conduit -to a base volume at given base concli-tions oE base pressure and base temperature. The apparatus includes tempera-ture and pressure transducers which provide signals corresponding to their measurements of the -tempera-ture and pressure, respectively, of the flowing gas. A meter connected in -tlle condui-t measures the uncorrec-ted volume of the flowing gas and provides -to the appara-tus a volume pulse in response to measuring a unit volume of the gas. A set oE
constants derived from customer supplied data as to base con-ditions and gas content are stored in the apparatus on a diode matrix card. In response to the occurrence of a volume pulse, the stored constants and the measured temperature and pressure values are utilized for performing a series of cal-culations to derive the supercompressibility factor and in turn a correc-ted volume. All calculations are performed utilizing integer arithmetic, rather than floating point arithmetic, in order to efficiently utilize memory and achieve a cost savillg. The outpu-t of the apparatus is a first counter which indicates the uncorrected volume and a second counter which indicates the corrected volume.
In accordance with an aspect oE this invention, a -test unit is provided whicll may be plugged into the apparatus and is powered thereby. This test uni-t does not interfere with the operation of the apparatus or the meter. The test unit can be activated to display flowing pressure and temperature, to cancel out of limit indications, to verify system opera-tion and also may be utilized to test the apparatus counter.
DESCRIPTION OF THE DRAWINGS
The foregoing will be more readily apparent upon readingthe following description in conjunction with the drawings wherein:
FIG. 1 illustrates the moun-ting of volume corrector apparatus constructed in accordance with the principles of this invention and its relationsh.ip -to a meter connected in a conduit;
FIG. 2 illustrates a -test unit, constructed in accord-ance with -the principles of this invention, which may be plugged into the volume corrector apparatus shown in FIG. l;
FIG. 3 illustrates a diode matrix board which forms a part of the volume corrector apparatus and is used for stor-ing constants derived from customer supplied data;
FIG. 4 is a block diagram of the illustrative volume corrector apparatus and test unit of FIGS. 1, 2 and 3;
FIG. 5 is a flow diagram illustrating the overall sys-tem operation of the volume corrector apparatus constructed in accordance with the principles of this invention; and FIGS. 6 through 11 are flow diagrams of subroutines which form a part of the system operation shown in FIG. 5.
DL`rL'~IL~D DESCRIPTION
Referring now to the drawings, wherein like elemen-ts in different figures thereo~ have tlle same reference character applied -thereto, FIG. 1 illustrates volume corrector appara-tus, designated generally by the reference character 20,mounted on a me-ter 22 connected in a conduit 24 through which yas flows. The meter 22 does not :Eorm a part of the present invention and may be any -type of meter so long as it satisfies the requirement that the corrector 20 needs a low speed input derived from the output register drive shaft of the meter 22.
Alternatively, the corrector 20 may be mounted remotely from the meter 22 and in this case, the input to the corrector 20 will be an electrical switch closure derived from the output register drive shaft of the meter 22, in a manner well known lS in the art. The corrector 20 also derives input signals from a temperature -transducer 26 and a pressure transducer 28 which e~tend into the conduit 24. The temperature transducer 26 is illustratively a model ~C2626~ tempera-ture transducer manufactured by ~nalog Devices and is an integrated circuit housed in a stainless steel tubular probe which produces an output current linearly proportional to absolute temperature.
The pressure transducer 28 is illustra-tively a model ITQH-24 pressure transducer manufactured by Kulite Semiconductor Products and includes a solid state sensing element which is a monolithic integrated circuit Wheatstone bridge directly formed on a silicon diaphragm, and is available in different ranges, depending upon the desired application. The output of the pressure transducer 28 is a voltage which is related, over the range, to the pressure of the gas flowing through the conduit 24.
Since the corrector apparatus 20 is designed for use at - remote locations, such as in a desert area, where commercially available power may not be available, the apparatus 20 is designed to be battery operated. Further, a solar battery charger 27 may be provided mounted above the apparatus 20.
5~
, If the enclosed corrector apparatus 20 were to be exposed to direct sw~ ht, its interior temperature would rise to an unacceptable level. There~ore, a sunshade 29 is also pro-vided -to shield the apparatus 20 from the direct rays of the sun.
The corrector apparatus 20 has as i-ts output two count-ers. ~ first counter 30 is a mechanical coun-ter which dis-plays the uncorrected volume. The counter 30 is incremented by rotation of -the output register drive shaft of the meter 22. If the corrector 20 is not mounted on the meter 22, the uncorrected counter 30 is replaced by the original meter register. The second counter 32 is the corrected counter and is an electromechanical or electronic counter which dis-plays the corrected volume. It is incremen-ted by signals genera-ted within the corrector 20 in response to inp~ts from the meter 22 and calculations based UpOIl measured temp~rature and pressure, in a manner to be described in detail herein-after. The corrector apparatus also includes a low battery indica-tor 33.
FIG. 2 illustrates a test unit, denoted generally by the reference numeral 34, which is a portable instrument used in the shop and field to check the operation of the corrector 20. The test unit 34 includes a cable and connector assembly 36 which plugs into a suitable receptacle, not shown, in the corrector 20. Power for the test unit 34 is obtained from the corrector 20. The test unit 34 includes a numerical dis-play 38 and a plurality of test buttons 40, 42, 44, 46 and 48. When the test unit 34 is coupled to the corrector 20 via connector assembly 36, -the counter 32 may be checked by depressing the button 40. When the button 40 is depressed, the counter 32 is advanced one count. The flowing pressure may be read directly on the display 38 by depressing the but-ton 42. The flowing temperature may be read directly in C or F on the display 38 by depressing the button 44. When the button 46 is depressed, the display 38 will display a l,~.tit~
number which has been detersnined to be the "si~nature" of the corrector 20 when it is operating correctly. If the display 3~ displayed colons along with numbers when any of tlle buttons ~2, 44 or 46 was depressed, -th:Ls indicates that some time after the last check was made either the pressure or temperature was out of specified limits. The display of colons will not indicate wnich parameter was out of limit or if the high or low limi-t was exceeded. Depressing the button 48 will remove the colons from the display 38 and reset the corrector 20. When the but-tons 46 and 43 are depressed simultaneously, the display 38 will display a num-ber indicating the correction multiplier for the presently flowing conditions of pressure and temperature.
When a cus-tomer places an order for a correc-tor 20 to be used at a particular location, -the customer also speci-fies certain condi-tions at that location. Tlle customer must specify the type of flowing gas which is to be measured, its composition, -the range of pressures at which the gac; will Elow, and the base tempera-ture and press~lre -to wllich the fl~w volume is to be corrected. These values are utilized to cal-culate a series of constants which are stored in -the correc-tor 20 for subsequent utilization in making correction cal-culations. sefore the operation of the corrector 20 is described in further detail, at this point a description of -the mathematical basis for its operation is in order.
An examination of the compressibility tables for any gas within the range for which the corrector apparatus 20 - is designed for use, will provide the supercompressibility factor which is proportional to pressure divided by tempera-ture. It can be assumed that the following relationship nolds:
P
Fpv ~ 1 = f . (3) QTf i,!35~ ~
.~ ~
Then, Q = Pf . (4) ~Fpv ~ l)TE
Examining a table of values of Q indicates that in the ran~e of temperatures being considered, i.e. Tf = 520 + 80, a linear fit of Q as a function of Tf is possible. In fact, two fits are actually required, one for Tf below a ~iven value and one for Tf above that given value. Therefore, let:
Q = S + CTf . (5) In addition, C and S can be expressed as linear equations which are functions of the pressure Pf. Then, a form as shown below can be derived:
S = Ki+1 + ICi f (6) and C = Ki+3 + Ki-~2 ----lS where i = 1 when Tf is less than a given value and i = 5 when Ifis greater than or equal that given value.
Thus, based upon customer supplied data, the K constants are calculated. These constants Kl - K8 are stored within the corrector 20 on a diode matrix card 50 as shown in FIG.
3. Additionally, a constant Kg which equals 256 (utilized in e~uations (6) and (7) is stored on the card 50. The card S0 stores these values in binary coded decimal (sCD) and when voltages are applied to the appropriate leads 52, the leads - 54 are selectively energized in a manner well known in the art. Addi-tionally, i}le matrix card 50 stores the base pres-sure factor B which e~uals the atmospheric pressure divided 5~1 l~) by the base p,ressure, the maximum gage pressure for which readings are accurate, the range factor R of the pressure transducer 28 which equals the maximum gage pressure divided by the base pressure, the counter multiplier and -the base tem~erature Tb. These values are stored on the diode matrix card 50 by selectively connecting diodes be-tween the leads 52 and the leads 54, as is well known in the art, in a BCD
format. Alterna-tively, -the diode matrix card 50 may be replaced by a programmable ROM.
The mathematics utilized in calculating the supercompres-sibility factor and, accordingly, the corrected volume, utll-izing the measured pressure and temperature and the constants stored on the diode matrix card 50, in response to an input meter pulse, will now be described. Utilizing the stored constant values and the measured pressure and temperature, -the following calculations are performed:
Xl = RP t8) X 1000 Tb (9) - Tf X3 = Xl + B (10) X4 = X2X3 (11) where:
R is the range factor of the pressure transducer 28, which is stored on the diode matrix card 50 P is the measured pressure and varies from 0 to 1000 as a linear proportion of the range of the pressure trans-ducer 28 :~1. ~ t~:1 Tb is the base -temperature in degrees Rankine, and is stored on the diode matrix card 50 TE is -the Elowing temperature in degrees Rankine and equals the tempe.rature measured by -the temperature -transducer 26 (in degrees Fahrenheit) plus 460 B is the base factor and equals the atmos-pheric pressure divided by the base pressure, this cons-tant being stored on the diode matrix card 50.
Next, S and C are calculated from equations (6) and (7), utilizing the constants stored on the diode matrix card 50 (depending upon the measured temperature) and the measured pressure. Utilizing the calculated values of S and C, and the measured temperature and pressure, the following equa-tions (12~ - (16) are utilized to calculate -the supercom-pressibility factor Fpv.
CT
l ~ (12) . C2 =Cl + S (13) C3 = TfC2 (14) :
~: C = loooop ( 15) : C3 FpV = lO000 + C~ (16) where Pg is the gage pressure and equals the measured pres-25 sure P times the maximum gage pressure.
l l t '`~
The followincJ e-luations (17) and (18) are then utilized to calculate the corrected volume Vc:
Fz = _ _v)_ (17) Vc -4 Z ' (18) To increment the counter 32, the following equation (19) is utilized -to get a corrected count Vc, where M is the counter multiplier stored on the diode matrix card 50:
Vc c . (19) In the volume corrector apparatus 20, -the forego.incJ calcula-tiolls are performed each -time a pulse is received from the meter 22. These calculatiolls are perormed util:izing integ~r arithmetic to avoid the cost of floatincJ point arithmetic.
It has been determined that -the accuracy of the above calcu-lations is to within + 0.1~.
Referring now to FIG. 4, shown therein is an overall block diagram of volume corrector apparatus operating with accordance with the present invention, as described above.
All the functions of the volume corrector apparatus shown in FIG. 4 are controlled by a microprocessor 100, illustratively a type 1802 microprocessor manufactured by RCA Corporation.
The corrector apparatus is battery powered, by battery 102, and in order to reduce quiescent battery drain, the tempera-ture transducer 26 and the pressure transducer 28 are only energized through the power switch 103 when the microproces-sor 100 requires inputs therefrom. An illustrative arrange-ment for reducing quiescent battery drain is disclosed in U.S. Patent No. 4,0,6,717, and the reader is referred thereto ~ i;3~ 3 _~
if f~rther cletails are clesired. Whellever there is a siynal at the ou-tpu-t of the latch 104, through the control switch 106 to the microprocessor 100, the microprocessor 100 will start its internal program. An output Erom the latch 10 will occur ln response to either a request from the test unit 34 or a meter input switch pulse over the lead 108.
The meter input switch pulse is generated in response to rotation of the ou-tput recJister drive shaft oE the meter 22.
Illustratively, that shaft has mounted t'nereon a small per-manent magnet. A switching device located in close proximityto the magnet will provide two pulses over the lead 110 for every complete rotation of the output register drive shaft.
Each rotation of the output register drive shaft will also mecnanically increment the uncorrected counter 30, in a man-ner well known in the art. The pulses over the lead 110 pass through a Schmi-tt trigger circuit 112 which ~unctions as a squaring and debounce circuit, and then passes to the divide-by-two or divide-by-twen-ty circult 114, so that only every other or every twen-tie-th pulse will -trigger the one shot circui-t 116 -to se-t the l.atch 104. The reason that a divide-by-twenty opera-tion would be required is that if a large capacity meter with a ten foot drive is utilized, it is desirable -to reduce the number of input pulses to the corrector apparatus in order to conserve the batteries.
The latch 104 is also set by depression of any of the but-tons 42, 44 or 46 when the test unit 34 is connected to the corrector 20.
The microprocessor 100 is controlled by a fixed program contained in the ROM 120. The RAM 122 is used for the temp-orary storage of variables and calculations. Whenever thereis a signal at the output of the. latch 104, the microproces-sor 100 will start its program. An input meter pulse always has top priority and is always serviced regardless of inform-ation being requested by the test unit 34. The data bus 124 is a bidirectional signal highway from the ROM 120, the RAM
122, the output por-t 130 and the input port 123, to the micro-processor 100. The port select circuit 126 receives an out-put from the microprocessor 100 and direc-ts signals to the input port 128 or the outpu-t port 130. When the inpu-t port 128 is selected, the data from the tempera-ture -transducer 26, the pressure transducer 28 and the diode matrix 50 i5 Illade available -ta the microprocessor 100 via the analog-to-digi-tal conver-ter 132. The output port 130 directs data to the test unit display 38, the corrected counter 32, and strobes the analog-to-digital converter 132 to convert the information on pressure and temperaturej as will be described. The pressure transducer 28, through the instrument amplifier 134, or the temperature transducer 26, are coupled to the analog-to-digital converter 132 through the multiplexer 136. The multi-plexer 136 outputs either -temperature or pressure analog information to the analog-to-digital converter 132 which be-gins conversion upon receiving a star-t conversion signal from ou-tput port 130. The ou-tput :Erom the analog-to-digital converter 132 is in sequential ~CD, as con-trolled by the strobing :Erom the output po~t 130 upon receiving a conver-sion complete signal from converter 132.
The "signature" of the corrector apparatus is the cor-. rection factor obtainecl by using 50.5~ of the full scale value of maximum gage pressure, a temperature of 505R, and all the values supplied by the customer and converted into the cons-tants on -the diode matrix card 50. This signa-ture is calculated and displayed on the display 38 when the test unit 34 is connected to the corrector 20 and -the button 46 is depressed. If either the button 42 or the button 44 is depressed, this will cause the microprocessor 100 to be held in either the pressure or temperature mode and display on the display 38 updated information as to the pressure and temperature for as long as either of the buttons 42 or 44 is depressed, unless a meter input pulse occurs. In the event that either the pressure or temperature is outside the i'3~
operating limits set by the program in ROM 120, the limit de-tect and hold circuit 140 will be set which will cause the display 38 to display colons. If the cancel limit button 48 is depressed, this will reset -the limit detect and hold cir-cuit 140, cancelling the display of colons. However, shouldthe over ran~e condition still exis-t, the limit detect and hold circuit 140 will be reset immediately upon release of the cancel limi-t bu-tton 48 and the display of colons will return. Depressing but-tons 46 and 48 simultaneously simu-lates a meter input pulse. The correction factor is displayedon the tes-t unit display 38 but an output to the corrected counter 32 is inhibited.
FIG~ 5 is a flow diagram illustrating the overall opera-tion of the system described above. This operation is con-trolled by the microprocessor 100 operatin~ in accordance with a program s-tored in ROM 120. AS shown in F~G. 5, when power is first applied to the corrector apparatus, an initiclL-ization rou-tine is performed. The microprocessor 100 tllen goes into its ~START (warm start) state where it awaits a 20 signal ~rom the control swi-tch 106 that the latch 10~ has been set. When such a signal is recognized the battery con-dition is checked. If the battery condition is okay then -the program continues. If the battery condition is low then the program returns to WSTART and no calculations are performed.
As described above, -the first priority is an input meter pulse. In the event that the latch 104 was set in response to an input meter pulse, the microprocessor 100 must then collect all the data it requires for a correction calculation.
This data is from the temperature transducer 26, the pressure transducer 28 and the constants stored on the diode matrix card 50. This data, which i~ in Binary Coded Decimal form, is converted to hexadecimal form for calculation purposes.
This data is stored in the RAM 122.
5ti~
The correction calculations are nex-t performed. First, the PTCALC subroutine shown in EIG. 6 is performed. In that subroutine, blocks 202, 204 and 206 calculate Xl utilizing equation (8). Blocks 208 and 210 calculate X3 utilizing equation (10~. Blocks 212, 214 and 216 calculate X2 utiliz-ing equa-tion (9). Finally, blocks 218 and 220 calculate X4 utilizing equation (11). The results o:E -this calculation are then stored for later use, as shown by block 222. The program then returns to the main program where the nex-t s-tep is to do the supercompressibility calculation utilizing the FPVCLC-subroutine shown in FIG. 7. In this subroutine, it is first determined whether the measured temperature is less than or greate.r than a given value so that the proper value of i is utilized for equations (6) and (7). First, the CPGAG~ subroutine as shown in FIG. 8 is u-tilized -to calcu-late the gage pressure. Next, -the TYPCLC subrout:Lne is utilized -to calcula-te S, according to equation (6), clS 9hOWn in FIG. 9. Then, a~ain utiliæing the T~PCLC subroutine, C
is calculated ~ltilizin~ eq~lation (7)~ Nex-k, as shown in 20 block 224, Cl is calculated u-tiliæing equa-tion (12). Then, as shown in block 226, C2 and C3 are calculated utilizing equations (13) and (14). Utilizing equation (15), C4 is calculated as shown in block 228. Then, u-tilizing equation (16), Fpv is calculated as shown in block 230. Fz is then 25 calculated utilizing equation (17), as shown in block 232.
~Finally, as shown in block 234, the corrected volume is cal-culated utilizing equation (18). Control is then returned to the main program.
After the corrected volume has been calculated, the COUNT subroutine (FIG. 10) is called to update the corrected counter 32. As shown in FIG. 10, tne corrected volume which was calculated is added to a remainder value from a previous calculation. This sum is then divided by the counter multi-plier which results in an integral number of counts plus a new remainder, both of which are stored in the RAM 122. The i';3'-iti~
integral number of counts is then u-tilized to increment the corrected counter 32. Control is then returned to the main program which remains in the WSTART state awaiting another input pulse from the controL switch 106.
In the event that the latch 104 is set in response to an input Erom the tes-t unit 34, and not as a result of a meter input pulsel -the microprocessor 100 checks -to see whe-ther the pressure button 42, the tempera-ture button 44, or the system test button 46 was depressed, as shown in FIG. 5.
FIG. ll illustrates the subroutines for responding to depression of the buttons 42, 44 and 46. In -the event the pressure button 42 is depressed, the TPR~SS subroutine is performed First, the appropriate data is retrieved from the pressure transducer 28 and the diode matrix card 50 and converted -to hexadecimal. The pressure data is then examined to see if it is within the appropriate limi-ts. IE so, the CPGAGE subroutine (FIG. 8) is called to calculate the c3a~e pressure. The calculated ~age pressure in hexadecimal is then converted to binary coded decimal and displayed on the display 38 of the te~-t uni-t 34. This is used for calibration and check purposes. The program then returns to -the WSTART
state.
In the event that the temperature button 42 is depressed, the TTEMP subroutine (FIG. ll) is performed. First, the temperature data from tiie temperature transducer 26 is obtained, converted -to hexadecimal, and checked to see whe-ther it is within prescribed limits. Next, the temperature is conver-ted to degrees Fahrenheit and then converted to Binary Coded Decimal, in which form it is displayed on -the display 38. This is used for calibration and check purposes.
The program then returns to the WSTART state.
In -the event that the system test button 46 was depressed, the program causes the TTEST subroutine (FIG. ll) to be performed. First, data is retrieved from the diode matrix card 50 and in place of temperature and pressure 3~
readings, the Eixed constant 0505 is placed on data bus 124 via input port 123. Next, the calculations set forth in the calculation block of FIG. 5 are performed. This should result in a particular "signature" for -the volume corrector apparatus. This signa-ture is converted to Binary Coded Decimal and displayed on the display 33. The program then returns -to -the WSTART s-ta-te.
In -the event -tha-t bo-th the system test bu-tton 46 and the cancel limit button 4~ are depressed simultaneously, the pro-gram causes the TTEST. subroutine ~FIG. 11) to be executed.However, detection of simultaneous button pushes causes the program to read the pressure 28 and temperature 26 trans-duce`rs instead of presenting the fixed number 0505 to the in-put port 123, and the resulting calculation proceeds accord-ing to the calculation block of FIG. 5.
All of the calculations which have been described are performed utilizing integer arithmetic, rather than float-ing point arithmetic. Rccordingly, a large amoul~t of memory in tl~e RO~l 120 i.s saved, resulting in a cost saving. In integer arithmetic, 3 ' 2 = 1 (the 0.5 is lost). However, if somewhexe in -the procedure there is a multiplication by 10, one may say instead that 30 T 2 - 15. Accordingly, in the calculations described above, there are many multiplica-tions and divisions by powers of 10. ~owever, the overall truncation errors are not severe and the calculations are within + 0.1~ up -to 1000 psi for all Tf. From 1000 to 1500 psi and flowing temperatures above 0F the calculations are with +0.1~. All accuracies are over an ambient temperature range of -40F to +140F.
Accordingly, there has been disclosed a method and appa-ratus for correcting a measurea unit volume of flowing gas - to a base volume at given base conditions of base pressure and base temperature. It is understood that the above-described embodiment is merely illustrative of the applica-tion of the principles of this invention. Numerous other ~;,t~
embocliments may be devised by those skillecl in the art with-out depar-ting from the spirit and scope of -this inven-tion as defined by the appended claims.
.
Claims (19)
1. Apparatus for correcting a measured unit volume of gas flowing through a conduit to a base volume at given base conditions of base pressure and base temperature comprising:
means for measuring the volume of the flowing gas and providing a volume pulse in response to measuring said unit volume;
means responsive to said volume pulse for measuring the temperature of the flowing gas and providing a first elec-trical signal corresponding thereto;
means responsive to said volume pulse for measuring the pressure of the flowing gas and providing a second electrical signal corresponding thereto;
means for storing a first plurality of constant values;
means responsive to said volume pulse for utilizing said stored first plurality of constant values and the measured pressure and temperature values to calculate a second con-stant value;
means for utilizing said stored first plurality of con-stant values and the measured pressure value to calculate a third plurality of constant values;
means for utilizing said calculated third plurality of constant values and the measured pressure and temperature values to calculate a supercompressibility factor;
means for utilizing said supercompressibility factor and said second calculated constant value to calculate a correction factor; and means for deriving a corrected volume from the measured volume and the correction factor.
means for measuring the volume of the flowing gas and providing a volume pulse in response to measuring said unit volume;
means responsive to said volume pulse for measuring the temperature of the flowing gas and providing a first elec-trical signal corresponding thereto;
means responsive to said volume pulse for measuring the pressure of the flowing gas and providing a second electrical signal corresponding thereto;
means for storing a first plurality of constant values;
means responsive to said volume pulse for utilizing said stored first plurality of constant values and the measured pressure and temperature values to calculate a second con-stant value;
means for utilizing said stored first plurality of con-stant values and the measured pressure value to calculate a third plurality of constant values;
means for utilizing said calculated third plurality of constant values and the measured pressure and temperature values to calculate a supercompressibility factor;
means for utilizing said supercompressibility factor and said second calculated constant value to calculate a correction factor; and means for deriving a corrected volume from the measured volume and the correction factor.
2. The apparatus according to Claim 1 further includ-ing:
a counter;
means for converting said corrected volume into an inte-gral number of increments for said counter plus a remainder;
means for storing said remainder; and means for incrementing said counter by said integral number of increments.
a counter;
means for converting said corrected volume into an inte-gral number of increments for said counter plus a remainder;
means for storing said remainder; and means for incrementing said counter by said integral number of increments.
3. The apparatus according to Claim 2 wherein said converting means adds the previously stored remainder to the corrected volume prior to the conversion.
4. The apparatus according to Claim 1 wherein the stor-ing means includes an interchangeable diode matrix board.
5. The apparatus according to Claim 1 wherein the stor-ing means includes a programmable read only memory.
6. The apparatus according to Claim 1 further includ-ing a display and an operator actuable switching element, said apparatus responding to actuation of said switching element for activating said display to display the pressure of the flowing gas.
7. The apparatus according to Claim 1 further including a display and an operator actuable switching element, said apparatus responding to actuation of said switching element for activating said display to display the temperature of the flowing gas.
8. The apparatus according to Claim 1 further includ-ing a display and an operator actuable switching element, said apparatus responding to actuation of said switching element for calculating the correction factor utilizing predetermined values for the temperature and pressure of the flowing gas and activating said display to display the cal-culated correction factor.
9. The apparatus according to Claim 1 further includ-ing a display and an operator actuable switching element, said apparatus responding to actuation of said switching ele-ment for calculating the correction factor utilizing the mea-sured pressure and temperature values and activating said display to display the calculated correction factor.
10. The apparatus according to Claim 2 further includ-ing an operator actuable switching element, said apparatus responding to actuation of said switching element for incrementing said counter.
11. The apparatus according to Claims 6 or 7 further including:
means for establishing range limits for the temperature and pressure of the flowing gas;
a latch;
means responsive to either the temperature or pressure going outside its respective range for setting said latch;
means responsive to actuation of said switching element when said latch is set for activating said display to display a fault indication;
a second operator actuable switching element; and means responsive to actuation of said second switching element for resetting said latch.
means for establishing range limits for the temperature and pressure of the flowing gas;
a latch;
means responsive to either the temperature or pressure going outside its respective range for setting said latch;
means responsive to actuation of said switching element when said latch is set for activating said display to display a fault indication;
a second operator actuable switching element; and means responsive to actuation of said second switching element for resetting said latch.
12. The apparatus according to Claims 6, 7 or 8 wherein said display and said operator actuable switching element are contained in a separate test unit and further including means for coupling said test unit to said appara-tus and means for supplying power to said test unit through said coupling means.
13. The apparatus according to Claim 1 wherein all calculations are performed by a programmed digital computer utilizing integer arithmetic.
14. The apparatus according to Claim 1 further includ-ing a battery adapted to power the apparatus and means con-nected between the battery and the apparatus for applying battery power to the apparatus only in response to said volume pulse.
15. The apparatus according to Claim 14 wherein said battery is rechargeable, said apparatus further including means for recharging said battery.
16. The apparatus according to Claim 15 wherein said recharging means is solar actuated.
17. The apparatus according to Claim 14 further includ-ing means for monitoring the condition of said battery and means responsive to the battery condition being unsatisfac-tory for inhibiting all calculations by said apparatus.
18. The apparatus according to Claim 17 further includ-ing means for providing a visual indication when the battery condition is unsatisfactory.
19. The apparatus according to Claim 9 wherein said display and said operator actuable switching element are contained in a separate test unit and further including means for coupling said test unit to said apparatus and means for supplying power to said test unit through said coupling means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US241,328 | 1981-03-06 | ||
| US06/241,328 US4390956A (en) | 1981-03-06 | 1981-03-06 | Apparatus for correcting measured gas flow |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1169561A true CA1169561A (en) | 1984-06-19 |
Family
ID=22910260
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000394508A Expired CA1169561A (en) | 1981-03-06 | 1982-01-20 | Apparatus for correcting measured gas flow |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US4390956A (en) |
| JP (1) | JPS57158521A (en) |
| AU (1) | AU549340B2 (en) |
| CA (1) | CA1169561A (en) |
| DE (1) | DE3203781A1 (en) |
| DK (1) | DK98682A (en) |
| FR (1) | FR2501365B1 (en) |
| GB (1) | GB2094521B (en) |
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| US4531193A (en) * | 1981-07-30 | 1985-07-23 | Fuji Electric Company, Ltd. | Measurement apparatus |
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| US4581708A (en) * | 1982-02-19 | 1986-04-08 | Laboratory Equipment Corp. | Motor vehicle performance monitoring system |
| US4553433A (en) * | 1983-05-13 | 1985-11-19 | The Singer Company | Rotary meter with integral instrument housing |
| JPS6024420A (en) * | 1983-07-20 | 1985-02-07 | Tokyo Tatsuno Co Ltd | Flow-rate measuring device |
| CA1223464A (en) * | 1983-11-21 | 1987-06-30 | Robert E. Hall | Digital flow meter for dispensing fluids |
| US4734873A (en) * | 1984-02-02 | 1988-03-29 | Honeywell Inc. | Method of digital process variable transmitter calibration and a process variable transmitter system utilizing the same |
| JPS60244848A (en) * | 1984-05-21 | 1985-12-04 | Ketsuto Kagaku Kenkyusho:Kk | Electric moisture meter |
| US4584868A (en) * | 1985-05-16 | 1986-04-29 | American Meter Company | Apparatus for determining the supercompressibility factor of a flowing gas |
| US4663977A (en) * | 1986-01-03 | 1987-05-12 | Badger Meter, Inc. | Sonic measurement of gas flow |
| US4829449A (en) * | 1986-02-05 | 1989-05-09 | Rockwell International Corporation | Method and apparatus for measuring and providing corrected gas flow |
| GB2197957B (en) * | 1986-11-22 | 1990-10-17 | Motorola Ltd | Sensor systems |
| SE460929B (en) * | 1987-04-24 | 1989-12-04 | Dresser Wayne Ab | SET AND DEVICE MEASURING THE VOLUME OF A VOLUME THAT FLOWS THROUGH A MEETING CHAMBER DURING A MEASURING PERIOD |
| US4799169A (en) * | 1987-05-26 | 1989-01-17 | Mark Industries, Inc. | Gas well flow instrumentation |
| CA1293568C (en) * | 1987-10-01 | 1991-12-24 | Romet Limited | Electronic volume correctors |
| US4831866A (en) * | 1987-11-09 | 1989-05-23 | Tokheim Corporation | Automatic meter proving and calibration system |
| JPH01191019A (en) * | 1988-01-26 | 1989-08-01 | Akitoshi Kitano | Instrumental error correcting method for flowmeter |
| US4881183A (en) * | 1988-03-25 | 1989-11-14 | Sun Electric Corporation | Method and apparatus for emission testing |
| US4958070A (en) * | 1988-11-07 | 1990-09-18 | The Babcock & Wilcox Company | Digital electronics for controlling a fiber optic shedding flowmeter |
| US5046369A (en) * | 1989-04-11 | 1991-09-10 | Halliburton Company | Compensated turbine flowmeter |
| JPH02287120A (en) * | 1989-04-27 | 1990-11-27 | Mitsubishi Heavy Ind Ltd | Dyestuff type flow measuring device |
| US5247467A (en) * | 1989-08-16 | 1993-09-21 | Hewlett-Packard Company | Multiple variable compensation for transducers |
| AU630263B2 (en) * | 1989-12-22 | 1992-10-22 | Gas Cylinder Services Pty Ltd | Liquefied gas metering |
| US5251149A (en) * | 1991-08-02 | 1993-10-05 | Great Plains Industries, Inc. | Electronic nutating disc flow meter |
| AT398643B (en) * | 1991-09-09 | 1995-01-25 | Vaillant Gmbh | DEVICE FOR CONTROLLING THE LEAKAGE TEMPERATURE |
| US5323657A (en) * | 1991-11-04 | 1994-06-28 | Badger Meter, Inc. | Volumetric flow corrector and method |
| FR2685766B1 (en) * | 1991-12-30 | 1994-04-08 | Gaz De France | METHOD AND DEVICE FOR MEASURING GAS FLOW. |
| US5435180A (en) * | 1992-10-07 | 1995-07-25 | Hitachi, Ltd. | Method and system for measuring air flow rate |
| DE4312837C1 (en) * | 1993-04-20 | 1994-10-06 | Lancier Masch Peter | Apparatus for flow measurement in compressed air installations and flow measuring device for this |
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| US5553493A (en) * | 1994-03-02 | 1996-09-10 | Graco Inc. | High resolution flowmeter with wear detection |
| US5656784A (en) * | 1997-01-03 | 1997-08-12 | Eagle Research Corp. | Fluid density variation compensation for fluid flow volume measurement |
| HUP9701034A3 (en) * | 1997-06-11 | 1999-10-28 | Foevarosi Gazmuevek Rt | Method and ptz corrector for correcting of measured volume of flowing gas |
| DE19920393B4 (en) * | 1999-05-04 | 2009-09-24 | Elster Gmbh | Arrangement for determining a volume of a gas stream |
| ES2170652B1 (en) * | 2000-04-07 | 2004-02-16 | Siemens Sa | GAS VOLUME CORRECTOR SYSTEM. |
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| WO2007068242A1 (en) * | 2005-12-16 | 2007-06-21 | Flonidan Dc A/S | Method for volumetric measuring of gas and diaphragm gas meter |
| EP2107351A1 (en) * | 2008-04-02 | 2009-10-07 | Actaris SAS | Remote meter reading device |
| DE102011011871A1 (en) * | 2011-01-06 | 2012-07-12 | Walter Mehnert | Method and device for determining the mass of a fluid flowing through a flow meter in a consumption time interval |
| US8930157B2 (en) | 2012-02-21 | 2015-01-06 | Dresser, Inc. | Temperature compensated digital pressure transducer |
| DE102014018099A1 (en) * | 2014-12-06 | 2016-06-09 | Hydac Accessories Gmbh | Method for determining a quantity of gas and device for carrying out this method |
| US11187566B2 (en) | 2017-10-20 | 2021-11-30 | Honeywell International Inc. | Safety incident detection and reporting through a connected EVC (electronic volume corrector) |
| RU210797U1 (en) * | 2021-09-12 | 2022-05-05 | Елена Владимировна Кудрявцева | Electronic gas volume corrector |
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| FR1467112A (en) * | 1965-12-08 | 1967-01-27 | Thomson Houston Comp Francaise | Improvements to methods and devices for determining the density of a gas |
| US3701280A (en) * | 1970-03-18 | 1972-10-31 | Daniel Ind Inc | Method and apparatus for determining the supercompressibility factor of natural gas |
| US3752393A (en) * | 1971-08-02 | 1973-08-14 | Teledyne Ind | Digital flow calculator |
| US3729995A (en) * | 1971-08-26 | 1973-05-01 | Fischer & Porter Co | Pressure and temperature compensation system for flowmeter |
| US3755806A (en) * | 1972-05-24 | 1973-08-28 | Bowmar Ali Inc | Calculator display circuit |
| US4149254A (en) * | 1975-06-25 | 1979-04-10 | American Chain & Cable Co., Inc. | Method and apparatus for flow metering |
| US4056717A (en) * | 1976-10-27 | 1977-11-01 | The Singer Company | Temperature correction systems for a fluid flow meter |
| US4173891A (en) * | 1978-01-12 | 1979-11-13 | Rockwell International Corporation | Method and apparatus for measuring gas flow |
| US4238825A (en) * | 1978-10-02 | 1980-12-09 | Dresser Industries, Inc. | Equivalent standard volume correction systems for gas meters |
| US4253156A (en) * | 1979-06-22 | 1981-02-24 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Automatic flowmeter calibration system |
-
1981
- 1981-03-06 US US06/241,328 patent/US4390956A/en not_active Expired - Fee Related
-
1982
- 1982-01-20 CA CA000394508A patent/CA1169561A/en not_active Expired
- 1982-01-25 GB GB8202015A patent/GB2094521B/en not_active Expired
- 1982-02-04 DE DE19823203781 patent/DE3203781A1/en not_active Ceased
- 1982-02-24 FR FR8203017A patent/FR2501365B1/en not_active Expired
- 1982-03-02 JP JP57032972A patent/JPS57158521A/en active Pending
- 1982-03-05 AU AU81146/82A patent/AU549340B2/en not_active Ceased
- 1982-03-05 DK DK98682A patent/DK98682A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| FR2501365A1 (en) | 1982-09-10 |
| AU549340B2 (en) | 1986-01-23 |
| AU8114682A (en) | 1984-06-21 |
| GB2094521A (en) | 1982-09-15 |
| US4390956A (en) | 1983-06-28 |
| FR2501365B1 (en) | 1986-02-14 |
| JPS57158521A (en) | 1982-09-30 |
| GB2094521B (en) | 1985-02-06 |
| DE3203781A1 (en) | 1982-10-28 |
| DK98682A (en) | 1982-09-07 |
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