|Publication number||US3673392 A|
|Publication date||Jun 27, 1972|
|Filing date||Feb 2, 1970|
|Priority date||Feb 2, 1970|
|Also published as||CA962779A, CA962779A1, DE2104820A1|
|Publication number||US 3673392 A, US 3673392A, US-A-3673392, US3673392 A, US3673392A|
|Inventors||Holm Wayne E|
|Original Assignee||Hydril Co|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Referenced by (8), Classifications (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent Holm June 27, 1972 154] REMOTE TERMINAL COMPUTING 3,351,910 11/1967 Milleretal. .340 1725 UNIT TO COMPUTE BIA x C VALUES, 2.313.222 2 3 3 a v t gig/ 2:
, l 66 e eta ll FOR USE BY CENTRAL COMPUTER 2,912,162 11/1959 Shou-l Nee ..235!'l58 Inventor:
Wayne E. Holm, Costa Mesa, Calif.
Hydril Company, Los Angeles, Calif.
Feb. 2, 1970 U.S.Cl ..235/150.5,235/l50.52,235/l5l.34,
1111.01. ..G06j 1/00 Field oiSearch ..235/l56,l64,158,151.34,
References Cited UNITED STATES PATENTS 4/l 971 lO/l 968 4/l968 5/l969 Valentine Kerbow et al... ....235/l5l.34 X
Davis ,...235/l5l.34 X Schmoock et al ..235/l5l.34 X
Primary Examiner-Malcolm A. Morrison Assistant Examiner-David H. Malzahn Attorney-White & l-laefliger ABSTRACT A computing unit adapted for use in a computing system, but located proximate the parameter measurement location, comprises converter means that includes a digital to analog converter (and may also include an analog to digital converter); an input terminal for a variable A to be connected to the converter means to provide reference input, and an input terminal for a variable B to be connected to the converter means operating as a divider during a first time interval to produce an output representative of the quantity BIA; and an input terminal for a variable C to be connected to the digital to analog converter operating as a multiplier during a second time interval to produce an output representative of the quantity B/A X C.
I7 Claims, 6 Drawing Figures PAIZZIIIEIIIIIIIN m2 3. 673 392 sum 2 or 3 I AP. I I I I I 1 ADC. I f 45a I I I e SAMPLE I 2 mac QuTEu-r REGISTER 1 m A o n CONTROL AW -:.:P.* I if? 43 RAP I /T I d T AccumuLm'oR 24 I I 32 I 1' k? 2 I I I GATING I I 26 f I 3 REFERENCE I 34 su pw I I 322: COMPARATOR I I CIRCUITRY DIGITAL m- ANALOG I I CONVERTER H T 9 Q0 J P 350. 29a. a
I 12 [95 450. P 0 I I I A I i @I I I A P o SAMPLE. I ADC OUTPUT REGIETEE I I A p ANZJZLD 1 CONTROL. (DIGITAL) 1 44 24 I II I r d T I ACCUMULATOI? i 4/ 26a I I I GATING 26 l I f I REFERENCE 40 I -34 A53 suu pm L SQUARE I I I I QooT COMPARATOR fiaJ CIRcu/rRY DIGITAL-TO- ANALOG I x I CONVERTER I T I I L I I [1:] L q .I I
29 t Ij/55Q J/VVEA/ T02 WS A/E E. HOLM REMOTE TERMINAL COMPUTING UNIT TO COMPUTE B/A X C VALUES, FOR USE BY CENTRAL COMPUTER BACKGROUND OF THE INVENTION This invention relates generally to telemetry and control systems, and more particularly concerns the preliminary processing and storage of data gathered from multiple transducers at a location which may be relatively close to the transducers, for subsequent transmission to a central processor. While the concepts and principles of the invention have wide application, the discussion of their application will for the most part be directed to gas flow measurement, although not all claims will be so limited.
When crude oil from a producing well is lifted or otherwise delivered to the surface, it releases natural gas. This gas is normally collected and payment must be made to the lessor for all gas removed from his property, necessitating accurate measurement of gas flow. When a well is artificially pressurized by introducing natural gas from an external source to cause the crude oil to rise to the surface, it also becomes necessary to accurately measure the gas flow for control purposes.
Total net flow is determined by measuring the absolute pressure P of the gas in a pipeline, the differential pressure AP or pressure drop across an orifice in the line, and the gas temperature T in the line. The flow rate is proportional to (AP/T X I which, when multiplied by a known constant, corrects to standard cubic feet per unit of time. If the sampling rate is known, then the flow rate can be integrated to derive total net flow of gas in standard cubic feet over a given time span.
In actual practice, it is possible to transmit the AP, P and T data from each of a large number (say, hundreds) of measurement locations or stations to a central computer for computation of the net flow or total flow. For this purpose, the data would be transmitted to the computer in sequence from the many different stations during sampling intervals. It is found that the data bandwidth requirements for a computer-based system becomes very large for the high sampling rates needed for accuracy where data from hundreds of stations is sampled, necessitating a large, expensive central computer installation.
SUMMARY OF THE INVENTION It is a major object of the invention to provide a means for overcoming the above problems in a manner resulting in reduced system installation cost and operational expense, as well as affording many additional advantages which will appear.
Basically, the invention is embodied in a computing unit, as for example a remote terminal unit (or RTU) adapted for use in a computing system but located proximate the parameter measurement location. The unit comprises converter means that includes a digital to analog converter (i.e. DAC); an input terminal for a variable A to be connected to the converter means to provide reference input, and an input terminal for a variable B to be connected to the converter means operating as a divider during a first time interval to produce an representative of the quantity B/A to be transmitted to the DAC; and an input terminal for a variable C to be connected to the DAC operating as a multiplier during a second time interval to produce an output representative of the I'i/A X C. As will appear, the converter means may include an analog to digital converter (i.e., ADC), or a frequency to digital converter, to which the first terminal is connected, and the DAC may be incorporated within or without the ADC; also, transducers for signals representing T, AP and P as defined above may be connected with the three terminals associated with the variables A, B and C as referred to. Thus A, B and C represent any signals which are to be processed in the manner described to derive the quantity B/A X C, the square root of which may also be computed by the computing unit. Thus, they may also represent power line voltage E, the inverse of power line current I and cos b in the expression E/I X cos d where s is the phase angle between E and I.
It is a further object of the invention to provide circuitry connected in operative relation with the converter means for effecting derivation of the quantity (BM X C). Such circuitry may include a square root amplifier connectible between a sample and hold amplifier storing the quantity (BIA X c) and the converter means to perform the square root operation during a third time interval, the converter means digitizing the root for transmission to and storage in an accumulator. A central computer may be connected in scanning relation with multiple such accumulators associated with computing units as defined, and the bandwidth requirements for the data lines to the computer will then be greatly reduced by comparison with bandwidth requirements for data lines to transmit each of the many signals A, B and C to the central computer. Other methods of square root extraction operating in conjunction with the ADC include use of odd digits apparatus, and use of an algorithm control, as will be explained.
Additional advantages realized by the invention include a lower sampling-rate capacity requirement for the central computer input/output bus; fewer priority interrupts are required for the central computer; smaller core storage for the central computer is needed inasmuch as the core need not be sized to accommodate peak possible data rates; data reliability is greater because data is stored in both the central computer and the RTUs, with concomitant reduced probability of loss of data from any one equipment malfunction; and conversion to manual operation in the event of computer malfunction is easier because the data is stored in the RTU accumulators.
These and other objects and advantages of the invention, as well as the details of illustrative embodiments, will be more fully understood from the following description and drawings, in which:
DRAWING DESCRIPTION FIG. I is a system block diagram;
FIGS. 2, 3 and 4 are block diagrams of a remote terminal unit showing operation of different modes at different times;
FIG. 5 is a block diagram of a modified remote terminal unit; and
FIG. 6 is a block diagram of another modified remote terminal unit.
DETAILED DESCRIPTION Referring first to FIG. 1, a first series of remote terminal units (RTUs) is indicated at X,as connected with a party line Y,; another series of RTUs is indicated at X as connected with party line Y and a third series of RTUs X,,is connected with party line Y,,. The party lines are also connected with a computer interface unit 10 which is connected at I] with the computer 12, the latter being connectible if desired to the remote data processing facility 13 via interface 14. Input/output devices 15 and disc file I6 are connected with computer I2; and manual control console 17 is connected with the unit 10. It will be understood that the computer 12 scans the RTUs (and specifically the data storage units thereof) on a repetitive basis.
Each RTU operates as a computing unit, and may for example have three signal inputs A, B and C and an output which is a function of A, B and C, expressed as follows:
RTUoutpul=f(A,B, C) E 1.
More specifically, the RTUs to be described incorporate analog to digital converters utilized during different time intervals to perform different calculations. Thus, during one time interval 1, the conversion means performs the division operation B/A; during a second time interval the conversion means performs the multiplication operation BIA X C; and during a third time interval 1;, the conversion means may perform the square root operation (BIA X C). Thus the device output may be expressed as follows:
Output (BIA x C) Eq. 2.
As will be brought out, such preprocessing of the data at a remote location near transducers which generate the signals A, B and C, results in a much lower bandwidth requirement as respects data transmission to the central computer, as compared with a system wherein each of A, B and C is transmitted to the computer. Also, a much smaller central computer may then be utilized.
Extending the description to FIGS. 2 4, the RTU illustrated at X incorporates an ADC (i.e. analog digital con verter) 19, a DAC (i.e. digital to analog converter) 20, and the DAC may be incorporated within the ADC as shown, or may be a separate item. The RTU has an input for a variable A (as for example input terminal T for signal voltage representative of temperature as sensed by a transducer 21) to provide reference input to the ADC. The RTU also has an input for a variable B (as for example input terminal AP, for signal voltage representative of a gas pressure difference as measured across an orifice in a gas flow line by transducer 22). Other pressure differences AP, and AP may also be measured. Finally, the RTU has an input terminal for a variable C (as for example input terminal P for signal voltage representative of gas line pressure P as measured near the orifice, by a transducer 23).
In this regard, total net flow Q is determined by first measuring the absolute pressure P of the flow in a line; the differential pressure AP across an orifice in the line; and the temperature T. The gas flow rate is proportional to (AP/T X P), and the latter when multiplied by a suitable constant yields the flow in standard cubic feet per unit of time. If the sampling rate is known, then the flow rate can be integrated to produce a total net flow in standard cubic feet over a given time span. The invention takes advantage of the fact that an ADC is basically a divider; that a DAC is basically a multiplier; that all ADCs have a DAC; and that pressure in a non-vacuum system will always exceed or be equal to zero.
During a first time interval t of sampling of a given lease gasline, as seen in FIG. 2, the analog voltage representing differential pressure AP, is used as the ADC input via switch arm 24, sample and hold amplifier 25 and switch arm 26. Specifically, the comparator 27 receives that input as well as the output of the DAC 20 via line 28 and switch arm 29, the reference input to the DAC being the temperature T via switch arm 35. As a result, the comparator output at 30 fed to the output register 31 via control 32 and control output 33 causes a digital value representing AP/T to appear in the register 31. The digital value stored in the latter is transmitted at 52 and 53 via gating 34 to the DAC to complete the loop. Switches 24, 26, 29 and 35 are controlled at 240, 26a, 29a and 350,
During the second time interval as seen in FIG. 3, the analog voltage representing pressure P is used as the ADC reference, via switch arm 35, controlled at 350, and the resistance ladder, which is the DAC 20 (still set to a value proportional to AP/T is now used to obtain a value proportional to the produce AP/T X P. The latter value appearing at the DAC output 28 is stored in the sample and hold amplifier 25 via switch arm 24. During this interval, there is no input to the comparator, as is clear from FIG. 3.
FIG. 4 shows the square root extraction step during time in terval t with the square root amplifier connected between the output 41 of the sample and hold amplifier 25 and the ADC input via switch arm 26 and comparator 27. The (AP/T X P) output of the ADC at 42 is fed via switch arm 43 (controlled at 430) to the accumulator 44 for scanning by the computer. In this mode, the ADC 19 functions as an ADC.
Alternatively, as shown in FIG. 5, the output AP/T X P of ADC register 31 is connected via switch arm 43 with one input of a subtractor 46, an odd number generator 47 being connected with the other subtractor input at 48. The subtractor output is returned at 49 to the register 31 and also is fed to accumulator 44. Register 31 is here used as a shift register, and working in conjunction with the subtractor 46, odd number generator 47 and the accumulator 44, during t extracts the square root of AP/T X P, using the sum of the odd digits al' gorithm (ie, the root corresponds to the number of odd digits beginning with the number I which can be subtracted from the quantity AP/T X P before obtaining a negative result, the odd digits being I, 3, 5, 7, etc.
FIG. 6 illustrates a third method of square root extraction using an algorithm modification control 50 the output of which is connected at 5| with control 32. During time t, the ADC 19 operates as a function generator upon the AP/T X P input from the sample and hold amplifier 25, in response to any chosen algorithm control input at 51, (as for example Newton-Rapheson) technique) described on pages 73-79 of Mathematics and Computers, by Stibnitz and Larrivee, Mc Graw-Hill Book Company, 1957 to produce the digital value of the desired function in the register 31, for transmission to the accumulator 44. For example, the square root function (APfI' X P), (or more generally the function (BIA X C)" may be so produced. Alternatively, any non-linear function of the analog input to the ADC may be produced in response to algorithm control.
Finally, the computer 12 may function to compute the flow rate at each terminal by multiplying the quantity AP/T X P by a constant which corrects to standard cubic feet per unit of time. Also, since the sampling rate is known, the computer may, for each terminal, determine the total net flow per unit of time in standard cubic feet, by integrating the computed flow rate.
In FIGS. 2 6, transducers 21, 22 and 23 may also represent devices to produce signals corresponding to the inverse of power line current, i.e. I-l; power line voltage E; and cos d) where a is the phase angle between E and I. Other variables may also be used.
l. A computing unit comprising a. computing means for computing from analog input variables A,B and C an analog output representative of the quantity B/A X C, and including an ADC which includes a multiplying DAC,
b. an input path for variable A to be connected to the computing means to provide reference input, and an input path for variable B to be connected to the computing means operating as a divider during a first time interval to produce a digital output representative of the quantity BIA, and
c. an input path for a variable C to be connected to the multiplying DAC responsive to said digital output and operating as a multiplier during a second time interval to produce an analog output representative of the quantity B/A X C,
d. The ADC including a comparator having inputs connected to the output of the multiplying DAC and to the variable B input path during the first time interval, and disconnected therefrom during the second time interval.
2. The unit of claim 1 wherein the paths for inputs C, B and A are respectively connected to means for measuring the absolute pressure, means for measuring differential pressure across an orifice and means for measuring temperature, of gas flowing through a pipeline.
3. The unit of claim 1 including circuitry connected in operative relation with the computing means for effecting derivation of the quantity (B/A X C).
4. A computing system including a central computer, and multiple computing units as defined in claim 3, each unit including an accumulator in which is stored digital data corresponding to the quantity (B/A X CW the computer operatively connected in scanning relation with the multiple accumulators.
5. A computing unit comprising a. computing means for computing from analog input variables A,B and C an analog output representative of the quantity B/A X C, and including an ADC which includes a multiplying DAC,
b. an input path for a variable A to be connected to the ADC to provide reference input, and an input path for a variable 8 to be connected to the ADC operating as a divider during a first time interval to produce a digital output representative of the quantity BIA, and
c. an input path for a variable C to be connected to the rim]- tiplyin g DAC responsive to said digital output and operating as a multiplier during a second time interval to produce an analog output representative of the quantity B/A X C.
6. The unit of claim 5 wherein the input paths for inputs CB and A are respectively connected to means for measuring the absolute pressure, means for measuring differential pressure across an orifice and means for measuring temperature, of gas flowing through a pipeline.
7. The unit of claim 5 wherein the input paths A,B and Care connected to means for measuring AC power line voltage, means for measuring power line current and means for measuring cos d; where d: is the phase angle between said power line current and voltage.
8. The unit of claim 5 including an accumulator, and means for transmitting to the accumulator digital data corresponding to a version of the quantity B/A X C, for storage in the accumulator.
9. The unit of claim 8 including multiple units as defined, a central computer, and means for sequentially sampling the said data stored in the accumulators for transmission to the computer.
10. The unit of claim 5 including circuitry connected in operative relation with the ADC for efi'ecting derivation of the quantity (BIA X C).
ll. The unit of claim 10 including an accumulator operatively connected with said circuitry for storing the quantity B/A X C), to be sampled and transmitted to a central computer.
12. The unit of claim 10 wherein said ADC includes an output register operable as a shift register. and said circuitry includes an odd number generator, subtractor, and accumulator opcratively connected with said output register to derive the digital quantity (B/A X C) from the quantity (B/A X C). for
storage in the accumulator.
13. The unit of claim 10 wherein said circuitry includes a sample and hold amplifier and square root circuitry connected between the multiplying DAC output and an input terminal of the ADC whereby the ADC is operable to digitize the quantity (B/A X C)" during another time interval.
14. The unit of claim 13 including switch structure and controls therefor operable to connect the sample and hold amplifier in series between said B variable input terminal and the ADC during said first time interval.
15. The unit of claim 14 wherein said switch means connects the sample and hold amplifier input with the DAC output and disconnects the sample and hold output from the ADC, during the second time interval.
16. The unit of claim 5 including circuitry including an algorithm control connected with the ADC to modify ADC functioning so as to produce a digital version of the quantity (B/A X C).
17. in apparatus for accumulating gas flow rate data from a plurality of gas flow line locations. the combination at each location comprising a. means for computing the quantity B/A X C in response to reception of input signals .4, B and C corresponding to T, APand P, said means including an ADC, where AP= gas flow pressure differential across an orifice communicating with the line,
P= gas flow pressure in the line T= gas temperature in the line b. said means operating upon at least two of the signals during a first time interval for producing and storing a resultant quantity, and said means operating upon said resultant quantity and the third of said signals during a second time interval for producing the quantity 8 X CIA and (5. other means operatively connected with said computing means for receiving said quantity B GA and for derivin t e uare rootthereof.
g h sq t l l l i UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,673,392 Dated June 27, 1972 Inventor(s) Wayne lm It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 6, line 18; (B/A x (3)." should read 2 (B/A x c) Signed and sealed this 22nd day of May 1973.
EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents
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|U.S. Classification||708/7, 702/130, 702/47, 708/3|