Method and apparatus for monitoring variation in the current value of a rate of fluid flow through a flow meter

• US 5,747,703 A
• Filed: 10/07/1996
• Issued: 05/05/1998
• Est. Priority Date: 12/07/1993
• Status: Expired due to Fees

• Current Assignee: Schlumberger Industries Incorporated (SLB)
• Original Assignee: Schlumberger Industries Incorporated (SLB)
• Inventors: Janet, Philippe, Puybaret, Frederic, Plisson, Fran.cedilla.ois
• Primary Examiner(s): Dombroske, Geroge M.
• Assistant Examiner(s): AMROZOWICZ, PAUL DOUGLAS
• Application Number:
  US08/656,182
• Time in Patent Office: 575 Days
• Field of Search: 73/861.77, 73/861.78
• US Class Current: 73/861.77
• CPC Class Codes: G01F 15/00 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
• CPC Class Codes: G01F 15/105 Preventing damage by hydraulic shocks

Abstract

The invention provides a method of monitoring variation in the current value of a rate of fluid flow through a fluid meter which includes a measurement unit and a rotary shaft connected to said measurement unit and suitable for rotating about its own axis when a volume of fluid passes through the measurement unit, the method consisting in detecting rotary movements rather than rotation of the shaft at a sampling frequency that is variable in application of a predetermined sampling relationship, said frequency being defined as a function of at least one predetermined fluid flow rate value, and in electronically processing bits corresponding to detection and to non-detection of a rotary movement of the shaft at said sampling frequency in order to determine the current value of the fluid flow rate over a continuum of flow rates and relative to the predetermined fluid flow rate value included in said continuum of flow rates.

Claims

1. A method of monitoring variation in the current value of a rate of fluid flow through a fluid meter which includes a measurement unit and a rotary shaft connected to said measurement unit and suitable for rotating about its own axis when a volume of fluid passes through the measurement unit, the method consisting in detecting rotary movements rather than rotation of the shaft at a sampling frequency that is variable between two frequencies in application of a predetermined sampling relationship according to corresponding predetermined fluid flow rate values, and in electronically processing bits corresponding to detection and to non-detection of a rotary movement of the shaft at said sampling frequencies in order to determine the current value of the fluid flow rate over a continuum of flow rates and relative to the predetermined fluid flow rate values included in said continuum of flow rates.

2. A method according to claim 1, wherein rotary movements rather than rotation of the shaft are detected at at least two sampling frequency values f₁ and f₂ predetermined by the sampling relationship in such a manner that f₁ is defined as a function of a first predetermined fluid flow rate value Q₁, and f₂ is defined as a function of Q₁ and of a second predetermined fluid flow rate value Q₂, where f₁ <

f₂ and Q₁ <

Q₂, with the frequencies f₁ and f₂ thus defining two ranges of flow rates of the continuum, which ranges overlap partially, one extending up to a flow rate value Q'"'"'₁ defined by the frequency f₁, where Q₁ <

Q'"'"'₁ <

Q₂, and the other extending from a flow rate value Q'"'"'₂ defined by said frequency f₁ and up to a value Q₂, where Q₁ <

Q'"'"'₂ <

Q'"'"'₁, and the bits are processed electronically as a function of said frequencies f₁ and f₂ in order to determine the current value of the fluid flow rate relative to said ranges of flow rates.

3. A method according to claim 2, wherein, prior to processing the bits electronically, said method consists in performing the following steps:

1) a plurality of consecutive electrical signals are generated at the sampling frequency which is variable in application of the predetermined sampling relationship;

2) at least one sensor is powered with each of said electrical signals, said sensor being placed facing the path of at least one mark associated with the rotary shaft and being designed to deliver a binary output state depending on the position of said sensor relative to said mark; and

3) said binary output states are used to form an output signal representative of the succession in time of bits corresponding to detection and to non-detection of a rotary movement of the shaft, each detection representing a given volume of fluid.

4. A method according to claim 3, wherein, during step 1):

a) during a first time interval Δ

t1, at least one electrical signal is generated at the frequency f1;

b) during a second time interval Δ

t2 consecutive to Δ

t1, at least one electrical signal is generated at the frequency f2; and

c) the above steps are repeated.

5. A method according to claim 4, wherein:

a) the bits representing detection and non-detection of rotary movement of the shaft coming from the output signal are continuously processed electronically at the sampling frequency f1;

b) at the end of a time interval Δ

t1 during which the bits are electronically processed at said frequency f1, the bits representing detection and non-detection of rotary movement of the shaft coming from said output signal are simultaneously processed electronically at the sampling frequency f2; and

c) the above two steps are repeated.

6. A method according to claim 2, wherein the frequency f2 depends on the frequency f1.

7. A method according to claim 2, wherein the frequency f2 is greater than or equal to δ

Q2/2Q'"'"'2ρ

f1 where δ

xρ

represents the first integer greater than or equal to x.

8. A method according to claim 2, wherein the sampling frequency f1 is greater than twice the value of the rotary frequency of the shaft which is obtained when the current value of the fluid flow rate is equal to Q1.

9. A method according to claim 3, wherein a plurality of marks are associated with the rotary shaft.

10. A method according to claim 4, wherein a plurality of marks are associated with the rotary shaft and wherein, instead of generating a plurality of consecutive signals at respective frequencies f1 and f2, a plurality of consecutive signals are continuously generated at a sampling frequency f3 greater than the frequency f2 and selected as a function of a predetermined fluid flow rate value Q3, where Q3<

Q1, as a function of f2, and as a function of the number of marks, and the number of detections of rotary movement of the shaft is counted in order to determine the current fluid flow rate value relative to the predetermined values Q1 and Q3.

11. A method according to claim 10, wherein simultaneously the bits of the output signal are continuously electronically processed at the sampling frequencies f1 and f2 to determine the current value of the fluid flow rate relative to the predetermined values Q₁ and Q₂, and more particularly relative to the two flow rate ranges.

12. A method according to claim 10, wherein the frequency f₃ is greater than the product of the number of marks multiplied by the frequency f₂.

13. A method according to claim 5, wherein, during electronic processing of the bits at the sampling frequency f₁, a number I₁ of bits are selected by being stored at the sampling frequency f₁ over a time interval I₁ /f₁, the I₁ bits are summed as they are stored in order to determine the current fluid flow rate value up to the predetermined value Q'"'"'₂ with accuracy that depends on I₁ and f₁.

14. A method according to claim 13, wherein, prior to summing the I₁ bits, each of them is given a weighting coefficient so as to improve accuracy in determining the current fluid flow rate value.

15. A method according to claim 14, wherein the I₁ bits are stored in a shift register having I₁ bit positions, and an identical and maximum weighting coefficient is given to each of the central bit positions while respectively increasing and decreasing coefficients are given to the bit positions corresponding to the last and first bits stored.

16. A method according to claim 5, wherein, during electronic processing of the bits at the sampling frequency f₂, a predefined number I₂ of output signal bits are selected and the number of bits in said I₂ bits and representing detections of shaft movement is identified, and if the identified number is not less than a predetermined number I₃, then the current fluid flow rate value lies between the predetermined fluid flow rate values Q'"'"'₂ and Q₂, otherwise said current value is less than Q'"'"'₂.

17. A method according to claim 16, wherein the predefined number I₂ of bits depends on f₂, Q₁, and on the number of marks.

18. A method according to claim 16, wherein the number I₃ depends on Q₁, and on the number of marks.

19. A method according to claim 1, wherein it is determined whether the movement of the shaft is a rotary movement or an oscillatory movement by powering another sensor in alternation and by identifying and selecting the successive binary output states of the sensors.

20. A method according to claim 2, wherein the sensor is an optical sensor.

21. A fluid meter comprising a measurement unit for measuring a volume of fluid, which unit is connected to a rotary shaft for which each revolution represents a volume of fluid passing through said measurement unit, and apparatus for monitoring variation in the current value of the fluid flow rate on the basis of rotation of said shaft wherein said apparatus comprises:

at least one sensor placed facing the path of at least one mark associated with the rotary shaft and designed to deliver an output bit depending on the position of said sensor relative to said mark;

means for generating consecutive electrical signals at a sampling frequency that is variable between two frequencies in application of a predetermined sampling relationship to power said optical sensor, each frequency value being defined as a function of at least one predetermined fluid flow rate value;

means for forming an output signal on the basis of the binary output states delivered by the sensor, said output signal representing the succession in time of bits corresponding to detection and non-detection of a rotary movement of the shaft; and

electronic bit processing means for processing said bits depending on said sampling frequency in order to determine the current value of the fluid flow rate over a continuum of flow rates and relative to the predetermined fluid flow rate value on which the value of the sampling frequency depends.

22. A fluid meter according to claim 21, wherein the electronic bit processing means, comprise, in particular, means for selecting a predefined number of bits of the output signal which number is different for each value taken by the sampling frequency.

23. A fluid meter according to claim 22, wherein the electronic bit processing means comprise means for selecting a predefined number I₁ of output signal bits at a value f₁ of the sampling frequency selected as a function of a predetermined fluid flow rate value Q₁, said means being storage means, together with summing means for summing the stored I₁ bits to determine the current value of the fluid flow rate over a range of flow rates of the continuum extending up to a value greater than Q₁ and defined by the value selected for f₁, with said determination having accuracy that depends on I₁ and f₁.

24. A fluid meter according to claim 23, wherein the bit storage means comprise at least one shift register constituted by I₁ bit positions each designed to receive one bit at the sampling frequency f₁.

25. A fluid meter according to claim 24, wherein the electronic processing means also comprise weighting means for weighting the I₁ bits in application of a relationship that applies an identical and maximum weighting coefficient to each of the central bit positions and respectively increasing and decreasing weighting coefficients for the bit positions corresponding to the last and first stored bits, said weighting relationship serving to improve the accuracy with which the current flow rate value is determined.

26. A fluid meter according to claim 23, wherein the electronic bit processing means comprise means for selecting a predefined number I₂ of bits of the output signal at a value f₂ for the sampling frequency, f₂ depending on f₁, on Q₁, and on a second predetermined fluid flow rate value Q₂, where f₁ <

f₂ and Q₁ <

Q₂, I₂ depending on f₂, on Q₁, and on the number of marks, and also means for identifying amongst said I₂ bits the number of bits representing detection of shaft movement, said number serving to determine whether the current fluid flow rate value lies in the range of flow rates going up to the value greater than Q₁, or in a range that extends from said value up to Q₂.

27. A fluid meter according to claim 21, wherein the sensor is an optical sensor and the marks are visible marks.

28. A fluid meter according to claim 27, wherein the apparatus for monitoring variation in the current value of a fluid flow rate includes a wheel constrained to rotate with rotation of the shaft and provided with a number of teeth or visible marks equal to D1.

29. A fluid meter according to claim 28, wherein the apparatus for monitoring variation in the current value of the fluid flow rate includes another wheel constrained to rotate with the shaft and provided with a number of teeth or visible marks equal to D2, where D2>

D1.

30. A fluid meter according to claim 21, wherein the apparatus for monitoring variation in the current value of the fluid flow rate include means for determining whether the movement of the shaft is a rotary movement or an oscillatory movement.

31. A fluid meter according to claim 30, wherein the means for determining whether the movement of the shaft is a rotary movement or an oscillatory movement comprise a second optical sensor for each wheel and disposed relative to the first optical sensor at an angle equal to half the width to one of the teeth, together with electronic processing means for identifying and selecting the successive output states of the optical sensors.

32. A fluid meter according to claim 28, wherein each optical sensor is constituted by an emitter and a receiver placed facing each other on either side of the path of teeth of the wheel.