Multi-measurement vortex flow meter

• US 7,212,928 B2
• Filed: 09/06/2002
• Issued: 05/01/2007
• Est. Priority Date: 09/06/2002
• Status: Active Grant

• Current Assignee: Schneider Electric Systems USA, Inc. (Schneider Electric SE)
• Original Assignee: Invensys Systems Incorporated (Invensys PLC)
• Inventors: Allstrom, Peter E., Lewicke, Joseph J., Vignos, James H., Cook, Warren E.
• Primary Examiner(s): Bui; Bryan
• Assistant Examiner(s): Bhat; Aditya S.
• Application Number:
  US10/235,835
• Publication Number:
  US 20040049358A1
• Time in Patent Office: 1,698 Days
• Field of Search: 702/45, 702/47, 702/50, 702/54, 702/98, 702/100, 738/612.2, 701/101, 701/104, 700/28, 700/44, 700/52, 264/40.1, 425/149
• US Class Current: 702/45
• CPC Class Codes: G01F 1/3259 for detecting fluid pressure oscillations
• CPC Class Codes: G01F 1/86 Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure
• CPC Class Codes: G01F 15/024 involving digital counting
• CPC Class Codes: G01F 25/10 of flowmeters
• CPC Class Codes: G01N 9/26 by measuring pressure differences
• CPC Class Codes: G05F 3/02 Regulating voltage or current

Abstract

Two-wire transmitters are described in which the required voltage that a control room must supply to the transmitter is lower at high current than at low current, thus freeing up more voltage for other uses, and in which a constant set of operating voltages may be maintained. A corrected pressure in a vortex flow meter may be determined that reflects the mass flow rate. Thus, the mass flow rate may be determined based on the corrected pressure reading and a measured volumetric flow rate. Density may be determined from pressure and temperature using a table containing error values based on a standard density determination and a relatively simple approximation. During operation of a flow meter, the stored error values may be linearly interpolated and the approximation may be computed to determine the density from the stored error value.

Claims

1. A method of determining a pressure, the method comprising:

measuring a pressure of a fluid flowing through a system;

measuring a temperature of the flowing fluid;

determining a density based on the pressure and the temperature;

determining a velocity of the flowing fluid;

determining a corrected pressure for the flowing fluid based on the pressure, the temperature, and the velocity, the corrected pressure corresponding to a density reflective of the velocity and a mass flow rate, and wherein determining the corrected pressure comprises using the following formula;

2. The method of claim 1 wherein the constant k_diff is determined during a calibration procedure for a portion of the pressurized system, during which the mass flow rate is known.

3. The method of claim 2 wherein the calibration procedure comprises:

measuring a calibration pressure;

measuring a calibration temperature;

determining a calibration density based on the calibration pressure and the calibration temperature;

determining a calibration velocity;

determining a calibration volumetric flow rate;

determining the corrected pressure using the known mass flow rate, the calibration temperature, and the calibration volumetric flow rate; and

determining the constant k_diff by using the following formula;

4. The method of claim 2 wherein the calibration procedure comprises:

measuring a calibration pressure;

measuring a calibration temperature;

determining a calibration density based on the calibration pressure and the calibration temperature;

determining a calibration velocity;

determining a volumetric flow-rate; and

determining the constant k_diff by using the following formula;

5. The method of claim 1 wherein determining the velocity comprises using a vortex flow meter to determine the velocity.

6. A computer-readable medium having instructions stored thereon that when executed result in at least the following:

measuring a pressure of a fluid flowing through a system;

measuring a temperature of the flowing fluid;

determining a density based on the pressure and the temperature;

determining a velocity of the flowing fluid;

determining a corrected pressure for the flowing fluid based on the pressure, the temperature, and the velocity, the corrected pressure corresponding to a density reflective of the velocity and a mass flow rate, and wherein determining the corrected pressure comprises using the following formula;

7. The device of claim 6 wherein the device comprises a compact diskette.

8. The device of claim 6 wherein the instructions for determining the velocity comprise instructions for determining the velocity based on input describing a frequency of vortex-shredding pressure variations of the fluid.

9. The device of claim 6 further comprising a controller that is part of a transmitter in a vortex flow meter system, the controller being operable to execute the instructions.

10. A method of calibrating a device, the method comprising:

measuring a pressure of a fluid flowing in a system;

measuring a temperature of the flowing fluid;

determining a density of the flowing fluid based on the pressure and the temperature;

determining a velocity of the flowing fluid;

determining a volumetric flow rate of the flowing fluid;

determining a corrected pressure using a mass flow rate, the determined volumetric flow rate, and the measured temperature, wherein the corrected pressure corresponds to a corrected density reflective of the determined velocity and the mass flow rate;

determining a calibration constant k_diff according to the following equation;

11. The method of claim 10 wherein the calibration constant k_diff can be used to determine another corrected pressure during operation with a second mass flow rate according to the following equation:

12. The method of claim 10 wherein:

the device comprises a vortex flow meter,

the method further comprises using the vortex flow meter to measure a vortex frequency of the flowing fluid, and

the velocity is determined based on the measured vortex frequency.

13. A device comprising a storage medium having instructions stored thereon that when executed result in at least the following:

measuring a pressure of a fluid flowing in a system;

measuring a temperature of the flowing fluid;

determining a density of the flowing fluid based on the pressure and the temperature;

determining a velocity of the flowing fluid;

determining a volumetric flow rate of the flowing fluid;

determining a corrected pressure using a mass flow rate, the determined volumetric flow rate, and the measured temperature, wherein the corrected pressure corresponds to a corrected density reflective of the determined velocity and the mass flow rate;

determining a calibration constant k_diff according to the following equation;

14. The device of claim 13 further comprising a controller that is part of a transmitter in a vortex flow meter system, the controller being operable to execute the instructions.

15. A method of calibrating a device, the method comprising:

measuring a pressure of a fluid flowing in a system;

measuring a temperature of the flowing fluid;

determining a density of the flowing fluid based on the pressure and the temperature;

determining a velocity of the flowing fluid;

determining a volumetric flow rate of the flowing fluid;

determining a calibration constant, using a known speed of sound in the flowing fluid and a mass flow rate, according to the following equation;

16. The method of claim 15 wherein:

the calibration constant k_diff can be used to determine a corrected pressure during operation with a second mass flow rate according to the following equation;

17. The method of claim 15 wherein:

the device comprises a vortex flow meter,

the method further comprises using the vortex flow meter to measure a vortex frequency of the flowing fluid, and

the velocity and the volumetric flow rate of the flowing fluid are determined based on the vortex frequency.

18. A device comprising a storage medium having instructions stored thereon that when executed result in at least the following:

measuring a pressure of a fluid flowing in a system;

measuring a temperature of the flowing fluid;

determining a density of the flowing fluid based on the pressure and the temperature;

determining a velocity of the flowing fluid;

determining a volumetric flow rate of the flowing fluid;

determining a calibration constant, using a known speed of sound in the flowing fluid and a mass flow rate, according to the following equation;

19. The device of claim 18 further comprising a controller that is part of a transmitter in a vortex flow meter system, the controller being operable to execute the instructions.

20. A method of computing density, the method comprising:

accessing a pressure input and a temperature input;

determining a density error for the pressure input and temperature input based on one or more stored density errors, wherein the one or more stored density errors each reflect error between a density approximation and a standard density value for a different pressure input and temperature input;

determining a density approximation for the pressure input and temperature input, according to the following equation;

21. The method of claim 20 wherein determining the density error for the pressure input and temperature input comprises interpolating between at least two stored density errors.

22. The method of claim 21 wherein interpolating comprises linear interpolating.

23. The method of claim 20 wherein the one or more stored density errors comprises multiple stored density errors and the multiple stored density errors represent density errors for different pressure and temperature inputs that are not equally spaced in at least one of pressure or temperature.

24. The method of claim 23 wherein the spacing of at least one of pressure and temperature is closer for a first pressure and temperature range than for a second pressure and temperature range, and density changes more rapidly within the first range than the second range.

25. The method of claim 20 wherein the one or more stored density errors comprises multiple stored density errors and the multiple stored density errors have each been scaled.

26. The method of claim 20 wherein error between a given density approximation and a given standard density value is expressed as a ratio involving the given density approximation and the given standard density value.

27. The method of claim 20 wherein the one or more stored density errors comprises stored density errors for pressure and temperature inputs on both a first side and a second side of a saturation line, and stored density errors for pressure and temperature inputs on the second side are based on an extrapolation of standard density values for pressure and temperature inputs on the first side.

28. The method of claim 20 wherein:

determining the density approximation for the pressure input and temperature input comprises using an approximation equation that is a third order, or lower order, equation, and

an error between the determined density value and a standard density value for the pressure input and temperature input is 0.1% or less.

29. The method of claim 20 wherein determining the density approximation for the pressure input and temperature input comprises using a virial equation.

30. The method of claim 20 wherein determining the density approximation for the pressure input and temperature input comprises using an approximation equation that has been tailored to a range of densities needed.

31. The method of claim 30 wherein the approximation equation comprises a virial equation having coefficients that have been tailored to the range of densities needed.

32. The method of claim 20 further comprising:

determining a volumetric flow rate of a fluid based on input describing a frequency of vortex-shredding pressure variations of the fluid; and

determining mass flow rate of the fluid based on the volumetric flow rate and the density value.

33. The method of claim 20 further comprising:

determining a volumetric flow rate of a fluid using a vortex flow meter; and

determining mass flow rate of the fluid based on the volumetric flow rate and the density value.

34. A device comprising a storage medium having instructions stored thereon that when executed result in at least the following:

accessing a pressure input and a temperature input;

determining a density error for the pressure input and temperature input pair based on one or more stored density errors, wherein the one or more stored density errors each reflect error between a density approximation and a standard density value for a different pressure input and temperature input;

determining a density approximation for the pressure input and temperature input, according to the following equation;

35. The device of claim 34 further comprising a controller that is part of a transmitter in a vortex flow meter, the controller being operable to execute the instructions.