Multi-measurement vortex flow meter

• US 20040049358A1
• Filed: 09/06/2002
• Published: 03/11/2004
• 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.
• Granted Patent: US 7,212,928 B2
• Time in Patent Office: Days
• 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 specifying a transmitter, the transmitter for regulating an amplitude of a supplied current to encode a parameter, the method comprising providing a set of data to a customer, wherein the set of data represents a maximum allowable load at one or more supply voltage levels, and the set of data has a first segment operable only for a lower range of currents below a transition current and has a second segment operable only for a higher range of currents above the transition current.

2. The method of claim 1 wherein:

the first segment results from the transmitter multiplying a regulated current by a first non-unitary factor when the regulated current is within the lower range of currents, and

the second segment results from the transmitter multiplying the regulated current by a second non-unitary factor when the regulated current is within the higher range of currents.

3. The method of claim 2 wherein the first segment approximates a first line having a first slope, the second segment approximates a second line having a second slope, and the first slope is at least twice as large as the second slope.

4. A method of controlling a current signal, the method comprising:

receiving a current with a variable amplitude over a line, the amplitude being regulated;

multiplying the regulated amplitude by a first non-unitary factor when the regulated amplitude is below a first level;

multiplying the regulated amplitude by a second non-unitary factor when the regulated amplitude is above a second level;

maintaining a constant set of operating voltages whether the regulated amplitude is multiplied by the first non-unitary factor or the second non-unitary factor; and

providing the multiplied amplitude and the constant set of operating voltages to circuitry.

5. The method of claim 4 wherein:

receiving the variable current comprises receiving the current at a transmitter, and

the amplitude is regulated by the transmitter to communicate an output parameter by encoding a value of the output parameter on the current.

6. The method of claim 4 wherein maintaining a constant set of operating voltages comprises using a reversible power transformation.

7. The method of claim 6 wherein:

multiplying by the first non-unitary factor comprises injecting the regulated current into an input of a first multiplier and coupling an output of the first multiplier to an input of a second multiplier,

multiplying by the second non-unitary factor comprises injecting the regulated current into the input of the second multiplier and into the output of the first multiplier, and

maintaining the constant set of operating voltages comprises using a reversible multiplier for the first multiplier, allowing regulated current that is coupled to the output of the first multiplier to produce a current emanating from the input to the first multiplier and having an amplitude approximately equal to the regulated current divided by the first non-unitary factor.

8. The method of claim 7 wherein maintaining the constant set of operating voltages further comprises regulating a voltage at the input of the first multiplier, providing the same voltage whether the regulated current is injected into the input of the first multiplier or the input of the second multiplier.

9. The method of claim 4 wherein the transmitter receives power from a supply over the line.

10. The method of claim 9 wherein the regulated current extends over a range of about 4 milliamps to 20 milliamps.

11. The method of claim 5 wherein the output parameter is a vortex frequency, a linear flow rate, or a volumetric flow rate.

12. The method of claim 4 wherein:

receiving the variable current comprises receiving the current at a transmitter, and the amplitude is regulated before being received by the transmitter.

13. A transmitter comprising:

a switching circuit configured to couple a regulated current to either a first output or a second output based on an amplitude of the regulated current;

a first non-unitary current multiplier having an input and an output, with the input of the first non-unitary multiplier being coupled to the first output of the switching circuit, the first non-unitary multiplier operable in a forward direction as a current multiplier and in a backward direction as a current divider; and

a second non-unitary multiplier having an input and an output, with the input of the second non-unitary multiplier coupled to both the second output of the switching circuit and the output of the first non-unitary multiplier.

14. The transmitter of claim 13 further comprising a current regulator coupled to an input of the switching circuit and configured to regulate the amplitude of the current to encode a value of an output parameter on the current.

15. The transmitter of claim 14 wherein the current regulator is configured to receive the current over a line in a two-wire system.

16. The transmitter of claim 15 wherein the current regulator is configured to regulate the amplitude over a range extending at least from 4 milliamps to 20 milliamps.

17. The transmitter of claim 14 wherein the current regulator is configured as part of a vortex flow meter system and is configured to encode a value of a vortex frequency, a linear flow rate, or a volumetric flow rate.

18. A transmitter comprising:

switching means, having a first output and a second output, for coupling a regulated current to either the first output or the second output based on an amplitude of the regulated current;

first means for multiplying current by a non-unitary number, the first means having an input and an output, with the input of the first means being coupled to the first output of the switching means, the first means being operable in a forward direction as a current multiplier and in a backward direction as a current divider; and

second means for multiplying current by a non-unitary number, the second means having an input and an output, with the input of the second means being coupled to both the second output of the switching means and the output of the first means.

19. The transmitter of claim 18 further comprising regulating means coupled to the switching means for regulating the amplitude of the current to encode a value of an output parameter on the current.

20. 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 velocity of the flowing fluid; and

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.

21. The method of claim 20 further comprising determining a density based on the pressure and the temperature, and wherein determining the corrected pressure comprises using the following formula:

22. The method of claim 21 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.

23. The method of claim 22 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;

$k_{\mathrm{diff}}=\frac{2\times <br><br>\left(P_c-P_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}\right)}{{\mathrm{\rho <br><br>}}_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}\times <br><br>V_{\mathrm{VOR}}^2}.$

24. The method of claim 22 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;

$k_{\mathrm{diff}}=2\times <br><br>{\left(\frac{c}{V_{\mathrm{VOR}}}\right)}^2\times <br><br>\left(\frac{Q_m}{{\mathrm{\rho <br><br>}}_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}\times <br><br>Q_v}-1\right).$

25. The method of claim 20 further comprising:

determining a volumetric flow rate from the velocity;

determining the density; and

determining a mass flow rate from the volumetric flow rate and the density.

26. The method of claim 20 wherein determining the velocity comprises:

using a vortex flow meter to determine a vortex frequency; and

determining the velocity based on the vortex frequency.

27. 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 through a system;

measuring a temperature of the flowing fluid;

determining a velocity of the flowing fluid; and

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.

28. The device of claim 27 further comprising a controller that is part of a transmitter in a vortex flow meter system, the controller being operable to execute the instructions.

29. The device of claim 27 wherein the device comprises a compact diskette.

30. 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; and

determining a calibration constant k_diff according to the following equation;

$k_{\mathrm{diff}}=\frac{2\times <br><br>\left(P_c-P_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}\right)}{{\mathrm{\rho <br><br>}}_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}\times <br><br>V_{\mathrm{VOR}}^2}.$

31. The method of claim 30 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:

32. The method of claim 30 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.

33. 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; and

determining a calibration constant k_diff according to the following equation;

$k_{\mathrm{diff}}=\frac{2\times <br><br>\left(P_c-P_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}\right)}{{\mathrm{\rho <br><br>}}_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}\times <br><br>V_{\mathrm{VOR}}^2}.$

34. The device of claim 33 further comprising a controller that is part of a transmitter in a vortex flow meter system, the controller being operable to execute the instructions.

35. 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; and

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

$k_{\mathrm{diff}}=2\times <br><br>{\left(\frac{c}{V_{\mathrm{VOR}}}\right)}^2\times <br><br>\left(\frac{Q_m}{{\mathrm{\rho <br><br>}}_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}\times <br><br>Q_v}-1\right).$

36. The method of claim 35 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;

$P_c\cong <br><br>P_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}+\frac{1}{2}\times <br><br>k_{\mathrm{diff}}\times <br><br>{\mathrm{\rho <br><br>}}_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}\times <br><br>V_{\mathrm{VOR}}^2,\mathrm{and}$

the corrected pressure corresponds to a corrected density reflective of the determined velocity and the second mass flow rate.

37. The method of claim 35 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.

38. 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; and

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

$k_{\mathrm{diff}}=2\times <br><br>{\left(\frac{c}{V_{\mathrm{VOR}}}\right)}^2\times <br><br>\left(\frac{Q_m}{{\mathrm{\rho <br><br>}}_{p<br><br>\text{\hspace{1em}<br><br>}<br><br>s}\times <br><br>Q_v}-1\right).$

39. The device of claim 38 further comprising a controller that is part of a transmitter in a vortex flow meter system, the controller being operable to execute the instructions.

40. 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; and

determining a density value for the pressure input and temperature input based on the density error for the pressure input and temperature input and the density approximation for the pressure input and temperature input.

41. The method of claim 40 wherein determining the density error for the pressure input and temperature input comprises interpolating between at least two stored density errors.

42. The method of claim 41 wherein interpolating comprises linear interpolating.

43. The method of claim 40 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.

44. The method of claim 43 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.

45. The method of claim 40 wherein the one or more stored density errors comprises multiple stored density errors and the multiple stored density errors have each been scaled.

46. The method of claim 40 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.

47. The method of claim 40 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.

48. The method of claim 40 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.

49. The method of claim 40 wherein determining the density approximation for the pressure input and temperature input comprises using a virial equation.

50. The method of claim 40 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.

51. The method of claim 50 wherein the approximation equation comprises a virial equation having coefficients that have been tailored to the range of densities needed.

52. 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; and

determining a density value for the pressure input and temperature input based on the density error for the pressure input and temperature input and the density approximation for the pressure input and temperature input.

53. The device of claim 52 further comprising a controller that is part of a transmitter in a vortex flow meter, the controller being operable to execute the instructions.

54. A device comprising a storage medium having stored thereon density errors computed using at least the following operations:

determine a standard density value for each of multiple pressure and temperature input pairs;

determine a density approximation for each of the multiple pressure and temperature input pairs; and

determine a density error, based on the standard density value and the density approximation, for each of the multiple pressure and temperature input pairs.

55. The device of claim 54 wherein the multiple pressure and temperature input pairs are not equally spaced in at least one of pressure or temperature.

56. The device of claim 55 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.

57. The device of claim 54 wherein the multiple determined density errors are scaled before being stored on the storage medium.

58. The device of claim 54 wherein determining the density error for each of the multiple pressure and temperature input pairs comprises determining a ratio involving the standard density value and the density approximation for each of the pressure and temperature input pairs.

59. The device of claim 54 wherein:

the multiple pressure and temperature input pairs include pairs on both a first side and a second side of a saturation line, and

determining a standard density value for pressure and temperature input pairs on the second side is based on an extrapolation of standard density values for pressure and temperature input pairs on the first side.

60. The device of claim 54 wherein determining the density approximation for each of the multiple pressure and temperature input pairs comprises using an approximation equation that is a third order, or lower order, equation.

61. The device of claim 54 wherein determining the density approximation for each of the multiple pressure and temperature input pairs comprises using a virial equation.

62. The device of claim 54 wherein determining the density approximation for each of the multiple pressure and temperature input pairs comprises using an approximation equation that has been tailored to a range of the determined standard density values.

63. The device of claim 54 wherein determining the density approximation for each of the multiple pressure and temperature input pairs comprises using a virial equation having coefficients that have been tailored to the range of the determined standard density values.