System for validating calibration of a coriolis flowmeter

• US 6,092,409 A
• Filed: 01/29/1998
• Issued: 07/25/2000
• Est. Priority Date: 01/29/1998
• Status: Expired due to Term

• Current Assignee: Micro Motion Incorporated (Emerson Electric Company)
• Original Assignee: Micro Motion Incorporated (Emerson Electric Company)
• Inventors: Patten, Andrew T., Stack, Charles Paul
• Primary Examiner(s): NOLAND, THOMAS
• Application Number:
  US09/015,737
• Time in Patent Office: 908 Days
• Field of Search: 73/1.34, 73/1.31, 702/100
• US Class Current: 73/1.34
• CPC Class Codes: G01F 1/8413 means for influencing the flowmeter's motional or vibrational behaviour, e.g., conduit support or fixing means, or conduit attachments
• CPC Class Codes: G01F 1/8431 electronic circuits
• CPC Class Codes: G01F 1/8436 signal processing
• CPC Class Codes: G01F 1/8477 with multiple measuring conduits

Abstract

A System for validating a flow calibration factor for a Coriolis flow meter. In accordance with the present invention, the period of oscillation of a flow tube is measured as a material of a known density flow through the flow tube. The period of oscillation is used in an equation derived from an equation used to calculate the density of material flowing through the flow tube to find a result. The result is then compared to a result derived from the known density of the material to detect a possible error condition in the flow tube. If an error condition exists an error signal is generated that indicates the Coriolis flow meter should be inspected.

Claims

1. A system for validating a mass flow calibration of a Coriolis flowmeter comprising:

means for flowing a material through a flow tube of said Coriolis flowmeter;

means for oscillating said flow tube as said material flows through said flow tube;

means for measuring a period of oscillation of said flow tube as said material flows through said flow tube;

means responsive to measuring of said period of oscillation for detecting a calibration error condition; and

means responsive to a detection of said calibration error condition for signaling said calibration error condition exists.

2. The system of claim 1 wherein said material flowing through said flow tube has a known density and said means for detecting said calibration error condition comprises:

means responsive to measuring of said period of oscillation for computing a calculated density for said material;

means for comparing said calculated density of said material to said known density of said material; and

means responsive to said calculated density not being equal to said known density for determining said calibration error condition exists.

3. The system of claim 1 wherein said material flowing through said flow tube has a known density and said means for detecting said calibration error condition comprises:

means for computing a calculated density of said material from said period of oscillation of said flow tube;

means for calculating a deviation of said calculated density from said known density;

means for comparing said deviation to an acceptable tolerance range; and

means for determining said calibration error condition exists responsive to said deviation being outside of said acceptable tolerance range.

4. The system of claim 3 wherein said validating of said mass flow calibration of said Coriolis flowmeter is performed at periodic intervals and said system further comprises:

means for storing said deviation calculated for each validation of said mass flow calibration performed;

means responsive to storing said deviation of each validation for determining an upper limit of said tolerance range for said deviation of each said validation of said mass flow calibration performed; and

means responsive to storing said deviation of each validation for determining a lower limit of said tolerance range for said deviation of each said validation of said mass flow calibration performed.

5. The system of claim 1 wherein said means for detecting said calibration error condition comprises:

means for measuring the density of said material flowing through said flow tube;

means for determining a calculated density of said material from said period of oscillation of said flow tube;

means for comparing said calculated density of said material and said measured density of said material; and

means for determining a calibration error condition exists responsive to said calculated density of said material not being equal to said measured density of said material.

6. The system of claim 1 wherein a first density constant for calculating a density of a material flowing through said flow tube squared is known and said means for detecting said calibration error condition comprises:

means for calculating a new first density constant from said measured period of oscillation for said material;

means for comparing said first density constant to said known first density constant; and

means responsive to said new first density constant not being equal to said known first density constant for determining said calibration error condition exists.

7. The system of claim 6 wherein said means for determining said new first density constant comprises:

means for calculating a square of said measured period of oscillation of said flow tube;

means for subtracting a known square of period of oscillation of said flow tube for a reference material having a known density from said square of said measured period of oscillation to determine a first result;

means for subtracting said known density of said reference material from said known density of said material flowing through said flow tube to determine a second result; and

means for dividing said second result by said first result to determine said second slope to determine said new first density constant.

8. The system of claim 7 further comprising:

means for measuring the density of said material flowing through said flow tube.

9. The system of claim 7 wherein the density of said material is known.

10. The system of claim 6 further comprising:

means responsive to a detection of said calibration error condition for detecting uniform corrosion in said flow tube.

11. The system of claim 10 further comprising:

means responsive to determining of said uniform corrosion in said flow tube for dividing said new first density constant by said known first density constant to determine a result;

means responsive to determining said second result for multiplying a Flow Calibration Factor of said flow tube by said result to determine a new Flow Calibration Factor to be used in a determination of mass flow rates in said Coriolis flowmeter.

12. The system of claim 10 further comprising:

means responsive to a detection of uniform corrosion for determining the amount of uniform corrosion.

13. The system of claim 1 wherein said means for detecting said calibrationerror condition comprises:

means for comparing said measured period of oscillation of said material to an expected period of oscillation for said material; and

means for determining said calibration error condition exists responsive to said measured period of oscillation for said material not being equal to said expected period of oscillation of said material.

14. The system of claim 13 further comprising:

means for determining said expected period of oscillation for said material from the density of said material.

15. The system of claim 14 further comprising:

means for determining the density of said material flowing through said flow tube.

16. A method for validating a mass flow calibration of a Coriolis flowmeter comprising the steps of:

flowing a material through a flow tube of said Coriolis flowmeter;

oscillating said flow tube as said material flows through said flow tube;

measuring a period of oscillation of said flow tube as said material flows through said flow tube;

detecting a calibration error condition responsive to measuring said period of oscillation; and

signaling said calibration error condition exists responsive to a detection of said calibration error condition.

17. The method of claim 16 wherein said material flowing through said flow tube has a known density and said step for detecting said calibration error condition comprises the steps of:

computing a calculated density for said material responsive to said period of oscillation;

comparing said calculated density of said material to said known density of said material; and

determining said calibration error condition exists responsive to said calculated density not being equal to said known density.

18. The method of claim 16 wherein said material flowing through said flow tube has a known density and said step for detecting said calibration error condition comprises the steps of:

computing a calculated density of said material from said period of oscillation of said flow tube;

calculating a deviation of said calculated density from said known density;

comparing said deviation to an acceptable tolerance range; and

determining said calibration error condition exists responsive to said deviation being outside of said acceptable tolerance range.

19. The method of claim 18 wherein said method validating said mass flow calibration factor of said Coriolis flowmeter is performed at periodic intervals and said system further comprises:

storing said deviation calculated for each validation of said mass flow calibration performed;

determining an upper limit of said tolerance range on said deviation of each said validation of said mass flow calibration performed responsive to storing said deviation of each validation; and

determining a lower limit of said tolerance range for said deviation of each said validation of said mass flow calibration performed responsive to storing said deviation of each validation.

20. The method of claim 16 wherein said step for detecting said calibration error condition comprises the steps of:

measuring the density of said material flowing through said flow tube;

determining a calculated density of said material from said period of oscillation of said flow tube;

comparing said calculated density of said material and said measured density of said material; and

determining a calibration error condition exists responsive to said calculated density of said material not being equal to said measured density of said material.

21. The method of claim 16 wherein a first density constant for calculating a density of a material flowing through said flow tube squared is known and said step for detecting said calibration error condition comprises the steps of:

calculating a new first density constant from said measured period of oscillation for said material;

comparing said new first density constant to said known first density constant; and

determining said calibration error condition exists responsive to said new first density constant not being equal to said known first density constant.

22. The method of claim 21 wherein said step for determining said new first density constant comprises the steps of:

calculating a square of said measured period of oscillation of said flow tube;

subtracting a known square of period of oscillation of said flow tube for a reference material having a known density from said square of said measured period of oscillation to determine a first result;

subtracting said known density of said reference material from said known density of said material flowing through said flow tube to determine a second result; and

dividing said second result by said first result to determine said second slope to determine said new first density constant.

23. The method of claim 22 further comprising the steps of:

measuring the density of said material flowing through said flow tube.

24. The method of claim 22 wherein the density of said material is known.

25. The method of claim 21 further comprising the step of:

detecting uniform corrosion in said flow tube responsive to said calibration error condition being detected.

26. The method of claim 25 further comprising the steps of:

dividing said new first density constant by said known first density constant to determine a result responsive to a detection of said uniform corrosion in said flow tube;

multiplying a Flow Calibration Factor of said flow tube by said result to determine a new Flow Calibration Factor to be used in a determination of mass flow rates in said Coriolis flowmeter responsive to determining said second result.

27. The method of claim 25 further comprising the steps of:

determining the amount of corrosion of said flow tube responsive to a detection of corrosion.

28. The method of claim 16 wherein said step for detecting said calibration error condition comprises steps of:

comparing said measured period of oscillation of said material to an expected period of oscillation for said material; and

determining said calibration error condition exists responsive to said measured period of oscillation for said material not being equal to said expected period of oscillation of said material.

29. The method of claim 28 further comprising the step of:

determining said expected period of oscillation for said material from the density of said material.

30. The method of claim 29 further comprising step of:

determining the density of said material flowing through said flow tube.