Vibrating tube meter
AssigneeABB AB
InventorTroy Wray
Life of this patent
Estimating the term…
Abstract
In a vibrating tube meter such as a Coriolis meter, an accurate measurement of a fluid parameter such as density can be obtained, substantially independent of stress, by measuring vibrational characteristics, particular resonant frequencies of two different vibrational modes. Stress or other variables can be determined from the measurement. Because the measurement of or compensation for stress is based directly on the vibrational characteristics, better accuracy may be obtained than by using a conventional strain gauge to measure stress. The techniques disclosed can give accurate results without requiring particular constraints on meter design.
Claims62
Use of measurements of resonant frequencies for two or more independent vibrational modes of a metering tube to obtain a measure of density of fluid in the metering tube compensated for variation of stress in the metering tube or to obtain a measure of stress in the metering tube, the method comprising wherein the ratio of said resonant frequencies is dependent on density and wherein the stress is determined as a non-linear function of ratio of said resonant frequencies.
Apparatus for obtaining a measure of stress in a fluid metering tube, the fluid having a density, the apparatus comprising:
- exciter means for inducing first and second vibration modes in the tube and obtaining a first resonant frequency of the first vibration mode which is a first function of stress and density;
- frequency measurement means for obtaining a second resonant frequency of the second vibration mode which is a second function of stress and density;
- and
- processing means for deriving said measure of stress from said first and second resonant frequencies based on determining possible pairs of values of stress and density corresponding to one of the first and second resonant frequency and selecting a pair of values based on the other of the first and second resonant frequencies.
Apparatus for obtaining a measure of density of a fluid in a metering tube, the tube being subjected to stress, the apparatus comprising:
- exciter means for inducing first and second vibration modes in the tube and obtaining a first resonant frequency of the first vibration mode which is a first function of stress and density;
- frequency determining means for obtaining a second resonant frequency of the second vibration mode which is a second function of stress and density;
- and
- processing means for deriving said measure of density from said first and second resonant frequencies based on modeling the fluid density as a first function of stress and the first resonant frequency and modeling the fluid density as a second function of stress and the second resonant frequency and solving to eliminate stress.
A method of obtaining a measure of density of fluid in a metering tube, the tube being subjected to a stress, the method comprising inducing first and second vibration modes in the tube and obtaining a first resonant frequency of the first vibration mode which is a first function of stress and density;
- obtaining a second resonant frequency of the second vibration mode which is a second function of stress and density;
- and deriving said measure of density from said first and second resonant frequencies based on modeling the fluid density as a first function of stress and the first resonant frequency and modeling the fluid density as a second function of stress and the second resonant frequency and solving to eliminate stress.
A method of obtaining a measure of stress in a fluid metering tube, the fluid having a density, the method comprising inducing first and second vibration modes in the tube and obtaining a first resonant frequency of the first vibration mode which is a first function of stress and density;
- obtaining a second resonant frequency of the second vibration mode which is a second function of stress and density;
- and deriving said measure of stress from said first and second resonant frequencies based on determining possible pairs of values of stress and density corresponding to one of the first and second resonant frequency and selecting a pair of values based on the other of the first and second resonant frequencies.
Apparatus for obtaining a measure of stress in a fluid metering tube, the fluid having a density, the apparatus comprising:
- exciter means for inducing first and second vibration modes in the tube and obtaining a first resonant frequency of the first vibration mode which is a first function of stress and density;
- frequency measurement, means for obtaining a second resonant frequency of the second vibration mode which is a second function of stress and density;
- and
- processing means for deriving said measure of stress from said first and second resonant frequencies based on modeling the fluid density as a first function of stress and the first resonant frequency and modeling the fluid density as a second function of stress and the second resonant frequency and solving to determine stress as a function of said frequencies.
A method of obtaining a measure of stress in a fluid metering tube, the fluid having a density, the method comprising inducing first and second vibration modes in the tube and obtaining a first resonant frequency of the first vibration mode which is a first function of stress and density;
- obtaining a second resonant frequency of the second vibration mode which is a second function of stress and density;
- and deriving said measure of stress from said first and second resonant frequencies based on modeling the fluid density as a first function of stress and the first resonant frequency and modeling the fluid density as a second function of stress and the second resonant frequency and solving to determine stress as a function of said frequencies.
Dependencies are inferred from the claim text.