HK1114900B - Coriolis flow meter and method for determining flow characteristics - Google Patents

Description

Coriolis flow meter and method for determining flow characteristics

Technical Field

The present invention relates to a coriolis flow meter and method for determining flow characteristics, and more particularly to a coriolis flow meter and method for determining flow characteristics using two or more vibrational responses.

Background

Vibrating conduit sensors, such as coriolis mass flowmeters, typically operate by detecting the motion of a vibrating conduit containing a flow material. A characteristic associated with the substance in the conduit, such as mass flow, density, etc., may be determined by processing measurement signals received from a motion transducer associated with the conduit. The vibration modes of a vibrating mass-filled system are generally affected by the combined mass, stiffness and damping characteristics of the containing conduit and the mass contained therein.

A typical coriolis mass flowmeter includes one or more conduits that are connected in series in a pipeline or other transport system and carry material, such as liquid, slurry, or the like, in the system. Each conduit can be viewed as having a set of natural vibration modes including, for example, simple bending, torsional, radial, and coupled modes. In a typical coriolis mass flow measurement application, a conduit is excited in one or more vibration modes as a material flows through the conduit, and the motion of the conduit is measured at various points spaced along the conduit. The excitation is typically provided by an actuator, e.g. an electromechanical device, such as a voice coil type driver, which perturbs the conduit in a periodic manner. By measuring the time delay or phase difference between the motions at multiple transducer locations, the mass flow rate can be determined. Two such transducers (or pickoff sensors) are typically employed to measure the vibrational response of the flow conduit or conduits, and are typically located at positions upstream and downstream of the actuator. The two pickoff sensors are connected to the electronics by cabling, such as two pairs of independent wires. The instrument receives signals from the two pickoff sensors and processes the signals to derive a mass flow rate measurement.

Conventional coriolis mass flowmeters provide continuous measurements of the mass flow rate, density, and temperature of the flow medium flowing through the flowmeter. However, any change in the flow characteristics of the flowing medium can cause an increase or decrease in the mass loaded on the flow meter, thus causing an error, particularly in the indicated density.

Designers of vibrating element transducers, such as coriolis mass flowmeters or densitometers, typically attempt to maximize sensitivity to mass, density, and temperature while minimizing the sensitivity of the transducer to viscosity, VOS, shear rate, pressure, and reynolds number. Thus, typical prior art flow meters are capable of accurately measuring mass, density, and temperature, but are not capable of accurately measuring additional flow characteristics, such as one or more of viscosity, VOS, shear rate, pressure, and reynolds number. In flowmeter applications, other flow characteristics besides mass, density and temperature need to be measured.

Disclosure of Invention

The present invention helps to address problems associated with determining flow characteristics of a flow meter.

According to one embodiment of the present invention, a coriolis flow meter is provided. The coriolis flow meter includes one or more flow tubes, at least two pickoff sensors secured to the one or more flow tubes, a driver configured to vibrate the one or more flow tubes, and meter electronics coupled to the at least two pickoff sensors and the driver. The meter electronics is configured to: vibrating the one or more flow tubes of the flow meter with a first vibration frequency and in a first out-of-phase bending mode; measuring a first vibrational response of the one or more flow tubes, wherein the first vibrational response is generated in response to a first vibrational frequency; vibrating the one or more flow tubes with at least a second vibration frequency and in a first out-of-phase bending mode; measuring a second vibrational response, wherein the second vibrational response is generated in response to a second vibrational frequency; and determining at least the mass flow rate and the viscosity using the first vibrational response and the second vibrational response.

In accordance with one embodiment of the present invention, a method for determining flow characteristics in a coriolis flow meter is provided. The method comprises the following steps: one or more flow tubes of the flow meter are vibrated with a first vibration frequency and in a first out-of-phase bending mode, and a first vibrational response of the one or more flow tubes is measured. The first vibrational response is generated in response to a first vibrational frequency. The method further comprises the following steps: the one or more flow tubes are vibrated with at least a second vibration frequency and in a first out of phase bending mode, and a second vibrational response is measured. The second vibrational response is generated in response to a second vibrational frequency. The method further comprises the following steps: the first vibrational response and the second vibrational response are used to determine at least a mass flow rate and a viscosity of the flowing medium.

In accordance with one embodiment of the present invention, a coriolis flow meter software product for determining flow characteristics in a coriolis flow meter is provided. The software product includes control software configured to direct a processing system to: vibrating one or more flow tubes of the flow meter with a first vibration frequency and in a first out-of-phase bending mode; measuring a first vibrational response of the one or more flow tubes, wherein the first vibrational response is generated in response to a first vibrational frequency; vibrating the one or more flow tubes with at least a second vibration frequency and in a first out-of-phase bending mode; measuring a second vibrational response, wherein the second vibrational response is generated in response to a second vibrational frequency; and using the first vibrational response and the second vibrational response to determine at least a mass flow rate and one or more flow characteristics. The software product further includes a storage system storing the control software.

Several aspects

In one aspect, the determining further comprises determining a density.

In another aspect, the determining step includes determining a shear rate.

In yet another aspect, the determining further comprises determining a reynolds number.

In yet another aspect, the determining further includes determining a speed of sound (VOS).

In yet another aspect, the determining further comprises determining a pressure.

In yet another aspect, the viscosity comprises kinematic (kinematical) viscosity.

In yet another aspect, the viscosity comprises a dynamic viscosity.

In yet another aspect, the vibrating further comprises hopping between the first vibration frequency and the second vibration frequency.

In yet another aspect, the vibrating further comprises vibrating the one or more flow tubes substantially simultaneously with the first vibration frequency and the second vibration frequency.

In yet another aspect, the vibrating further comprises sweeping between the first vibration frequency and the second vibration frequency over a predetermined sweep period.

In yet another aspect, the first vibration frequency and the second vibration frequency are substantially equally spaced above and below a fundamental frequency of the one or more flow tubes.

In yet another aspect, the one or more flow tubes comprise two substantially U-shaped flow tubes.

Drawings

Fig. 1 illustrates a coriolis flow meter including a flow meter assembly and meter electronics.

FIG. 2 shows meter electronics according to one embodiment of the present invention.

Fig. 3 is a flow chart of a method of determining flow characteristics in a coriolis flow meter according to an embodiment of the invention.

FIG. 4A shows a diagram for a damping factorAnd figure 4B shows the corresponding phase response characteristic.

Fig. 5 shows a feedback loop for controlling the frequency of vibration applied to the flow meter assembly.

Detailed Description

Fig. 1-5 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will recognize variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. Accordingly, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.

Fig. 1 shows a coriolis flow meter 5 comprising a flow meter assembly 10 and meter electronics 20. Meter electronics 20 is connected to flow meter assembly 10 via leads 100 to provide density, mass flow rate, volumetric flow rate, total mass flow rate, temperature and other information on path 26.

The flow meter assembly 10 includes a pair of flanges 101 and 101 ', manifolds 102 and 102 ', a driver 104, a pickoff sensor 105 and 105 ', and flow tubes 103A and 103B. The driver 104 and pickoff sensors 105 and 105' are connected to the flow tubes 103A and 103B.

Flanges 101 and 101 'are secured to manifolds 102 and 102'. Manifolds 102 and 102' are secured to opposite ends of spacer 106. The spacer 106 maintains the spacing between the manifolds 102 and 102' to prevent undesirable vibration in the flow tubes 103A and 103B. When the flowmeter assembly 10 is inserted into a pipeline system (not shown) carrying the measured material, the material enters the flowmeter assembly 10 through the flange 101, passes through the inlet manifold 102 where all of the material is directed into the flow tubes 103A and 103B, flows through the flow tubes 103A and 103B, and returns to the outlet manifold 102 'where all of the material exits the flowmeter assembly 10 through the flange 101'.

Flow tubes 103A and 103B are selected and appropriately mounted to inlet manifold 102 and outlet manifold 102 ' so as to have substantially the same mass distribution, moment of inertia, and modulus of elasticity about bending axes W-W and W ' -W ', respectively. In a substantially parallel manner, the flow tubes extend outwardly from the manifold.

The flow tubes 103A-B are driven by the driver 104 in opposite directions about their respective bending axes W and W' and in a so-called first out of phase bending mode of the flow meter. Driver 104 may comprise one of many well-known structures, such as a magnet mounted to flow tube 103A and an opposing coil mounted to flow tube 103B. An alternating current is passed through the opposing coils to cause the two flow tubes to oscillate. A suitable drive signal is applied by the meter electronics 20 to the driver 104 via the conductor 100.

Meter electronics 120 transmits sensor signals on wires 111 and 111', respectively. Meter electronics 120 generates a drive signal on lead 110 that causes driver 104 to oscillate flow tubes 103A and 103B. The meter electronics 120 processes the left and right velocity signals from the pickoff sensors 105 and 105' to calculate the mass flow rate. The passageway 26 provides input and output means that allow the meter electronics 120 to interface with an operator. The description of fig. 1 is provided merely as an example of the operation of a coriolis flow meter and is not intended to limit the teachings of the present invention.

FIG. 2 shows meter electronics 20 according to one embodiment of the present invention. The meter electronics 20 includes a communication interface 201, a processing system 202, and a storage system 203. The processing system 202 is coupled to the communication interface 201.

The communication interface 201 enables communication between the meter electronics 20 and external devices. The communication interface 201 enables the calculated flow characteristic to be communicated to an external device via the pathway 26. The external devices may include the flow meter assembly 10 (via the leads of fig. 1), one or more monitoring devices (via the pathway 26 of fig. 1), or any form of user interface or communication device. The communication interface 201 enables the reception of flow measurements from the flow meter assembly 10 via the conductor 100. The communication interface 201 can enable any manner of electronic, optical, or wireless communication, for example. The interface 26 enables communication via a telephone system and/or a digital data network. Thus, the meter electronics 20 can communicate with a remote flow meter, remote processing/monitoring equipment, remote storage media, and/or a remote user.

The processing system 202 directs the operation of the meter electronics 20 and processes flow measurements from the flow meter assembly 10. Processing system 202 executes processing program 210 and processes the flow measurements to generate one or more flow characteristics. The processing system 202 may comprise a general purpose computer, a micro-processing system, a logic circuit, or some other general purpose or custom processing device. Processing system 202 may be distributed among multiple processing devices. Processing system 202 may include any manner of integrated or stand-alone electronic storage media, such as storage system 203. Alternatively, storage system 203 may include a separate electronic storage medium in communication with processing system 202.

The storage system 203 may store flow meter parameters and data, software programs, constant values, and variable values. In one embodiment, the storage system 203 includes a handler 210 that is executed by the processing system 202. The memory system 203 stores variables used to operate the flow meter assembly 10. In one embodiment, the storage system 203 stores variables such as a first vibration frequency 213, at least a second vibration frequency 212, a first vibration response 213, a second vibration response 214, and a sweep period 215.

The storage system 203 stores one or more flow characteristics obtained from the flow measurements. In one embodiment, the storage system 203 stores flow characteristics such as mass flow rate 220, density 221, kinematic viscosity 222, dynamic viscosity 223, shear rate 224, Reynolds number 225, velocity of sound (VOS)226, and damping factor (or quality factor) 227. It should be understood that other flow characteristics may also be determined and recorded, such as temperature and/or pressure.

The mass flow rate 220 is a measure of the mass flow through the flow meter assembly 10. Density 221 is the density of the flow material in flowmeter assembly 10.

The viscosity of a fluid can be defined as the resistance of the fluid to shear or flow and is a measure of the adhesive/bonding properties of the fluid. This resistance is caused by intermolecular friction forces exerted when a first fluid layer attempts to slide through another fluid layer. Measurement of the viscosity of a fluid is desirable in order to properly design and operate equipment for pumping, measuring, or otherwise handling the fluid.

Kinematic viscosity 222 may be defined as the ratio of kinematic viscosity to density. Kinematic viscosity 222 may be calculated from kinematic viscosity 223 and density 221. Kinematic viscosity 223 may be defined as the tangential force per unit area required to move one horizontal plane at a unit velocity relative to another while maintaining a unit distance separation by the fluid.

Shear rate 224 may be defined as the rate of change of the velocity of fluid passing one layer over another.

Reynolds number 225 may be defined as a measure of the importance of inertia to viscosity effects. At high reynolds numbers, the flow may become turbulent, showing different behavior in nature compared to the same liquid at low reynolds numbers.

The VOS206 is the speed of sound in the flowing medium. For example, the VOS206 may vary with the flowing medium, may vary with the density of the flowing medium, or may vary with the composition of the flowing medium.

The damping factor 227 may be defined as a measure of how the flow medium damps vibrations. Alternatively, the damping factor 227 may be defined as a measure of the viscosity of the flowing medium.

To determine the one or more flow characteristics, processing system 202 executes processing program 210. When executed by the processing system 202, the handler 210 configures the processing system 202 to: vibrating one or more flow tubes 103 of the flow meter 5 with a first vibration frequency 211; measuring a first vibrational response 213 of the one or more flow tubes 103, wherein the first vibrational response 213 is generated in response to the first vibrational frequency 211; vibrating the one or more flow tubes 103 at least a second vibration frequency 212; measuring a second vibrational response 214, wherein the second vibrational response 214 is generated in response to the second vibrational frequency 212; and using the first vibrational response 213 and the second vibrational response 214 to determine at least the mass flow rate 220 and the viscosity of the flow medium (see fig. 3).

The first vibration frequency 211 and the second vibration frequency 212 may include any desired frequency. In one embodiment, the first vibration frequency 211 and the second vibration frequency 212 are substantially equally spaced above and below the fundamental frequency of the flow meter assembly 10. However, other frequencies may be used depending on the flowing medium and the surrounding environment.

In one embodiment, the handler 210 may jump between the first vibration frequency 211 and the second vibration frequency 212. In an alternative embodiment, the processing program 210 may vibrate the one or more flow tubes 103 using the first vibration frequency and the second vibration frequency substantially simultaneously. In yet another alternative embodiment, the handler 210 may sweep the vibration of the driver 104 between a first vibration frequency 211 and a second vibration frequency 212, where the actual drive frequency is stepped between the two frequencies according to the sweep period 215.

Fig. 3 is a flow chart 300 of a method for determining flow characteristics in a coriolis flow meter 5 according to an embodiment of the invention. In step 301, the flow tube apparatus 10 is vibrated by the driver 104 with a first vibration frequency 211 and in a first out of phase bending mode. The first vibration frequency 211 can be a fundamental vibration frequency of the flow meter assembly 10, or can be a frequency above or below the fundamental frequency.

In step 302, a first vibrational response 213 is measured. The measurement includes receiving a signal from the pickoff sensors 105 and using the pickoff signals to determine a phase difference between the two pickoff sensors 105. A first vibrational response 213 is generated by the flow meter assembly 10 in response to the first vibrational frequency 211 generated by the driver 104.

In step 303, the flow tube apparatus 10 is vibrated by the driver 104 using the second vibration frequency 212 and in the first out of phase bending mode. The second vibration frequency 212 may be any frequency other than the first vibration frequency 211. In one embodiment, the first vibration frequency 211 and the second vibration frequency 212 are substantially equally spaced above and below the fundamental frequency of the flow meter assembly 10. However, as previously described, the first vibration frequency 211 and the second vibration frequency 212 may include any desired frequency.

In step 304, a second vibrational response 214 is measured. A second vibrational response 214 is generated by the flow meter assembly 10 in response to the second vibrational frequency 212 generated by the driver 104.

In step 305, mass flow rate and other flow characteristics are determined by the meter electronics 20 from the first vibrational response 213 and the second vibrational response 214. By collecting two or more vibrational responses, the meter electronics 20 can determine a number of flow characteristics. The flow characteristics may include the density 221, kinematic viscosity 222, dynamic viscosity 223, shear rate 224, reynolds number 225, VOS 226, and damping factor 227 of the flow material in the flow meter assembly 10.

The vibrating structure of the coriolis flowmeter 5 can be described as a single degree of freedom resonator, which obeys the differential equation:

wherein the right side represents a normalized oscillating external force function, anIs the damping factor. Where x is the instantaneous flow tube displacement, and the terms dx/dt and dx²/dt²First and second derivatives of displacement, respectively.

The frequency response of this system is given by:

wherein the magnitude response is:

and the phase response Φ is:

FIG. 4A shows a diagram for a damping factorAnd figure 4B shows three corresponding phase response curves. The three curves reflect the damping factorThus, as can be seen from the figure, the damping factorCan be operated at least two frequencies omega₁And ω₂The phase and amplitude of the vibrational response thereon are correlated and derived therefrom.

The purity of the sustained oscillation (purity) of the resonator is captured in the form of a quality factor Q, defined as:

Q＝|G(ω)|_max (5)

wherein the quality factor Q corresponds to the damping factor。

For light damping systems (i.e. wherein) The quality factor Q can be expressed as:

wherein ω is₁And ω₂Is the half power point at which the amplitude response of the flowmeter assembly 10 drops toThe value of (c). Quantity:

Δω＝ω₂-ω₁ (7)

also referred to as the 3dB bandwidth of the system. Note that the maximum response ω₀Is generally given by:

this equation indicates the maximum response ω₀Occurring below the natural frequency ω without damping_nAt the frequency of (c).

The dynamic viscosity v of the flow medium through the coriolis mass flowmeter will directly change the quality factor Q of the structure. The greater the viscosity of the flowing medium, the greater the damping of the system. In fact, the dynamic viscosity v of the flowing medium and the quality factor Q are related by:

Q＝K_v/√(v) (9)

wherein K_vIs the proportionality constant divided by the square root of the viscosity v. This implies a damping factor that enables the flow meter 5 to measure the system(or equivalent to its quality factor Q) which will yield a kinematic viscosity v after appropriate calibration.

There are many methods that can be used to determine the quality factor Q. The first method comprises measuring the peak amplitude | G (ω) & gtnon_maxTo measure the quality factor Q defined directly by equation (5). To do this, flowmeter assembly 10 may be driven open loop by including ω₀Of the drive frequency. As a method of standardization, this is done while keeping the drive power constant. The difficulty with this approach is that it requires some type of absolute amplitude response calibration, which can be noisy and inaccurate, and does not account for variations in pick-up efficiency.

The second method drives the flow tube or tubes to their nominal displacement amplitude and periodically releases the driving force while monitoring the amplitude decay of the oscillations. The time it takes for the amplitude to decrease to 0.707 of its peak will provide an alternative measure of the quality factor Q. The difficulty encountered with this approach stems from the discontinuous nature of the drive function, which will momentarily and periodically perturb the quality of the mass flow rate measurement.

The third method is by continuing at half-power point ω₁And ω₂At and at the maximum response ω₀The flowmeter assembly 10 is driven to measure the quality factor Q of the flowmeter assembly 10. This is an attractive approach because the quality factor is completely dependent on the mechanical properties of the resonator and not on the efficiency of the driver 104 or the efficiency of the pickup sensor 105. A difficulty with this approach is that when the flowmeter assembly 10 transitions from one frequency to another (e.g., from ω)₁To omega₀) The flow meter assembly 10 will be stuck in a upset and will take time to settle back into its steady state. During this stabilization period, all process information (viscosity, density and mass flow rate) may be lost, or the measurement quality may be severely degraded.

The present invention provides a substantially continuous and undamaged measurement of at least mass flow rate, density and viscosity.

Fig. 5 shows a feedback loop for controlling the frequency of vibration applied to the flow meter assembly 10. The feedback loop may include a coriolis sensor 500 (i.e., flow meter 5), a phase shifter 501, a digital-to-analog (D/a) converter 502, an analog-to-digital (a/D) converter 503, and a phase sensor 504. In operation, phase shifter 501 generates a digital drive signal that is converted to an analog drive signal by D/a502 and provided to coriolis sensor 500. The pick-up signal output is provided to the a/D503, which a/D503 digitizes the analog pick-up signal and provides it to the phase shifter 501. The phase sensor 504 compares the input (drive) phase with the output (sensor) phase and generates a phase difference signal to the phase shifter 501. Accordingly, phase shifter 501 may control the phase shift and frequency of the drive signal provided to coriolis sensor 500.

As shown in the figure, the present invention controls the phase between the input and output of the sensor so as to resonate the closed loop at a first vibration frequency ω₁And a second vibration frequency omega₂While maintaining the system under closed loop control. This phase control can be implemented digitally using standard phase-locked loop techniques. In one embodiment, closed loop control may be performed by a suitably programmed Digital Signal Processor (DSP). However, other feedback or loop control techniques may be employed and are within the scope of the description and claims.

The target phase set point shown in fig. 5 is a periodic function of time, for example:

Ф(t)＝Ф₀+ΔФsin(2πt/T_φ) (10)

in one embodiment, the phase modulation index Δ φ and the modulation period T_φOn the order of a few seconds. With this slowly varying phase change, the closed loop oscillation frequency of the system will track continuously as predicted by the phase curve shown in fig. 4B. Thus, for each time period T_φBy at the entire continuous operating point omega_E[ω₁，ω₂]With a medium tracking relative amplitude response, all relevant variables (ω) can be measured₀、ω₁、ω₂And mass flow rate) without requiring absolute calibration of the amplitude response.

The density ρ may be determined in various ways depending on the required response time. For example, in one embodiment, the phase points ρ are calibrated by passing the density every time the phase passes_calThe density p may be determined by periodically updating the density output. In another embodiment, the density ρ is determined dynamically by applying a frequency correction factor, wherein the frequency correction factor depends on the actual phase and the viscosity of the product.

By utilizing the mass flow rate 220 through the flow meter assembly 10 and from the natural resonant frequency of the flow meter assembly 10, the shear rate 224 can be determined. Thus, the shear rate 224 can be changed by changing the flow rate and/or by changing the resonant frequency of the flow meter 5 in different vibration modes. This ability results in the ability to substantially instantaneously resolve (profile) non-newtonian or liquid products. Fluids in which shear stress is linearly related to the rate of shear strain are known as newtonian fluids. Newtonian substances are called true liquids because their viscosity or consistency is not affected by shear, e.g. stirring or pumping at constant temperature. Fortunately, most common fluids (liquids and gases) are newtonian, including water and oil.

From the three primary measurements simultaneously measured by the flow meter assembly 10, the Reynolds number R of the flowing medium can be determined_e225 Reynolds number R_e225 may be determined from mass flow rate 220, density 221, and from kinematic viscosity 223.

The vibrational response produced by coriolis flow meter 5 can be used for other purposes in addition. For example, in one embodiment, the two or more vibrational responses may be used to determine a flexural stiffness of flow meter assembly 10. The flexural stiffness can be used to correct a Flow Calibration Factor (FCF) based on the stiffness change.

The factors that affect the flexural stiffness also affect the sensitivity (flow calibration factor) of the coriolis flowmeter. Flexural stiffness is the static elastic coefficient derived by bending a flow tube with a known force pattern and measuring the displacement of the flow tube. Any force mode can be used to measure the flexural stiffness as long as it is constant. For example, the flexural stiffness of the clamping beam is as follows:

wherein:

f-force (N);

E-Young's modulus (N/m)²)；

I-moment of inertia (m)⁴)；

L-length (m);

K_flex-flexural stiffness of the flow tube.

For coriolis flowmeters, if the flexural stiffness changes, the calibration factor must be changed. The flexural stiffness of a coriolis flow meter is defined as:

K_flex＝C_PC_GC_S[EI] (12)

wherein:

C_P-the influence of force patterns on flexural stiffness;

C_G-the effect of the non-deflected tube bending geometry on the flexural stiffness;

C_Seffect of non-flexural tube stress on flexural stiffness.

For straight tube coriolis flowmeters without prestressing, the following expression shows the dependence of the calibration factor on EI:

thus, the Flow Calibration Factor (FCF) for a straight pipe is:

where C is a constant determined by the mode shape and pickup position.

The flow tube flexural stiffness can also be determined by estimating a point on the tube Frequency Response Function (FRF) at a given frequency. These points are then used to make a single degree of freedom model fit to the data and determine the DC (e.g., zero crossing) points on the FRF.

The flow calibration factor may be verified using a multi-frequency estimation process. Identifying the constant m by using any time or frequency domain system identification method₁、c₁、k₁、ζ₁、ω₁And A₁To begin multi-frequency estimation. A rational continuous-time transfer function model is fitted to complex frequency response vector H using a curve fitting process with frequency groups in vector W (in radians/sec). The number and location (frequency) of the FRF data points does affect the quality of the fit. A good fit is achieved using as few as 2 frequency response data points. The derived model has the following form:

the drive pick-up mobility (speed) frequency response data is converted to an acceptable (displacement) form. The measured mobility frequency response data H must be multiplied by 1/(i ω). The measured mobility drives the ring frequency response H should be from the drive coil current (proportional to force) to the pickup voltage (proportional to velocity).

Converting the mobility data to acceptable data yields h(s) having the form:

wherein a (1) ═ 1. The modal parameters of interest are extracted from the transfer function model as follows:

A₁＝b (1)

ζ₁＝a(2)/2/ω₁

the physical parameters can then be calculated using the following equation:

m₁＝1/A₁

c₁＝2ζω₁/A₁ (18)

k₁＝ω₁ ²/A₁

once the physical parameters are determined, variations in the flow calibration factor, as well as other parameters (including variations in the mass and length of the flow tube), are determined and corrected.

In additional features, the two or more vibrational responses can also be used to detect and distinguish flow meter structural changes such as erosion, corrosion, and coating of the flow tube. In one such embodiment, coriolis flow meter 5 vibrates at its resonant frequency to enable flow meter 5 to measure mass and density. The quality measurement is based on the following equation:

wherein:

is the mass flow rate;

FCF is the flow calibration factor;

Δ t is the time delay; and

Δt₀is the time delay at zero flow.

The FCF term is proportional to the stiffness of the meter. Stiffness is a major parameter affecting the performance of the flowmeter. If the stiffness of the flow meter changes, the FCF of the flow meter will change. Changes in flowmeter performance can be caused by, for example, erosion, corrosion, and coating.

To reflect the stiffness, equation (19) may be rewritten as:

wherein:

g is a geometric constant associated with a particular sensor;

e is Young's modulus; and

i is the moment of inertia.

When the flow tube of the flow meter changes, the area moment of inertia I changes. For example, if the pipe erosion reduces the wall thickness, the area moment of inertia is reduced.

In one embodiment, the invention includes a process for detecting and distinguishing structural changes in a flow meter based on indicated changes in flow rate. The process begins with the use of multiple modes and the following equation for mass flow rateDetermination of (1):

when multiple modes are excited by flow noise or forced vibration, the vibration of the modes will couple with the mass flow through the flow tube, causing a coriolis response for each mode. The coriolis response produces an associated Δ t that is used to calculate the mass flow reading for each mode.

The mass flow readings for each mode are compared. The resulting mass flow rate must be the same for each mode. If the mass flow readings are equal, the comparison generates a "correct operation" signal and the process begins anew. The "correct operation" signal may be in the form of a signal that is visible or audible to the user, for example.

When a deviation occurs between the mass flow rates (which is outside acceptable limits), an error signal is generated. The error signal may cause various actions to occur. For example, the error signal may cause the process to be stopped, or a visible or audible alarm may be signaled to an operator who then takes appropriate action.

The density measurement for coriolis flowmeter 5 is based on the following equation:

wherein:

k is the stiffness of the assembly;

m is the mass of the assembly;

f is the oscillation frequency; and

t is the period of oscillation.

Equation (22) is a solution to the equation of motion for a single degree of freedom system. The coriolis flowmeter is represented by the expansion of equation (22) at zero flow, generating:

wherein:

e is Young's modulus;

i is the cross-sectional moment of inertia;

G_ρis a geometric constant;

a is the cross-sectional area;

ρ is the density;

f represents the fluid in the flow meter; and

t denotes the material of the flow tube.

By rearranging the terms, equation (23) can be rewritten as:

ρ_f＝C₁T²-C₂ (24)

wherein:

and (25)

Geometric constant G_ρTaking into account geometrical parameters such as the length and shape of the tube. Constant C₁And C₂Is determined as part of a standard calibration procedure at zero flow for two different fluids.

In one embodiment, the invention includes a process for detecting and distinguishing structural changes in a flow meter from changes in indicated density. The process begins with the determination of the density ρ using multiple modes. Multiple modes may be excited by flow noise or forced vibration.

The density readings for each mode are compared. The resulting density readings must be the same for each mode. If the density readings are equal, the process generates a "correct operation" signal and the process restarts. The "correct operation" signal may be in the form of a signal that is visible or audible to the user.

When a deviation occurs between the density readings (which is outside acceptable limits), an error signal is generated. The error signal may cause various actions to occur. For example, the error signal may cause the process to be stopped, or a visible or audible alarm may be signaled to an operator, who then takes appropriate action.

If desired, a coriolis flow meter and method according to the present invention may be employed according to any of the described embodiments to provide several advantages. The invention provides a flowmeter capable of measuring various flow characteristics. The present invention uses at least first and second vibration frequencies to excite a flow meter assembly to measure flow characteristics. The present invention advantageously operates a coriolis flowmeter to provide additional measurements of dynamic viscosity, kinematic viscosity, and density without compromising the mass flow measurement performance of the flowmeter. The invention may additionally provide shear rate, reynolds number, VOS and damping factor values. These various flow characteristics advantageously give more detailed and more specific information on the composition and characteristics of the flowing medium.

In virtually all major industries, there is a large number of applications for products that measure mass flow, density and viscosity simultaneously. In one example, the present invention may be used for marine fuel blending, where kerosene is blended with fuel to a given kinematic viscosity specification. The resulting mixture can be simultaneously metered onto the vessel. To provide a solution for this application, measurements of mass flow rate, density and viscosity are required.

In another example, the present invention may be used for lube oil barreling. Many different lubricating oils exist and they are typically manufactured in single stream and batch barrels. During batch barreling, the interface between different lube products must be accurately detected in order to prevent contamination. Using the viscosity measurements provided by the present invention, the interface is detected by a change in product viscosity. Using the mass flow rate measurements provided by the present invention, the mass flow output is used to accurately batch barreling.

In another example, the present invention may be used to receive a High Fructose Corn Syrup (HFCS) solution, such as HFCS-55. During the reception of the HFCS solutions, each solution will have a specific density (in Brix) and viscosity mass specification. Brix has been defined as a measure of the percentage of solids in the plant juice, or alternatively as a measure of the percentage of sucrose (sugar). Clearly, having the ability to measure these mass parameters and mass flow rates simultaneously has significant benefits to the customer.

Claims (25)

1. A coriolis flow meter (5) comprising one or more flow tubes (103), at least two pickoff sensors (105, 105') secured to the one or more flow tubes (103), and a driver (104) configured to vibrate the one or more flow tubes (103), the coriolis flow meter (5) characterized by:

meter electronics (20) coupled to the at least two pickoff sensors (105, 105') and the driver (104), the meter electronics (20) configured to: vibrating the one or more flow tubes (103) of the flow meter with a first vibration frequency and in a first out-of-phase bending mode; measuring a first vibrational response of the one or more flow tubes (103), wherein the first vibrational response is generated in response to a first vibrational frequency; vibrating the one or more flow tubes (103) with at least a second vibration frequency and in a first out-of-phase bending mode; measuring a second vibrational response, wherein the second vibrational response is generated in response to a second vibrational frequency; and using the first and second vibrational responses to determine at least a mass flow rate and a viscosity.

2. The coriolis flow meter (5) of claim 1, with the determining further comprising determining a density.

3. The coriolis flow meter (5) of claim 1, with the determining further comprising determining a shear rate.

4. The coriolis flow meter (5) of claim 1, with the determining further comprising determining a reynolds number.

5. The coriolis flow meter (5) of claim 1, with the determining further comprising determining a velocity of sound (VOS).

6. The coriolis flow meter (5) of claim 1, with the determining further comprising determining a pressure.

7. The coriolis flow meter (5) of claim 1, with the viscosity comprising a kinematic viscosity.

8. The coriolis flow meter (5) of claim 1, with the viscosity comprising a dynamic viscosity.

9. The coriolis flow meter (5) of claim 1 further comprising: hopping between the first vibration frequency and the second vibration frequency.

10. The coriolis flow meter (5) of claim 1 further comprising: simultaneously vibrating the one or more flow tubes (103) using the first vibration frequency and the second vibration frequency.

11. The coriolis flow meter (5) of claim 1 further comprising: scanning between the first vibration frequency and the second vibration frequency over a predetermined scanning period.

12. The coriolis flow meter (5) of claim 1, with the first vibration frequency and the second vibration frequency being equally spaced above and below a fundamental frequency of the one or more flow tubes (103).

13. The coriolis flow meter (5) of claim 1, with the one or more flow tubes (103) comprising two U-shaped flow tubes.

14. A method for determining flow characteristics in a coriolis flow meter, the method comprising: vibrating one or more flow tubes of the flow meter with a first vibration frequency and in a first out-of-phase bending mode; and measuring a first vibrational response of the one or more flow tubes, wherein the first vibrational response is generated in response to a first vibrational frequency, the method characterized by:

vibrating the one or more flow tubes with at least a second vibration frequency and in a first out-of-phase bending mode;

measuring a second vibrational response, wherein the second vibrational response is generated in response to a second vibrational frequency; and is

At least the mass flow rate and the viscosity of the flowing medium are determined using the first vibrational response and the second vibrational response.

15. The method of claim 14, the determining further comprising determining a density.

16. The method of claim 14, the determining further comprising determining a shear rate.

17. The method of claim 14, the determining further comprising determining a reynolds number.

18. The method of claim 14, the determining further comprising determining a speed of sound (VOS).

19. The method of claim 14, the determining further comprising determining a pressure.

20. The method of claim 14, the viscosity comprising kinematic viscosity.

21. The method of claim 14, the viscosity comprising a kinematic viscosity.

22. The method of claim 14, further comprising: hopping between the first vibration frequency and the second vibration frequency.

23. The method of claim 14, further comprising: simultaneously vibrating the one or more flow tubes using the first vibration frequency and the second vibration frequency.

24. The method of claim 14, further comprising: scanning between the first vibration frequency and the second vibration frequency over a predetermined scanning period.

25. The method of claim 14, the first vibration frequency and the second vibration frequency being equally spaced above and below a fundamental frequency of the one or more flow tubes.