HK1213043B - Improved detection of a change in the cross-sectional area of a fluid tube in a vibrating meter - Google Patents

Description

Improved detection of changes in cross-sectional area of fluid tube in vibrating meter

Technical Field

The embodiments described hereinafter relate to a vibrating meter, and more particularly, to improved detection of changes in the cross-sectional area of a fluid tube in a vibrating meter.

Background

It is known to use a vibrating meter to measure mass flow and other information of a material flowing through a pipe. One particular type of vibrating meter is the vibrating Coriolis (Coriolis) flow meter disclosed in U.S. patent No. 4,491,025 issued to j.e. Smith et al, 1/1985, and reissued patent No. 31,450 issued to j.e. Smith, 2/11/1982. These vibrating meters have one or more fluid tubes. Each flow tube configuration in a coriolis mass flowmeter has a set of natural vibration modes that may be of the purely flexural, torsional, radial, transverse, or coupled (coupled) type. Each fluid tube is driven to oscillate at resonance in one of these natural modes. The vibration modes are generally affected by the combined mass, stiffness and damping characteristics of the fluid tube contained and the material contained in the fluid tube. Therefore, mass, stiffness, and damping are typically determined during initial calibration of the vibrating meter using well-known techniques. Material flows from the connected pipe into the flow meter on the inlet side of the vibrating meter. The material is then directed through one or more fluid tubes and out of the flow meter to a conduit connected on the outlet side.

The driver applies a force to the one or more fluid tubes. The force oscillates the one or more fluid tubes. When no material flows through the flowmeter, all points along the flow tube oscillate with the same phase. As the material begins to flow through the fluid tube, coriolis accelerations cause each point along the fluid tube to have a different phase relative to other points along the fluid tube. The phase on the inlet side of the fluid tube lags the drive, while the phase on the outlet side leads the drive. The sensors are placed at two different points on the fluid tube to produce sinusoidal signals representative of the motion of the fluid tube at the two points. The phase difference of the two signals received from the sensors is calculated in units of time.

The time difference between the two sensor signals is proportional to the mass flow rate of the material flowing through the one or more fluid tubes. The mass flow rate of the material is determined by multiplying the time difference by a flow calibration factor. The flow calibration factor depends on the material properties, the geometry of the pipe, and the cross-sectional properties of the fluid pipe. One of the main characteristics of the fluid tube that affects the flow calibration factor is the stiffness of the fluid tube. The flow calibration factor is determined by a calibration process prior to installation of the flowmeter into the pipeline. In the calibration process, fluid is conveyed through a fluid tube at a given flow rate, and a ratio between the time difference and the flow rate is calculated. As is generally known in the art, the stiffness and damping characteristics of the fluid tube are also determined during the calibration process.

One advantage of coriolis flow meters is that the accuracy of the measured mass flow rate is not affected by wear of moving parts in the meter (e.g., gears do not slip, etc.). The flow rate is determined by multiplying the time difference between two points on the fluid tube by a flow calibration factor. The only input is the sinusoidal signal from the sensor indicating the oscillation of two points on the fluid tube. A time difference is calculated from the sinusoidal signal. There are no moving parts in the vibrating fluid tube. The flow calibration factor is proportional to the material and cross-sectional properties of the fluid pipe. Thus, the measurement of the phase difference and the flow calibration factor are not affected by wear of moving parts in the flow meter.

However, a problem is that the cross-sectional properties of the fluid tube can change during use of the vibrating meter. The changes in the material and cross-sectional properties of the fluid pipe can be caused by corrosion, erosion, and coating of the fluid pipe due to the material flowing through the fluid pipe.

While the prior art has attempted to provide methods for detecting changes in the cross-sectional area of a fluid pipe in situ, these attempts have been relatively limited. For example, U.S. patent 6,092,409, which is assigned to the present applicant in its literal sense, discloses a system for detecting changes in the cross-sectional area of a fluid pipe based on changes in the oscillation period of the fluid pipe. The problem with this method is that it requires a known density to flow within the fluid tube during the measurement. In the case where a fluid is not known to flow through a fluid pipe, the change in the oscillation period may be caused by a change in the cross-sectional area of the fluid pipe, or may be caused by a change in the density of the fluid. This method is therefore not very useful in the following fields, namely: if the fluid flowing through the vibrating meter may have an unknown or varying density.

There are also a number of examples of prior art that explain how to determine the stiffness of a fluid pipe based on the vibrational response of the fluid pipe. As mentioned above, the stiffness of the fluid tube is typically determined during initial calibration, and is required to accurately determine the flow calibration factor of the meter. In addition to initial calibration methods known in the art and widely utilized in the vibrating meter industry, other prior art examples attempt to determine the stiffness of a fluid pipe in situ using existing driver and sensing element arrangements. For example, U.S. patent 6,678,624, which is assigned to the present applicant in its literal sense, discloses a method of determining a modal dynamic stiffness matrix and subsequently determining the stiffness of a fluid pipe. U.S. patent 7,716,995, assigned to the present applicant in its literal sense, discloses another prior art method that utilizes two or more vibrational responses and solves a single degree of freedom differential equation to determine stiffness, damping and mass characteristics of a fluid tube in addition to other characteristics of a vibrating meter. As discussed in the' 995 patent, the vibration of a coriolis meter can be characterized using a simple spring equation (springequestration), in accordance with the most basic explanation:

wherein:

f is the oscillation frequency;

m is the mass of the assembly;

τ is the period of oscillation; and

k is the stiffness of the assembly.

Equation (1) can be rearranged to solve for stiffness k and the mass of the assembly can be easily measured using existing assemblies of drivers and pickoffs.

Another prior art attempt to detect changes in the cross-sectional area of a fluid pipe is disclosed in U.S. patent 7,865,318, which is assigned to the present applicant in its literal sense, and is hereby incorporated by reference herein for all that it teaches. The' 318 patent measures the stiffness of the fluid tube based on the resonant drive frequency. The' 318 patent explains that the vibrational response of the flow meter can be represented by an open-loop, second-order drive model, which includes:

wherein:

f is the force applied to the system;

is the physical displacement of the fluid pipe;

is the velocity of the fluid tube;

is the acceleration of the fluid tube;

m is the mass of the system;

c is damping characteristic; and

k is the stiffness characteristic of the system.

The '318 patent performs several alternatives and finally arrives at equation (3) (equation9 in the' 318 patent), which is summarized as follows:

wherein:

ζ is a damping characteristic;

v is a driving voltage;

is the sensitivity factor of the sensitive element;

is the sensitivity factor of the driver; and

i is the drive current.

The sensitivity factor of the pickoffs and the sensitivity factor of the driver are generally known or measured for each pickoff sensor and driver. The damping characteristic is typically determined by: the vibrational response of the flow meter is allowed to decay down to the vibrational target while the decay is measured. Thus, as explained in the' 318 patent, the stiffness parameter (K) can be determined by measuring/quantifying the damping characteristic (ζ), the drive voltage (V), and the drive current (I). Although the method set forth in the' 318 patent may provide satisfactory results under certain conditions (e.g., when drive mode stiffness changes), testing has shown that changes in the cross-sectional area of a bent fluid pipe, particularly due to erosion or corrosion, typically occur in the outer radius of the pipe bend, slightly downstream of the pipe bend, or at the welded joint of the pipe/manifold. While M, C, K and ζ are described above as mode-dependent, current methods measure the drive mode resonant frequency in the drive modeAnd M, C, K and ζ. When the wall thickness of the fluid tube is changed, the drive mode stiffness (K) is changed. However, because corrosion generally results in changes in the bend, changes in these areas generally have very little effect on the generally measured bending mode that is typical of the bend modeAt a resonant frequency of the drive mode as discussed in, for example, the' 318 patentTo vibrate. In order to detect the change in the bent portion, it is necessary to generate stress/strain in the bent portion, which generally does not occur when the fluid pipe is driven in the driving mode. Thus, prior art gauges typically cannot use current driver and sensing element architectures to detect changes in the cross-sectional area of the fluid pipe.

It will be appreciated that for virtually all vibrating meters, the stiffness and damping characteristics of the fluid tube need to be determined. Thus, although specific equations are provided above, they should in no way limit the scope of the embodiments described below. One skilled in the art will readily recognize alternative equations and methods for determining the stiffness of a fluid tube based on a measured vibrational response.

Due to the deficiencies of currently available stiffness determinations, there is a need in the art for a system that detects possible changes in the material and/or cross-sectional properties of a fluid tube that indicate that the measurements provided by a vibrating meter may be inaccurate. The embodiments described hereinafter overcome these and other problems and achieve an advance in the art. The embodiments described hereinafter provide a vibrating meter that is capable of vibrating in a lateral mode in addition to the typical drive mode (bending). Because the change in cross-sectional area generally occurs at the outer radius of the tube bend, the change in cross-sectional area will affect the transverse mode stiffness of the fluid tube to a much greater extent than the drive mode stiffness. In other words, a change in the stiffness of the transverse mode will not have a significant effect on the drive mode vibration frequency, but will generally change the vibration resonance frequency of the transverse mode.

Disclosure of Invention

According to an embodiment, a method for determining a lateral mode stiffness of one or more fluid tubes in a vibrating meter is provided. According to an embodiment, the method comprises the steps of: vibrating at least one of the one or more fluid tubes in a drive mode vibration; and receiving a drive mode sensor signal based on the vibrational response to the drive mode vibration. The method further comprises the steps of: vibrating at least one of the one or more fluid tubes in a lateral mode vibration, wherein the lateral mode is substantially perpendicular to the drive mode; and receiving a lateral mode sensor signal based on the vibrational response to the lateral mode vibration. According to an embodiment, the method further comprises the step of determining a lateral mode stiffness based on the lateral mode sensor signal.

According to an embodiment, there is provided meter electronics for a vibrating meter including a processing system. The processing system is configured to: generating a drive mode drive signal to vibrate the at least one fluid tube in a drive mode vibration; and receiving a drive mode sensor signal based on the vibrational response to the drive mode vibration. According to an embodiment, the processing system is further configured to generate a lateral mode drive signal to vibrate the at least one fluid tube in a lateral mode vibration, wherein the lateral mode is substantially perpendicular to the drive mode. The processing system is further configured to: receiving a lateral mode sensor signal based on a vibrational response to the lateral mode vibration; and determining a lateral mode stiffness based on the lateral mode sensor signal.

According to an embodiment, a vibrating meter is provided that includes a sensor assembly and meter electronics. The vibrating meter includes: one or more fluid tubes; and a first driver coupled to the one or more fluid tubes and oriented to induce drive mode vibrations in the one or more fluid tubes. One or more pickoffs are coupled to the one or more fluid tubes and oriented to sense drive mode vibrations in the one or more fluid tubes. According to an embodiment, a second driver is coupled to the one or more fluid tubes and oriented to induce lateral mode vibrations in the one or more fluid tubes. According to an embodiment, the vibrating meter further comprises one or more sensing elements coupled to the one or more fluid tubes and oriented to sense lateral mode vibrations in the one or more fluid tubes.

Aspect(s)

According to one aspect, a method for determining a lateral mode stiffness of one or more fluid tubes in a vibrating meter includes the steps of:

vibrating at least one of the one or more fluid tubes in a drive mode vibration;

receiving a drive mode sensor signal based on a vibrational response to the drive mode vibration;

vibrating at least one of the one or more fluid tubes in a lateral mode vibration, wherein the lateral mode is substantially perpendicular to the drive mode;

receiving a lateral mode sensor signal based on a vibrational response to the lateral mode vibration; and

determining a lateral mode stiffness based on the lateral mode sensor signal.

Preferably, the step of vibrating at least one of the one or more fluid tubes in a lateral mode vibration comprises vibrating at least one fluid tube at more than one lateral mode frequency.

Preferably, the step of vibrating at least one of the one or more fluid tubes in a lateral mode vibration comprises vibrating two fluid tubes in a lateral mode vibration relative to each other.

Preferably, the step of vibrating at least one of the one or more fluid tubes in a lateral mode vibration comprises vibrating the fluid tubes in a lateral mode vibration relative to the housing.

Preferably, the step of determining the transverse mode stiffness is based on the transverse mode sensor signal and the drive mode sensor signal.

Preferably, the method further comprises the step of comparing the determined transverse mode stiffness with an expected transverse mode stiffness.

Preferably, the expected lateral mode stiffness is based on a measured density of fluid within the one or more fluid tubes.

According to another aspect, meter electronics for a vibrating meter including a processing system is configured to:

generating a drive mode drive signal to vibrate the at least one fluid tube in a drive mode vibration;

receiving a drive mode sensor signal based on a vibrational response to the drive mode vibration;

generating a lateral mode drive signal to vibrate the at least one fluid tube in a lateral mode vibration, wherein the lateral mode is substantially perpendicular to the drive mode;

receiving a lateral mode sensor signal based on a vibrational response to the lateral mode vibration; and

determining a lateral mode stiffness based on the lateral mode sensor signal.

Preferably, the processing system is configured to generate more than one transverse mode drive signal at more than one transverse mode frequency.

Preferably, the processing system is configured to apply the generated transverse mode drive signal to two fluid tubes to cause the two fluid tubes to vibrate in a transverse mode vibration relative to each other.

Preferably, the processing system is configured to apply the generated transverse mode drive signal to a fluid tube to vibrate the fluid tube in a transverse mode vibration with respect to the housing.

Preferably, the processing system is further configured to determine a lateral mode stiffness based on the lateral mode sensor signal and the drive mode sensor signal.

Preferably, the processing system is further configured to compare the determined transverse mode stiffness to an expected transverse mode stiffness.

Preferably, the expected lateral mode stiffness is based on a measured density of fluid within the one or more fluid tubes.

According to another aspect, a vibrating meter including a sensor assembly and meter electronics includes:

one or more fluid tubes;

a first driver coupled to the one or more fluid tubes and oriented to cause drive mode vibrations in the one or more fluid tubes;

one or more pickoffs coupled to the one or more fluid tubes and oriented to sense drive mode vibrations in the one or more fluid tubes;

a second driver coupled to the one or more fluid tubes and oriented to induce lateral mode vibrations in the one or more fluid tubes; and

one or more sensing elements coupled to the one or more fluid tubes and oriented to sense transverse mode vibrations in the one or more fluid tubes.

Preferably, the first portion of the second driver is coupled to a first fluid tube and the second portion of the second driver is coupled to a second fluid tube.

Preferably, a first portion of the one or more pickoffs oriented to sense transverse mode vibrations is coupled to the first fluid tube and a second portion is coupled to the second fluid tube.

Preferably, a first portion of the second driver is coupled to the first fluid tube and a second portion of the second driver is coupled to the housing.

Preferably, a first portion of the one or more pickoffs oriented to sense lateral mode vibrations is coupled to the first fluid tube and a second portion is coupled to the housing.

Drawings

Fig. 1 shows a prior art vibrating meter.

Fig. 2 shows a vibrating meter according to an embodiment.

FIG. 3 shows meter electronics according to an embodiment.

FIG. 4 illustrates a lateral mode stiffness determination routine according to an embodiment.

FIG. 5 shows a vibrating meter according to another embodiment.

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 an embodiment of the vibrating meter. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the description. Those skilled in the art will appreciate that the features described hereinafter can be combined in various ways to form multiple variations of a vibrating meter. As a result, the embodiments described below are not limited to the specific examples described below, but only by the claims and their equivalents.

FIG. 1 illustrates a prior art vibrating meter 5 in the form of a meter including a sensor assembly 10 and one or more meter electronics 20. The vibrating meter 5 may include a coriolis flow meter, a vibrating volumetric flow meter, a vibrating densitometer, or the like. Meter electronics 20 is connected to sensor assembly 10 by leads 100 to measure properties of the substance, such as fluid density, mass flow rate, volumetric flow rate, cumulative mass flow, temperature, and other information through path 26.

The sensor assembly 10 of the present example includes: a pair of flanges 101, 101'; manifolds 102, 102'; a driver 104; the sensitive elements 105, 105'; and conduits 103A, 103B. Driver 104 and pickoffs 105, 105' are coupled to fluid tube 103A and fluid tube 103B as is generally known in the art. In use, the flanges 101, 101' can be coupled to a pipe (not shown) carrying a fluid.

It should be understood by those skilled in the art that it is within the scope of the present embodiments to use the principles discussed herein in conjunction with any type of vibrating meter, including vibrating meters that lack the measurement capabilities of a coriolis flow meter. Examples of such devices include vibrating densitometers, positive displacement flow meters, and the like.

The flanges 101, 101 'of the present example are coupled to manifolds 102, 102'. Manifolds 102, 102' of the present example are fixed to opposite ends of fluid tubes 103A, 103B. Support bars (break bar) 120-. When the sensor assembly 10 is inserted into a piping system (not shown) carrying a substance, the substance enters the sensor assembly 10 through the flange 101, moves through the inlet manifold 102, wherein the total amount of material is directed into the tubes 103A, 103B, the substance flows through the tubes 103A, 103B, and back into the outlet manifold 102', where it exits the sensor assembly 10 through the flange 101'.

As is generally known in the art, the driver 104 is capable of vibrating the fluid tubes 103A, 103B in a drive mode in the z-direction substantially about the x-axis. Thus, the drive mode vibrates the fluid tubes 103A, 103B in a direction substantially perpendicular to the longitudinal axis of the fluid tubes. As the flow tubes 103A, 103B vibrate about the x-axis, the flowing fluid induces Coriolis deflections (Coriolis deflections) in the two flow tubes 103A, 103B, which are measured as the phase difference between the first pickoff 105 and the second pickoff 105'. The phase difference between the sensing elements 105, 105' is multiplied by a flow calibration factor to calculate the mass flow rate. As discussed above, changes in the cross-sectional area of the fluid tubes 103A, 103B can affect the stiffness of the fluid tubes 103A, 103B, which can change the flow calibration factor.

As mentioned above, the change in the sectional area of the fluid pipe 103A, 103B generally occurs first at the outer bend (outer bend) of the bent fluid pipe 103A, 103B. The outer bends are depicted as 130, 131, 132, and 133, where "a" and "B" are designated for the first fluid tube 103A and the second fluid tube 103B, respectively. Changes to these sections of the fluid tubes 103A, 103B generally do not affect the drive mode (bending) stiffness. Therefore, when the change in the cross-sectional area starts in the fluid pipes 103A, 103B, for example, when corrosion initially starts in the fluid pipes 103A, 103B, the vibration frequency of the drive mode may not change. Thus, the fluid pipes 103A, 103B may corrode or erode to a dangerous level before a problem is detected. Therefore, a need exists for early detection techniques.

Fig. 2 shows a vibrating meter 50 according to an embodiment. The vibrating meter 50 includes a sensor assembly 210 and meter electronics 200. The vibrating meter 50 is similar to the vibrating meter 5 shown in fig. 1, and like components share like reference numerals with fig. 1. In addition to the components of the vibrating meter 5, the vibrating meter 50 is provided with a second driver 204 and a third sensor 205. Second driver 204 can be electrically coupled to meter electronics 200 via lead 214, while third pickoff 205 is electrically coupled to meter electronics 200 via lead 215.

It should be understood that because two pickoffs 105, 105' are shown in FIG. 1, pickoff 205 is depicted as including a third pickoff. However, in embodiments where only one pick-off is used to sense the drive mode vibration, pick-off 205 may comprise a second pick-off. This may be the case, for example, if the vibrating meter 50 comprises a vibrating densitometer. Thus, the particular number of sensitive elements should in no way limit the scope of the present embodiments. As can be appreciated, the second driver 204 and the third pickoff 205 can include similar coil/magnet combinations for the first driver 104 and the first and second pickoff 105, 105'. However, the second driver 204 is oriented to vibrate the fluid tubes 103A, 103B in a direction perpendicular to the driving motion and parallel to the fluid flow (i.e., about the z-axis), and the third pick-off element 205 is oriented to sense motion of the fluid tubes 103A, 103B in a direction perpendicular to the driving motion, rather than being oriented to drive and sense motion of the fluid tubes 103A, 103B about the x-axis. Thus, according to an embodiment, the second driver 204 is capable of inducing a lateral mode vibration frequency and the third pick-off 205 is capable of sensing the lateral mode vibration frequency. As can be appreciated, while the prior art vibrating meters are capable of determining the drive mode stiffness as discussed above, the driver 204 and the pickoff 205 allow the meter electronics 20 of the present embodiment to determine the lateral mode stiffness of the fluid tubes 103A, 103B. In many cases, a change in lateral mode stiffness can indicate a change in the drive mode stiffness before such a change would indicate a change in the cross-sectional area of the fluid pipe due to corrosion, erosion, or coating. Thus, in detecting problems with the sensor assembly, it is advantageous to determine the transverse mode stiffness based on the vibrational response from the third pick-off 205 over prior art methods that rely on detecting changes in bending mode stiffness.

According to the embodiment shown in fig. 2, the second driver 204 is positioned to vibrate the fluid tubes 103A, 103B in a lateral mode relative to each other. In other words, one portion of the driver 204 is coupled to the first fluid tube 103A while a second portion of the driver 204 is coupled to the second fluid tube 103B. As an example, if the second driver 204 comprises a conventional coil/magnet combination, the coil can be coupled to the first fluid tube 103A and the magnet can be coupled to the second fluid tube 103B. Thus, the fluid tubes 103A, 103B will vibrate in a scissor-like motion. Likewise, a first portion of the sensing element 205 is coupled to the first fluid tube 103A while a second portion of the sensing element 205 is coupled to the second fluid tube 103B. Using the example for the driver 204, the coil of the pickoff 205 can be coupled to the first fluid tube 103A and the magnet can be coupled to the second fluid tube 103B. Thus, the third pick-off 205 is oriented to sense transverse mode vibrations excited by the second driver 204.

FIG. 3 shows meter electronics 200 according to an embodiment of the present invention. The meter electronics 200 can include an interface 301 and a processing system 303. The processing system 303 may include a storage system 304. The storage system 304 may include internal memory as shown, or alternatively, may include external memory. The processing system 303 of the meter electronics 200 can generate a drive mode drive signal 311 and provide the drive mode drive signal 311 to the first driver 104 of the sensor assembly 210. The processing system 303 of the meter electronics 200 can also receive a vibrational response in the form of a drive mode sensor signal 310 from the sensor assembly 210. More specifically, the drive mode sensor signal 310 can be received from the first pick-off 105 and the second pick-off 105'. The processing system 303 of the meter electronics 200 can process the drive mode sensor signal 310 to obtain a density 311, a volumetric flow rate 314, and a mass flow rate 315 of the material flowing through the conduit 201. As those skilled in the art will readily appreciate, the drive mode sensor signal 310 may be used to determine other fluid characteristics, and the particular examples provided should in no way limit the scope of the present embodiments.

According to an embodiment, the meter electronics 200 can also generate a transverse mode drive signal 316 and provide the transverse mode drive signal 316 to the second driver 204. The meter electronics 200 can receive a second vibrational response in the form of a transverse mode sensor signal 317 from a third pick-off sensor 205. The meter electronics processing system 303 can process the lateral mode sensor signal 317 to determine the lateral mode stiffness 318 of the fluid tubes 103A, 103B. The processing system 303 of the meter electronics 200 can determine the transverse mode stiffness 318 using one of the equations provided above or using some other known technique. It should be appreciated that the meter electronics 200 can determine the transverse mode stiffness 318 in a substantially similar manner as how the bending mode stiffness is typically determined during an initial calibration routine. However, instead of using the resonant drive frequency used during the initial calibration routine, one or more transverse mode vibration frequencies could be used instead.

As can be appreciated, the interface 301 may perform any necessary or desired signal conditioning, such as formatting, amplifying, buffering, and the like, in any manner. Alternatively, some or all of the signal conditioning can be performed in the processing system 303. Further, the interface 301 can enable communication between the meter electronics 200 and a remote processing system (not shown). The interface 301 can allow any manner of electronic, optical, or wireless communication.

In one embodiment, interface 301 can include a digitizer (not shown); wherein the sensor signals 310, 317 comprise analog sensor signals. The digitizer is capable of sampling and digitizing the analog sensor signal and generating a digital sensor signal. The digitizer can also perform any required decimation (decimation), wherein the digital sensor signal is decimated in order to reduce the amount of signal processing required and reduce the processing time.

The processing system 303 is capable of performing the operations of the meter electronics 200. Processing system 303 is capable of performing the data processing required to implement one or more processing routines (e.g., lateral mode stiffness determination routine 313). The transverse mode stiffness determination routine 313 can use any of the equations listed above, along with the resulting density 312 and mass flow rate 315, to generate the transverse mode stiffness 318. As can be appreciated, the resonant frequency of the transverse mode drive signal 316 will depend on the mass of the system, which depends on the density/mass of the fluid within the fluid tubes 103A, 103B. Therefore, in order to accurately determine the transverse mode stiffness, the mass of the system may be required. In some embodiments, the determined transverse mode stiffness 318 may be compared to an expected transverse mode stiffness. The expected lateral mode stiffness may be based on the measured density 312 of the fluid in the fluid tubes 103A, 103B. During initial calibration, tables, graphs, etc. can be generated with the respective transverse mode resonant frequencies taken at different fluid densities. Thus, changes in the resonant frequency of the transverse mode drive signal 316 can be compensated by changes in the fluid density, rather than due to changes in the transverse mode stiffness 318.

It should be understood that meter electronics 220 may include various other components and functions generally known in the art. For the sake of brevity, these additional features are omitted from the description and drawings. Therefore, the invention should not be limited to the specific embodiments shown and discussed.

FIG. 4 illustrates a lateral mode stiffness determination routine 313 according to an embodiment. According to an embodiment, the lateral mode stiffness determination routine 313 can be performed, for example, by the meter electronics 200. According to an embodiment, the lateral mode stiffness determination routine 313 may be executed during normal operation of the vibrating meter 50. While the lateral mode stiffness determination routine 313 may be performed substantially continuously, in other embodiments, the routine 313 may be performed at periodic intervals or when a user initiates the routine 313. It should be appreciated that the transverse mode stiffness determination routine 313 can be performed while making normal measurements, unlike prior art methods for determining changes in cross-sectional properties of the tubes 103A, 103B of a vibrating meter that interfere with normal operation.

According to an embodiment, the lateral mode stiffness determination routine 313 begins at step 401, where the one or more fluid tubes 103A, 103B vibrate in a drive mode. According to an embodiment, the one or more fluid tubes 103A, 103B can be vibrated in the drive mode, for example using a first driver 104.

According to an embodiment, the lateral mode stiffness determination routine 313 can continue to step 402, where the drive mode sensor signal 311 is received. As explained above, the drive mode sensor signal 311 can be received, for example, from the first pick-off sensor 105 and the second pick-off sensor 105'. As can be appreciated, steps 401 and 402 are not unique to the present embodiment and are taken during normal operation of the vibrating meter.

However, in step 403, the one or more fluid tubes 103A, 103B vibrate in a lateral mode. According to an embodiment, the one or more fluid tubes 103A, 103B can be vibrated in the lateral mode, for example using a second driver 204. According to one embodiment, step 403 may be performed after step 401. In an alternative embodiment, step 403 may be performed substantially simultaneously with step 401. Thus, the one or more fluid tubes 103A, 103B can vibrate in the drive mode and the lateral mode substantially simultaneously. The one or more fluid tubes 103A, 103B may vibrate at one or more lateral mode vibration frequencies. Therefore, the present embodiment should not be limited to a single transverse mode vibration frequency.

According to an embodiment, in step 404, a lateral mode sensor signal 317 can be received. The transverse mode sensor signal 317 can be received from the third pick-off sensor 205, as explained above, the third pick-off sensor 205 being oriented to sense transverse mode vibrations of the one or more fluid tubes 103A, 103B.

The lateral mode stiffness determination routine 313 can continue to step 405 where the lateral mode stiffness is determined based on the lateral mode sensor signal. As discussed above, for more accurate measurements, a measurement of the mass of the system, i.e. the fluid density, is required to determine the transverse mode stiffness. Therefore, the drive mode sensor signal 311 is generally required to accurately determine the quality of the system. Therefore, in some embodiments, the lateral mode stiffness is determined based on the drive mode sensor signal 310 and the lateral mode sensor signal 317. Without the drive mode sensor signal 310, it is necessary to assume the density of the fluid within the one or more fluid tubes 103A, 103B, or alternatively, the lateral mode drive signal 316 can vibrate at more than one frequency. Vibration at more than one frequency can allow mass, stiffness, and damping to be determined as explained in more detail in the' 995 patent mentioned above.

In some embodiments, in determining the lateral mode stiffness of the one or more fluid tubes 103A, 103B, the determined lateral mode stiffness can be compared to an expected lateral mode stiffness. For example, the expected lateral mode stiffness may be based on a previously determined value. The previously determined values may be obtained from previously generated maps or tables as mentioned hereinabove. According to an embodiment, a user or operator may be alerted to a problem if the difference between the determined lateral mode stiffness and the expected lateral mode stiffness exceeds a threshold amount.

According to another embodiment, the lateral mode stiffness can be compared to a stiffness previously determined using the lateral mode stiffness determination routine 313. For example, if the lateral mode stiffness changes by a threshold amount between the operations of routine 313, the user or operator may be alerted that a problem exists. For example, problems may be caused by corrosion, erosion, or coatings.

As can be appreciated, the lateral mode stiffness determination routine 313 is advantageous over previous methods for determining changes in the cross-sectional area of one or more fluid tubes 103A, 103B because the routine 313 can be run substantially simultaneously for normal operation of the vibrating meter 50. Furthermore, routine 313 can detect problems earlier than previous approaches because the transverse mode stiffness can be affected before or more than the bending mode stiffness. Therefore, the user and the operator can be warned of the problem earlier than in the related art.

Fig. 5 shows a vibrating meter 50 according to another embodiment. The vibrating meter 50 shown in fig. 5 is similar to the vibrating meter 50 shown in fig. 2. However, in fig. 5, a housing 500 is provided. Only a portion of the housing 500 is shown so that the interior of the housing 500 can be seen. Another difference between the embodiment shown in fig. 2 and the embodiment shown in fig. 5 is that only one fluid pipe 103B vibrates in a lateral mode in fig. 5. Thus, a first portion of the second driver 504 is coupled to the fluid tube 103B and a second portion of the second driver 504 is coupled to the enclosure 500. Thus, the fluid pipe 103B vibrates in a lateral mode with respect to the housing 500, not with respect to the other fluid pipe 103A. Further, the third sensing element 505 includes a first portion coupled to the fluid pipe 103B and a second portion coupled to the housing 500. This type of configuration may be used in a dual tube vibrating meter; however, the configuration is also useful in a single tube vibrating meter. Thus, by vibrating the fluid tube 103B in a lateral mode relative to the housing 500, it can be seen that the lateral mode stiffness determination routine 313 can be used with a single tube vibrating meter.

The embodiments described hereinabove provide an improved system for determining transverse mode stiffness. As explained above, the embodiments are capable of detecting possible problems in a vibrating meter that may be caused by corrosion, erosion, or coatings affecting the stiffness of the transverse mode. Thus, because these changes in the cross-sectional area of the fluid tube generally affect the lateral mode stiffness earlier than the bending mode stiffness, the embodiments can be used to alert the user to problems with the vibrating meter earlier than in the prior art.

The detailed description of the embodiments described above is not an exhaustive description of all embodiments that the inventors contemplate as falling within the scope of the description. Indeed, those skilled in the art will recognize that certain elements of the above-described embodiments may variously be combined or eliminated to create additional embodiments, and that such additional embodiments fall within the scope and teachings of the present specification. It will also be apparent to those skilled in the art that the above-described embodiments may be combined, in whole or in part, to create additional embodiments within the scope and teachings of the specification.

Thus, while specific embodiments have been described herein for purposes of illustration, various equivalent modifications are possible within the scope of the description, as those skilled in the relevant art will recognize. The teachings provided herein can be applied to other vibrating meters, not just the embodiments described above and shown in the figures. Accordingly, the scope of the embodiments described hereinabove should be determined from the claims that follow.

Claims (19)

1. A method for determining a lateral mode stiffness of one or more fluid tubes in a vibrating meter, comprising the steps of:

vibrating at least one of the one or more fluid tubes in a drive mode vibration;

receiving a drive mode sensor signal based on a vibrational response to the drive mode vibration;

vibrating at least one of the one or more fluid tubes in a lateral mode vibration, wherein the lateral mode is substantially perpendicular to the drive mode;

receiving a lateral mode sensor signal based on a vibrational response to the lateral mode vibration; and

determining a lateral mode stiffness based on the lateral mode sensor signal.

2. The method of claim 1, wherein the step of vibrating at least one of the one or more fluid tubes in the lateral mode vibration comprises vibrating the at least one fluid tube at more than one lateral mode frequency.

3. The method of claim 1, wherein the step of vibrating at least one of the one or more fluid tubes in the lateral mode vibration comprises vibrating two fluid tubes in a lateral mode vibration relative to each other.

4. The method of claim 1, wherein the step of vibrating at least one of the one or more fluid tubes in the lateral mode vibration comprises vibrating a fluid tube in the lateral mode vibration relative to a housing.

5. The method of claim 1, wherein the step of determining the transverse mode stiffness is based on the transverse mode sensor signal and the drive mode sensor signal.

6. The method of claim 1, further comprising the step of comparing the determined transverse mode stiffness to an expected transverse mode stiffness.

7. The method of claim 6, wherein the expected lateral mode stiffness is based on a measured density of fluid within the one or more fluid tubes.

8. Meter electronics (200) for a vibrating meter (5) comprising a processing system (303) configured to:

generating a drive mode drive signal (311) to vibrate the at least one fluid tube (103A, 103B) in a drive mode vibration;

receiving a drive mode sensor signal based on a vibrational response to the drive mode vibration (310);

generating a lateral mode drive signal (316) to vibrate the at least one fluid tube (103A, 103B) in a lateral mode vibration, wherein the lateral mode is substantially perpendicular to the drive mode;

receiving a lateral mode sensor signal based on a vibrational response to the lateral mode vibration (317); and

determining a lateral mode stiffness (318) based on the lateral mode sensor signal (317).

9. The meter electronics (200) of claim 8, wherein the processing system (303) is configured to generate more than one transverse mode drive signal (316) at more than one transverse mode frequency.

10. The meter electronics (200) of claim 8, wherein the processing system (303) is configured to apply the generated lateral mode drive signal (316) to two fluid tubes (103A, 103B) to vibrate the two fluid tubes (103A, 103B) in a lateral mode vibration with respect to each other.

11. The meter electronics (200) of claim 8, wherein the processing system (303) is configured to apply the generated lateral mode drive signal (316) to a fluid tube (103A, 103B) to vibrate the fluid tube (103A, 103B) in a lateral mode vibration relative to a housing (500).

12. The meter electronics (200) of claim 8, wherein the processing system (303) is further configured to determine the lateral mode stiffness based on the lateral mode sensor signal (317) and the drive mode sensor signal (310).

13. The meter electronics (200) of claim 8, wherein the processing system (303) is further configured to compare the determined lateral mode stiffness to an expected lateral mode stiffness.

14. The meter electronics (200) of claim 13, wherein the expected lateral mode stiffness is based on a measured density of fluid within the one or more fluid tubes.

15. A vibrating meter (5) including a sensor assembly (210) and meter electronics (200), comprising:

one or more fluid pipes (103A, 103B);

a first driver (104) coupled to the one or more fluid tubes (103A, 103B) and oriented to cause drive mode vibrations in the one or more fluid tubes (103A, 103B);

one or more pickoffs (105, 105') coupled to the one or more fluid tubes (103A, 103B) and oriented to sense drive mode vibrations in the one or more fluid tubes (103A, 103B);

a second driver (204) coupled to the one or more fluid tubes (103A, 103B) and oriented to induce lateral mode vibrations in the one or more fluid tubes (103A, 103B); and

one or more sensing elements (205) coupled to the one or more fluid tubes (103A, 103B) and oriented to sense transverse mode vibrations in the one or more fluid tubes (103A, 103B).

16. The vibrating meter (5) of claim 15, wherein a first portion of the second driver (204) is coupled to a first fluid tube (103A) and a second portion of the second driver (204) is coupled to a second fluid tube (103B).

17. The vibrating meter (5) of claim 16, wherein a first portion of the one or more pickoffs (205) oriented to sense transverse mode vibrations is coupled to the first fluid tube (103A) and a second portion is coupled to a second fluid tube (103B).

18. The vibrating meter (5) of claim 15, wherein a first portion of the second driver (204) is coupled to a first fluid tube (103A) and a second portion of the second driver (204) is coupled to a housing (500).

19. The vibrating meter (5) of claim 18, wherein a first portion of the one or more pickoffs (205) oriented to sense lateral mode vibrations is coupled to the first fluid tube (103A) and a second portion is coupled to the housing (500).