Method and apparatus for calculating Q value of a vibration meter

Abstract

A vibration meter (100) is provided that is operable to determine at least one of a viscosity and a density of a fluid therein. The vibration meter (100) includes a driver (112), a vibration element (104) that is vibrated by the driver (112), and the vibration element (104) is operable to contact the fluid. A vibration sensor (114) is configured to detect a vibration response of the vibration element (104). Meter electronics (118) is configured to send an excitation signal to the driver (112) and receive the vibration response, and is further configured to measure a first vibration response point and a second vibration response point of the vibration response. The second vibration response point is one of interpolated and extrapolated from other measured response points. The meter electronics (118) is further configured to calculate a Q value of the vibration element (104) using the first vibration response point and the second vibration response point.

Description

Technical Field

[0001] The embodiments described below relate to vibrating meters, and more particularly to densitometers and viscometers. Background Art

[0002] Vibration meters, including densitometers and viscometers, are important tools for measuring the density or viscosity of fluids. A vibrating meter can include a vibrating element, such as a fork, a cylindrical member, or a planar resonator, that is exposed to the fluid being measured. One example of a vibrating meter includes a cantilevered cylindrical member, the inlet end of which is connected to an existing pipeline or other structure, while the outlet end is free to vibrate. The member can vibrate at resonance, and the resonant response frequency can be measured. The density of the fluid being measured can be determined by measuring the reduced response frequency of the vibrating element. According to well-known principles, the resonant frequency of the vibrating element will vary inversely with the density of the fluid in contact with the conduit.

[0003] Viscosity is a fluid property that describes the resistance to flow. The usual definition of viscosity is a measure of the internal friction of a fluid. In particular, this internal friction becomes apparent when one layer of fluid is moved relative to another layer. Therefore, viscosity is usually described as the resistance experienced by one part of a material moving over another part of the material. Viscosity is commonly used to characterize petroleum fluids, such as fuels, oils, and lubricants, and these petroleum fluids are usually specified in the trade and classification of petroleum products. For example, the kinematic viscosity of petroleum products is usually measured using a capillary viscometer by a standard method, such as the method described by the American Society for Testing and Materials (ASTM) D445 standard. Such a measurement involves measuring the time it takes a fixed amount of liquid to flow through a calibrated glass capillary under the action of gravity at a given temperature and under a repeatable force. The capillary viscometer is primarily defined by the Hagen-Poiseuille equation. In Newtonian fluids, shear stress is proportional to shear rate, and the proportionality constant is called viscosity.

[0004] Meters using mechanical resonators, such as vibrating tuning forks, can be used to determine viscosity by balancing the Navier-Stokes equations with Newton's laws of motion, yielding an equation of the form:

[0005]

[0006] Where μ is the fluid viscosity, ρ is the fluid density, ω0 is the undamped angular resonant frequency (2πf0), A is a constant related to the Q of the resonator in a vacuum, and B is a constant related to the stiffness, mass, and geometry of the sensor. Q is a dimensionless parameter that describes the underdamping of an oscillator or resonator.

[0007] Density and resonant frequency are related by an equation of the form:

[0008]

[0009] where C and D are constants related to the stiffness, mass, and geometry of the resonator, thus giving:

[0010]

[0011] For simplicity, the resonant frequency can be considered the same as f0, which is the undamped resonant frequency. For many practical applications, the viscosity sensor will be calibrated on a fluid similar to the fluid being measured in the field, and therefore the frequency will not change, so the frequency can be considered a constant, and the equation can therefore take a form similar to the following:

[0012]

[0013] Where E is essentially a constant based on the stiffness, mass, and geometry of the sensor and the nominal resonant frequency. The equations provided are provided as non-limiting examples.

[0014] The principle of measuring liquid viscosity using a vibration sensor is well known. An example is the Micro Motion Fork Viscosity Meter (FVM), which is based on the principle of a vibrating element, whereby the resonance characteristics are affected by the density and viscosity of the fluid. The FVM uses this operating principle to determine the viscosity of a liquid. In particular, the viscosity is determined by measuring the quality factor (Q value) of the resonance and thus the damping of the resonator. For example, but not limited to, Equation 5 describes a possible method for determining viscosity:

[0015] Viscosity = V0 + V2 / Q 2 (5)

[0016] in:

[0017] V0 and V2 are calibration constants.

[0018] The Q value can be measured by dividing the resonant frequency by the bandwidth as follows:

[0019] in:

[0020]

[0021] The geometric Q value can be calculated as:

[0022]

[0023] in:

[0024] T A The time point of the first 3dB bandwidth measurement point

[0025] T B The time point of the last 3dB bandwidth measurement point

[0026] Figure 1 The 3dB time point T is shown in the form of time period A and T B . Figure 2 The 3 dB time points F1 , F0 and F2 are illustrated in terms of frequency.

[0027] One disadvantage of the method of alternating measurements of the first and last 3dB points is that the measurement at point B is not made simultaneously with the measurement at point A. Therefore, if the fluid density is changing, an erroneous Q value measurement is made. Figure 3 is shown in terms of frequency. It will be apparent that F1 is updated on odd sample numbers and F2 on even sample numbers. The Q value is calculated each cycle using the latest values ​​of F1 and F2, so either F1 or F2 will be out of date by one cycle. In this case, the calculated Q value will oscillate high and low, even though the bandwidth and Q value should be relatively constant.

[0028] The Q value is very sensitive to changes in frequency or time period, which is why an improved method is needed. Figure 3 For example, the frequency is nominally 1350 Hz, and the frequency variation is about 0.09 Hz per sample. Although the frequency drift is very small, the result of the Q value measurement is oscillation of 1% per sample (see Figure 7 ). That is, the effect on Q is more than 100 times greater than the fundamental frequency drift. This drift can be the result of a steady change in fluid composition or it can be caused by temperature changes.

[0029] The present embodiment relates to an apparatus and method for obtaining readings corresponding to F1 and F2 at the same moment, so that the Q value measurement is more accurate even if the fluid density is changing. Summary of the Invention

[0030] According to one embodiment, a vibrating meter operable to determine at least one of a viscosity and a density of a fluid therein is provided. The vibrating meter includes a driver and a vibrating element vibrated by the driver, and the vibrating element is operable to contact the fluid. A vibration sensor is configured to detect a vibration response of the vibrating element. The meter electronics is configured to send an excitation signal to the driver and receive the vibration response, and is further configured to measure a first vibration response point of the vibration response and calculate a second vibration response point of the vibration response, wherein the second vibration response point is one of interpolated and extrapolated from other measured response points, and wherein the meter electronics is further configured to calculate a Q value of the vibrating element using the first vibration response point and the second vibration response point.

[0031] According to one embodiment, a method for determining the viscosity or density of a fluid using a vibrometer is provided. The method includes sending an excitation signal to a driver, and driving a vibrating element with the driver. Vibration of the vibrating element is detected. A first vibration response point of the vibration response is measured. A second vibration response point of the vibration response is calculated, where the second vibration response point is one of interpolated and extrapolated from other measured response points. A Q value of the vibrating element is calculated using the first and second vibration response points.

[0032] All aspects

[0033] According to one aspect, a vibrating meter is operable to determine at least one of a viscosity and a density of a fluid therein. The vibrating meter includes a driver and a vibrating element that is vibrated by the driver and is operable to contact the fluid. A vibration sensor is configured to detect a vibration response of the vibrating element. The meter electronics is configured to send an excitation signal to the driver and receive the vibration response, and is further configured to measure a first vibration response point of the vibration response and calculate a second vibration response point of the vibration response, wherein the second vibration response point is one of interpolated and extrapolated from other measured response points, and wherein the meter electronics is further configured to calculate a Q value of the vibrating element using the first vibration response point and the second vibration response point.

[0034] Preferably, the meter electronics is configured to use the Q value to determine the viscosity of the fluid

[0035] Preferably, the first vibration response point includes one of a front 3dB bandwidth measurement point and a rear 3dB bandwidth measurement point, and the second vibration response includes one of a front 3dB bandwidth measurement point and a rear 3dB bandwidth measurement point, and the second vibration response point is different from the first vibration response point.

[0036] Preferably, the first vibration response point and the second vibration response point include frequencies.

[0037] Preferably, the first vibration response point and the second vibration response point include a time period.

[0038] Preferably, the vibrating element is cantilevered.

[0039] Preferably, the first vibration response point and the second vibration response point of the vibration response correspond to the same moment.

[0040] Preferably, the other measured response points include at least two points.

[0041] According to one aspect, a method for determining the viscosity or density of a fluid using a vibrometer is provided. The method includes sending an excitation signal to a driver, and driving a vibrating element with the driver. Vibration of the vibrating element is detected. A first vibration response point of the vibration response is measured. A second vibration response point of the vibration response is calculated, where the second vibration response point is one of interpolated and extrapolated from other measured response points. A Q value of the vibrating element is calculated using the first and second vibration response points.

[0042] Preferably, the method includes the step of determining the viscosity of the fluid using the Q value.

[0043] Preferably, the first vibration response point includes one of a front 3dB bandwidth measurement point and a rear 3dB bandwidth measurement point, and the second vibration response includes one of a front 3dB bandwidth measurement point and a rear 3dB bandwidth measurement point, and the second vibration response point is different from the first vibration response point.

[0044] Preferably, the first vibration response point and the second vibration response point include frequencies.

[0045] Preferably, the first vibration response point and the second vibration response point include a time period.

[0046] Preferably, the first vibration response point and the second vibration response point of the vibration response correspond to the same moment.

[0047] Preferably, the other measured response points include at least two points. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The same reference numerals represent the same elements throughout the drawings.It should be understood that the drawings are not necessarily drawn to scale.

[0049] Figure 1 The 3dB time point T is shown in the form of a time period A and T B ;

[0050] Figure 2 The 3dB time points F1 and F2 are shown in frequency form;

[0051] Figure 3 shows the prior art measurement of the 3dB point in relation to the Q value calculation;

[0052] Figure 4 A vibrometer is shown;

[0053] Figure 5 shows the measurement of the 3dB point in relation to the Q value calculation according to an embodiment;

[0054] Figure 6 shows the measurement of the 3dB point in relation to the Q value calculation according to an alternative embodiment;

[0055] Figure 7 shows a comparison of the Q values ​​measured over time by the prior art and the Q values ​​measured according to an embodiment;

[0056] Figure 8 shows meter electronics according to an embodiment; and

[0057] Figure 9 A method of calculating a Q value according to an embodiment is shown. DETAILED DESCRIPTION

[0058] Figures 1 to 9 The following description depicts the following specific examples to teach those skilled in the art how to make and use the best mode of implementation of the vibrating meter. For the purpose of teaching the principles of the invention, 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 this description. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the vibrating meter. Therefore, the embodiments described below are not limited to the specific examples described below, but are limited only by the claims and their equivalents.

[0059] The provided embodiments relate to densitometers and viscometers and related methods for accurately calculating the Q value measurement of vibrating components. In particular, the first 3dB bandwidth measurement point (T A ) and the last 3dB bandwidth measurement point (T B ) reading is used in the Q value measurement calculation corresponding to the same moment, so that the Q value measurement remains accurate even if the fluid density changes.

[0060] Figure 4 A vibrating meter 100 is depicted. For example, the vibrating meter 100 can be configured to measure the density and / or viscosity of a fluid, such as a liquid or gas. The vibrating meter 100 includes a housing 102, wherein a vibrating element 104 is at least partially located within the housing 102. The housing 102 helps maintain fluid pressure as the vibrating element 104 oscillates. A portion of the housing 102 is cut away. In an example, the vibrating meter 100 can be placed inline in an existing pipe. However, in another example, the housing 102 can include a closed end with an orifice to receive a fluid sample. In many instances, the housing 102 or the vibrating element 104 can include a flange or other member for operatively coupling the vibrating meter 100 to a pipe or similar fluid transport device in a fluid-tight manner. In an example of the vibrating meter 100, the vibrating element 104 is cantilevered to the housing 102 at a first end 106. The vibrating element 104 is free to vibrate at a second end 108.

[0061] The example vibrating meter 100 is immersed, meaning that the measured fluid can be found all around the vibrating element 104. The vibrating element 104 can take the form of a tube, a sheet, a modified sheet, a fork (as shown), a rod, or any other shape known in the art. The vibrating element 104 can be fixed at one or both ends, and in some embodiments can be cantilevered, such as shown. According to the example shown, the vibrating element 104 can include a plurality of fluid orifices (not shown) near the first end 106. The fluid orifices can be provided to allow some of the fluid entering the vibrating meter 100 to flow between the housing 102 and the vibrating element 104. In other examples, orifices can be provided in the housing 102 to expose the measured fluid to the outer surface of the vibrating element 104. However, in yet another example, the fluid can enter the vibrating meter through a channel in a metal product near the first end 106.

[0062] Figure 4 Also shown are a driver 112 and a vibration sensor 114 positioned within the barrel 116. Driver 112 and vibration sensor 114 can include coils, but other implementations are possible, such as piezoelectric sensors, optical sensors, strain gauges, and the like. Supplying current to the coils induces a magnetic field in the vibrating element 104, causing it to vibrate. Conversely, the vibration of the vibrating element 104 induces a voltage in the vibration sensor 114. Driver 112 receives a drive signal from meter electronics 118 to vibrate the vibrating element 104 at one of the resonant frequencies of one of a number of vibration modes, including, for example, simple bending, torsional, radial, or coupled modes. Vibration sensor 114 detects the vibration of the vibrating element 104, including the frequency of its vibration, and transmits the vibration information to meter electronics 118 for processing. As the vibrating element 104 vibrates, fluid in contact with the walls of the vibrating element, as well as fluid within a short distance from the barrel, vibrates along with the vibrating element 104. The added mass of the fluid in contact with vibrating element 104 lowers the resonant frequency. The new, lower resonant frequency of vibrating element 104 is used to determine the density of the liquid. The resonant response, or quality factor, can also be used to determine the viscosity of the fluid. If a measured fluid is present, the Q value of vibrating element 104 will change inversely proportional to the fluid's viscosity.

[0063] In an embodiment, a first frequency response point and a second frequency response point are measured for Q value calculation. Alternatively, a first time point and a second time point are measured. Figure 3 and Figure 4In an embodiment, for at least one of the first 3dB bandwidth measurement point (F1) and the last 3dB bandwidth measurement point (F2), the frequency response reading of the vibrating element 104 is fitted to a straight line such that two values ​​from the same time period are used. As shown, such values ​​can be continuous or non-continuous. Such readings are calculated by the meter electronics 118. It should be noted that either time periods or frequencies can be used for the 3dB bandwidth measurement points.

[0064] exist Figure 5 In FIG, the interpolation of F1 values ​​between the points actually measured is shown by way of example. In this case, the interpolation of F2 values ​​occurs between sample numbers 4 and 6. It will be clear that this point in time corresponds to the point at which F1 was measured, namely sample 5. This point corresponds to Figure 5 Then, when the F1 value is measured, the interpolated F2 value is used in combination with the measured F1 value to calculate the Q value. It should be noted that this is merely an example, and the F1 value can be interpolated, where the F2 measurement is used for the Q value calculation. In addition, the sample number is also provided for the purpose of illustrative example only, and any consecutive or non-consecutive sample number can be used.

[0065] The disadvantage of this method is that the calculation of the Q value always lags behind the real-time measurement. Figure 6 An alternative approach that does not result in hysteresis is shown in . In this embodiment, a line is fitted between consecutive F2 measurements at sample numbers 2 and 4, and then extrapolated to the time point at which sample number 5 was taken. This point corresponds to Figure 6 It should be noted again that this is merely an example and that the F1 values ​​can be extrapolated, with the F2 measurements used for the Q value calculations. Furthermore, the sample numbers are also provided for example purposes only and any consecutive or non-consecutive sample numbers may be used.

[0066] In the above examples, only two points are used to calculate the interpolated or extrapolated values. Multiple points, averages, moving averages, slope equations, etc. and their combinations can also be used to calculate the interpolated and / or extrapolated values.

[0067] Figure 7 The time varying nature of the calculated Q value is shown where the density varies using offset 3dB bandwidth measurement points employed by prior art devices. It will be clear that the measured Q value is not stable. Superimposed on this line are examples of improved Q value measurements as a result of interpolation or extrapolation, such as Figure 3 and Figure 4 shown.

[0068] Figure 8 is a block diagram of meter electronics 118 according to an embodiment. In operation, the vibrating meter 100 provides various measurements that can be output, including one or more of measurements or averages of density, viscosity, and flow rate.

[0069] The vibrating meter 100 generates a vibration response. The vibration response is received and processed by the meter electronics 118 to generate one or more fluid measurement values. These values ​​can be monitored, recorded, stored, totaled, and / or output.

[0070] Meter electronics 118 includes an interface 201, a processing system 200 in communication with interface 201, and a storage system 202 in communication with processing system 200. Although these components are shown as distinct blocks, it should be understood that meter electronics 118 may include various combinations of integrated and / or discrete components.

[0071] The interface 201 may be configured to couple to the guide and exchange signals with, for example, the driver 112, the vibration sensor 114, and a temperature or pressure sensor (not shown). The interface 201 may also be configured to communicate with an external device through a communication path.

[0072] The processing system 200 may include any type of processing system. The processing system 200 is configured to retrieve and execute stored routines to operate the vibrating meter 100. The storage system 202 may store routines including a general meter routine 204. The storage system 202 may store measurements, received values, operating values, and other information. In some embodiments, the storage system stores mass flow (m) 220, density (ρ) 208, viscosity (μ) 210, temperature (T) 212, pressure 214, drive gain 205, frequency and / or time period 216, Q value 218, routines such as the drive gain routine 206, and any other variables or routines known in the art. Other measurement / processing routines are contemplated and are within the scope of the specification and claims.

[0073] The universal meter routine 204 can generate and store fluid quantitative values ​​and flow measurement values. For example, the universal meter routine 204 can generate viscosity measurement values ​​and / or density measurement values ​​and store the viscosity measurement values ​​in the viscosity 210 storage device of the storage system 202, and store the density measurement values ​​in the density 208 storage device of the storage system 202. As previously discussed and known in the art, the viscosity 210 value can be determined from the Q value 218.

[0074] Figure 9 The method according to an embodiment is depicted. The method starts at step 300. In step 300, the vibrating element 100 is driven to vibrate by the driver 112. The excitation signal that controls the driver 112 is sent from the meter electronics 118.

[0075] The method continues to step 302. In step 302, vibrations of the vibrating element 104 are detected.

[0076] In step 304 , a first vibration response point of the vibration response is measured.

[0077] In step 306, a second vibration response point of the vibration response is calculated. The second vibration response point is calculated via one of interpolation and extrapolation from other measured response points.

[0078] As described herein, in step 308 , the Q value of the vibration element 104 is calculated using the first vibration response point and the second vibration response point.

[0079] The detailed description of the above embodiments is not an exhaustive description of all embodiments contemplated by the inventors to fall within the scope of this specification. Indeed, those skilled in the art will recognize that certain elements of the above embodiments may be variously combined or removed to produce further embodiments, and that these further embodiments fall within the scope and teachings of this specification. It will also be apparent to those of ordinary skill in the art that the above embodiments may be combined in whole or in part to produce additional embodiments within the scope and teachings of this specification.

[0080] Therefore, although specific embodiments are described herein for illustrative purposes, various equivalent modifications are possible within the scope of this specification, 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 accompanying drawings. Therefore, the scope of the above-described embodiments should be determined by the appended claims.

Claims

1. A vibrating meter (100) operable to determine at least one of viscosity and density of a fluid therein, comprising: driver(112); a vibrating element (104) vibrable by the driver (112) and operable to contact the fluid; a vibration sensor (114) configured to detect a vibration response of the vibrating element (104); Meter electronics (118) configured to send an excitation signal to the driver (112) and receive the vibration response, and further configured to measure a first vibration response point of the vibration response and calculate a second vibration response point of the vibration response, wherein the second vibration response point is one of interpolated and extrapolated from other measured response points, and wherein the meter electronics (118) is further configured to calculate a Q value of the vibration element (104) using the first vibration response point and the second vibration response point, wherein the first vibration response point and the second vibration response point of the vibration response correspond to the same time instant.

2. The vibrating meter (100) according to claim 1, wherein The meter electronics (118) is configured to use the Q value to determine the viscosity of the fluid.

3. The vibrating meter (100) according to claim 1, wherein The first vibration response point includes one of a front 3dB bandwidth measurement point (F1) and a rear 3dB bandwidth measurement point (F2), and the second vibration response point includes one of a front 3dB bandwidth measurement point (F1) and a rear 3dB bandwidth measurement point (F2), and the second vibration response point is different from the first vibration response point.

4. The vibrating meter (100) according to claim 3, wherein The first vibration response point and the second vibration response point include frequencies.

5. The vibrating meter (100) according to claim 1, wherein The vibrating element (104) is cantilevered.

6. The vibrating meter (100) according to claim 1, wherein The other measured response points include at least two points.

7. A method of determining the viscosity or density of a fluid using a vibrating meter (100), comprising: sending an excitation signal to a driver (112); Using the driver (112) to drive the vibration element (104); detecting vibration of the vibration element (104); measuring a first vibration response point of the vibration response; calculating a second vibration response point of the vibration response, wherein the second vibration response point is one of interpolated and extrapolated from other measured response points; wherein the first vibration response point and the second vibration response point of the vibration response correspond to the same moment; and The Q value of the vibration element (104) is calculated using the first vibration response point and the second vibration response point.

8. The method of claim 7, comprising the step of determining the viscosity of the fluid using the Q value.

9. The method according to claim 7, wherein: The first vibration response point includes one of a front 3dB bandwidth measurement point (F1) and a rear 3dB bandwidth measurement point (F2), and the second vibration response point includes one of a front 3dB bandwidth measurement point (F1) and a rear 3dB bandwidth measurement point (F2), and the second vibration response point is different from the first vibration response point.

10. The method according to claim 7, wherein: The first vibration response point and the second vibration response point include frequencies.

11. The method according to claim 7, wherein: The other measured response points include at least two points.

Images