METHOD AND APPARATUS FOR CALCULATING A VIBRATORY METER Q

Abstract

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

Claims

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

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

3. The vibrating meter (100) of claim 1, wherein the first vibrational response point comprises one of a leading 3 dB bandwidth measurement point (F.sub.1) and a trailing 3 dB bandwidth measurement point (F.sub.2), and the second vibrational response comprises one of a leading 3 dB bandwidth measurement point (F.sub.1) and a trailing 3 dB bandwidth measurement point (F.sub.2), and the second vibrational response point is different from the first vibrational response point.

4. The vibrating meter (100) of claim 3, wherein the first and second vibrational response points comprise a frequency.

5. The vibrating meter (100) of claim 3, wherein the first and second vibrational response points comprise a time period.

6. The vibrating meter (100) of claim 1, wherein the vibrating element (104) is cantilevered.

7. The vibrating meter (100) of claim 1, wherein the first vibrational response point and a second vibrational response point of the vibrational response correspond to the same moment in time.

8. The vibrating meter (100) of claim 1, wherein the other measured response points comprise at least two points.

9. A method of determining a viscosity or a density of a fluid using a vibrating meter (100) comprising: sending an excitation signal to a driver (112); driving a vibrating element (104) with the driver (112); detecting vibrations of the vibrating element (104); measuring a first vibrational response point of the vibrational response; calculating a second vibrational response point of the vibrational response, wherein the second vibrational response point is one of interpolated and extrapolated from other measured response points; calculating a Q of the vibrating element (104) using the first vibrational response point and the second vibrational response point.

10. The method of claim 9, comprising the step of determining a viscosity of the fluid using the Q.

11. The method of claim 9, wherein the first vibrational response point comprises one of a leading 3 dB bandwidth measurement point (F.sub.1) and a trailing 3 dB bandwidth measurement point (F.sub.2), and the second vibrational response comprises one of a leading 3 dB bandwidth measurement point (F.sub.1) and a trailing 3 dB bandwidth measurement point (F.sub.2), and the second vibrational response point is different from the first vibrational response point.

12. The method of claim 9, wherein the first and second vibrational response points comprise a frequency.

13. The method of claim 9, wherein the first and second vibrational response points comprise a time period.

14. The method of claim 9, wherein the first vibrational response point and a second vibrational response point of the vibrational response correspond to the same moment in time.

15. The method of claim 9, wherein the other measured response points comprise at least two points.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The same reference number represents the same element on all drawings. It should be understood that the drawings are not necessarily to scale.

[0034] FIG. 1 illustrates 3 dB time points T.sub.A and T.sub.B in time period terms;

[0035] FIG. 2 illustrates 3 dB time points F.sub.1 and F.sub.2 in frequency terms;

[0036] FIG. 3 illustrates prior art measurement of 3 dB points related to Q calculations;

[0037] FIG. 4 illustrates a vibrating meter;

[0038] FIG. 5 illustrates measurement of 3 dB points related to Q calculations according to an embodiment;

[0039] FIG. 6 illustrates measurement of 3 dB points related to Q calculations according to an alternate embodiment;

[0040] FIG. 7 illustrates a comparison of prior art measured Q over time versus measured Q according to embodiments;

[0041] FIG. 8 illustrates meter electronics according to an embodiment; and

[0042] FIG. 9 illustrates a method of calculating Q according to an embodiment.

DETAILED DESCRIPTION

[0043] FIGS. 1 - 9 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of embodiments of a 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 present description. Those skilled in the art will appreciate that the features described below may be combined in various ways to form multiple variations of the 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.

[0044] The embodiments provided relate to densitometers and viscometers and related methods for accurately calculating Q measurements of vibratory members. In particular, readings for the leading 3 dB bandwidth measurement point (T.sub.A) and trailing 3 dB bandwidth measurement point (T.sub.B) are utilized in Q measurement calculations which correspond to the same moment so that even if the fluid density is changing, the Q measurement remains accurate.

[0045] FIG. 4 depicts a vibrating meter 100. The vibrating meter 100 may be configured to measure a density and/or viscosity of a fluid, such as a liquid or a gas, for example. Vibrating meter 100 includes a housing 102 with a vibrating element 104 located at least partially within the housing 102. Housing 102 helps to retain the fluid pressure as vibrating element 104 oscillates. A portion of housing 102 is cut away. In examples, vibrating meter 100 may be placed in-line in an existing pipeline. In further examples, however, the housing 102 may comprise closed ends with apertures to receive a fluid sample. In many instances, the housing 102 or vibrating element 104 may include flanges or other members for operatively coupling vibrating meter 100 to a pipeline or similar fluid delivering device in a fluid-tight manner. In the example of vibrating meter 100, vibrating element 104 is cantilever mounted to housing 102 at first end 106. Vibrating element 104 is free to vibrate at a second end 108.

[0046] The example vibrating meter 100 is immersive, meaning that the fluid under measurement is found all around vibrating element 104. The vibrating element 104 may take the form of a tube, sheet, modified sheet, fork (as illustrated), rod, or any other shape known in the art. The vibrating element 104 may be affixed at one or both ends, and may be cantilevered in some embodiments, such as that illustrated. According to the example shown, the vibrating element 104 may include a plurality of fluid apertures (not shown) near the first end 106. The fluid apertures 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, apertures may be provided in the housing 102 to expose the fluid under test to the outer surface of the vibrating element 104. In further examples, however, fluid may enter the vibrating meter through channels in the metal work near the first end 106.

[0047] Further shown in FIG. 4 is a driver 112 and a vibrating sensor 114 positioned within a cylinder 116. The driver 112 and vibrating sensor 114 may comprise coils, but other implementations are also possible, such as piezo sensors, optical sensors, strain gages, etc. If an electric current is provided to the coil, a magnetic field is induced in the vibrating element 104 causing the vibrating element 104 to vibrate. Conversely, the vibration of the vibrating element 104 induces a voltage in the vibrating sensor 114. The driver 112 receives a drive signal from a meter electronics 118 in order to vibrate the vibrating element 104 at one of its resonant frequencies in one of a plurality of vibration modes, including for example simple bending, torsional, radial, or coupled type. The vibrating sensor 114 detects the vibration of the vibrating element 104, including the frequency at which the vibrating element 104 is vibrating and sends the vibration information to the meter electronics 118 for processing. As the vibrating element 104 vibrates, the fluid contacting the vibrating element’s wall, and the fluid a short distance from the cylinder will vibrate along with the vibrating element 104. The added mass of the fluid contacting the vibrating element 104 lowers the resonant frequency. The new, lower, resonant frequency of the vibrating element 104 is used to determine the density of the fluid. The resonance response, or the quality factor, may also be used to determine the viscosity of the fluid. If a fluid under test is present, the Q of the vibrating element 104 will change inversely proportionally to the fluid viscosity.

[0048] In embodiments, a first frequency response point and a second frequency response point are measured for use in Q calculations. Alternatively, first and second time points are measured. Turning to FIGS. 3 and 4, in embodiments, readings of a frequency response of the vibrating element 104 for at least one of the leading 3 dB bandwidth measurement point (F.sub.1) and trailing 3 dB bandwidth measurement point (F.sub.2) is to fit a straight line, such that two values are used from the same time period. Such values may be consecutive, as illustrated, or non-consecutive. Such readings are computed by the meter electronics 118. It should be noted that either time period or frequency may be utilized in relation to 3 dB bandwidth measurement points.

[0049] In FIG. 5, it is illustrated by example that the F.sub.1 value is interpolated between points of actual measurement. In this case, a value is interpolated for F.sub.2 between sample numbers 4 and 6. It will be clear that this point in time corresponds with the point where F.sub.1 is measured—i.e. sample 5. This point corresponds to the arrow shown in FIG. 5. The interpolated F.sub.2 value is then utilized in conjunction with the measured F.sub.1 value at the time of F.sub.1 value measurement to calculate Q. It should be noted that this is merely an example, and the F.sub.1 value could be interpolated, with the F.sub.2 measurement being utilized for Q calculations. Furthermore, the sample numbers are also only provided for the purpose of illustrative example, and any sample numbers, consecutive or non-consecutive, may be used.

[0050] A disadvantage of this approach is that calculations for Q always lag behind the live measurement. An alternative method that does not result in a lag is illustrated in FIG. 6. In this embodiment, a line is fit between consecutive F.sub.2 measurements at sample number 2 and 4, and then extrapolated to a time point where sample number 5 is taken. This point corresponds to the arrow shown in FIG. 6. It should be noted again that this is merely an example, and the F.sub.1 value could be extrapolated, with the F.sub.2 measurement being utilized for Q calculations. Furthermore, the sample number is also only provided for the purposes of the example, and any sample numbers, consecutive or non-consecutive, may be used.

[0051] In the above examples, only two points are used for calculating an interpolated or extrapolated value. Multiple points, averages, running averages, slope equations or the like, and combinations thereof may also be used for calculating interpolated and/or extrapolated values.

[0052] FIG. 7 illustrates the nature of the calculated Q values over time where density is changing utilizing the offset 3 dB bandwidth measurement points that are employed by prior art devices. It will be clear that the measured Q is not stable. Superimposed upon this line is an example of the improved Q value measurement as a result of interpolation or extrapolation, as shown in FIGS. 3 and 4.

[0053] FIG. 8 is a block diagram of the meter electronics 118 according to an embodiment. In operation, the vibrating meter 100 provides various measurement values that may be outputted including one or more of a measured or averaged value of density, viscosity, and flow rate.

[0054] The vibrating meter 100 generates a vibrational response. The vibrational response is received and processed by the meter electronics 118 to generate one or more fluid measurement values. The values can be monitored, recorded, saved, totaled, and/or output.

[0055] The meter electronics 118 includes an interface 201, a processing system 200 in communication with the interface 201, and a storage system 202 in communication with the processing system 200. Although these components are shown as distinct blocks, it should be understood that the meter electronics 118 can be comprised of various combinations of integrated and/or discrete components.

[0056] The interface 201 may be configured to couple to the leads and exchange signals with the driver 112, vibrating sensors 114, and temperature or pressure sensors (not shown), for example. The interface 201 may be further configured to communicate over a communication path to external devices.

[0057] The processing system 200 can comprise any manner of processing system. The processing system 200 is configured to retrieve and execute stored routines in order to operate the vibrating meter 100. The storage system 202 can store routines including a general meter routine 204. The storage system 202 can store measurements, received values, working values, and other information. In some embodiments, the storage system stores a mass flow (m) 220, a density (ρ) 208, a viscosity (.Math.) 210, a temperature (T) 212, a pressure 214, a drive gain 205, a frequency and/or time period 216, a Q 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 description and claims.

[0058] The general meter routine 204 can produce and store fluid quantifications and flow measurements. The general meter routine 204 can generate viscosity measurements and store them in the viscosity 210 storage of the storage system 202, and/or density measurements and store them in the density 208 storage of the storage system 202, for example. The viscosity 210 value may be determined from the Q 218, as previously discussed and as known in the art.

[0059] FIG. 9 depicts a method in accordance with an embodiment. The method begins with step 300. In step 300, a vibrating element 100 is driven to vibrate by the driver 112. An excitation signal that controls the driver 112 is sent from meter electronics 118.

[0060] The method continues with step 302. In step 302, the vibrations of the vibrating element 104 are detected.

[0061] In step 304, a first vibrational response point of the vibrational response is measured.

[0062] In step 306, a second vibrational response point of the vibrational response is calculated. The second vibrational response point is calculated via one of interpolation and extrapolation from other measured response points.

[0063] A Q of the vibrating element 104 is calculated in step 308 using the first vibrational response point and the second vibrational response point, as described herein.

[0064] The detailed descriptions of the above embodiments are not exhaustive descriptions of all embodiments contemplated by the inventors to be within the scope of the present description. Indeed, persons skilled in the art will recognize that certain elements of the above-described embodiments may variously be combined or eliminated to create further embodiments, and such further embodiments fall within the scope and teachings of the present description. It will also be apparent to those of ordinary skill 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 present description.

[0065] Thus, although specific embodiments are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the present description, as those skilled in the relevant art will recognize. The teachings provided herein may be applied to other vibrating meters, and not just to the embodiments described above and shown in the accompanying figures. Accordingly, the scope of the embodiments described above should be determined from the following claims.