Patent ID: 12215992

DETAILED DESCRIPTION OF THE INVENTION

FIGS.1-8and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention and will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.

FIG.1illustrates an example of a flowmeter5in the form of a Coriolis flowmeter comprising a sensor assembly10and one or more meter electronics20. The meter electronics20are connected to the sensor assembly10to measure a fluid characteristic of a flowing material, such as, for example, density, mass flow rate, volume flow rate, totalized mass flow, temperature, and other information.

The sensor assembly10includes a pair of flanges101and101′ and a conduit103. Flanges101and101′ of the present example are affixed to spacers102and102′. Spacers102and102′ of the present example are affixed to opposite ends of conduit103. The spacers102and102′ maintain the spacing between flanges101and101′ and the conduit103in the present example to prevent undesired vibrations in the conduit103. The conduit103extends outwardly from the flanges101,101′. When the sensor assembly10is inserted into a pipeline system (not shown) which carries a flowing material, the material enters the sensor assembly10through flange101, passes into conduit103, where it exits the sensor assembly10through the flange101′. The flanges101,101′ may have mounting holes106,106′ configured to receive a fastener for purposes of installation to the pipeline system. The conduit103may, in an embodiment, be affixed to a case114via brace bars115,115′. In another embodiment, the brace bars115,115′ are independent of the conduit103, and may be used to support structures associated with the sensor assembly10.

The sensor assembly10includes a driver104. The driver104is affixed to conduit103in a position where the driver104can vibrate the conduit103in a drive mode. More particularly, the driver104includes a first driver component (not shown) affixed to conduit103and a second driver component affixed to a structure other than the conduit103. The driver104may comprise one of many well-known arrangements, such as a magnet mounted to the conduit103and an opposing coil mounted to a mounting bracket113, for example. The case114may have end caps116,116′ attached thereto.

In the present example, the drive mode is the first out-of-phase bending mode and the conduit103is selected and appropriately mounted to flanges101and101′ so as to provide a balanced system having a relatively predictable and/or constant mass distribution, moment of inertia, and elastic modulus about a longitudinal bending axis. In the present example, where the drive mode is the first out of phase bending mode, the conduit103is driven by the driver104. A drive signal in the form of an alternating current can be provided by one or more meter electronics20, such as for example via pathway110, and passed through a driver coil to cause conduit103to oscillate. Those of ordinary skill in the art will appreciate that other drive modes may be used within the scope of the present embodiments.

The sensor assembly10shown includes a pair of pickoffs105,105′ that are affixed to conduit103. More particularly, a first pickoff component (not shown) is located on conduit103and a second pickoff component is located on a structure independent of the conduit103. In the embodiment depicted, the pickoffs105,105′ may be electromagnetic detectors, for example—pickoff magnets and pickoff coils that produce pickoff signals that represent the velocity and position of the conduit103. For example, the pickoffs105,105′ may supply pickoff signals to the one or more meter electronics20via pathways111,111′. Those of ordinary skill in the art will appreciate that the motion of the conduit103is proportional to certain characteristics of the flowing material, for example, the mass flow rate and density of the material flowing through the conduits103.

It should be appreciated that while the sensor assembly10described above comprises a single conduit flowmeter, it is well within the scope of the present embodiments to implement a multi-conduit flowmeter. Furthermore, while the flow conduit103is shown as comprising a straight flow conduit configuration, the present embodiments may be implemented with a flowmeter comprising a curved/bent flow conduit configuration. It should also be appreciated that the pickoffs105,105′ can comprise strain gages, optical sensors, laser sensors, or any other sensor type known in the art. Therefore, the particular embodiment of the sensor assembly10described above is merely one example and should in no way limit the scope of the present embodiments.

In the example shown inFIG.1, the one or more meter electronics20receive the pickoff signals from the pickoffs105,105′. Path26provides an input and an output means that allows one or more meter electronics20to interface with an operator. The one or more meter electronics20measure a characteristic of a flowing material, such as, for example, a phase difference, a frequency, a time delay, a density, a mass flow rate, a volume flow rate, a totalized mass flow, a temperature, a meter verification, and other information. More particularly, the one or more meter electronics20receives one or more signals, for example, from pickoffs105,105′ and, in an embodiment, one or more temperature sensors107, such as a resistive temperature device (RTD), and use this information to measure a characteristic of a flowing material.

It should be appreciated that while the sensor assembly10described above comprises a single conduit flowmeter, it is well within the scope of the present invention to implement a dual conduit or multi-conduit flowmeter. Furthermore, while the flow conduit103is shown as comprising a straight conduit, a curved flow conduit configuration is well within the scope of the present invention. Therefore, the particular embodiment of the sensor assembly10described above is merely one example and should in no way limit the scope of the present invention.

FIG.2shows the meter electronics20according to an embodiment of the invention. The meter electronics20can include an interface301and a processing system303. The processing system303may include a storage system304. The storage system304may comprise an internal memory and/or may comprise an external memory. The meter electronics20can generate a drive signal311and supply the drive signal311to the driver104. In addition, the meter electronics20can receive sensor signals310from the pickoffs105,105′, such as pickoff/velocity sensor signals, strain signals, optical signals, or any other signals known in the art. In some embodiments, the sensor signals310can be received from the driver104. The meter electronics20can operate as a densitometer or can operate as a mass flowmeter, including operating as a Coriolis flowmeter. It should be appreciated that the meter electronics20may also operate as some other type of vibrating sensor assembly and the particular examples provided should not limit the scope of the present invention. The meter electronics20can process the sensor signals310in order to obtain flow characteristics of the material flowing through the flow conduits103A,103B. In some embodiments, the meter electronics20may receive a temperature signal312from one or more resistive temperature detector (RTD) sensors or other temperature sensors107, for example.

The interface301can receive the sensor signals310from the driver104or pickoffs105,105′, via pathways110,111,111′. The interface301may perform any necessary or desired signal conditioning, such as any manner of formatting, amplification, buffering, etc. Alternatively, some or all of the signal conditioning can be performed in the processing system303. In addition, the interface301can enable communications between the meter electronics20and external devices. The interface301can be capable of any manner of electronic, optical, or wireless communication.

The interface301in one embodiment can include a digitizer302, wherein the sensor signal comprises an analog sensor signal. The digitizer302can sample and digitize the analog sensor signal and produce a digital sensor signal. The digitizer302can also perform any needed decimation, wherein the digital sensor signal is decimated in order to reduce the amount of signal processing needed and to reduce the processing time.

The processing system303can conduct operations of the meter electronics20and process flow measurements from the sensor assembly10. The processing system303can execute one or more processing routines, such as a general operating routine314and calibration routine316, and thereby process inputs in order to produce one or more flow measurements that are accurate under a wide variety of conditions.

As an example of an overview of an embodiment of a calibration routine316, the system may be calibrated with a factory zero value at no-flow conditions. A user, at any time, may additionally, and optionally, perform a push-button zero. These various zero values are stored in the storage system304. As part of the operating routine314, the meter electronics20may generate and store values associated with process functions, such as the flow rate of process material, the density of process material, as well as any user-specified settings, such as any post-calibration compensation, for example, without limitation.

Meter electronics20inputs/measurements, saved values/constants, user settings, saved tables, etc. may be employed by the calibration routine316. The calibration routine316monitors flowmeter5conditions and applies the calibration algorithm deemed most appropriate for the conditions. Conditions may include user-input conditions, for example without limitation. Conditions may also include any combination of temperature, fluid density, flow rate, meter specifications, viscosity, Reynold's number, post calibration compensation, etc. There may be any number of algorithms applied as part of the calibration routine316. Additionally, besides differing algorithms, different constants, such as a flow calibration factor (FCF), for example without limitation, may be applied to the chosen algorithm based on operating conditions or user preference.

In addition, in the meter electronics20according to the invention, the vibrational response is also processed in order to determine a stiffness parameter (K) of the meter assembly10. Furthermore, the meter electronics20can process two or more such vibrational responses, over time, in order to detect a stiffness change (AK) in the meter assembly10. The stiffness determination can be made under flow or no-flow conditions. A no-flow determination may offer the benefit of a reduced noise level in the resulting vibrational response.

The Flow Calibration Factor (FCF) reflects the material properties and cross-sectional properties of the flow tube. A mass flow rate of flow material flowing through the flow meter is determined by multiplying a measured time delay (or phase difference/frequency) by the FCF. The FCF can be related to a stiffness characteristic of the meter assembly. If the stiffness characteristic of the meter assembly changes, then the FCF will also change. Changes in the stiffness of the flow meter therefore will affect the accuracy of the flow measurements generated by the flow meter.

The operating routine may comprise a mass flow routine, such as Equation (1) or Equation (2), below:
{dot over (M)}=FCF*(δtflow−δtzero)*(1−FT*TT−FTG*(TT−Tavg))*(1−FFQ*(τc−K2))  (2)
Where:
τc=τm*{1−DT*TT−DTG*(TT−Tavg)}1/2(3){dot over (M)}=Mass flow rateTavg=Average of reference tube and case temperatureδtflow=Time delay during flowδtzero=Time delay during zero flowFT=Flow tube temperature compensationFTG=Flow temperature gradient compensationDT=Density tube temperature compensationTT=Tube temperatureFFQ=Tube period compensationK2=High density tube periodDTG=Density gradient temperature compensationτm=Measured tube period

The operating routine may comprise a mass flow routine, such as Equation (4), below:

ρ=(C1*τcp2-C2)*{1+DFQ⁢1*(τcp-K⁢2)2+DFQ⁢2*(τcp-K⁢2)}(4)Where:C1=D⁢2-D⁢1K⁢22-K⁢12(5)C2=C1*K⁢12-D⁢1(6)τcp=τfd*{1-DT*TT-DTG*(TT-Tavg)}1/2(7)τfd=τm-Fd*δ⁢t2(8)ρ=Densityτm=Measured tube periodTT=Tube temperatureFd=Fluid density compensationDT=Density tube temperature compensationτfd=Mass flow rate compensated tube periodτcp=Mass flow rate and temperature compensated tube periodDTG=Density gradient temperature compensationDFQ1/DFQ2=Density linearization factorsTavg=Average of reference tube and case temperatureδt=Time delayD1=Low density fluid densityD2=High density fluid densityK1=Low density tube periodK2=High density tube period

The processing system303can comprise a general purpose computer, a micro-processing system, a logic circuit, or some other general purpose or customized processing device. The processing system303can be distributed among multiple processing devices. The processing system303can include any manner of integral or independent electronic storage medium, such as storage system304.

The processing system303processes the sensor signal310in order to generate a drive signal, among other things. The drive signal is supplied to the driver104via pathway110in order to vibrate the associated flow tube(s), such as the conduit103ofFIG.1.

It should be understood that the meter electronics20may include various other components and functions that are generally known in the art. These additional features are omitted from the description and the figures for the purpose of brevity. Therefore, the present invention should not be limited to the specific embodiments shown and discussed.

Turning toFIG.3, the flowmeter5was tested at a range of operating temperatures, starting at a flow tube temperature of around 20° C. to about 40° C. No flow-correction or temperature-correction was applied with the meter electronics20. Multiple measurements were made each at 20° C., 30° C., and 40° C., labelled A, B, and C, respectively. It will be clear that flow error increased drastically as the tube temperature increased.

FIG.4illustrates that flow error is easily corrected on a meter-by-meter basis, by adjusting FCF, FTC, FTG, and FTQ. This is accomplished on a test bench, and the correction is specific for the meter under test only. The tests necessary and correction calculations employed take many hours to implement, and are simply not practical for manufacturing, as the process is too labor intensive and cost prohibitive.

By way of example, averaged global correction factors for FCF, FTC, FTG, and FTQ were applied to three different flowmeters inFIGS.5A,5B, and5C. As noted above, straight tube flowmeters are particularly sensitive to thermal changes, which is due to the straight tube being constrained inside a rigid balance bar that restricts thermal expansion. When the meter changes temperature, the flow tube is either put into compression (higher temperatures) or tension (lower temperatures), thereby changing the stress state, which is in addition to the change in modulus caused by the change in temperature and manufacturing variations. Comparing the trend line (T) in each graph, it will be clear that global correction factors are not an adequate solution, as manufacturing tolerances result in errors that cannot be predicted. For example, the flowmeter illustrated byFIG.5Ahas a slightly negatively sloping error trend, and this is far more severe in the flowmeter illustrated byFIG.5B. Turning to the flowmeter illustrated byFIG.5C, the error trend slopes in the opposite direction. Such wildly varying error patterns are simply not acceptable for production units, and again it will be clear that global correction factors cannot simply be applied to flowmeters, for the measurement errors are too great and too unpredictable.

Typically, the mass flow equation, Equation 1, is corrected for temperature changes by simply multiplying the FCF by a Flow Tube Temperature Compensation, FTC, (% T Chg/100° C.). This works well for a curved tube meter where the effects of thermal expansion are minimal and the FTC term is only correcting for modulus changes. However, with a straight tube meter, the FTC term is attempting to correct the modulus change and the stress state that is set during manufacturing. This stress state can vary from meter to meter and makes using a global FTC inaccurate, as illustrated above.

In an embodiment, several flowmeters of the same size/model were used to determine meter specific FTC values. These FTC values are then correlated with a “stress state” value. In an embodiment, the “stress state” is the ratio of the K values. The K values, K1 and K2, are values determined during a standard calibration process, and comprise the tube period of the sensor filled with air (K1) and water (K2). If the K Ratio (K1 divided by K2) is compared with the meter specific FTC values of the above-referenced “several flowmeters of the same size/model” (the several flowmeters are illustrated as flowmeter1, F1; flowmeter2, F2; and flowmeter3, F3), a linear relationship is determined, as illustrated byFIG.6.

Using the slope intercept formula derived fromFIG.7, the following may be calculated, by way of example:

FTC=0.1⁢665⁢(K⁢1K⁢2)-0.1⁢8⁢1⁢8(9)

Relying on Equation 9, a meter-specific FTC value is determined at the point of standard calibration using values that would already be collected during calibration—i.e. K1 and K2. It should be noted that this slope value is merely an example and should in no way limit the embodiments of the invention, as slope, y-intercept, and K values will differ depending on the meter under test and the test conditions. It is also contemplated that other non-linear relationships besides a sloped line may also be utilized. Furthermore, curves that are averaged or fit to a particular motif are also contemplated. Also, instead of formulae, lookup tables stored in meter electronics20are also contemplated.

The same three different flowmeters inFIGS.5A,5B, and5Care represented inFIGS.7A,7B, and7C. However, inFIGS.7A-7C, the stiffness-correlated coefficient, FTC, has been applied to each flowmeter, according to an embodiment. It will be clear that utilizing the stiffness-correlated FTC value results in flow error that is far lower than using a global/average FTC value.

It should also be noted that this method could also be used with curved tubes as well, but the variation between the FTC values would be less than with straight tube meters.

FIG.8is a flow chart that illustrates an embodiment of a method of calibrating a flowmeter. In step800, the FTC is measured in a plurality of flowmeters of the same model type. In step802, flowmeter5tube periods K1 and K2 are determined for the plurality of flowmeters of the same model type from step800. These are tube periods measured with air and water in the flow conduit, respectively, as discussed herein.

In step804, a relationship between the FTC of step800and the tube periods of step802is determined. In an embodiment, the K1:K2 ratio is correlated with the measured FTC values. As noted above, this correlation is represented by a sloped line. It will be appreciated that other non-linear relationships besides a sloped line, may also be utilized. Furthermore, curves that are fit to a particular motif are also contemplated.

In step806, a flowmeter's tube periods, K1 and K2, are measured, as part of a calibration process. These tube periods are for the particular flowmeter under test.

In step808, a stiffness-correlated coefficient, FTC, is calculated using the measured flowmeter tube periods, K1 and K2, and the relationship between previously measured FTC values and previously measured K1:K2 ratios. In an embodiment, an equation having the structure of Equation 9 is utilized to determine the stiffness-correlated coefficient, FTC, from the measured flowmeter tube periods, K1 and K2.

The present invention as described above provides various methods and apparatuses to determine and apply coefficient determination to a vibrating flowmeter, such as a Coriolis flowmeter. Although the various embodiments described above are directed towards flowmeters, specifically Coriolis flowmeters, it should be appreciated that the present invention should not be limited to Coriolis flowmeters, but rather the methods described herein may be utilized with other types of flowmeters, or other vibrating sensors that lack some of the measurement capabilities of Coriolis flowmeters.

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 invention. 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 invention. 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 invention. Accordingly, the scope of the invention should be determined from the following claims.