HK1198202B

HK1198202B - Method and apparatus for determining differential flow characteristics of a multiple meter fluid flow system

Info

Publication number: HK1198202B
Application number: HK14111654.8A
Authority: HK
Inventors: Joel Weinstein; Paul J. Hays
Original assignee: Micro Motion, Inc.
Filing date: 2011-07-07
Publication date: 2018-03-16

Description

Method and apparatus for determining differential flow characteristics of a multi-meter fluid flow system

Technical Field

The embodiments described below relate to vibrating meters, and more particularly, to a method and apparatus for determining differential flow characteristics of a fluid flow system having a plurality of vibrating meters.

Background

Vibration sensors, such as vibration density meters and Coriolis flow meters, are generally well known and are used to measure the mass flow rate and other information of a material flowing through a conduit in a flow meter. Exemplary Coriolis flow meters are disclosed in U.S. patent 4,109,524, U.S. patent 4,491,025, and reissue patent 31,450 (both to j.e. smith et al). These flow meters have one or more conduits in a straight or curved configuration. Each conduit configuration in a Coriolis mass flow meter has a set of natural vibration modes that can be of a simple bending, torsional, or coupled type. The conduits may be driven to oscillate in a preferred mode.

The material flows from the connecting line on the inlet side of the flow meter to the flow meter, is directed through the conduit, and exits the flow meter through the outlet side of the flow meter. The natural vibration modes of the vibrating material filled system are defined in part by the combined mass of the conduit and the material flowing inside the conduit.

When there is no flow through the flow meter, the driving force applied to the tubing causes all points along the tubing to oscillate with the same phase or a small "zero offset" (zero offset is the time delay measured at zero flow). As the material begins to flow through the flow meter, Coriolis forces cause various points along the pipe to have different phases. For example, the phase at the inlet end of the meter lags the phase at the centered driver position, while the phase at the outlet leads the phase at the centered driver position. Pick-off sensors on the pipe generate sinusoidal signals representative of the pipe motion. The signal outputs from the pickoff sensors are processed to determine the time delay between the pickoff sensors. The time delay between two or more pickoff sensors is proportional to the mass flow rate of material flowing through the pipe.

Meter electronics connected to the driver generates drive signals to operate the driver and determines mass flow rate and other characteristics of the material based on the signals received from the pickup sensors. The driver may comprise one of many well-known arrangements; however, magnets and opposing drive coils have met with great success in the flow meter industry. An alternating current is flowed to the drive coil to vibrate the conduit at a desired flow tube amplitude and frequency. It is also known in the art to provide a pick-off sensor in a magnet and coil arrangement very similar to the driver arrangement. However, while the driver receives current that causes motion, the pickup sensor may generate a voltage using the motion provided by the driver. The amount of time delay measured by the pickup sensor is very small; often in the form of nanoseconds. Therefore, the sensor output must be made very accurate.

In general, an initial calibration may be performed on a Coriolis flow meter and a flow correction factor may be generated with zero offset. In use, the flow correction factor can be multiplied by the time delay measured by the pickup sensor minus the zero offset to generate the mass flow rate. In most cases, an initial calibration of the Coriolis flow meter is typically made by the manufacturer and an accurate measurement is assumed to be provided without subsequent calibration. Additionally, one prior art method includes zero calibration of the flow meter by stopping flow, closing the valve, by the user after installation, thereby providing the meter with a zero flow reference under process conditions.

As noted above, there may be zero offset in many vibration sensors, including Coriolis flow meters, for which prior art methods initially correct. While this initially determined zero offset may properly correct the measurement under limited circumstances, the zero offset may change over time due to changes in various operating conditions (primarily temperature), which results in only partial correction. However, other operating conditions may also affect the zero offset, including pressure, fluid density, sensor mounting conditions, and the like. Also, the zero offset may vary at different rates from meter to meter. It would be of particular interest to connect more than one meter in series such that the reading of each meter should be the same if the same flow rate is measured. Examples of such situations include applications for fuel consumption and leak detection.

It is known to determine different zero offsets to configure two meters to read substantially the same flow rate when the flow through the meters is substantially the same (as taught in international publication WO/2011/019344, assigned to the applicant of the present invention and the entire contents of its teachings incorporated herein by reference). However, there is still a need for improvements in the differential measurements obtained from multi-sensor systems. The embodiments described below overcome this and other problems and achieve an advance in the art. In the embodiments described below, the differential flow measurements obtained from two or more vibrating meters are refined by adding a low differential flow cutoff value (which corrects for the determined differential flow and other flow characteristics if the determined differential flow is below a threshold or band).

Disclosure of Invention

A fluid flow system is provided according to an embodiment. The fluid flow system includes a line having a flowing fluid and a first vibratory meter including a first sensor assembly located within the line and configured to determine one or more flow characteristics including a first flow rate. According to an embodiment, the fluid flow system further comprises a second vibratory meter comprising a second sensor assembly located within the pipeline and in fluid communication with the first sensor assembly and configured to determine one or more flow characteristics comprising a second flow rate. According to an embodiment, the fluid flow system further comprises a system controller in electrical communication with at least one of the first or second vibratory meters. The system controller is configured to receive the first and second flow rates and determine a differential flow rate based on the first and second flow rates. According to an embodiment, the system controller is further configured to compare the differential flow rate to a threshold value or band and to correct one or more flow characteristics if the differential flow rate is less than the threshold value or band.

In accordance with an embodiment, meter electronics for a first sensor assembly located within a pipeline and in fluid communication with a second sensor assembly of a vibrating meter in electrical communication with the meter electronics is provided. The meter electronics is configured to receive the sensor signal from the first sensor assembly and determine one or more flow characteristics including a first fluid flow rate. According to an embodiment, the meter electronics is further configured to receive a second fluid flow rate from a second vibratory meter and determine a differential flow rate based on the first and second fluid flow rates. According to an embodiment, the meter electronics is further configured to compare the differential flow rate to a threshold value or band and to correct one or more flow characteristics if the differential flow rate is less than the threshold value or band.

A method of operating a fluid flow system including a first vibratory meter and a second vibratory meter in fluid communication with the first vibratory meter is provided according to an embodiment. The method includes the steps of receiving a first sensor signal from the first vibratory meter and receiving a second sensor signal from the second vibratory meter. According to an embodiment, the method further comprises the step of determining one or more flow characteristics including first and second flow rates based on the first and second sensor signals and determining a differential flow rate based on the first and second flow rates. According to an embodiment, the method further comprises the step of comparing the differential flow rate with a threshold value or band and correcting one or more flow characteristics if the differential flow rate is smaller than the threshold value or band.

Aspect(s)

According to one aspect, a fluid flow system comprises:

a pipeline having a flowing fluid;

a first vibratory meter comprising a first sensor assembly located within a pipeline and configured to determine one or more flow characteristics including a first flow rate;

a second vibratory meter comprising a second sensor assembly located within the pipeline and in fluid communication with the first sensor assembly and configured to determine one or more flow characteristics comprising a second flow rate;

a system controller in electrical communication with the first and second vibratory meters and configured to:

receiving the first and second flow rates;

determining a differential flow rate based on the first and second flow rates;

comparing the differential flow rate to a threshold value or band; and

if the differential flow rate is less than a threshold value or band, one or more flow characteristics are corrected.

Preferably, the correcting comprises setting the differential flow rate to zero.

Preferably, one of the first or second flow rates is determined using a differential zero offset.

Preferably, the system controller is further configured to determine a new differential zero offset if the differential flow rate is less than the threshold value.

Preferably, the system controller is further configured to determine a new differential zero offset if the differential flow rate is less than the threshold for a predetermined amount of time.

Preferably, the system controller is further configured to apply a group delay to one of said first or second flow rates such that said first and second flow rates represent flow rates occurring at substantially the same time.

According to another aspect, meter electronics for a first sensor assembly (the first sensor assembly being located within a pipeline and in fluid communication with a second sensor assembly of a vibrating meter, the vibrating meter being in electrical communication with the meter electronics) is configured to:

receiving a sensor signal from a first sensor assembly and determining one or more flow characteristics including a first fluid flow rate;

receiving a second fluid flow rate from a second vibratory meter;

determining a differential flow rate based on the first and second fluid flow rates;

comparing the differential flow rate to a threshold value or band; and

correcting one or more flow characteristics if the differential flow rate is less than the threshold value or band.

Preferably, the meter electronics is further configured to determine the first fluid flow rate using differential zero offset.

Preferably, the meter electronics is further configured to determine a new differential zero offset if the differential flow rate is less than the threshold value or band.

Preferably, the meter electronics is further configured to determine a new differential zero offset if the differential flow rate is less than the threshold or band for a predetermined amount of time.

Preferably, the meter electronics is further configured to determine the differential flow rate using a group delay applied to the first flow rate such that the first and second flow rates represent flow rates occurring at substantially the same time.

According to another aspect, a method of operating a fluid flow system (the fluid flow system including a first vibratory meter and a second vibratory meter in fluid communication with the first vibratory meter) includes the steps of:

receiving a first sensor signal from the first vibratory meter and receiving a second sensor signal from the second vibratory meter;

determining one or more flow characteristics including first and second flow rates based on the first and second sensor signals;

determining a differential flow rate based on the first and second flow rates;

comparing the differential flow rate to a threshold value or band; and

Preferably, the method further comprises the step of determining a new differential zero offset if the differential flow rate is less than the threshold value or band.

Preferably, the method further comprises the step of determining a new differential zero offset if the differential flow rate is less than the threshold or band for a predetermined amount of time.

Preferably, the step of determining the differential flow rate comprises applying a group delay to one of the first or second flow rates such that the first and second flow rates represent flow rates occurring at substantially the same time.

Drawings

Fig. 1 shows a vibrating meter according to an embodiment.

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

Fig. 3 illustrates a fluid flow system according to an embodiment.

Fig. 4 shows a graph of mass flow rate versus time.

Fig. 5 shows a graph of mass flow rate versus time for varying supply flow rates.

FIG. 6 shows a graph of differential flow rate and engine consumption at various group delay conditions.

Fig. 7 shows a processing routine according to an embodiment.

Detailed Description

Fig. 1-7 and the following description depict specific examples that teach those skilled in the art how to make and use the best mode of an embodiment of a sensor assembly. 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 below can be combined in various ways to form multiple variations of a vibrating meter system. Accordingly, the embodiments described below are not limited to the specific examples described below, but only by the claims and their equivalents.

FIG. 1 shows an example of a vibrating meter 5 in the form of a Coriolis flow meter, which includes a sensor assembly 10 and one or more meter electronics 20. The meter electronics 20 is connected to the sensor assembly 10 via leads 100 to measure one or more flow characteristics of the material, such as, for example, density, mass flow rate, volume flow rate, total mass flow, temperature, and other information.

The sensor assembly 10 includes a pair of flanges 101 and 101', manifolds 102 and 102', and conduits 103A and 103B. Manifolds 102,102' are attached to opposite ends of conduits 103A, 103B. The flanges 101 and 101 'of the present embodiment are attached to manifolds 102 and 102'. The manifolds 102 and 102' of the present embodiment are attached to opposite ends of the spacer 106. In the present embodiment, spacers 106 maintain the spacing between manifolds 102 and 102' to prevent undesirable vibrations in conduits 103A and 103B. The conduits 103A and 103B extend outwardly from the manifold in a substantially parallel manner. When sensor assembly 10 is inserted into a pipeline system carrying a flowing material (see fig. 3), the material enters sensor assembly 10 through flange 101, passes through inlet manifold 102 (where the total amount of material in inlet manifold 102 is directed into conduits 103A and 103B), flows through conduits 103A and 103B and back into outlet manifold 102 '(where the material exits sensor assembly 10 through flange 101').

The sensor assembly 10 includes a driver 104. The driver 104 is attached to the conduits 103A and 103B at a position where the driver can vibrate the conduits 103A,103B in the driving mode. More specifically, the driver 104 includes a first driver component (not shown) attached to the conduit 103A and a second driver component (not shown) attached to the conduit 103B. Driver 104 may comprise one of many well-known arrangements, such as a magnet mounted to conduit 103A and an opposing coil mounted to conduit 103B.

In the present example, the drive mode is the first out of phase bending mode, and the conduits 103A,103B are preferably selected and suitably mounted to the inlet and outlet manifolds 102,102 'so as to provide a balanced system having substantially the same mass distribution, moment of inertia, and modulus of elasticity about the bending axes W-W and W' -W, respectively. In the present example (where the drive mode is the first out of phase bending mode), the driver 104 drives the conduits 103A,103B in opposite directions about respective bending axes W-W and W '-W' of the conduits 103A, 103B. The meter electronics 20 may provide the drive signal in the form of an alternating current (e.g., such as via channel 110), and the passage of the current through the coil causes the conduits 103A,103B to oscillate. Those skilled in the art will appreciate that other drive modes may be employed within the scope of the present embodiments.

The sensor assembly 10 also includes a pair of pickoff sensors 105,105' attached to the conduits 103A, 103B. More specifically, a first pick-up member (not shown) is located on the conduit 103A and a second pick-up member (not shown) is located on the conduit 103B. In the illustrated embodiment, the pick-off sensors 105,105' may be electromagnetic detectors, such as pick-off magnets and pick-off coils that produce pick-off signals representative of the velocity and position of the conduits 103A, 103B. For example, the pickoff sensors 105,105 'may provide pickoff signals to the meter electronics 20 via channels 111, 111'. Those skilled in the art will appreciate that the motion of the conduits 103A,103B is proportional to certain flow characteristics (e.g., mass flow rate, density, volumetric flow rate, etc.) of the material flowing through the conduits 103A, 103B.

It should be understood that while the sensor assembly 10 is described above as including a dual flow conduit sensor assembly, it is beneficial within the scope of the present embodiment to employ a single conduit sensor assembly. Also, while the flow conduits 103A,103B are illustrated as including a curved flow conduit configuration, the present embodiment may be implemented with a sensor assembly including a straight flow conduit configuration. Accordingly, the particular embodiment of the sensor assembly 10 described above is merely an example, and should not limit the scope of the present embodiments in any way.

In the embodiment shown in FIG. 1, the meter electronics 20 receives pickup signals from the pickup sensors 105, 105'. Path 26 provides input and output means that allow meter electronics 20 to be connected to an operator or to another meter electronics (see fig. 3). The meter electronics 20 measures one or more characteristics of the system, such as phase difference, frequency, time delay, density, mass flow rate, volume flow rate, total mass flow rate, temperature, meter verification, and other information. More specifically, the meter electronics 20 may receive one or more signals from the pickoff sensors 105,105' and one or more temperature sensors (not shown) and use this information to measure various properties of the material.

In addition, the sensor assembly 10 may include a temperature sensor 107, such as a Resistance Temperature Device (RTD), to measure the temperature of the fluid inside the conduits 103A, 103B. The RTD may be in electrical communication with the meter electronics 20 via lead 112.

Techniques for measuring flow characteristics using vibrating meters (e.g., Coriolis flow meters or density meters) are well known; therefore, the detailed description is omitted for the sake of brevity and clarity.

As briefly described above, one problem associated with vibrating meters (e.g., Coriolis flow meters) is the presence of zero offset, which is the time delay to pick up a sensor 105,105' measurement at zero fluid flow. If zero offset is not considered in calculating flow rate and various other flow characteristics, the flow characteristics measured in the measurement will typically contain errors. A typical prior art method for compensating for zero offset is to measure the initial zero offset (Δ t) during an initial correction process₀) The initial calibration process typically includes closing the valve and providing a zero flow reference condition. Such calibration procedures are well known in the art and a detailed description is omitted for the sake of brevity and clarity. Once the initial zero offset is determined, during operation, the flow measurement is corrected by subtracting the initial zero offset from the measured time delay according to equation (1).

=FCF(Δt_{Measured by}–Δt ₀) (1)

Wherein:

= mass flow rate;

FCF = flow correction factor;

Δt_{measured by}= measured time delay; and

Δt₀= initial zero offset.

It should be understood that equation (1) is provided merely as an example and should not limit the scope of the present embodiment in any way. Although equation (1) is provided to calculate mass flow rate, it should be understood that various other flow measurements may be affected by zero offset and therefore may also be corrected.

While this approach may provide adequate results in a single sensor assembly system, there are some instances in which multiple sensor assemblies in series are incorporated. For example, as explained in the above-mentioned international publication WO/2011/019344, in some cases the difference between two measured flow rates (differential flow rates) determined by two or more sensor assemblies is of greater concern than the absolute flow rate as determined by any one single sensor assembly. In this case, one vibrating meter may comprise a reference meter of the vibrating meter to be calibrated to provide substantially the same mass flow rate when the flow through the two meters is the same.

Because the two meters are configured to produce the same measurement under the same conditions, the absolute zero offset of the meters is not as important as in a single-meter system. Thus, according to embodiments, the meter electronics 20, or more than one meter electronics, may be configured to produce a differential zero offset between two or more sensor assemblies. The differential zero offset may include an initial zero offset of the sensor assembly combined with a differential error between two or more sensor assemblies. A differential zero offset may be required to produce substantially the same flow rate through the corrected sensor and the reference sensor. In other words, referring to equation (1) above, if the same fluid flow rate flows through the calibrated sensor and the reference sensor, then the two sensors can produce two mass flow rates for each sensor using equation (1). If the mass flow rate of the reference sensor is assumed to be equal to the mass flow rate of the corrected sensor assembly, then the differential zero offset of the corrected sensor can be calculated. This new offset is essentially a differential offset and is shown in equations (2 and 3).

== FCF_C[Δt_c- (Δt_C0+ Δt_E](2)

(3)

Wherein:

= mass flow rate calculated by reference sensor;

= mass flow rate calculated by the calibrated sensor;

Δt_0c= initial zero offset of the corrected sensor;

Δt_E= differential error;

Δt_C= measurement delay of the sensor being corrected; and

FCF_C= flow correction factor of the sensor being corrected.

Equation (3) can be further simplified by combining the zero offset of the corrected sensor with the differential error. The result is a formula defining the differential zero offset, which is shown in formula (4).

(4)

Wherein:

Δt_Ddifferential zero offset.

Thus, as explained in international publication WO/2011/019344, a differential zero offset may account for the difference in measured flow characteristics between two or more sensor assemblies (which measure substantially the same flow). When the differential zero offset used in the sensor is corrected instead of the initial zero offset to solve equation (1), the differential measurement performance of the sensor pair can be greatly improved. For example, the differential zero offset may be stored in the meter electronics 20.

Fig. 2 shows meter electronics 20 according to an embodiment. The meter electronics 20 may include an interface 201 and a processing system 203. The processing system 203 may include a storage system 204. The storage system 204 may include internal memory as shown, or alternatively, may include external memory. The meter electronics 20 can generate the drive signal 211 and provide the drive signal 211 to the driver 104. Additionally, the meter electronics 20 can receive sensor signals 210, such as pickup sensor signals, from the flow meter 10 and/or sensor assembly 10' shown below. In some embodiments, the sensor signal 210 may be received from the driver 104. The meter electronics 20 can be used as a density meter or can be used as a mass flow meter, including as a Coriolis mass flow meter. It should be understood that the electronic meter 20 may also be used as some other type of vibrating meter, and the particular example provided should not limit the scope of the present embodiment. The meter electronics 20 may process the sensor signal 210 to generate one or more flow characteristics of the material flowing through the conduits 103A, 103B. One or more flow characteristics may be generated using the stored differential zero offset 213. In some embodiments, the meter electronics 20 may receive the temperature signal 212, for example, from one or more resistance temperature measurement device (RTD) sensors or other temperature measurement devices.

The interface 201 may receive the sensor signal 210 from the driver 104 or the pickoff sensors 105,105 'via lead 110,111,111'. The interface 201 may perform any necessary or desired signal conditioning, such as any form of formatting, amplification, buffering, and the like. Alternatively, some or all of the signal conditioning may be performed in the processing system 203. In addition, the interface 201 may allow communication between the meter electronics 20 and external devices. The interface 201 may be competent for any form of electronic, optical, or wireless communication.

In one embodiment, the interface 201 may include a digitizer (not shown), wherein the sensor signal comprises an analog sensor signal. The digitizer may sample and digitize the analog sensor signal and generate a digital sensor signal. The digitizer may also perform any required decimation, where the digital sensor signals are decimated to reduce the amount of signal processing required and shorten the processing time.

The processing system 203 may perform the operations of the meter electronics 20 and process the flow measurements from the flow meter 10. The processing system 203 may execute one or more processing routines, such as the differential offset determination routine 213, to process the flow measurements to produce one or more flow characteristics that compensate for drift in the sensor zero offset.

The processing system 203 may comprise a general purpose computer, a micro-processing system, a logic circuit, or some other general purpose or custom processing device. The processing system 203 may be distributed among a plurality of processing devices. The processing system 203 may include any of a variety of integral or separate electronic storage media, such as storage system 204.

It should be understood that the meter electronics 20 may include various other components and functions as are well known in the art. These other features have been omitted from the description and drawings for the sake of brevity and clarity. Accordingly, the present embodiments should not be limited to the specific configurations illustrated and described.

Although the vibrating meter described above may be implemented as a single vibrating meter system, there are many applications that use multiple vibrating meters in series. In many of these applications, the absolute flow rates measured by each individual sensor assembly are not of particular interest, rather the difference between the flow rates measured by the various sensor assemblies (i.e., differential flow rates) are flow characteristics of primary interest to a user or operator. Two common examples of such situations are in the application of fuel consumption measurements and leak detection measurements. The fuel consumption application is shown in fig. 3; however, the figure is equally applicable to other situations (such as leak detection systems) in which a plurality of sensor assemblies are implemented in series and the difference in measured values between at least two sensor assemblies is of interest.

Fig. 3 illustrates a block diagram of a fluid flow system 300, according to an embodiment. Although the fluid flow system 300 is illustrated as a typical fuel consumption system, it should be understood that fuel is only one exemplary fluid and that the fluid flow system 300 is equally applicable to other fluids. Thus, the use of fuel should not limit the scope of the present embodiment.

The fluid flow system 300 includes: a fuel supply 301, a line 302, a first sensor assembly 10 located in the line 302, a fuel outlet 304, and a second sensor assembly 10' located in the line 302. Thus, the line 302 provides a fluid communication path between the first and second sensor assemblies 10, 10'. The second sensor assembly 10' may include a sensor assembly similar to the first sensor assembly 10 as shown in fig. 1. Typically, an engine or other fuel consuming device will be located between the first and second sensor assemblies 10,10' in the fuel outlet 304; however, this device has been omitted from the figure to reduce the complexity of the illustration.

Also shown in FIG. 3 are first and second meter electronics 20,20' in electrical communication with respective sensor assemblies 10,10' via leads 100,100 '. In addition, the first meter electronics 20 is in electrical communication with the second meter electronics 20' via leads 26. Thus, the second meter electronics 20 'may receive sensor signals from both sensor assemblies 10, 10'. Alternatively, the first meter electronics 20 may process the sensor signal from the first sensor assembly 10 and provide the measured flow characteristic to the second meter electronics 20'. The second meter electronics 20 'is illustrated in electrical communication with the system controller 310 via leads 26'. The system controller 310 may output information to a host system (not shown). Accordingly, the system controller 310 may comprise a central processing system, a general purpose computer, or some other type of general or customized processing device that may process signals received from both meter electronics 20, 20'. Thus, the system controller 310 may not comprise a part of the vibrating meter 5,5', but may instead be configured to process signals from the vibrating meter 5, 5'. The system controller 310 may also be in electrical communication with a user interface (not shown). This may allow a user to configure the system controller 310 according to the user's preferences or requirements.

In other embodiments, both sensor assemblies 10,10' may be coupled directly to the same meter electronics. Alternatively, both meter electronics 20,20' may be coupled to the system controller 310. According to an embodiment, the first and second vibrating meters 5,5' comprise Coriolis flow meters. However, the vibratory meter may include other types of vibratory sensors that lack the measurement capabilities of a Coriolis flow meter. Thus, the present embodiments should not be limited to Coriolis flow meters.

In use, fluid (e.g., fuel) may be provided to the first sensor assembly 10 via line 302. As described above, the first vibration sensor 5 can calculate various flow characteristics (including the first fluid flow rate). The fuel then leaves the first sensor assembly 10 and flows towards the fuel consuming device and to the fuel outlet 304 or the second vibrating meter 5'. If fuel is drawn from the fuel outlet 304 (such as, for example, if the engine is running and consuming fuel), only a portion of the fuel exiting the first sensor assembly 10 will flow to the second sensor assembly 10' because the engine is not combusting all of the fuel provided. The second vibratory meter 5' can calculate various flow characteristics (including a second fluid flow rate). If the engine is running and consuming fuel, the first and second flow rates measured by the first and second vibrating meters 5,5' will be different, which results in a differential flow rate as defined by equation (5).

-= Δ(5)

Wherein:

is the mass flow rate measured by the first vibratory meter 5;

is the mass flow rate measured by the second vibratory meter 5'; and

Δis the differential flow rate.

Although equation (5) is provided in terms of mass flow rate, one skilled in the art will readily recognize how similar equations would be developed for volumetric flow rates. The differential flow rate is substantially equal to the amount of fuel consumed by the engine, and therefore, the flow rate is of interest for fuel consumption purposes.

Unused fuel flows through the second sensor assembly 10' and may be returned to the fuel supply 301 as shown. It should be understood that while the fluid flow system 300 shows only one fuel outlet 304 and two vibrating meters 5,5', in some embodiments there will be multiple fuel outlets, and thus more than 2 vibrating meters.

As discussed in International publication WO/2011/019344, the flow rate (fluid consumption) of fuel exiting the fuel outlet 304 is typically much less than the flow rate in the supply and return conduits 302,306, which results in an oversized sensor assembly 10, 10'. It can be readily appreciated that even small drifts in the zero offset of each individual vibrating meter can adversely affect the overall system. However, since the difference between the two flow rates is a value of interest, the calibration measurement does not require an absolute zero offset of the separate vibrating meter 5, 5'. Instead, the initially corrected zero offset of the first vibrating meter 5 may be used, and a differential zero offset may be calculated for the second vibrating meter 5' (as defined above and explained in more detail in the application of international publication WO/2011/019344). Although the second vibratory meter 5' is illustrated downstream of the first vibratory meter 5, the sequence may be switched while still remaining within the scope of the present embodiment. By way of example, the second vibrating meter 5' may be referenced against the first vibrating meter 5. However, the particular meter used as the reference meter is not important. Thus, in embodiments where the zero offset comprises a differential zero offset, one of the vibrating meters can be considered a reference meter, while the zero offset of the other vibrating meters is corrected to match the reference meter. Therefore, the differential zero offset can be calculated using the above equation (4).

While improvements have been made in differential flow measurement using differential zero offset, there are sometimes small differences that can occur between the zeroing operations when two meters measure the same flow. Although these differences are often small, the differences can be substantial when the total timing is over time. For example, if the engine is shut down for a long period of time while fuel is still flowing through the system, the summed differential flow rates between the two flow rates from the first and second vibratory meters 5,5' can accumulate to a significant error. During this situation, if the second vibratory meter 5' measures a flow rate that is less than the flow rate measured by the first vibratory meter 5, then the user or operator may assume that there is a leak in the system. Conversely, if the second vibratory meter 5' measures a flow rate greater than that measured by the first vibratory meter 5, the system essentially concludes that the engine is producing fuel, which may obviously be unrealistic.

Fig. 4 shows a graph of exemplary flow rate measurements obtained from the first and second vibrating meters 5, 5'. Between time zero and about 12:00, the flow rate through the fluid flow system 300 is about 2600 kg/hr. However, at about 12:00, the engine starts and fuel begins to be consumed by exiting the fuel outlet 304. Thus, the fuel provided is increased slightly to about 2750 kg/hr to ensure that sufficient fuel is provided to the engine, as measured by the first vibratory meter 5 and shown on line 405 in FIG. 4. However, the second vibratory meter 5 'measures a mass flow rate of approximately 1850 kg/hr (as shown by line 405'). Thus, meter electronics 20' or system controller 310 may determine that the difference in the flow rates measured by first and second vibratory meters 5,5' (i.e., the differential flow rate between first and second vibratory meters 5,5') is about 900 kg/hr. As mentioned above, this differential flow rate is a value of interest in fuel consuming applications.

Fig. 4 also shows that the engine is shut down at approximately 18:00 (where the mass flow rates measured by the first and second vibratory meters 5,5' are substantially equal). According to an embodiment, the meter electronics 20' may ensure that the differential flow rate measured when the engine is off and therefore not consuming fuel is corrected. According to an embodiment, the meter electronics 20' may, for example, compare the determined differential flow rate to a threshold value or band. If the determined differential flow rate is less than the threshold value or band, the system controller 310 or the meter electronics 20' may correct one or more flow characteristics of the fluid flow system 300.

According to an embodiment, the correcting may comprise determining that the differential flow rate is zero. According to an embodiment, the differential flow rate may be set to zero by setting the second flow rate measured by the second vibratory meter 5' equal to the first flow rate measured by the first vibratory meter 5. In other words, even if the flow rates determined by the first and second vibratory meters 5,5 'are not equal, the meter electronics 20' or the system controller 310 may output a differential flow rate of zero. This is similar to the low flow cutoff as known in prior art single meter systems. However, low flow cutoff values cannot be used in some embodiments of the fluid flow system 300 because each vibrating meter 5,5 'still has appreciable fluid flow through the sensor assembly 10, 10'. Thus, rather than using a low flow cutoff, the differential flow rate can be compared to a threshold value or band (range of values). The threshold value or band may include a differential flow rate (if below which the determined differential flow rate is attributable to error rather than actual differential flow). The particular values for the threshold or band will generally depend on the particular environment of the fluid flow system 300. For example, what typical differential flow rate values are included during normal use. Preferably, the threshold value or band will be sufficiently far from the usual differential flow rate that it is defined that the determined flow rate will not fall below said threshold value or band when the engine assembly is consuming fuel.

According to another embodiment, the correction performed when the differential flow rate is determined to be below the threshold value or band may include setting the differential flow rate to zero by determining a new differential zero offset. For example, if the differential flow rate is below a threshold value or band, then the determined differential flow rate may be attributed to the change in differential zero offset determined above. Thus, when the differential flow rate is below the threshold or band, the meter electronics 20 'may assume, for example, that the flow rates through the vibrating meters 5,5' are substantially the same, and a new differential zero offset may be determined. According to an embodiment, the new differential zero offset may be determined at any time when the differential flow rate is below a threshold or band. Alternatively, a new differential zero offset may be determined at any time when the differential flow rate is below the threshold or takes a predetermined amount of time. When the differential flow rate is below the threshold or band for a predetermined amount of time and the flow rates through the first and second vibratory meters 5,5' are substantially constant, a new differential zero offset may be determined. This may prevent a new differential zero offset from being determined during a flow variation. In another alternative embodiment, if the user initiates a new zeroing routine and the differential flow rate is below the threshold or band, a new zero offset may be determined.

According to another embodiment, the correction of one or more flow characteristics when the differential flow rate is determined to be less than the threshold value or band may include a correction of a flow characteristic other than the flow rate. For example, if the differential flow rate is less than the threshold value or band, then substantially the same fluid flows through both sensor assemblies 10, 10'. Thus, the flow characteristics (such as density, viscosity, volumetric flow rate, etc.) should be substantially the same, assuming a substantially constant temperature. Thus, in the event that the differential flow rate is below the threshold value or band, the various flow characteristics determined by the first and second vibratory meters 5,5' may be compared to each other to ensure that the determined characteristics are substantially equal. When they are not equal to each other or within threshold limits, the meter electronics 20,20 'or the system controller 310 may recalibrate one or both of the vibrating meters 5,5' so that the vibrating meters calculate substantially equal values for the various flow characteristics. Alternatively, when the differential flow rate is less than the threshold value or band, the correction may include reporting an error message if the various flow characteristics do not substantially match or are within the threshold limits. One skilled in the art will readily recognize that the temperature inside an engine or other fluid consuming device may vary significantly. Thus, due to temperature variations in the fluid, the density and/or viscosity of the flow through the first and second vibrating meters 5,5' may be different even when the flow rates are substantially the same. Therefore, if the fluid temperature is different inside the first and second vibrating meters 5,5', a corresponding correction is required. For example, if the flow rate is measured as a mass flow rate, the volumetric flow rate may be obtained by conversion with density at a standard temperature.

In addition to the variations in differential zero offset that can occur between the first and second vibrating meters 5,5' over time, another problem associated with multi-meter systems is the delays that can occur when signals are transmitted between two or more vibrating meters. For example, as shown in fig. 3, the first meter electronics 20 is in electrical communication with the second meter electronics 20' via leads 26. While the leads 26 may comprise a variety of different communication protocols, one particularly popular communication protocol in the flow meter industry is Hart ® protocol. As is well known in the art, Hart ® protocols often have a delay between the time a signal is transmitted and the time a signal is received, which can affect the measurements.

By way of example, according to an embodiment, the second meter electronics 20' may obtain a measurement signal from the first meter electronics 20. However, the measurement of the signal received by the second meter electronics 20' may be delayed from the time the sensor signal was initially received by the first meter electronics 20 from the sensor assembly 10 over a predetermined interval. For example, the second meter electronics 20' may receive a measurement signal based on a sensor signal obtained 0.5 seconds prior to the sensor assembly 10. The delay may be due to processing delays or sampling delays. When the measurement signal is received, the second meter electronics 20 'may then compare the first flow rate obtained by the first vibratory meter 5 to a second flow rate determined based on the sensor signal received from the second sensor assembly 10' to determine a differential flow rate. An acceptable differential flow rate can be determined as long as the flow remains substantially constant during this sampling time. However, if the flow rate varies between sampling times, the sensor signal from the second sensor assembly 10 'will be compared to the erroneous flow rate received from the first vibratory meter 5, i.e., the second meter electronics 20' will compare measurements obtained based on two different flow rates taken at different times. This problem is illustrated in fig. 5.

Fig. 5 shows a graph of mass flow versus time. As can be seen, the mass flow provided by the fuel supply 301 varies over time. Further, the mass flow to the engine varies, for example, due to engine start-up and shut-down. When the fuel consumption changes, the measured differential flow rate as determined based on the first and second flows measured from the first and second vibrating meters 5,5' also changes. However, in addition to the differential flow rate variation due to the fuel consumption variation, the figure also shows various transient peaks 501 in the determined differential flow rate when the fuel supply is varied. These peaks occur without changing the fuel consumption rate. The peak 501 in the determined differential flow rate is due to processing delays that occur when the feed flow rate changes abruptly between sampling times. This results in a differential flow rate being determined using the sensor signals obtained at different times. To overcome the processing delay, a delay may be added to the sensor signal from the second sensor assembly 10'. So-called "group delay" may be added to better match the time of receiving the sensor signal from the first sensor assembly 10 to the time of receiving the sensor signal from the second sensor assembly 10' (even if the measurement signal is received from the first meter electronics 20 at a later point in time).

FIG. 6 shows a graph of mass flow rate versus time with various group delays applied to the sensor signal received from the second sensor assembly 10'. The engine consumption, as determined by a separate flow meter (not shown), is compared to the differential flow rate determined based on the sensor signals received from the first and second sensor assemblies 10, 10'. As shown on the far right, a large peak in the determined differential flow rate is seen when the engine consumption increases or decreases rapidly when no group delay is applied to the measurement. Conversely, when a group delay is applied to the sensor signal from the second sensor assembly 10', these peaks are greatly reduced, thereby improving the determined differential flow rate. For the Hart protocol, the group delay is about 650-; however, the particular group delay applied to the sensor signals may vary from application to application. Therefore, the particular values illustrated should not limit the scope of the present embodiments in any way.

The present embodiment implements a group delay that is applied to the sensor signal received from the second sensor assembly 10 'due to the processing delay caused by transmitting the measurement signal from the first meter electronics 20 to the second meter electronics 20'. The group delay may be equally applied to the sensor signals received from the first sensor assembly 10. It should be understood that the particular group delay required may depend on the particular communication protocol employed. Also, in embodiments where a single meter electronics receives sensor signals from both sensor assemblies 10,10', a group delay may also be required. Furthermore, those skilled in the art will readily recognize that in embodiments where the measurement signals are transmitted from the first and second meter electronics 20,20' to the system controller 310 for further processing, a group delay may also be required; for example, in embodiments where the system controller 310 performs differential flow calculations.

Fig. 7 illustrates a processing routine 700 according to an embodiment. For example, the processing routine 700 may be stored in and executed by one of the meter electronics 20 or 20'. Alternatively, the processing routine 700 may be stored in and executed by the system controller 310. The process routine 700 may be used to prevent reporting and aggregating false differential flow rates. The process routine 700 may also be used to update the differential zero offset of the corrected vibration sensor.

The processing routine begins at step 701, where a first sensor signal is received from a first sensor assembly 10 and a second sensor signal is received from a second sensor assembly 10'.

At step 702, first and second flow characteristics are determined based on the first and second sensor signals. According to an embodiment, the first and second flow characteristics may comprise first and second flow rates. According to an embodiment, one of the first and second flow rates may be determined using the differential zero offset as described above. The first and second flow rates may comprise mass flow rates. Alternatively, the first and second flow rates may comprise volumetric flow rates.

At step 703, a differential flow rate is determined based on the first and second flow characteristics. According to one embodiment, the differential flow rate may be determined using a group delay applied to the second flow rate, such that the differential flow rate is determined using the first and second flow rates obtained at substantially the same time.

At step 704, the differential flow rate is compared to a threshold value or band. The threshold or band may be predetermined by the manufacturer. Alternatively, for example, the threshold or band may be selected by the user. If the differential flow rate is less than the threshold value or band, then meter electronics 20 'may correct one or more flow characteristics of first or second vibratory meter 5,5' at step 705. As described above, the differential flow rate may drop below a threshold value or band for a variety of reasons. In the fuel consuming application discussed above, the differential flow rate may drop below a threshold or band when the engine is shut down.

As described above, the correction may include outputting a differential flow rate of zero. According to another embodiment, the correction may include calculating a new differential zero offset. A new differential zero offset can be calculated to produce substantially equal first and second flow rates. This new differential zero offset can then be used for subsequent measurements. For example, correcting may also include outputting an error message or correcting for other flow characteristics, such as, for example, a determined density, or temperature. If the differential flow rate is not less than the threshold value or band, the process routine may return to step 701 or end.

The above-described embodiments provide an apparatus and method for correcting one or more flow characteristics of a fluid flow system (which uses multiple vibratory meters). These embodiments provide a method for preventing erroneous differential flow rates from being summed and/or reported as actual flows. Conversely, if the differential flow rate determined by two or more vibrating meters is below a threshold value or band, the differential flow rate may be set to zero. The differential flow rate can simply be set to zero and output. Or a new differential zero offset may be calculated to equalize the first and second flow rates, thereby effectively setting the differential flow rate to zero. Furthermore, the above embodiments may account for delays due to signal processing or signal sampling (which may affect the differential flow rate if the flow rate through the system varies).

The above detailed description of the embodiments is not an exclusive description of all embodiments that the inventors intend to be within the scope of the present description. Indeed, those skilled in the art will recognize that certain elements of the above-described embodiments may be variously combined or eliminated to produce yet other embodiments, and that such other 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 produce other embodiments within the scope and teachings of the present description.

Thus, while specific embodiments of, and examples for, the sensor assembly are described herein for illustrative purposes, 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 sensor assemblies, not just to the embodiments described above and shown in the drawings. Accordingly, the scope of the above-described embodiments is to be determined in accordance with the following claims.

Claims

1. A fluid flow system (300), comprising:

a pipeline (302) having a flowing fluid;

a first vibratory meter (5) comprising a first sensor assembly (10), the first sensor assembly (10) being located within a pipeline (302) and configured to determine one or more flow characteristics comprising a first flow rate;

a second vibratory meter (5') including a second sensor assembly (10'), the second sensor assembly (10') being located within the pipeline (302) and in fluid communication with the first sensor assembly (10) and configured to determine one or more flow characteristics including a second flow rate;

a system controller (310), the system controller (310) in electrical communication with the first and second vibratory meters (5,5') and configured to:

receiving the first and second flow rates;

determining a differential flow rate based on the first and second flow rates;

comparing the differential flow rate to a threshold value or band;

correcting one or more flow characteristics if the differential flow rate is less than a threshold value or band; and

applying a group delay to one of the first or second flow rates such that the first and second flow rates represent flow rates occurring at substantially the same time.

2. The fluid flow system (300) of claim 1, wherein said correcting comprises setting said differential flow rate to zero.

3. The fluid flow system (300) of claim 1, wherein one of the first or second flow rates is determined using a differential zero offset.

4. The fluid flow system (300) of claim 3, wherein the system controller (310) is further configured to determine a new differential zero offset if the differential flow rate is less than the threshold.

5. The fluid flow system (300) of claim 3, wherein the system controller (310) is further configured to determine a new differential zero offset if the differential flow rate is less than the threshold for a predetermined amount of time.

6. A meter electronics (20') for a first sensor assembly located within a pipeline (302) and in fluid communication with a second sensor assembly of a vibrating meter (5), the vibrating meter (5) in electrical communication with meter electronics (20'), the meter electronics (20') configured to:

receiving a second fluid flow rate from a second vibratory meter (5);

comparing the differential flow rate to a threshold value or band;

correcting one or more flow characteristics if the differential flow rate is less than the threshold value or band; and

the differential flow rate is determined using a group delay applied to the first flow rate such that the first and second flow rates represent flow rates occurring at substantially the same time.

7. The meter electronics (20') of claim 6, wherein the correcting comprises setting the differential flow rate to zero.

8. The meter electronics (20') of claim 6, further configured to determine the first fluid flow rate using a differential zero offset.

9. The meter electronics (20') of claim 8, further configured to determine a new differential zero offset if the differential flow rate is less than the threshold value or band.

10. The meter electronics (20') of claim 8, further configured to determine a new differential zero offset if the differential flow rate is less than the threshold or band for a predetermined amount of time.

11. A method of operating a fluid flow system including a first vibratory meter and a second vibratory meter in fluid communication with the first vibratory meter, the method comprising the steps of:

determining a differential flow rate based on the first and second flow rates by applying a group delay to one of the first or second flow rates such that the first and second flow rates represent flow rates occurring at substantially the same time;

comparing the differential flow rate to a threshold value or band; and

12. The method of claim 11, wherein the correcting comprises setting the differential flow rate to zero.

13. The method of claim 11, wherein one of the first or second flow rates is determined using a differential zero offset.

14. The method of claim 13, further comprising the step of determining a new differential zero offset if the differential flow rate is less than the threshold value or band.

15. The method of claim 13, further comprising the step of determining a new differential zero offset if the differential flow rate is less than the threshold or band for a predetermined amount of time.