HK1234484B - Fluid momentum detection method and related apparatus - Google Patents

Description

Fluid momentum detection method and related device

Technical Field

The embodiments described below relate to the field of fluid flow, and more particularly to improved fluid momentum detection methods and related apparatus.

Background Art

Vibrating conduit sensors (e.g., Coriolis mass flowmeters) and vibrating densitometers typically operate by detecting the motion of a vibrating conduit containing a flowing material. Properties related to the material in the conduit, such as mass flow and density, can be determined by processing measurement signals received from a motion transducer associated with the conduit. The vibration modes of a system filled with a vibrating material are typically influenced by the combined mass, stiffness, and damping characteristics of the conduit and the material contained therein.

The use of vibrating flowmeters to measure mass flow and other properties of material flowing through a pipe is well known. For example, U.S. Patent Nos. 4,491,025, issued to J.E. Smith et al., and Re. 31,450, also issued to J.E. Smith, disclose vibrating Coriolis flowmeters. These flowmeters have one or more fluid tubes (or "flowtubes"). Each flowtube configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which can be simple bending, torsional, radial, transverse, or coupled. Each flowtube is driven to oscillate at resonance in one of these natural modes. The vibration modes are generally influenced by the combined mass, stiffness, and damping characteristics of the flowtube and the material contained therein, and thus the mass, stiffness, and damping are typically determined during the initial calibration of the flowmeter using well-known techniques.

The material flows into the flow meter from the connected piping on the inlet side of the flow meter.The material is then directed through one or more flow tubes and out of the flow meter to the connected piping on the outlet side.

A driver (e.g., a voice coil-style driver) applies a force to one or more flow tubes. This force causes the flow tubes to oscillate. When no material is flowing through the flowmeter, all points along the flow tubes oscillate with the same phase. When material begins to flow through the flow tubes, Coriolis acceleration causes each point along the flow tubes to have a different phase relative to other points along the flow tubes. The phase on the inlet side of the flow tubes lags behind the driver, while the phase on the outlet side leads the driver. Sensors are typically placed at two different points along the flow tubes to generate sinusoidal signals representing the motion of the flow tubes at the two points. The phase difference between the two signals received from the sensors is calculated in units of time.

The phase difference between the two sensor signals is proportional to the mass flow rate of the material flowing through the one or more flow tubes. The mass flow rate of the material is determined by multiplying the phase difference by a flow calibration factor. The flow calibration factor depends on the material properties and cross-sectional characteristics of the flow tube. One of the main characteristics of the flow tube that affects the flow calibration factor is the stiffness of the flow tube. Before the flow meter is installed in the pipeline, the flow calibration factor is determined by a calibration process. During the calibration process, flow is passed through the flow tube at a given flow rate, and the ratio between the phase difference and the flow rate is calculated. The stiffness and damping characteristics of the flow tube are also determined during the calibration process, as is generally known in the art.

One advantage of Coriolis flowmeters is that the accuracy of the measured mass flow rate is primarily affected by wear of the moving parts in the flowmeter, whereas there are no moving parts in a vibrating flow tube. The flow rate is determined by multiplying the phase difference between two points on the flow tube by a flow calibration factor. The only input is a sinusoidal signal from a sensor that indicates the oscillations of the two points on the flow tube. The phase difference is calculated from the sinusoidal signal. Because the flow calibration factor is proportional to the material and cross-sectional properties of the flow tube, the phase difference measurement and the flow calibration factor are unaffected by wear of the moving parts in the flowmeter.

A typical Coriolis flow meter includes one or more transducers (or pickoff sensors, or simply "pickoffs"), typically employed to measure the vibration response of one or more flow conduits and located both upstream and downstream of the driver. The sensors are connected to electronic instrumentation. The instrumentation receives information from both sensors and processes the signals to derive, among other things, a mass flow rate measurement.

A typical Coriolis flowmeter measures flow and/or density by using coils and magnets as sensors to measure the motion of the meter's vibrating flow tube(s). The mass flow rate through the meter is determined based on the phase difference between the signals from multiple sensors located near the inlet and outlet of the meter's flow tubes. However, it is possible to use strain gauges instead of coil/magnet sensors to measure flow. The basic difference between the two sensor types is that coil/magnet sensors measure the velocity of the flow tube, while strain gauges measure the strain of the flow tube, which is proportional to the tube's displacement. Therefore, placement of each sensor type will not necessarily be in the same location.

Strain gauges offer several advantages over coil/magnet sensors. They are cheaper to produce and implement than coil/magnet sensors. They also help eliminate point masses that can adversely affect system operation. Furthermore, strain gauges do not require a reference point from which to measure strain, as coil/magnet sensors do. This allows for single-flow tube designs, which are not possible with coil/magnet sensors.

The principle of conservation of momentum requires that momentum at a given time remain constant as steady flow occurs through an isolated system of fluid (e.g., through the flow tube of a vibrating flowmeter). Because momentum is a vector quantity, a change in the direction of the flow causes a decrease in momentum in the original direction, which is an added offset in the new direction. Fluid traveling through a bend in a pipe, for example, exerts a force on the pipe that must be counteracted by the anchoring force to prevent movement. This is why thrust blocks are often installed near pipe bends, such as in municipal water pipe systems.

In the case of a U-bend, such as is often found in the flow tubes of vibrating flow meters, the fluid entering the flow tube changes direction 180°, so the return flow travels in the opposite direction in the same direction from which the fluid entered the flow tube. This change in direction causes the flow to exert two axial y-directed forces on the flow tube: internal pressure and momentum redirection.

The embodiments described below provide means for measuring fluid momentum. The purpose is to provide embodiments for measuring fluid momentum in a pipeline. The purpose is to provide embodiments for measuring fluid momentum in a vibrating meter. The purpose is to provide embodiments for measuring fluid momentum to detect pipe coating or blockage in a pipeline. The purpose is to provide embodiments for detecting pipe coating or blockage in a vibrating meter. The purpose is to use the measurement of fluid momentum to calculate mass and volume flow rates in a vibrating meter.

Summary of the Invention

According to an embodiment, a method for determining momentum of a fluid passing through one or more conduits is provided. The method includes the steps of receiving an extension signal from an extension sensor indicating extension of the one or more conduits due to flowing fluid and calculating a momentum term.

According to an embodiment, a flow meter is provided that includes a sensor assembly and meter electronics. According to an embodiment, the flow meter includes one or more flow tubes and a driver coupled to the one or more flow tubes and oriented to induce drive-mode vibrations in the one or more flow tubes. At least two sensors are coupled to the one or more flow tubes and configured to detect the drive-mode vibrations. One or more extension sensors are coupled to the one or more flow tubes, wherein the one or more extension sensors are configured to output a signal whose amplitude is proportional to a strain caused by fluid momentum in the one or more flow tubes, and wherein the meter electronics are configured to calculate a momentum term.

aspect

According to one aspect, a method for determining momentum of a fluid through one or more conduits includes the steps of receiving an extension signal from an extension sensor indicative of extension of the one or more conduits due to flowing fluid, and calculating a momentum term.

Preferably, calculating the momentum term comprises the step of deriving the momentum term from an axial strain equation comprising:

mv is the momentum term;

ε _y is the axial strain of the conduit or conduits;

F _Ay is the anchoring force of one or more catheters;

A _t is the cross-sectional area of the conduit or conduits;

E is the elastic modulus of the conduit or conduits;

m is the mass flow rate of the fluid;

v is the fluid velocity of the fluid;

A is the cross-sectional area of the fluid; and

Pavg _is the average static pressure of the fluid.

Preferably, the method for determining the momentum of a fluid through one or more conduits comprises the steps of receiving a temperature signal from a temperature sensor and calculating a temperature corrected momentum term.

Preferably, calculating the temperature corrected momentum term comprises the step of deriving the temperature corrected momentum term from an axial strain equation comprising:

F _Ay is the anchoring force;

mv is the momentum term;

ε _y is the axial strain of the conduit or conduits;

A _t is the cross-sectional area of the conduit or conduits;

E is the elastic modulus of the conduit or conduits;

m is the mass flow rate of the fluid;

v is the fluid velocity of the fluid;

A is the cross-sectional area of the fluid;

P _avg is the average static pressure of the fluid;

α _T is the coefficient of linear thermal expansion of the one or more conduits; and

ΔT is the change in temperature of one or more conduits.

Preferably, the one or more conduits comprise one or more flow tubes of a vibrating flow meter.

Preferably, a method for determining momentum of a fluid passing through one or more conduits comprises the steps of vibrating at least one of the one or more flow tubes in a drive-mode vibration; providing a first sensor and a second sensor on at least one of the one or more flow tubes; receiving a first sensor signal and a second sensor signal from the first sensor and the second sensor, respectively, based on a vibration response to the drive-mode vibration; calculating a difference between the first sensor signal and the second sensor signal; determining a mass flow based on the sensor signal difference; and comparing the mass flow to a momentum term.

Preferably, the step of comparing the mass flow and momentum terms comprises calculating the velocity v comprising m = ρ A v , where:

m is the mass flow rate of the fluid;

ρ is the density of the fluid; and

A is the cross-sectional area of the fluid; and

Computing a calculated momentum product term by multiplying the velocity and the mass flow rate; comparing the calculated momentum product term to a momentum term; and indicating an error if the calculated momentum product term deviates from the momentum term by more than a predetermined threshold.

Preferably, the step of providing an extension sensor on one or more conduits proximate a conduit region subjected to momentum redirecting forces comprises the steps of: receiving first and second extension sensor signals from the first and second extension sensors, respectively, based on a vibration response to a drive mode vibration; calculating a first momentum term from the first extension sensor signal and a second momentum term from the second extension sensor signal; comparing the first momentum term to the second momentum term; and determining the presence of flow asymmetry between the first and second flow tubes.

Preferably, the method for determining the momentum of a fluid through one or more conduits comprises the step of indicating the presence of flow asymmetry if the difference in the first momentum term and the second momentum term is greater than a predetermined threshold.

Preferably, the method for determining the momentum of a fluid through one or more conduits comprises the steps of calculating the mass flow rate and the volume flow rate using density and momentum terms of the fluid.

Preferably, the step of providing the density of the fluid comprises the step of measuring the density of the fluid.

According to one aspect, a flow meter including a sensor assembly and meter electronics includes: one or more flow tubes; a driver coupled to the one or more flow tubes and oriented to induce drive-mode vibrations in the one or more flow tubes; at least two sensors coupled to the one or more flow tubes and configured to detect the drive-mode vibrations; and one or more extension sensors coupled to the one or more flow tubes, wherein the one or more extension sensors are configured to output a signal whose amplitude is proportional to fluid momentum-induced strain in the one or more flow tubes, and wherein the meter electronics is configured to calculate a momentum term.

Preferably, the momentum term is derived from an axial strain equation comprising:

mv is the momentum term;

ε _y is the axial strain of the catheter;

F _Ay is the anchoring force of the catheter;

A _t is the cross-sectional area of the conduit;

E is the elastic modulus of the catheter;

m is the mass flow rate of the fluid;

v is the fluid velocity of the fluid;

A is the cross-sectional area of the fluid; and

Pavg _is the average static pressure of the fluid.

Preferably, at least one temperature sensor is coupled to the one or more flow tubes, wherein the meter electronics are configured to calculate a temperature corrected momentum term.

Preferably, the temperature corrected momentum is derived from an axial strain equation comprising:

F _Ay is the anchoring force;

mv is the momentum term;

ε _y is the axial strain of the catheter;

A _t is the cross-sectional area of the conduit;

E is the elastic modulus of the catheter;

m is the mass flow rate of the fluid;

v is the fluid velocity of the fluid;

A is the cross-sectional area of the fluid;

P _avg is the average static pressure of the fluid;

α _T is the coefficient of linear thermal expansion of the conduit; and

ΔT is the change in the catheter temperature.

Preferably, the extension sensor comprises at least one of a strain gauge, an optical sensor and a laser.

Preferably, the one or more flow tubes include at least one of a 180° U-bend and an ω-bend.

Preferably, the signal is a drag force having an amplitude proportional to the strain caused by the momentum of the fluid.

Preferably, the one or more extension sensors coupled to the one or more flow tubes include a first extension sensor coupled to a first flow tube of the one or more flow tubes and a second extension sensor coupled to a second flow tube of the one or more flow tubes.

Preferably, the meter electronics is configured to detect flow asymmetry between the first and second flow tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

Like reference numerals represent like elements throughout the drawings. The drawings are not necessarily to scale.

FIG1 shows a prior art flow meter;

FIG2 shows an embodiment of a flow meter;

FIG3 is a diagram of the meter electronics;

FIG4 is a flow chart illustrating an embodiment of a method of calculating a momentum term;

5 is a flow chart illustrating an embodiment of a method of calculating a temperature-corrected momentum term;

6 is a flow chart illustrating an embodiment of a method of calculating a momentum term in a flow meter;

7 is a flow chart illustrating an embodiment of a method of calculating a momentum term in a flow meter and indicating the presence of a measurement error;

8 is a flow chart illustrating an embodiment of a method of calculating flow asymmetry in a flow meter;

FIG9 is a flow chart illustrating an embodiment of a method of calculating mass flow and volume flow rates; and

10 is a graph showing measured fluid momentum strain versus mass flow rate in a Coriolis flow meter.

DETAILED DESCRIPTION

Figures 1-10 and the following description depict specific examples of best modes for teaching those skilled in the art how to make and use embodiments of methods and related devices for detecting fluid momentum. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will recognize variations from these examples that fall within the scope of the present invention. Those skilled in the art will recognize that the features described below can be combined in various ways to form multiple variations of the present invention. Therefore, the present invention is not limited to the specific examples described below, but only by the claims and their equivalents.

FIG1 illustrates a prior art flowmeter 5, which can be any vibrating meter, such as a Coriolis flowmeter. The flowmeter 5 includes a sensor assembly 10 and meter electronics 20. The sensor assembly 10 is responsive to the mass flow rate and density of the process material. The meter electronics 20 is connected to the sensor assembly 10 via leads 100 to provide density, mass flow rate, and temperature information along a path 26, as well as other information not relevant to the present invention. The sensor assembly 10 includes flanges 101 and 101', a pair of manifolds 102 and 102', a pair of parallel flow tubes 103 (a first flow tube) and 103' (a second flow tube), a driver 104, a temperature sensor 106, such as a resistance temperature detector (RTD), and a pair of sensors 105 and 105', such as magnet/coil sensors, strain gauges, optical sensors, or any other sensors known in the art. Flow tubes 103 and 103' have inlet legs 107 and 107', respectively, and outlet legs 108 and 108', respectively. The flow tubes 103 and 103' bend at at least one symmetrical location along their length and are substantially parallel throughout their length. Each flow tube 103, 103' oscillates about an axis W and W' respectively.

The legs 107, 107', 108, 108' of the flow tubes 103 and 103' are fixedly attached to the flow tube mounting blocks 109 and 109' and these blocks are in turn fixedly attached to the manifolds 102 and 102'. This provides a continuous closed material path through the sensor assembly 10.

When flanges 101 and 101' are connected to a process line (not shown) carrying the process material being measured, the material enters first end 110 of flow meter 5 through a first hole in flange 101 (not visible in the view of FIG1 ) and is directed to flow tube mounting block 109 through manifold 102. Within manifold 102, the material is distributed and routed through flow tubes 103 and 103'. Upon exiting flow tubes 103 and 103', the process material recombines in a single stream within manifold 102' and is thereafter routed to exit second end 112 connected by flange 101' to a process line (not shown).

Flow tubes 103 and 103' are selected and appropriately mounted to flow tube mounting blocks 109 and 109', respectively, to have substantially identical mass distributions, moments of inertia, and Young's moduli about bending axes W--W and W'--W'. Because the Young's modulus of flow tubes 103 and 103' changes with temperature, and this change affects flow and density calculations, temperature sensors 106 are mounted to flow tubes 103 and 103' to continuously measure the flow tube temperature. The flow tube temperature, and therefore the voltage appearing across temperature sensor 106 for a given current passing through it, is primarily governed by the temperature of the material passing through the flow tube. The temperature-dependent voltage appearing across temperature sensor 106 is used by meter electronics 20, in a known manner, to compensate for changes in the elastic modulus of flow tubes 103 and 103' due to any changes in flow tube temperature. The temperature sensor is connected to meter electronics 20.

The two flow tubes 103, 103' are driven by a driver 104 in opposite directions about their respective bending axes W and W' in a mode known as the first out-of-phase bending mode of the flow meter. This driver 104 can include any of a number of well-known arrangements, such as a magnet mounted to the flow tube 103' and an opposing coil mounted to the flow tube 103, with an alternating current passed through the flow tube 103 to cause the two flow tubes to vibrate. An appropriate drive signal is applied to the driver 104 by the meter electronics 20 via leads 113.

Meter electronics 20 receives the temperature signal on lead 114 and the left and right velocity signals appearing on leads 115 and 115', respectively. Meter electronics 20 generates a drive signal appearing on lead 113 to driver 104 and causes flow tubes 103, 103' to vibrate. Meter electronics 20 processes the left and right velocity signals and the temperature signal to calculate the mass flow rate and density of the material passing through sensor assembly 10. This information, along with other information, is applied by meter electronics 20 to a utilization device on path 26.

FIG2 shows an embodiment of a flowmeter 5. While a Coriolis flowmeter configuration is described, it will be apparent to those skilled in the art that the present invention can be implemented as a vibrating tube densitometer without the additional measurement capabilities provided by a Coriolis mass flowmeter. In fact, the present invention can be utilized in pipes of all sizes, with or without means for measuring mass flow, density, etc. Elements common to the prior art device of FIG1 share the same reference numerals.

Flow tubes 103 and 103' are driven by a driver 104 about their respective bending axes W and W' in opposite directions and in a mode referred to as the first out-of-phase bending mode of the flow meter. This driver 104 can include any of a number of well-known arrangements, such as a magnet mounted to flow tube 103' and an opposing coil mounted to flow tube 103, with an alternating current passed through flow tube 103 to cause both flow tubes to vibrate. It should be noted that flow tubes 103, 103' are substantially rigid—e.g., made of metal—so that they are capable of only limited motion, such as the vibrational motion induced by the driver. An appropriate drive signal is applied to driver 104 by meter electronics 20 via leads 113.

As a fluid flows through a tube or flow tube (hereinafter referred to simply as a flow tube) exhibiting a 180° U-bend, the fluid is redirected in the opposite direction in the same direction from which it entered the flow tube. The 180° U-bend is merely an example of a contemplated configuration. Other shapes and degrees of bend are contemplated within the scope of the present specification and claims. The flow tube thus experiences two axial y-directed forces due to fluid momentum, namely, internal pressure and momentum redirection. Summing the forces on the fluid control volume equals the anchoring force in the y-direction, as shown in Equation (1):

(1)

in:

m = mass flow rate

v = fluid velocity

A = cross-sectional area of the fluid

p = static pressure

The minus sign in equation (1) indicates that the direction of the force required to maintain the flow tube in the static position is in the negative y-direction. It should be noted that in many cases, an x-axis component will exist, such as for a 90° bend in the flow tube, because there will also be a force component acting in the x-direction. Because the flow tube in the transient case has a symmetrical bend (e.g., a 180° U-bend), the x-direction forces cancel.

As indicated in equation (1), the reaction force due to the change in fluid momentum causes the flow tube to extend in the y-direction. The pressure will also cause the flow tube to extend in the y-direction, but will also strain the flow tube radially. The magnitude of the y-direction extension can be predicted using the negative anchoring force F _Ay to indicate the force exerted by the fluid, as illustrated by equations (2) and (3).

(2)

(3)

in:

σ _y = axial strain

A _t = cross-sectional area of the flow tube

E = elastic modulus

ε _y = axial strain

By combining equations (2) and (3), an expression for the axial strain is derived in terms of the required fluid anchoring force due to the pressure and momentum terms, as shown by equation (4).

(4)

Applying the above equation to the embodiment _of flow meter 5, a constant cross-sectional geometry is applied, _so A1 = A2 . Also assuming a linear drop in pressure across the flow tube, a simplified equation is derived, equation (5):

(5)

in:

P _avg = average pressure in the flow tube

FIG3 illustrates meter electronics 20 for flow meter 5 according to an embodiment of the present invention. Meter electronics 20 may include an interface 201 and a processing system 203. For example, meter electronics 20 receives first and second sensor signals 115, 115' from sensor assembly 10 (e.g., from sensors 105, 105'). Meter electronics 20 processes first and second sensor signals 115, 115' to derive flow characteristics of the flowing material flowing through sensor assembly 10. For example, meter electronics 20 may determine one or more of phase difference, frequency, time difference (Δt), density, mass flow rate, fluid velocity, pressure, temperature, strain, and volume flow rate from the sensor signals. Furthermore, other flow characteristics may be determined according to the present invention.

Interface 201 receives sensor signals from sensors 105, 105' via leads 100 shown in Figure 2. Interface 201 may perform any necessary or desired signal conditioning, such as formatting, amplification, buffering, etc. Alternatively, some or all of the signal conditioning may be performed in processing system 203.

Furthermore, for example, interface 201 may enable communication between meter electronics 20 and external devices, such as via communication path 26. Interface 201 may be capable of any manner of electronic, optical, or wireless communication.

In one embodiment, the interface 201 includes a digitizer 202, wherein the sensor signal comprises an analog sensor signal. The digitizer samples and digitizes the analog sensor signal and produces a digital sensor signal. The interface/digitizer may also perform any required decimation, wherein the digital sensor signal is decimated to reduce the amount of signal processing required and reduce processing time.

The processing system 203 performs the operation of the meter electronics 20 and processes the measurements from the sensor assembly 10. The processing system 203 executes one or more processing routines and thereby processes the measurements to produce one or more characteristics.

Processing system 203 may include a general-purpose computer, a microprocessor system, a logic circuit, or some other general-purpose or custom processing device. Processing system 203 may be distributed among multiple processing devices. Processing system 203 may include any form of integrated or independent electronic storage media (e.g., storage system 204).

In the illustrated embodiment, processing system 203 determines flow characteristics based on signals derived from at least sensors 105, 105', temperature sensor 106, and extension sensor 120. Processing system 203 may determine at least the amplitude, strain, phase difference, time difference, and frequency of two or more responses from sensors 105, 105'. In an embodiment, sensors 105, 105', and/or extension sensor 120 include strain gauges. A voltage from at least one bridge circuit (not shown) (e.g., a Wheatstone bridge circuit) in electrical communication with at least one strain gauge is input to meter electronics 20. In some embodiments, only a single bridge circuit is present, while in other embodiments, at least two bridge circuits are present.

The storage system 204 can store flow meter parameters and data, software routines, constant values, and variable values. In one embodiment, the storage system 204 includes routines executed by the processing system 203. In one embodiment, the storage system 204 stores a fluid momentum routine 212, a flow asymmetry routine 215, a frequency routine 216, a time difference (Δt) routine 217, a flow characteristics routine 218, and a flow asymmetry alarm flag and/or routine 219.

In one embodiment, storage system 204 stores variables used to operate flow meter 5. In one embodiment, storage system 204 stores variables such as vibration responses 220, 221, 222, and 226 received/derived from sensors 105 and 105'. Any routine with meter electronics 20 can utilize variables such as, for example, phase difference 220, frequency 221, time delay 222, mass flow rate 223, density 224, volume 225, strain 226, and temperature 227, without limitation. In some embodiments, strain 226 may also be received from extension sensor 120. Other variables may include, for example, anchoring force 228, axial strain 229, elastic modulus 230, fluid velocity 231, cross-sectional area of the fluid 232, cross-sectional area of the conduit 233, pressure 234, linear thermal expansion coefficient 235, and momentum term 236, without limitation. In some embodiments, storage system 204 stores one or more values generated by meter electronics 20. In some embodiments, storage system 204 stores one or more flow characteristics measured from the sensors. In some embodiments, storage system 204 stores one or more constant variables.

Embodiments sense flow by directly measuring the relative motion of the outlet 108, 108' (or inlet 107, 107') side of a flow tube 103, 103' relative to the inlet 107, 107' (or outlet 108, 108') side of the same flow tube 103, 103'. In embodiments where strain gauges are used as sensors 105, 105', they can be connected to at least one bridge circuit and configured to produce a zero-amplitude signal during no-flow conditions (corresponding to the normal mode shape of the drive mode, i.e., no phase between the inlet and outlet of the tube). During flow, the same configuration will produce a sinusoidal signal output whose amplitude is a function of the flow rate (corresponding to a mode shape of increased complexity, i.e., due to the inlet/outlet phase of the flow). In a related embodiment, a combined signal from one or more strain gauges on the inlet side of the meter and a combined signal from one or more strain gauges on the outlet side of the meter are input into meter electronics 20. These signals are then processed like coil/magnet sensor signals, with a phase measurement derived from the inlet and outlet signals. In these embodiments, a bridge circuit can be used to amplify the signal. However, in other embodiments, the strain signals from the inlet and outlet sections of the flow tubes 103, 103' are combined in a bridge circuit. In this case, there is only one signal input to the meter electronics, whose amplitude is proportional to the phase.

The bridge circuit converts small changes in the strain gauge's resistance into relatively large changes in voltage. The bridge circuit consists of a supply voltage, _Vs , four resistors ( _R1 to _R4 ), and an output voltage, _V0 . When _R1 = _R2 and _R3 = _R4 , the bridge circuit is considered balanced, and the output voltage is 0 volts. A change in any of the resistors will cause the bridge to become unbalanced, and the output voltage will no longer be zero. The relationship between the supply voltage, resistance, and output voltage is shown in Equation (6).

(6)

Any or all of the resistors in the bridge circuit may be replaced by strain gauges.The above equations are used as examples only, and other equations or algorithms are contemplated herein.

In an embodiment, a first strain gauge sensor 105 is located on the inlet leg 107 of the first flow tube 103, and a second strain gauge sensor 105' is located on the outlet leg 108 of the first flow tube 103. The primary difference between a coil/magnet sensor and a strain gauge is that a coil/magnet sensor measures the velocity of the flow tube, while a strain gauge measures the strain of the flow tube. Each strain gauge disclosed herein can be oriented to detect strain caused by the drive mode motion of the flow tube 103, 103'. In an embodiment, the strain gauge is oriented substantially parallel to the longitudinal axis of the flow tube to which it is coupled.

For coil/magnet type sensors 105, 105', the maximum velocity amplitude is near the driver 104, which is typically located at the center of the "U" of the flow tube 103, 103'. However, coil/magnet type sensors 105, 105' are not placed in this location because this would place the sensors too close to the driver 104, and rather, they are located in an area that provides suboptimal, yet resolvable, velocity amplitudes for detecting phase signal differentials. However, the maximum strain amplitude is near the distal region of the inlet/outlet legs 107, 107', 108, 108' of the flow tube 103, 103', and this is where strain gauges may be located in the embodiments disclosed herein, although other strain gauge locations are contemplated. In the above embodiments, two strain gauges are mentioned, but additional strain gauges are also contemplated. It should be noted that when strain gauges are used as extension sensors 120, in embodiments, they are placed near the area of the flow tube 103, 103' that is subject to momentum redirecting forces. One example is placement near a straight portion of a flow tube 103, 103'. In another example, the strain gauge is located near the apex of a curve on a U-shaped or ω-shaped flow tube 103, 103'. However, in other embodiments, the extension sensor may be placed on or near a flow tube mounting block 109, 109'.

FIG4 is a flow chart illustrating a routine executed according to an embodiment, such as the fluid momentum routine 212 or the flow characteristics routine 218. This routine outlines a method for determining the momentum of a fluid passing through one or more conduits. An extension sensor 120 may be provided on one or more conduits. In an embodiment, the extension sensor 120 comprises at least one of a strain gauge, an optical sensor, and a laser. The extension sensor 120 may be placed proximate to a region of the conduit subject to momentum redirection forces. In an embodiment, such as for relatively large coils or water pipes, the region subject to momentum redirection forces may include, without limitation, an expansion joint. In another embodiment, such as for flow meter 5, by way of example and without limitation, the region subject to measurable momentum redirection forces may include at least one of an 180° U-bend and an ω-bend of the flow tubes 103 and 103′. Measurements may occur on one or more flow tubes 103 and 103′. However, other symmetrical flow tube configurations are also contemplated. Fluid may be provided through one or more conduits. The fluid may be a liquid, a gas, or any combination of liquids, gases, and/or solids. In step 400, an extension signal is received from the extension sensor 120 indicating the extension/strain of one or more conduits due to the flowing fluid. In step 405, a momentum term is calculated. In one embodiment, the momentum term mv can be derived from the axial strain equation, equation (5). This equation is used as an example and should not limit the equation or algorithm used to derive the momentum term.

FIG5 is a flow chart illustrating a routine performed according to an embodiment. As in the flow chart of FIG4 , this routine summarizes a method for determining the momentum of a fluid passing through one or more conduits, but additionally takes into account temperature correction to compensate for thermal expansion. Changes in conduit temperature will cause changes in the dimensions of the conduits. Furthermore, changes in conduit temperature will typically cause changes in the elastic modulus of the conduit material, thereby affecting the strain resulting from equation (5). In order to accurately measure the fluid momentum and derive the momentum term, potential temperature-related interferences may be taken into account. To do so, the conduit temperature must be accurately measured. An extension sensor 120 may be provided on one or more conduits, which may be placed proximate to a region of the conduit that is subject to momentum redirecting forces. Fluid may be provided through one or more conduits. In step 500, an extension signal is received from the extension sensor 120 indicating the extension/strain of the one or more conduits due to the fluid flow. A temperature sensor 106 may be placed on one or more conduits. The temperature sensor may be a resistance temperature detector (RTD), but any sensor known in the art is contemplated. In step 505, a temperature signal is received from the temperature sensor. In step 510, a temperature-corrected momentum term is calculated. The temperature-corrected momentum term can be derived from the modified axial strain equation (5) comprising: F _Ay is the anchoring force, mv is the temperature-corrected momentum term, ε _y is the axial strain of the conduit, A _t is the cross-sectional area of the conduit, E is the elastic modulus of the conduit at the operating temperature, m is the mass flow rate of the fluid, v is the fluid velocity of the fluid, A is the cross-sectional area of the fluid, P _avg is the average static pressure of the fluid, α _T is the coefficient of linear thermal expansion of the conduit, and ΔT is the change in conduit temperature. This equation is used as an example and in no way limits the equation or algorithm used to derive the temperature-corrected momentum term.

FIG6 is a flow chart illustrating, for example, a routine executed according to an embodiment, such as the fluid momentum routine 212 for the flow meter 5 . Without limitation, this routine summarizes a method for determining the momentum of a fluid passing through one or more flow tubes 103 , 103 ′, such as those found in a Coriolis mass flow meter. An extension sensor 120 may be provided on one or more flow tubes 103 , 103 ′. The extension sensor 120 may be positioned proximate to a region of the flow tube that is subject to momentum redirecting forces, such as a 180° U-bend or ω-bend commonly found on flow meter flow tubes. A fluid may be provided through one or more flow tubes 103 , 103 ′. In step 600 , an extension signal is received from the extension sensor 120 indicating the extension/strain of the one or more flow tubes 103 , 103 ′ caused by the flowing fluid. In step 605 , a momentum term is calculated, as described herein. In embodiments, this may be a temperature-corrected momentum term. Two or more sensors 105 , 105 ′ may be provided for each flow tube 103 or 103 ′. In step 610, one or more flow tubes 103, 103' are vibrated in a drive-mode vibration. In step 615, a first sensor signal and a second sensor signal are received based on the vibration response to the drive-mode vibration from the first sensor 105 and the second sensor 105', respectively. In step 620, a difference between the first sensor signal and the second sensor signal is calculated, and in step 625, a mass flow is determined based on the sensor signal difference. The meter electronics 20 may then compare the mass flow to a momentum term, as shown in step 630. For example, if the density of the fluid is known, the momentum term may be used in conjunction with the density to compare with the measured mass flow for diagnostic purposes, or as a means of measuring mass and volume flow rates.

7 is a flow chart illustrating a routine executed according to an embodiment to diagnostically check measurements of the main flow meter 5 using a momentum term. In step 700, an extension signal is received from the extension sensor 120 indicating the extension/strain of one or more flow tubes 103, 103' caused by the flowing fluid. In step 705, a momentum term is calculated, as described herein. In an embodiment, this may be a temperature corrected momentum term. Two or more sensors 105, 105' may be provided for each flow tube 103 or 103'. In step 710, one or more flow tubes 103, 103' are vibrated in a drive mode vibration. In step 715, a first sensor signal and a second sensor signal are received based on the vibration response to the drive mode vibration from the first sensor 105 and the second sensor 105', respectively. In step 720, a difference between the first sensor signal and the second sensor signal is calculated, and in step 725, a mass flow is determined based on the sensor signal difference. In step 730, the velocity v is calculated using equation (7) as an example without limitation:

(7)

in:

m is the mass flow rate of the fluid;

ρ is the density of the fluid; and

A is the cross-sectional area of the fluid.

It should be clear that other equations or algorithms besides equation (7) are contemplated. In step 725, the mass flow is measured directly by the flow meter 5, and in step 730, the velocity is derived via equation (7) after measuring the density. This method provides a diagnostic check to verify the mathematical product of mass and density. In particular, the calculated momentum product term is calculated by multiplying the velocity and the mass flow rate, as indicated in step 735. In step 740, the calculated momentum product term is then compared to the momentum term calculated in step 705. If the calculated momentum product term deviates from the momentum term to an extent greater than a predetermined threshold, an error is indicated in step 745.

FIG8 is a flow chart illustrating a routine executed according to an embodiment, whereby a momentum term is used to indicate the presence of flow asymmetry between the flow tubes 103, 103' of the flow meter 5, such as for the flow asymmetry routine 215. A problem with prior art flow meters is their inherent lack of obstruction or build-up detection. Relative motion is typically measured using coil/magnet sensors, so flow asymmetry between the flow tubes is undetectable. Consequently, a blockage or debris buildup in one of the flow tubes does not interfere with mass flow measurement. It is precisely this "benefit" of coil/magnet sensors that limits their use for detecting blockages or debris buildup in flow tubes. FIG8 summarizes an embodiment of a method for determining flow asymmetry, and therefore potential blockages or debris buildup, in the flow tubes 103, 103'. In an embodiment, a first flow tube 103 is provided for a first extension sensor 120, and a second flow tube 103' is provided for a second extension sensor 120. A fluid can be provided through the flow tubes 103, 103'. First and second extension sensor signals based on the vibration response to the drive mode vibration are then received from the first and second extension sensors 120, respectively, as indicated in step 800. In step 805, a first momentum term is calculated from the first extension sensor signal and a second momentum term is calculated from the second extension sensor signal. These values (the first and second momentum terms) are compared to each other in step 810. A determination is then made in step 815 as to whether flow asymmetry exists between the first and second flow tubes 103, 103'. The presence of flow asymmetry indicates a possible blockage or debris accumulation in one of the flow tubes 103, 103', as a pair of unobstructed flow tubes should exhibit a symmetrical response. In one embodiment, step 820 is provided, where the presence of flow asymmetry is indicated if the difference between the first and second momentum terms is greater than a predetermined threshold.

FIG9 is a flow chart illustrating a routine performed according to an embodiment suitable for meter applications, in which fluid density (known or measured) is used in conjunction with a momentum term to measure and output mass and volume flow rates. In an embodiment, an extension sensor 120 is provided on a conduit. A fluid may be introduced and flowed through the conduit, and an extension signal is received from the extension sensor in step 900. A momentum term is calculated in step 905. A measured or known density is also provided in step 910. Finally, as shown in step 915, the density and momentum terms are used to calculate the mass and volume flow rates.

It should be noted that for all disclosed embodiments, dedicated extension sensors (e.g., strain gauges that resolve momentum terms) can be placed on flow tubes 103, 103' independently of sensors 105, 105'. They can be placed at any point along flow tubes 103, 103'. In the case of strain gauges, their orientation on a particular flow tube can be designed to minimize temperature or pressure effects. In one embodiment, a strain gauge can be placed in an axial direction, and a second strain gauge on the same flow tube can be placed in a circumferential orientation. Depending on how these gauges are connected to the bridge circuit, the signal within or between flow tubes can be canceled or alternatively amplified, depending on the application. However, because the pressure and temperature between the flow tubes are substantially the same, obstacle detection derived from the relative momentum term should be relatively insensitive to such variations.

Turning now to FIG. 10 , this graph illustrates testing conducted on a Coriolis mass flowmeter with a stainless steel flow tube. When the flow rate is 0 lb/min, no momentum signal is present. However, as the flow rate increases up to 5000 lb/min, the measured strain also increases, thereby validating the use of an extended sensor to detect momentum-induced strain as a viable method for deriving a momentum term, indicating flow asymmetry, and calculating mass and volume flow rates in non-Coriolis meter implementations.

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

Therefore, although specific embodiments and examples of the present invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the present invention, as will be appreciated by those skilled in the relevant art. The teachings provided herein may be applied to other devices and methods, and not just to the embodiments described above and shown in the accompanying drawings. Therefore, the scope of the present invention should be determined based on the following claims.

Claims (12)

1. A method for determining the momentum of a fluid passing through one or more conduits, comprising the steps of: vibrating at least one of the one or more conduits in a drive mode vibration; receiving an extension signal from an extension sensor indicating extension of the one or more conduits due to the flowing fluid; and calculating a momentum term based on the extension signal; providing a first sensor (105) and a second sensor (105') on at least one of the one or more conduits; receiving a first sensor signal and a second sensor signal from a first sensor (105) and a second sensor (105'), respectively, based on a vibration response to the drive mode vibration; calculating a difference between the first sensor signal and the second sensor signal; Determine mass flow based on sensor signal differences; comparing the mass flow and momentum terms; Calculate velocity ( v ); The momentum product term is calculated by multiplying the velocity by the mass flow rate; comparing the calculated momentum product term to the momentum term; and If the calculated momentum product term deviates from the momentum term to an extent greater than a predetermined threshold, an error is indicated. 2. The method for determining the momentum of a fluid through one or more conduits of claim 1 , wherein calculating the momentum term comprises the step of deriving the momentum term from an axial strain equation including: mv is the momentum term; ε _y is the axial strain of the one or more conduits; F _Ay is the anchoring force of the one or more catheters; A _t is the cross-sectional area of the one or more conduits; E is the elastic modulus of the one or more conduits; m is the mass flow rate of the fluid; v is the fluid velocity of the fluid; A is the cross-sectional area of the fluid; and Pavg is the average static _pressure of the fluid. 3. The method for determining fluid momentum through one or more conduits of claim 1 , further comprising the steps of: receiving a temperature signal from a temperature sensor; and Calculate the temperature-corrected momentum term. 4. The method for determining the momentum of a fluid through one or more conduits of claim 3, wherein calculating the temperature-corrected momentum term comprises the step of deriving the temperature-corrected momentum term from an axial strain equation including: F _Ay is the anchoring force; mv is the momentum term; ε _y is the axial strain of the one or more conduits; A _t is the cross-sectional area of the one or more conduits; E is the elastic modulus of the one or more conduits; m is the mass flow rate of the fluid; v is the fluid velocity of the fluid; A is the cross-sectional area of the fluid; P _avg is the average static pressure of the fluid; α _T is the coefficient of linear thermal expansion of the one or more conduits; and ΔT is the change in temperature of the one or more conduits. 5. The method for determining the momentum of a fluid passing through one or more conduits of claim 1 , wherein Calculate the velocity v , including m = ρ A v , where: m is the mass flow rate of the fluid; ρ is the density of the fluid; and A is the cross-sectional area of the fluid. 6. A method for determining the momentum of a fluid through one or more conduits as claimed in claim 1, wherein the step of providing an extended sensor on the one or more conduits proximate to a region of the conduit experiencing momentum redirecting forces, wherein the method comprises the steps of: receiving first and second extension sensor signals from first and second extension sensors, respectively, based on a vibration response to the drive mode vibration; calculating a first momentum term from the first extension sensor signal and a second momentum term from the second extension sensor signal; comparing the first momentum term to the second momentum term; and The presence of flow asymmetry between the first and second conduits is determined. 7. The method for determining the momentum of a fluid passing through one or more conduits of claim 6, further comprising the steps of: If the difference between the first momentum term and the second momentum term is greater than a predetermined threshold, the presence of flow asymmetry is indicated. 8. The method for determining the momentum of a fluid passing through one or more conduits of claim 1 , comprising the steps of: The density of the fluid and the momentum term are used to calculate mass flow rate and volume flow rate. 9. A method for determining the momentum of a fluid passing through one or more conduits as claimed in claim 8, wherein the step of providing the density of the fluid comprises the step of measuring the density of the fluid. 10. A flow meter (5) comprising a sensor assembly (10) and meter electronics (20), adapted to perform the method of one of claims 1 to 9, comprising: one or more flow tubes (103, 103'); a driver (104) coupled to the one or more conduits and oriented to induce drive-mode vibrations in the one or more conduits; at least two sensors (105, 105') coupled to the one or more conduits and configured to detect the drive mode vibrations; and a first extension sensor (120) coupled to a first conduit of the one or more conduits and a second extension sensor (120) coupled to a second conduit, wherein the first and second extension sensors are configured to output signals having amplitudes proportional to fluid momentum-induced strain of the one or more conduits, and wherein the meter electronics (20) is configured to calculate a momentum term; Wherein the meter electronics (20) is configured to detect flow asymmetry between the first and second conduits. 11. The flow meter (5) comprising a sensor assembly (10) and meter electronics (20) as claimed in claim 10, wherein the extension sensor (120) comprises at least one of a strain gauge, an optical sensor, and a laser. 12. A flow meter (5) comprising a sensor assembly (10) and meter electronics (20) as claimed in claim 10, wherein the signal is a drag force having an amplitude proportional to the strain caused by the fluid momentum.