WO2000066979A1

WO2000066979A1 - Force-sensing mass flow meter

Info

Publication number: WO2000066979A1
Application number: PCT/US2000/012089
Authority: WO
Inventors: Frank F. Larry
Original assignee: Venture Measurement Company, Llc
Priority date: 1999-05-05
Filing date: 2000-05-03
Publication date: 2000-11-09
Also published as: AU4983400A

Abstract

A flow meter (100) for measuring a mass flow rate of a fluid flowing through a conduit (112) includes a target (132), having an area, capable of being inserted into the conduit, a rod (134) having a first end (136) and an opposite second end (138), the first end affixed to the target, and a connecting member (160) having a first portion (162), a spaced-apart second portion (164), and a flexible portion disposed (166) between the first portion and the second portion. The first portion is capable of being secured to the conduit and the second portion is affixed to the second end of the rod. The flexible portion has a flexibility so that movement of the target results in a translated movement of the second portion via the rod. Thus, movement of the second portion is proportional to the movement of the target. A sensor (140) senses displacement of the second portion along a first axis (C'-C') that is substantially parallel to a direction (A) of fluid flow within the conduit and also senses movement of the second portion along a second axis that is transverse to the first axis. A device (170), responsive to the sensor, determines a flow rate of a fluid flowing through the conduit, based on the displacement sensed by the sensor along the first axis and the movement sensed by the sensor along the second axis.

Description

FORCE-SENSING MASS FLOW METER

This application claims the benefit of U.S. Application Serial No. 09/305,893 filed May 5, 1999, which is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to flow meters, and, more specifically, to a flow meter that determines mass flow rate based on a determination of fluid velocity and fluid density.

2. Description of the Prior Art

Most of the flow meters used in industrial measurement are volumetric flow meters that measure the volumetric rate of a fluid flowing through a conduit. However, many applications require a measurement of mass flow rate, rather than volumetric flow rate (which may vary depending on fluid conditions such as temperature and pressure). In many chemical processes, measurement of mass flow rate is essential.

Several different types of mass flow meters are currently used in industry. However, some such flow meters often involve relatively high energy losses associated with the measurement of the mass flow rate. Some mass flow meters measure the volumetric flow rate of the fluid passing through the flow meter and then multiply that rate by the density of the fluid. The density of the fluid is determined in one of several ways. In one method of determining the density, the fluid is periodically sampled and the density is directly measured. This method has the disadvantage of being time consuming, subject to operator error and inaccurate because the density of the fluid may change between sampling episodes. Another method of determining density includes calculating the density based on measured properties of the fluid and applying these properties to ideal fluid laws (e.g. Boyle-Charles' law, in the case of a gas). This method has the disadvantage of introducing inaccuracies when the fluid is not an ideal fluid (i.e., the fluid is not homogenous, etc.). To achieve a sufficient level of reliability, some flow meters need to add sensors to measure such parameters as temperature to compensate for any disuniformities in the fluid being measured.

Nowhere in the prior art is there a relatively simple flow meter that determines the density of a non-uniform fluid on a real time basis while measuring the volumetric flow rate of the fluid, thereby giving an accurate indication of the fluid's mass flow rate.

Furthermore, many of the sensors employed in mass flow meters have the disadvantage of not being immune from the effects of extreme operating conditions, such as high temperature. Nowhere in the prior art is there a mass flow meter where the sensor is insulated from the conduit so as to decrease the effects of operating conditions on the sensor.

SUMMARY OF THE INVENTION

The disadvantages of the prior art are overcome by the present invention which, in one aspect, is a flow meter for measuring a mass flow rate of a fluid flowing through a conduit. The flow meter includes a target, having an area, capable of being inserted into the conduit, a rod having a first end and an opposite second end, the first end affixed to the target, and a connecting member having a first portion, a spaced-apart second portion, and a flexible portion disposed between the first portion and the second portion. The first portion is capable of being secured to the conduit and the second portion is affixed to the second end of the rod. The flexible portion has a flexibility so that movement of the target results in a translated movement of the second portion via the rod. Thus, movement of the second portion is proportional to the movement of the target. A sensor senses displacement of the second portion along a first axis that is substantially parallel to a direction of fluid flow within the conduit and also senses movement of the second portion along a second axis that is transverse to the first axis. A device, responsive to the sensor, determines a flow rate of a fluid flowing through the conduit, based on the displacement sensed by the sensor along the first axis and the movement sensed by the sensor along the second axis.

In another aspect, the invention is a flow meter for measuring a flow rate of a fluid flowing through a conduit, that includes a bluff body target, having an area, capable of insertion into the conduit and capable of shedding vortices as the fluid flows around the target. The first end of a rod, having a first end and an opposite second end, is affixed to the bluff body target. A connecting member has a first portion, a spaced- apart second portion, and a tube defining a cylindrical passage therethrough that opens to a first end, the first end being affixed to the first portion, and an opposite second end, is affixed to the second portion. The rod passes through the passage and the second portion is affixed to the second end of the rod. The first portion is capable of being secured to the conduit. The tube has a flexibility so that movement of the target results in a translated movement of the second portion via the rod, the movement of the second portion being proportional to the movement of the target. A sensor senses displacement of the second portion along a first axis that is substantially parallel to a direction of fluid flow and movement of the second portion along a second axis that is transverse to the first axis. Movement along the second portion indicates the frequency at which vortices are shed by the bluff body target. A computer that is responsive to the sensor is capable of determining a mass flow rate of a fluid flowing through the conduit, based on displacement sensed by the sensor along the first axis and based on the frequency at which vortices are shed by the bluff body target.

In yet another aspect, the invention is a flow meter for measuring a flow rate of a fluid flowing through a conduit. As in the above-recited aspects, the flow meter includes a target, a rod and a connecting member with the second portion having a reflective outer surface. An optical sensor directs a beam of radiation toward the reflective outer surface and senses a reflection of the beam of radiation from the outer surface, thereby sensing variations in position of the outer surface. A device, that is responsive to the optical sensor, determines a flow rate of a fluid flowing through the conduit, based on movement of the outer surface of the second portion sensed by the optical sensor.

These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of the invention employing an optical displacement sensor.

FIG. 2 is a top plan view of a target in a conduit showing vortices shed in a fluid flowing through the conduit.

FIG. 3 is a top perspective view of the embodiment of FIG. 1.

FIG. 4 is a top perspective view of an embodiment of the invention employing strain gauges to sense movement.

FIG. 5 A is a cross-sectional view of an embodiment of the invention employing a capacitive sensor to sense movement.

FIG. 5B is a top plan view of the sensor employed in the embodiment shown in FIG. 5A. DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of "a," "an," and "the" includes plural reference, the meaning of "in" includes "in" and "on."

As shown in FIG. 1, one embodiment of the invention is a flow meter 100 for determining the mass flow rate of a fluid flowing through a passage 114 in a conduit 112 having a cross-sectional area. The flow meter 100 includes a fitting 120, that is secured to an opening 116 in the conduit, a target/rod assembly 130 that transmits movement to a connecting member 160 as a result of a fluid flowing, as in direction A, through the passage 114. A sensor 140 detects movement of the connecting member 160 and generates a signal representative thereof. A processor 170, or other type of computer, that is responsive to the signal from the sensor 140 calculates the flow rate in the passage 114. The processor 170 is programmed to calculate the mass flow rate of a fluid flowing through the conduit 112, wherein the mass flow rate equals the density of the fluid times the cross-sectional area of the conduit 112 times the velocity of the fluid.

The target/rod assembly 130 includes a bluff body target 132 that is capable of being inserted into the conduit 112 (i.e., its diameter allows it to pass through the opening 116 in the conduit). Referring to FIG. 2, the target 130 causes a fluid flowing in direction A to shed vortices 202 in the path of the fluid flow A. The vortices 202 alternate from side to side of the target 130 and the frequency at which vortices 202 are generated is proportional to the velocity of the fluid. As the vortices 202 are generated, they impart lateral force on the target in a direction T_L and T_R that is transverse to the direction of fluid flow A. Also, the fluid flowing against the target 130 imparts a force on the target 130 in direction A. As will be demonstrated below, this force is proportional to the density of the fluid. Returning to FIG. 1, the target/rod assembly 130 transmits movement of the target 132 through a rod 134 having a first end 136 and an opposite second end 138, the first end 136 being affixed to the target 132.

The connecting member 160 has a first portion 162, a spaced-apart second portion 164, and a flexible portion 166 disposed between the first portion 162 and the second portion 164. The first portion 162 is secured to the conduit 112 through the fitting 120. In one embodiment, the fitting 120 will have an internally threaded section 122 and the first portion 162 will have a complementary externally threaded section 168 (a thread sealer may also be employed to prevent leakage). Although FIG. 1 shows a threaded fitting 120, it will be understood that the scope of the invention extends to all types of fittings commonly used to secure flow meters to conduits (including, e.g., welded fittings, etc.). The second portion 164 is affixed to the second end 138 of the rod 134. The flexible portion 166 has a flexibility so that movement of the target 132 results in a translated movement of the second portion 164 via the rod 134. Thus, movement of the second portion 164 is proportional to the movement of the target 132. Because the target 132 moves in direction A in proportion to the force imparted on it by the fluid, displacement of the second portion 164 is also in proportion to the force imparted on the target 132 by the fluid. The flexible portion 166 and the first portion 162 form a tube that defines a passage 152 that opens to the opening 116 in the conduit 112. The rod 134 passes through the passage 152 from the target 132 to the second portion 164 of the connecting member 160.

In one illustrative embodiment, the first portion 162 is made from Va" 316L stainless steel hex stock. One end of the stock extending 1.125" is rounded and a remaining 0.5" is left with a hexagonal cross section. The round end is threaded 122 with 1/8-27 NPTF-I Dryseal pipe threads based on the USA pipe thread standard. By using Dryseal threads, a pressure-tight seal may be accomplished without using sealing compounds. Although stainless steel was chosen for this illustrative embodiment, it is to be understood that other materials could also be used, e.g., 6061 aluminum. In this embodiment, the connecting member 160 is made from stainless steel. The wall of the flexible portion 166 of the connecting member 160 has a thickness which could range from 0.010" (for applications where the normal operating pressure does not exceed 1,000 PSIA) to 0.050" (for applications where the normal operating pressure does not exceed 20,000 PSIA). Generally, a thicker wall requires greater force on the target to achieve a meaningful result.

In one embodiment, the sensor 140 senses displacement of the second portion 164 along a first axis C - C2" that is substantially parallel to a direction A. In such an embodiment, the sensor senses the force imparted on the target 132 by the fluid. This embodiment can be used as a force sensing mass flow meter. The velocity of the fluid can be determined by the processor 170 using the following formula:

force x k v = density x target area x drag

where

"velocity" is the average velocity of the fluid flowing through the conduit 112 in direction A;

"force" is the amount of force imparted on the target 132 by the fluid flowing through the conduit 112;

"k" is a constant, depending on the system of units employed;

"target area" is the area of the target 132; and "drag" is a coefficient proportional to an amount of drag imparted on the fluid by the target 132.

The volumetric flow rate of the fluid flowing through the conduit may then be determined by applying the following formula: volumetric flow rate = velocity x area

where area is the cross-sectional area of the conduit 112.

In another embodiment, the sensor 140 also senses movement of the second portion 164 along a second axis that is transverse to the first axis. For example, as shown in FIG. 3, axis C'-C" runs along the flow direction A of the fluid and axis D'- D" is transverse to axis C'-C". Displacement along the first axis C'-C" is proportional an amount of force imparted on the target by a fluid flowing through the conduit. Wherein movement along the second axis D'-D" is proportional to a velocity of a fluid flowing through the conduit. In such an embodiment the movement along the transverse axis would be manifested as oscillations induced by the shedding of vortices, the frequency of which would be proportional to the velocity of the fluid. In this embodiment, the velocity of the fluid is determined according to the following formula: v = (fx d) / S_t, where

"v" is the average velocity of the fluid flowing through the conduit 112; "S_t" is the Strouhal number of the bluff body target 132; "f ' is the frequency of vortex shedding by the bluff body target 132; and "d" is the diameter of the bluff body target 132.

Density is then figured according to the following formula: force x k density = =- target area x drag coefficient x v where

"k" is a constant, depending on the system of units employed;

"target area" is the area of the target 132; and

"drag" is a coefficient proportional to an amount of drag imparted on the fluid by the target 132.

From these two equations, the mass flow rate of the fluid may be determined by the processor 170 according to the following formula:

mass flow rate = density x velocity x area This embodiment has advantage in that a mass flow rate can be determined without knowing the density of the fluid. This embodiment also has the advantage of producing a more accurate result when determining the mass flow rate of a fluid in which the density of the fluid varies from time to time as it flows through the conduit 112.

The sensor 140 of the embodiment shown in FIGS. 1 and 3 is an optical displacement sensor that includes a reflective outer surface 150 disposed on the second portion 164 of the connecting member 160. A source 142 of electromagnetic radiation (such as a laser) directs a beam 146 of radiation toward the reflective outer surface 150 and a detector 144 senses a position of the reflected beam 148. The detector 144 generates a signal having a value based on the position of the reflected beam 148. In one illustrative embodiment, the source 142 is 5 mW laser produced by LASERLYTE of Cottonwood Arizona (part no. DLLC) set to operate in the 630 nm range and the detector 144 is a quadrant array-type light detector produced by SEMICOA of San Jose, California (part no. SCA-006C/B1). The reflective outer surface 150 could be an aluminum mirror such as one available from Edmond Scientific of Barrington, New Jersey (part no. P32942), which may be secured to the second portion 164 using Milbond Adhesive also from Edmond Scientific (part no. P53288). It is understood that the parts disclosed herein are presented for illustrative purposes only and that many other embodiments employing many other types of devices and materials would be within the scope of the invention.

The processor 170 is responsive to the signal from the detector 144 and determines the flow rate of the fluid flowing through the conduit 112, based on the displacement sensed by the sensor 140. The processor 170 could be a personal computer or an embedded microprocessor connected to the sensor 144 via an interface. The interface would include an analog-to-digital converter and any other signal conditioning electronics necessary to make the signal from the sensor compatible with that of the analog-to-digital converter. In the volumetric flow meter embodiment discussed above, the sensor 144 senses displacement of the reflected beam 148 along the B'-B" axis. This movement is proportional to displacement of the second portion 164 along the C'-C" axis, which is proportional to displacement of the target 132 along direction A.

In the mass flow meter embodiment discussed above and shown in FIG. 3, the detector 144 is capable of sensing displacement of the reflective outer surface 150 along an axis C'-C" that is parallel to direction A and is capable of sensing movement of the reflective outer surface 150 along an axis D'-D" that is transverse to direction A. As discussed above, displacement along axis C'-C" is proportional to the force imparted on the target 132 by the fluid flowing through the conduit 112, whereas the frequency of movement back-and-forth along axis D'-D" as a result of the vortices being shed by the target 132 is proportional to the velocity of the fluid flowing through the conduit 112.

FIG. 3 also shows a voltage source 343 supplying the light source 142. The voltage source 343 could be a battery or a DC power supply, in accordance with the manufacturer's specifications of the light source 142. Also shown in FIG. 3 is an example of a mounting member 320 that could be employed to secure the light source 142 and the detector 144 to the conduit 112. This example of a mounting member 320 includes a plate 322 that is affixed to either the conduit 112 or the connecting member 160, or both. Affixed to the place 322 is a frame 324 to which the light source 142 and the detector 144 are secured. As will be readily appreciated, many configurations of the mounting member 320 could be employed without departing from the scope of the invention.

As shown in FIG. 4, another embodiment of the invention employs a plurality of strain gauges 440a-d to sense movement of the tube 460 of the connecting member 160. The tube 460 comprises an outer surface 464 having a first arcuate surface 464a; a parallel and opposite second arcuate surface 464b, a first plane 462a bisecting the first arcuate surface 464a and the second arcuate surface 464b; a third arcuate surface 464c bisected by a second plane 462b that is transverse to the first plane 462a; and a fourth arcuate surface 464d that is bisected by the second plane 462b. A first strain gauge 440a is disposed on the first arcuate surface 464a and is capable of generating a signal proportional to strain on the first arcuate surface 464a. A second strain gauge 440b is disposed on the second arcuate surface 464b and is capable of generating a signal proportional to strain on the second arcuate surface 464b. A third strain gauge 440c is disposed on the third arcuate surface 464c and is capable of generating a signal proportional to strain on the third arcuate surface 464c . A fourth strain gauge 440d is disposed on the fourth arcuate surface 464d and is capable of generating a signal proportional to strain on the fourth arcuate surface 464d. Strain gauges 440a-b and detect displacement along axis C'-C" and strain gauges 440c-d detect movement along axis D'-D". The strain gauges 440a-d are affixed to the connecting member 160 using an adhesive. Although four strain gauges are show in the embodiment of FIG. 4, an embodiment using only two strain gauges, one disposed along plane 462a, and one disposed along plane 462b could also be employed without departing from the scope of the invention. To improve sensitivity, multiple strain gauges may be used on a single plane. In such a situation, they could be set up in pairs to form a Wheatstone bridge configuration in accordance with the practice known to the flow meter art.

As shown in FIGS. 5A-5B, another embodiment of the invention employs a capacitive sensor 540 to detect movement of the second portion 164 of the connecting member 160. In a single axis embodiment, shown in FIG. 5 A, a moveable electrode 544 is affixed to the second portion 164 with an insulating adhesive 546, or other insulating fastener. A first stationary electrode 542a is spaced apart from the moveable electrode 544 across a first air gap 548a-b, thereby forming a first capacitor. On the opposite side of the moveable electrode 544, a second stationary electrode 542c is spaced apart from the moveable electrode 544 across a second air gap 548c-b, thereby forming a second capacitor. A voltage, or potential, may be applied to the first capacitor with a first voltage source 574a-b and the capacitance C_A._B across the first capacitor is sensed with a first capacitance sensor 572a-b. Capacitance C_A._B is proportional to the width of the first air gap 548a-b, which varies as the second portion 164 is displaced along direction A. Similarly, a voltage may be applied to the second capacitor with a second voltage source 574c-b and the capacitance C_C._B across the second capacitor is sensed with a second capacitance sensor 572c-b. Capacitance C_C._B is proportional to the width of the first air gap 548c-b, which also varies as the second portion 164 is displaced along direction A. Because the width of the air gaps 548a-b and 548c-b are proportional to the displacement of the target 132 along direction A, the first and second capacitances are also proportional to the displacement of the target 132 along direction A. Therefore, the processor 570 then determines the force on the target 132 according to the formulae disclosed above in proportion to the measured capacitances of the first and second capacitor.

As shown in FIG. 5B, the capacitive embodiment may also be employed in a two transverse axis device, of the type discussed above. In such a device, a plurality of stationary electrodes 542a-d are disposed around the moveable electrode 544. In one embodiment, the two axes 562a and 562b are orthogonal to each other. However, if appropriate geometric corrections are performed by the processor 570, the axes 562a and 562b could have a non-orthogonal configuration. Although four stationary electrodes are shown, a two transverse axis device could be embodied using only two stationary electrodes, so long as the capacitor formed by each stationary electrode lies along an axis that is transverse to the axis of the other capacitor. Ideally, the transverse axes are orthogonal to each other, wherein one is parallel to direction A and the other is perpendicular to direction A.

It is believed that no prior art flow meter employs either optical displacement sensors or capacitive sensors in either uniaxial or biaxial sensing configurations. It is further believed that no prior art flow meter employs biaxial sensing configurations.

The above described embodiments are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.

Claims

CLAIMSWhat is claimed is:

1. A flow meter for measuring a mass flow rate of a fluid flowing through a conduit, comprising: a. a target, having an area, capable of being inserted into the conduit; b. a rod having a first end and an opposite second end, the first end affixed to the target; c. a connecting member having a first portion, a spaced-apart second portion, and a flexible portion disposed between the first portion and the second portion, the first portion capable of being secured to the conduit and the second portion affixed to the second end of the rod, the flexible portion having a flexibility so that movement of the target results in a translated movement of the second portion via the rod, movement of the second portion being proportional to the movement of the target; d. a sensor that senses displacement of the second portion along a first axis that is substantially parallel to a direction of fluid flow within the conduit and that senses movement of the second portion along a second axis that is transverse to the first axis; and e. a device, responsive to the sensor, that is capable of determining a flow rate of a fluid flowing through the conduit, based on the displacement sensed by the sensor along the first axis and the movement sensed by the sensor along the second axis.

2. The flow meter of Claim 1, wherein the flexible portion of the connecting member comprises a tube defining a cylindrical passage therethrough that opens to a first end, affixed to the first portion, and an opposite second end, affixed to the second portion, the rod passing through the passage.

3. The flow meter of Claim 2, wherein the tube comprises an outer surface having: a. a first arcuate surface; b. a parallel and opposite second arcuate surface, a first plane bisecting the first arcuate surface and the second arcuate surface; c. a third arcuate surface bisected by a second plane that is transverse to the first plane; and d. a fourth arcuate surface that is bisected by the second plane.

4. The flow meter of Claim 3, wherein the sensor comprises: a. a first strain gauge disposed on the first arcuate surface and capable of generating a signal proportional to strain on the first arcuate surface; b. a second strain gauge disposed on the second arcuate surface and capable of generating a signal proportional to strain on the second arcuate surface; c. a third strain gauge disposed on the third arcuate surface and capable of generating a signal proportional to strain on the third arcuate surface; and d. a fourth strain gauge disposed on the fourth arcuate surface and capable of generating a signal proportional to strain on the fourth arcuate surface.

5. The flow meter of Claim 1, wherein the sensor comprises: a. a movable electrode affixed to the second portion of the connecting member; b. a first stationary electrode disposed along a first axis and spaced apart from the movable electrode so as to define a first gap, therebetween, having a first width; c. a second stationary electrode disposed along a second axis and spaced apart from the movable electrode so as to define a second gap, therebetween, having a second width; d. a first voltage source electrically coupled to both the movable electrode and the first stationary electrode so as to be capable of applying a first electric potential therebetween; e. a second voltage source electrically coupled to both the movable electrode and the second stationary electrode so as to be capable of applying a second electric potential therebetween; f. a first capacitance sensing circuit, electrically coupled to the movable electrode and the first stationary electrode, that is capable of sensing a first capacitance between the movable electrode and the first stationary electrode, the first capacitance being a function of the first width, the first capacitance sensing circuit capable of generating a signal proportional to the first capacitance; and g. a second capacitance sensing circuit, electrically coupled to the movable electrode and the second stationary electrode, that is capable of sensing a second capacitance between the movable electrode and the second stationary electrode, the second capacitance being a function of the second width, the second capacitance sensing circuit capable of generating a signal proportional to the second capacitance.

6. The flow meter of Claim 1, wherein the sensor is an optical displacement sensor.

7. The flow meter of Claim 6, wherein the optical displacement sensor comprises: a. a reflective outer surface disposed on the second portion of the connecting member; b. a source that directs a beam of radiation toward the reflective outer surface; and c. a detector that senses a position of the beam after it has been reflected from the reflective outer surface.

8. The flow meter of Claim 1, wherein displacement along the first axis is proportional an amount of force imparted on the target by a fluid flowing through the conduit and wherein movement along the second axis is proportional to a velocity of a fluid flowing through the conduit.

9. The flow meter of Claim 8, wherein the conduit has a cross-sectional area and wherein the flow rate determining device comprises a computer programmed to calculate the mass flow rate of a fluid flowing through the conduit, wherein the mass flow rate equals the density of the fluid times the cross-sectional area of the conduit times the velocity of the fluid.

10. The flow meter of Claim 9, wherein the computer determines the density of the fluid according to the following formula: density = (force x k) / (target area x drag coefficient x velocity²), where

"force" is the amount of force imparted on the target by the fluid flowing through the conduit; "k" is a constant, depending on the system of units employed; "target area" is the area of the target; "drag coefficient" is a coefficient proportional to an amount of drag imparted on the fluid by the target; and "velocity" is the average velocity of the fluid flowing through the conduit.

11. The flow meter of Claim 9, wherein the target comprises a bluff body having a Strouhal number and capable of shedding vortices in the fluid flowing through the conduit.

12. The flow meter of Claim 11, wherein the computer determines the velocity of the fluid according to the following formula: v = (fx d) / S_t, where

"S," is the Strouhal number of the bluff body target;

"f ' is the frequency of vortex shedding by the bluff body target;

"d" is the diameter of the bluff body target; and

"v" is the average velocity of the fluid flowing through the conduit.

13. A flow meter for measuring a flow rate of a fluid flowing through a conduit, comprising: a. a bluff body target, having an area, capable of insertion into the conduit and capable shedding vortices as a fluid flows around the target, wherein the vortices are shed at a frequency; b. a rod having a first end and an opposite second end, the first end affixed to the bluff body target; c. a connecting member having a first portion, a spaced-apart second portion, and a tube defining a cylindrical passage therethrough that opens to a first end, the first end being affixed to the first portion, and an opposite second end affixed to the second portion, the rod passing through the cylindrical passage, the first portion capable of being secured to the conduit and the second portion affixed to the second end of the rod, the tube having a flexibility so that movement of the target results in a translated movement of the second portion via the rod, the movement of the second portion being proportional to the movement of the target; d. a sensor that senses displacement of the second portion along a first axis that is substantially parallel to a direction of fluid flow and movement of the second portion along a second axis that is transverse to the first axis, wherein movement along the second portion indicates the frequency at which vortices are shed by the bluff body target; and e. a computer, responsive to the sensor, that is capable of determining a mass flow rate of a fluid flowing through the conduit based on displacement sensed by the sensor along the first axis and based on the frequency at which vortices are shed by the bluff body target.

14. The flow meter of Claim 13, wherein displacement along the first axis is proportional an amount of force imparted on the target by a fluid flowing through the conduit and wherein movement along the second axis is proportional to a velocity of a fluid flowing through the conduit and wherein the conduit has a cross-sectional area and wherein the mass flow rate equals the density of the fluid times the cross-sectional area of the conduit times the velocity of the fluid and wherein the computer determines the density of the fluid according to the following formula: density = (force x k) / (target area x drag coefficient x velocity²), where

15. The flow meter of Claim 13 , wherein the computer determines the velocity of the fluid according to the following formula: v = (fx d) / S„ where

"S_t" is the Strouhal number of the bluff body;

"f ' is the frequency of vortex shedding by the bluff body;

"d" is the diameter of the bluff body; and

"v" is the average velocity of the fluid flowing through the conduit.

16. The flow meter of Claim 13, wherein the tube comprises an outer surface having: a. a first arcuate surface; b. a parallel and opposite second arcuate surface, a first plane bisecting the first arcuate surface and the second arcuate surface; c. a third arcuate surface bisected by a second plane that is transverse to the first plane; and d. a fourth arcuate surface that is bisected by the second plane.

17. The flow meter of Claim 16, wherein the sensor comprises: a. a first strain gauge disposed on the first arcuate surface; b. a second strain gauge disposed on the second arcuate surface; c. a third strain gauge disposed on the third arcuate surface; and d. a fourth strain gauge disposed on the fourth arcuate surface.

18. The flow meter of Claim 13, wherein the sensor comprises: a. a movable electrode affixed to the second portion of the connecting member; b. a first stationary electrode disposed along the first axis and spaced apart from the movable electrode so as to define a first gap having a first width; c. a second stationary electrode disposed along the second axis and spaced apart from the movable electrode so as to define a second gap having a second width; d. a first voltage source electrically coupled to both the movable electrode and the first stationary electrode so as to be capable of applying a first electric potential therebetween; e. a second voltage source electrically coupled to both the movable electrode and the second stationary electrode so as to be capable of applying a second electric potential therebetween; f. a first capacitance sensing circuit, electrically coupled to the movable electrode and the first stationary electrode, that is capable of sensing a first capacitance between the movable electrode and the first stationary electrode, the first capacitance being a function of the first width, the first capacitance sensing circuit capable of generating a signal proportional to the first capacitance; and g. a second capacitance sensing circuit, electrically coupled to the movable electrode and the second stationary electrode, that is capable of sensing a second capacitance between the movable electrode and the second stationary electrode, the second capacitance being a function of the second width, the second capacitance sensing circuit capable of generating a signal proportional to the second capacitance.

19. The flow meter of Claim 13, wherein the second portion of the connecting member has a reflective outer surface and wherein the sensor comprises an optical sensor that directs a beam of radiation toward the reflective outer surface and that senses a reflection of the beam of radiation from the outer surface, thereby sensing variations in position of the outer surface.

20. A flow meter for measuring a flow rate of a fluid flowing through a conduit, comprising: a. a target, capable of insertion into the conduit; b. a rod having a first end and an opposite second end, the first end affixed to the target; c. a connecting member having a first portion, a spaced-apart second portion, and a flexible portion disposed between the first portion and the second portion, the first portion capable of being secured to the conduit and the second portion affixed to the second end of the rod, the flexible portion having a flexibility so that movement of the target results in a translated movement of the second portion via the rod, the movement of the second portion being proportional to the movement of the target, the second portion having a reflective outer surface; d. an optical sensor that directs a beam of radiation toward the reflective outer surface and that senses a reflection of the beam of radiation from the outer surface, thereby sensing variations in position of the outer surface; and e. a device, responsive to the optical sensor, that is capable of determining a flow rate of a fluid flowing through the conduit, based on movement of the outer surface of the second portion sensed by the optical sensor.

21. A flow meter for measuring a flow rate of a fluid flowing through a conduit, comprising: a. means for receiving force from a fluid flowing through a conduit; b. means for translating movement, along two transverse axes, of the force receiving means to a position outside the conduit; c. means for sensing movement of the translating means along the two transverse axes; and d. means for determining a flow rate of a fluid flowing through the conduit, based on movement sensed by the sensing means along the two transverse axes.