CLIAMS:1. A near field probe comprising:
a housing comprising a bore;
a pin comprising a sensing tip, disposed at a center of the bore; and
a non-magnetic seal disposed in the bore, between the pin and the housing, wherein the non-magnetic seal comprises a hemispherical-shaped portion disposed covering the sensing tip of the pin.

2. The near field probe of claim 1, wherein the housing and the pin are made of a metal.

3. The near field probe of claim 1, wherein the non-magnetic seal is made of glass.

4. The near field probe of claim 1, wherein the non-magnetic seal is made of ceramic filled glass.

5. The near field probe of claim 1, wherein the non-magnetic seal further comprises a non-hemispherical shaped portion, wherein the hemispherical-shaped portion comprises ceramic and the non-hemispherical shaped portion comprises glass.

6. The near field probe of claim 1, wherein the hemispherical-shaped portion has a radius of curvature in a range of 5 degrees to 45 degrees.

7. A flow meter comprising:
a microwave source;
a near field probe coupled to the microwave source, wherein the near field probe comprises:
a housing comprising a bore;
a pin comprising a sensing tip, disposed at a center of the bore, wherein the sensing tip is disposed in near field proximity to a process fluid flowing through a conduit; and
a non-magnetic seal disposed in the bore, between the pin and the housing, wherein the non-magnetic seal comprises a hemispherical-shaped portion disposed covering the sensing tip of the pin;
a microwave detector coupled to the near field probe; and
a flow determination circuitry coupled to the microwave detector and the microwave source.

8. The flow meter of claim 7, wherein the housing and the pin are made of a metal.

9. The flow meter of claim 7, wherein the non-magnetic seal is made of glass.

10. The flow meter of claim 7, wherein the non-magnetic seal is made of ceramic filled glass.

11. The flow meter of claim 7, wherein the non-magnetic seal further comprises a non-hemispherical shaped portion, wherein the hemispherical-shaped portion comprises ceramic and the non-hemispherical shaped portion comprises glass.

12. The flow meter of claim 7, wherein the hemispherical-shaped portion has a radius of curvature in a range of 5 degrees to 45 degrees.

13. The flow meter of claim 7, wherein the flow determination circuitry comprises a microprocessor.

14. A method comprising:
actuating a microwave source to generate a microwave signal;
applying the microwave signal to a process fluid via a near field probe, wherein the near field probe comprises:
a housing comprising a bore;
a pin comprising a sensing tip, disposed at a center of the bore, wherein the sensing tip is disposed in near field proximity to the process fluid; and
a non-magnetic seal disposed in the bore, between the pin and the housing, wherein the non-magnetic seal comprises a hemispherical-shaped portion disposed covering the sensing tip of the pin;
detecting a reflected near field microwave signal from the near field probe in response to the applied microwave signal; and
determining at least one of a flow rate and composition of the process fluid based on the reflected near field microwave signal.

15. A method comprising:
disposing a seal preform comprising a non-magnetic seal material, on a bore of a housing;
holding a pin comprising a sensing tip, at a center of the bore of the housing via a fixture such that the pin extends through an opening of the seal preform;
heating the seal preform via a heating device in accordance with a first predefined thermal profile such that the seal preform melts and flows into the bore; and
cooling the non-magnetic seal material to form a non-magnetic seal between the pin and the housing; wherein the non-magnetic seal comprises a hemispherical-shaped portion formed covering the sensing tip of the pin.

16. The method of claim 15, further comprising forming the seal preform having a diameter less than a bore diameter.

17. The method of claim 15, wherein the housing and the pin are made of a metal.

18. The method of claim 15, wherein the non-magnetic seal material comprises glass.

19. The method of claim 18, further comprising forming the hemispherical-shaped portion comprising a ceramic material.

20. The method of claim 19, further comprising forming the hemispherical-shaped portion separately by pressing and sintering the ceramic material in accordance with a second predefined thermal profile.

21. The method of claim 19, further comprising joining the hemispherical-shaped portion to a non-hemispherical shaped portion of the non-magnetic seal made of glass.

22. The method of claim 15, further comprising determining a quantity of the non-magnetic seal material based on a volume of the bore.
,TagSPECI:BACKGROUND
[0001] The invention relates generally to near field probes, and more particularly to a near field probe for a multiphase flow meter.
[0002] Industrial processes are used in the manufacturing and refinement of various fluids or components. Examples include oil refining or distribution, paper pulp facilities, and others. In many instances, it is desirable to measure a flow rate of a process fluid. Various techniques are employed to measure flow rates including differential pressure drop across an orifice plate, vortex sensing techniques, magnetic based techniques and others. However, measurement of flow rate of multiphase process fluids (process fluids which are not homogenous and may include different materials in more than one phase such as gas, liquid or solid) has been problematic. A near field microwave probe may be used to interact in a near field with a process fluid, for example, a multiphase process fluid. The probe uses near field microwave measurements to determine the flow rate of the process fluid flowing through a pipe.
[0003] A near field probe used in a multiphase flow meter requires a receiver structure such as a metal pin within a cylindrical metal bore of a housing. Such a metal bore has to be sealed to prevent any fluid leaking out of the bore. Sealing material should have a low and constant dielectric loss at all operating temperatures. Erosion and fouling of the metal pin occurs in a near field probe where the metal pin is exposed to the fluid flow over a long period of time. Further, associated problems include scaling of the metal pin which reduces the sensitivity of the probe.
[0004] There is a need for an enhanced near field probe.

DRAWINGS
[0005] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
[0006] FIG. 1 is a schematic diagrammatical representation of a flow meter coupled to a conduit in accordance with an exemplary embodiment;
[0007] FIG. 2 is a block diagram of a flow meter in accordance with an exemplary embodiment;
[0008] FIG. 3 is a schematic diagrammatical representation of a near field probe in accordance with an exemplary embodiment;
[0009] FIG. 4 is a perspective view of a near field probe in accordance with an exemplary embodiment of FIG. 3;
[0010] FIG. 5 is a perspective view of a manufacturing facility used for manufacturing a near field probe in accordance with an exemplary embodiment of FIG. 3;
[0011] FIG. 6 is a graphical representation of a first predefined thermal profile in accordance with the embodiment of FIG. 5;
[0012] FIG. 7 is a perspective view representative of a plurality of steps involved in manufacturing a near field probe in accordance with an exemplary embodiment;
[0013] FIG. 8 is a schematic diagrammatical representation of a near field probe in accordance with another exemplary embodiment;
[0014] FIG. 9 is a graphical representation of a second predefined thermal profile in accordance with the embodiment of FIG. 8; and
[0015] FIG. 10 is a graphical representation indicative of a variation in sensitivity of different types of near field probes.
DETAILED DESCRIPTION
[0016] In accordance with certain embodiments of the present invention, a near field probe is disclosed. The near field probe includes a housing having a bore. A pin having a sensing tip, is disposed at a center of the bore. A non-magnetic seal is disposed in the bore, between the pin and the housing. The non-magnetic seal includes a hemispherical-shaped portion disposed covering the sensing tip of the pin. In accordance with one embodiment, a flow meter having the near field probe is disclosed. In accordance with another embodiment, a method of operation for the flow meter is disclosed. In accordance with yet another embodiment, a method of manufacturing the near field probe is disclosed. The exemplary non-magnetic seal prevents erosion, fouling, and scaling of the pin having the sensing tip. The hemispherical-shaped portion allows a flow of a fluid while protecting the pin from scaling and fouling.
[0017] FIG. 1 is a schematic diagrammatical representation of a flow meter 10 coupled to a conduit 12 in accordance with an exemplary embodiment. The conduit 12 is used to transfer a process fluid 14, for example, a multi-phase fluid. The flow meter 10 is configured to measure flow of the process fluid 14 through the conduit 12. In the illustrated embodiment, the flow meter 10 is coupled to a remote control room 16 via a control loop 18. The control loop 18 may be in accordance with any configuration such as a two-wire control loop based upon a predefined communication protocol. The flow meter 10 further includes a near field probe 20 configured to interact with the process fluid 14. As discussed herein, the flow meter 10 uses near field microwave measurements to determine at least one of a flow rate and composition of the process fluid 14.
[0018] FIG. 2 is a block diagram of the flow meter 10 in accordance with an exemplary embodiment. The flow meter 10 includes a microwave source 21 which is used to generate and transmit a plurality of microwave signals 23 to a directional coupler 22. The directional coupler 22 is coupled via a coaxial cable 24 to a near field probe 26 disposed in contact with the process fluid 14. The near field probe 26 interacts with the process fluid 14 via the microwave signals 23 generated by the microwave source 21. The directional coupler 22 and the co-axial cable 24 together form a microwave detector 25. A near field can be defined as measurements occurring within a distance which is much less than the wavelength of the microwave signals 23. The near field probe 26 is explained in greater detail with reference to subsequent figures.
[0019] The microwave near field interaction with the process fluid 14 generates a microwave reflection signal 27 back through the near field probe 26 and the coaxial cable 24 to the directional coupler 22. Such a reflected signal 27 is related to a size, shape, consistency, permeability, area, volume, and other features of components in the process fluid 14. The directional coupler 22 directs the reflected signal 27 to a feedback circuitry 28. The feedback circuitry 28 is configured to control the microwave source 21 and provide an output signal 30 to an analog-to-digital converter 32 based on the reflected signal 27 directed by the directional coupler 22. The output signal 30 may include, for example, a voltage signal which is related to the near field reflection from the process fluid 14. A microprocessor 34 is configured to analyze the output signal 30 and generate an output signal 33. The microprocessor 34 is configured to operate in accordance with a plurality of instructions stored in a memory 36. The memory 36 may also be used for temporary or permanent storage of other data or information including configuration data. The feedback circuitry 28, the analog-to-digital converter 32, the microprocessor 34, and the memory 36 together form a flow determination circuitry 37.
[0020] The microprocessor 34 may include at least one arithmetic logic unit, general purpose controller or other processor arrays programmed to perform the desired computations. In one embodiment, the microprocessor 34 is a custom device configured to perform functions of the flow meter 10. In another embodiment, the microprocessor 34 is a digital signal processor or a microcontroller. In some embodiments, other types of processors, operating systems, and physical configurations are envisioned.
[0021] The memory 36 may be a non-transitory computer readable storage medium. For example, the memory 36 may be a dynamic random access memory (DRAM) device, a static random access memory (SRAM) device, flash memory, or other memory devices. In one embodiment, the memory 36 may include a non-volatile memory or similar permanent storage device, and media such as a hard disk drive, a floppy disk drive, a compact disc read only memory (CD-ROM) device, a digital versatile disc read only memory (DVD-ROM) device, a digital versatile disc random access memory (DVD-RAM) device, a digital versatile disc rewritable (DVD-RW) device, a flash memory device, or other non-volatile storage devices. In one embodiment, the memory 36 may be communicatively coupled to the microprocessor 34. In an alternate embodiment, the memory 36 is an on-board memory of the microprocessor 34.
[0022] In one embodiment, the non-transitory computer readable storage medium encoded with a program or operating instructions, instructs the microprocessor 34 to perform a statistical analysis of the output signal 30. For example, the frequency of peaks in the output signal, the width of peaks in the output signal, the duration of peaks or other variations in the signal may be monitored and statistically analyzed. Statistics include average, median, variance, and spatial and temporal correlation coefficients. The data can be correlated with the flow rate and composition of the process fluid 14. It should be noted herein that the illustrated configuration of the flow meter 10 is an exemplary embodiment and should not be construed as limitation of the invention.
[0023] FIG. 3 is a schematic diagrammatical representation of the near field probe 26 in accordance with an exemplary embodiment. In the illustrated embodiment, the near field probe 26 includes a housing 38 having a bore 40. A pin 42 having a sensing tip 44, is disposed concentrically at a center 39 of the bore 40. The pin 42 and the housing 38 are made of a same material capable of exhibiting high corrosion and erosion resistance. In one such specific embodiment, the pin 42 and the housing 38 are made of a metal. In one such specific embodiment, the pin 42 and the housing 38 are made of a metal such as stainless steel or metal alloy such an Inconel alloy, haste alloy, and other corrosion and erosion resistant alloys. Impedance of the probe 26 is related to the diameter of the pin 42 and the housing 38. The diameter of the pin 42 is determined based on the diameter of the bore 40 so as to maintain the impedance of the probe 26 constant. A non-magnetic seal 46 is disposed in the bore 40, between the pin 42 and the housing 38. The non-magnetic seal 46 does not interfere with the transmitted microwave signals (electromagnetic signals). The non-magnetic seal 46 includes a hemispherical-shaped portion 48 disposed covering the sensing tip 44 of the pin 42. In one embodiment, the non-magnetic seal 46 is made of glass. Examples of glass include borosilicate glass, alumino-silicate glass, or the like. In one specific example, glass includes 20% by weight of calcium fluoride, 64% by weight of boron trioxide, 10% by weight of aluminum oxide, 1% by weight of dysprosium oxide, and 5% by weight of calcium sulfate. In another embodiment, the non-magnetic seal 46 is made of ceramic filled glass (physical mixture of glass and ceramic). In one specific example, ceramic filled glass includes 80% by weight of glass and 20% by weight of alumina. The hemispherical-shaped portion 48 has a radius of curvature in a range of 5 degrees to 45 degrees. The non-magnetic seal 46 is capable of withstanding fluid pressure, for example, 1000 bars under operational subsea conditions and also prevents leakage of the process fluid through the bore 40. The non-magnetic seal 46 has a low and constant dielectric loss at all operating temperatures.
[0024] The sensing tip 44 of the pin 42 is disposed proximate to the flow of the process fluid. Specifically, the sensing tip 44 protrudes slightly beyond a flow side 50 of the housing 38. A portion 52 of the pin 42 protrudes outward beyond an opposite side 54 of the housing 38. The non-magnetic seal 46 has a meniscus portion 56 proximate to the opposite side 54 of the housing 38. In another embodiment, the non-magnetic seal 46 may have a flat portion instead of the meniscus portion 56.
[0025] If the metal pin of a traditional near field probe is exposed to a fluid flow, erosion of the metal pin occurs over a period of time. Further, fouling and scaling of the metal pin may occur which reduces the sensitivity of the probe. Formation of a meniscus at a flow side of a seal accelerates the erosion of the seal and the pin. In the illustrated embodiment, the sensing tip 44 of the pin 42 is concealed from the process fluid via the hemispherical-shaped portion 48 of the non-magnetic seal 46. The hemispherical shape of the portion 48 creates a large angle with reference to the housing 38 so as to guide the process fluid flowing inside the conduit and around the sensing tip 44. The hemispherical-shaped portion 48 prevents formation of a fluid meniscus on the flow side 50 of the probe 26, thereby protecting the sensing tip 44 from scaling and fouling.
[0026] FIG. 4 is a perspective view of the flow side 50 of the near field probe 26 in accordance with an exemplary embodiment of FIG. 3. As discussed previously, the pin 42 having the sensing tip 44, is disposed concentrically at a center 39 of the bore 40. The non-magnetic seal 46 includes the hemispherical-shaped portion 48 disposed covering the sensing tip 44 of the pin 42.
[0027] FIG. 5 is a perspective view of a manufacturing facility 74 used for manufacturing the near field probe 26 in accordance with an exemplary embodiment of FIG. 3. A seal preform 75 made of a non-magnetic seal material, is disposed on the bore 40 of the housing 38. The quantity of the non-magnetic seal material is determined based on the volume of the bore 40. The diameter of the seal preform 75 is less than the diameter of the bore 40. A fixture 76 is used for holding the pin 42 at the center 39 of the bore 40 of the housing 38 in such a way that the pin 42 extends through an opening 78 of the seal preform 75. In the illustrated embodiment, specifically, one end of the pin 42 is supported by a top support 80 of the fixture 76 and the housing 38 is supported by a bottom support 82 of the fixture 76. In other embodiments, the type of fixture may vary depending on the application.
[0028] The seal preform 75 is subjected to heating via a heating device 84 in accordance with a first predefined thermal profile such that the seal preform 75 melts and flows into the bore 40. In one embodiment, the heating device 84 is a tubular furnace having a gas purging facility. The first predefined thermal profile is explained in greater detail with reference to a subsequent figure. The temperature for glassing the seal preform 75 is chosen based on a glass transition temperature and a required viscosity. The non-magnetic seal material is then cooled to form the non-magnetic seal 46 (shown in FIG. 3) between the pin 42 and the housing 38.
[0029] FIG. 6 is a graphical representation of a first predefined thermal profile in accordance with the embodiment of FIG. 5. The X-axis is represented by time in minutes and the Y-axis is represented by temperature in degrees Celsius. A curve 86 is representative of the first predefined thermal profile of the seal preform 75 during formation of the non-magnetic seal 46. In the illustrated embodiment, the seal preform 75 is heated from a room temperature to a temperature of 900 degrees Celsius in 180 minutes at a rate of 5 degrees Celsius per minute as represented by a curve portion 88. Then the seal preform material is maintained at 900 degrees Celsius (dwell period) for about 30 minutes as represented by a curve portion 90. Further, the seal preform material is heated to around 950 degrees Celsius (at a rate of 2 degrees Celsius per minute) in another 25 minutes as represented by a curve portion 92. Then the seal preform material is maintained at 950 degrees Celsius (dwell period) for about 30 minutes as represented by a curve portion 94. Thereafter, the seal preform material is cooled to the room temperature in around 235 minutes at a rate of 5 degrees Celsius per minute to form the non-magnetic seal 46 between the pin 42 and the housing 38 as referenced by a curve portion 96. It should be noted herein that in other embodiments, the thermal profile and the corresponding values may vary depending on the application.
[0030] FIG. 7 is a perspective view representative of a plurality of steps involved in manufacturing the near field probe 26 in accordance with the embodiment of FIG. 3. Reference numeral 98 is indicative of a graphite sheet 100 disposed in the bore 40 of the housing 38. Reference numerals 102, 103 are representative of a step in which the pin 42 is held extending through a central hole 104 of the graphite sheet 100 such that the pin 42 is disposed concentrically at a center 39 of the bore 40 of the housing 38. Reference numeral 106 is representative of a step in which the seal preform 75 is disposed on the bore 40. The pin 42 is disposed extending through the seal preform 75. Reference numeral 108 is indicative of melting of the seal preform 75 and formation of the non-magnetic seal 46 in the bore 40, between the pin 42 and the housing 38. The non-magnetic seal 46 includes the hemispherical-shaped portion 48 disposed covering the sensing tip 44 of the pin 42.
[0031] FIG. 8 is a schematic diagrammatical representation of a near field probe 58 in accordance with another exemplary embodiment. The near field 58 is similar to the near field probe 26 shown in FIG. 3. In the illustrated embodiment, the near field probe 58 includes a housing 60 having a bore 62. A pin 64 having a sensing tip 66, is disposed at a center 61 of the bore 62. The pin 64 and the housing 60 are made of a same material. A non-magnetic seal 68 is disposed in the bore 62, between the pin 64 and the housing 60. The non-magnetic seal 68 includes a hemispherical-shaped portion 70 and a non-hemispherical shaped portion 72. The hemispherical-shaped portion 70 is disposed covering the sensing tip 66 of the pin 64. In the illustrated embodiment, the hemispherical-shaped portion 70 is made of ceramic such as alumina and the non-hemispherical shaped portion 72 is made of glass.
[0032] In the illustrated embodiment, the hemispherical-shaped portion 70 is formed separately by pressing and sintering the ceramic material in accordance with a second predefined thermal profile. The second predefined thermal profile is explained in detail with reference to a subsequent figure. The hemispherical-shaped portion 70 is joined to the non-hemispherical shaped portion 72 by glassing. In one embodiment, the pin 64 may be made of molybdenum or niobium.
[0033] FIG. 9 is a graphical representation of a second predefined thermal profile in accordance with the embodiment of FIG. 8. The X-axis is representative of time in hours and the Y-axis is representative of temperature in degrees Celsius. A curve 110 is representative of the second predefined thermal profile. The sintering involves heating the ceramic material from a room temperature to a temperature of 650 degrees Celsius in 2 hours as represented by a curve portion 112. The ceramic material is maintained at a temperature of 650 degrees Celsius for 3 hours (dwell period) as represented by a curve portion 114. Further, the ceramic material is heated to a temperature of 1200 degrees Celsius in 3 hours as represented by a curve portion 116. The ceramic material is maintained at a temperature of 1200 degrees Celsius for 3 hours (dwell period) as represented by a curve portion 118. Further, the ceramic material is heated to a temperature of 1675 degrees Celsius in 4 hours as represented by a curve portion 120. The ceramic material is maintained at a temperature of 1675 degrees Celsius for 5 hours (dwell period) as represented by a curve portion 122. Then the ceramic material is cooled to the room temperature in 12 hours to form the hemispherical-shaped portion 70 as represented by a curve portion 124. It should be noted herein that the thermal profile and associated values discussed herein are exemplary and should not be construed as a limitation of the invention.
[0034] FIG. 10 is a graphical representation indicative of a variation in sensitivity of different types of near field probes. The X-axis representative of time in seconds and the Y-axis is representative of admittance of the probes. A curve 126 is representative of a variation in sensitivity of a near field probe having a flush pin (i.e. pin flushed with glass surface of a seal). A curve 128 is representative of a variation in sensitivity of a near field probe having a stub pin (i.e. pin projecting out of a glass surface of a seal). A curve 130 is representative of a variation in sensitivity of a near field probe having a coated pin (i.e. pin submerged under a glass surface of a seal). A curve 132 is representative of a variation in sensitivity of a reference near field probe in accordance with the exemplary embodiments of the present invention.
[0035] It should be noted herein that with respect to the reference near field probe, the probe with the stub pin has a higher sensitivity and the probe having the flush pin has a lower sensitivity. The probe with the coated pin has a much lower sensitivity compared to the reference near field probe and the probe having the flush pin. In other words, an exposed pin has best sensitivity whereas concealing a pin for reduced erosion and fouling, has a pronounced effect on the sensitivity. In accordance with the embodiments of the present invention, the reference near field probe has good sensitivity and reduced erosion and fouling.
[0036] In accordance with the embodiments of the present invention, a hemispherical-shaped portion of a seal is provided around a sensing tip of the pin, so as to conceal the pin from the fluid flow, thereby controlling erosion, fouling, and scaling of the pin. The hemispherical-shaped portion is made up of glass, or ceramic filled glass, or ceramic glass composite which is erosion resistant and capable of withstanding a fluid pressure inside a conduit.
[0037] While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.