US20080253058A1 - Pressure and mechanical sensors using titanium-based superelastic alloy - Google Patents
Pressure and mechanical sensors using titanium-based superelastic alloy Download PDFInfo
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- US20080253058A1 US20080253058A1 US11/787,048 US78704807A US2008253058A1 US 20080253058 A1 US20080253058 A1 US 20080253058A1 US 78704807 A US78704807 A US 78704807A US 2008253058 A1 US2008253058 A1 US 2008253058A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
- G01L9/0072—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance
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- the present invention relates to mechanical sensors, such as capacitive pressure sensors, that have deflectable components.
- the present invention relates to a sensor with a deflectable component formed of a titanium-based alloy having an extremely low Young's modulus, an extremely high tensile strength, and stable characteristics over a large temperature range.
- Capacitive pressure sensors have found widespread use in industrial, aerospace, and other control and monitoring systems. Capacitive pressure sensors can be configured to sense absolute pressure, gauge pressure, differential pressure, or combinations of those pressures.
- Capacitive pressure sensors have been fabricated from a variety of materials, including metal, glass, sapphire, and silicon.
- the performance of capacitive pressure sensors depends upon the physical characteristics of the material forming the deflectable components of the sensor, such as the center diaphragm of a two chamber capacitive pressure sensor. These physical characteristics include elastic modulus (or Young's modulus), tensile strength of the material, temperature dependence of the elastic modulus and tensile strength, thermal expansion properties, and hysteresis effects.
- the present invention is an improved sensor that includes a deflectable component formed of a titanium-based alloy having a Young's modulus of less than about 80 GPa and a tensile strength of greater than about 1,000 MPa.
- the titanium-based superelastic alloy may include, for example, titanium, a group IVa element, a group Va element other than titanium, and an interstitial element.
- the titanium alloy may be, for example, of a composition of the alloy group Ti-24 at. % (Nb+Ta+V) ⁇ (Zr, Hf)—O.
- the senor is a capacitive pressure sensor, and the component is a diaphragm that deflects as a function of pressure to be sensed.
- the titanium alloy provides a near zero temperature dependence and near zero linear thermal expansion over a temperature range of about 100° K to 500° K.
- the high tensile strength results in low hysteresis, extended operating range, and improved over-pressure characteristics.
- the low Young's modulus results in a higher signal-to-noise ratio than achieved with a conventional pressure sensor having a diaphragm such as stainless steel.
- FIG. 1 is a cross-sectional view of a differential pressure cell having a titanium-based superelastic alloy center diaphragm and isolation diaphragms.
- FIG. 2 is a graph comparing Young's modulus as a function of temperature for a titanium-based superelastic alloy, NiSpan and Elgilloy.
- FIG. 3 is a graph comparing linear thermal expansion of titanium-based superelastic alloy, NiSpan and Elgilloy.
- FIG. 4 is a graph comparing pressure hysteresis characteristics of NiSpan and titanium-based superelastic alloy.
- FIG. 5 is a cross-sectional view showing a pressure sensor with a deflectable superelastic alloy diaphragm with attached strain sensor.
- FIG. 6 shows a pressure sensor with a deflectable superelastic alloy diaphragm with a resistance that varies as a function of pressure.
- FIG. 1 is a cross-sectional view of differential pressure sensor 10 , which makes use of titanium-based superelastic alloy components.
- Pressure sensor 10 includes cell halves 12 and 14 , central diaphragm 16 , insulators 18 and 20 , electrodes 22 and 24 , isolator tubes 26 and 28 , and isolator diaphragms 30 and 32 .
- central diaphragm 16 and isolator diaphragms 30 and 32 are formed of a titanium alloy having a Young's modulus of less than about 80 GPa and a tensile strength of greater than about 1000 GPa.
- differential pressure sensor 10 is a capacitive sensor.
- Central diaphragm 16 divides the space between cell halves 12 and 14 into first chamber 34 and second chamber 36 .
- Isolator tubing 26 extends from isolator diaphragm 30 through cell half 12 to first chamber 34 .
- isolator tubing 28 extends from isolator diaphragm 32 to second chamber 36 .
- Electrode 22 is formed on the inner wall of insulator 18
- electrode 24 is formed on the inner wall of insulator 20
- Electrode 22 and central diaphragm 16 form a first sensing capacitor having capacitance C 1
- second electrode 24 and central diaphragm 16 form a second sensing capacitor having capacitance C 2 .
- Chambers 34 and 36 and isolator tubes 26 and 28 are filled with a dielectric fill fluid.
- process fluid applies a pressure P 1 to isolator diaphragm 30 , that pressure is transmitted by the dielectric fill fluid through isolator tube 26 into chamber 34 .
- pressure P 2 is transmitted by fill fluid through isolator tube 28 to second chamber 36 .
- Capacitances C 1 and C 2 change as central diaphragm 16 deflects in response to applied pressures P 1 and P 2 .
- the amount of deflection is a function of the difference between pressures P 1 and P 2 .
- This differential pressure can be derived by measuring capacitances C 1 and C 2 .
- Signal processing circuitry 40 converts measured capacitances C 1 and C 2 into an output value that is representative of differential pressure.
- Differential pressure sensor 10 makes use of titanium-based alloys having a very low Young's modulus, high tensile strength, near zero linear thermal expansion, and near zero temperature dependence of the Young's modulus.
- the low Young's modulus results in improved signal-to-noise performance of pressure sensor 10 because the lower the Young's modulus, the larger the strain (deflection) for a given pressure.
- the higher tensile strength results in low hysteresis (essentially zero up to the elastic limit), extended operating range, and a higher overpressure limit.
- the low thermal expansion coefficient and low temperature dependence of Young's modulus results in reduced temperature correction of pressure sensor 10 , improved stability, and reduced temperature hysteresis.
- titanium superelastic alloys examples include Saito et al. U.S. Pat. No. 6,607,693; Furuta et al. U.S. Pat. No. 6,979,375; Kuramoto et al. U.S. Patent Publication No. 2004/0055675; Furuta et al. US Patent Publication No. 2004/0115083; and Whang et al. US Patent Publication No. 2005/0072496.
- These titanium-based superelastic alloys are referred to by the trade designation GUM METAL® by Toyota Central R&D Labs, Inc., Aichi, Japan.
- the titanium-based superelastic alloys include titanium, a IVa group element (such as zirconium (Zr) or hafnium (Hf)), a group Va element other than titanium (such as vanadium (V), niobium (Nb), or tantalum (Ta)), and an interstitial element such as oxygen, nitrogen, or carbon.
- the group IVa element (Zr or Hf) contributes to lower Young's modulus and increase strength.
- the group Va elements (V, Nb, and Ta) contribute to lower Young's modulus.
- the interstitial element (O, N, or C) contributes to increased strength.
- the alloy has a body centered cubic or body centered tetragonal crystal structure.
- the titanium-based superelastic alloy can be formed by a melting process or by sintering. The alloy is then subjected to cold working, which significantly increases its tensile strength. The low Young's modulus and high tensile (elastic limit) strength, with high elastic deformation capability, allows the alloy to have good cold working properties.
- the titanium-based superelastic alloys have a Young's modulus of 80 GPa or less, and preferably have a Young's modulus in the range of about 60 to 70 GPa.
- the elastic limit tensile strength of the alloy is at least about 1,000 MPa, and in some cases is 1,200 MPa or greater.
- the linear expansion coefficient does not exceed 2 ⁇ 10 ⁇ 6 /° K over a temperature range from 100° K to 500° K.
- the cold-worked titanium-based alloys exhibit linear expansion coefficient similar to Invar alloys but over a wider temperature range.
- the temperature dependence of the Young's modulus is also near zero over an extended temperature range. As reported by Saito et al., the Young's modulus of the cold-worked titanium-based superelastic alloy remained essentially constant between 77° K and 500° K. This near zero temperature dependence is comparable to Elinvar alloys, but is present over a much wider temperature range.
- the high strength and low Young's modulus, when used in the deflecting element (central diaphragm 16 ) of pressure sensor 10 offers very high resolution and precise pressure measurement.
- the temperature characteristics provide improved temperature stability performance over a wide range of 100° K to 500° K.
- isolation diaphragms 30 and 32 can also be formed of the same material as central diaphragm 16 .
- the low thermal expansion of the titanium-based superelastic alloys allows central diaphragm 16 and isolation diaphragms 30 and 32 (as well as other components such as cups 12 and 14 ) to be used in conjunction with common low expansion solid state materials.
- Titanium-based superelastic alloys have three additional common characteristics. First, they have a compositional average balance electron number [electron/atom (ea) ratio] of about 2.24. Second, they have a bond order (Bo value) of about 2.86 to about 2.90 based on the DV-X ⁇ cluster method, which represent the bonding strength. Third, they have a “D” electron-orbital energy level (Md value) of about 2.43 to about 2.49. Examples of compositions meeting the criteria include Ti-12Ta-9Nb-3V—Zr—O and Ti-23Nb-0.7Ta-2Zr—O [mole percent (mol %)].
- Stainless steel is a material most commonly used for industrial precision pressure and deflecting mechanical sensors.
- the tensile strength of the titanium-based superelastic alloy at room temperature may be 1200 GPa, which is three times higher than conventional stainless steel.
- the Young's modulus at 300° K (room temperature) of the titanium-based superelastic alloy may be, for example, 60 GPa, which is four times lower than conventional stainless steel.
- the combination of extremely low Young's modulus and high tensile strength, together with the favorable thermal properties yields substantial improvement over sensors which use conventional stainless steel for the deflecting elements.
- FIGS. 2-4 compare characteristics of titanium-based superelastic alloys with two other alloy materials (Elgilloy and NiSpan) that have been used for pressure sensors due to their relatively low Young's modulus.
- FIG. 2 shows a comparison of Young's modulus for Elgilloy, NiSpan, and titanium-based superelastic alloy over a temperature range between ⁇ 40° C. (233° K) and 100° C. (373° K).
- the titanium-based superelastic alloy has a substantially lower Young's modulus at all temperatures, and the variation in Young's modulus with temperature is less than either Elgilloy or NiSpan.
- FIG. 3 shows linear expansion or displacement in millimeters as a function of temperature.
- the temperature of coefficient of titanium-based superelastic alloy is about 1.16 ⁇ 10 ⁇ 5 /° C. This compares to NiSpan at 1.63 ⁇ 10 ⁇ 5 /° C. and Elgilloy at 6.17 ⁇ 10 ⁇ 6 /° C.
- FIG. 4 shows pressure hysteresis characteristics of NiSpan and titanium-based superelastic alloy.
- tensile stress is shown as a function of % strain.
- NiSpan exhibits hysteresis as strain increases from 0% to about 0.25%.
- titanium-based superelastic alloy shows no hysteresis for strain between 0% and 0.6%.
- the differential pressure sensor shown in FIG. 1 represents only one example of a mechanical sensor using a titanium-based superelastic alloy as a deflecting sensing component.
- other capacitive pressure sensors using titanium-based superelastic alloy can be configured to measure absolute pressure or gauge pressure.
- the differential capacitive pressure sensor can be configured with cell halves in side-by-side configuration, with two deflecting diaphragms, rather than the configuration shown in FIG. 1 .
- differential pressure sensor shown in FIG. 1 can include additional electrodes to create additional capacitors for linearization purposes.
- additional electrodes is shown, for example, in U.S. Pat. No. 6,295,875.
- a capacitive pressure sensor of the type described in U.S. Pat. No. 6,843,133 uses a titanium-based superelastic alloy as the deflecting sensing component (diaphragm).
- the sensor can feature direct contact of process fluid with the titanium-based superelastic alloy diaphragm, or can include an isolator and a delelctric fill fluid similar to the sensor shown in FIG. 1 .
- FIG. 5 shows pressure sensor 50 , which includes chamber 52 , superelastic alloy diaphragm 54 , strain sensitive bridge sensor 56 , electronic signal processing compartment 58 , and signal processing circuitry 60 .
- Process pressure P is delivered to sensing chamber 52 and applies pressure against superelastic alloy diaphragm 54 .
- the process pressure can be delivered directly by the process fluid, or by a dielectric fill fluid.
- the fluid pressure causes deflection of diaphragm 54 , which in turn causes strain in strain sensitive bridge 56 .
- Strain sensitive bridge 56 may be, for example, a silicon piezoresistive bridge that is bonded to, deposited on, or embedded in superelastic alloy diaphragm 54 .
- the signals from bridge 56 are processed by signal processing circuitry 60 to produce an output which is a function of process pressure P.
- Compartment 58 may be vacuum sealed, so that the output is representative of absolute pressure, or may be maintained at atmospheric pressure, so that the output from signal processing circuitry 60 is representative of gauge pressure.
- FIG. 6 shows pressure sensor 70 , which includes sensing chamber 72 , reference chamber 74 , superelastic alloy diaphragm 76 , electrical contacts 78 and 80 , and signal processing circuitry 82 .
- Diaphragm 76 deflects based upon a difference in pressure between the process fluid pressure in chamber 72 and the pressure within reference chamber 74 . If the reference pressure within chamber 74 is a vacuum, pressure sensor 70 measures absolute pressure. If the reference pressure is atmospheric, sensor 70 measures gauge pressure.
- Signal processing circuitry 82 provides an output representative of measured pressure based upon the resistance between contact 78 and 80 .
- the resistance of diaphragm 76 is a function of resistivity of the titanium-based superelastic alloy, the length of diaphragm 76 between contact 78 and 80 , and the cross-sectional area of diaphragm 76 .
- diaphragm 76 deflects so that its length between contact 78 and 80 increases.
- the cross-section area does not change appreciably, and the resistivity is unchanged. As a result, increased pressure results in increased resistance between contact 78 and 80 .
- the titanium-based superelastic alloy diaphragm deflects as a function of pressure, and that deflection can be used to produce an output representative of pressure using sensed capacitance, sensed strain, or sensed resistance.
Abstract
Description
- The present invention relates to mechanical sensors, such as capacitive pressure sensors, that have deflectable components. In particular, the present invention relates to a sensor with a deflectable component formed of a titanium-based alloy having an extremely low Young's modulus, an extremely high tensile strength, and stable characteristics over a large temperature range.
- Capacitive pressure sensors have found widespread use in industrial, aerospace, and other control and monitoring systems. Capacitive pressure sensors can be configured to sense absolute pressure, gauge pressure, differential pressure, or combinations of those pressures.
- Capacitive pressure sensors have been fabricated from a variety of materials, including metal, glass, sapphire, and silicon. The performance of capacitive pressure sensors depends upon the physical characteristics of the material forming the deflectable components of the sensor, such as the center diaphragm of a two chamber capacitive pressure sensor. These physical characteristics include elastic modulus (or Young's modulus), tensile strength of the material, temperature dependence of the elastic modulus and tensile strength, thermal expansion properties, and hysteresis effects.
- Other mechanical sensors which rely upon deflection of a sensing component are also affected by the same material properties. There is a continuing need for improvements to capacitive pressure sensors and other mechanical sensors having deflectable sensing components to provide extended operating range, low hysteresis, greater signal-to-noise ratio, reduced correction for temperature effects, and improved stability in temperature hysteresis.
- The present invention is an improved sensor that includes a deflectable component formed of a titanium-based alloy having a Young's modulus of less than about 80 GPa and a tensile strength of greater than about 1,000 MPa. The titanium-based superelastic alloy may include, for example, titanium, a group IVa element, a group Va element other than titanium, and an interstitial element. The titanium alloy may be, for example, of a composition of the alloy group Ti-24 at. % (Nb+Ta+V)−(Zr, Hf)—O.
- In one embodiment, the sensor is a capacitive pressure sensor, and the component is a diaphragm that deflects as a function of pressure to be sensed. In this embodiment, the titanium alloy provides a near zero temperature dependence and near zero linear thermal expansion over a temperature range of about 100° K to 500° K. The high tensile strength results in low hysteresis, extended operating range, and improved over-pressure characteristics. The low Young's modulus results in a higher signal-to-noise ratio than achieved with a conventional pressure sensor having a diaphragm such as stainless steel.
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FIG. 1 is a cross-sectional view of a differential pressure cell having a titanium-based superelastic alloy center diaphragm and isolation diaphragms. -
FIG. 2 is a graph comparing Young's modulus as a function of temperature for a titanium-based superelastic alloy, NiSpan and Elgilloy. -
FIG. 3 is a graph comparing linear thermal expansion of titanium-based superelastic alloy, NiSpan and Elgilloy. -
FIG. 4 is a graph comparing pressure hysteresis characteristics of NiSpan and titanium-based superelastic alloy. -
FIG. 5 is a cross-sectional view showing a pressure sensor with a deflectable superelastic alloy diaphragm with attached strain sensor. -
FIG. 6 shows a pressure sensor with a deflectable superelastic alloy diaphragm with a resistance that varies as a function of pressure. -
FIG. 1 is a cross-sectional view ofdifferential pressure sensor 10, which makes use of titanium-based superelastic alloy components.Pressure sensor 10 includescell halves central diaphragm 16,insulators electrodes isolator tubes isolator diaphragms central diaphragm 16 andisolator diaphragms 30 and 32 (and optionallycell halves 12 and 14) are formed of a titanium alloy having a Young's modulus of less than about 80 GPa and a tensile strength of greater than about 1000 GPa. - In this embodiment,
differential pressure sensor 10 is a capacitive sensor.Central diaphragm 16 divides the space betweencell halves first chamber 34 andsecond chamber 36.Isolator tubing 26 extends fromisolator diaphragm 30 throughcell half 12 tofirst chamber 34. Similarly,isolator tubing 28 extends fromisolator diaphragm 32 tosecond chamber 36. -
Electrode 22 is formed on the inner wall ofinsulator 18, whileelectrode 24 is formed on the inner wall ofinsulator 20. Electrode 22 andcentral diaphragm 16 form a first sensing capacitor having capacitance C1, whilesecond electrode 24 andcentral diaphragm 16 form a second sensing capacitor having capacitance C2. -
Chambers isolator tubes isolator diaphragm 30, that pressure is transmitted by the dielectric fill fluid throughisolator tube 26 intochamber 34. Similarly, when a process fluid applies a second pressure P2 toisolator diaphragm 32, pressure P2 is transmitted by fill fluid throughisolator tube 28 tosecond chamber 36. - Capacitances C1 and C2 change as
central diaphragm 16 deflects in response to applied pressures P1 and P2. The amount of deflection is a function of the difference between pressures P1 and P2. This differential pressure can be derived by measuring capacitances C1 and C2.Signal processing circuitry 40 converts measured capacitances C1 and C2 into an output value that is representative of differential pressure. -
Differential pressure sensor 10 makes use of titanium-based alloys having a very low Young's modulus, high tensile strength, near zero linear thermal expansion, and near zero temperature dependence of the Young's modulus. The low Young's modulus results in improved signal-to-noise performance ofpressure sensor 10 because the lower the Young's modulus, the larger the strain (deflection) for a given pressure. The higher tensile strength results in low hysteresis (essentially zero up to the elastic limit), extended operating range, and a higher overpressure limit. The low thermal expansion coefficient and low temperature dependence of Young's modulus results in reduced temperature correction ofpressure sensor 10, improved stability, and reduced temperature hysteresis. - Examples of titanium superelastic alloys are described in Saito et al. U.S. Pat. No. 6,607,693; Furuta et al. U.S. Pat. No. 6,979,375; Kuramoto et al. U.S. Patent Publication No. 2004/0055675; Furuta et al. US Patent Publication No. 2004/0115083; and Whang et al. US Patent Publication No. 2005/0072496. These titanium-based superelastic alloys are referred to by the trade designation GUM METAL® by Toyota Central R&D Labs, Inc., Aichi, Japan. They also have been described in Saito et al., Multifunctional Alloys Obtained via a Dislocation-Free Plastic Deformation Mechanism, Science, Vol. 300, 464-467 (April 2003); Nishino, Super Multifunctional Alloy “GUM METAL”, R&D Review of Toyota CRDL Vol. 38, No. 3 (2003); and Kuramoto et al., Plastic Deformation in a Multifunctional Ti—Nb—Ta—Zr—O Alloy, Metallurgical and Materials Transactions A, vol. 37A, 657 (2006).
- The titanium-based superelastic alloys include titanium, a IVa group element (such as zirconium (Zr) or hafnium (Hf)), a group Va element other than titanium (such as vanadium (V), niobium (Nb), or tantalum (Ta)), and an interstitial element such as oxygen, nitrogen, or carbon. The group IVa element (Zr or Hf) contributes to lower Young's modulus and increase strength. The group Va elements (V, Nb, and Ta) contribute to lower Young's modulus. The interstitial element (O, N, or C) contributes to increased strength. The alloy has a body centered cubic or body centered tetragonal crystal structure. The titanium-based superelastic alloy can be formed by a melting process or by sintering. The alloy is then subjected to cold working, which significantly increases its tensile strength. The low Young's modulus and high tensile (elastic limit) strength, with high elastic deformation capability, allows the alloy to have good cold working properties.
- For mechanical sensors having a deflectable component (such as capacitive pressure sensor 10), the titanium-based superelastic alloys have a Young's modulus of 80 GPa or less, and preferably have a Young's modulus in the range of about 60 to 70 GPa. The elastic limit tensile strength of the alloy is at least about 1,000 MPa, and in some cases is 1,200 MPa or greater.
- As reported by Saito et al. in Science, vol. 30, 464 (2003), for 90% cold-worked alloys, the linear expansion coefficient does not exceed 2×10−6/° K over a temperature range from 100° K to 500° K. Thus the cold-worked titanium-based alloys exhibit linear expansion coefficient similar to Invar alloys but over a wider temperature range.
- The temperature dependence of the Young's modulus is also near zero over an extended temperature range. As reported by Saito et al., the Young's modulus of the cold-worked titanium-based superelastic alloy remained essentially constant between 77° K and 500° K. This near zero temperature dependence is comparable to Elinvar alloys, but is present over a much wider temperature range.
- The high strength and low Young's modulus, when used in the deflecting element (central diaphragm 16) of
pressure sensor 10 offers very high resolution and precise pressure measurement. The temperature characteristics provide improved temperature stability performance over a wide range of 100° K to 500° K. - Because the alloys are corrosion resistant,
isolation diaphragms central diaphragm 16. The low thermal expansion of the titanium-based superelastic alloys allowscentral diaphragm 16 andisolation diaphragms 30 and 32 (as well as other components such ascups 12 and 14) to be used in conjunction with common low expansion solid state materials. - Titanium-based superelastic alloys have three additional common characteristics. First, they have a compositional average balance electron number [electron/atom (ea) ratio] of about 2.24. Second, they have a bond order (Bo value) of about 2.86 to about 2.90 based on the DV-Xα cluster method, which represent the bonding strength. Third, they have a “D” electron-orbital energy level (Md value) of about 2.43 to about 2.49. Examples of compositions meeting the criteria include Ti-12Ta-9Nb-3V—Zr—O and Ti-23Nb-0.7Ta-2Zr—O [mole percent (mol %)].
- Stainless steel is a material most commonly used for industrial precision pressure and deflecting mechanical sensors. By way of comparison, the tensile strength of the titanium-based superelastic alloy at room temperature may be 1200 GPa, which is three times higher than conventional stainless steel. In addition, the Young's modulus at 300° K (room temperature) of the titanium-based superelastic alloy may be, for example, 60 GPa, which is four times lower than conventional stainless steel. The combination of extremely low Young's modulus and high tensile strength, together with the favorable thermal properties yields substantial improvement over sensors which use conventional stainless steel for the deflecting elements.
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FIGS. 2-4 compare characteristics of titanium-based superelastic alloys with two other alloy materials (Elgilloy and NiSpan) that have been used for pressure sensors due to their relatively low Young's modulus.FIG. 2 shows a comparison of Young's modulus for Elgilloy, NiSpan, and titanium-based superelastic alloy over a temperature range between −40° C. (233° K) and 100° C. (373° K). The titanium-based superelastic alloy has a substantially lower Young's modulus at all temperatures, and the variation in Young's modulus with temperature is less than either Elgilloy or NiSpan. -
FIG. 3 shows linear expansion or displacement in millimeters as a function of temperature. The temperature of coefficient of titanium-based superelastic alloy is about 1.16×10−5/° C. This compares to NiSpan at 1.63×10−5/° C. and Elgilloy at 6.17×10−6/° C. -
FIG. 4 shows pressure hysteresis characteristics of NiSpan and titanium-based superelastic alloy. InFIG. 3 , tensile stress is shown as a function of % strain. As shown inFIG. 4 , NiSpan exhibits hysteresis as strain increases from 0% to about 0.25%. In contrast, titanium-based superelastic alloy shows no hysteresis for strain between 0% and 0.6%. - The differential pressure sensor shown in
FIG. 1 represents only one example of a mechanical sensor using a titanium-based superelastic alloy as a deflecting sensing component. For example, other capacitive pressure sensors using titanium-based superelastic alloy can be configured to measure absolute pressure or gauge pressure. In addition, the differential capacitive pressure sensor can be configured with cell halves in side-by-side configuration, with two deflecting diaphragms, rather than the configuration shown inFIG. 1 . - In addition, the differential pressure sensor shown in
FIG. 1 can include additional electrodes to create additional capacitors for linearization purposes. The use of additional electrodes is shown, for example, in U.S. Pat. No. 6,295,875. - In still another embodiment, a capacitive pressure sensor of the type described in U.S. Pat. No. 6,843,133 uses a titanium-based superelastic alloy as the deflecting sensing component (diaphragm). The sensor can feature direct contact of process fluid with the titanium-based superelastic alloy diaphragm, or can include an isolator and a delelctric fill fluid similar to the sensor shown in
FIG. 1 . -
FIG. 5 showspressure sensor 50, which includeschamber 52,superelastic alloy diaphragm 54, strainsensitive bridge sensor 56, electronicsignal processing compartment 58, andsignal processing circuitry 60. Process pressure P is delivered to sensingchamber 52 and applies pressure againstsuperelastic alloy diaphragm 54. The process pressure can be delivered directly by the process fluid, or by a dielectric fill fluid. The fluid pressure causes deflection ofdiaphragm 54, which in turn causes strain in strainsensitive bridge 56. Strainsensitive bridge 56 may be, for example, a silicon piezoresistive bridge that is bonded to, deposited on, or embedded insuperelastic alloy diaphragm 54. The signals frombridge 56 are processed bysignal processing circuitry 60 to produce an output which is a function of processpressure P. Compartment 58 may be vacuum sealed, so that the output is representative of absolute pressure, or may be maintained at atmospheric pressure, so that the output fromsignal processing circuitry 60 is representative of gauge pressure. -
FIG. 6 showspressure sensor 70, which includessensing chamber 72,reference chamber 74,superelastic alloy diaphragm 76,electrical contacts signal processing circuitry 82.Diaphragm 76 deflects based upon a difference in pressure between the process fluid pressure inchamber 72 and the pressure withinreference chamber 74. If the reference pressure withinchamber 74 is a vacuum,pressure sensor 70 measures absolute pressure. If the reference pressure is atmospheric,sensor 70 measures gauge pressure. -
Signal processing circuitry 82 provides an output representative of measured pressure based upon the resistance betweencontact diaphragm 76 is a function of resistivity of the titanium-based superelastic alloy, the length ofdiaphragm 76 betweencontact diaphragm 76. As pressure increases,diaphragm 76 deflects so that its length betweencontact contact - As illustrated by the embodiments shown in
FIGS. 1 , 5, and 6, the titanium-based superelastic alloy diaphragm deflects as a function of pressure, and that deflection can be used to produce an output representative of pressure using sensed capacitance, sensed strain, or sensed resistance. - Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
Claims (33)
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JP2010502997A JP2010523999A (en) | 2007-04-13 | 2008-02-15 | Pressure and mechanical sensors using titanium-based superelastic alloys |
PCT/US2008/002017 WO2008127498A1 (en) | 2007-04-13 | 2008-02-15 | Pressure and mechanical sensors using titanium-based superelastic alloy |
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WO2015138843A1 (en) * | 2014-03-14 | 2015-09-17 | Rosemount Inc. | Corrosion rate measurement |
WO2017209909A1 (en) * | 2016-06-03 | 2017-12-07 | Honeywell International Inc. | Fill fluid thermal expansion compensation for pressure sensors |
WO2018204304A1 (en) * | 2017-05-02 | 2018-11-08 | General Electric Company | Overpressure protection system |
US10190968B2 (en) | 2015-06-26 | 2019-01-29 | Rosemount Inc. | Corrosion rate measurement with multivariable sensor |
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JP6515477B2 (en) * | 2014-10-06 | 2019-05-22 | 大日本印刷株式会社 | Mechanical quantity sensor and mechanical quantity measuring device |
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Also Published As
Publication number | Publication date |
---|---|
US7437939B1 (en) | 2008-10-21 |
CN101730840A (en) | 2010-06-09 |
JP2010523999A (en) | 2010-07-15 |
WO2008127498A1 (en) | 2008-10-23 |
EP2140242B1 (en) | 2019-04-10 |
EP2140242A1 (en) | 2010-01-06 |
EP2140242A4 (en) | 2012-05-09 |
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