Abstract:
Methods for making and systems employing pressure and temperature sensors are described. Embodiments include a capacitive element including a first conductor plate and a second conductor plate. Each plate includes a conductor layer formed on a substrate. In a pressure sensor embodiment, seal is positioned at or near the edges of the conductor plates, and a gas retained in a gap defined between the plates. In a temperature sensor embodiment, the gap defined between the plates is in fluid communication with the external environment.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation of U.S. patent application Ser. No. 12/026,795, filed on Feb. 6, 2008, which in turn claims the benefit of priority to U.S. Provisional Application Ser. No. 60/899,629, filed Feb. 6, 2007, the entire contents of each of which are incorporated herein in their entirety by reference. 
     
    
     FIELD 
       [0002]    The present invention relates generally to temperature and pressure transducers and more particularly to transducers that shift a frequency of a reflected signal based on a response to temperature or pressure. 
       BACKGROUND 
       [0003]    In operations, piping can extend hundreds or thousands of feet below ground to a well through a harsh downhole environment. Devices have been used for monitoring downhole conditions of a drilled well so that an efficient operation can be maintained. These downhole conditions include temperature and pressure, among others. A pressure sensor implemented in this environment should be configured operate within the potentially difficult environmental conditions. Likewise, a temperature sensor implemented in this environment should have a response that is relatively insensitive to changes in pressure. 
       SUMMARY 
       [0004]    A device in accordance with an embodiment includes a pressure sensor having a first conductor plate that includes a first layer formed on a first substrate. The first layer has a high coefficient of thermal expansion relative to the first substrate. The pressure sensor also has a second conductor plate that includes a second layer formed on a second substrate. The second layer has a high coefficient of thermal expansion relative to the second substrate. A hermetic seal is located at the edges of the first and second conductor plates. The first and second conductor plates are fixed relative to one another, and a gas is retained in an adjustable gap between the first and second conductor plates. 
         [0005]    A device in accordance with an embodiment includes a temperature sensor having a first conductor plate that includes a first layer formed on a first substrate. The first layer has a first coefficient of thermal expansion relative to the first substrate. The temperature also includes a second conductor plate having a second layer formed on a second substrate. The second layer has a second coefficient of thermal expansion relative to the second substrate. An adjustable gap is located between the first conductor plate and the second conductor plate, and a vent is formed in at least one of the first conductor plate and the second conductor plate. 
         [0006]    A system in accordance with another embodiment includes a an enclosure having a signal generator for generating an electromagnetic energy signal, an oscillating component for generating a ringing signal based on the electromagnetic energy, a component for adjusting a frequency of a ringing signal in response to a change in pressure applied thereto, and a processor for correlating the adjusted frequency to a pressure at the enclosure. 
         [0007]    A system in accordance with another embodiment of the invention includes an enclosure having a signal generator for generating an electromagnetic energy of signal, an oscillating component for generating a ringing signal based on the electromagnetic energy, an element for adjusting a frequency of an electromagnetic signal based on a temperature in the enclosure, and a processor for correlating the adjusted frequency to the observed temperature of the enclosure. 
         [0008]    A method in accordance with an embodiment of the invention includes using a system having a capacitor with a first plate and a second plate, retaining a gas in a gap between the first and second plates, generating a signal having a predetermined frequency, shifting the frequency of the generated signal based on a warping of at least one of the first plate and the second plate due to a pressure of the gas retained between the first and second plates, and correlating the shift in frequency to a pressure value. 
         [0009]    A method in accordance with an embodiment of the invention includes using a system having a capacitor with a first plate having a first coefficient of thermal expansion and a second plate having a second coefficient of thermal expansion and a vent provided in at least one of the first and second plates. The method includes generating a signal having a characteristic frequency, shifting the characteristic frequency of the signal based on a bending of at least one of the first plate and the second plate due to temperature, wherein the bending adjusts a gap between the first plate and the second plate, and correlating the shift in frequency to a temperature value. 
         [0010]    A method in accordance with another embodiment includes bonding a first layer having a high expansion coefficient to a second layer having a low expansion coefficient to form a first plate, forming a first dielectric layer on the first layer of the first plate, bonding a third layer having a high expansion coefficient to a fourth layer having a low expansion coefficient to form a second plate, forming a second dielectric layer on the third layer of the second plate, mounting the first plate and the second plate such that the first and second dielectric layers are adjacent, and sealing edges of the mounted plates so that a gas is retained between the first and second plates. 
         [0011]    A method in accordance with another embodiment includes bonding a first layer having a high expansion coefficient to a second layer having a low expansion coefficient to form a first plate, forming a first dielectric layer on the first layer of the first plate, bonding a third layer having a high expansion coefficient to a fourth layer having a low expansion coefficient to form a second plate, forming a second dielectric layer on the third layer of the second plate, forming a vent in at least one of the first plate and the second plate, mounting the first plate and the second plate such that the first and second dielectric layers are adjacent and a gap is established between the plates, and bonding edges of the first plate and second plate together. 
         [0012]    In accordance with another embodiment of the invention, a machine-readable medium includes machine-executable instructions for performing the methods or operating the systems described herein. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    Embodiments will be described in greater detail in reference to the drawings, wherein: 
           [0014]      FIG. 1  illustrates a pressure sensor in accordance with an embodiment; 
           [0015]      FIG. 2  illustrates a temperature sensor in accordance with an embodiment; 
           [0016]      FIG. 3  illustrates a second temperature sensor in accordance with an embodiment; 
           [0017]      FIGS. 4A-4E  illustrates a method of manufacturing a pressure sensor in accordance with an embodiment; 
           [0018]      FIGS. 5A-5E  illustrates a method of manufacturing a temperature sensor in accordance with an embodiment; 
           [0019]      FIG. 6  illustrates an overview of a system for measuring pressure in an enclosure in accordance with an embodiment; 
           [0020]      FIG. 7  is an overview of a telemetry system for measuring temperatures in an enclosure in accordance with an embodiment; and 
           [0021]      FIG. 8  is a flowchart of a method of measuring temperature or pressure in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  illustrates a pressure sensor  100  in accordance with an embodiment. The pressure sensor  100  includes a first conductor plate  102  and a second conductor plate  104 . 
         [0023]    The first conductor plate  102  includes a substrate  106  and a metal layer  108  formed on the substrate  106 . The metal layer  108  is formed from a metal that has a coefficient of thermal expansion (CTE 2 ) that is greater than the coefficient of thermal expansion (CTE 1 ) of the substrate  106 . A dielectric layer  110  is formed on the metal layer  108 . 
         [0024]    The second conductor plate  104  includes a substrate  112  and a metal layer  114  formed on the substrate  112 . The metal layer  114  is formed from a metal that has a coefficient of thermal expansion (CTE 4 ) that is greater than the coefficient of thermal expansion (CTE 3 ) of the substrate  112 . A dielectric layer  116  is formed on the metal layer  114 . 
         [0025]    The first conductor plate  102  is mounted on the second conductor plate  104  such that the dielectric layer  110  of the first conductor plate  102  is adjacent to the dielectric layer  116  of the second conductor plate  104 . A hermetic seal  118  is formed at the edges of the first conductor plate  102  and the second conductor plate  104  such that the first and second conductor plates  102  and  104  are fixed relative to one another. The first conductor plate  102  and the second conductor plate  104  are fixed relative to one another such that a gap (G) between approximately one to twenty thousandths of an inch (0.001″-0.020″) is established between the plates. A gas is retained in the gap between the conductor plates  102  and  104 . Conductive (e.g., metallic) leads  120  and  122  are connected to the first conductor plate  102  and the second conductor plate  104 , respectively. The leads  120  and  122  enable the pressure sensor  100  to connect to external circuitry. 
         [0026]    The first metal layer  108  of the first conductor plate  102  has a coefficient of thermal expansion (CTE 2 ) that is greater for the coefficient of thermal expansion (CTE 4 ) of the second metal layer  114  of the second conductor plate  104 . Moreover, to respond to pressure changes of the surrounding environment, the gas retained between the conductor plates  102  and  104  can be an inert gas such as nitrogen or argon. It should be readily apparent that any gas may be retained in the gap based on the desired response. The gas can be selected based, for example, on its propensity to provide a reproducible and predictable response to pressure changes of the surrounding environment. 
         [0027]    The substrates  106  and  112  of the first conductor plate  102  and the second conductor plate  104 , respectively, may be formed of an insulating material having a coefficient of thermal expansion that is substantially equal to zero (0). The insulating material of which the substrates  106  and  112  is formed should be resilient and capable of insulating and providing structural integrity to the pressure sensor  100  for use in harsh environments. A suitable material for forming as substrates  106  and  112  is carbon fiber fabric, however, it should be readily apparent that the choice of materials is not limited to this selection. 
         [0028]    The metal layers  108  and  114  of the conductor plates  102  and  104 , respectively, are formed from a material having a high coefficient of thermal expansion relative to the material of the respective substrates  106  and  112 . Materials known to provide good performance in use as the metal layers  108  and  114  include copper and stainless steel, for example, however, the metal layers  108  and  114  are not limited solely to these materials and may be formed of any metal having a coefficient of thermal expansion that provides the desired response. For low coefficient of thermal expansion materials, metals such as iron-nickel alloys may be suitable. For example 36FeNi (sold under the trade name Invar) or FeNi42 may be suited to low coefficient of thermal expansion applications. Likewise a ceramic material such as Zerodur may be useful in this regard. Where it is necessary to have an insulative property, the metallic alloys may be coated or covered in an insulating material. 
         [0029]    During operation, the pressure sensor  100  responds to external pressure by adjusting the size of the gap between the conductive plate  102  and  104  based on the bending (e.g., degree of warpage) of at least one of the respective conductor plates. The gas retained in the gap acts as a spring to move the conductive plates  102  and  104  further apart at lower external pressures and compresses the conductive plates  102  and  104  closer together at higher external pressures. When the metal layers  108  and  114  are formed of a metal such as copper, for example, that has a high coefficient of thermal expansion, the metal layers  108  and  114  also experience bending (e.g., warpage) due to changes in temperature. This bending can be a exhibited by an inward or outward bowing of the respective metal based on temperature. The substrates  106  and  112 , when formed from carbon fiber material, for example, have a lower coefficient of thermal expansion and are thus more stable with respect to changes in temperature than the copper of metal layers  108  and  114 . In this case, the substrates  106  and  112  can counteract the temperature related warpage of the metal layers  108  and  114 , respectively, and reduce the effects of external temperature changes on pressure monitoring. As will be appreciated, the same effect may be achieved by providing both a substrate and a conductor layer having low coefficient of thermal expansion. By selection of relative thicknesses of each layer in addition to proper material selection, the device can be made to be relatively more sensitive to pressure than to temperature. 
         [0030]      FIG. 2  illustrates a temperature sensor  200  of an embodiment. The temperature sensor  200  includes a first conductor plate  202  and a second conductor plate  204 . 
         [0031]    The first conductor plate  202  includes a substrate  206  and a metal layer  208  formed on the substrate  206 . The metal layer  208  has a substantially higher coefficient of thermal expansion (CTE 2 ) than the coefficient of thermal expansion of the substrate  206  (CTE 1 ). A dielectric layer  210  is formed on the metal layer  208 . 
         [0032]    The second conductor layer  204  includes a substrate  212  and a metal layer  214  formed on the substrate  212 . The metal layer  214  has a substantially higher coefficient of thermal expansion (CTE 4 ) than the coefficient of thermal expansion of the substrate  212  (CTE 3 ). A dielectric layer  216  is formed on the metal layer  214 . 
         [0033]    A vent  218  is formed through the first conductor plate  202  such that the vent  218  extends from an outer surface of the substrate  206 , through the metal layer  208 , to an outer surface of the dielectric layer  210 . The vent  218  provides an escape path for any gas that is retained between the conductor plates  202  and  204 . By providing an escape path for the gas, the vent  218  ensures that external pressure has relatively little influence on the temperature response of the sensor  200 . 
         [0034]    The first conductor plate  202  and the second conductor plate  204  are mounted such that the dielectric layers  210  and  216  are adjacent. Furthermore, the conductor plates  202  and  204  are mounted such that a gap (G) between one and twenty thousandths of an inch (0.001″ to 0.020″ or lesser or greater as desired) is established therebetween. Metal leads  220  and  222  are attached to the first conductor plate  202  and the second conductor plate  204 , respectively. These metal leads enable the temperature sensor  200  to be connected to external circuitry. 
         [0035]    The substrates  206  and  212 , the metal layers  208  and  214 , and the dielectric layers  210  and  216  may be formed from the same materials as described above with respect to the corresponding components of the pressure sensor  100 . 
         [0036]    During operation, as the temperature of the surrounding environment increases, the metal layers  208  and  214  bend (e.g., warp) inwardly to reduce the size of the gap (G). The degree of warpage of metal layers  208  and  214  can be related to the coefficient of thermal expansion associated with each respective layer. Additionally, the coefficient of thermal expansion and the thickness of the substrates  206  and  212  can also determine the degree of warpage of the metal layers  208  and  214 . 
         [0037]      FIG. 3  illustrates a temperature sensor  300  of an embodiment. Temperature sensor  300  includes a conductor plate  302  having a substrate  306 , a metal layer  310 , and a dielectric layer  314 . The temperature sensor  300  also includes a conductor plate  304  having a substrate  308 , a metal layer  312 , and a dielectric layer  316 . The conductor plates  302  and  304  are implemented through the same materials and employ the same characteristics as described above with respect to the temperature sensor  200  of  FIG. 2 . In addition to these components, the temperature sensor  300  also includes a vent  318  in the conductor plate  302  and a vent  320  in the conductor plate  304 . The vent  318  extends from an outer surface of substrate  306  to an outer surface of dielectric layer  314 . The vent  320  extends from an outer surface of substrate  308  to an outer surface of the dielectric layer  316 . 
         [0038]    During operation, the temperature sensor  300  responds to external temperatures in the manner as described above with respect to temperature sensor  200  of  FIG. 2 . The use of the additional vent  320  can further reduce or eliminate effects of external pressure by enabling an additional path of escape for any gas retained between the conductor plates  302  and  304 . 
         [0039]      FIGS. 4A through 4E  illustrate a process of manufacturing a pressure sensor of an embodiment. In  FIG. 4A , the metal layer  108  is formed on the substrate  106 . The metal layer  108  may be bonded to the substrate  106  through any known processes, including lamination through an epoxy resin and explosive bonding, for example. In  FIG. 4B , the dielectric layer  110  is formed on the metal layer  108 . Both conductive plates of the pressure sensor are formed in the previously described manner.  FIG. 4C  illustrates the conductive plate  104  having the metal layer  114  and dielectric layer  116  formed sequentially on the substrate  112 . Those of ordinary skill in the art will appreciate that conductive plates  102  and  104  may be formed through the same or a similar process. 
         [0040]    In  FIG. 4D , the first conductive plate  102  is mounted on the second conductive plate  104  such that a gap (G) between approximately one and twenty thousandths of an inch (0.001″ to 0.020″, or less or greater as desired) is established between the dielectric layers of each plate. In  FIG. 4E , the two plates are hermetically sealed together at their edges to create a pressure vessel. At the time the two plates are hermetically sealed, air or a gas can be deliberately trapped in the gap (G) between the plates. Alternatively, the air or gas can be injected into the cavity between the plates. 
         [0041]      FIGS. 5A through 5E  illustrate a process of manufacturing a temperature sensor of an embodiment. In  FIG. 5A , a metal layer  208  is bonded to the substrate  206 . The metal layer  208  may be bonded to the substrate  206  through processes including but not limited to, for example, lamination using an epoxy resin, and an explosive bonding process. In  FIG. 5B , a dielectric layer  210  is applied and formed on the metal layer  208 . 
         [0042]    In  FIG. 5C , a second conductor plate  204  may be formed in a manner similar to that previously discussed with respect to the first conductor plate  202 . For this reason, the process of forming the second conductor plate  204  will not be discussed in greater detail. 
         [0043]    In  FIG. 5D , a vent  218  is formed in the first conductor plate  202 . The vent  218  is formed by drilling a small hole from the outer surface of the substrate  206  through the metal layer  208 , to an outer surface of the dielectric layer  210 . It should be readily apparent that this same process may be used to form a vent  218  in the second conductor plate  204 . 
         [0044]    In  FIG. 5E , the first conductor plate is mounted onto the second conductor plate such that a gap (G) between approximately one and twenty thousandths of an inch (0.001″ to 0.020″, or lesser or greater as desired) is established between the two plates. The edges of the two plates are fixedly attached to one another but not sealed so that any influence of pressure is canceled. 
         [0045]    The materials used to construct the pressure and temperature sensors should be properly balanced to achieve a desired response to changes in the pressure and temperature of the environment. For example, the thickness of the substrate determines the effectiveness of the substrate in canceling the warping effect of an associated metal layer. Layers may be formed of varying thicknesses and/or have a multilayered structure. Additionally, the substrates of the pressure or temperature sensor may be constructed such that one or both of the conductive plates warp in response to the external temperature or pressure. In an embodiment, the warping or active conductive plate is formed on a substrate having a thickness that enables the plate to effectively warp or bow based on the external pressure or temperature to achieve the desired response. For example, the substrate of the active plate may be formed from a single 0.011″ thick carbon fiber fabric. The non-warping or inactive plate is multilayered or otherwise formed at a thickness that restricts the ability of the inactive plate to bow. For example, the substrate of the non-active plate may be formed from a single or multi-layer carbon fiber fabric having a total thickness of 0.033″. 
         [0046]      FIG. 6  illustrates an embodiment of a system  600  for measuring pressure in an enclosure (E). 
         [0047]    The enclosure (E) may be implemented in numerous shapes and sizes and may be a partial or full enclosure. The enclosure (E), as illustrated, is a representation of a full enclosure that is a high temperature and/or high pressure vessel. By way of example, the temperature within the enclosure may reach up to 600° F. 
         [0048]    The high temperatures and pressures realized in the enclosure (E) may be generated by any of numerous industrial applications such as drilling, manufacturing, or construction operations, for example. Those of ordinary skill in the art will appreciate that high temperatures and pressures of the enclosure (E) may also be generated through the innate environmental conditions experienced by the enclosure (E) itself. 
         [0049]    The system  600  includes a device, such as a signal generator  602 , for generating an electromagnetic signal or an electromagnetic pulse (EMP). The frequency of the signal can be in a range that includes, but is not limited to, RF frequencies such as 3 Hz-30 GHz, or lesser or greater as desired. The signal is communicated to the enclosure (E) through a suitable medium such as cabling, conductive piping, or over-air, for example. 
         [0050]    The system  600  also includes a device, such as the capacitive sensor  100 , for adjusting the frequency of the signal based on the pressure of the enclosure. The capacitive sensor  100  can be included in a resonant circuit  604 . 
         [0051]    The resonant circuit  604  includes means such as an antenna  606  for receiving the signal. The resonant circuit  604  also includes means, such as an inductor  608 , for connecting the resonant circuit  604  to the antenna  606 . The resonant circuit  604  also includes a circuit resistance  610  and circuit inductance  612  which represent the impedance of circuit casing. The resonant circuit  604  receives the signal through the antenna  606 , and rings at its natural frequency. The capacitive sensor  100  senses the pressure of the enclosure, and modulates the frequency induced in the resonant circuit  604 . The capacitive sensor  100  modulates the frequency by bending (e.g., warping) at least one of the first plate and the second plate relative to the pressure exerted on the gas that is retained in the gap (G) between the plates, by the enclosure (E). The modulated frequency can be processed to provide a measure of the pressure of the enclosure. That is, the vibration frequency induced by the electromagnetic energy is modulated by the sensed pressure of the enclosure, and this modulation of the frequency can be processed to provide a measure of the characteristic. 
         [0052]    The system  600  also includes a device, such as a correlator  614 , for correlating the modulated frequency to the observed pressure of the enclosure. Those skilled in the art will appreciate that the correlator  614  may be a processor or computer device. The correlator  614  can be programmed to process the modulated vibration frequency to provide a measurement of the sensed characteristic. The measurement can, for example, be displayed to a user via a graphical user interface (GUI). The correlator  614  can perform any desired processing of the detected signal including, but not limited to, a statistical (e.g., Fourier) analysis of the modulated vibration frequency. Commercial products are readily available and known to those skilled in the art for performing suitable frequency analysis. For example, a fast Fourier transform that can be implemented by, for example, MATHCAD available from Mathsoft Engineering &amp; Education, Inc., or other suitable product to deconvolve the modulated ring received from the resonant network device. The processor can be used in conjunction with a look-up table having a correlation table of modulation frequency-to sensed characteristics (e.g., temperature, pressure, and so forth) conversions. 
         [0053]      FIG. 7  illustrates an embodiment of a system  700  for measuring temperature in an enclosure (E). 
         [0054]    The system  700  includes a signal generator  702 , a capacitive sensor  200  and, a correlator  714 . It should be readily apparent that the signal generator  702 , and the correlator  714  are similar to the corresponding elements, as illustrated in the embodiment of  FIG. 6 . 
         [0055]    The capacitive sensor  200  adjusts the frequency of the RF signal resonant circuit based on the temperature of the enclosure. The capacitive sensor  200  can be included in a resonant circuit  704 . It will be appreciated that the resonant circuit  704  may be similar to the corresponding element as illustrated in the embodiment of  FIG. 6  and likewise includes an antenna  706 , inductor  708 , circuit resistance  710 , circuit inductance  712 . The capacitive sensor  200  adjusts the frequency of the resonant circuit  704  by bending (e.g., warping) at least one of the first plate and the second plate relative to the temperature of the enclosure (E). 
         [0056]      FIG. 8  is a flowchart that illustrates an embodiment of a method of measuring temperature on pressure in an enclosure. To measure pressure, the method is implemented using the system  600  having a pressure sensor  100  as discussed above. To measure temperature, the method is implemented using the system  700  having a temperature sensor  200  as discussed above. 
         [0057]    As shown in  FIG. 8  at  800 , a signal generator generates an electromagnetic signal or an electromagnetic pulse (EMP) at a frequency between, for example, 3 Hz and 30 GHz. The resonant circuit  604 ,  704  receives the signal ( 802 ). The capacitive sensor  100 ,  200  of the resonant circuit  604 ,  704  adjusts the frequency of the received signal by bending (e.g., warping) at least one of the first plate and the second plate in response to pressure or temperature depending on the application ( 804 ). The bending of the plates adjusts the spacing of the gap between the plates, thereby changing the capacitance of the capacitive sensor  100 ,  200 . 
         [0058]    The receiver  602 ,  702  receives the signal ( 806 ) and the correlator  608 ,  708  uses a look-up table to correlate the modulation of the frequency to an observed pressure or temperature value ( 808 ). 
         [0059]    While the invention has been described with reference to specific embodiments, this description is merely representative of the invention and is not to be construed as limiting the invention. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.