Abstract:
A temperature sensor system includes a body and window arrangement. The body defines an air intake and is flush mounted to a mobile platform having a boundary layer. The window arrangement is integrated into the body and transfers a first signal and receives a second signal. The second signal represents energy from the first signal that is reflected by air particles beyond the boundary layer. The second signal is processed to determine a temperature beyond the boundary layer. The air intake receives air particles, transfers a first set of the air particles to a first air vent into the mobile platform, receives the first set of the air particles from a second air vent from the mobile platform, vents the first set of the air particles, and vents a second set of the air particles that bypass the first air vent.

Description:
GOVERNMENT-FUNDED INVENTION  
       [0001]     The invention was made with Government support under Agreement No. 98-C-00031 awarded by the Federal Aviation Administration. The Government has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention is related to the field of temperature sensors, and in particular, to a temperature sensor system that detects the temperature outside of the boundary layer of a mobile platform.  
         [0004]     2. Statement of the Problem  
         [0005]     Airplanes continuously sense the outside air temperature while in flight. When in flight, airplanes have a boundary layer that is formed by airflow around the airplane. The boundary layer typically extends about 3 inches above the skin of the airplane. The friction between the airflow and the airplane skin heats the air in the boundary layer, which is referred to as frictional heating. Thus, the air temperature within the boundary layer is artificially increased by the frictional heating.  
         [0006]     To obtain an accurate outside air temperature that is unaffected by frictional heating, temperature sensors have been developed that attach to an airplane and extend outward beyond the boundary layer. Some of these sensors have redundant sensor components for reliability. Unfortunately, these temperature sensors do not have sufficient accuracy for scientific applications and optimal engine performance.  
         [0007]     Because the temperature sensors extend away from the airplane through the boundary layer, the sensors introduce drag and increase fuel consumption. The extended temperature sensors reduce the stealth characteristics of the airplane. The extended temperature sensors also collect unwanted materials, such as ice and feathers, that cause sensor failure. Heaters are typically required for the extended sensors to prevent icing, but the heaters add cost, are subject to failure, and they can add errors to the temperature measurement.  
         [0008]     An alternative temperature sensor includes a laser that directs a beam through the boundary layer. Energy from the beam is reflected from beyond the boundary layer and back to the temperature sensor. The temperature sensor processes the reflected energy to detect the temperature outside of the boundary layer. Although this alternative temperature sensor is more accurate than the above-described temperature sensors, the laser-based sensor does not provide accurate results in the presence of heavy fog, clouds, or precipitation that interfere with the laser beam and its reflection.  
       SUMMARY OF THE SOLUTION  
       [0009]     Some examples of the invention include a temperature sensor system and its method of operation. The temperature sensor system includes a body and window arrangement. The body defines an air intake and is configured for flush mounting to a mobile platform having a boundary layer. The window arrangement is integrated into the body and configured to transfer a first signal and to receive a second signal. The second signal represents energy from the first signal that is reflected by air particles beyond the boundary layer. The second signal is processed to determine a temperature beyond the boundary layer. The air intake is configured to: receive air particles, transfer a first set of the air particles to a first air vent into the mobile platform, receive the first set of the air particles from a second air vent from the mobile platform, vent the first set of the air particles, and vent a second set of the air particles that bypass the first air vent.  
         [0010]     In some examples of the invention, the window arrangement comprises a first window configured to pass the first signal and a second window configured to pass the second signal.  
         [0011]     In some examples of the invention, the temperature sensor system includes the first air vent and the second air vent.  
         [0012]     In some examples of the invention, the temperature sensor system further comprises a measurement cell coupled to the first air vent and the second air vent. The measurement cell may include one or two temperature sensors and a pressure sensor.  
         [0013]     In some examples of the invention, the air intake is configured to accelerate the air particles so the first set of the air particles enter the first air vent and the second set of the air particles by pass the first air vent.  
         [0014]     In some examples of the invention, the second set of the air particles are heavier than the first set of the air particles.  
         [0015]     In some examples of the invention, the temperature sensor system comprises a device configured to generate the first signal. The device could be a laser device and the first signal could be a laser signal.  
         [0016]     In some examples of the invention, the temperature sensor system comprises a telescope configured to receive the second signal from the window arrangement.  
         [0017]     In some examples of the invention, the temperature sensor system comprises an optical interface and sensor configured to receive and process the second signal to determine the temperature beyond the boundary layer.  
         [0018]     In some examples of the invention, the temperature sensor system comprises: the first air vent and the second air vent; a measurement cell coupled to the first air vent and the second air vent, wherein the measurement cell includes a temperature sensor configured to determine a first temperature; an optical interface and sensor configured to receive and process the second signal to determine a second temperature; and circuitry configured to receive and process the first temperature and the second temperature to determine the temperature beyond the boundary layer.  
         [0019]     In some examples of the invention, the temperature sensor system comprises: the first air vent and the second air vent; a measurement cell coupled to the first air vent and the second air vent, wherein the measurement cell includes a first temperature sensor configured to determine a first temperature and a second temperature sensor configured to determine a second temperature; an optical interface and sensor configured to receive and process the second signal to determine a third temperature; and circuitry configured to receive and process the first temperature, the second temperature, and the third temperature to determine the temperature beyond the boundary layer.  
         [0020]     In some examples of the invention, the temperature sensor system comprises: the first air vent and the second air vent; a measurement cell coupled to the first air vent and the second air vent, wherein the measurement cell includes a temperature sensor configured to determine a first temperature and a pressure sensor configured to determine a pressure; an optical interface and sensor configured to receive and process the second signal to determine a second temperature; and circuitry configured to receive and process the first temperature, the second temperature, and the pressure to determine the temperature beyond the boundary layer.  
         [0021]     In some examples of the invention, the temperature sensor system comprises: an optical interface and sensor configured to receive and process the second signal to determine the temperature beyond the boundary layer and to determine a signal-to-noise ratio for the second signal; and circuitry configured to process the a signal-to-noise ratio to determine if the mobile platform is in clear air or in unclear air.  
         [0022]     In some examples of the invention, the mobile platform comprises an airplane.  
         [0023]     In some examples of the invention, the mobile platform comprises a ground vehicle.  
         [0024]     In some examples of the invention, the mobile platform comprises an unmanned vehicle. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0025]     The same reference number represents the same element on all drawings.  
         [0026]      FIG. 1  illustrates a top view of a temperature sensor system in an example of the invention.  
         [0027]      FIG. 2  illustrates a front view of a temperature sensor system in an example of the invention.  
         [0028]      FIG. 3  illustrates a side view of a temperature sensor system in an example of the invention.  
         [0029]      FIG. 4  illustrates a front view of a temperature sensor system in an example of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]      FIGS. 1-4  and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.  
         [0031]      FIG. 1  illustrates a top view of temperature sensor system  100  in an example of the invention. Temperature sensor system  100  is typically attached to an airplane, although sensor system  100  could be attached to other mobile platforms, such as ground vehicles, alternative aircraft, unmanned mobile systems, or the like. Temperature sensor system  100  includes body  101 , air intake  102 , transmit window  103 , and receive window  104 . Body  101  could be comprised of aluminum or some other suitable material. Air intake  102  is formed by body  101 . Windows  103 - 104  could be glass, plastic, or some other material suitable to pass signals  105 - 106 . Note the direction of the airflow through air intake  102 , which is largely generated by the motion of the airplane.  
         [0032]      FIG. 2  illustrates a front view of temperature sensor system  100  in an example of the invention. Temperature sensor system  100  is attached to an airplane. The connection to the airplane typically includes a filler plate, which is familiar to those skilled in the art and is omitted for clarity. Temperature sensor system  100  includes body  101 , air intake  102 , transmit window  103 , receive window  104 , and flow enhancer  116 . If desired, a steel ring may form the entrance of air intake  102 . On  FIG. 2 , the direction of airflow is into the page, and the motion of the airplane is out of the page.  
         [0033]     Note the boundary layer that exists above skin of the airplane. The boundary layer is created by the airflow around the airplane as the plane flies. The boundary layer is typically around 3 inches, but the thickness of the boundary layer can vary. The air within the boundary layer experiences frictional heating caused by the airplane. Thus, accurate temperature measurements should be taken outside of the boundary layer, or should remove the frictional heating component from any temperature measurement taken within the boundary layer.  
         [0034]     Transmit signal  105  is generated and transferred through transmit window  103  and the boundary layer. Energy from transmit signal  105  is reflected from air particles outside of the boundary layer to form reflected signal  106 . Note that the air particles outside of the boundary layer are not artificially heated by the frictional heating within the boundary layer. Reflected signal  106  is received and processed to determine the temperature outside of the boundary layer. Advantageously, the temperature inaccuracy caused by the frictional heating is minimized or eliminated by sensing the temperature outside of the boundary layer. In some examples of the invention, signals  105 - 106  are optical signals that have a wavelength of less than one centimeter, such as a laser signal.  
         [0035]      FIG. 3  illustrates a side view of temperature sensor system  100  in an example of the invention. Body  101  and windows  103 - 104  are not shown for clarity. Air intake  102  includes flow enhancer  116 . Air intake  102  is coupled to air vents  111 - 112 . Measurement cell  113  is coupled to air vents  111 - 112 . Measurement cell  113  includes temperature sensors  117 - 118 . Note that temperature sensor  117  is positioned in the middle of measurement cell  113 , and temperature sensor  118  is positioned near the end of measurement cell  113 . Temperature sensors  117 - 118  could be platinum-resistance thermometers. Air vents  111 - 112  could be stainless steel tubes, Kevlar hoses, or the like, and in some examples of the invention, air vents  111 - 112  may represent mere openings between air intake  102  and measurement cell  113 .  
         [0036]     Air intake  102  has some aerodynamic features to note. The front of air intake  102  has a tapered shape that narrows from its entrance to air vent  111 . Flow enhancer  116  is a surface that is above the lower level of air intake  102  at air vents  111 - 112 . Flow enhancer  116  could be a rectangular block placed on the bottom of air intake  102 . In some examples, additional flow enhancers could be added that form arcs from air vents  111 - 112  to flow enhancer  116 , where the arcs extend above the surface of flow enhancer  116 .  
         [0037]     The aerodynamic features accelerate the air entering air intake  102  before the air reaches air vent  111 . The acceleration adds momentum to heavier air particles, such as ice, water, and aerosols, and the added momentum causes the heavier air particles to pass over air vent  111 . These heavier air particles are eventually vented from the back end of air intake  102 . In the context of the invention, air particles include aerosols, ice crystals, water droplets, and molecules (such as nitrogen, oxygen, or other molecules found in the air).  
         [0038]     Lighter air particles enter air intake  102  and follow air vent  111  to measurement chamber  113 . Within measurement chamber  113 , temperature sensors  117 - 118  measure air temperatures and transfer corresponding temperature signals. The air particles in measurement chamber  113  flow through air vent  112  and back to air intake  102 . Air intake  102  vents the lighter air particles from air vent  112  along with the heavier air particles that bypassed air vent  111 .  
         [0039]      FIG. 4  illustrates a front view of temperature sensor system  100  in an example of the invention. Temperature sensor system  100  is attached to an airplane, and the direction of airflow is into the page, while the motion of the airplane is out of the page. Temperature sensor system  100  includes body  101 , air intake  102 , windows  103 - 104 , air vents  111 - 112 , measurement cell  113 , flow enhancer  116 , and temperature sensors  117 - 118 . Note that temperature sensor  117  is positioned in the middle of measurement cell  113 , and temperature sensor  118  is positioned on the side of measurement cell  113 . Temperature sensor system  100  also includes laser  120 , signal paths  121 - 122 , optical interface  123 , optical fiber  124 , optical sensor  125 , and circuitry  131 .  
         [0040]     As the airplane flies, air particles are directed to through air intake  102  and air vent  111  to measurement cell  113 . In measurement cell  113 , sensors  117 - 118  sense temperatures and transfer temperature signals  126 - 127  to circuitry  131 . In addition, laser  120  transfers transmit signal  105  through signal path  121  and window  103 . Signal path  121  may include mirrors to direct signal  105  from laser  120  to transmit window  103 . Transmit signal  105  reflects off of air particles to form reflected signal  106 . Reflected signal  106  propagates through window  104  and signal path  122  to optical interface  123 . Signal path  122  may include a telescope to collect and focus reflected signal  106  onto optical interface  123 .  
         [0041]     Optical interface  123  collects reflected signal  106  and transfers a corresponding optical signal over optical fiber  124  to optical sensor  125 . Optical sensor  125  processes the optical signal to determine the temperature outside of the boundary layer—referred to as T L . Optical sensor  125  transfers temperature signal  128  indicating T L  to circuitry  131 . Optical sensor  125  could include a Fabry-Perot interferometer.  
         [0042]     Circuitry  131  could be programmed general-purpose circuitry, special purpose circuitry, or a combination of both. Circuitry  131  may be distributed in various locations in the airplane. Circuitry  131  receives temperature signals  126 - 127  from sensors  117 - 118 . The temperature that is indicated by signal  126  from sensor  117  is referred to as T ST . The temperature that is indicated by signal  127  from sensor  118  is referred to as T SA . Circuitry  131  also receives data signals  129   130  from the airplane, where data signals  129 - 130  respectively indicate air speed (mach number) and air pressure. Circuitry  131  processes signals  126 - 130  to determine the air temperature outside of the boundary layer—referred to as TA. Circuitry  131  generates and transfers signal  132  indicating T A .  
         [0043]     Circuitry  131  calculates three separate versions of T A  based the three separate data inputs (T ST , T SA , T L .) from the three separate sensors ( 117 ,  118 ,  125 ). For T L  from sensor  125 , circuitry  131  uses the simple equation T A =T L . For T SA  from sensor  118 , circuitry  131  removes the frictional heating component to obtain T A  using the following equation: 
 
 T   A   =T   SA −( a   S1   +a   S2   M+a   S3   M   2 ); where 
        M=the air speed mach number; and     a S1 , a S2 , and a S3  are coefficients that are obtained through empirical testing using a method of least squares as a maximum likelihood estimator of the coefficients.        
 
         [0046]     For T ST  from sensor  117 , circuitry  131  removes the frictional heating component to obtain T A  using the following equation: 
 
 T   A   =T   ST −( a   T1   +a   T2   M+a   T3   M   2 ); where 
        M is the air speed mach number; and     a T1 , a T2 , and a T3  are coefficients that are obtained through empirical testing using a method of least squares as a maximum likelihood estimator of the coefficients.        
 
         [0049]     After calculating the three versions of T A , circuitry  131  selects one of the versions to output as signal  132 . Typically, circuitry  131  selects the T A  that is derived from the laser obtained temperature T L . However, T L  may become unreliable due to fog, clouds, precipitation, or mechanical failure. The Signal-to-Noise Ratio (SNR) of sensor  125  will indicate if T L  becomes unreliable, so if this SNR exceeds a threshold, then circuitry  131  selects the T A  that was derived from T SA  and/or T ST . For example, circuitry  131  may average the two T A  values derived from T SA  and T ST . Circuitry  131  could use a Kalman filter to make the selection based on the SNR. Note that sensor system  100  has three independent sources to obtain T A  to provide very-high reliability.  
         [0050]     Based on the SNR data for optical sensor  125 , circuitry  131  could determine if the airplane is in clear air or is in fog, clouds, or heavy precipitation. Circuitry  131  could indicate the clear/unclear status correlated with time in a data signal. Circuitry  131  could also label the temperature data for T A  with the clear/unclear status.  
         [0051]     If desired a pressure measurement can be used to improve accuracy, since pressure affects frictional heating in the boundary layer. Different coefficients suited for different pressures can be developed during the empirical testing. Circuitry  131  could process the pressure indication in data signal  130  to select the most suitable coefficients given the current pressure. If desired, a pressure sensor could be added to measurement cell  113  to provide the pressure data to circuitry  131 .  
         [0052]     In one example, sensor system  100  has the following dimensions, although the included components and dimensions may vary in other examples. Dimensions are given in height, width, and length. 
    Maximum dimensions of body  101 : 0.787 inches×4.277 inches×5.369 inches     Diameter of the entrance of air intake  102 : 0.418 inches     Distance of air intake  102  from the entrance to air vent  111 : 0.540 inches     Diameter of air intake  102  at air vent  111 : 0.380 inches     Distance of air intake  102  from air vent  111  to air vent  112 : 1.874 inches     Diameter of air intake  102  at air vent  112 : 0.380 inches     Dimensions of flow enhancer  116 : 0.068 inches×0.125 inches×1.875 inches     Diameter of air vent  111 : 0.250 inches     Dimensions of measurement cell  113 : 0.787 inches×0.787 inches×2.374 inches     Diameter of air vent  112 : 0.250 inches     Diameter of windows  103 - 104 : 1.575 inches    
 
         [0064]     Various technical aspects that are applicable to the present invention are described in U.S. patent application Ser. No. 10/304,577; filed on Nov. 26, 2002; entitled “An Aerial Sampler System”; having the same inventor as the present invention; and which is hereby incorporated by reference into this patent application.  
         [0065]     In an alternative example of the invention, the laser components ( 103 - 104 ,  120 - 125 , and  128 ) could be replaced by other suitable electro-magnetic systems.  
         [0066]     In an alternative example of the invention, a heated ring could be added to the rim of the entrance to air intake  102 .  
         [0067]     In an alternative example of the invention, windows  103  and  104  could be integrated together.  
         [0068]     In another alternative example of the invention, the laser components ( 103 - 104 ,  120 - 125 , and  128 ) are omitted, and only temperature sensors  117 - 118  are used to determine TA. This alternative sensor system is less expensive than one with the laser components. The laser-based sensor could be used in testing to optimize the coefficients and algorithms used by the alternative system.  
         [0069]     In an alternative example of the invention, one of the temperature sensors  117 - 118  and its associated processing are omitted. Only one of temperature sensors  117 - 118  would be used to back-up the laser-based sensor  125 .  
         [0000]     Advantages  
         [0070]     Some examples of the invention provide the following advantages, although other examples of the invention may not provide these advantages. Temperature sensor system  100  is highly accurate. The high accuracy is more suitable for scientific and aviation applications. For example, highly accurate temperature data could be obtained by airplanes using temperature sensor system  100 . The highly-accurate temperature data could be processed with satellite-derived temperature data to provide improved temperature maps of the atmosphere, especially in the upper troposphere, tropopause, and lower stratosphere.  
         [0071]     Temperature sensor system  100  has a highly-aerodynamic profile. The highly-aerodynamic profile reduces drag to increase fuel efficiency. The highly-aerodynamic profile improves the stealth capabilities of the airplane. The highly-aerodynamic profile reduces or eliminates the collection of ice, feathers, and the like. Thus, the aerodynamic profile allows heating elements to be omitted if desired.  
         [0072]     Temperature sensor system  100  is highly-reliable. The aerodynamic design provides reliability by eliminating the heater which is prone to failure, and by eliminating the collection of unwanted debris, such as ice and feathers. The back-up temperature sensors provide accurate temperature data even if one of the sensors fails or becomes unreliable.