Abstract:
An improved optic system for measuring and/or controlling displacement, force, pressure, position, or chemistry is disclosed. This apparatus allows for more accurate, robust, and economical communication between the transducer (or control input element) and the reader device (or control output), allows the use of a single optic fiber and/or or a gap for the communication link, and produces substantial insensitivity to attenuation due to mechanical, chemical, thermal, and radiation effects acting on the optic fiber or open space in which the signal propagates. It is also significantly immune to interference from electromagnetic radiation, since the link can be easily produced as a non-conductor which will not propagate unwanted electrical energy or lightning, and is intrinsically safe from igniting fires or explosions. It also facilitates use on rotating machinery and remote location of the transducer by the ability to transmit the signal across a large gap or air space.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     No Federal sponsorship was received for this invention. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to the field of instrumentation and control, especially to areas where the intrinsic fire/explosion safety, immunity to electrical disturbances, immunity to eavesdropping and ability to propagate a signal through air or empty space of the present invention are features which are desirable VS conductor wires, strain gauge or capacitance diaphragm based devices and current optic based devices. 
     2. Description of Related Art 
     Devices for sensing and/or controlling weight, force, displacement, position, and chemistry are common in everyday life and commerce. Communication in the form of electric signals carried in wires or light signals carried in optic fibers are commonplace and well known. 
     A well known application of electronic controls translating a deliberate input from an operator or pilot into an output quantity would be the “fly by wire” systems developed for aircraft where a small, low force displacement of a lever by the pilot is translated via wires to a machine powered by the craft&#39;s electric or hydraulic system to create a large, forceful displacement of an aerodynamic control surface, replacing the earlier, more limited systems relying on the strength of the pilot to directly place the aerodynamic control surface via cables or hydraulics. 
     Systems which measure a physical quantity and are constructed of an excitation device, sometimes referred to as a signal conditioner, which powers it&#39;s transducer, and a transducer which converts a physical quantity such as pressure, position, force, or chemical condition into an electric or optic signal, and a communication link consisting of a wire or an optic fiber to transmit the excitation energy to the transducer and to transmit the signal from the transducer to a reader device, and a reader device which converts the signal to a display or indicator position expressing the quantity being measured in some number of units or which communicate with other equipment for reporting, process monitoring or control are known. A common example of such an electronic device is the well known strain gauge scale or strain gauge pressure sensor which provides electrical power to a Wheatstone bridge, the output of which is a predictable function of the strain experienced by the gauge elements, usually expressed in millivolts of output voltage per volt of input voltage per unit of strain or microstrain. These electronic devices are all vulnerable to the effects of interference from stray or deliberate electromagnetic energy, thus reducing accuracy or destroying the device. To avoid these problems shielding is often employed which increases weigh, size, and cost and decreases flexibility. These electronic gauges also present the danger of their own electric signals facilitating eavesdropping or unintentionally igniting flammables and explosives. Optic devices are known to solve some of these issues such as the Knute device of U.S. Pat. No. 5,065,010 which uses a reader/generator which communicates via an optic link of four separate fibers; two outgoing (one each “signal” and “reference”) and two return (one each “signal and “reference”) to and from a transducer which is exposed to an environment to measure some quantity, in this case pressure. Notably, this device would be vulnerable to inaccuracies due to any physical phenomena that affect any one, two, or three of those fibers in a manner not exactly equal to the others. A single fiber device would offer advantages in accuracy, robustness, economy, and miniaturization over a multi-fiber device. Further, if using a multi-fiber design such as Knute&#39;s or any similar analog system which converts light intensity into output in units being measured is employed in a disposable or replaceable device, then the transducer, fiber optic link, and optic emitting and receiving elements must all be part of the disposable or replacement component and then interface to the “reader” via electrical connections, thus adding cost. This type of connection is necessary for accuracy in that type of device due the unpredictable attenuation of signal whenever an optic fiber connection is made. There is also no ability in the Knute device for the reader or conditioning device to observe the transducer output through a gap or from a distance. 
     Another type of well known sensor device is the capacitance diaphragm gauge. This device uses the deflection of a conductive diaphragm which reacts to pressure. The device is constructed such that the position of the diaphragm relative to a fixed electrode is used to measure pressure as a function of the capacitance between the reactive and fixed elements. This sort of device has limitations in part because it is electronic and subject to interference and other aforementioned problems with electronic transducers, and as importantly, it has sensitivity issues at low absolute pressures. One intrinsic limitation of the capacitance based device is that there is a point where the electrical excitation of the capacitor begins to significantly influence the position of the reactive diaphragm. This is an issue which is avoided entirely by using light to detect position of the reactive element. 
     BRIEF SUMMARY OF THE INVENTION 
     In light of the aforementioned problems or shortcomings of prior devices, it is an object of the present invention to provide a system which employs a means of communication between a pressure, force, displacement, or chemical condition transducer and it&#39;s reader or between a control input and a corresponding control output that is immune to electronic interference, is intrinsically safe in flammable and explosive environments, has the ability to transmit across a gap, can be produced with a disposable transducer and a disposable communication link, determines the condition of the reactive element using a technique which does not exert forces upon the reactive element, and possesses an accuracy which is significantly unaffected by attenuation of the signal. This communication link is achieved by using light instead of either electrical resistance or electrical capacitance, and examining a particular characteristic of the light emanating from the transducer to the reader device instead of measuring simple intensity of light, and by propagating the light signal from the transducer to the reader device in a single optic fiber or through a space. This is accomplished by the device causing the character of the signal emanating from the transducer to shift in a predictable manner as the quantity being measured increases or decreases or causing the character of the signal emanating from the control input to shift in a predictable manner with intentional input by the user. Means offered to affect this involve the emission of two or more components of light or emission of light of a particular character by the transducer or control input device. In this, a “reference channel” of light of a known wavelength, range of wavelengths, color, or timing, which is weakly or relatively unaffected by the active element of the transducer or affected in a predictable manner by the active element and thus by the quantity being measured. At substantially the same time, a “signal channel” of a different wavelength, range of wavelengths, color, or timing is generated in a manner that is strongly affected by the reactive element and thus by quantity being measured in a predictable manner which is different from the aforementioned reference channel. The “signal” and “reference” channels could be distinguishable from each other by some easily separable feature such as wavelength, or the signal could be encoded in the total spectral character of light received at the reader. Another means to distinguish the signal and reference channels is timing features such as length of time of the signal or the point in time in which it occurs. Measurement is affected by examination of the spectral or timing character of the combined light reaching the reader device and comparing signal and reference to each other. Both “signal” and “reference” are generated in close proximity to each other and travel substantially the same length of optic fiber or jump the same gap to the reader device. In this manner, the actual strength of the total light received by the reader device is not especially important to accurate reading so long as the particular wavelengths or timed pulses of the signal and reference light are affected in similar manner by the multitude of phenomena which serve to attenuate power of light carried in an optic fiber, air, open space, or other media in it&#39;s propagation from the transducer to the reader device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the present invention, which are believed to be novel, are set forth with particularity to the appended claims. The present invention, both as to it&#39;s organization and manner of operation, together with further objects and advantages, may be best understood by reference to the following description, taken in connection with the accompanying drawings, of which: 
         FIG. 1  is a preferred embodiment of the present invention, configured as a pressure, force, or displacement measuring device. 
         FIG. 2  is a view of a preferred embodiment of the present invention used as a control device to position an aircraft aerodynamic control surface. 
         FIG. 3  is a preferred embodiment of the device employed as a gap jumping measuring device for use on rotating machinery. 
         FIG. 4  shows a close view of the transducer of  FIG. 1   
         FIG. 5  shows a cut away view of  FIG. 4   
         FIG. 6  shows a close up view of DETAIL E of  FIG. 5   
         FIG. 7  shows an embodiment of the device using optic filters to create light signals of two different spectral characters 
         FIG. 8  shows an embodiment of the device employing a prism and spherical reflector to separate incoming light into signals of different spectral character for differential attenuation. 
         FIG. 9  shows a cutaway of  FIG. 8 . 
         FIG. 10  shows an embodiment of the invention constructed as a chemical state sensor. 
         FIG. 11  shows an embodiment of the invention constructed to discriminate signal from reference by timing methods 
         FIG. 12  shows a cut-away view of  FIG. 11   
         FIG. 13  shows a close up view of DETAIL E of  FIG. 12   
         FIG. 14  shows an example of typical input and output on a graph of power VS wavelength in some condition. 
         FIG. 15  shows an example of typical input and output on a graph of power VS wavelength in some condition different from the preceding  FIG. 14 . 
         FIG. 16  shows an example of typical input and output of light on a graph of power VS wavelength for a spherical reflector device using a prism to separate “white” excitation light into component wavelengths. 
         FIG. 17  shows an example of typical input and output of light on a graph of power VS wavelength for a spherical reflector device using a prism to separate multi-wavelength excitation light into component wavelengths. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a system configured to measure some displacement DX 1  of the distal end of the transducer  43  due to some pressure or force or some imposed displacement. Excitation light is generated at source  41  in with some wavelength or range of wavelengths λ 1  launched into input optic fiber  47 . This light energy propagates past the splitter  46  and continues the length of the optic fiber  42  and into the transducer  43 . Once inside the transducer, the incoming light is divided by wavelength or used to generate a florescent response in the form of two or more light signals and returned in part along optic fiber  42 , past the splitter  46 , causing some of the returning light energy to launch into output optic fiber  48  and continue on into the meter. The construction of the transducer causes the return light to be divided into two or more signals having different spectral character, and which receive different treatment inside the transducer. The light signal shown as λ 2  is not strongly affected by the degree of displacement DX 1  and is used as a reference, however the signal shown as λ 3  is strongly affected by DX 1 . Thus as DX 1  changes, the ratio of light energy λ 2 :λ 3  changes in a predictable manner. Note  FIG. 14  and  FIG. 15 . These charts show the input power λ 1  and the output power of the reference channel λ 2  and signal channel λ 3  charted against wavelength before (“Condition A”) and after (Condition “B”) some change in the quantity being measured causing a change in the position of the movable reflector. In the case of a florescent device, the outputs would be known wavelengths longer than then input light and determined by the chemical makeup of the florescent elements. This shows that other things being substantially equal, particularly the input power λ 1 , the reference channel output λ 2  changes little or any between the “A” condition shown in  FIG. 14  and the “B” condition of  FIG. 15 , however the signal channel λ 3  changes. In this case, the excitation light λ 1  is represented to be some discrete wavelength. While this may present advantages it is not absolutely necessary, as the device will function if λ 1  is some range of wavelengths or even “white light” so long as it serves to excite the florescent media. If the device operates by selective reflectance or filtering, then these wavelengths would need to be present in λ 1 . 
     This relationship can be used to detect the condition of DX 1 . The characteristics of the optic fiber and the emission wavelengths are chosen such that they are affected similarly by physical phenomena that would attenuate signal such that both λ 2  and λ 3  are affected similarly by all phenomena other than the physical quantity being measured to the greatest extent achievable. 
       FIG. 2  shows a system configured to translate input from a user, driver or pilot, DX 2  into an output in the form of placement of a mechanical element, in this case an aerodynamic control surface  51  of a wing  54 , which correspondingly moves DX 5  in a predictable relationship with DX 2 . In this instance, the spectral character shift transducer  43  is in a position fixed relative to the system and is thus compelled to deform some amount DX 3  due to the control input of DX 2 . Just as in  FIG. 1 , some input energy in the form of excitation light λ 1  is launched into the input optic fiber  47 , causing signal and reference waves emerge propagating along output optic fiber  48 . The waves of differing spectral character emerging from output optic fiber  48  are resolved in resolver  44 B in this case, rather than a meter as in the previous. Power is input from power source  55 . The resolver  44 B responds to the input by generating an electronic command and supplying a certain power or command to an electromotive or hydraulic device to produce displacement DX 4 , which results in control output DX 5 . In this manner a human pilot or operator can control strong mechanical movements quickly, accurately, and with inputs requiring little force. The control circuit from the input to the resolver would be optic and thus immune to electromagnetic interference, eavesdropping, or the possibility of igniting a fire or explosion. The characteristics of the optic fiber and the emission wavelengths are chosen such that λ 2  and λ 3  are affected similarly by physical phenomena that would attenuate the signal in such a manner that the information pertaining to the measurement, such as the ratio λ 2 :λ 3  is not changed. 
       FIG. 3  shows a representation of the device employed in an application requiring transmission of the signal across a gap or open airspace as would be required by rotating machinery. In this particular case a pressure monitoring application for an aircraft landing gear tire is shown. The tire  56 B is shown cut-away to reveal the pressure gauge inside. As it is necessary for the tire to rotate about it&#39;s axis, prior art does not afford a means to transmit the optic signal. Current technology using strain gauges to sense condition and/or electromagnetic energy to transmit the information may not be useable due to interference from numerous sources including the use of radar and radio. This device is configured as a pressure sensor with a transducer  43  which is supplied with excitation light or energy λ 1  by source  41 . This energy propagates to the transducer along input  57 , which may be an optic fiber or a conducting wire. The signal emanating from the transducer propagates along an optic fiber, or a bundle of optic fibers shown as  48 . These optic fibers emit the signal through a port placed in the rim  56 A of the landing gear assembly. This port could be constructed air-tight to allow use of tubeless tires. The emitted signal contains the information in the form of a spectral character λ 2 :λ 3 , which describes the inflation level of the tire. 
       FIG. 4  shows a possible representation of the end or “transducer” of the system that would be exposed to the quantity to be measured, in this instance pressure, force or some mechanical displacement measured directly or as the result of a force being measured acting upon the bellow. As can be seen from the diagram, this version of the device includes a bellow in the construction as a pressure summing element, displacement transducer, or force transducer. This is the “reactive element” referred to earlier. 
       FIG. 5  shows the invention in cut-away to reveal the internal construction. This device is configured to use the focusing/defocusing effect encountered in moving a curved mirror as described in Coleman U.S. Pat. No. 6,604,427. In  FIG. 5 , the device is seen being energized by incoming light energy represented by ray λ 1  launched into the optic fiber  42  from the excitation source. This input light continues down the optic fiber  42  encountering ball element  60 . This ball element may be doped or treated such that light passing through it is diffused or filtered. At this point, some of the input light λ 1  exits element  60 , in part due to reflection from a coating shown as element  69  in  FIG. 6  and some passes through to element  61 . This relationship is relatively unaffected by condition of the reactive element, described by DX 6 . The light energy which exits element  60  then reflects from a mirror element  66  to mirror element  62 , At the zero condition, this light is focused onto element  63  which is treated such that light emanating from it by reflection or florescence is of a characteristic wavelength or range of wavelengths, a ray of which is represented by ray  58 A of  FIG. 5  and which possesses a spectral character: a distinct wavelength(s) or range of wavelengths noted as λ 3 . This signal element  63  may be doped or treated such that light passing through, reflecting, or emitting from it is diffused or filtered by spectral character and may have a reflective coating, and/or layers of florescent and reflective coatings and/or wavelength selective filtering shown as  70  in  FIG. 6  such that light emanating from element  63  will be of a characteristic wavelength or spectral character. Note that this coating may extend to the entire surface of element  63  or only to the half spherical surface shown depending whether it is constructed as a filtering, florescent, or reflective element. Ray  58 A, which is generated by or reflected from element  63  is then reflected off mirror element  62 , which is constructed to aim the beam to mirror element  66 , which is constructed to focus such a ray into element  60  resulting in light of the said characteristic wavelength λ 3  launched as return signal  58 B into optic fiber  42  in the direction of the reader device. It can be seen that if mirror element  62  is moved some distance such as represented by DX  6  from it&#39;s zero condition location, as shown in  FIG. 5 , then the focal point of said mirror is also moved away from signal element  63 . The result is less excitation light of ray  65  from element  60  reaching signal element  63 , represented by ray DX  65  and thus less response in the form of light represented by DX 58 A emanating from signal element  63 . Of this reduced emission, less reaches element  60  since less of this emission is aimed such that it will reach element  60 , compounding the effect of reducing the light energy to be found in return light ray  58 B. This is the “signal channel” that will be received at the reader device.  FIG. 5  shows the ray DX  65  “missing the target” of element  63 , and similarly, ray DX  58 A is shown on a course to “miss the target” of element  60  with the effect of reducing the amount of light energy of characteristic wavelength λ 3  to the reader. This comprises the “signal channel”. The portion of excitation light λ 1  entering the transducer and passing through element  60  continues to reference element  61 , where it serves to excite the reference channel. The reference element may be doped or coated such that it emits via reflection or florescence a light of spectral character λ 2 . Note that the conditions the device is adapted to measure via deformation DX 6  does not affect the production of  22  shown in ray  59  in  FIG. 6 , much of which passes through element  60  and propagates along optic fiber  42  as ray  59 B. This is relatively unaffected by the condition being measured and comprises the “reference channel”. 
     The output results would be substantially similar to the proceeding example depicted in  FIG. 14  and  FIG. 15 . The earlier note concerning reflective VS florescent devices also applies: for reflective devices, λ 1  must contain wavelength components equal to λ 2  and λ 3  whereas florescent devices need only contain the wavelength required to excite the florescent media though other wavelengths may be present as well. 
       FIG. 7  depicts an embodiment of the present invention which separates the incoming light excitation light λ 1  into components λ 2  and λ 3  using filters  59  and  71 . 
       FIG. 8  depicts the system using a prism  71  to separate the incoming light into a reference and signal channel. 
       FIG. 9  is a cutaway view of the device depicted in  FIG. 8 . As the incoming excitation light λ 1  enters the transducer after propagating along fiber optic  42 , it encounters a prism, causing the shorter wavelength components of λ 1  to deviate more from the original path than the longer wavelengths at some angel shown as ∠1. Shorter wavelengths will take a path with a greater ∠1. At the zero condition, longer and shorter wavelength rays are both substantially reflected off the spheroid surface  72  back into the prism  71  and re-launched back into the optic fiber  42  to propagate along the fiber to the meter or resolver to be translated into a pressure, force, or displacement reading as in  FIG. 1  or a mechanical motion as described in  FIG. 2 . As can be seen  FIG. 9 , at the zero condition all waves emanate from the effective center of a sphere, thus striking the reflective surface of  72  at an effective perpendicular. As the spheroid surface  72  is displaced by the quantity being measured or the control input, the shorter wavelength rays will not be reflected back to the prism, as is shown here. The shorter wavelengths will thus tend to miss the re-entry target and not be present in the return signal to a greater extent than the longer wavelengths, which will be less affected by this deflection since they will strike a more nearly perpendicular surface that is less disturbed from it&#39;s original angle to the beam of light emanating from the prism. This change in spectral character of the returning light is predictable with deflection DX 7  and can be used to measure such a deflection. 
       FIG. 16  shows a typical graph of anticipated input/output power VS wavelength for a system using multiple component light, such as generated by an incandescent bulb. λ 1  is launched into the optic fiber. This chart assumes both that the fiber carries components of light from approximately 0.2 to approximately 3.2 microns in wavelength and the source generates something akin to incandescent light similar to a Planck distribution of radiation from a hot black-body for the purposes of the illustration. In this case, for the zero condition (ie the reflector is substantially undisturbed, DX 7 =effectively zero) the returning signal light λ 2 , though lower in power than the excitation light due to unavoidable real world losses such as attenuation by the fiber and losses from connections, contains effectively the same mix of wavelengths as λ 1 . This is illustrated by the power VS wavelength curve labeled “λ 2  for DX small”. When DX 7  is increased, shorter wavelengths are lost from the mix of returning signal light, changing it&#39;s spectral character as illustrated by the curve labeled “λ 2  for DX large”. 
     The same mechanism also may be employed using two or more distinct ranges of wavelengths or two or more monochromatic inputs or inputs along narrow bands as illustrated by  FIG. 17 . In this application, λ 1  and λ 2  refer to two different wavelengths of light, whether input or output light. In this case, output light of both wavelengths are decreased in power from input levels, however the shorter wavelength λ 1  in the return light is affected to a greater degree as DX 7  is increased. 
       FIG. 10  depicts the system configured to sense a chemical condition. In this configuration an excitation light λ 1  is launched into the optic fiber. Upon reaching the distal end of the fiber, some of the excitation light strikes sensor element  76 , and some strikes reference element  77 . Both elements possess florescent properties and thus respond by emitting light at some characteristic wavelength λ 3  for the signal from the sensor, and a different wavelength λ 2  for the reference. In this construction, the sensor element  76  is exposed to the chemical condition being measured, directly or through a permeable membrane. The florescent reference element  77  is constructed such that it is not affected by the chemistry being measured, so it&#39;s response to incoming light λ 1  is predominantly a function of how much excitation light reaches it. Secondarily, other phenomena that may serve to affect light output such as temperature, pressure, etc would act upon both florescent media to the substantially same amount. One of the florescent media would be constructed to be sensitive to the intended quantity to be measured. The “quenching” effect of certain chemical conditions (or lack thereof) such as Ph, or dissolved gasses in liquids such as concentration of Oxygen in blood on the amount of output light emitted by florescent media are known. Signal element  76  is constructed such that it&#39;s florescent response in the form of λ 3  is a function not only of the excitation light received, as is reference element  77 , but of the chemical condition being measured. As the chemical condition changes, other factors being equal, the amount of reference light λ 2  will not vary. Both elements  76  and  77  are constructed such that significant variables such as the amount of light received affect both elements in a similar or predictable manner. The characteristics of the optic fiber and the emission wavelengths are chosen such that they are affected similarly by physical phenomena that would attenuate signal such that both λ 2  and λ 3  are affected similarly by phenomena other than the quantity being measured. The chemical condition can then be determined by comparing the intensity ratio of λ 2 :λ 3  at the meter. 
       FIG. 11  shows an embodiment of the device constructed to discriminate the signal (λ 3 ) from reference (λ 2 ) by timing methods. This is shown in cut-away and close-up in  FIG. 5  and  FIG. 6  respectively. This series of illustration is intentionally made similar to  FIGS. 4  thru  6 . In this case of timing discrimination, the reference generating element  61  is not required. The reference channel will emanate from element  60  in this case. Element  60  may be doped or treated to diffuse light passing through it. The excitation light λ 1  would be generated as a short pulse. The reference channel would be the light, which reflects directly off the reflector element  69  and back to the meter or resolver as illustrated in  FIGS. 1 and 2 . This would comprise reference channel λ 2 . Some of the light input as λ 1  will, upon reaching reflector element  69 , be reflected out of element  60  to take a course to reflect from elements  66 ,  62 , and  63  with the same effects of attenuation of the returning light pulse due to deflection of the mirror element  62  by some DX 6  as previously described for  FIG. 4 ,  FIG. 5  and  FIG. 6 . This happens independently of λ 2 , which is already on it&#39;s way to the meter or resolver at that point in time. With λ 1  generated as a sufficiently short duration pulse, there will be two distinct return pulses, the first of which is not strongly affected by DX 6 , and a second which is strongly affected by DX 6 . The condition of DX 6  can then be measured as in the wavelength discrimination systems as a ratio λ 2 :λ 3 . 
     Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims the invention may be practiced other than as specifically described herein.