Abstract:
Described are optical sensing systems. The systems may perform reliably in explosive environments and provide eye protection should breakage of an optical fiber be detected. Sensors of the systems additionally may be self-managing, acquiring and transmitting sensed data as available electrical power permits. The systems beneficially may be used on-board aircraft.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/739,168, filed Dec. 19, 2012, and entitled “System for Airborne Optical Powered Smart Sensors,” the entire contents of which application are incorporated herein by this reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to sensing systems configured for reliable use in explosive (or other hazardous) environments and which provide eye protection should an optical fiber break. More particularly, the invention relates principally, but not necessarily exclusively, to systems in which free-running fuel sensors are powered optically on-board aircraft, with optical fibers both transmitting power to the sensors and receiving data signals from them. 
     BACKGROUND OF THE INVENTION 
     Various optically-powered sensor systems exist today. U.S. Pat. No. 4,820,916 to Patriquin discusses one such system, in which optical energy is transmitted along a bus for distribution to sensors of the system. Return pulses from the sensors likewise are transmitted on the bus to a system controller. Sensor-specific time delays are provided to produce a pre-determined, time-multiplexed sequence of the return pulses. 
     U.S. Pat. No. 4,963,729 to Spillman, et al., discloses techniques for improving signal conditioning in optically-powered sensor systems. As with the system of the Patriquin patent, that of the Spillman patent transmits optical energy along a bus for distribution to sensors of the system. The bus also transmits return pulses from the sensors. 
     Yet another optically-powered sensor system is identified in U.S. Pat. No. 5,223,707 to Bjork. In some versions of the system, a controller may provide optical power to sensors and receive optical signals from the sensor locations on a single optical fiber. Alternatively, multiple optical fibers may be employed. Protocols are described which allow multiple sensors to communicate with a controller over a single optical fiber. 
     U.S. Pat. No. 7,965,948 to Bugash, et al., finally, also addresses using a single fiber and systems for “receiving a light power signal via the single fiber optic . . . and, in response to a pause in the received light power signal, transmitting a light data signal via the single optical fiber.” The systems may be deployed in aircraft fuel tanks, with optical fibers used in lieu of electrical wires. Incorporated herein in their entireties by this reference are the contents of the Patriquin, Spillman, Bjork, and Bugash patents. 
     Absent from any of these patents is, for example, any method of detecting or predicting breakage of an optical fiber. Likewise absent, therefore, is any systematic reaction to fiber breakage, which could result in injury should a human eye be exposed to an unattenuated light signal emanating from a broken fiber. Further absent from patents of this sort is any electronic safety barrier circuitry designed to limit supplied power below accepted maximums for explosive environments. Power-optimizing schemes in which sensors act based on available power rather than directly on command of a controller also are omitted; consequently, no extra energy (for “worst-case” scenarios) need necessarily be sent. 
     SUMMARY OF THE INVENTION 
     The present invention provides optically-powered sensing systems supplying these advantageous features. An optical interface uses light to deliver energy in order to power typically remote, isolated circuits. This approach avoids need for any metallic wires, use of which can increase risk of explosion in certain hazardous environments. 
     Photovoltaic power converters are currently available. However, many require levels of optical radiation greater than appropriate for use in explosive environments or when the radiation might impinge on a human eye. The present invention, by contrast, does not. Instead, systems of the present invention employ voltage- and current-limiting circuitry to limit optical radiation present in at least the explosive environments. Additional hardware (or software) controls may adjust or de-energize the light power source under conditions suggesting such adjustment or de-energization is likely appropriate. 
     Embodiments of the invention may include a system controller, one or more optical fibers, and one or more sensors. Typically multiple optical fibers and sensors are deployed, with a master microcontrol unit of the system controller separately controlling each sensor via a sensor control. Presently preferred is that a single optical fiber connect each sensor and its corresponding control—i.e. that a 1:1 correspondence exist between sensors and optical fibers—although such correspondence is not always necessary. 
     Beneficially included within sensors useful with the present inventions are such components as light couplers, photovoltaic cells, power supply management circuitry, controllers, and transducers. Data light emitters also may be included within the sensors. The emitters may transfer data via the optical fibers to the corresponding sensor controls. 
     Advantageously included with each sensor control may be a light power source, a light coupler, and a data light receiver. Also desirably comprising a sensor control may be circuitry providing automatic power reductions, normal and eye-protection light controls, and an electronic safety barrier. The safety barrier, when present, may function to ensure optical radiation levels do not exceed ignition levels of explosives extant in the environments of the systems, for example. 
     Preferably independent circuits, the normal and eye-protection controls allow adjustment of light power levels or de-energization of light power sources. Power level adjustments may be made normally for efficiency or unusually for eye protection, for example. Additionally, either circuit may de-energize a light power source when appropriate to do so. Automatic power adjustments, including de-energization of the light power source, also may occur if a sensor does not transmit light data within a pre-determined (or determinable) period—as, for example, when an optical fiber has broken. 
     As noted above, microcontrol units or other controllers may be included within the sensors themselves. Their presence allows sensors to self-manage available energy and hence be “free-running”—i.e. operable independent of the system controller. When electrical power is sufficient to do so, values may be acquired from transducers of the sensors and the acquired values transmitted by the data light emitter to the data light receiver via the light couplings and optical fibers. 
     Although potentially useful for many purposes, systems of the present invention may have especial value in connection with aircraft fuel tanks. They may provide reliable service notwithstanding placement in explosive environments, may facilitate avoidance of eye injuries during certain repair or maintenance operations, and may supply reliability compatible with aircraft fuel tank applications. Integrity of transmitted data further may be enhanced through use of a digital encoding data bus. 
     It thus is an optional, non-exclusive object of the present invention to provide improved optical sensing systems. 
     It is a further optional, non-exclusive object of the present invention to provide sensing systems configured for reliable use in certain hazardous environments, including within fuel tanks of vehicles such as aircraft. 
     It is also an optional, non-exclusive object of the present invention to provide sensing systems avoiding need for any metallic wires to transmit power or data through an explosive environment. 
     It is, moreover, an optional, non-exclusive object of the present invention to provide sensing systems with automatic power reduction capabilities should, for example, breakage of an optical fiber be detected. 
     It is an additional optional, non-exclusive object of the present invention to provide self-managing, “free-running” sensors that may operate independent of a system controller. 
     It is another optional, non-exclusive object of the present invention to provide optical sensing systems in which preferred versions have a 1:1 correspondence between sensors and optical fibers. 
     Other objects, features, and advantages of the present invention will be apparent to those skilled in the appropriate field with reference to the remaining text and the drawings of this application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an exemplary system consistent with the present invention. 
         FIG. 2  is a schematic diagram of a sensor component of the system of  FIG. 1 . 
         FIG. 3  is a schematic diagram of control and sensor components of the system of  FIG. 1 . 
         FIG. 4  is a schematic diagram of an exemplary electronic safety barrier circuit for use as part of the system of  FIG. 1 . 
         FIGS. 5-6  are block diagrams of an implementation of the safety barrier circuit of  FIG. 4 . 
         FIG. 7  is a diagram illustrating exemplary timing of operation of an automatic power reduction circuit useful as part of the system of  FIG. 1 . 
         FIG. 8  is a block diagram of interfaces of the automatic power reduction circuit of  FIG. 7 . 
         FIG. 9  is another schematic diagram of the sensor component of  FIG. 2 . 
         FIG. 10  is a functional diagram of the system of  FIG. 1  as used in a fuel tank. 
         FIG. 11  is a partly-schematicized depiction of a sensor consistent with  FIGS. 2 and 9 . 
         FIG. 12  is a partly-schematicized depiction of a controller consistent with  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Illustrated in  FIG. 1  is an exemplary sensing system  10  of the present invention. Included as part of system  10  may be system controller  14 , one or more sensors  18 , and one or more optical fibers  22 . Optical fibers  22  function to transmit energy (power) and data between the sensors  18  and the system controller  14 . The optical fibers  22  thus replace metal wires often used to transfer energy or information in the form of electricity. 
     As shown in  FIG. 1 , system controller  14  may include both microcontrol unit  26  and one or more sensor controls  30 . In the preferred version of system  10  depicted in  FIG. 1 , a single optical fiber  22  couples each sensor  18  to a corresponding sensor control  30 . While presently preferred, such 1:1 correspondence among fibers  22 , sensors  18 , and sensor controls  30  is not absolutely necessary, however. 
       FIG. 2  shows a sensor  18  together with its corresponding optical fiber  22 . Sensor  18  may comprise one or more transducers  34  (and associated interfaces) capable of measuring or otherwise sensing information of value to system  10 . Transducers may be capacitive or resistive (e.g. capacitive probe level, capacitance index compensator, NTC or PTC thermistance, water level) or otherwise as desired. Sensor  18  additionally may include a controller such as microcontrol unit  38  configured to receive information from transducers  34  and process the information sufficiently for communication to data light emitter  42 , which in cooperation with light coupling  46  may emit light for conveyance through optical fiber  22 . Also illustrated as part of sensor  18  are photovoltaic cell  50  and power supply management circuitry  54 , which may form part of the smart system electronics  58  of  FIG. 3 . 
     Additionally detailed in  FIG. 3  are components of sensor control  30 . Such components may include light coupling  58 , data light receiver  62 , and automatic power reduction circuitry  66 . Also preferably present in sensor control  30  are eye-protection light control circuitry  70 , normal light control circuitry  74 , system controller electronics  78 , and light power source  82 . Yet additionally, safety barrier circuitry  86  may be included as part of sensor control  30 . 
     One of multiple possible examples of safety barrier circuitry  86  appears in  FIG. 4 . As disclosed in U.S. Pat. No. 5,144,517 to Wieth, whose entire contents are incorporated herein by this reference, barrier module “E” of that patent includes zener diodes functioning to shunt current paths should overvoltages or overcurrents arise. Resulting when necessary is opening of a fuse, thereby precluding current flow.  FIGS. 5-6  provide block diagrams of similar exemplary circuitry  86 , illustrating fuse  90 , (preferably) parallel voltage suppressors  94  to limit overvoltages, and resister network  98  to limit overcurrents. Types and values of these elements may be selected by those skilled in the art so as to prevent emitted optical radiation from exceeding ignition levels of any explosive substance through which the radiation passes. 
     Eye-protection light control circuitry  70  and normal light control circuitry  74 , preferably independent circuits, may be interposed in series between light power source  82  and ground. Circuitry  70  and  74  thus allow current circulation through the light power source  82 , hence allowing light emission. Advantageously, normal light control circuitry  74  is controlled by system controller electronics  78 , which may energize or de-energize light power source  82 , or adjust its power level for power efficiency optimization (or otherwise). Power levels of light power source  82  may be adjusted using refresh times of measurements and achieved via pulse width modulation (PWM) or linear regulation, for example. Preferably, average power during a measurement cycle may be used to define a power level. Evaluating power levels as a function of refresh times may beneficially allow a health monitoring of optical paths, permitting preventative maintenance to be scheduled before occurrence of any failure which might ground an aircraft for unscheduled maintenance. 
     Eye-protection light control circuitry  70 , by contrast, beneficially is controlled by automatic power reduction circuitry  66  (see  FIG. 8 ) and may de-energize light power source  82  (or, in some versions, adjust its power level) when necessary. As shown in  FIG. 7 , automatic power reduction circuitry  66  preferably de-energizes light power source  82  if no data transmission from data light emitter  42  is received during a selected interval (T wait ). The interval may be initialized by light reception or by the release of power. 
       FIG. 9  illustrates, among other things, inclusion of microcontrol unit  38  in sensor  18 . Using information from power supply management circuitry  54 , microcontrol unit  38  acquires information from transducers  34  when available electrical power is sufficient to do so. In at least this sense sensor  18  thus is free-running, with microcontrol unit  38  acquiring information from transducers  34  as fast as possible given the electrical power then-currently available. Or, stated differently, sensor  18  harvests energy and performs when sufficient energy is available. Hence, sensor  18  is not synchronized with system controller  14 ; no extra energy need ever be sent to sensor  18 , and essentially no energy is wasted. After acquiring information, microcontrol unit  38  may transmit, using a digital encoding protocol, the measurements (or other information) through data light emitter  42 . Use of the digital bus allows for integrity data checks to occur, with such possible checks including, but not being limited to, parity bits, checksums, or cyclic redundancy checks depending on importance of the data. Additionally, need for maintenance may be predicted if power increases are necessary to obtain a desired refresh rate. 
     As noted earlier, system  10  is especially useful as sensors of fuel-related information in aircraft fuel tanks.  FIG. 10  depicts system  10  deployed in this manner, with sensors  18  (designated with the prefix “FOPSS”) being inside a fuel tank and control  30  (designed “FOPSC”) being outside the tank. Control  30  may communicate with other systems AS of an aircraft in any appropriate manner. Because optical fibers  22  extend between connectors  102  of control  30  and sensors  18 , no metal wires need connect control  30  and sensors  18 .  FIG. 11  shows a sample sensor  18  comprising two concentric tubes  106  and  110 , top and bottom brackets  114  and  118 , respectively, optical connector  102  with optical fiber  22 , and terminal block  122  including electronics.  FIG. 12  depicts a sample control  10  including optical connectors  102  for connection to aircraft systems AS and sensor  18 . 
     The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention.