Abstract:
A passively powered gas sensor for remotely reading and transmitting a gas pressure of a system, comprising a hollow cylindrical body, a stem axially aligned and extending outwardly from a first surface of the hollow cylindrical body, a pressure sensing element in the stem, and an antenna coupled to the pressure sensing element, where the antenna is located within the hollow cylindrical body and the stem. The pressure sensing device is polled remotely by a polling device, and powered by the polling device.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority from U.S. application Ser. No. 61/732,160, filed Nov. 30, 2012, incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     In many engineering applications, it is necessary to monitor a supply or flow of a pressurized gas, such as oxygen. This is particularly applicable in the fields of medicine and aviation. Current devices that monitor an oxygen system&#39;s status for medical and aircraft applications are generally by one of two types. The first type of such monitoring system relies on the use of pneumatic gages that may be prone to inaccuracies, and are neither durable or reliable. The second type of such system uses electronic sensors or switches that may be more durable and accurate that the pneumatic gages, but are prohibitively expensive in many applications and therefore not cost effective. 
     A typical application (e.g., an aircraft gaseous oxygen system) is illustrated in  FIG. 1 . Although throughout this document the term “oxygen” is used to discuss the gas, it should be understood that air or any other pressurized gas could be used with the present invention. A similar discussion could apply to a medical oxygen systems or other types of oxygen systems. In the system depicted in  FIG. 1 , high pressure oxygen such as 2000 psi is stored in the oxygen cylinder assembly  18 , secured by cylinder mounting brackets  21 . The oxygen cylinder assembly  18  includes a high pressure hose  6  that leads to an overboard discharge outlet  25  in case of overpressurization. A first high pressure line  20  leads to a fill valve  5  and a second high pressure line  22  mates with a tee fitting  23 , that leads to a pressure transducer  19  and a pressure gauge  2  for monitoring the pressure. A low pressure hose  17  feeds another system via a low pressure switch  3 . A regulating device that is a component of the oxygen cylinder assembly maintains an operating output pressure of 70 psi. In order to determine the amount of oxygen remaining in the system, the pressure in the cylinder is monitored by both a pressure gauge  2  and pressure transducer  19 . Additionally, a low pressure switch or another pressure transducer  3  monitors the regulated output and remains closed as long as a minimum regulated pressure is present. These devices are in continuous operation and the pressure transducer  19  and low pressure switch  3  are continuously drawing power whenever the aircraft is operating. Thus, it would be beneficial to provide a system and method which is more accurate and draws less power than previous systems. 
     SUMMARY OF THE INVENTION 
     The present invention utilizes solid state sensors with passive RF energy harvesting technology to monitor the status of an oxygen system by measuring the pressure and/or flow of oxygen in the oxygen storage/delivery system. The condition (pressure or flow) is only read and presented when a mechanic or operator needs the information and makes an inquiry using either a fixed or portable instrument reader. By employing only passive energy readers, the system is more reliable, requires less maintenance, saves energy, and reduces both weight and cost over prior art systems. 
     Other features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments in conjunction with the accompanying drawings, which illustrate, by way of example, the operation of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of a prior art pressurized gas system in an aircraft. 
         FIG. 2  is an elevated perspective view of a first embodiment of the sensor of the present invention; 
         FIG. 3  is another elevated perspective view of the embodiment of  FIG. 2 ; 
         FIG. 4  is a cross sectional view of the embodiment of  FIG. 2  and  FIG. 3 ; and 
         FIG. 5  is an elevated perspective view of an installation employing the embodiment of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An example of a new gas sensor RF device  100  is shown in  FIGS. 2-4  for an aircraft application such as that described with respect to  FIG. 1 . As shown in  FIGS. 2-4 , the gas sensor RF device  100  is designed to be installed into a standard regulating component via a standard threaded fitting so that no modification of current equipment is required. For example, two gas sensor RF pressure sensing devices would be installed in the system depicted in  FIG. 1 . In this oxygen monitoring system, both gas sensor devices are designed to read the actual gas pressure at the sensor. The first gas sensor RF device would be installed in the high pressure port that the high pressure line  22  (see  FIG. 1 ) occupies. The second gas sensor RF device could be installed in any unused low pressure port such as at the tee fitting  23  as shown in  FIG. 1 . These two gas sensor RF devices would replace the low pressure switch  3  and the high pressure line  22  in  FIG. 1 . 
       FIG. 2  shows a gas sensor pressure reader  100  having a hexagonal profile housing  110 , although other profile configurations are possible. Since any polygonal configuration will work, the term “cylindrical” herein may be used to describe a broad number of configurations that includes a hexagonal a profile, as well as octagonal and other polygons. Cylindrical could also include circular profiles, where the outer surface would preferably be knurled or include some ridges to allow a user to grasp and rotate the sensor. The benefit of the hexagonal shape is that it can easily be installed and removed with a standard socket or wrench. On a lateral face  112  of the hexagonal housing  110 , an outwardly projecting stem  114  is axially aligned and includes a pressure sensing element  116  disposed therein. The stem  114  is preferably threaded externally and includes an open distal end  118  where the sensing element  116  is present. When the external stem  114  is threaded into the pressure system, the stem  114  is exposed to the internal pressure of the system, such that it can determine the pressure inside the tank/line/system. The sensing element  116  is preferably part of a printed circuit board  120 , which is passively powered by a remote reader using, for example, harvested RF energy. The circuit board  120  is coupled to an antenna  122  that forms a closed loop passing through the stem&#39;s interior and around the hexagonal housing  110 .  FIGS. 3 and 4  illustrate the antenna  122  and the position of the circuit board  120  within the housing  110 . The remainder of the interior of the housing is filled with an encapsulating material  124  that protects the antenna and the circuit board from moisture, dust, and debris.  FIG. 4  illustrates the antenna  122  and the encapsulating material  124  within the interior of the hexagonal housing. 
       FIG. 5  illustrates two gas sensor RF devices  100  installed on an oxygen tank  200 . In this arrangement, components  2 ,  3 ,  19 ,  22  and  23  in  FIG. 1  are eliminated. The gas sensor RF devices  100  preferably utilize coding protocol such as ISO/IEC 18000-6 to store and transmit the information to a remote receiving device, such as such as a hand held or fixed data receiving device. Sensor readers poll the gas sensor RF devices to make the data available to the mechanic or operator. The sensor readers (not shown) can either be fixed or portable, and are initiated by the operator&#39;s command or actuated electronically at selected time intervals. The readers preferably read the sensors  100  remotely using a wireless connection, permitting data exchange in areas where the oxygen supply may be inaccessible or difficult to access. The reader then displays, stores, or transmits the value so that the mechanic or operator evaluate the status or condition of the oxygen storage system. Portable readers can include those commercially available that are capable of reading passive RF information that comply with ISO/IEC 18000-6. These readers are preferably utilized when a portable device can be employed so that one reader can serve multiple sensors, or in maintenance conditions when power to a fixed reader may not be available. Alternatively, fixed readers can also be used that are similar to the portable reader, with the exception that they are adapted to a stationary location. Readers with dual power sources can also be utilized that use stored or harvested energy, but are also capable of automatic switching to generated power when needed. 
     There are numerous advantages of the present invention over methods of gas monitoring systems of the prior art. An important primary advantage is the reduction and conservation of power consumption in the instruments. The gas sensor RF device of the present invention is a passive element that is powered by the reader. The reader uses batteries or harvested power, so they do not normally require system-generated or line power for operation. Moreover, power from the associated reader is utilized on an intermittent basis, only during the period that an actual reading is occurring. Thus, power drain on the system is minimal. 
     Another advantage of the present invention is that standard Bourdon-type tube gauges are susceptible to the problems associated with moisture and dust, and operate effectively in a narrow temperature range. These gages can be easily damaged by shock and vibration, and lack the accuracy and precision of electronic devises. Conversely, the present invention has no moving parts, does not draw power except during the period that the reading is being made, and is therefore far more reliable. 
     Using the present invention, a mechanic or technician can accurately determine the status of the remaining oxygen capacity in an oxygen storage system without powering up the system. Using the wireless embodiment, the mechanic can easily make a reading when the gas cylinder is in a location that is not easily accessible because direct access is not required. Because the system is free of wires or cables, there is less clutter and less opportunity to have wires become damaged or broken, further enhancing the reliability of the system. Moreover, with the gas sensor RF device reading the pressure directly at the source, there is no adjustment necessary for temperature effects that can complicate the reading or cause errors in measuring the true status of the system. The Sensor RF device reads actual values present. 
     Another advantage that is especially important to aircraft applications is the reduction in weight of the system. When using the application shown in  FIG. 1 , the estimated net weight of the system with current technology compared to a system using Senor RF devices 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 FIG. 1 System 
                 Weight 
               
               
                   
                   
               
             
             
               
                   
                 Transducer 
                 150 grams 
               
               
                   
                 L.P. Switch 
                 120 grams 
               
               
                   
                 HP Line 
                  36 grams 
               
               
                   
                 Bulkhead Tee 
                 158 grams 
               
               
                   
                 Gauge (Bourdon) 
                  54 grams 
               
               
                   
                 TOTAL 
                 518 grams 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 FIG. 1 System with Sensor RF devices 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Sensor RF HP 
                  35 grams 
               
               
                   
                 Sensor RF LP 
                  35 grams 
               
               
                   
                 Reader Fixed 
                 280 grams 
               
               
                   
                 TOTAL 
                 350 grams 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Net Weight Reduction 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 TOTAL 
                 −168 grams 
               
               
                   
                   
               
             
          
         
       
     
     A prototype of the present invention showed that the device can read up to 2900 psi using RF energy from a remote reader, and rates of between 0.5 lpm to 600 lpm. The device can be used for aircraft systems, medical systems, therapeutic systems, and clinical systems. As an alternative embodiment, the sensor can be a hybrid powered system where the power source is used as a back-up to the RF reader supplied energy. 
     The present invention also simplifies installation and replacement/removal of the system. With fewer connections to the system, removal of the oxygen cylinder assembly is much easier. The present invention eliminates the need for electrical cables to connect or disconnect, and there are fewer leak paths that can lead to leakage problems. Yet another advantage of the present system is that it monitors actual flow, i.e., it takes direct reading of flow rates to detect abnormal operation, leaks, or operational trends. Also, direct reading of flow rates and pressures without direct connection to the unit under test simplifies test set up and makes the collection of data less affected by the collection means. 
     The foregoing descriptions and illustrations are intended to be exemplary but not exclusive. One of ordinary skill in the art would recognize various modifications to the description of the embodiments depicted, and the present invention is intended to encompass all such modifications. 
     Other features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments in conjunction with the accompanying drawings, which illustrate, by way of example, the operation of the invention.