Patent Document

[0001]    This application claims priority to, and the benefit of, copending U.S. Provisional patent application Ser. No. 61/515,834 filed Aug. 5, 2011 which is incorporated herein by reference hereto in its entirety. The application claims priority to, and the benefit of, copending U.S. Provisional patent application Ser. No. 61/542,261 filed Oct. 2, 2011 which is incorporated herein by reference hereto in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of invention is the field of intelligent gas sensors with the capability to measure the pressure and temperature of one or more target gas substances contained in a known volume and to compute the mass of gas so contained as it varies in time due to additions or losses. The invention is also in the field of intelligent networked sensor nodes that exchange sensor information and sensor configuration and control information over communication networks. The field of invention also includes sensors that measure time-varying environmental conditions such as ambient temperature, atmospheric pressure, ambient light conditions, ambient sound levels, as well as various electrical conditions of equipment adjacent systems including AC and DC voltages and currents. The invention also comprises the field of dielectric gas sensors and gas leakage sensors. 
       BACKGROUND OF THE INVENTION 
       [0003]    There is a clear need for a low cost, network manageable, advanced gas sensor for sulfur hexafluoride gas (SF 6 ) used in high voltage electric switchgear. SF 6  plays a crucial arc-suppression role in this equipment. An expensive commodity and a potent greenhouse gas (GWP 23,900 times that of CO2), SF 6  lost through leakage is a costly problem justifying an effective monitoring system. The instant invention appreciates the application requirements and the sensor and communications network technologies required to meet them. The invention further supports security aspects that are paramount and tolerates the outdoor substation application environment which is challenging. 
         [0004]    Worldwide, of 7 million kg of SF 6  produced annually, most (˜75% or 5.5 metric tones per annum) is used for electric power equipment. Consequences for the environment and cost implications for electrical energy producers and users are clearly conveyed. Lower-impact, lower-cost alternatives to SF 6 , though sought, are not found. Techniques for estimating emissions have been based predominately upon indirect, mass-balance accounting methods that are costly and error-prone. Trials using expensive equipment (e.g. IR camera) combined with substantial labor have nonetheless shown that environmental impacts and gas expense arising from leakage are significant and can be reduced. 
         [0005]    Presently, SF 6  contributes 3% CO 2 -equivalent emissions. As global electric usage (3×10 6  Wh/capita) ascends to U.S. levels (1.3×10 7  Wh/capita), global generation increases 5-fold. While CO 2  emission per kWh generated must surely decrease, SF 6  emissions will scale with distribution. Switchgear equipment manufacturers and utilities need a low cost, network manageable, advanced gas sensor to achieve reductions in SF 6  emissions per kWh. 
         [0006]    All electric producers and users benefit. The instant invention targets economical, distributed sensor technology that can be applied worldwide to achieve a 100-fold reduction in emissions rate—a tremendous opportunity for the environment and economies worldwide. 
         [0007]    References Cited and incorporated herein by reference hereto in their entirety follow: 
         [0008]    [1] United States Environmental Protection Agency, “Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008”, Washington, D.C., Apr. 15, 2010, Available at http://www.epa.gov/climatechange/emissions/downloads10/US-GHG-Inventory-2010_Report.pdf. 
         [0009]    [2] Debra Knopman, Katie Smythe, “2004-2006 SF6 Data Summary”, PM-2327-NEMA, June, 2007, Prepared for the National Electrical Manufacturers Association, Available at http://www.epa.gov/electricpower-sf6/documents/04-06_data_summary.pdf. 
         [0010]    [3] United States Environmental Protection Agency, “SF6 Emission Reduction Partnership for Electric Power Systems—2007 Annual Report”, Washington, D.C., December, 2008, Available at http://www.epa.gov/electricpower-sf6/documents/sf6 — 2007_ann_report.pdf. 
         [0011]    [4] Jos Olivier, Joost Bakker, Jan Willem Wouda, Rainer Bitsch, and Manfred Maiss, “Global Emission Sources of Greenhouse Gas Emissions from Industrial Processes: SF6”, IPCC Task Force on National Greenhouse Gas Inventories, January, 2003, Available at &lt;http://www.ipcc-nggip.iges.or.jp/public/gp/bgp/3 — 9_Global_Sources_Industrial_Processes_SF6.pdf. 
         [0012]    [5] L. G. Christophorou, J. K. Olthoff, and D. S. Green, “Gases for Electrical Insulation and Arc Interruption: Possible Present and Future Alternatives to Pure SF6”, NIST Technical Note 1425, November, 1997, Available at &lt;http://www.epa.gov/electricpower-sf6/documents/new_report_final.pdf. 
         [0013]    [6] United States Environmental Protection Agency, “Electric Transmission and Distribution Equipment Use—Final Rule: Mandatory Reporting of Greenhouse Gases (40 CFR 98, Subpart DD)”, November, 2010, Available at &lt;http://www.epa.gov/climatechange/emissions/downloads10/Subpart-DD_infosheet.pdf. 
         [0014]    [7] Alfieri, M. 2002. “Partner Case Study: Con Edison”, Presented on behalf of Con Edison at the International Conference on SF6 and the Environment: Emission Reduction Strategies. San Diego, Calif., Nov. 21-22, 2002. Available at &lt;http://www.epa.gov/highgwp1/sf6/proceedings/agenda.html. 
         [0015]    [8] Robert Madding and Robert Benson, “Detecting SF6 Insulating Gas Leaks with an IR Imaging Camera”, Electricity Today, pp. 12-15, November/December, 2007, Available at &lt;http://www.electricity-today.com/et/issue0907/ir_camera.pdf. 
         [0016]    [9] Jan-Martin Rhiemenier, Sina Wartmann, Marcello Pagnotta, Natalia Makowska, and Xingyu Li, “Update on global SF6 Emissions trends from electrical equipment—Edition 1.1”, Ecofys Germany GmbH, July, 2010, Available at &lt;http://www.ecofys.com/com/publications/brochures_newsletters/documents/ESI-SF6_Finalreport_edition11 — 100701_v01.pdf. 
         [0017]    [10] U.S. Department of Energy, “U.S. Energy Information Administration Electric Power Annual 2009”, Washington, D.C., November, 2010, Available at &lt;http://www.eia.gov/cneaf/electricity/epa/epa_sum.html&gt; 
         [0018]    [11] WIKA Alexander Wiegand GmbH &amp; Co. KG, “Gas Density Monitor (GDM) with Integrated Gas Density Transmitter, Model 233.52.100 TI”, Klingenberg, Germany, May, 2009, Available at &lt;http://en-co.wika.de/upload/DS_SP6005_GB — 7922.PDF. 
         [0019]    [12] J. Blackman, M. Averyt, and Z. Taylor, “SF6 Leak Rates from High Voltage Circuit Breakers—U.S. EPA Investigates Potential Greenhouse Gas Emissions Source”, presented at the International Conference on SF6 and the Environment: Electric Power Systems—Partnership Update, Nov. 28, 2006, Available at &lt;http://www.epa.gov/electricpower-sf6/documents/leakrates_circuitbreakers.pdf. 
         [0020]    [13] General Electric Company, “72.5 kV Circuit Breakers Data Sheet”, Nov. 10, 1999, Available at &lt;http://www.geindustrial.com/publibrary/checkout/72.5DAT?TNR=Data%20Sheets|72.5DAT|PDF. 
         [0021]    [14] General Electric Company, “121 kV Circuit Breakers Data Sheet”, Mar. 1, 2002, Available at &lt;http://www.geindustrial.com/publibrary/checkout/121DATA?TNR=Data%20Sheets|121DATA|PDF. 
         [0022]    [15] General Electric Company, “145 kV Circuit Breakers Data Sheet”, Nov. 10, 1999, Available at &lt;http://www.geindustrial.com/publibrary/checkout/Data%20Sheets|145DATA|PDF. 
         [0023]    [16] General Electric Company, “169 kV Circuit Breakers Data Sheet”, Nov. 10, 1999, Available at &lt;http://www.geindustrial.com/publibrary/checkout/Data%20Sheets|169DATA|PDF. 
         [0024]    [17] General Electric Company, “242 kV Circuit Breakers Data Sheet”, Nov. 10, 1999, Available at &lt;http://www.geindustrial.com/publibrary/checkout/Data%20Sheets|242DATA|PDF. 
         [0025]    [18] General Electric Company, “362 kV Circuit Breakers Data Sheet”, Nov. 10, 1999, Available at &lt;http://www.geindustrial.com/publibrary/checkout/Data%20Sheets|362DATA5|PDF. 
         [0026]    [19] General Electric Company, “550 kV Circuit Breakers Data Sheet”, Nov. 10, 1999, Available at &lt;http://www.geindustrial.com/publibrary/checkout/Data%20Sheets|550DATA4|PDF. 
         [0027]    [20] Solon Manufacturing Company, “2TC, SF Gas Density Switch, Intrinsic Gauge Design”, Chardon, Ohio, Available at &lt;http://www.solonmfg.com/controls/techdocs/documents/2tcspec.pdf. 
         [0028]    [21] Giancarlo Scalabrin, Luigi Bettio, Paolo Marchi, and Paolo Stringari, “A Fundamental Equation of State for Sulfur Hexafluoride (SF6) in Extended Equation of State Format”, JPCRD 36(2) pp.  617 -662, 2007, Available at &lt;http://energyfromthorium.com/forum/download/file.php?id=44&amp;sid=275692ae3353 e590221 el226f0501ac1. 
         [0029]    [22] Maryland Department of the Environment, “Maryland CO2 Budget Trading Program, COMAR 26.09.03”, Baltimore, Md., August, 2009, Available at &lt;http://www.mde.state.md.us/programs/Air/RGGI/Documents/www.mde.state.md.us/assets/document/air/RGGI/04_SF6_Offset_FINAL.pdf. 
         [0030]    [23] California Environmental Protection Agency, Air Resources Board, “Proposed Regulation Order: Regulation for Reducing Sulfur Hexafluoride Emissions from Gas Insulated Switchgear”, Sacramento, Calif., Jan. 7, 2010, Available at &lt;http://www.arb.ca.gov/regact/2010/sf6elec/appa.pdf. 
         [0031]    [24] United Nations Framework Convention on Climate Change, “SF6 Emission Reductions in Electrical Grids”, Bonn, Germany, Sep. 29, 2006, Available at &lt;http://cdm.unfccc.int/filestorage/CDMWF_AM — 5WABPI8CK9HOSTV8E9CKDPFZM7UKQU/EB26_repan02_AM0035_NM0135.pdf?t=ekZ8MTI5MTM5NDM5NS45NA═|3FfpdD3nIBJADrv6dXLw5eW37cE=. 
         [0032]    [25] United States Department of the Interior Bureau of Reclamation, “Management and Safe Handling Procedures for Sulfur Hexaflouride (SF6) Gas”, March, 2004, Available at &lt;http://www.usbr.gov/power/data/fist/fist5 — 9/fist5 — 9.pdf. 
         [0033]    Each of the foregoing references is included with an information disclosure statement filed contemporaneously with the filing of the instant patent application. 
       SUMMARY OF THE INVENTION 
       [0034]    Although this patent application emphasizes use of the invention for sensing SF 6  in electric breaker applications, it is an important goal of the invention to be readily adaptable to many different gases and gas mixtures used in a broad range of processes. 
         [0035]    This invention combines the mechanical, electronic, algorithmic, and network facets needed to create a technology platform for highly integrated gas sensors. These sensors are of great value to electric utility companies and therefore to the manufacturers of equipment used by the utilities. A sensor will be usefully integrated into each gas insulated tank of each breaker and switch unit manufactured (tens of thousands of sensors). These sensors integrated into high voltage switchgear products, deployed by electric utility end users in replacement and expansion cycles, function to detect and mitigate atmospheric pollution caused by leaking SF 6 . As its associated gas insulated tank is charged with 10 to 350 lbs. of SF 6 , each gas sensor monitors its local cache of gas, accurately sensing and computing fractional percentage losses (emissions) and gains (maintenance replacement) in SF 6  mass, storing data in onboard data logs, and communicating data when triggered by detection events or in response to remote requests over a hierarchical communications network, a process that continues without labor until a fractional leak is automatically detected and reported creating the opportunity for early leak mitigation. Sensors also detect and log repair events including the addition of gas made to replace losses, thus closing the overall monitoring and mitigation loop. 
         [0036]    Although a variety of devices and systems for monitoring and measuring aspects of SF 6  gas in laboratory and field settings are currently described in the research and trade literature, none represent a fully integrated, economical, network interface-able component for automatically monitoring SF 6  gas trends in real-time on a tank-by-tank globally distributed basis. Approaches based upon IR imaging such as EPRI and FUR devices are expensive in both equipment and labor and therefore find use monitoring for gas leaks only on a spot versus continuous basis. 
         [0037]    High voltage breakers and gas insulated switchgear (GIS) require their SF 6  content to be carefully monitored and controlled. Arc-suppression safety becomes an issue when gas supply is insufficient. Overpressure is problematic with excess gas levels. Determining that gas levels are in the desired range is generally achieved by gas density estimates which in turn are generally derived from gas pressure measurements appropriately compensated for temperature variations. The well known ideal gas law provides a simple model which conveys the concept: 
         [0000]    
       
         
           
             
               
                 
                   pV 
                   = 
                   
                     
                       nRT 
                       ∴ 
                       
                         n 
                         V 
                       
                     
                     = 
                     
                       p 
                       RT 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0038]    Where P is gas pressure in the system, V is the volume of gas which is fixed by the equipment&#39;s rigid tank, R is a constant, T is temperature, and n is the mass quantity of gas. With V and R constant, measuring P and T determines n/V, the gas density. 
         [0039]    Two types of products have been developed which address the gas content control task. One type, which may generally be referred to as a gas density “monitor”, detects gas density by comparing relatively few thresholds such as: a) high limit, b) nominal limit, c) low limit, and d) low lockout limit. This allows the user to resolve gas density into one of five broad bins: 1) above a, 2) between a and b, 3) between b and c, 4) between c and d, and 5) below d. As illustrated in table 1, while this information is sufficient to enforce the above mentioned safety functions, it falls short of the resolution needed for meaningful emissions mitigation. Manufacturers producing gas density monitor-type products include Solon Manufacturing, Wika, and Comde. In general, these products, unlike IR cameras, are relatively low cost (under $1 k USD), of a simple and robust design, well accepted in the marketplace, and therefore in wide use. 
         [0040]    A second type of product for gas control applications may generally be referred to as a gas density “transmitter”. This variant measures gas parameters including pressure and temperature to higher resolution, incorporates electronics to derive a temperature compensated density from those measurements, and transmits a density proportional electrical output such as the standard 4-20 mA current loop. These devices, newer to the market, tend to be substantially more complex and costly. The higher resolution density measurement is a step closer to being useful for meaningful emissions detection and mitigation, but a substantial amount of additional functionality must be added externally by the user to interpret the density signal, track and log trends, and communicate decisive information over the user&#39;s management network. 
         [0041]    Accounting for the impact of temperature variation is of course an important aspect of accurate gas density and therefore accurate gas mass predictions. The operating temperature range for breakers of table 1 is uniformly −40° C. to 40° C. At a nominal pressure of 75 psig at 20° C., this temperature variation corresponds to a −15 psi to +5 psi variation in pressure. Under equilibrium conditions, the temperature compensation is straight forward. However, temperature is rarely expected to be “at equilibrium” in the case of breakers and Gas Insulated Switch (GIS) equipment deployed in outdoor environments across the land. A host of factors including sun, wind, precipitation, and weather in general will drive short-term and diurnal temperature variations which in turn will create temperature gradients across tanks of SF 6  gas. Applying the necessary algorithms to effectively compensate temperature dynamics to achieve the desired detection accuracies yet avoid false alarms is a major accomplishment of this invention. 
         [0042]    In summary, achieving SF 6  detection and mitigation efficiency several orders of magnitude better that current practice, to maintain or improve on current levels of leakage in the face of anticipated global electrical consumption increases, according to the foregoing analyses, requires a 100-fold improvement which in turn implies gas sensor detection sensitivities of 0.5 kg to 1.0 kg reliably achieved over dynamic thermal conditions. The instant invention, achieving the aforementioned detection sensitivity and combining network communications to trigger early service mitigation, brings the 100-fold improvement goal within reach. 
         [0043]    Practically speaking, the invention represents an advanced gas sensor that both leverages the advantages of existing technology and applies innovations to overcome its shortcomings with respect to the SF 6  emissions mitigation application. It can be globally deployed on breakers and GIS equipment, will accurately track gas additions and losses in real-time, and will be readily integrated into a broad network management infrastructure enabling cost-effective emissions mitigation. 
         [0044]    The economic and ecological importance of improved SF 6  gas management has been emphasized. In real terms, each of 6.8 billion humans on earth is a stakeholder. The future of his environment, the quality and cost of his electricity, and the cost of all other goods and services he covets (that rely upon electricity) are at stake. 
         [0045]    The most immediate beneficiaries of this invention and its technology will be companies that manufacture and sell the advanced sensors it enables. This invention and technology is conceived to be low ingredient cost and designed for manufacturability from inception. Inherently software configurable, it supports flexible optioning and extensible functionality. As to their customers, advanced gas sensor component manufacturers will enjoy the same growing market now shared by conventional gas density switch manufacturers, namely breaker and GIS switchgear OEMs, electric utilities, and other electric substation designers and operators. For example, a manufacturer of gas density switches in North American markets, estimates annual sales over 10,000 units with significant market growth. For the customers&#39; sakes, this invention and technology is conceived to support the surgical detection, tracking, and mitigation of SF 6  loss through equipment leakage with products that represent low component and operating cost burdens to the user. The economic benefits are manifold:
       Gas expense savings (demand for SF 6  and therefore gas costs, already ˜$10/lb, is increasing)   Direct process data captured automatically inexpensively demonstrates regulatory compliance, compared to costly, complex, and error prone mass balance procedural alternatives   Avoidance of regulatory fines for emissions; and,   Capture of offset credits       
 
         [0050]    What is the market size for customers that desire these benefits? Based upon a weighted, average nameplate SF 6  capacity of 73 kg, and considering global annual SF 6  utilization for electric equipment of 5,500 metric tons, and assuming 3 pole tanks per breaker, one can estimate a global population of equipment increasing at approximately 200,000 tanks per year. Assuming this corresponds to a growth rate of 5%, the global established market can be inferred to be approximately 4 million tanks. This is the immediate market for my sensor invention in the upgrade space. Please see, J. Blackman, M. Averyt, and Z. Taylor, “SF6 Leak Rates from High Voltage Circuit Breakers—U.S. EPA Investigates Potential Greenhouse Gas Emissions Source”, presented at the International Conference on SF6 and the Environment: Electric Power Systems—Partnership Update, Nov. 28, 2006, Available at http://www.epa.gov/electricpower-sf6/documents/leakrates_circuitbreakers.pdf and incorporated here by reference in its entirety and also submitted herewith through an information disclosure statement. 
         [0051]    This invention is conceived to be market friendly, utilizing a mechanical bellows technology and form factor well entrenched in the present market. Flexible network interface functionality renders this sensor easy to integrate in the user&#39;s network management system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0052]      FIG. 1  is a perspective view of the gas sensor apparatus. 
           [0053]      FIG. 2  is a perspective view of the gas sensor apparatus with covering and housing removed. 
           [0054]      FIG. 3  is a perspective view of the gas sensor apparatus similar to  FIG. 2  with the pushbutton removed. 
           [0055]      FIG. 4  is a perspective view of the gas sensor apparatus similar to  FIG. 3  with the temperature sensors and their mounting plate removed. 
           [0056]      FIG. 5  is a perspective view of the gas sensor apparatus similar to  FIG. 4  with the processor printed circuit board removed. 
           [0057]      FIG. 6  is a left side view of the gas sensor apparatus of  FIG. 5 . 
           [0058]      FIG. 6A  is an enlarged portion of  FIG. 6 . 
           [0059]      FIG. 6B  is a right side view of the gas sensor apparatus of  FIG. 5 . 
           [0060]      FIG. 7  is a top view of the of the gas sensor apparatus as illustrated in  FIG. 6  with the printed circuit board removed illustrating the lever and switch. 
           [0061]      FIG. 8  is a bottom view of the printed circuit board. 
           [0062]      FIG. 8A  is a bottom perspective view of the printed circuit board. 
           [0063]      FIG. 9  is a bottom perspective view of the gas sensor apparatus. 
           [0064]      FIG. 10  is a front view of the sensor internal components. 
           [0065]      FIG. 10A  is front view of the gas sensor apparatus internal components with the riser cutaway illustrating the bellows. 
           [0066]      FIG. 10B  is an enlargement of a portion of  FIG. 10A . 
           [0067]      FIG. 11  is a top view of gas sensor apparatus internal components. 
           [0068]      FIG. 11A  is a cross-section of  FIG. 11 . 
           [0069]      FIG. 12  is a top view of the gas sensor apparatus internal components. 
           [0070]      FIG. 12A  is a cross-sectional view of the gas sensor apparatus of  FIG. 12 . 
           [0071]      FIG. 13  is a hardware block diagram. 
           [0072]      FIG. 14  is a processing block diagram. 
           [0073]      FIG. 15  is a graph lever position as a function of gas pressure at 25° C. 
           [0074]      FIG. 16  is a normalized sensor response as a function of lever position. 
           [0075]      FIG. 17  is a graph of pressure compensation required as a function of temperature. 
           [0076]      FIG. 18  is a graph of temperature of normalized temperature sensor response. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0077]    As stated above, the instant invention supports a 100-fold reduction in gas emissions. What does this imply for gas density measurement requirements? To address this question, begin by considering that, at a temperature of 20° C., the operating pressure for the breakers of table 1 ranges from 64 psig to 82 psig, a span of 18 psi. 
         [0078]    Table 1 also gives the nominal gas mass change attributable to pressure change for each breaker under the aforementioned isothermal conditions. The function is simply proportional to the differential tank volume of the various breakers given the isothermal assumption. As expected, the largest tank represents a worst case requirement for mass sensing resolution since smaller pressure changes accompany larger gas losses (large mass changes). In general, larger tanks will require higher resolution measurements to detect unit changes in gas mass. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Breaker Model Designation 
               
             
          
           
               
                   
                 HS 
                 HP-1 
                 HP-2 
                 HP-3 
                 HPI-1 
                 HPI-2 
               
               
                   
                   
               
             
          
           
               
                 Rated Maximum Voltage (kV) 
                 72.5 
                 145 
                 169 
                 242 
                 345 
                 550 
               
               
                 Interrupting Current Rating (kA) 
                 31.5 
                 40 
                 40 
                 40 
                 362 
                 40 
               
               
                 Tank Volume (cubic meters) 
                 0.151 
                 0.561 
                 0.732 
                 1.171 
                 3.367 
                 3.542 
               
               
                 SF6 weight at fill pressure (kg) 
                 5.2 
                 19.1 
                 24.9 
                 39.9 
                 114.8 
                 120.7 
               
               
                 SF6 weight at nominal (kg) 
                 4.7 
                 17.4 
                 22.7 
                 36.3 
                 104.3 
                 109.8 
               
               
                 SF6 weight at alarm (kg) 
                 4.3 
                 16.0 
                 20.9 
                 33.4 
                 96.1 
                 101.1 
               
               
                 SF6 weight at lockout (kg) 
                 4.0 
                 14.8 
                 19.3 
                 31.0 
                 89.0 
                 93.6 
               
               
                 SF6 Emission between 
                 0.8 
                 3.1 
                 4.1 
                 6.5 
                 18.7 
                 19.7 
               
               
                 fill and alarm (kg) 
               
               
                 SF6 mass per unit pressure (kg/psi) 
                 0.063 
                 0.232 
                 0.302 
                 0.484 
                 1.391 
                 1.464 
               
               
                 Distribution frequency [12] 
                 50% 
                 14% 
                 13% 
                 15% 
                 6% 
                 2% 
               
               
                   
               
             
          
         
       
     
         [0079]    Table 1—Representative gas insulated breakers with OEM recommended SF6 fill conditions. If filled to just below fill capacity, breaker type HPI-2 would emit 19.7 kg of SF6 before the alarm threshold would trigger. Typically the so-called “nameplate capacity” will be three times larger than the above tank capacity since the breaker comprises three phases each with its individual tank The approximate frequency with which various sizes occur in practice is attributable from Blackman. 
         [0080]    Now the question arises, what is the magnitude of gas loss one needs to begin detecting? SF6 emission rates studied by various methods to date appear to place gas emissions in the range of 5% to 10% of total nameplate capacity annually. Accounting for frequency of distribution of breakers by voltage rating (and therefore by tank size), the weighted average of the nameplate capacities is approximately 73 kg (remember—3 tanks per breaker typically). In a study of 2,329 breakers by Blackman, 170 (7.3%) were found to be leaking. The amount of gas emitted to atmosphere annually may thereby be estimated at 3.7 kg to 7.3 kg per breaker (5% to 10% of 73 kg). The actual leaks arise from the aforementioned 7.3% of the breaker population. Therefore, the average leakage amount per leaking breaker is on the order of 50 kg to 100 kg annually. 
         [0081]    The sensor-gas interface mechanism as one component of the advanced gas sensor has many important aspects. The use a mechanical bellows approach is utilized for several reasons. These reasons include the bellow&#39;s simplicity, reliability, and broad use in SF 6  gas density switch applications. The use of a mechanical bellows leads to a requirement for detecting and processing mechanical displacement information. Processing the displacement information supports accurate gas pressure inferences. 
         [0082]    The advanced gas sensor combines a bellows sensing element with an MCU Electronics module comprising electronics and software for acquiring raw displacement and temperature information and processing these into accurate measurements. 
         [0083]    Reliable pressure and temperature readings must ultimately be rendered from raw sensor data. The present invention utilizes an efficient signal processing chain for this purpose. Noise, stability, and other potential problems are thereby identified and overcome. 
         [0084]    Processed pressure and temperature readings must be interpreted to predict gas density which in turn predicts gas mass changes in light of known, rigid tank volumes. The process, in isothermal conditions, is relatively straight forward. Under conditions of changing temperature, the process becomes more challenging. Ideal gas law and virial equations with alternative techniques for calculating temperature dependent coefficients form the foundations of the algorithms utilized for this purpose. 
         [0085]    As stated earlier, the present invention uses a mechanical bellows approach to gas interface and pressure sensing. The advantages of this choice are described above. Mechanical bellows components are readily available from a variety of sources including Solon Manufacturing of Chardon, Ohio. Mechanical bellows are widely used in mechanical, gas density monitoring products that enjoy a dominant share of the North American alarm-monitoring market. 
         [0086]    The bellows expands under increasing pressure. In the configuration of the embodiments set forth herein, the bellows actuates a rigid coupling to a platen. The platen&#39;s starting position and translational gain are simultaneously adjusted with a counter-biasing coil spring. Nominal gain in the range of 0.001″ platen deflection per 1 psi change is typically achieved. 
         [0087]    In the mechanical density monitor application, the platen carries bi-metal elements that in turn actuate snap-action micro-switches under conditions of sufficient displacement. The bi-metal elements provide a mechanical temperature compensation mechanism. 
         [0088]    Contrastingly, in the instant invention, the platen is adapted to carry displacement sensor components which take the form of reflective surfaces, magnets, and other components supporting displacement detection alternatives.  FIG. 16  shows the normalized sensor response of an embodiment which utilizes an infrared reflective object sensor (ROS) and another embodiment that uses a Hall Effect sensor (HES).  FIGS. 6 ,  6 A,  9 ,  10 ,  10 A,  10 B, and  12 A show the mechanical aspect of embodiments using the reflective object sensor and Hall effect sensor components respectively. 
         [0089]    As stated above, the invention targets supporting a 100-fold reduction in gas emissions. In the discussion above, it was deduced that a 100-fold improvement in emissions mitigation implies gas sensor sensitivities of 0.5 kg to 1.0 kg. According to table 1 above, this suggests a differential pressure resolution on the order of 16 psi to 0.35 psi. Recall that the operating span of interest is approximately 18 psi. Thus the required pressure measurement resolution (before correction) is in the range of 1 part in 1.2 to 1 part in 52.7. In digital measurement terms, this corresponds to a 1 bit to 6 bit dynamic range, which is achieved using a microcontroller and 12 bit analog to digital converters. 
         [0090]    Core bellows devices, prior to any modification, have been bench tested for displacement response over the pressure range of interest at 20° C. Conventional gauge room equipment was used to measure displacement. Regulated compressed air provided pressure actuation. Pressure gradients in both directions have been utilized to quantify hysteresis, and several runs are made to assess short-term repeatability. Analysis of data captured in these tests was analyzed and definitively demonstrates the bellows fitness for the application in this invention as shown hereinbelow. 
         [0091]    A microcontroller  1301  is used to perform displacement sensing and temperature sensing, and to communicate raw data to the other controller functions (via asynchronous serial communications initially).  FIG. 13  is a simplified block diagram of the MCU  1301  and its interactions with the other elements of the invention. The Hi-RES transducer  1310  can optionally be the aforementioned infrared reflective object sensor (ROS), Hall Effect sensor (HES), or other displacement transducer. The temperature probes can be thermistors  507 B,  507 D,  617 B,  617 D, thermocouples, RTD, or other suitable temperature transducers.  FIG. 13  illustrates, diagrammatically, temperature probes  1308 A,  1308 B,  1308 C,  1308 D located within the switchgear housing. Reference numerals  1308 A-D indicate, generically, many different types of temperature probes which may be used.  FIG. 13  also illustrates the battery  1311 , a temperature interface  1307 , a displacement interface  1309 , as well as a test controller (network manageable controller)  1312 , a communication subsystem  1302 , an analog to digital controller  1303 , and a digital to analog controller  1304 , a digital I/O interface subsystem  1305 , and a safety limit detection subsystem  1306 . 
         [0092]    MCU subsystem modularity allows easy substitution of alternative circuits for the powered by battery DISPLACEMENT INTERFACE  1309  and HI-RES TRANSDUCER  1310 . The MCU  1301  monitors battery state of charge and computes circuit power consumption as well, an important distinguishing characteristic of circuit and algorithmic alternatives. The FLASH memory based MCU  1301  may be conveniently reprogrammed to adapt to varying sensing requirements. Operating parameters may be programmed and acquired data retrieved over the bidirectional, asynchronous communications interface. 
         [0093]    Initial choices for HI-RES TRANSDUCER  1310  used to measure platen  601  displacement include Hall Effect and photo diode/transistor technologies. The optical alternatives comprise both transmission and reflective technologies. Piezo strain gauge and ultrasonic systems are possible as well. 
         [0094]    Processing and calibration requirements for rendering accurate pressure readings from displacement data are included. Temperature channels are also logged during operation. All data generated by the displacement and temperature measurement blocks is forwarded to the Temperature and Pressure Processing blocks. The invention covers the operating and temperature ranges of interest. Temperature gradient and leak rate tests are also satisfied. The invention includes the signal processing necessary for rendering reliable pressure and temperature readings from raw displacement and temperature sensor data. 
         [0095]      FIG. 14  is a processing block diagram  1400  which illustrates the general topology for processing displacement data. A similar signal chain is utilized for temperature data. The order of the functions utilized is based upon the characteristics of the raw data and the desired resolution and accuracy of the processed readings. Reference numeral  1401  signifies raw conversions from displacement and temperature subsystems which are input into a system which enhances the signal to noise ratio. Reference numeral  1403  signifies a system which linearizes the displacement to pressure calculation. Reference numeral pressure calibration signifies a pressure calibration system and reference numeral  1405  signifies a digital filtering subsystem. Reference numeral  1406  signifies signal processing parameters which are included in the signal to noise ration subsystem and the linearization of displacement into pressure. Reference numeral  1407  signifies pressure readings output to gas mass calculations and user interfaces. 
         [0096]      FIG. 15  is a graph lever position  1500  as a function of gas pressure at 25° C. Reference numeral  1501  indicates the lever response from 0 psig to 60 psig. It will be noticed that line  1501  represents the displacement of the lever with respect over pressure range of 0 to 60 psig and with the lever acting against the ball nose spring plunger. Reference numeral  1502  is a line on the graph of the lever position from 60 to 100 psig for the coil spring  608  and bimetal hinge  708 . Reference numeral  1503  is a particular lever position of 0.026″ corresponding to a pressure  1504  of 81 psig. 
         [0097]      FIG. 16  is a normalized sensor response  1600  as a function of lever position at 25° C.  FIG. 16  is a normalized sensor response  1600  as a function of lever position. Reference numeral  1601  is the response of reflective object sensor and reference numeral  1602  is the response of Hall effect sensor (HES). Reference numeral  1603  is a particular HES response of 0.55 corresponding to a particular lever position  1604  of 0.026″. 
         [0098]    N.B. Calibration is achieved entirely using digital techniques to determine coefficients stored onboard in nonvolatile memory. Use of precision or adjustable components is avoided in favor of standard tolerance, inexpensive, high stability components. 
         [0099]    An equation of state model is required to compute the target gas density from calibrated temperature and pressure data. A first order Gas Density Model is used and provides satisfactory results in many cases. 
         [0100]    The well known virial form set forth below as equation 2 utilizing coefficient functions for SF 6  selected from various perspectives is an alternative embodiment: 
         [0000]    
       
         
           
             
               
                 
                   
                     pV 
                     nRT 
                   
                   = 
                   
                     1 
                     + 
                     
                       
                         B 
                          
                         
                           ( 
                           T 
                           ) 
                         
                       
                        
                       
                         n 
                         V 
                       
                     
                     + 
                     
                       
                         C 
                          
                         
                           ( 
                           T 
                           ) 
                         
                       
                        
                       
                         
                           n 
                           2 
                         
                         
                           V 
                           2 
                         
                       
                     
                     + 
                     … 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0101]    Where p, V, n, R, and T have their usual meanings in the ideal gas law, and B(T) and C(T) are the second and third virial coefficients respectively, each non-linear functions of temperature T. 
         [0102]    This step further draws upon recent work by Scalabrin describing a computationally efficient neural network technique for computing coefficients in a certain form of state equation. 
         [0103]    It is an important aspect of the instant invention to use a micro-power microcontroller platform to sense gas density to sufficient accuracy to discern 0.5 kg emission events under a range of conditions of interest for the largest tank volumes expected. 
         [0104]      FIG. 1  is a perspective view  100  of the gas sensor apparatus. Cover  101  and liquid tight pushbutton  102  are shown in  FIG. 1 . Cover  101  is affixed to housing  104  by cover retaining screws  103 . Sensor connector  103  provides communications between the gas sensor apparatus and the exterior of the switchgear cabinet. Power to the apparatus is also supplied through the connector pins  105 A. Connector nut  105 B affixes the connector to the housing  104 . Manifold block  106  includes a first gas port  106 B for admission of gas to the gas sensor apparatus. Manifold block bolt hole  106 A includes bolts which secure the manifold in place. A display deadfront  109  (display cover) and gasket  107 A are illustrated. 
         [0105]      FIG. 2  is a perspective view  200  of the gas sensor apparatus with covering  107  and housing  104  removed. Liquid tight pushbutton  102  when depressed provides a temperature compensated pressure readout. Pushbutton cable  202  and connector  203  enables electrical communication between the pushbutton and the electronics on board the gas sensor apparatus. Connector  203  interconnects with processor PCB pushbutton connector  204 . Processor printed circuit board  205  is illustrated in  FIG. 2 . 
         [0106]      FIG. 3  is a perspective view  300  of the gas sensor apparatus similar to  FIG. 2  with the pushbutton removed. Perspective view  300  of the sensor with pushbutton removed. Display printed circuit board  301  is illustrated as being mounted to the processor printed circuit board  205  using a standoff (spacer  303 ) and screw  302 . Display digits  304  communicate a temperature compensated pressure readout (display). In the approximate middle of the printed circuit board  301 , are processor printed circuit board connectors. The display printed circuit board includes a coil spring clearance hole  306 . 
         [0107]      FIG. 4  is a perspective view  400  of the gas sensor apparatus similar to  FIG. 3  with the temperature sensors and the mounting plate for the temperature sensors removed. The temperature sensors  1308 A-D, are best viewed, diagramatically in  FIG. 13 . The temperature sensors will be located in the switchgear compartment or housing in various places so as to obtain accurate temperature readings of the gas being measured. A typical gas used in switchgear is sulfur hexafluoride gas (SF 6 ). SF 6  plays a crucial arc-suppression role in this equipment. Other gases may be used in the switchgear. Further, this invention is equally applicable to the determination of loss of any gas from any containment structure. As described in further detail hereinbelow, the loss of gas is determined by a change in the temperature compensated pressure. 
         [0108]    Referring to  FIGS. 11 ,  11 A,  12 , and  12 A, some of the important internal elements of the invention are disclosed.  FIG. 11  is a top view  1100  of gas sensor apparatus internal components.  FIG. 11A  is a cross-section view  110 A of  FIG. 11 .  FIG. 12  is a top view  1200  of the gas sensor apparatus internal components.  FIG. 12A  is a cross-sectional view  1200 A of the gas sensor apparatus of  FIG. 12 . Switch printed circuit board  501  includes a microcontroller unit  1103 ,  1301 . Base plate  602  is affixed to the adapter flange  604  by unnumbered screws. Lever  601  pivots about a pivot portion (unnumbered) of the coupling  1002  of the bellows  103 . Stabilizers  1104  of the coupling  1002  tend to center the coupling  1002  of the bellows as the bellows is raised and lowered in response to pressure within the bellows. Gas port  1101  communicates gas into the bellows  1003 . Riser  603 , adapter flange  604 , base plate  602  provide a foundation for operation of the lever  601 . Lever  601  pivots about coupling  1002 . Bimetallic strip  708  is affixed to the lever  601  by retaining plate  706 . Bimetallic strip  708  is also affixed to an unnumbered block by retaining plate  619 .  FIG. 7  illustrates the bimetallic strip  708  and notches cut therein for desired performance thereof. The material of the bimetallic strip  708  is not limited in this specification. The bimetallic strip functions to compensate for the influence temperature of the gas has on gas pressure. 
         [0109]    One important object of the invention is to determine if gas is being loss from the switchgear. The gas sensor apparatus operates over a wide range of temperature and pressure conditions other than standard temperature and pressure conditions. If pressure of the gas rises, but the mass of the gas within a known volume stays the same (ie no loss occurs), then the apparent pressure in the volume (tank) appears to increase. The bimetallic strip  708 , however, adds a downward force on lever  601  to counteract the additional force of the gas within the bellows due to an increase in gas temperature. If pressure of the gas decreases, but the mass of the gas within a known volumes stays the same (ie no loss of gas occurs), then the apparent pressure in the volume (tank) appears to decrease. In a similar manner, an apparent decrease in gas pressure due to a relatively low temperature, is compensated by an upward force on lever  601  to counteract the reduction in force of the gas within the bellows due to a decrease in gas temperature. 
         [0110]    A magnet is affixed to the lever  601 . A reflective surface is also affixed to the lever  601 . A hall effect sensor is applied to the switch printed circuit board  501 . A reflective object sensor is affixed to the switch printed circuit board. In  FIG. 12A , reference numeral  1102  is being used to denote the magnet and the reflective surface. In  FIG. 12A , reference numeral  1103  is being used to denote the hall effect sensor, the reflective object sensor and the processor module. 
         [0111]      FIG. 9  is a bottom perspective view  900  of the gas sensor apparatus. Hall effect sensor  609  and reflective object sensor  610  are illustrated in  FIG. 9  on the underside of switch printed circuit board  501 . Magnet  611  and reflective surface boss  614  are illustrated residing on lever  601 . Lever  601  moves vertically with a small amount of pivotal movement as well as can be visualized in  FIG. 12 . As lever  601  moves, the hall effect sensor  609  and the reflective object sensor  610 , detect the movement. Processor  1301  is not visualized in  FIG. 9 , but it can reside on the underside of printed circuit board  501  as illustrated in  FIG. 12A . Alternatively, processor  1301  can be located on the upper or top side of printed circuit board  501 . 
         [0112]    Referring to  FIG. 13 , processor  1301  receives temperature inputs from temperature probes within the cabinet and processes the various temperature signals for further evaluation of the pressure information received from the high resolution temperature transducers  1310 . Reference numeral  1310  indicates that “OPTION X” temperature transducer(s) may be used. This means that one or both of the hall effect sensor and/or the reflective object sensor may be used in the calculation of movement of the lever. Movement of the lever in combination with use temperature data, determines the gas density. In this patent application, various parameters are expressed by the ideal gas law stated above. 
         [0000]    
       
         
           
             pV 
             = 
             
               
                 nRT 
                 ∴ 
                 
                   n 
                   V 
                 
               
               = 
               
                 p 
                 RT 
               
             
           
         
       
     
         [0113]    Where P is gas pressure in the system, V is the volume of gas which is fixed by the equipment&#39;s rigid tank, R is a constant, T is temperature, and n is the mass quantity of gas. With V and R constant, measuring P and T determines n/V, the gas density. 
         [0114]    The gas sensor apparatus includes switch actuator elements  704  which reside on lever  601  which engage the actuators  618 AA of snap action switches  618 A-D as illustrated in  FIG. 8 .  FIG. 8  is a bottom view  800  of the printed circuit board  501 . Switches  618 A,  618 B,  618 C and  618 D protrude downwardly from printed circuit board  501 . Each switch includes an actuator  618 AA although only one such actuator is labeled with reference numeral  618 AA. When the actuator elements  702  engage the actuators  618 AA, then contacts within the switch are electrically joined or completed which results in an alarm, warning, or other signal sent to a user. These switch functions include the temperature compensation provided by the bimetallic strip. Hall effect sensor  609 , reflective object sensor  610 , reflective object sensor phototransistor  610 A, and reflective object sensor infrared LED emitter  610 B are illustrated in  FIG. 8 . 
         [0115]      FIG. 8A  is a bottom perspective view  800 A of the switch printed circuit board  501  wherein the sensor connector  105  and the sensor connector contact pin  105 A are illustrated along with the printed circuit board  501 . Connector support  502  is affixed to PCB flexible circuit element  503 . First  507 B and second  507 D thermistors are illustrated in  FIG. 8A  as are third  617 B and fourth  617 D thermistors. First thermistor stalk  507 A and second thermistor stalk  507 C are illustrated well in  FIG. 8A . Third thermistor stalk  617 B and fourth thermistor stalk  617 C are illustrated well in  FIG. 8A . 
         [0116]      FIG. 5  is a perspective view  500  of the gas sensor apparatus similar to  FIG. 4  with the processor printed circuit board  205  removed. Reference numeral  501  is the switch printed circuit board and reference numeral  502  is the switch printed circuit board connector. Flexible circuit element  503  is interconnects the connector  502  to the switch printed circuit board  501 . Screws  504  retain the printed circuit board to the main structure of the apparatus. Switch connections  506  are viewed in  FIG. 5  and enable attachment of the snap-action switches from the bottom side of the printed circuit board  501 . The bottom side of printed circuit board is best viewed in  FIGS. 8 and 8A . Each of the switches  618 A-D is actuated by spring loaded metallic actuator elements  704  best viewed in  FIG. 7 . The spring loaded actuator elements  704  are very slightly bowed depending on the amount of adjustment  702  which bias the elements  704  and, therefore, control the actuation of the switches. The spring loaded elements  704  are affixed to bimetallic hinge retaining plate  706 . Still referring to  FIG. 7 , the reflector  613 , the magnet  611 , and the spring stud  701  are illustrated. 
         [0117]      FIG. 7  is a top view  700  of the of the gas sensor apparatus as illustrated in  FIG. 6  with the printed circuit board  501  removed illustrating the lever  601  and switch actuator elements. Manifold block  106 , lever  601 , base plate  602 , coil spring nut  606 , spring stud  701 , switch PCB mounting bosses  709 A-D,  611  magnet, reflective surface  613 , bimetal hinge base retaining plate  619 , bimetal hinge base retaining plate nut  620 , switch actuator element adjuster screws  702 , switch actuator elements  704 , switch actuator elements flange screw  705 , bimetal hinge lever retaining plate  706 , bimetal hinge lever retaining plate nut  707  and bimetal hinge  708  are all well illustrated in  FIG. 7 . 
         [0118]    Referring to  FIG. 5  again, thermistor  507 A, thermistor stalk  507 B and thermistor connections  507  are illustrated. Further, the connection  508  for the reflective object sensor and the cutout  509  for the coil spring are shown. 
         [0119]      FIG. 6  is a left side view  600  of the gas sensor apparatus of  FIG. 5 .  FIG. 6  illustrates manifold block  106 , switch PCB  501 , switch PCB processor PCB connector  506 , first thermistor stalk  507 A, first thermistor  507 B, third thermistor stalk  507 C, and third thermistor  507 D. Lever  601 , base plate  602 , riser  603 , and adapter flange  604  are illustrated in  FIG. 6 . Second gas port  605 , coil spring nut  606 , coil spring washer  607  and coil spring  608  are illustrated in  FIG. 6  as well. Riser  603  is generally cylindrically shaped and extends from the adapter flange  604  to the base plate  602 . 
         [0120]      FIG. 6A  is an enlarged portion  600 A of  FIG. 6 .  FIG. 6A  illustrates the lever  601 , the Hall effect sensor  609 , the reflective object sensor  610 , the magnet  611 , the magnet boss  612 , the reflective surface  613 , the reflective surface boss  614 , the ball  615 , and the ball spring adjuster  616 . 
         [0121]      FIG. 6B  is a right side view  600 B of the gas sensor apparatus of  FIG. 5 . Switches  618 A-D are illustrated attached to the switch printed circuit board  501 . Switch PCB connector PCB  502  and the switch PCB flexible circuit element  503  are illustrated in  FIG. 6B  as well. Third  617 B and fourth  617 D thermistors are illustrated along with their respective stalks  617 A,  617 C. 
         [0122]      FIG. 10  is a front view  1000  of the sensor internal components. Ball  615  is illustrated in  FIG. 10  as is switch actuator element adjuster screw boss  1001 .  FIG. 10A  is front view  1000   a  of the gas sensor apparatus internal components with the riser cutaway illustrating the bellows  1003 . Bellows lever coupling  1002  is illustrated in  FIG. 10A  in engagement with lever  601 . Lever  601  is movable vertically depending on the pressure applied to the bellows and depending on the action of the bimetallic hinge. As shown in  FIGS. 10 and 10A , gap  1004  is the distance between the lever  601  and the ball  615 , in other words reference numeral  1004  is the lever displacement dimension. 
         [0123]      FIG. 10B  is an enlargement  100 B of a portion of  FIG. 10A  illustrating the gap  1004  between the lever  601  and the spring loaded ball  615 . As illustrated in  FIGS. 10 ,  10 A and  10 B, vertically movable lever  601  is positioned by virtue of pressure greater than 60 psig and less than 82 psig. 
         [0000]    The ideal gas law restated: 
         [0000]    
       
         
           
             
               
                 
                   pV 
                   = 
                   
                     
                       nRT 
                       ∴ 
                       n 
                     
                     = 
                     
                       p 
                       RT 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0124]    p=absolute pressure (pounds per square inch or psi) 
         [0125]    V=volume (cubic meters) 
         [0126]    T=temperature (Kelvin) 
         [0127]    n=gas quantity in moles (mol) 
         [0128]    R=gas constant=1.2095×10 −3    
         [0129]    It should be noted that, p, the pressure in (1) is the absolute pressure (reference to a vacuum) which differs by atmospheric or barometric pressure from the pressure indicated by a typical gauge in atmospheric conditions. This can be stated mathematically as: 
         [0000]        p=p   abs   =p   g   +p   atm    (3)
 
         [0130]    p=p abs =absolute pressure (psi) 
         [0131]    pg=gauge pressure (psi) 
         [0132]    P atm =atmospheric pressure (psi) 
         [0133]    With n the gas quantity in mol known, the mass quantity for a particular gas is derived from its molar weight: 
         [0000]      m=nM m    (4)
 
         [0134]    m=gas quantity in grams (g) 
         [0135]    n=gas quantity in moles (mol) 
         [0136]    M m =molar mass of gas species (g/mol) 
         [0137]    A sequence of measurements of gas mass m i =m 1 , m 2 , . . . m j  can be derived using corresponding sequences of pressure p i  and temperature T i  measurements given only that the volume V, atmospheric pressure p atm , and gauge pressure p g  corresponding to each point in the sequence are known. A change in gas mass foretells a leak when a measurement m, is less than a measurement m k  made sometime earlier (k&lt;j). Conversely, the addition of gas is detected when m j  is greater than m k . In a non-leaking system, all of the m i  will be substantially equal. 
         [0138]    Acquiring temperature sequence T, begins by microcontroller  1301  using analog to digital converter  1303  applied to temperature interface  1307  accessing temperature probes  1308 A through  1308 D to acquire raw sensor measurements. Raw sensor measurements are then converted to accurate temperature readings through a calibration process such as that depicted in  FIG. 18  wherein sensor response is converted to temperature in degrees centigrade for each sensor. Centigrade temperatures are converted to requisite absolute temperatures by addition of the offset 273.15 degrees. A point T, can then be recorded as a particular weighted average of the different sensor&#39;s derived absolute temperatures. In the preferred embodiment, the temperature sensors  1308 A through  1308 D correspond to thermistors  507 B,  507 D,  617 B, and  617 D. 
         [0139]    Acquiring pressure sequence pi is somewhat more involved. It begins again with microcontroller  1301  using analog to digital converter  1303  applied to displacement interface  1309  accessing high resolution displacement transducer  1310  to acquire raw displacement sensor measurements. Unlike temperature measurements, there is no simple transformation of raw displacement measurements to absolute pressure, however. Firstly, a raw displacement sensor measurement is utilized by the MCU to compute calibrated lever displacement dimension according to calibration data such as that depicted in  FIG. 16 . In a preferred embodiment, the high resolution displacement transducer is the combination of a reflective object sensor  610  in combination with a reflective surface  613 . In this case sensor response is calibrated using data such as that of curve  1601 . In another embodiment, the high resolution displacement transducer is the combination of Hall Effect sensor  609  in combination with magnet  611 . In this case sensor response is calibrated using data such as that of curve  1602 . 
         [0140]    Once calibrated lever displacement dimension is derived, initial gauge pressure estimate can be computed using secondary calibration data as depicted in  FIG. 15 . For example, if Hall Effect sensor response is measured to be 0.55 ( 1603 ), lever displacement dimension is determined to be 0.026 inch ( 1604 ). This lever location 0.026 inch can be transferred to the graph of  FIG. 15  ( 1503 ) and used to determine an initial gas gauge pressure estimate of 82 psi ( 1604 ). 
         [0141]    The intrinsic temperature compensation of the lever system comprising bi-metal hinge  708  must now be taken into account. In the absence of the bi-metal element, lever position would simply track temperature variations. For the fixed volume V, gas pressure increases proportional to increasing temperature (and vice versa). With only the resistance of coil spring  608 , lever dimension  1004  would increase proportionately with the varying force exerted by bellows  1003 . The bi-metal element is conceived to neutralize this temperature induced pressure variation. As temperature increases, the bi-metal exerts approximately equal magnitude equal force directed oppositely to the increased upward force of the bellows with the approximate result that the lever dimension remains constant. The converse occurs as temperature decreases. These mechanics alone allow the mechanism to operate as a low resolution density monitor wherein eventual changes in lever position represent approximate changes in gas mass (as opposed to pressure variations due to temperature), and, for fixed volume V, gas density. With the advent of the microcontroller in the present invention, it is possible to improve accuracy and flexibility of gas monitoring including the electronic measurement of pressure, temperature, gas content, and gas density as explained above. 
         [0142]    To complete the derivation of absolute gas pressure p from displacement and temperature sensor measurements, the initial gas gauge pressure estimate as above must itself be compensated for the temperature behavior introduced by the bi-metal element. The appropriate compensation is derived from the data in  FIG. 17  using temperature Ti as above. For example, if Ti is 303K corresponding to a temperature of 29.85 C ( 1703 ), a temperature compensation of approximately 2 psi is indicated ( 1704 ). Therefore, in the current example, a calibrated gauge pressure is computed equal to 82 psi+2 psi equals 84 psi. A reasonable estimate of atmospheric pressure is used based on typical or measured data. An example of a typical value for atmospheric pressure is 14.7 psi. The measurement of absolute pressure p, is computed as the sum of the gas gauge pressure and the atmospheric pressure, 98.7 psi in the example. 
         [0143]    To complete the example, given a typical tank volume V of 1 cubic meter, along with a molar mass for SF 6  gas of 146.055 g/mol, the gas mass m, is computed according to (1) and (4) to be 38.62 kg. The entire process is implemented by microcontroller  1301  in combination with the electronic elements of  FIG. 13  and is represented in block diagram form in  FIG. 14 . All data described above is recorded in microcontroller memory including the raw sensor measurements through the final derived measurement sequences T i , p i , and m i . 
       REFERENCE NUMERALS 
       [0000]    
       
           100  perspective view of sensor 
           101  cover 
           102  liquid tight pushbutton 
           103  cover retaining screw 
           104  housing 
           105  sensor connector 
           105 A sensor connector contact pin 
           105 B connector nut 
           106  manifold block 
           106 A manifold block bolt hole 
           106 B first gas port 
           107  display deadfront 
           107 A deadfront gasket edge 
           200  perspective view of the sensor with cover and housing removed 
           202  pushbutton cable 
           203  pushbutton cable connector 
           204  processor PCB pushbutton connector 
           205  processor PCB 
           204  processor PCB pushbutton connector 
           205  processor PCB 
           300  perspective view of the sensor with pushbutton removed 
           301  display PCB 
           302  display PCB retaining screw 
           303  display PCB standoff 
           304  display digit 
           305  display PCB processor PCB connector 
           306  display PCB coil spring clearance hole 
           204  processor PCB pushbutton connector 
           205  processor PCB 
           400  perspective view of the sensor with display PCB removed 
           401  processor PCB retaining screw 
           402  processor PCB standoff 
           403  processor PCB coil spring clearance hole 
           404  processor PCB display PCB connector 
           405  processor PCB switch PCB connector 
           105  sensor connector 
           105 A sensor connector contact pin 
           500  perspective view of the sensor with processor PCB removed 
           501  switch PCB 
           502  switch PCB connector PCB 
           503  switch PCB flexible circuit element 
           504  switch PCB retaining screw 
           505  switch PCB processor PCB connector 
           506  switch connections 
           507  thermistor connections 
           507 A thermistor 
           507 B thermistor stalk 
           508  reflective object sensor connection 
           509  switch PCB coil spring and switch adjustment clearance cutout 
           507 A first thermistor stalk 
           507 B first thermistor 
           507 C third thermistor stalk 
           507 D third thermistor 
           600  left side view of the sensor internal components 
           600 A detail of lever and displacement mechanisms 
           600 B right side view of the sensor internal components 
           600 A detail of lever and displacement mechanisms 
           601  lever 
           602  base plate 
           603  riser 
           604  adapter flange 
           605  second gas port 
           606  coil spring nut 
           607  coil spring washer 
           608  coil spring 
           601  lever 
           609  Hall effect sensor 
           610  reflective object sensor 
           611  magnet 
           612  magnet boss 
           613  reflective surface 
           614  reflective surface boss 
           615  ball 
           616  ball spring adjuster 
           617 A third thermistor stalk 
           617 B third thermistor 
           617 C fourth thermistor stalk 
           617 D fourth thermistor 
           618 A first switch 
           618 B second switch 
           618 C third switch 
           618 D fourth switch 
           619  bimetal hinge base retaining plate 
           620  bimetal hinge base retaining plate nut 
           700  top view of the sensor lever and switch actuator elements 
           701  coil spring stud 
           702  switch actuator element adjuster screws 
           703  unused actuator element adjuster screw threaded hole 
           704  switch actuator elements 
           705  switch actuator elements flange screw 
           706  bimetal hinge lever retaining plate 
           707  bimetal hinge lever retaining plate nut 
           708  bimetal hinge 
           709 A first switch PCB mounting boss 
           709 B second switch PCB mounting boss 
           709 C third switch PCB mounting boss 
           709 D fourth switch PCB mounting boss 
           800  bottom view of switch PCB 
           800 A perspective view of switch PCB from bottom 
           900 A perspective view of sensor internal components from bottom 
           1000  front view of sensor internal components 
           1001  switch actuator element adjuster screw boss 
           1000 A front view of sensor internal components with riser cutaway 
           1000 B front view of lever displacement detail 
           1002  bellows lever coupling 
           1003  bellows 
           1004  lever displacement dimension 
           1004  lever displacement dimension 
           1100  top view of sensor internal components 
           1100 A crosssection view from right side of sensor internal components 
           1101  gas port 
           1102  sensor module 
           1103  processor module 
           1104  stabilizer 
           1200  top view of sensor internal components 
           1200 A crosssection view from front of sensor internal components 
           1300  hardware block diagram 
           1301  MCU (microcontroller unit) 
           1302  communication subsystem 
           1303  analog to digital converter subsystem 
           1304  digital to analog converter subsystem 
           1305  digital I/O interface subsystem 
           1306  safety limit detection subsystem 
           1307  temperature interface 
           1308 A first temperature sensor 
           1308 B second temperature sensor 
           1308 C third temperature sensor 
           1308 D fourth temperature sensor 
           1309  displacement transducer interface subsystem 
           1310  high resolution displacement transducer 
           1311  battery 
           1312  network management controller 
           1400  processing block diagram 
           1401  raw conversions from displacement and temperature subsystems 
           1402  signal to noise enhancement 
           1403  displacement to pressure calculation 
           1404  pressure calibration 
           1405  digital filtering subsystem 
           1406  signal processing parameter set 
           1407  pressure readings output to gas mass calculations and user interfaces 
           1500  lever position as a function of gas pressure at 25 C 
           1501  lever response from 0 psig to 60 psig, ball nose spring plunger operating 
           1502  lever response from 60 to 100 psig, coil spring and bimetal hinge only 
           1503  a particular lever position of 0.026″ 
           1504  a pressure of 81 psig corresponds to position of 0.026″ 
           1600  normalized sensor response as a function of lever position 
           1601  response of reflective object sensor 
           1602  response of Hall effect sensor 
           1603  a particular HES sensor response of 0.55 
           1604  a particular lever position of 0.026″ corresponds to sensor response of 0.55 
           1700  graph of pressure compensation required as a function of temperature 
           1701  pressure compensation required as a function of temperature 
           1702  zero compensation required at reference temperature 
           1703  a particular temperature 
           1704  a particular pressure compensation corresponds to a particular temperature 
           1800  graph of temperature as a function of normalized temperature sensor response

Technology Category: 3