Abstract:
A system and method for concurrently measuring odorant concentration and also compensating for changes in relative air density when measuring odor intensity levels may be used to provide more accurate and reliable readings from an odorometer. Odorometers typically measure the concentration of a given target gas in a gas-air mixture. Because changes in air density make it difficult to accurately determine how much air is in the gas-air mixture sample, a method of compensating for changes in the air density is able to produce a more accurate concentration reading. By measuring the relative temperature and pressure of the air at calibration and when a particular reading is taken, the final reading can be corrected to account for changes in the air density. By correlating the odor intensity readings with odorant concentration readings a wide array of advantages may be realized.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 USC 119(e) to U.S. Provisional Application No. 62/050,851 filed Sep. 16, 2014, and U.S. Provisional Application No. 62/218,929 filed Sep. 15, 2015, both of which are incorporated herein by reference in their entirety. 
     
    
     FIELD 
       [0002]    The present invention relates to apparatus and methods for detecting combustible gas odor intensity levels and providing concurrent measurements of odor intensity and odorant concentration in a gas stream. 
       BACKGROUND 
       [0003]    Combustible gases are commonly odorized to provide a simple, effective, and safe way for an individual to detect the presence of a combustible gas. An odorant is frequently deployed into the combustible gas stream. This odorization allows potential gas leaks and other dangerous conditions to be detected by an individual with an average sense of smell. Detection of the odor does not require the use of any particular tools or equipment, but equipment may be used to detect the odor. It is to be appreciated that references to “gas” or “target gas” in a gas-air mixture implies odorized gas which is not 100% composed of any particular gas (e.g., methane or propane). 
         [0004]    Multiple separate regulatory schemes are commonly used for regulating combustible gases world-wide. The relative concentration of a target gas in gas-air mixtures which produces a readily detectable odor intensity to a human with an average sense of smell is a commonly used factor for regulatory compliance in the United States. This system relies on human operators to gradually increase the relative concentration of a target gas in a gas-air mixture until the gas odor is readily detectable by the operator. The operator may then use a device to measure the gas concentration in that gas-air mixture. Alternate regulatory schemes may involve direct measurement of the odorant concentration in the combustible gas stream, frequently using an electro-chemical sensor. It is to be appreciated that the concentration of odorant in a target gas stream is a completely separate measurement from the concentration of a target gas in a gas-air mixture. 
         [0005]    In order to accurately determine the concentration of gas in a gas-air mixture, the quantities of both gas and air entering a testing apparatus must be accurately known. Traditionally, a mass flow sensor has been used to accurately quantify the amount of gas entering the apparatus while air enters the apparatus via a blower or fan. Mass flow sensors are less affected by changes in elevation, weather, and/or time of year as compared to volumetric flow sensors. Many complicating factors can change the pressure and temperature of the ambient air and thus its density. This makes accurately determining the precise amount of air that has been mixed with a gas more difficult. What is needed is an alternate solution for compensating for changes in air density, such that instruments sensitive to such changes may provide accurate readings despite changing atmospheric conditions. 
         [0006]    Due to the potential danger associated with combustible gases, many areas have developed regulatory schemes governing the odorants frequently added to combustible gases. Stand-alone odor intensity meters or odorometers, may be used to determine the relative concentration of gas in a gas-air mixture at which a human operator determines there is a readily detectable odor. Odorant concentration devices may alternatively be used to determine the actual concentration of an odorant as opposed to the human perceived intensity of the odor. Each of these techniques has benefits and limitations. In order to provide high quality of odor intensity and odorant concentration data, what is needed is a device which allows for the concurrent measurement of odor intensity and odorant concentration from substantially the same sample. 
       SUMMARY 
       [0007]    In one aspect, embodiments disclosed relate to a method for compensating and/or correcting odorometer device readings for changes in relative air density. Odorometers may be used to measure the concentration of a given target gas in a gas-air mixture. Changes in the air density may make it difficult to accurately quantify the amount of air in the gas-air mixture. By applying a correction technique that accounts for the changes in temperature and pressure between the conditions at which the device is calibrated and the conditions under which a given measurement is taken, a more accurate reading may be produced. 
         [0008]    In another aspect, embodiments disclosed relate to a method for providing a corrected reading in an odorometer with a fixed speed blower. 
         [0009]    In yet another aspect, embodiments disclosed relate to a system for measuring relative gas concentration in a sample and correcting for changes in air density. The system may comprise a metering valve, an exhaust port, a mass flow sensor, a pressure sensor, a temperature sensor, an electronics package, and a processor capable of applying a correction program to readings provided by the sensors. 
         [0010]    In still another aspect, embodiments disclosed may relate to concurrently measuring odorant concentration in a target gas and the concentration of a target gas at a readily detectable odor intensity in a gas-air mixture. This and other embodiments may additionally record all data for analysis, training, oversight, and/or regulatory compliance. 
         [0011]    In another aspect, embodiments disclosed relate to recording, transmitting, and/or displaying a corrected concentration of target gas in a gas-air mixture and a concurrently measured odorant concentration within the target gas. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  depicts one potential embodiment of the top panel assembly and housing. 
           [0013]      FIG. 2  illustrates a more detailed view of one embodiment of the apparatus. 
           [0014]      FIG. 3  depicts a block diagram of a particular disclosed embodiment. 
           [0015]      FIG. 4  illustrates a flow chart of the steps for operating certain embodiments of the disclosed apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    An apparatus and method for automatically correcting odorometer readings in an apparatus used to monitor odor intensity levels in gas streams is disclosed. In a preferred embodiment, the apparatus  100  may concurrently measure the concentration of an odorant in a gas stream and measure the odor intensity level from that same gas stream sample. In some embodiments, the apparatus  100  may contain a top panel assembly  152  and a housing  150 . Components may also include a flow metering valve  230  to introduce gas samples to the apparatus  100  through gas inlet  222 , a sample gas regulator  532 , a solid state mass flow sensor  584 , an absolute pressure sensor  582 , a flow system temperature sensor  586 , an air intake  224 , a blower  570  to mix the gas sample with air for evaluation, electronics  262  with non-volatile memory storage, a processor  264 , an odorant concentration sensor  510 , a GNSS receiver  258 , communications  254  which may include USB, Bluetooth, and/or WiFi, a digital display  256 , and/or a keypad  260 . The apparatus  100  may produce a mix of natural gas (e.g., methane), propane gas or other combustible target gas and air in concentrations from zero to approximately 2% for natural gas or approximately 1% for propane. The operator may slowly open the flow metering valve  230  which may allow a sample gas to enter the apparatus  100  and then the operator may sniff the mixed exhaust gases at the exhaust port  220 . This operation may be continued until the odor intensity level in the exhaust is readily detectable at which time the operator may press the “read” key to observe the relative percent gas concentration in air on the display  256  (e.g., digital display) and trigger the automatic recording of the dataset. In certain embodiments, the “read” key may also activate the odorant concentration sensor, causing an odorant concentration reading to be taken at substantially the same time as the odor intensity level is determined. 
         [0017]    Atmospheric conditions may differ significantly depending on geographic location, elevation, weather conditions and/or time of year, thus affecting the volumetric flow of a substantially fixed speed blower  570  due to potential changes in air density. As such, an instrument sensitive to changes in air density may beneficially provide a method to compensate for changes in air density and correct its readings accordingly. 
         [0018]    In one embodiment, the apparatus  100  corrects all readings using a combination of local meteorology sensors and an embedded program in the firmware. For example, pressure, temperature, and optionally humidity sensors, among others, may be used. Blower speed may be held constant. Reading correction may be based on the ratio of calibration air density to the actual air density measured while performing a test. Sample gas influence may be ignored if desired, as it usually contributes less than 1% error in most cases. A similar reading correction may be implemented by applying independent pressure, temperature, and optionally humidity and other sensor coefficients to air density. The difference between using independent sensor based coefficients and air density ratio is that the air density ratio typically models the correction relationship more intrinsically and because of that, it may be easier to implement in firmware. 
         [0019]    In preferred embodiments, reading corrections based on air density ratio are derived as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     Corrected 
                      
                     
                         
                     
                      
                     Reading 
                   
                   = 
                   
                     
                       { 
                       
                         Uncorrected 
                          
                         
                             
                         
                          
                         Reading 
                       
                       } 
                     
                     × 
                     
                       k 
                       LCD 
                     
                     × 
                     
                       ( 
                       
                         
                           ρ 
                           cal 
                         
                         
                           ρ 
                           actual 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
       
         
           
             where,
           The “uncorrected reading” may be obtained by digitizing and applying the output of the mass flow sensor  584  to a memory-based mass flow sensor response curve for a given calibration target value and type (e.g., 1.00% methane);   k LCD  is a scale factor to normalize the reading to the calibration target value based on a reference gas and flow;   ρ is air density;   β cal  is the air density present at calibration;   β actual  is the actual air density present while taking a reading;   
         
             To derive ρ: 
           
         
       
     
         [0000]    
       
         
           
             PV 
             = 
             
               nRT 
                
               
                   
               
                
               
                 ( 
                 
                   ideal 
                    
                   
                       
                   
                    
                   gas 
                    
                   
                       
                   
                    
                   law 
                 
                 ) 
               
             
           
         
       
       
         
           
             ρ 
             = 
             
               
                 weight 
                 volume 
               
               = 
               
                 n 
                 V 
               
             
           
         
       
       
         
           
             Therefore, 
           
         
       
     
         [0000]    
       
         
           
             ρ 
             = 
             
               
                 P 
                 RT 
               
                
               
                   
               
                
               
                 ( 
                 
                   in 
                    
                   
                       
                   
                    
                   units 
                    
                   
                       
                   
                    
                   of 
                    
                   
                       
                   
                    
                   
                     kg 
                     
                       m 
                       3 
                     
                   
                 
                 ) 
               
             
           
         
       
       
         
           
             Substituting ρ into Equation 1 yields Equation 2 (R cancels resulting in a relative air density ratio term): 
           
         
       
     
         [0000]    
       
         
           
             
               
                 
                   
                     Corrected 
                      
                     
                         
                     
                      
                     Reading 
                   
                   = 
                   
                     
                       { 
                       
                         uncorrected 
                          
                         
                             
                         
                          
                         reading 
                       
                       } 
                     
                     × 
                     
                       k 
                       LCD 
                     
                     × 
                     
                       ( 
                       
                         
                           
                             P 
                             cal 
                           
                           × 
                           
                             T 
                             actual 
                           
                         
                         
                           
                             T 
                             cal 
                           
                           × 
                           
                             P 
                             actual 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
       
         
           
             For algorithm deployment, let: 
           
         
       
     
         [0000]    
       
         
           
             
               k 
               cal 
             
             = 
             
               
                 P 
                 cal 
               
               
                 T 
                 cal 
               
             
           
         
       
       
         
           
             Therefore the final algorithm is: 
           
         
       
     
         [0000]    
       
         
           
             
               
                 
                   
                     Corrected 
                      
                     
                         
                     
                      
                     Reading 
                   
                   = 
                   
                     
                       { 
                       
                         uncorrected 
                          
                         
                             
                         
                          
                         reading 
                       
                       } 
                     
                     × 
                     
                       k 
                       LCD 
                     
                     × 
                     
                       k 
                       cal 
                     
                     × 
                     
                       ( 
                       
                         
                           T 
                           actual 
                         
                         
                           P 
                           actual 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   3 
                 
               
             
           
         
       
       
         
           
             where pressure is measured in Pascals and temperature is measured in degrees Kelvin. 
           
         
       
     
         [0032]    With reference to  FIG. 4 , one potential method of operating and taking corrected readings using the apparatus is described below. A factory calibration  401  may be initially performed on the apparatus and the values k LCD , P cal , T cal  and k cal  may be determined and/or recorded. These values may be used to determine a calibration air density  402 . Upon powering “on” the apparatus, sensors may begin continually monitoring atmospheric conditions  403 . The signals from these sensors may be digitized and recorded. This monitoring may be in real-time, periodically, or when desired. Sensor data may be recorded to memory continually, periodically, and/or when desired. Sensor data averaging may optionally be employed to filter out unwanted noise. When the time comes to take a target gas concentration reading, the sensors may be measured and/or digitized using the then-current actual atmospheric conditions  404  (e.g., T actual  and P actual ). An initial reading of the target gas concentration may be taken  405 . The sensor values may be used to determine the air density at which the initial reading is taken. Using the calibration and actual atmospheric conditions, the relative air density ratio may be calculated using the Equation 3 or a similar equation  406 . This ratio may be applied to correct the initial target gas concentration reading  407 . A corrected reading, which may be a corrected relative percent gas concentration in a gas-air mixture, may be displayed to the operator and/or the dataset may be recorded and/or transmitted  408 . 
         [0033]    In addition to correcting odor intensity readings based on changes in atmospheric conditions, certain embodiments may also be equipped with odorant concentration sensors. It is to be appreciated that odor intensity is commonly perceived by a human as described above, while odorant concentration is typically a quantized reading measured by a device. Generally, stand-alone odorant concentration measurement instruments are known in the art. 
         [0034]    When measuring the concentration of an odorant, the result may be a quantized concentration, which may be expressed in mg/m 3 , parts-per-million (ppm) or any other appropriate unit. Measuring the concentration of odorants, both naturally occurring and artificially added, may be performed through many analytical methods. Odorants commonly used in combustible gas streams include mercaptans, thiophenes, sulfur containing molecules and/or others. Various electro-chemical sensors may be employed. Additionally, the concentration of odorants in gas systems may be measured using spectrophotometry, UV spectroscopy, ion-mobility spectrometry, flame ionization, gas chromatography, specific gravity, mass spectrometry, infrared sensing and/or other techniques. 
         [0035]    Using certain embodiments of the disclosed device, concurrent odor intensity and odorant concentration measurements may be obtained. Additionally, these concurrent measurements may be obtained by two independent sensor channels. This arrangement may allow for rapid data acquisition as well as fully correlated data for further corroboration and analysis. While stand-alone instruments may perform similar individual measurements, concurrent analysis provides for a wider range of advantages over measurement of either odor intensity or odorant concentration in isolation. By measuring both variables concurrently, using substantially the same gas samples, the measurements are inherently coordinated. This coordination may be used to cross check each measurement against the other and ensure a high degree of accuracy. These measurements may be compared with previous measurements and used to identify anomalous measurements which may indicate a faulty reading. If the measured odor intensity does not generally align with the measured odorant concentration, it is likely a sign of a problem in at least one of the measurement systems, possibly including the human operator. The measuring device may be damaged and may be producing inaccurate readings. Alternatively, the human operator may be more or less sensitive during a particular measurement as compared to previous measurements. This redundant and correlated data allows for greater confidence that a particular measurement is correct. 
         [0036]    Measuring both of these factors concurrently allows for more educated deployment of odorant into the gas stream and may help troubleshoot problems associated with odorant deployment. Analysis of this correlated data may help ensure that odorant is deployed sufficiently and/or efficiently depending on the circumstances. Additional benefits include increased regulatory compliance across a wide range of standards, more objective measurement as compared to relying exclusively on the sensitivity of a single human operator, the ability to cross check multiple human operators against each other and many others. By taking concurrent measurements, significant man hours and the resources associated with line testing may be saved. This may result in an overall reduction in the cost of odor related testing for combustible gas related industries. 
         [0037]    Many embodiments of the disclosed apparatus  100  may optionally be configured to automatically record all readings, a dataset, geographic locations, UTC timestamps, and/or waypoints. The apparatus  100  may additionally include Global Navigation Satellite System (“GNSS”)  258  receivers using the GPS, GLONASS, Galileo, Beidou and/or other GNSS systems. Automatic timestamp and real-time clock management may be provided via the GNSS. Additionally, the apparatus  100  may include an odorization survey audit system for regulatory compliance. The apparatus  100  may be operated in conjunction with PC software for database management, mapping, report generation, tools and/or ease of integration with corporate GIS and/or asset management systems. The apparatus  100  may be connected to other systems via USB, Bluetooth and/or WiFi communications  254 . By automatically recording the timestamp, geographical location, odor intensity, and/or odorant concentration data the correlation between the two primary sensors channels may be preserved for analysis. 
         [0038]    Certain embodiments of the apparatus  100  may be configured to take advantage of the recording and communication abilities for operator qualification, training, and/or monitoring reasons. Using the automatic data recording and communication capabilities, a remotely located trainer may observe the operations of the device in real-time or near-real-time. The trainer may also review recorded data at a later time. A trainer or supervisor may perform any and/or all of these activities using the WiFi or other connectivity found in certain embodiments of the apparatus. This connectivity may be supported using a web based or other type of computer application. Data to be monitored or reviewed includes, but is not limited to, odor intensity readings, odor concentration readings, GNSS location readings, timestamps, and waypoints. Software tools for report generation may include maps and excel compatible files. These tools may document the operator&#39;s experience, qualification and/or training among other possible variables. Work schedule and/or productivity of the operator may additionally be monitored. By verifying the geographic location and timestamps correlated with the data recorded, the general schedule and productivity of the operator may be extrapolated. This data may be used in order to promote operational efficiency and verify actual reading locations. 
         [0039]    A flow self-test of the apparatus may be performed by an operator to check that the apparatus  100  is working properly. The flow self-test typically requires a source of gas (e.g., pipeline gas or propane from a tank). First, the operator may purge the apparatus  100  with gas, condition the apparatus (in part by allowing the apparatus to reach approximately the same temperature as the gas), and then zero the apparatus. 
         [0040]    The operator may verify the metering valve  230  is fully or at least significantly opened. The operator may wait for the system to adjust, typically at least 10 seconds, and then press a “Self-Test” key. The uncorrected reading on the display  256  should be greater than or equal to the calibration target value (e.g., 1.00%). The calibration target value is the percent concentration of gas used during factory calibration of the apparatus. This flow self-test reading may be recorded along with the standard dataset which frequently includes atmospheric conditions. Readings below the calibration target value produce an “Error” and are also recorded. The flow self-test configuration may be checked and the test may be repeated when an “Error” occurs. Upon successfully passing the flow self-test, the operator may choose to exit the procedure and purge the apparatus  100  with air or continue on to the readily detectable test procedure. 
         [0041]    The apparatus may be configured to maintain a number of data files in support of calibration, readings, periodic GNSS fix, self-test and/or errors. Individual folders may contain the respective files, for example purposes only, “Config” may contain configuration (e.g., calibration and/or instrument configuration) files, “R” may contain readings files, “F” may contain fix (e.g., periodic fixes) files, and/or “S” may contain system (e.g., self-test and/or error) files. It will be appreciated that the folders and files may be identified by any desired folder or file name. 
         [0042]    In one embodiment, specific usage of each file type may be as follows. The configuration file may include calibration values and/or instrument configuration settings. Calibration values may include but are not limited to k LCD , k CAL , blower speed, calibration date, calibration time, and/or target value. Configuration values often include operational times for various functions. The recorded “dataset” in the readings file may include, but is not limited to, raw sensor data, corrected readings, P actual , T actual , actual longitude, actual latitude, UTC timestamp taken when the “read” key was pressed, and/or satellite information. The periodic fix file may include, but is not limited to, actual longitude, actual latitude, concurrent UTC timestamp, and/or satellite information. Self-test and error files may be contained in the system folder. Self-test files may include but are not limited to self-test status, uncorrected reading, actual longitude, actual latitude, concurrent UTC timestamp, satellite information, battery level, and/or blower speed. The error file, if any, can contain status information related to any operational aspect of the instrument including, but not limited to, battery level, power supplies, communications, GNSS module, memory, file system, real-time clock, sensors, Bluetooth module, USB, WiFi, blower speed, configuration, and/or keypad.