Abstract:
In some aspects, olfactory devices include a housing having a first inlet and a second inlet, an ambient air inlet cartridge defining a channel in fluid communication with the first inlet, and a position sensor. The ambient air inlet cartridge includes a first member defining a first orifice, and a second member moveable relative to the first member, the second member defining a second orifice, where a degree of overlap between the first orifice and the second orifice controls a flow capacity of the channel. The position sensor signals the degree of overlap between the first orifice and the second orifice.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to systems and methods for assessing odors. 
       BACKGROUND 
       [0002]    Field olfactometry is the use of a technique or device to measure odor in ambient air by a single individual. Field olfactometry can be used to detect levels of odor in ambient air near industrial, agricultural, and municipal operation sites, such as facilities for wastewater treatment, landfills, composting, and manufacturing. Many governmental bodies require that the level of odor in the air surrounding such sites conform to various regulatory guidelines to reduce the impact on the general public. 
       SUMMARY 
       [0003]    Field olfactometry works generally by measuring the quantity of odor in ambient air by dynamically mixing filtered, clean non-odorous air with ambient, odorous air. The odorous ambient air is added to the filtered, clean air in increasing quantities by changing the ratio of air volumes until the odor is detected by a human&#39;s senses. The point at which the odor is first detected is called the dilution to threshold ratio (D/T), which means that an odor has been diluted to the threshold where a human&#39;s olfactory nerves detect the odor in the ambient air. Controllably varying the dilution to threshold ratio through a continuous range of dilutions can provide a highly precise quantification of the levels of present at a site being assessed. 
         [0004]    In an aspect, olfactory devices include a housing having a first inlet and a second inlet, an ambient air inlet cartridge defining a channel in fluid communication with the first inlet, and a position sensor. The ambient air inlet cartridge includes a first member defining a first orifice, and a second member moveable relative to the first member, the second member defining a second orifice, where a degree of overlap between the first orifice and the second orifice controls a flow capacity of the channel. The position sensor signals the degree of overlap between the first orifice and the second orifice. 
         [0005]    In an aspect, olfactory devices include a housing having a first inlet and a second inlet, and an ambient air inlet cartridge defining a channel in fluid communication with the first inlet. The ambient air inlet cartridge includes a first member defining a first orifice, and a second member moveable relative to the first member, the second member defining a second orifice where a degree of overlap between the first orifice and the second orifice controls a flow capacity of the channel, the second member being movable relative to the first member between a first terminal end position, where the first and second orifices are offset from one another, and a second end position, where the first and second orifices are completely aligned. As the second member moves between the first terminal end position and the second terminal end position, the degree of overlap between the first orifice and the second orifice increases over a continuous range. 
         [0006]    In an aspect, methods of assessing odor include withdrawing an amount of filtered air into a housing, withdrawing an amount of ambient air into the housing to form a mixture, where the amount of ambient air is less than the amount of filtered air, determining the presence of an odor in the mixture, in response to determining that no odor is present, increasing the amount of ambient air withdrawn into the housing, the amount of ambient air being increased through a continuous range, and when an odor is detected, determining a ratio of the amount of filtered air to the amount of ambient air being withdrawn into the housing. 
         [0007]    Embodiments can include one or more of the following features. 
         [0008]    In some embodiments, the position sensor includes a visual scale formed on the first member or the second member. 
         [0009]    In some embodiments, the position sensor includes a potentiometer to detect a position of the second member relative to the first member and output a position signal. In some cases, the potentiometer includes a detection membrane secured to the first member and a position indicator secured to the second member. In some cases, the olfactory device also includes a controller to receive the position signal to determine a characteristic relating to the position of the second member relative to the first member. In some cases, the olfactory device also includes a display unit to display the characteristic. In some cases, the characteristic is an approximated air flow ratio of an amount of air entering the housing through the second inlet to an amount of air entering the housing through the first inlet. 
         [0010]    In some embodiments, the second orifice overlaps the first orifice to define a compounding air flow passage that increases over a continuous range as the second member moves between a first position and a second position. In some cases, when the second member is in the first position, an amount of air that can enter the housing through the ambient air inlet cartridge is greater than the amount of air that can enter the housing through the ambient air inlet cartridge when the second member is in the second position. In some cases, when the second member is in the second position, the first orifice is covered by the second member and the second member limits air flow from entering the housing through the ambient air inlet cartridge. 
         [0011]    In some embodiments, the second member is a disk and the disk is rotatable relative to the first member. 
         [0012]    In some embodiments, the first and second orifices have the same general shape and size. 
         [0013]    In some embodiments, the second orifices has a first end having a first width and a second end having a second width, the second width being greater than the first end. 
         [0014]    In some embodiments, the housing includes a face mask. 
         [0015]    In some embodiments, the outlet is sized to be temporarily secured around a human nasal area. 
         [0016]    In some embodiments, determining the ratio includes reading the ratio from a display unit. 
         [0017]    In some embodiments, determining the ratio includes detecting a relative position of two orifices that move relative to one another to form a compounding air flow passage to allow the ambient air to enter the housing. In some cases, the compounding air flow passage changes in size along a continuous range. 
         [0018]    Embodiments can have one or more of the following advantages. 
         [0019]    The described systems and methods can be used to precisely quantify levels of odor present in ambient air by providing an ambient air inlet opening that can smoothly and continuously change in size to allow a continuous range of ratios of filtered air to ambient air. 
         [0020]    The systems and methods described can enable a user to view an instantaneous dilution ratio to threshold as the user adjusts the olfactometer by including a display unit that provides the dilution to threshold ratio at a given time. 
         [0021]    The details of one or more embodiments of the systems and methods are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages of the systems and methods will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0022]      FIG. 1  is a perspective view of a mask scentometer. 
           [0023]      FIG. 2A  is a perspective view of an ambient air dilution cartridge of the mask scentometer of  FIG. 1 . 
           [0024]      FIG. 2B  is an exploded view of the ambient air dilution cartridge of the mask scentometer of  FIG. 1 . 
           [0025]      FIGS. 2C-2E  are top views of a pivoting disk rotating on a fixed disk to create an ambient air opening for the mask scentometer of  FIG. 1 . 
           [0026]      FIG. 3A  is a perspective view of a nasal scentometer. 
           [0027]      FIG. 3B  is a front and back view of a fixed disk of an ambient air dilution cartridge of the nasal scentometer of  FIG. 3A . 
           [0028]      FIG. 3C  is a front and back view of a pivoting disk of the ambient air dilution cartridge of the nasal scentometer of  FIG. 3A . 
           [0029]      FIGS. 3D and 3E  are front views of a pivoting disk rotated on a fixed disk to create an ambient air opening for the nasal scentometer of  FIG. 3A . 
           [0030]      FIG. 3F  is an enlarged view of the ambient air opening of  FIG. 3A . 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Olfactory devices that mix filtered, clean air (i.e., air without an odor) with ambient, odorous air can be used to quantify a level of odor in the ambient air. The olfactory devices can vary a ratio of clean, filtered air to ambient, odorous air being administered to a person (e.g., a tester) to determine a dilution to threshold ratio (D/T) at which a human subject begins to detect the odor. Using an adjustable orifice formed by two orifices that are movable relative to one another to introduce the ambient air to enter an inhalation device (e.g., a gas mask) allows operators to assess odors throughout a continuous range of dilution to threshold ratios. 
         [0032]    Scentometers can control the ratio of filtered to ambient air by controlling the size of the filtered air inlet and/or the ambient air inlet through which air enters the scentometer. The clean air cartridge typically has a fixed inlet size and the ambient air cartridge has a variable inlet size. Some scentometers have clean air cartridges with variable inlet sizes and/or ambient air cartridges with a fixed inlet size. The variable-sized inlets can be provided by two structural members (e.g., flat plates or disks) which each have apertures through which air can flow. The two structural members are movable relative to each other. The relative movement of the structural members adjusts the relative position of their apertures and controls the cross-sectional area of the portion of the flow path of air entering the device through the variable-sized inlet. Controlling the cross-sectional area controls the amount of air flowing through the variable-sized inlet. Thus, the ambient air dilution cartridge can allow a user to adjust the amount of unfiltered air that enters the mask. 
         [0033]    Referring to  FIG. 1 , a scentometer (e.g., a mask scentometer)  100  includes a face mask  102 , a clean air inlet cartridge  104 , an ambient air dilution cartridge  106 , and a display unit  107  (e.g., a digital display, a dial indicator, or similar device). The clean air inlet cartridge  104  and the ambient air dilution cartridge  106  are arranged on holes on opposite sides of the face mask  102  to allow both filtered and ambient air to flow into and mix within the face mask  102 . The face mask  102  can be made from any of various suitable types of commercially available gas masks or face masks that cover the nose and mouth and can be secured to the face of the user (e.g., with straps). Commercially available masks having two odor reducing charcoal filters (e.g., one filter on each side of the mask) can be modified by removing and replacing one of the odor reducing charcoal filters with an ambient air dilution cartridge  106 . 
         [0034]    The clean air inlet cartridge  104  includes an odor reducing filter (e.g., a charcoal filter) that removes odors from the ambient air entering the mask  102  through the clean air inlet cartridge  104 . Any of various suitable odor reducing filters can be used. As discussed above, commercially available odor reducing gas masks having activated charcoal filters can be retrofit by replacing one of the filters with the ambient air dilution cartridge  106 . 
         [0035]    Referring to  FIG. 2A-2E , the ambient air dilution cartridge  106  includes a first structural member that is fixed in place and a second structural member that is movable relative to the first structural member. In the exemplary ambient air dilution cartridge  106 , the first structural member is a fixed disk  108  and the second structural member is a pivoting disk  110  that pivots relative to the fixed disk  108 . Some cartridges with variable-sized inlets have other configurations. For example, some ambient air dilution cartridges include rectangular plates that are laterally slidable relative to each other rather than disks which a rotatable relative to each other. 
         [0036]    The fixed disk  108  and the pivoting disk  110  each include an orifice  109 ,  111  formed respectively extending through the disks  108 ,  110  to permit ambient air to flow into the mask  102 . The pivoting disk  110  pivots relative to fixed disk  108  to vary the size of an air flow opening  113  (shown cross hatched for clarity in  FIGS. 2A ,  2 D, and  2 E) formed by the overlapping orifices  109 ,  111 . In the example shown, as the pivoting disk  110  rotates counter-clockwise with respect to the fixed disk  108 , the air flow opening  113  gets larger as the orifices  109 ,  111  align with each other. 
         [0037]    The orifices  109 ,  111  have substantially the same shape. The pivoting disk  110  is moveable from a first position in which the two orifices  109 ,  111  align with one another (see  FIG. 2E ) to a second position in which the two orifices  109 ,  111  are offset from each other (see  FIG. 2C ). Each orifice increases in width as it extends circumferentially around each disk  108 ,  110 . Each orifice  109 ,  111  has a first end  109 A,  111 A having a small width and smoothly extends into a second end  109 B,  111 B having a width that is wider than the first end  109 A,  111 A. Relative movement of the disks initially provides a very small opening  113  as a user begins to align the orifices  109 ,  111 . The size of the opening  113  can be increased in a slow and controlled manner through a continuous range of sizes. In the illustrated device, the orifices  109 ,  111  are in the shape of a French curve. The orifices  109 ,  111  are formed along approximately 50% of the disks to provide a large adjusting range of the pivoting disk  110  relative to the fixed disk  108 . In some embodiments, the orifices are different shapes. For example, some devices include rectangular plates having triangular orifices extending through the plates. As discussed below, the disks  108 ,  110  can include additional features or recesses. 
         [0038]    The fixed plate  108  is attached to a chamber ring  112  connected to a chamber plate  114 . The fixed disk  108 , chamber ring  112 , and the chamber plate  114  form a buffer chamber to allow the ambient air entering the ambient air dilution cartridge  106  to temporarily decelerate while a user is inhaling to smell. This allows air entering through the clean air inlet cartridge  104  and the ambient air dilution cartridge  106  to properly mix in the mask  102 . Without such a chamber, air could potentially travel directly from the ambient environment to the nasal area of the user without first mixing with the clean, filtered air, which can result in incorrect detection readings. The chamber plate  114  includes an outlet hole  116  to receive a fitting  118  and attach the chamber plate  114  (i.e., and the fixed disk  108 ) to the mask  102  for mounting the varying air flow opening  113  formed by the fixed disk  108  and the pivoting disk  110  to the mask  102 . 
         [0039]    A position sensor measures the relative position of the structural members relative to each other. In this exemplary device, the position sensor includes a potentiometer having a sensor membrane  120  secured to the top surface of the fixed disk  108  that provides an output signal that varies as the position of the pivoting disk  110  changes relative to the fixed disk  108 . Some embodiments include other types of position sensors. 
         [0040]    The sensor membrane  120  has an inner sensor portion  120   a  and a ribbon connector portion  120   b . The inner sensor portion  120   a  tracks the position of the pivoting disk  110  by detecting the relative position of pivoting disk  110 . The ribbon connector portion  120   b  is connected to the display unit  107 , or an alternative control unit, to transmit electrical signals regarding the detected relative position of the pivoting disk  110 . The fixed disk  108  includes a recess sized to receive the sensor membrane  120  so that a top surface of the sensor membrane  120  is flush with the top surface of the fixed disk  108 . In some embodiments, the fixed disk  108  does not include a recess to receive the sensor membrane  120 . The inner sensor portion  120   a  is contacted by a feature (e.g., a wiper  122 ) of the pivoting disk  110  and the sensor  120  outputs a voltage based on the relative position of the wiper  122 . The wiper  122  is secured in a recess of the pivoting disk  110  and moves along the sensor membrane  120  to produce a voltage based on the position of the pivoting disk  110  with respect to the fixed disk  108  can be determined. The wiper  122  is made from various suitable materials (e.g., metal). For example, the wiper  122  can be a threaded fastener secured in a threaded hole in the pivoting disk  110 . 
         [0041]    The sensor  120  is calibrated and the voltage output by the sensor  120  when the pivoting disk  110  is at various relative positions with respect to the fixed disk  108  is measured and stored as calibration data in a control unit or memory device. During use, the changing voltage output by the sensor  120  is sent to a control unit and the control unit, based on the stored calibration data, determines the relative position of the pivoting disk  110  with respect to the fixed disk  108 . 
         [0042]    A gasket  124  arranged on top of the fixed disk  108  limits air flow entering the orifice  109  from the space between the rotating disk  110  and the fixed disk  108  when the pivoting disk  110  is secured to the fixed disk  108 . Air flows through the air opening  113  (see  FIGS. 2A ,  2 D and  2 E) formed by the orifices  109 ,  111  (i.e., not from between the disks  108 ,  110  and through the orifice  109 ) to help accurately control of the amount of ambient air flowing into the mask  102 . The gasket  124  includes an inner recess  126  to allow the sensor wiper  122  to travel freely inside the gasket  124 . The inner recess  126  also includes a flat region  126   a  that, when the gasket  124  is installed on the fixed disk  108 , abuts a raised portion  128  extending upward from the fixed disk  108  to keep the gasket  124  properly oriented to the fixed disk  108  when the pivoting disk  110  rotates. A guide  130  inserted through a hole in the gasket  124  and fastened to the fixed disk  108  secures the gasket  124  to the fixed disk  108 . The guide  130  also limits the rotation of the pivoting disk  110  during use. The guide  130  can be in the form of various structurally suitable elements. For example, in some implementations, the guide is a fastener (e.g., a cap screw). Other devices and techniques can be used to secure and align the gasket  124  to the fixed disk  108 . Additionally, in some implementations, other types of sealing devices (e.g., O-rings) limit air flowing in the orifice  109  from the space between the fixed disk  108  and the pivoting disk  110 . 
         [0043]    The pivoting disk  110  also includes a guide slot  134  formed near an outer edge of the pivoting disk  110  over about  50 % of the pivoting disk  110 . When the pivoting disk  110  is mounted on the fixed disk  108 , the guide  130  of the fixed disk  108  fits into the guide slot  134  so that as the pivoting disk  110  rotates atop the fixed disk  108 , the guide  130  limits the rotation between a fully closed position and a fully open position. 
         [0044]    The pivoting disk  110  is secured to the fixed disk  108  using a fastener  136  that passes through a recess  138  in the pivoting disk  110  and is secured into a recess  140  (e.g., a threaded hole) formed in the fixed disk  108 . A spring  142  is arranged between the fastener  136  and the pivoting disk  110  to provide a downward force onto to pivoting disk  110  to help ensure an adequate seal between the pivoting disk  110  and the fixed disk  108 . 
         [0045]    During use, the pivoting disk  110  rotates to vary the amount of ambient air that can enter the mask  102  through the opening  113 . The sensor  120  determines the relative rotational position of the pivoting disk  110  (i.e., the position of the wiper  122 ) with respect to the fixed disk  108 . The relative position reading (i.e., the voltage output by the sensor  120 ) is used to determine (e.g., calculate) the ratio of ambient air entering the mask  102  to clean filtered air entering the mask  102  (i.e., the dilution to threshold ratio) when a user is wearing the mask scentometer  100  and breathing in. 
         [0046]    Since the dilution to threshold ratio represents a flow ratio of clean filtered air to ambient air entering the mask  102 , the size and shape of the opening  113  can be used to estimate the dilution to threshold ratio. Additionally, estimated dilution to threshold ratios based on the size of the opening  113  can be verified or otherwise determined by testing and calibration. For example, the dilution to threshold ratio based on the relative position of the pivoting disk  110  could be determined empirically by drawing air (e.g., by producing a flow to simulate a human inhaling) into the mask  102  while adjusting the pivoting disk  110  and measuring the flow of air through the filtered, clean air inlet filter  104  and the ambient air dilution cartridge  106 . Once the relative flow rates through the filtered, clean air inlet filter  104  and the ambient air dilution cartridge  106 , based on relative position of the pivoting disk  110 , are determined, the dilution to threshold ratio for each relative position can be calculated. 
         [0047]    A control unit  144  receives relative position information from the sensor  120  (i.e., a voltage output based on the position of the wiper  122 ), uses that relative position information to determine a corresponding dilution to threshold ratio based on the relative position, and displays that dilution to threshold ratio on the display unit  107 . The user can typically read the dilution to threshold ratio at a given time while using the mask scentometer  100 . The display unit  107  can be mounted on the mask  102  so that it is generally visible by a user while the user is wearing the mask  102 . Alternatively, the display unit  107  can be in the form of a separate unit that is connected to the mask  102 . For example, the display unit can be a separate unit that can be carried by a user and is tethered to the mask  102  or wirelessly connected to the mask  102 . In some cases, the control unit  144  is built into the mask  102  and is electrically connected to the display  107 . 
         [0048]    Alternatively or additionally, as another example of a position sensor that can signal the degree of overlap between the first and second orifices, the disks (e.g., the fixed disk  108 , the pivoting disk  110 , or both) can include a visual scale or dial indicator to denote the relative position of the pivoting disk  110  with respect to the fixed disk  108 . The scale can also include corresponding dilution to threshold ratio information for the different relative positions. 
         [0049]    The concepts discussed above can also be implemented in other types of scentometers. For example, these concepts can be implemented in a nasal scentometer. 
         [0050]    Referring to  FIG. 3A , a nasal scentometer  200  includes an inhalation apparatus  202 , two clean air inlet cartridges  104 , an ambient air dilution cartridge  106 , and a display unit  107 . The clean air inlet cartridges  104  are arranged on holes on opposite sides of the inhalation apparatus  202  and the ambient air dilution cartridge  106  is arranged on a hole at a far end of the inhalation apparatus  202  to allow both filtered and ambient air to flow into and mix within the inhalation apparatus  202 . 
         [0051]    The inhalation apparatus  202  includes a handle  204  extending from a tube-like member  206  and a flexible (e.g., made of plastic or rubber) nose piece  208 . The nose piece  208  is configured to sufficiently seal around a nose of the user. As shown, the inhalation apparatus  202  and nose piece  208  are configured to be gripped by a user and held securely against the face of the user during use. The tube-like member  206  serves as an air mixing chamber for filtered air to mix with ambient odorous air. 
         [0052]    The inhalation apparatus  202  includes a pressure sensor positioned inside the inhalation apparatus  202  to measure the pressure at which a user inhales air into the inhalation apparatus  202 . In some cases, certain inhalation pressures are used to generate desired flow characteristics in order to properly measure the dilution to threshold ratio. The pressure sensor can be connected to a control unit and an exterior display to indicate that greater or less inhalation pressure is desired from the user. The exterior display can be the display unit  107  for displaying the dilution to threshold ratio or, alternatively, it can be a separate display. Some embodiments do not include a pressure sensor within the inhalation apparatus. 
         [0053]    Like the mask scentometer discussed above, the ambient air dilution cartridge  106  includes two cooperating disks (e.g., a fixed disk  108  and a pivoting disk  110 ) that adjust the amount ambient air that can enter the inhalation apparatus  202 . However, in this example, one of the disks (e.g., the fixed disk  108 ), referring to  FIGS. 3B and 3C , includes a round orifice  109  and the pivoting disk  110  includes one or more non-uniform orifices  111  that vary in size. The non-uniform orifice  111  has a first end having a small width and smoothly extends into a second end having a width that is wider than the first end. Some embodiments include different shaped orifices. The pivoting disk  110  includes multiple orifice portions separated by regions of the disk (e.g., blanks). In some embodiments, one orifice is formed around the majority of the pivoting disk  110 . Referring to  FIGS. 3D-3F , when the pivoting disk  110  is pivotally secured to the fixed disk  108 , the pivoting disk  110  can be rotated to align portions of the non-uniform orifices  111  with the round orifice  109 . By aligning the orifices  109 ,  111 , a variable-sized air opening  113  (shown in expanded  FIG. 3F ) is formed to allow ambient air to enter the inhalation apparatus  202 . To provide an adequate seal between the round orifice  109  and the non-uniform orifice  111 , the fixed disk  108  includes a seal member (e.g., an O-ring  146 ) arranged around the round orifice  109 . 
         [0054]    Referring again to  FIG. 3B , the fixed disk  108  includes a sensor mount recess  148  formed to receive a potentiometer sensor  120 . The sensor  120  is secured to the fixed disk  108  to detect the relative position of the pivoting disk  110  with respect to the fixed disk  108 . To indicate the relative position of the pivoting disk  110  on the sensor  120 , the pivoting disk  110  includes a sensor wiper  130  to move along the sensor  120  to generate a voltage output which corresponds to the relative position of the wiper  130  and therefore also of the pivoting disk  110 . 
         [0055]    The ambient air dilution cartridge  106  can also include an indexing mechanism to temporarily secure the pivoting disk in particular orientations with respect to the fixed disk. For example, referring to  FIGS. 3B and 3C , the fixed disk  108  includes multiple raised portions  150  to engage indentations  152  formed along the adjoining face of the pivoting disk  110 . The raised portions  150  and corresponding indentations  152  can be arranged around the disks  108 ,  110  at various positions to allow a user to select and maintain certain orientations or relative positions. Alternatively, other techniques or mechanisms can be used to secure the pivoting disk to the fixed disk. 
         [0056]    The display unit  107  is used to indicate the dilution to threshold ratio based on the relative position of the pivoting disk  110  with respect to the fixed disk  108 , as measured by the sensor  120 . The display unit  107  includes a control unit  144  for receiving relative position signals from the sensor  120 , determining a dilution to threshold ratio based on the measured position, and then displaying the dilution to threshold ratio on the display unit  107 . Alternatively, the display unit  107  can be connected to an external control unit that processes the relative position signals and determines a dilution to threshold ratio. In cases where the nasal scentometer  200  includes a pressure sensor inside the inhalation apparatus  202 , the pressure sensor can be connected to the control unit  144  so that the inhalation pressure can be considered when determining the dilution to threshold ratio. 
         [0057]    The scentometers can be used, for example, in determining an odor level in areas surrounding odor producing environments (e.g., feed lots, industrial facilities, sewage plants, and other similar environments). The odor of a body of ambient air is typically quantified by determining a dilution to threshold ratio (D/T) of clean, filtered air to ambient, odorous air at which a human test subject begins to detect the odor in the ambient air. 
         [0058]    Typically, a user will travel (e.g., in an automobile) to the area to be analyzed. While still in the automobile or in a structure (e.g., a building, an office, a job trailer, or other a similar structure), to prevent exposure to the ambient air containing the odor, the user places a mask scentometer  100  on their face and secures it using the straps. With the mask scentometer  100  secured to the face, the user rotates the pivoting disk  110  to a fully closed position where the pivoting orifice  111  does not overlap the fixed orifice  109  (i.e., no opening  113  is formed) so that no air enters the mask  102  through the ambient air dilution cartridge  106 . Alternatively, if using a nasal scentometer  200 , instead of securing a mask to the user&#39;s face, the nose piece  208  is held in place on the user&#39;s nose. With the ambient air dilution cartridge  106  closed, the user only breaths air that passes through the clean air inlet filter  104  and therefore has been filtered and has little to no odor from the ambient environment. Once the user is breathing only filtered air, the user can leave the automobile or building to begin analyzing the ambient air. 
         [0059]    Once in the environment to be tested, the user slowly opens the ambient air dilution cartridge  106  (i.e., by rotating the pivoting disk  110 ) to allow ambient, unfiltered air to begin entering the mask  102  (or inhalation apparatus  202  when a nasal scentometer  200  is used). The user rotates the pivoting disk  110  in a slow and controlled manner in increments (e.g., small rotational distances), continuously smelling the air entering the mask  102  or the inhalation apparatus  202  in an attempt to detect an odor. The user continues to rotate the pivoting disk  110  to increase the size of the opening  113  and increase the flow of ambient odorous air entering the mask  102  or the inhalation apparatus  202 . When the user detects the odor, he or she stops rotating the pivoting disk  110  and determines dilution to threshold ratio of air entering the mask  102  or inhalation apparatus  202  when the pivoting disk  110  is at that particular position. The dilution to threshold ratio can be determined from reading the display unit  107  or alternatively by reading the scale (e.g., graduations) formed on the fixed disk  108  or the pivoting disk  110 . 
         [0060]    In some cases, the user adjusts the pivoting disk  110  until he or she detects an odor in order to obtain an initial, coarse dilution to threshold ratio reading. Then, once the user knows the general range of the dilution to threshold ratio, the user will adjust the pivoting disk  110  more slowly to obtain a second, finer and more accurate dilution to threshold ratio reading. 
         [0061]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.