Patent Publication Number: US-2003230716-A1

Title: Multi-gas analyzer

Description:
This application claims the benefit of U.S. Provisional Application No. 60/372,094, filed on Apr. 12, 2002 which application is incorporated herein by reference. 
    
    
     
       Technical Field of the Invention  
       [0001] One or more embodiments of the present invention pertain to a multi-gas analyzer.  
       BACKGROUND OF THE INVENTION  
       [0002] As is known, multi-gas analyzers have been in use for years. Typically, such prior art multi-gas analyzers are comprised of handheld, one-to-five gas analyzers that measure one or more of hydrocarbons (“HC”), carbon monoxide (“CO”), carbon dioxide (“CO 2 ”), oxygen (“O 2 ”), and nitrogen oxide (“NO x ”). Such prior art multi-gas analyzers are problematic for one or more of the following reasons: (a) they have slow response times, for example, five (5) seconds or greater; (b) they entail the use of disposable O 2  and NO x  sensors that have a limited lifetime and a slow response; and (c) they are bulky.  
       [0003] In light of the above, there is a need in the art for a multi-gas analyzer that solves one or more of the above-identified problems.  
       SUMMARY OF THE INVENTION  
       [0004] One or more embodiments of the present invention solve one or more of the above-identified problems. In particular, one embodiment of the present invention is an analyzer of a multiplicity of gases in a sample gas that comprises: (a) a source of infrared radiation; (b) a multiplicity of band-pass filters, including a reference band-pass filter, and an opaque area; (c) a movement mechanism that places the band-pass filters and the opaque area in front of the infrared radiation at predetermined times, and includes a location pickup mechanism; (d) a location pickup mechanism detector that detects the location pickup mechanism and generates movement mechanism timer signals; (e) a sample cell through which the sample gas travels, which sample cell is disposed in a path of the infrared radiation after it has passed through the band-pass filters; (f) a gas temperature sensor that detects a temperature of the sample gas in the sample cell and generates a temperature signal; (g) a pressure transducer that detects a pressure of the sample gas in the sample cell and generates a pressure signal; (h) a detector that detects infrared radiation that has passed through the sample cell and generates detector signals; and (i) a controller that analyzes the movement mechanism timer signals, the detector signals, the temperature signal, and the pressure signal to provide concentrations of the multiplicity of gases. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0005]FIG. 1 is a perspective view of an analyzer cell used to fabricate a gas analyzer in accordance with one or more embodiments of the present invention;  
     [0006]FIG. 2 is an exploded view of the analyzer cell shown in FIG. 1;  
     [0007]FIG. 3 is a block diagram of a gas analyzer that is fabricated in accordance with one or more embodiments of the present invention;  
     [0008]FIG. 4 is a block diagram of a processing module that may be used to fabricate a gas analyzer in accordance with one or more embodiments of the present invention; and  
     [0009]FIG. 5 is a flowchart of a method used to determine concentrations of N gases in accordance with one or more embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0010] One or more embodiments of the present invention are gas analyzers that measure concentrations of gases. In accordance with one or more such embodiments of the present invention, the concentrations of gases are expressed as a ratio of mass, for example and without limitation, in a percentage or as a parts-per-million (“PPM”).  
     [0011]FIG. 1 is a perspective view of hand-held analyzer cell  100  that is used to fabricate a gas analyzer in accordance with one or more embodiments of the present invention. As shown in FIG. 1, analyzer cell  100  includes gas cell  104  that is disposed between detector end module  101  and IR source end module  102 . As further shown in FIG. 1, gas cell  104  includes cell/gas pressure port  111  that is connected to pressure transducer  612  (see FIG. 3).  
     [0012] As further shown in FIG. 1, detector end module  101  includes: (a) infrared detector element  121  that is disposed at an outside end of detector end module  101 ; (b) gas inlet  122  that is disposed at an outside end of detector end module  101 ; and (c) gas temperature sensing port  123  that is disposed at an outside end of detector end module  101  and is connected to gas temperature sensor  611  (see FIG. 3). As further shown in FIG. 1, IR source end module  102  includes: (a) oxygen cell sensor module  131 ; (b) gas outlet  132 ; (c) filter temperature sensing port  136  that is connected to filter temperature sensor  606  (see FIG. 3); (d) chopper motor  517 ; (e) IR source module  134 ; and (f) optical pickup module  133  that is used to obtain a position of chopper wheel  514  (see FIG. 2).  
     [0013]FIG. 2 is an exploded view of analyzer cell  100  shown in FIG. 1. As shown in FIG. 2, in accordance with one or more embodiments of the present invention, gas cell  104  (connected between detector end module  101  and IR source end module  102 ) comprises three sections that are connected to form gas cell  104 : (a) cell  542  having a cylindrical inside volume; and (b) cells  541  and  543  that are disposed at opposite ends of cell  542 , each of which has an inner volume that is in the form of a truncated cone. In accordance with one embodiment of the present invention, cells  541  and  543  are each made up of a cylindrical tube whose inner diameter has a minimum at a first end and a maximum at a second end wherein the inner diameter is linearly increased from the first end to the second end to provide the truncated cone of the inner volume of the cell (as one can readily appreciate, in such an embodiment, the outside wall of the cell may be any shape). In accordance with one or more further embodiments of the present invention, gas cell  104  can be formed of: (a) one of the above-described cells having a conical inside wall; (b) two of the above-described cells having a conical inside wall wherein the cells are attached to each other with their larger, inner diameters intimately facing each other; or (c) two of the above-described cells having a conical inside wall wherein the cells are each attached to a cell section having an inside wall whose inner diameter is constant and is as large as the larger inner diameter of each of the cells (for example, as is the case for gas cell  104  shown in FIGS. 1 and 2). In accordance with one or more embodiments of the present invention, the inner walls of gas cell  104  are formed of, or coated with, a highly reflective, non-oxide forming, material such as, for example and without limitation, gold. In addition, as further shown in FIG. 2, ends  541 , and  543 , of cells  541  and  543 , respectively, are formed to enable them to be inserted into gas inlet manifold module  522  and gas outlet manifold module  511 , respectively.  
     [0014] In accordance with one or more embodiments of the present invention, gas is delivered to, and extracted from gas cell  104  using Radial Discharge technology. In particular, in accordance with such embodiments of the present invention, a series of small holes (not shown) are spaced around ends  541 , and  543 , of cells  541  and  543 , respectively, which holes are directed through the wall of cells  541  and  543  toward a central longitudinal axis of cells  541  and  543  (i.e., the holes are radially disposed). In accordance with one or more of such embodiments, gas is coupled through the holes in end  541   1  into cell  541  and through the holes in end  543   1  out of cell  543  utilizing, for example and without limitation, a banjo type collar (not shown) that is well known to those of ordinary skill. The banjo collars fit over ends  541   1  and  543   1  of cells  541  and  543 , respectively, and the banjo collars have holes that are aligned with the holes in ends  541   1  and  543   1  of cells  541  and  543 , respectively. Thus, in accordance with one or more such embodiments of the present invention, gas inlet manifold module  522  includes gas inlet  122  that is fixedly coupled to: (a) gas inlet manifold module  522  and (b) the banjo collar utilizing any one of a number of methods that are well known to those of ordinary skill in the art. As a result, in operation, gas flows into gas inlet  122 , into the banjo collar, through the holes in the banjo collar, and into end  541 , of cell  541  through holes that are aligned with the holes in the banjo collar. End  541   1  of cell  541  may be inserted (for example and without limitation, by a force fit, by a threaded connection, and so forth) into the banjo collar. In accordance with one or more embodiments of the present invention, gas outlet  132 , gas outlet manifold module  511 , a banjo collar, and end  543   1  of cell  543  are assembled in the same manner as that described above for gas inlet  122 , gas inlet manifold module  522 , a banjo collar, and end  541   1  of cell  541 .  
     [0015] In accordance with the above-described embodiment, the radial inlet of gas into gas cell  104  and the radial extraction of gas from gas cell  104  creates a convergence of gas along a central longitudinal axis of gas cell  104  whose turbulence is beneficial in purging gas cell  104  of gas as well as in uniformly dispersing the gas in gas cell  104 . In addition, the multiple radial hole outlet described above advantageously prevents collection of water in gas cell  104  by providing a direct exit at any angle from gas cell  104 .  
     [0016] It should be appreciated that further embodiments of the present invention exist wherein: (a) gas cell  104  may be fabricated using a structure having fewer pieces or more pieces than was the case for the structure described above; (b) an inner volume of gas cell  104  has a different shape than was the case for the structure described above; (c) gas cell  104  may be coupled to gas inlet  122  and gas outlet  132  using mechanisms that are different from the mechanism described above; and/or (d) gas inlet manifold module  522  and gas outlet manifold module  511  may be fabricated utilizing alternative construction mechanisms from that described above.  
     [0017] As further shown in FIG. 2, IR source housing module  516  is affixed to gas outlet manifold module  511  utilizing, for example and without limitation, screws  519   1 - 519   4 , and IR source housing module  516  holds: (a) chopper motor  517 ; (b) chopper wheel  514 ; and (c) IR (infrared) source  518 . In accordance with one or more embodiments of the present invention, chopper motor  517  is configured to cause chopper wheel  514  to rotate, and chopper wheel  514  includes a plurality of filter elements  515 . In fabricating a handheld embodiment of the present invention, chopper motor  517  is a micro/miniature motor such as, for example and without limitation, those obtained from JinLong Machinery &amp; Electronics Co., Ltd of China. As further shown in FIG. 2, sealer  513  (for example and without limitation, an o-ring) is inserted into a recess in the end of gas outlet manifold module  511 , and radiation window  512  (fabricated, for example and without limitation, from sapphire) is inserted against sealer  513  in the recess. In accordance with one or more such embodiments of the present invention, there is no dead space between an opening at end  543   1  of cell  543  and radiation window  512  (as such, sealer  513  prevents gas from escaping gas cell  104 ). Thus, in accordance with such an embodiment, gas exits gas cell  104  directly against radiation window  512 . Further, IR source  518  and chopper wheel  514  are aligned so that infrared (“IR”) radiation emitted by IR source  518  passes through filters  515  (as they are rotated into the path of the radiation), and the remaining radiation passes through radiation window  512  and enters gas cell  104 .  
     [0018] In accordance with one or more embodiments of the present invention, a sealer (not shown) (that is fabricated for example and without limitation, as an o-ring) is inserted into a recess in the end of gas inlet manifold module  522 , and a radiation window (not shown) (that is fabricated, for example and without limitation, from sapphire) is inserted against the sealer in the recess. In accordance with one or more such embodiments of the present invention, there is no dead space between an opening at end  541   1  of cell  541  and the radiation window (as such, the sealer prevents gas from escaping gas cell  104 ). Thus, in accordance with such an embodiment, gas enters gas cell  104  directly against the radiation window. As further shown in FIG. 2, detector housing module  521  is affixed to gas inlet manifold module  522  utilizing, for example and without limitation, screws (not shown), and detector housing module  521  holds infrared detector element  521 . As shown in FIG. 2, infrared detector element  121  is aligned so that it detects IR radiation transmitted through gas cell  104  and the radiation window.  
     [0019] As one can readily appreciate from the above, one or more of the above-described embodiments of the present invention provide an unobstructed 360 degree entry of gas into gas cell  104  and exit of gas from gas cell  104 . Further, advantageously due to the fact that the gas travels directly across the radiation windows, water vapor collection and deposits on the radiation windows are minimized.  
     [0020]FIG. 3 is a block diagram of gas analyzer  600  that is fabricated in accordance with one or more embodiments of the present invention. As shown in FIG. 3, gas analyzer  600  includes chopper wheel  514  that includes N+1 infrared filters or windows  515 , of any shape, that are used in accordance with one or more embodiments of the present invention to obtain information relating to N distinct gases. In accordance with one or more embodiments of the present invention, N+1 infrared filters  515  are located along a constant radius from a center of chopper wheel  514 , which constant radius is less than the overall radius of chopper wheel  514 . Further, in accordance with one or more such embodiments, chopper wheel  514 , in addition to N+1 infrared filters  515 , includes an infrared opaque area (not shown) that completely blocks infrared radiation.  
     [0021] As further shown in FIG. 3, chopper motor  517  (fabricated, for example and without limitation, as a miniature chopper motor to enable one to fabricate a hand-held version of gas analyzer  600 ) causes chopper wheel  514  to rotate utilizing any one of a number of mechanisms that are well known to those of ordinary skill in the art. For example and without limitation, chopper motor  517  may be coupled directly to chopper wheel  514  (in which case chopper wheel  514  will rotate at the same rotational speed as chopper motor  517 ), or chopper motor  517  may be coupled indirectly to chopper wheel  514  utilizing any one of a number of methods and mechanisms that are well known to those of ordinary skill in the art such as, for example and without limitation, a belt and pulley mechanism, a geared mechanism, a friction coupled mechanism, a magnetically coupled mechanism, or any other mechanism that will allow rotational torque to be transferred from chopper motor  517  to chopper wheel  514 . Further, chopper motor  517  may be any type of motor such as, for example and without limitation, a brushed DC motor, a brush-less DC motor, an induction motor, a synchronous motor, any type of reluctance motor, a stepper motor, or any type of device that produces rotation. As further shown in FIG. 3, chopper motor  517  is driven in response to signals received from chopper motor driver  622 , which chopper motor driver  622  is driven in turn by signals received from microprocessor  634  of processor module  700 . Chopper motor driver  622  may be fabricated utilizing any one of a number of such devices that are well known those of ordinary skill in the art, and chopper motor driver  622  may be driven by microprocessor  634  of processor module  700  utilizing any one of a number of methods that are well known to those of ordinary skill in the art.  
     [0022] As further shown in FIG. 3, gas analyzer  600  includes optical pickup  133  and chopper wheel  514  further includes wheel optical trigger mark  602 . Optical pickup  133  is disposed in IR source housing module  516  in a position configured for it to detect wheel optical trigger mark  602 . In accordance with one or more embodiments of the present invention, wheel optical trigger mark  602  is an aperture placed anywhere on chopper wheel  514  that passes radiation output by a radiation emitting device (not shown, which is located, for example and without limitation, in optical pickup  133 ) to a radiation detecting device (not shown, which is located, for example and without limitation, in optical pickup  133 ). For example and without limitation, the radiation emitting device and the radiation detecting device may be located on opposite sides of chopper wheel  517 . In accordance with an alternative embodiment, an area of the surface of chopper wheel  514  can be made to have adequate contrast for radiation emitted by the radiation emitting device so that it reflects with varying intensity. In such a case, a radiation detecting device placed near the radiation emitting device can receive the reflected radiation having varying intensity and produce a signal in response thereto, which radiation emitting device and which radiation detecting device may be disposed on the same side of chopper wheel  514 . In either case, the radiation emitting device and the radiation detecting device may be fabricated using any one of a number of such devices that are well known to those of ordinary skill in the art. Further, in either case, optical pickup  133 , generates a signal that is transmitted to optical pulse buffer  623 , and a digital representation of that signal is applied as input to microprocessor  634  of processor module  700  in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. Optical pulse buffer  623  may be fabricated utilizing any one of a number of such devices that are well known to those of ordinary skill in the art.  
     [0023] Microprocessor  634  of processor module  700  utilizes the signal from optical pulse buffer  623  to detect a position of chopper wheel  514  once per revolution of chopper wheel  514 , and thereby the location of each of infrared filters  515  in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. As one can readily appreciate, further embodiments of the present invention exist wherein a triggering mechanism that outputs a signal that is used to determine the location of each of infrared filters  515  can be fabricated utilizing any one of a number of non-contact triggering mechanisms that are well known to those of ordinary skill in the art such as, for example and without limitation, a trigger mechanism comprising a permanent magnet that is located on chopper wheel  514  and a magnetic field sensor such as, for example and without limitation, a Hall device, that is placed in sufficiently close proximity to chopper wheel  514  that it can sense a variation in the magnetic field as the permanent magnet passes by the sensor.  
     [0024] In accordance with one or more embodiments of the present invention, microprocessor  634  of processor module  700  interprets the “trigger signal” that indicates detection of wheel optical trigger mark  602  as a location corresponding to zero degrees of rotation of chopper wheel  514 . Microprocessor  634  uses the time between the last two trigger signals to determine a time period that corresponds to one revolution of chopper wheel  514 , which time is designated To. As such, To corresponds to a time interval during which chopper wheel  514  rotates by 360 degrees, and T 0 /360 corresponds to a time interval during which chopper wheel  514  rotates by one degree. Using this time interval (T 0 /360) and the known position of each side of each of infrared filters  515  in degrees from the location corresponding to zero degrees, microprocessor  634  converts the locations of each side of each of infrared filters  515  and the opaque area to time intervals from the trigger signal. In other words, microprocessor  634  computes t 0  and t 2  (for example and without limitation, in units of T 0 /360) for each filter and the opaque area where: (a) t 1  is the amount of time after the trigger signal is received at which the first side of the filter is in front of radiation output from IR source  518 ; and (b) t 2  is the amount of time after the trigger signal is received at which the second side of the filter is in front of radiation output from IR source  518 .  
     [0025] In accordance with one or more embodiments of the present invention, IR source  518  emits infrared radiation and has a native or synthesized aperture that is less than a width of each of infrared filters  515 . In accordance with one or more such embodiments of the present invention, IR source  518  has a wavelength spectrum in a range, for example and without limitation, from about 2 μm to about 20 μm. Such infrared sources are well known to those of ordinary skill in the art, and are available commercially. Such a wavelength spectrum ensures that a number of gases such as, for example and without limitation, hydrocarbons (“HC”), carbon monoxide (“CO”), carbon dioxide (“CO 2 ”), oxygen (“O 2 ”), and nitrogen oxide (“NO x ”) absorb energy at wavelengths within the specified range. As shown in FIG. 3, process module  700  sends a signal to IR source driver  621 , and IR source driver  621 , in turn, sends a signal to IR source  518  to cause it to emit infrared radiation. IR source driver  621  may be fabricated utilizing any one of a number of such devices that are well known to those of ordinary skill in the art.  
     [0026] In accordance with one or more such embodiments, each gas whose concentration is to be determined has a corresponding narrow bandwidth, band-pass filter associated with it that is placed on rotating chopper wheel  514  so that the filter is periodically placed after IR source  518  and before gas cell  104  and detector element  121 . In addition, in accordance with one or more embodiments of the present invention, a reference filter is placed on rotating chopper wheel  514  to measure the maximum IR radiation energy available from IR source  518  and measured by detector element  121  that does not depend on the concentrations of the constituents to be analyzed, which reference filter is a narrow bandwidth, band-pass filter having a center band-pass wavelength and band-pass width such that none of the gases to be analyzed absorbs energy transmitted by the reference filter band-pass (as such, the energy measured by detector element  121  for IR radiation passing through the reference filter will not be effected by changes in concentrations of constituents of the gas introduced into gas cell  104 ). Such infrared filters and the reference filter are well known to those of ordinary skill in the art, and are available commercially. Lastly an opaque area is placed on rotating chopper wheel  514  to measure the minimum energy measured by detector element  121 . Thus, upon one revolution of chopper wheel  514 , IR radiation will be blocked by one opaque area, passed through one reference window, and passed through a filter designed for each of the gases whose concentrations are to be determined.  
     [0027] In particular, infrared radiation output from IR source  518  passes through N+1 filters  515  as each is brought into alignment when chopper motor  517  causes chopper wheel  514  to rotate. After passing through one of filters  515 , the remaining infrared radiation passes through radiation window  512  in analyzer cell  100 , and passes through gas cell  104  (path  608  shown in FIG. 3) where various concentrations of gas(es) absorb varying amounts of the remaining infrared radiation. Next, the resulting infrared radiation passes through a radiation window in IR detection end module  101 , and reaches infrared detector element  121 , for example, a fast responding infrared detector. As described above, and in accordance with one or more embodiments of the present invention, IR source  518  outputs infrared radiation having a wavelength spectrum that is broad enough so that it envelops at least predetermined portions of the infrared absorption spectrum of the N gases that can be used to identify all N gases.  
     [0028] In order for infrared detector element  121  to observe a steady infrared radiation signal as chopper wheel  514  places one of infrared filters  515  in front of IR source  518  as the one of infrared filters  515  is rotated, an output aperture of IR source  518  ought to be less than an arc length across any of infrared filters  515 , which arc length is measured at a radius corresponding to a distance from the center of chopper wheel  514  to about an average of the center of infrared filters  515 . In accordance with one or more embodiments, this is achieved by selecting a source having a very small aperture (i.e., essentially a point source) or by fabricating an aperture whose diameter is less than an arc length of any of infrared filters  515 .  
     [0029] Infrared detector element  121  determines a measure of the energy of the infrared radiation impinging thereon, and in accordance with one or more embodiments of the present invention, infrared detector element  121  must have a response time that is sufficiently fast that it can accurately measure the rapid variation in energy of the radiation output from IR source  518  caused by movement of infrared filters  515 . In accordance with one or embodiments of the present invention, infrared detector element  121  is embodied utilizing a device whose resistance changes as varying amounts of infrared energy are detected. In accordance with one or more such embodiments, a constant current source (not shown) having a precision, for example and without limitation, of about ±2% drives a constant current into infrared detector element  121  in response to a signal (not shown) from microprocessor  634  of processor module  700 . In further accordance with one or more such embodiments, (a) the resistance of infrared detector element  121  is at a maximum value with no incident infrared radiation energy and at a minimum value with maximum incident infrared energy; and (b) the variation in resistance is linearly proportional to incident radiation energy. As a result, the use of a constant current source produces a voltage across infrared detector element  121  that is inversely proportional to the energy of infrared radiation incident upon its surface. The current source may be fabricated utilizing any one of a number of such devices that are well known to those of ordinary skill in the art. In accordance with one or more embodiments of the present invention, infrared detector element  121  is a lead selenide (PbSe), thermoelectrically cooled detector that is commercially available. Further, as shown in FIG. 3, in accordance with such an embodiment, cooler controller  614  is used to thermoelectrically cool infrared detector element  121  in response to a signal (not shown) from microprocessor  634  of processor module  700 . An advantage of using a current source in the manner described above is that its Thevenin or equivalent impedance can be in hundreds of M ohms, i.e., it is high enough that it will not affect the resistance of infrared detector element  121  itself. Another advantage of using such a current source is that it does not require high voltages to operate a typical embodiment of such an infrared detector element  121  and its series “load” resistance is typically equal to the dark resistance of such an infrared detector element  121 .  
     [0030] As further shown in FIG. 3, voltage amplifier  615  having sufficiently high input impedance, for example and without limitation, above about 1M ohm, detects the voltage across infrared detector element  121 , and amplifies and filters it so that a difference between the highest and lowest voltage is near the analog input range of analog to digital converter  633 , typically 0-5 VDC. The amplified voltage is applied as input to analog-to-digital converter  633 . In response, analog-to-digital converter  633  converts the input analog signal into a digital signal. In response to a signal from microprocessor  634 , analog-to-digital converter  633  applies the digital signal as input to microprocessor  634  of processor module  700 . Voltage amplifier  615  may be fabricated utilizing any one of a number of such devices that are well known to those of ordinary skill in the art, and analog-to-digital converter  633  may be fabricated utilizing any one of a number of such devices that are well known to those of ordinary skill in the art.  
     [0031] Since, as was described above, the relative angle at which sides of each one of filters  515  and the opaque area are disposed relative to the angle of wheel optical trigger mark  602  (taken, for example and without limitation, as zero degrees) are known, microprocessor  634  obtains measurements from detector element  121  at times when IR radiation impinges upon the filters  515  and the opaque area. As will be described in detail below, these measurements are utilized to determine the concentrations of the gases. In accordance with one or more embodiments of the present invention, to provide raw measurement values, microprocessor  634  obtains a number of measurements, for example and without limitation, 16 measurements, from detector element  121  as each one of filters  515  and the opaque area is rotated in front of the IR radiation. Then, in accordance with one or more embodiments of the present invention, this data is filtered to produce a raw measurement. For example and without limitation, for each one of filters  515  and the opaque area, the first 20% of the measurements obtained during the current rotation of chopper wheel  514  are averaged with the last 80% of the measurements obtained during the previous rotation of chopper wheel  514 . In accordance with one or more such embodiments, the amount of data used from the current revolution and the amount of data from the previous revolution may be varied, for example and without limitation, in response to user input. Further, in accordance with one or more still further embodiments, the raw data measurements may be filtered utilizing any one of a number of methods that are well known to those of ordinary skill in the art.  
     [0032] As further shown in FIG. 3, gas analyzer  600  includes pressure transducer  612  and temperature measuring device  611 , and as shown in FIG. 3, analog signals output from pressure transducer  612  and temperature measuring device  611  are applied as input to auxiliary analog-to-digital converter  632 . In response, analog-to-digital converter  632  converts the input analog signals into digital signals. In response to a signal from microprocessor  634 , analog-to-digital converter  632  applies the digital signals as input to microprocessor  634  of processor module  700 . Microprocessor  634  of processor module  700  uses these signals to measure the temperature and pressure of gas in gas cell  104 , which temperature and pressure are utilized to correct for density changes in the gas due to changes in temperature and pressure in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. This density correction is used to convert the gas concentration to that of the controlled conditions of temperature and pressure utilized during calibration in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. Pressure transducer  612  and temperature measuring device  611  may be fabricated utilizing any one of a number of such devices that are well known to those of ordinary skill in the art.  
     [0033] As shown in FIG. 3, pneumatic pump  629  is connected to gas inlet  122 , and pneumatic pump  629  pumps gas from a user determined origin, for example, a sample gas, into gas cell  104 . Then, infrared radiation output from IR source  518  (after being filtered by one or more of filters  515 ) is absorbed in gas cell  104  to provide infrared radiation having energy that depends upon the concentrations of particular constituents of the gas pumped into gas cell  104 . In accordance with one or more embodiments of the present invention, pump  629  provides a steady flow of gas into gas cell  104  to cause sampled gases to be moved therethrough so that variations in unknown gas concentrations can be measured quickly. As further shown in FIG. 3, pump  629  is driven in response to signals received from pump driver  624 , which pump driver  624  is driven in turn by signals received from microprocessor  634  of processor module  700 . Pump driver  624  may be fabricated utilizing any one of a number of such devices that are well known those of ordinary skill in the art, and pump driver  624  may be driven by microprocessor  634  of processor module  700  utilizing any one of a number of methods that are well known to those of ordinary skill in the art. Pump  629  may be fabricated utilizing any one of a number of such devices that are well known to those of ordinary skill in the art.  
     [0034] As further shown in FIG. 3, flow meter  626  is used to obtain a measure of gas flow into pump  629 . If flow into pump  629  is restricted, gas does not enter gas cell  104  and gas concentrations in the gas cannot be measured or the measurements may be incorrect. In accordance with one or more embodiments of the present invention, flow meter  626  is a gage pressure transducer that is placed, as shown in FIG. 3, at the inlet of pump  629 . As further shown in FIG. 3, analog signals output from flow meter  626  are converted to positive voltages that are amplified, conditioned, and applied as input to auxiliary analog-to-digital converter  632 . In response, analog-to-digital converter  632  converts the input analog signals into digital signals. In response to a signal from microprocessor  634 , analog-to-digital converter  632  applies the digital signals as input to microprocessor  634  of processor module  700 . Microprocessor  634  of processor module  700  uses these signals to measure gas pressure at the inlet to pump  629 . If there is a restriction at the inlet of pump  629 , the gage pressure measured will decrease due to a vacuum created at the inlet, for example, to a value less than atmospheric pressure. In accordance with one embodiment of the present invention, microprocessor  634  treats a pressure value less than a predetermined value to be a blocked inlet, and provides a flow restriction warning. For example, in accordance with one such embodiment of the present invention, microprocessor  634  transmits information to optional display device  643  to cause an appropriate warning such as a blinking signal to be displayed. Flow meter  626  may be fabricated utilizing any one of a number of such devices that are well known to those of ordinary skill in the art.  
     [0035] As further shown in FIG. 3, gas analyzer  600  includes chopper wheel/infrared filter temperature  606 . Output analog signals from chopper wheel/infrared filter temperature  606  are applied as input to auxiliary analog-to-digital converter  632 . In response, analog-to-digital converter  632  converts the input analog signals into digital signals. In response to a signal from microprocessor  634 , analog-to-digital converter  632  applies the digital signals as input to microprocessor  634  of processor module  700 . Microprocessor  634  of processor module  700  uses these signals to measure the temperature of chopper wheel  514 . In an embodiment wherein filter characteristics vary as a function of temperature, the temperature of chopper wheel  514  may be utilized in accordance with any one of a number of methods that are well known to those of ordinary skill in the art to provide corrections which are a function of temperature. Lastly, microprocessor  634  includes a module (not shown) to measure system voltage to enable it to provide an indication such as, for example and without limitation, an alarm in accordance with any one of a number of methods that are well known to those of ordinary skill in the art in case an interruption in power is detected.  
     [0036] As shown in FIG. 3, gas that exits gas cell  104  flows through oxygen cell sensor module  131  that detects the presence of oxygen (“O 2 ”). A suitable oxygen cell sensor module is available from Electrovac GmbH, an Austrian company. According to Electrovac (the oxygen sensor is based on an electrochemical pumping cell made of Zirconium), the principle of operation is as follows: “When voltage is applied to this cell, oxygen ions are pumped through the cell from the cathode to the anode side. By attaching a cap with a pinhole on the cathode side of the cell the current shows saturation due to the rate-limiting step in the transfer to the cathode. This limiting current is nearly proportional to the ambient oxygen concentration.” Thus, the gas stream will produce a current given a constant voltage excitation, which current is proportional to the oxygen concentration. In accordance with this embodiment of the present invention, a trans-impedance (current to voltage) amplifier is used to measure the current produced by oxygen cell sensor module  131  when it is being excited by a constant voltage, and to convert this current into a voltage level suitable for input to an analog-to-digital converter. As such, the output from the amplifier is applied as input to auxiliary analog-to-digital converter  632 . In response, analog-to-digital converter  632  converts the input analog signal into a digital signal. In response to a signal from microprocessor  634 , analog-to-digital converter  632  applies the digital signal as input to microprocessor  634  of processor module  700 . In accordance with one or more embodiments of the present invention, microprocessor  634  transmits information to optional display device  643  to cause the oxygen concentration to be displayed thereon. Alternatively, or in addition, microprocessor  634  may store the oxygen concentration in non-volatile storage  641  and/or on removable storage  645  (to enable future access to any data collected using a computer). Alternatively, or in addition, microprocessor  634  may transmit the oxygen concentration to other devices using transmitter  642  or equipment  646  and  647 . Such options may be input to microprocessor  634  using, for example, and without limitation, keypad  644  utilizing a human interface that may be fabricated utilizing any one of a number of methods that are well known to those of ordinary skill in the art. As such, one or more embodiments of the present invention can provide oxygen concentrations using non-infrared based means with response times comparable to the infrared based concentrations in any output format and in update intervals of less than half of a second. For example, the output can be provided to a user, for example and without limitation, through a display, wired or wireless analog voltage, or wired or wireless binary communication. It should be understood that further embodiments of the present invention exist where oxygen cell sensor module  131  may be any one of a number of oxygen chemical sensor cells that are commercially available from a number of sources.  
     [0037] Tachometer  652  is a device used to measure revolutions per minute (“RPM”) of crankshaft rotation or engine speed. For example, tachometer  652  may measure the rotational rate of a combustion engine by utilizing an inductive pickup that is placed over a spark plug wire. As is well known, the inductive pickup acts as a transformer to produce an EMF or voltage every time the selected spark plug fires (this occurs every other revolution in a four-stroke engine, or every revolution in a two-stroke engine). The voltage will be in the form of a pulse having a relatively short pulse width, and this pulse is amplified and used to trigger a monostable or one-shot trigger. For example, in accordance with one or more embodiments of the present invention, the monostable trigger will increase the trigger pulse width to a predetermined value. In accordance with one or more alternative such embodiments, the inductive pickup may be placed near the main ignition coil. In accordance with one or more further alternative embodiments, tachometer  652  directly senses the alternating current ripple produced by either the ignition system or the alternator/generator used to charge an on-board vehicle battery in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. In any event, as shown in FIG. 3, tachometer  652  outputs a pulse that is applied as input to microprocessor  634 . In response, microprocessor  634  counts the time between pulses in accordance with any one of a number of methods that are well known to those of ordinary skill in the art, and derives the RPM value. Tachometer  652  may be fabricated utilizing any one of a number of such devices that are well known to those of ordinary skill in the art. As such, microprocessor  634  measures the rotational speed of a combustion engine, for example and without limitation, in revolutions per minute (“RPM”). In accordance with one or more embodiments of the present invention, microprocessor  634  transmits information to optional display device  643  to cause the RPM measurement to be displayed. Alternatively, or in addition, microprocessor  634  may store the RPM measurement in non-volatile storage  641  and/or on removable storage  645  (to enable future access to any data collected using a computer). Alternatively, or in addition, microprocessor  634  may transmit the RPM measurement to other devices using transmitter  642  or equipment  646  and  647 . Such options may be input to microprocessor  634  using, for example, and without limitation, keypad  644  utilizing a human interface that may be fabricated utilizing any one of a number of methods that are well known to those of ordinary skill in the art. For example, the output can be provided to a user, for example and without limitation, through a display, wired or wireless analog voltage, or wired or wireless binary communication. In addition, the oxygen concentration measurements described above may be provided in all of the above-described methods to further include a correlation of the rotational speed and the oxygen concentrations.  
     [0038] As shown in FIG. 3, processor module  700  of gas analyzer  600  includes non-volatile memory  641  (for example and without limitation, one or more modules) that is connected to microprocessor  634  in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. Non-volatile memory  641  is used to store operating parameters such as, for example and without limitation, calibration curve constants (to be described below); user preferences such as, for example and without limitation, configuration information, number of gases to be analyzed, display formats, data to store, and the like; adjustable parameters such as, for example and without limitation, the number of filters on chopper wheel  514 , and the like; any dynamic values that need to be preserved; and to store data in accordance with user-specified requests. In accordance with one or more further embodiments of the present invention, complimentary devices such as, for example and without limitation, storage devices or data analyzers, data display devices, and so forth may be attached to or used in conjunction with gas analyzer  600  to attain or enhance information being taken thereby in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. For example, optional display  643  may be used to provide measurement outputs and to provide a user interface in accordance with any one of a number of methods that are well known to those of ordinary skill in the art; optional keypad  644  may be is used to receive user input, for example and without limitation, to set user preferences, to make user requests and so forth in accordance with any one of a number of methods that are well known to those of ordinary skill in the art; RS232 transceiver  642  is used to transmit and receive information from remote devices to perform functions such as, for example and without limitation, data acquisition, data storage, data display, and/or data analysis functions in accordance with any one of a number of methods that are well known to those of ordinary skill in the art; and octal digital-to-analog converter  646  and buffers  647  are used to transmit signals to devices such as, for example and without limitation, analog devices to perform functions such as, for example and without limitation, data acquisition, data storage, data display, and/or data analysis functions in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. Lastly, as shown in FIG. 3, processor module  700  of gas analyzer  600  includes removable storage  645  that is connected to microprocessor  634  in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. Removable storage  645  is used mainly for storage of data that can be transferred manually for use (for example and without limitation, analysis) of stored data such as measurements made utilizing gas analyzer  600 . It should be understood that processing module  700 , as has been explained above, may include at least some form of computer readable media, which computer readable media can be any available media such as, for example and without limitation, computer storage media including volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by microprocessor  634 . Further, it should be understood that processing module  700 , as has been explained above, may include at least some form of communication media such as, for example and without limitation, that embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the above should also be included within the scope of computer readable media.  
     [0039] As further shown in FIG. 3, gas selector driver  625  is driven in response to a selector signal applied as input from microprocessor  634  to activate a gas selector (not shown). In accordance with one or more embodiments of the present invention, gas selector is a switch, for example and without limitation, a solenoid-activated switch, that causes pump  629  to retrieve “zero” gas (i.e., a gas utilized to calibrate gas analyzer  600  in a manner to be described in detail below) or to retrieve “sample” gas (a gas whose constituents are to be analyzed). Microprocessor  634  generates the selector signal in response to user input provided, for example and without limitation, from keypad  644 .  
     [0040] As will be readily appreciated, when gas analyzer  600  is embodied as a portable device, it may not include peripheral devices that might otherwise be present in a general purpose processing system such as, for example and without limitation, a personal computer. However, alternate embodiments of the present invention may include any processing system. For example, other computing systems, environments, and/or configurations that may be suitable for use in fabricating one or more embodiments of the present invention include, but are not limited to, personal computers, server computers, held-held or laptop devices, multiprocessor systems, microprocessor-based systems, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like. One such example includes processing system  710  shown in FIG. 4. As shown in FIG. 4, processing system  710  includes: (a) central processing unit  712 ; (b) a system memory that includes read only memory (“ROM”)  732  and random access memory (“RAM”)  716 ; and (c) system bus  722  that couples various system components including the system memory to processor unit  700 . System bus  722  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus and a local bus using any of a variety of bus architectures. As shown in FIG. 4, a basic input/output interface (“BIOS”) which contains basic routines that help transfer information between elements within processing system  710  is stored in ROM  732 . Additional mass storage devices, and similar memory/data storage modules (not shown), in addition to ROM  732  may be present to provide data storage for computer executable program modules and programs as needed. A number of program modules may be stored on various mass storage devices, ROM  732  or RAM  716 . Generally, program modules include routines, programs, objects, components, data structures, and so forth that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments. One exemplary function of a program module or an application module according to one embodiment of the present invention includes performing a self-test or safety monitoring functions in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. It can be appreciated by one skilled in the art that there are a multitude of different, more or less complex, configurations of a general purpose computing system that may have an embodiment of the present invention embedded within it, such that it need not be shown or discussed herein. Data capture is a method or library of past readings of information taken by the gas analyzer and stored for later evaluation or simulation. As such data capture stores any processed data including, for example and without limitation, all N gas concentrations, oxygen concentration, external values from Add-On devices including but not limited to GPS data for calculating velocity, altitude, and course outline; and accelerometer values. These data may be used to provide correlations between, for example and without limitation, gas concentrations and/or oxygen concentrations correlated as a function of time (for example and without limitation, during particular driving conditions); as a function of particular driving conditions which may be indicated by correlation with GPS data for velocity, altitude and course outline (for example and without limitation, correlation with map information); as a function of driving conditions such as acceleration indicated as a function of accelerometer values, and so forth.  
     [0041] In accordance with one or more embodiments of the present invention, all of the above-described components of gas analyzer  600  are functionally interconnected and controlled by processing modules residing on processor module  700 , which processing modules are executed by microprocessor  634 .  
     [0042] In accordance with one or more embodiments of the present invention, gas analyzer  600  determines concentrations of gases contained in gas flowing through gas cell  104  using the following method which is illustrated in FIG. 5. First, as shown in step  811  of FIG. 5, microprocessor  634  (executing one or more program modules in a manner that is readily understood by those of ordinary skill in the art) determines the speed of rotation of chopper wheel  514  utilizing information received from optical pickup  133  (for example, in the form of pulses) and derives timing therefrom. Next, as shown in step  812  of FIG. 5, based on the speed of rotation of chopper wheel  514  and the predetermined location of filters  515  in chopper wheel  514 , microprocessor  634  (executing one or more program modules in a manner that is readily understood by those of ordinary skill in the art) determines times at which infrared radiation output from IR source  518  will impinge upon each of filters  515  and the opaque area, and reads signals generated by infrared detector element  121  at such times. Next, as shown in step  813  of FIG. 5, microprocessor  634  (executing one or more program modules in a manner that is readily understood by those of ordinary skill in the art) calculates transmittances as a difference between values of the detector signal (for example and without limitation, averages as described above) at times the infrared radiation output from IR source  518  impinges upon filters  515  on chopper wheel  514  and a value of the detector signal (for example and without limitation, averages as described above) at the time the infrared radiation output from IR source  518  impinges upon the opaque area on chopper wheel  514  (“dark value”). Microprocessor  634  (executing one or more program modules in a manner that is readily understood by those of ordinary skill in the art) normalizes these transmittances to a difference between the value of the detector signal (for example and without limitation, averages as described above) at the time the infrared radiation output from IR source  518  impinges upon the (N+1) st  one of filters  515 , i.e., a reference filter, whose filter center frequency is tuned to a region of the infrared spectrum of the infrared radiation output from IR source  518  where none of the gases to be identified will have an absorption spectrum (“reference value”) and the dark value. These values are further normalized and corrected for cross-talk between the gases in a manner that is described in detail below. Next, as shown in step  814  of FIG. 5, microprocessor  634  (executing one or more program modules in a manner that is readily understood by those of ordinary skill in the art) calculates concentrations of N gases using polynomial equations and the transmittances in a manner that is described in detail below, and adjusts for temperature and pressure in a manner that is described in detail below.  
     [0043] Lastly, as shown in step  815  of FIG. 5, optionally, in addition to computing the gas concentrations, microprocessor  634  (executing one or more program modules in a manner that is readily understood by those of ordinary skill in the art) computes one or more of: (a) lambda (as is well known, lambda is a stoichiometric or ideal air-fuel ratio that provides a complete combustion normalized to value of 1.0) in a manner that is described in detail below; (b) air-fuel ratio (AFR) (as is well known, AFR is a ratio of the concentration of oxygen to the concentration of hydrocarbons, i.e., AFR=lambda*14.6; and (c) the RPM of an engine using input from tachometer  652  (in a manner that was described above). In accordance with one or more embodiments of the present invention, all results, including correlations of such results with the RPM measurements, and/or oxygen concentration, are displayed on optional display  643  in any one of a number of formats that are provided in accordance with any one of a number of methods that are well known to those of ordinary skill in the art, and all results, may be optionally communicated to a host system (not shown) via RS232 serial interface  642 , which interface may optionally be a wireless transmission interface in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. Display  643  and serial interface  642  may be fabricated utilizing any one of a number of such devices that are well known to those of ordinary skill in the art.  
     [0044] The following describes an embodiment of gas analyzer  600  that determines the concentrations of HC, CO, and CO 2 . First, measurements made by detector element  121  are applied as input to microprocessor  634  by analog-to-digital converter  633  (ADC  633 ) and filtered as described above to provide raw values: C ref  (a raw value that is obtained with the reference filter in position); C dark  (a raw value that is obtained with the opaque area in position); C HC  (a raw value that is obtained with the hydrocarbon filter in position); C CO  (a raw value that is obtained with the carbon monoxide filter in position); and C CO2  (a raw value that is obtained with the carbon dioxide filter in position) In accordance with one or more embodiments of the present invention, these raw values are expressed in terms of counts out of a possible 2{circumflex over ( )}bits counts, where bits represents the resolution of ADC  633  shown in FIG. 3.  
     [0045] Using these raw values, the following values are determined, which values provide a measure of energy (i.e., a measure of infrared energy that passed through the gas mixture for each of the gases and the reference) and which values are also expressed in terms of counts out of a possible 2{circumflex over ( )}bits counts. These values are determined by subtracting the raw value for the dark or opaque area from the raw value for each filter: E reference =C reference −C dark , E HC =C HC −C dark , E CO =C CO −C dark , and E CO2 =C CO2 −C dark .  
     [0046] Next, transmittance values are determined. Transmittance is the amount of energy transmitted through the gas normalized to 1. The normalization is done against the value for the reference. Thus, a transmittance value of 1 means that all of the energy (100%) output from IR source  518  reached detector element  121 , and none was absorbed by the gas. (HC transmittance) T HC =E HC /E reference , (CO transmittance) T CO =E CO /E reference , and (CO 2  transmittance) T CO2 =E CO2 /E reference .  
     [0047] Because of factors such as filter construction, source temperature, and other uncontrolled parameters, a gas will have a transmittance value that is not exactly 1 even if that gas is 100% of the gas in gas cell  104 . In order to normalize the transmittances to 1, in accordance with one or more embodiments of the present invention, gas analyzer  600  is “zeroed.” The process of “zeroing” gas analyzer  600  comprises purging gas cell  104  with a gas that does not contain any of the gases whose concentration is to be determined (as set forth above, microprocessor  634  sends a signal that is applied as input to gas selector driver  625  and, in turn, gas selector driver  625  sends a signal to a gas selector switch to cause pump  629  to draw gas from the “zero” outlet shown in FIG. 3). For example and without limitation, nitrogen may be used for this purpose. Once gas cell  104  is purged, a transmittance value is recorded and stored, for example and without limitation, in memory  641  for each of the filters. These “zero” values are then used to normalize the transmittances to 1 as follows. (HC normalized transmittance) TZ HC =T HC /T HC(zero) , (CO normalized transmittance) TZ CO =T CO /T CO(zero) , and (CO 2  normalized transmittance) TZ CO2 =T CO2 /T CO2(zero) .  
     [0048] Next, the transmittances are corrected for cross-talk. Ideally, filters  515  are designed so that IR radiation transmitted by the passband of one filter will only be absorbed by one gas and not any others. In practice however, cross-talk occurs where IR radiation transmitted by one filter will be absorbed by more than one gas. As a result, a correction must be made to account for this effect. Such a correction is made as follows. TZ HC =C xtalkHC-CO *T CO +C xtalkHC-CO2 *T CO2 ; TZ CO2 =C xtalkC   O2-HC *T HC +C xtalkCO2-CO *T CO ; and TZ CO =C xtalkCO-HC *T HC +C xtalkCO-CO2 *T CO2 ; where C xtalkHC-CO ; C xtalkHC-CO2 ; C xtalkCO2-HC ; C xtalkCO2-CO ; C xtalkCO-HC ; and C xtalkCO-CO2  are cross-talk coefficients that are determined by calibration using gases having known concentrations of constituents in accordance with any one of a number of methods that are well known to those of ordinary skill in the art.  
     [0049] Next, concentrations of each gas are determined utilizing polynomial coefficients stored during calibration (as described below).  
     [0050] Next, the concentrations determined above are corrected using Boyle&#39;s law to account for the fact that the temperature and pressure of gas in gas cell  104  is different from the temperature and pressure of gas in gas cell  104  during calibration of gas analyzer  600 . For example, in accordance with one or more embodiments of the present invention, the following correction is made, for example, for HC.  
       C   HCcorrected   =C   HC * [( T   meas +273)/ T   calb +273)] γ   *[P   calb   /P   meas ] β   
     [0051] where: T meas  and T calb  are the temperatures during the measurement and calibration, respectively; P meas  and P calb  are the pressures during the measurement and calibration, respectively; and γ and β are constants that are determined in accordance with any one of a number of methods that are well known to those of ordinary skill in the art.  
     [0052] Next, in the last step of determining the concentration, the concentrations are multiplied by a multiplicative factor or “span” that is determined during field calibration (as described below).  
     [0053] As one can readily appreciate, the normalized transmittance for a particular type of gas, in the absence of that gas will always be  1 . Further, the presence of a particular gas in gas cell  104  will reduce the transmittance value from 1 based on an amount that depends on the concentration of the particular gas. However, the reduction in transmittance level for a given concentration of the particular gas can also vary from one gas analyzer to another depending on the length of gas cell  104 , the center frequency of the infrared filters, and the temperature of IR source  518  for the particular embodiment. Given these variations, it may be difficult to predict, with acceptable accuracy, the concentration of each gas. As a result, and in accordance with one or more embodiments of the present invention, a calibration process is used to mitigate these variations by providing information relevant to each particular gas analyzer. This is sometimes referred to as a “factory” calibration process. The factory calibration process is carried out as follows in accordance with one or more embodiments of the present invention. First, pressure transducer  612  is calibrated by: (a) taking a reading of voltage output by pressure transducer  612  at known values of high and low pressure; (b) calculating an offset and slope of a line defined by these two pressure points; and (c) storing the offset and slope in memory, for example and without limitation, non-volatile RAM  641 , that is accessible by microprocessor  634 . Next, transmittance values are obtained for each of filters  515  using, for example and without limitation, N 2  (this is referred to above as “zeroing” the gas analyzer). Next, measured values of transmittance are obtained at predetermined values of concentration (for example, at 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 percent) for a number of gases certified to have specified concentrations of specified gases (for example, Hexane (only take one sample point at 100%), Low Propane, Hi Propane, Low CO, High CO, and CO 2 ). For example, Low CO refers to a specific certified gas having a predetermined low concentration of CO (for example, 1%) and High CO refers to a specific certified gas having a predetermined high concentration of CO (for example,  10 %). Thus, for example, in the case of Low CO, measured values of transmittance are obtained at 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 percent of the predetermined low concentration. Next, a best-fit equation is generated to represent the concentration of a particular gas as a polynomial function of normalized transmittance where the best-fit equation has the form C(T)=A0+A1*T+A2*T{circumflex over ( )}2+A3*T{circumflex over ( )}3+ . . . ; where An represents coefficients derived from a best-fit, T is the normalized transmittance, and C(T) is the concentration of the particular gas at the given normalized transmittance. The best-fit is performed using any one of a number of methods that are well known to those of ordinary skill in the art. In accordance with one or more embodiments of the present invention, polynomials are generated for n=1 up to n=7 for propane, CO and CO 2 , and the polynomial providing the best fit to the data is chosen for each of these gases. Next, the coefficients for the chosen polynomial are stored in memory, for example and without limitation, in non-volatile memory  641  for later use. Then, utilizing a gas having a certified predetermined concentration of hexane, a concentration of the hexane is determined. Next, a hexane:propane equivalency factor (PEF) is determined, and stored in memory, for example and without limitation, in non-volatile memory  641  for later use. The PEF is a multiplicative constant that is used to convert the polynomial obtained using propane to an appropriate polynomial that can be used to determine the concentration of hexane.  
     [0054] In accordance with one or more further embodiments of the present invention, use of gas analyzer  600  may entail the use of a “field” calibration process. In accordance with such further embodiments of the present invention, the field calibration process (sometimes referred to as a “span” operation) entails making measurements of concentrations using a certified gas having predetermined concentrations of particular gases, and then determining a multiplicative factor (sometimes referred to in the art as a “span”) to apply to the final calculation performed by gas analyzer  600 , i.e., after correction for pressure and temperature.  
     [0055] As one can readily appreciate from the above, one or more embodiments of the present invention provide method and apparatus that determine concentrations of one or more gases, including oxygen, that are associated with but which are not limited to emissions from vehicles using internal combustion engines. Further, in accordance with one or more such embodiments, the apparatus provides to a user through a display, wired or wireless analog voltage, or wired or wireless binary communication, the concentrations of such gases. Still further, in accordance with one or more such embodiments, the apparatus provides the concentrations in any output format in update intervals of less than half of a second, for example and without limitation, at a rate of 10 Hz, which rate is limited by the speed of the various elements such as, for example and without limitation, the cycle time of microprocessor  634 .  
     [0056] As is well known, in order to calculate the value of lambda from measurements of combustion by-products in the exhaust of a gasoline engine, a mathematical model is necessary. In accordance with one or more embodiments of the present invention, an equation used to calculate lambda is derived from a model that is commonly referred to in the industry as Brettschneider&#39;s λ equation. In particular, in accordance with one or more embodiments of the present invention, the following algorithm is used. If C(O 2 ) is greater than 0.005, then lambda=1. Otherwise, lambda=N/D, where N=C(CO 2 )+C(CO)/2+C(O 2 )+(1.9*(3.5/(3.5+C(CO)/C(CO 2 ))); and D=1.425*(C(CO 2 )+C(CO)+0.0006*C(HC)).  
     [0057] Although various embodiments that incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.