Abstract:
A hand-held vehicle exhaust analyzer for testing gas content in exhaust emitted from a vehicle is disclosed. The vehicle exhaust analyzer is of a size and weight to be held in a user&#39;s hands. The system includes a housing with an inlet receiving exhaust emitted from the vehicle. A sensor assembly is disposed in the housing, receives the exhaust emitted from the vehicle through the inlet, and determines the content of a plurality of different gases in the exhaust. A control system is disposed in the housing and is operatively coupled with the sensor assembly to regulate operations of the sensor assembly and to receive and interpret results of operations of the sensor assembly. A power supplying apparatus is disposed in the housing to deliver power throughout the system. The housing, and all components disposed in the housing have a combined weight of no greater than about five pounds.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 08/824,895 filed Mar. 26, 1997, now U.S. Pat. No. 5,993,743 issued Nov. 30, 1999, for “Hand-Held Vehicle Exhaust Analyzer ” by J. Nordman, T. Wolf, P. E., J. Neal, T. Liebl and P. Johnson. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a portable, hand-held vehicle exhaust analyzer. 
     Due to government regulations, testing of vehicle exhaust emissions for compliance with minimum standards has become a necessary function for testing facilities and repair garages. Originally, only hydrocarbons and carbon monoxide had to be measured, but stricter standards have added oxygen and carbon dioxide, and still stricter regulations require oxides of nitrogen to be measured as well for compliance with statutory requirements. If a vehicle fails an emission test, it must be repaired. In the repair process, a mechanic must be able to tell whether the repairs have affected the content of the exhaust gas that was at an unacceptable level during the emission test. Therefore, there is a need for a vehicle gas analyzer that can be used by repair technicians to determine whether their repairs have remedied emission test failures. 
     Large platform engine analyzers were initially developed to measure gases emitted in vehicle exhaust. These platform engine analyzers were large devices that were transported by wheeling them around on a large cart. These large engine analyzers are typically utilized by government agencies to perform actual emission tests on vehicles, but their size and considerable expense make them difficult for smaller repair garages to own. 
     “Portable ” exhaust gas analyzers were subsequently developed to be used for repair purposes. While portable exhaust gas analyzers are smaller than the larger platform analyzers used previously, they still weigh over thirty pounds, and are too large to be held in the hands of a user during operation. The units contain a large heater, since the infrared sensing equipment in these units operates at a temperature greater than ambient temperature. Typically a chopper motor is employed to serve as a zero reference for infrared sensors operating in the analyzers. A large pump is also required to advance high volumes of exhaust gas through the analyzer. These components draw a large amount of power, compelling the implementation of a large power supply within the analyzer, take significant amounts of space, and generate substantial heat, necessitating the use of metal throughout the analyzer and reducing the analyzer&#39;s “portability”. In addition, it is often difficult to remove and replace the parts of the analyzer, such as filters or the pump, which regularly wear out. 
     Therefore, there is a need for an improved portable exhaust gas analyzer, such as a hand-held vehicle gas analyzer, which is of a size and weight to be carried easily by a user, while still performing the same functions of sampling and sensing gas content in vehicle exhaust as previous exhaust gas analyzers. 
     SUMMARY OF THE INVENTION 
     The present invention is a hand-held vehicle exhaust analyzer for testing gas content in exhaust emitted from a vehicle. The vehicle exhaust analyzer is of a size and weight to be held in a user&#39;s hands. The analyzer includes a housing having an inlet for receiving exhaust emitted from the vehicle under test. A sensor assembly is disposed in the housing and receives the exhaust emitted from the vehicle through the inlet, typically filtered to remove solid and liquid matter from the exhaust. The sensor assembly determines the content of a plurality of different gases in the exhaust emitted from the vehicle. A control system is disposed in the housing and is operatively coupled with the sensor assembly to regulate operations of the sensor assembly and receive and interprets results of operations of the sensor assembly. A power supplying apparatus is disposed in the housing, and receives power from a source located externally from the housing and delivers power throughout the vehicle gas analyzing system. The housing and all components disposed in the housing have a combined weight of no greater than about five pounds. 
     According to one aspect of the vehicle gas analyzing system, the sensor assembly functions at ambient temperature. The sensor assembly comprises an infrared sensor operating on the exhaust to determine the content of carbon monoxide, carbon dioxide and hydrocarbons in the exhaust, and chemical sensors operating on the exhaust to determine the content of oxygen and oxides of nitrogen in the exhaust. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective view of the hand-held vehicle gas analyzer of the present invention. 
     FIG. 2 is a rear perspective view of the hand-held vehicle gas analyzer shown in FIG.  1 . 
     FIG. 3 is a bottom perspective view of the hand-held vehicle gas analyzer shown in FIG.  1 . 
     FIG. 4 is an exploded assembly diagram of the hand-held vehicle gas analyzer shown in FIG.  1 . 
     FIG. 5 is a perspective view showing the sensor assembly depicted in FIG. 4 in more detail. 
     FIGS. 6 ( a-c ) are a perspective view showing the filter assembly depicted in FIG. 4 in more detail. 
     FIG. 7 is a block diagram of the functional elements of the hand-held vehicle gas analyzer shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a front perspective view of a portable, hand-held vehicle gas analyzer  10  according to the present invention. Gas analyzer  10  has a housing  12 , keyboards  14   a  and  14   b , and display  16 , and accepts exhaust gas samples from sample hose  17 . Housing  12  is preferably composed of a polymeric material, in order to provide sufficient strength with minimal weight. Housing  12  is preferably about 12 inches by 8 inches, and about 3 inches thick, so that it can be easily held in the hands of a user. Keyboards  14   a  and  14   b  each include a number of keys, such as cursor control keys  15   a  and  15   b , exit keys  18   a  and  18   b , enter keys  20 a and  20   b , function keys  22   a  and  22   b , and help keys  24   a  and  24   b . The number of keys and the functions of keys may be varied according to design preferences. Display  16  is preferably a liquid crystal display (LCD). Display  16  may optionally be backlit, and in an alternative embodiment may accept tactile input from a finger or stylus. Sample hose  17  preferably has an inside diameter of about one-eighth of an inch. 
     Keyboards  14   a  and  14   b  and display  16  are disposed on a top surface of housing  12 . In the embodiment shown in FIG. 1, keyboard  14   a  is positioned on the left side of display  16 , and keyboard  14   b  is positioned on the right side of display  16 , to accommodate both left- and right-handed users. In operation, a user enters commands and test parameters through keyboard  14   a  or  14   b , and views instructions and exhaust gas analysis on display  16 . 
     FIG. 2 is a back perspective view of the portable, hand-held vehicle gas analyzer  10  of the present invention. Gas analyzer  10  includes housing  12 , keyboards  14   a  and  14   b , and display  16 , and accepts exhaust gas samples from sample hose  17 . Housing  12  has a back surface which includes, arranged from right to left in FIG. 2, exhaust inlet nipple  19 , D-subminiature 9-pin connector  28 , D-subminiature 9-pin plug (DB9P) connector  30 , power connector  32 , and exhaust outlet  34 . Alternatively, exhaust outlet  34  may be located on a side surface of housing  12 . 
     Exhaust inlet nipple  19  makes a sealed connection to sample hose  17  so that exhaust gas from sample hose  17  may enter housing  12 . DB9S connector  28  allows gas analyzer  10  to be connected to a personal computer (not shown). DB9P connector  30  allows gas analyzer  10  to be connected to an external printer or modem (not shown). Power connector  32  allows gas analyzer  10  to be connected to an external power source (not shown). Exhaust outlet  34  serves as an escape path for exhaust gas that has passed through housing  12 . 
     FIG. 3 is a bottom view of the portable, hand-held vehicle gas analyzer  10  of the present invention. Gas analyzer  10  includes housing  12 , which includes access panel  36  to cover a cavity in the housing that contains the internal components of the gas analyzer, and exhaust gas samples are input to the housing through sample hose  17 . Housing  12  includes recessed hand grips  37  for ease of handling by a user, and also includes a recess  38  in which filter assembly  40  sits. Filter assembly  40  is shown in FIG. 6, and will be described in more detail later with reference to FIG.  6 . The design of access panel  36  and recess  38  allows a user to easily access internal components and filter assembly  40  of the gas analyzer, so that parts may be easily accessed and replaced. 
     FIG. 4 is an exploded assembly drawing of the portable, hand-held gas analyzer  10 , which is inverted and shows the internal and external parts of the gas analyzer. Gas analyzer  10  includes, from top to bottom in FIG. 4, access panel  36 , bottom housing  42 , sensor assembly  44 , controller printed circuit board (PCB)  46 , display  16 , lens  47 , filter assembly  40 , top housing  48 , and keyboard membranes  14   a  and  14   b . 
     Access panel  36  includes a quarter-turn connector  51  to provide for latching and unlatching of access panel  36 , to open and close access to the inside of the housing. Bottom housing  42  includes notches  52 ,  54 ,  56 ,  58  and  60  to accommodate exhaust inlet  19 , DB9S connector  28 , DB9P connector  30 , power connector  32 , and exhaust outlet  34 , respectively. Exhaust inlet nipple  19  provides a sealed path for exhaust to travel from a sample hose into the housing, and nipple fitting  61  provides a sealed path for exhaust to travel from filter assembly  40  to sensor assembly  44 . Bottom housing  42  also includes recess  38  to allow access to filter assembly  40 . 
     Sensor assembly  44  is shown in FIG. 5, and will be described in detail later with respect to FIG.  5 . Controller PCB  46  includes a cable assembly  62  for connecting controller PCB to sensor assembly  44 , and contains the control and power supply circuitry to operate gas analyzer  10 . Controller PCB  46  has DB9S connector  28 , DB9P connector  30 , and power connector  32  mounted thereon. The functional components of controller PCB  46  are shown in FIG. 7, and will be discussed in more detail later with respect to FIG.  7 . 
     Top housing  48  includes notches  64 ,  66 ,  68 ,  70  and  72  to accommodate exhaust inlet  19 , DB9S connector  28 , DB9P connector  30 , power connector  32 , and exhaust outlet  34 , respectively. Top housing  48  also includes an aperture  74  through which display  16  can be viewed through lens  47 . 
     Bottom housing  42  and top housing  48  are joined by screws  76  to form a housing to seal gas analyzer  10 . Access panel  36 , in its closed position, seals the internal components of the gas analyzer inside the housing. Sensor assembly  44  is mounted to top housing  48  by three screws  78 . Sensor assembly  44  sits inside the housing of gas analyzer  10  directly adjacent access panel  36 , so that the parts of sensor assembly  44  may be easily accessed and replaced by a user by simply opening access panel  36 . Controller PCB  46  is mounted to top housing  48  by four screws  80 , and is connected by cable assembly  62  to sensor assembly  44 . Display  16  is mounted to top housing  48  by four screws  82 . Lens  47  is positioned between display  16  and top housing  48 , to protect display  16  and allow viewing of the display through lens  47 . Filter assembly  40  is anchored to top housing  48 , and sits in recess  38  in bottom housing  42  so that it may be easily accessed and replaced by a user. Keyboard membranes  14   a  and  14   b  are mounted on the outside of top housing  48 , providing an interface for a user to input instructions to gas analyzer  10 . 
     The entire hand-held gas analyzer  10 , including all the components within the housing, has a weight of less than about five pounds, and the dimensions of the outer housing are preferably about 12 inches by 8 inches by 3 inches, so that the gas analyzer may be easily held in the hands of a user. 
     FIG. 5 is a perspective view showing in detail the parts of sensor assembly  44 . Sensor assembly  44  may preferably be a gas bench such as Part No. 886600-000 manufactured by Andros, Inc., and includes pump assembly  84 , infrared source  86 , sample tube  88 , optical block  90 , nitrous oxide (NOx) sensor  92 , and oxygen (O 2 ) sensor  94 . Sensor assembly  44  must be designed to fit inside a cavity in the housing of the gas analyzer, underneath the access panel in the bottom of the housing. 
     In one embodiment, exhaust is received into sensor assembly  44  by pump assembly  84 , which operates to deliver exhaust into sample tube  88 . While the exhaust is in sample tube  88 , infrared source  86  generates infrared light which travels through the exhaust in sample tube  88 , and is reflected into optical block  90 . The content of various gases (such as carbon monoxide, carbon dioxide, and hydrocarbons) can be determined by the response of different wavelengths of infrared light as they pass through the exhaust, as is known in the art. A zero reference is provided by a separate beam of infrared light, so that a chopper motor to repeatedly block the infrared sensing beam for a zero reference is not required. Exhaust then passes into NOx sensor  92  and O 2  sensor  94 , which are chemical sensors operable to determine the content of the respective gases in the exhaust. In this way, the content of five gases (as required in many government emissions programs) in exhaust emitted from a vehicle is determined. Exhaust then exits sensor assembly  44  and is eventually released from gas analyzer  10  through exhaust outlet  34 . 
     Sensor assembly  44  has a weight such that the weight of the entire gas analyzer  10  does not exceed about five pounds. Sensor assembly  44  preferably operates at ambient temperature, so that the housing of the gas analyzer can be composed of a polymeric material, which could not withstand high temperatures caused by a heater in the sensor assembly. Sensor assembly  44  is also designed to draw a small amount of power (preferably about 6 watts), so as not to require a large power supply which would destroy the portability of the gas analyzer  10 . Prior gas analyzers required a heater to take thermally stable gas readings, which necessitated a large power supply and metal construction. The absence of a heater in gas analyzer  10  allows the housing to be composed of a polymeric material, reduces the overall size and weight of gas analyzer  10 , and reduces the total power required by gas analyzer  10 , so that the power supply need only deliver about 8 watts of total power. Sensor assembly  44  preferably has a sample rate of less than about one liter per minute, so that a sample hose with as small as one-eighth of an inch inner diameter may be used, and a low power pump assembly may be used. 
     Parts of the sensor assembly such as the sample tube  88 , nitrous oxide sensor  92 , oxygen sensor  94  and pump assembly  84  can be easily replaced by a user, by accessing the sensor assembly  44  through access panel  36  on the bottom of the housing  12 . These parts are easily detachable from the sensor assembly  44 , and may be individually removed and replaced. 
     FIG. 6A shows a detailed perspective view of filter assembly  40 , showing the filter unscrewed from the filter manifold, FIG. 6B shows a cross-sectional view of the filter, and FIG. 6C shows a top view of the filter manifold. Filter assembly  40  includes manifold  96  and filter  97 . Manifold  96  includes inlet fitting nipple  19 , outlet hole  107 , threaded inlet hole  100 , and outlet nipple fitting  61 . Filter  97  includes threaded inlet  10   2 , filter body  104 , inner inlet holes  99 , outer chamber  105 , inner chamber  101 , hydrophilic filter  108 , and drain plug  106 . Threaded inlet  102  includes passage  103  therethrough. Filter  97  attaches to filter manifold  96  by engaging threaded inlet  102  into manifold hole  100 , and outer O-ring  98  of filter  97  seals against manifold  96 , so that outlet hole  107  is inside outer O-ring  98 . Drain plug  106  is provided to allow the filter to be emptied by a user when desired. 
     In operation, exhaust enters manifold  96  through inlet fitting nipple  19 . The exhaust travels through the labyrinth inside manifold  96 , up through outlet hole  107  in manifold  96 , and into filter  97  inside outer O-ring  98 . Manifold  96 , since it is made of metal, provides a cold point to condense moisture out of the exhaust. Once exhaust enters filter  97  inside outer O-ring  98 , it courses through the gap area in filter  97  and passes into outer chamber  105  through inner inlet holes  99 . While any number of inner inlet holes  99  may be provided, four is a preferred number. The exhaust then circulates through filter  108  into central chamber  101 . Filter  108  is preferably a hydrophilic membrane operating to remove both dirt and moisture from the exhaust. The filtered exhaust proceeds through passage  103  in threaded inlet  102  back into manifold  96 , and is outlet from manifold  96  through outlet nipple fitting  61  to be operated on by the sensor assembly. Drain plug  106  seals filter  97 , specifically outer chamber  105 , regardless of angular orientation of the gas analyzer  10 , so that moisture and dirt does not spill into sensor assembly  44  or other circuitry in gas analyzer  10  when gas analyzer  10  is held at an angle. Drain plug  106  is readily removable from its sealed position by a user, so that filter  97  can be drained of moisture and dirt at any time. Filter assembly  40  preferably sits in a recess in the back of the housing of the gas analyzer, so that its parts can be easily accessed. 
     FIG. 7 is a block diagram showing the logical electrical components of the portable, hand-held gas vehicle gas analyzer  10 . Gas analyzer  10  includes keyboards  14   a  and  14   b , display  16 , controller PCB  46 , sensor assembly  44 , filter assembly  40 , power port  32 , inlet port nipple  19  and outlet port  34 . A vehicle  110  under test includes a cigarette lighter receptacle  112  and a tailpipe  114 . 
     Controller PCB  28  includes DC power jack  116 , power supply circuit  118 , microcontroller  120 , one-time programmable read-only memory (OTPROM)  122 , flash memory  124 , static random access memory (SRAM)  126 , Dual Universal Asynchronous Receiver-Transmitter (DUART)  128 , realtime clock  130 , battery  132 , beeper  133 , RS-232 transceiver  134 , DB9S connector  28 , DB9P connector  30 , and header/harness  136 . Sensor assembly,  44  includes sample cell  88 , pump assembly  84 , NOx sensor  92 , O 2  sensor  94 , and sensor assembly controller  138 . 
     Display  16  may for example be a graphic LCD assembly including a backlight and PCB harnesses. Keyboards  14   a  and  14   b  may also include PCB harnesses. Display  16  is communicatively coupled to controller  28 . Keyboard  14  is also communicatively coupled to controller  28 . Display  16  and keyboard  14  together make up a user interface, allowing a user to input instructions and view results of operations of the gas analyzer. 
     Power is provided to gas analyzer  10  by either cigarette lighter receptacle  112  in vehicle  110  being tested, or by wall adapter  140 . 12-volt DC power is routed through plug  142  to gas analyzer  10  via power port  32 . Exhaust gas from vehicle  110  is emitted through tail pipe  114  to sample probe/hose  17 , which connects to nipple  19  to enter the gas analyzer. The exhaust then enters filter assembly  40  which operates to filter dirt and condensation from the exhaust. Exhaust then proceeds to sensor assembly  44 , and specifically to pump  84 . Pump  84  distributes the filtered exhaust to sample cell  88 , NOx sensor  92  and O 2  sensor  94 , for analysis of gas content in the exhaust. The sample rate is preferably less than about one liter per minute, enabling use of a small sample hose such as one-eighth inch inner diameter tubing and a low power pump assembly  84 . Sensor assembly  44  is controlled by its controller PCB  138  and its associated circuitry. Sensor assembly controller  138  also operates to communicate with the rest of gas analyzer  10 , through header/harness  136 . 
     Main controller PCB  46  operates to regulate operation of the gas analyzer  10 . Specifically, DC powerjack  116  receives external power through plug  142 . The power is delivered to power supply circuit  118 , which distributes power throughout the gas analyzer. Power is directly distributed to display  16  as 5V, −24V, adjust and 80 V signals, and to sensor assembly  44  as 5V, 12V, −12V and pump 12V signals. Power supply  48  supplies 5-volt and reset signals that are used by the circuitry contained within the controller  46 . Power supply  118  delivers 8 watts of total power to the gas analyzer  10  to power its operation. Preferably 6 watts are delivered to sensor assembly  44 , and 2 watts are delivered to the remainder of gas analyzer  10 . 
     Microcontroller  120  operates to control the various circuitry elements in the controller  46 . Microcontroller  120  may, for example, be a 68331 microprocessor manufactured by Motorola Corporation. Microcontroller  120  delivers control signals and receives input signals from display  16 , keyboards  14   a  and  14   b , OTPROM  122 , flash  124 , SRAM  126  and DUART  128 . Realtime clock  130  communicates with microcontroller  120  via the serial peripheral interface (SPI) of microcontroller  120  and provides an automatic time stamp for events recorded by the gas analyzer  10 . Battery  132  maintains power to realtime clock  130  when no power is delivered to gas analyzer  10 . Beeper  133  is connected to microcontroller  120  and is controlled to sound when certain events demanding a user&#39;s attention occur. RS-232 transceiver  134  conditions signals to and from microcontroller  120  via the serial communication interface (SCI) of microcontroller  120 . DUART  128  is coupled to microcontroller  120  and to RS-232 transceiver  134 , and along with RS-232 transceiver  134  provides an interpreting interface so that microcontroller  120  can communicate in RS-232 format. SRAM  126  is connected to microprocessor  120 , and contains temporary memory for program execution to operate the gas analyzer  10 . OTPROM  122  contains the boot code that is required for the gas analyzer  10  to power up. Flash memory  124  contains additional application code to be executed in operation of the gas analyzer  10 . Memory is divided in this fashion so that static code that does not need to undergo revisions is saved in a static memory such as OTPROM  122 , while dynamic code that is periodically revised can be changed by updating flash memory  124 . DB9S connector  28  and DB9P connector  30  are provided to allow connection to an external personal computer (PC) or to a printer or modem, respectively. PC bypass line  144  is provided to allow direct communication between sensor assembly  44  and an external PC. 
     In operation, a user manually couples sample hose/probe  17  to tailpipe  114  of vehicle  110 , and inserts the opposite end of sample hose/probe  17  into gas analyzer  10  through nipple  19 . Preferably, the user has previously calibrated gas analyzer  10  by connecting to a sample gas canister with known gas content and placing gas analyzer  10  in calibration mode by inputting appropriate instructions via keyboard  14   a  or  14   b . Exhaust from tail pipe  114  travels through sample hose/probe  17  and nipple  19  into filter assembly  40 . Filter assembly  40  operates to filter dirt and condensation from the exhaust. The filtered exhaust then travels into sample cell  88 , where the content of carbon monoxide, carbon dioxide and hydrocarbons is determined. Pump  84  then advances the exhaust into NOx sensor  92  and O 2  sensor  94 . Exhaust then exits gas analyzer  10  via nipple fitting  61  through exhaust outlet port  34 . 
     While the exhaust is being tested within sensor assembly  44 , controller  46  operates to convert raw data obtained by sensor assembly  44  and interpreted by sensor assembly controller  138  into useful vehicle diagnostic values such as air/fuel ratio (AFR), lambda values, and average mass values. Data from sensor assembly  44  (and specifically from sensor assembly controller  138 ) is communicated to controller  46  through header/harness  136 , and is interpreted by RS-232 transceiver  134 . RS-232 transceiver  134  communicates with microcontroller  120  by the serial communication interface (SCI) of microcontroller  120  and through DUART  128  connected to microcontroller  120 . Software for converting the data into usable values and for display formatting, etc., resides in flash memory  124  coupled to microcontroller  120 . The software includes user interfacing, menus to direct a user in operating the gas analyzer  10 , error messages, and the order in which operations occur. The software also preferably includes diagnostic algorithms to direct a repair technician in working on the vehicle under test. Data from sensor assembly  44  interpreted and converted by microprocessor  120  is updated on display  16  four times per second for viewing by a user. The data may be displayed as digital numerals or graphically, for example. Other software necessary for operation of gas analyzer  10  resides in OTPROM  122  and SRAM  126 , which are nonvolatile memories. 
     The software in flash memory  124  can be updated directly by downloading via a modem. DB9P connector  30  allows connection to a modem. A user purchasing a product such as gas analyzer  10  may also purchase certificates having a number that allows access to a remote bulletin board system which makes software updates available. Other security measures such as the serial number of the particular gas analyzer  10  may be stored in nonvolatile memory to ensure that software updates are only downloaded to authorized users. Updated software is downloaded by modem through RS-232 transceiver  134  and DUART  128 , and operates to re-flash memory  124  to contain the updated software. 
     The gas analyzer may alternatively operate in a mode utilizing PC bypass  144 . In this mode, when an external PC is coupled to gas analyzer  10  via DB9S connector  28 , RS-232 transceiver  134  “shuts off” communication with header/harness  136  and sensor assembly  44 . Sensor assembly  44  communicates directly with the external PC through header/harness  136  and PC bypass  144 . Although sensor assembly  44  does not communicate data with controller  46  in this mode, power is still provided to sensor assembly  44  through header/harness  136  from power supply circuit  118 . 
     Communication between sensor assembly  44  and the external PC through PC bypass  144  is in RS-232 format. Signal conditioning, formatting, and other software operations are performed by the external PC, so that data from sensor assembly  44  can be interpreted and converted into useable values for vehicle diagnostics. Because of the vast memory available for storing and executing software, and potentially superior display capabilities, it is occasionally desirable to utilize PC bypass  144  to analyze and/or display real-time parameters sensed by sensor assembly  44 . 
     The external PC may also be used in conjunction with the normal operation of gas analyzer  10 , wherein sensor assembly  44  is communicating data with controller  46  through header/harness  136  and RS-232 transceiver  134 . The external PC may monitor the conditioning of signals from sensor assembly  44 , along with other operations of controller  46 . In another configuration, controller  46  may store data received from sensor assembly  44  as an event, and download the event data to the external PC in a batch mode, for further analysis by the external PC. 
     The portable, hand-held vehicle gas analyzer  10  described above is of a size and weight to be easily held in the hands of a user. The gas analyzer preferably weighs less than about five pounds, and preferably has outer dimensions of about 12 inches by 8 inches by 3 inches. The housing of the gas analyzer is preferably composed of a polymeric material, which is possible because the sensor assembly in the gas analyzer operates at ambient temperature. The sensor assembly also does not require a chopper motor, and draws only about 6 watts of total power. Gas analyzer  10  therefore provides full functionality, measuring the content of up to five gases in exhaust emitted from a vehicle under test and displaying the results of its analysis, in a lightweight, hand-held package. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.