Abstract:
A portable stress monitor is provided for monitoring conditions under which physiological activity is occurring. The conditions monitored may be environmental, such as ambient temperature and humidity, or physiological, such as heart rate or body temperature. The monitor includes a main body portion and a hinged cover. The hinged cover includes a removable sensor module. One or more sensors are attached to the sensor module, each sensor may be pivotally mounted on a mast, such that the sensors extend outwardly from the hinged cover when the sensor module is in the deployed position and may be pivoted to sit substantially flush with the hinged cover when the sensor module is in the storage position. A central processing unit is contained within the main body, and is operable to process data acquired by the sensors according to a heat strain algorithm. A display is attached to the outer surface of the main body for providing read out information, and an input device is provided for user input.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority from provisional application Ser. No. 60/182,051 filed Feb. 11, 2000. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
         [0002]    Not Applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    The invention relates generally to the filed of environmental data acquisition systems, and particularly to portable environmental heat stress monitors that can be used to monitor the effects of exposure to extreme environmental conditions.  
           [0005]    2. Description of Related Art  
           [0006]    Military leaders, industrial managers and athletic trainers are all confronted with the problem of achieving high productivity or performance and safeguarding health under conditions of high heat or heat stress. Heat stress is the aggregate of all environmental and physical work factors that impose a heat load on the body. The environmental factors of heat stress include the air temperature, radiant heat, air movement, relative humidity and barometric pressure. Physical work contributes to the aggregate by producing metabolic heat in the body in direct proportion to the intensity of activity. The amount and type of clothing also can affect the heat load.  
           [0007]    Several methods have been developed to index the conditions that lead to heat stress. Of these, the Web Bulb Globe Temperature (WBGT) is a popular measure in use in military, government and industrial arenas. The WBGT index is relatively simple to compute. It is defined by:  
             WBGT= 0.7( WB )+0.2( GT )+0.1( DB )  
           [0008]    where:  
           [0009]    WB=natural wet-bulb temperature  
           [0010]    GT=6-inch diameter black Vernon-globe temperature (indicating radiant heat)  
           [0011]    DB=shaded dry-bulb temperature  
           [0012]    For indoor use involving radiant heat sources other than direct solar radiation, the equation modifies to:  
             WBGT   indoors =0.7( WB )+0.3( GT )  
           [0013]    Guidelines for determining work/rest schedules or protective measures for persons exposed to heat stress conditions, based on the WBGT index have been used in government and industry. However, the major use of WBGT measurements is in evaluation and quantification of the environment in industries such as aluminum production, steel production, foundry work, and the chemical and refinery fields where workers are routinely exposed to high radiant and convective heat. With accurate index to heat-stress levels, worker comfort and health can be assured while maintaining peak productivity and efficiency.  
           [0014]    While the WBGT has proved to be a workable index, there are several factors that contribute to heat stress that are not accounted for by the WBGT index. Therefore, there is a need for a more comprehensive measure for heat stress.  
           [0015]    Heat stress often affects workers in isolated locations, e.g., the battlefield, oil rigs, in mine shafts, in quarries etc. Accordingly, it is desirable to have a portable measurement device so that measurements can easily be taken in locations that are not readily accessible. Previous monitoring devices have sensors that are mounted to a tripod and attached to a separate display units by cables. This can limit their use to areas that can physically accommodate such equipment. Other devices use individual sensors that directly attach to the display unit, and are removed and placed in a protective case for storage. There is a need for a portable, self contained device that may be carried and operated by a worker without additional accessories.  
         SUMMARY OF THE INVENTION  
         [0016]    One embodiment of the invention may be realized by a portable stress monitor for monitoring conditions under which physiological activity is occurring. The conditions monitored may be environmental, such as ambient temperature and humidity, or physiological, such as heart rate or body temperature. The monitor includes a main body portion and a hinged cover. The hinged cover includes a removable sensor module. One or more sensors are attached to the sensor module, each sensor may be pivotally mounted on a mast, such that the sensors extend outwardly from the hinged cover when the sensor module is in the deployed position and may be pivoted to sit substantially flush with the hinged cover when the sensor module is in the storage position. A central processing unit is contained within the main body, and is operable to process data acquired by the sensors according to a heat strain algorithm. A sensor electronics circuit is contained within the sensor module, and is operable to perform sensor-related functions, such as signal conditioning and A/D conversion. A display is attached to the outer surface of the main body for providing read out information, and a keypad is provided for user input.  
           [0017]    An advantage of the heat/stress monitor according to the present invention is that tailored heat stress management guidance is provided based on clothing worn, acclimatization status and work level.  
           [0018]    Another advantage of the heat stress monitor according to the present invention is that the sensor suite and the central processor permit flexible implementation of additional physiological models or supplemental environmental stress parameters. More particularly, this invention permits facile adjustment of the heat strain algorithm.  
           [0019]    Still a further advantage of the invention is the removable sensor module allows rapid replacement of the sensors as a single unit for repair and calibration. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES.  
       [0020]    [0020]FIG. 1 is a block diagram of the heat stress monitor in accordance with the present invention.  
         [0021]    [0021]FIG. 2 is a computational diagram of a preferred heat strain algorithm in accordance with the present invention.  
         [0022]    [0022]FIG. 3 is a side view of an embodiment of the heat stress monitor of the invention illustrating the sensors in a deployed position.  
         [0023]    [0023]FIG. 4 is a top view of the embodiment shown in FIG. 3 depicting the sensors in a storage position.  
         [0024]    [0024]FIG. 5 is a side cut away view of the embodiment shown in FIG. 3 illustrating the sensors in a storage position and illustrating the system for coupling the sensors to the body.  
         [0025]    [0025]FIG. 6 is an exploded view of a sensor coupling system in accordance with the invention showing the mast and the cuff.  
         [0026]    [0026]FIG. 7 is an exploded view of the sensor coupling system of FIG. 6 illustrating only the cuff.  
         [0027]    [0027]FIG. 8 depicts the wind speed sensor and the dry bulb sensor in a storage position.  
         [0028]    [0028]FIG. 9 is a perspective front view of the stress monitor, with the sensor module in the “deployed” position.  
         [0029]    [0029]FIG. 10 is a perspective rear view of the stress monitor of FIG. 9.  
         [0030]    [0030]FIG. 11 is a perspective view of the sensor module of FIGS. 9 and 10.  
         [0031]    [0031]FIG. 12 is a perspective front view of the assembled main body of FIGS. 9 and 10.  
         [0032]    [0032]FIG. 13 is a block diagram of the main electronics contained within the main body.  
         [0033]    [0033]FIG. 14 is a block diagram of the sensor electronics contained within the sensor module. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    The apparatus, systems and methods of the present invention may be used for monitoring environmental conditions. A better understanding of the several embodiments of the invention and their use for monitoring environmental conditions will be achieved by reading the following description in conjunction with the above-incorporated references.  
         [0035]    The present invention encompasses a compact, self-contained monitor that measures environmental conditions and calculates related safety factors and environmental stress parameters. The monitor preferably includes a main body and a sensor module. The sensor module preferably includes a number of environmental sensors including an atmospheric pressure sensor, a humidity sensor, an air temperature sensor, a wind speed sensor, and a solar radiation sensor. The sensor module is preferably releasably engaged with the main body such that the sensor module may be movable between a deployed position and a storage position and such that the sensor module may be readily replaced according to the intended use of the environmental monitor.  
         [0036]    The sensor module may be provided with circuitry required to operate the various sensors. For example, the sensor module may be provided with A/D and D/A converters for processing current and voltage generated and/or required by the sensors and a memory device that stores calibration information for the sensors.  
         [0037]    The main body may include a main processor for operating the monitor, a display for exhibiting input parameters, a central processing unit for computing safety factors and environmental stress parameters using manually input as well as measured environmental parameters. In some embodiments, the main body may include a communication port for facilitating communication with a local or remote server.  
         [0038]    In other embodiments the central processing unit may be separate and distinct from the maim body and, for example, disposed in a server that communicates with the main body.  
         [0039]    In accordance with preferred aspect of the invention, the central processing unit may be programmed according to a heat strain prediction model to calculate selected environmental safety factors e.g., work/rest cycle limits, hourly drinking water requirements and maximum safe work times. These selected environmental safety factors may be calculated based upon inputs from the environmental sensors as well as manual inputs from a user and/or remote inputs from a server, e.g., type of clothing worn by subject, work rate, and acclimatization status.  
         [0040]    [0040]FIG. 1 illustrates an environmental data monitor in accordance with a preferred embodiment of the invention. A sensor module  10   b  is provided with a plurality of sensors including a dry bulb sensor  33 , a relative humidity sensor  34 , a globe sensor  35  and a wind speed sensor  36 . In addition, sensor module  10   b  also includes an atmospheric pressure sensor  37  not illustrated in FIG. 1. Sensors  33 - 37  each collect data to be transmitted to a central processing unit  110 . Each of the sensors  33 - 37  and central processing unit  110  are described in greater detail below in connection with specific embodiments of the invention. Sensor module  10   b  further includes sensor electronics  60  which may comprise signal conditioning circuitry  100  and collection and processing circuitry  105 . Signal conditioning circuitry  100  preferably converts signals transmitted and received by the sensors to a form usable by other system circuitry. Collection and processing circuitry  105  includes a suitable memory device that stores information unique to sensors  33 - 37 . For example, collection and processing circuitry  105  may store calibration information related to sensors  33 - 37  and facilitate recalibration. While it is preferable that sensor electronics  60  be included in sensor module  10   b , in other embodiments, sensor electronics may be disposed in main body  10   a.    
         [0041]    In some embodiments, a graphical display  57  may be disposed in main body  10   a . Display  57  is preferably provided with a menu that allows a user to select parameters to be input to central processing unit  110 . In accordance with the invention, the menu allows the user to select parameters related to environmental stress for input to central processing unit  110 . Display  57  is preferably a backlit LCD display of the type generally known to those of skill in the art.  
         [0042]    In other embodiments, no display is provided with main body  10   a . In these embodiments, a user may input environmental stress parameters at a remote location and those parameters may be transmitted to environmental monitor  10  by any method of signal transmission. For example, the signals may be transferred wirelessly, via the Internet, through a direct modem connection, via satellite, via spread spectrum techniques, or via optical communication links.  
         [0043]    In keeping with an aspect of the invention, environmental monitor  10  may be provided power management circuitry  115  to facilitate efficient energy consumption. Power management circuitry  115  preferably includes a power source  120  and a power manager  125  for controlling power output from power source  115 . Power manager  125  communicates with display  57  and controls powerup and shutdown of monitor  57 . For example, in accordance with the user&#39;s wishes, display  57  may be driven into low power consumption mode after a period of inactivity or it may be shut down all together. In addition, display  57  may be automatically powered up upon deployment of one or more of sensors  33 - 37  or upon some other event.  
         [0044]    Turning to a particularly preferred aspect of the invention, central processing unit  110  is preferably programmed to carry out a physiological heat strain model to determine at least the following safety factors for workers and others exposed to extreme heat: 1) optimal work/rest cycle limits, 2) hourly water consumption needs and 3) maximum safe work time. In addition, CPU  110  may compute the following environmental parameters WBGT (computed from, mean radiant temperature, dew point and air-cooling power). A preferred physiological heat strain model uses both measured parameters and user input parameters to calculate the above safety factors. More particularly, the preferred heat strain model employs the following measured inputs: air temperature, humidity, solar radiation, wind speed and barometric pressure. In addition, the preferred heat strain model uses the following user supplied inputs: clothing type, work rate and acclimation status. A particularly preferred heat strain model is that described in  Computer Biological Medicine,  by Pandolf et al., Vol. 16 No. 5, pp. 319-329, 1986, which is herein incorporated by reference.  
         [0045]    The heat strain model may be realized as software to provide real-time safety factors and environmental parameters upon demand for assessing the effects of heat stress on human beings. A diagram representing the steps to be performed by the software in the preferred embodiment is shown in FIG. 2. The software may be implemented as a computer program or other electronic device control program or an operating system. The software may be resident in the environmental monitor  10  in CPU  110 , if desired. Alternatively, CPU  110  including the software may be resident in a stand-alone device in communication with environmental monitor  10  either continuously or intermittently. The standalone device may be a standard personal computer (PC), a PAL device, a personal digital assistant (PDA), an e-book or other handheld or wearable computing devices (incorporating Palm OS, Windows CE, EPOC, or future generations like code-named Razor from 3Com or Bluetooth from consortium including IBM and Intel), or a specific purpose device receiving signals from environmental monitor  10 . Depending on the location of the software, the software may be stored, for example, in random access memory (RAM); in read only memory (ROM); on a storage device like a hard drive, disk, compact disc, punch card, tape or in other computer readable material; in virtual memory on a network such as an intranet or the Internet, computer or otherwise; on an optical storage device; on a magnetic storage device; and/or on an EPROM. The software may be modified or updated as desired.  
         [0046]    In operation, the user preferably deploys sensors  33 - 37  and activates monitor  10 . Monitor  10  may be activated automatically when sensors are deployed or may be manually activated by the user. Upon activation, display  57  preferably shows various parameters and indicia including date, time and power status. The user may then activate a selection menu on LCD  57  and select the appropriate input parameters, i.e., the type of clothing, the work rate and the acclimation status. The input parameters are then transferred to CPU  110 . The selection menu preferably provides the user with a variety of options for each parameter from which the user may select. Further, upon activation of the monitor  10 , sensors  33 - 37  collect data and transmit the collected to CPU  110 . The user may then request computation of any one or more of the safety factors and environmental parameters described above. In accordance with a preferred aspect of the invention, over a two-minute span, sensor measurements may be made at one-second intervals, averaged and input to CPU  110 . The safety factors may be calculated and output by CPU  110  either to display  57  or to a remote server in as little as three seconds. A preferred algorithm for calculation of safety factors and environmental parameters is depicted in FIG. 2. Accordingly, environmental monitor  10  provides real time computation of safety factors.  
         [0047]    In accordance with another feature of the invention, the environmental monitor  10  may be operated in automatic mode. That is, environmental monitor  10  may be set to log data from sensors  33 - 37 . The user may input start time, duration and interval for sensors to take readings. All data logged is saved and, when logging is complete, data may be viewed on display  57  and/or downloaded to a server for viewing and computation of safety factors via communication port  135 .  
         [0048]    Upon calculation of the safety factors, the safety factors may be displayed in graphical or alphanumerical fashion. For example, a cyclic work guidance display screen may show optimal minutes of work/rest per hour to keep predicted body core temperature within safe limits as well as amount of water to drink per hour to replace predicted sweat losses. A continuous work guidance display screen may show predicted maximum safe work time in minutes for a one-time bout of continuous work and the amount of drinking water needed to replace predicted sweat loss. An environmental data screen may show measured environmental parameters such as air temperature, relative humidity, wind speed, black globe temperature and barometric pressure. In addition, the environmental data screen may show calculated environmental parameters such as wet bulb temperature, mean radiant temperature, and the wet bulb-globe temperature (WBGT) index.  
         [0049]    The above-described display screens may be provided on display  57 , However, CPU  110  may also transmit the display information directly to a server simultaneously, serially or to the exclusion of display  57  for display on a server monitor. Of course, in embodiments of environmental monitor  10  that do not include display  57 , CPU  110  transmits the display information directly to the server and information is displayed on the server monitor.  
         [0050]    [0050]FIG. 3 illustrates a specific embodiment of the environmental monitor  10  in accordance with the invention. Environmental monitor  10  is adapted for use in monitoring environmental conditions associated with heat stress, and has sensors and programming appropriate for that application. However, monitor  10  could be easily adapted for monitoring other environmental conditions, such as cold, air quality, and noise. Appropriate sensors could be added or substituted for those described herein.  
         [0051]    Structurally, environmental monitor  10  is comprised of a case including a main body  10   a  and a sensor module  10   b . In FIG. 3, sensor module  10   b  is shown in the “deployed” position, positioned for operation of its sensors. A hinged cover  22   a  of main body  10   a  is open to facilitate deployment of the sensors.  
         [0052]    The main body  10   a  of monitor  10  has a front face  11   a , and a keypad  12  with individual keys  12   a . A CPU  110  for computation of safety factors and environmental stress parameters such as that described above may be disposed within main body  10   a.    
         [0053]    As illustrated in FIGS. 4 and 5, main body  10   a  includes a shelf  14   d  including a substantially spherical depression  14   e  dimensioned to accept the black globe sensor described in greater detail below when the sensors are in the rest or nestled position. More particularly, spherical depression  14   e  may have a diameter equal to or less than about 1.125″. Main body  10   a  may also be provided with a compartment  15   a  for storing a power source, e.g., a battery (not shown).  
         [0054]    Sensor module  10   b  is preferably releasably disposed in hinged cover  22   a . Sensor module  10   b  may be snap fit, friction fit or otherwise matingly engaged with hinged cover  22   a . A feature of the invention is that monitor  10  easily permits sensor modules  10   b  to be interchanged and used with the main body  10   a . All signal processing and calibration information is stored in the sensor module  10   b , with a digital control interface to the main body  10   a.    
         [0055]    Sensor module  10   b  is comprised of a substantially planar base  10   c  which supports a dry bulb sensor  33 , relative humidity sensor  34 , black globe sensor  35 , and wind speed sensor  36 . Sensors  33 - 36  are illustrated in FIG. 3 in their deployed position. That is, sensors  33 - 36  are position erect, substantially perpendicular to planar base  10   c . Sensors  33 - 36  may be placed in their storage position by folding down each sensor as described in detail below and closing hinged cover  22   a . In the storage position, sensors  33 ,  34  and  36  will be substantially flush with planar base  10   c  and the globe of sensor  35  will be nestled in depression  14   e . Accordingly, cover  22   a  may be closed and mated with main body  10   a . FIGS. 4 and 5 illustrate sensors  33 - 36  in their storage position, substantially parallel to planar base  10   c  prior to closing cover  22   a.    
         [0056]    Each of sensors  33 - 36  is attached to or coupled with a mast  23  and the mast is secured to planar base  10   c . Mast  23  is preferably comprised of a thin walled stainless steel tube member as depicted in FIGS.  6 - 8 . As best shown in FIG. 6, each mast has a substantially hemispherical closed end  24  and a clearance slot  25  disposed along a side of mast  23  proximate to closed end  24 . Closed end  24  is configured for hinged engagement with spring retainer cup  26  to permit rotation of sensors  33 - 36  through an angle of approximately  90 ° from rest position to deployed position. Spring retainer cup  26 , depicted in greater detail in FIG. 7, defines a collar having first and second wings  27   a  and  27   b . Spring retainer  26  is preferably formed form stainless steel or beryllium copper. Lodging mast  23  into spring retainer  26  and threading roll pin  28  through eyelets  29  and clearance slot  25  may establish a secure hinged connection. Wings  27   a  and  27   b  are inwardly biased to secure mast  23  in position as shown in FIG. 8. Spring retainer  26  is further provided with extension ears  28   a  that may be potted into planar base  10   c.    
         [0057]    Although a preferred coupling system for sensors  33 - 36  is described above, the invention is not limited to such a system. Sensors  33 - 36  may be coupled to planar base  10   c  using any mechanism that allows sensors  33 - 36  to be moved to and from and locked into their deployed and storage positions.  
         [0058]    As discussed above, each of sensors  33 - 36  are disposed on a mast  23  as shown. Dry bulb sensor  33  and wind speed sensor  36  are preferably disposed on the same mast  23 . FIG. 8. However, wind speed sensor  36  is preferably disposed above dry bulb sensor  33  near the top end of mast  23 . To prevent damage to wind speed sensor  36  and dry bulb sensor  33 , a protective covering  23   a  may be disposed about the respective sensors. An exemplary protective covering is illustrated in FIG. 8 is a stainless steel collar having a plurality of perforations  23   b  to facilitate airflow. Wind speed sensor  36  and dry bulb sensor  33  may be of a type known to those of skill in the art. For example, both wind speed sensor  36  and dry bulb sensor  33  may be realized by thermistors.  
         [0059]    Likewise, black globe sensor  35  and relative humidity sensor  34  are of the type generally known to those of skill in the art. In accordance with a feature of the invention, the wet bulb globe temperature (WBGT) may be obtained by measuring relative humidity with sensor  34  and the dry bulb temperature with sensor  33  and using a mathematical formula to determine wet bulb temperature. Alternatively, a dedicated wet bulb sensor could be used in sensor module  10   b.    
         [0060]    An atmospheric pressure sensor  37  is preferably located inside sensor module  10   b . In the embodiment of FIG. 4, pressure sensor  37  may be mounted on planar base  10   c . In addition, sensor electronics  60  may be disposed on the underside of planar base  10   c . In preferred embodiments, sensor electronics  60  may be implemented on a printed circuit board (not shown), which may be readily attached to planar base  10   c.    
         [0061]    In keeping with the invention, the user may control operation of environmental sensor  10  using keypad  12   a . Specifically, using keypad  12   a , the user may perform one or more of the following: a) input environmental stress parameters, b) control illumination of display  57  and c) direct CPU  110  to compute environmental stress parameters and environmental safety factors.  
         [0062]    FIGS.  9 - 15  illustrate still another embodiment of the invention. FIGS. 9 and 10 are exploded front and rear views of an environmental data monitor  10  in accordance with the invention, respectively. In the example of this description, monitor  10  is adapted for use in monitoring environmental conditions associated with heat stress, and has sensors and programming appropriate for that application. However, monitor  10  could be easily adapted for monitoring other environmental conditions, such as cold, air quality, and noise. Appropriate sensors could be added or substituted for those described herein.  
         [0063]    Structurally, monitor  10  is comprised of a main body  10   a  and a sensor module  10   b . In FIGS. 9 and 10, sensor module  10   b  is in the “deployed” position, positioned for operation of its sensors. A hinged rear cover  22  of main body  10   a  is open, but could be closed to protect the sensors of sensor module  10   b  during use.  
         [0064]    The main body  10   a  of monitor  10  has a front piece  11 , a keypad  12 , a CPU board  13 , with a midpiece  14 , a battery cover  21 , a rear cover  22  with latch  22   a , an endpiece  15 , and a sensor module connector  16 .  
         [0065]    CPU board  13  is located between front piece  11  and midpiece  14 . On its front side, CPU board  13  contains the graphics display and traces for keypad  12 . Other electronic components are on the rear side. The electrical circuitry of CPU board  13  is explained below in connection with FIG. 13.  
         [0066]    Midpiece  14  has a curved sensor bed  14   c  at its top end. As explained below, sensor bed  14   c , such that sensor module  10   b  may rotate at least  180  degrees. FIG. 10 illustrates this rotation.  
         [0067]    Sensor module connector  16  attaches to midpiece  14 , such as by screws. The attachment is after its wiring harness  16   a  is threaded to CPU board  13 . Sensor module connector  16  has alignment holes  16   b , which prevent a rotating connector  32  on sensor module  10   b  from making contact with sensor module connector  16  until it is properly aligned.  
         [0068]    A battery compartment  14   a  in midpiece  14  contains four AA-size batteries wired in series to provide a nominal six-volt DC power source. A battery cover  21  is a friction fit rubber cover, which seals the battery compartment  14   a  when rear cover  22  is closed.  
         [0069]    The ‘+’ and ‘−’ terminals of the batteries protrude through the battery compartment  14   a  and a wiring harness connects them to CPU board  13 . An external connector  14   b  also attaches to CPU board  13  with a wiring harness. All wiring harnesses are of sufficient length to allow CPU board  13  to be removed from the midpiece  14  and manipulated for repair.  
         [0070]    Once all wiring harnesses are attached to the CPU board  13 , keypad  12  is placed into the front piece  11 . Keypad  12  is made from conductive rubber and forms a weatherproof seal where it comes in contact with the midpiece  14 . The front piece  11  attaches to the midpiece  14  by screws that enter through the rear of the midpiece  14 .  
         [0071]    Rear cover  22  and midpiece  14  have a hinge-type attachment  22   a  along their bottom edges. A sliding latch  22   b  is attached to the rear cover  22  by compression springs, which hold latch  22   b  in its latched position. Operating the latch  22   b  opens the rear cover  22 . A compressible gasket may be attached to the perimeter of the rear cover  22  to serve as a seal and to allow the rear cover  22  to spring out from the midpiece  14  when unlatched.  
         [0072]    Sensor module  10   b  is cylindrical in shape, with a rotating connector  32  at one end and a rotation knob  17  at the other. Connector  32  permits sensor module  10   b  to rotate within the sensor bed  14   c  of midpiece  14 .  
         [0073]    When monitor  10  is in the “storage” position (not shown), sensor module  10   b  is rotated approximately 180 degrees from the “deployed” position illustrated in FIGS. 9 and 10. This permits its sensors to be placed under rear cover  22 , when cover  22  is hinged shut.  
         [0074]    For assembly, sensor module  10   b  is slid into position on the main body  10   a  with the sensors in their deployed position and the rear cover  22  unlatched. Once the sensor module  10   b  is seated properly, endpiece  15  is positioned over the knob  17  and attached to the midpiece  14  with screws. For the storage position of monitor  10 , the sensors can be rotated into the sensor cavities in the midpiece  14 , and the rear cover  22  can be closed.  
         [0075]    [0075]FIG. 11 illustrates sensor module  10   b  in further detail. A feature of the invention is that monitor  10  easily permits sensor modules  10   b  to be interchanged and used with the main body  10   a . All signal processing and calibration information is stored in the sensor module  10   b , with a digital control interface to the main body  10   a.    
         [0076]    Sensor module  10   b  is comprised of a cylindrical housing  31 , having an upper half  31   a  and a lower half  31   b . The two parts of housing  31  are screwed together, ultrasonically welded, glued, or otherwise attached.  
         [0077]    The upper half  31   a  provides a platform for various sensors. In the embodiment of FIG. 11, sensor module  10   b  has a dry bulb sensor  33 , relative humidity sensor  34 , black globe sensor  35 , and wind speed sensor  36 . Thus, monitor  10  has three thermistors: dry bulb, black globe, and wind speed. Wet bulb globe temperature (WBGT) is obtained by measuring relative humidity with sensor  34  and the dry bulb temperature with sensor  33  and using a mathematical formula to determine wet bulb temperature. Alternatively, a dedicated wet bulb sensor could be used.  
         [0078]    The dry bulb sensor  33 , globe sensor  35 , and wind speed sensor  36  are each located on a mast  33   a ,  35   a , and  36   a . These masts protrude perpendicular to the face of the cylindrical housing  31 . A removable light-shadowing housing  34   b  covers the humidity sensor  34 .  
         [0079]    Sensor PCB (printed circuit board)  38  is contained within sensor housing  31 , between upper half  31   a  and the lower half  31   b . Sensor PCB  38  contains the sensor electronics  50 , described below in connection with FIG. 14.  
         [0080]    An atmospheric pressure sensor  37  is located inside sensor module  10   b . In the embodiment of FIG. 11 pressure sensor  37  is mounted on the underside of sensor PCB  38 .  
         [0081]    At one end of sensor module  10   b  is a rotating connector  32 , which has a groove on its edge to allow it to rotate within cylindrical housing  31 . The upper half  31   a  and lower half  31   b  of housing  31  have mating ridges. An O-ring  32   b  is slipped onto the cylindrical housing  31 .  
         [0082]    When rotating connector  32  is plugged into fixed connector  16 , there is a seated rotating connection between sensor module  10   b  and main body  10   a . As a result of the rotating connector  32  and O-ring  32   b , sensor module  10   b  is sealed from the effects of the environment. Alignment pins  32   c  provide strain relief for the connector pins and sockets when sensor module  10   b  is rotated.  
         [0083]    Referring again to FIGS. 9 and 10, main body  10   a  has cavities into which the various sensors fit when sensor module  10   b  is rotated approximately 180 degrees into a “storage” position. The arrow is FIG. 10 illustrates the direction of rotation. The hinged rear cover  22  is closed to protect the sensors when they are stored. Cover  22  can also be re-closed after it is opened and the sensors are deployed into their “operate” position.  
         [0084]    As stated above in connection with FIGS. 9 and 10 and as also illustrated in FIG. 12, main body  10   a  has an endpiece  15 . The endpiece  15  fits over a rotation knob  17  on sensor module  10   b . It attaches to main body  10   a  and holds sensor module  10   b  in place. Endpiece  15  may be removed to permit sensor module  10   b  to be removed, such as for replacement or repair.  
         [0085]    Discrete wires  32   d  from the rotating connector  32  are attached to the sensor PCB  38 . When the assembled sensor module  10   b  is attached to the main body  10   a , rotating connector  32  is held in a fixed position with respect to the main body  10   a  by a mated connection. When the knob  17  is used to rotate the sensor module  10   b , the upper half  31   a , lower half  31   b , and sensor PCB  38  rotates around the rotating connector  32 .  
         [0086]    [0086]FIGS. 13 and 14 are functional block diagrams of the electronics of the present invention. FIG. 13 illustrates the main electronics  50  contained within main body  10   a . FIG. 14 illustrates the sensor electronics  60  contained within sensor module  10   b . A serial digital interface  50   a  provides the electrical connection between main electronics  50  and sensor electronics  60 .  
         [0087]    Main electronics  50  has a central processing unit (CPU)  51   a  with a peripheral system device (PSD)  51   b . The PSD  51   b  provides address decode logic, additional static RAM and digital I/O ports, and a bootloader routine for the flash memory  53 . A static RAM  54  provides both scratchpad memory and nonvolatile storage for data logging applications. RAM  54  is backed up by a lithium battery  55 . The lithium battery  55  also maintains a real time clock  56 , which can be used for timestamping logged data. The graphics display  57  is addressed by the CPU  51   a  and uses a digital potentiometer  57   a  for contrast adjustment. The backlight control for the graphics display  57  is controlled by the PSD  51   b . The keypad  52  is interfaced to digital I/O ports on the PSD  51   b.    
         [0088]    The system is powered by a DC power source, which may be either user-replaceable batteries placed in compartment  14   a  or an external power source.  
         [0089]    An RS-232 converter  58  converts the TTL-level signals on the CPU board  10  to RS-232 signals for the external serial connector. The main body  10   a  of monitor  10  functions as an intelligent user interface containing the graphics display, keypad, power supply CPU and associated digital electronics. The main body also contains an external port that can be used to supply external power and communicate with a personal computer through an RS-232 interface. Software can also be loaded into the device through this port and stored in flash memory.  
         [0090]    The connection between main body  10   a  and sensor module  10   b  provides battery power, supply voltage, and a digital control interface. All sensing electronics and storage for calibration and sensor identification information is located on the sensor module  10   b . This allows sensor module  10   b  to be calibrated independently of the main body  10   a  and to produce the same results when attached to any main body  10   a.    
         [0091]    The design of monitor  10  permits different types of sensor modules to be used with the main body, whereby the sensor module  10   b  can be queried by the main body  10   a  to determine the type of each sensor and its calibration information. The application software in the main body  10   a  can then configure itself to acquire and display the sensor data. Alternatively, a dedicated application for a given type of sensor module  10   b  can be loaded into the flash memory  53  through an external port.  
         [0092]    Referring to FIG. 14, the sensor electronics  60  contains signal conditioning circuitry for the dry bulb sensor  33 , the black globe sensor  35 , the relative humidity sensor  34 , the wind speed sensor  36 , and the pressure sensor  37 .  
         [0093]    The analog voltages produced by the various sensors are digitized by the A/D converter  62 . A D/A converter  63  is used to provide current to the wind speed sensor  36  and to heat it to a constant temperature above the dry bulb temperature. The amount of power required to heat the wind speed sensor  36  is related to the wind speed.  
         [0094]    An EEPROM  64  stores all calibration information related to the sensors  33 - 37 . The calibration information may include various calibration constants, unique to each sensor. In general, all circuitry and programming unique to any sensor is placed on sensor module  10   b  rather than in main body  10   a  so that sensor modules having the same, or different, sensors may be easily interchanged.  
         [0095]    A/D converter  62 , D/A converter  63 , and EEPROM  64  all share the same serial control lines on the interface  50   a , with the exception of their chip select signals. This minimizes the number of connections that need to be made between the CPU electronics  50  and the sensor electronics  60 .  
         [0096]    Voltage regulator  65  produces a stepped-up voltage for the sensor electronics  60 . The battery voltage is delivered to the sensor electronics  60 , where it is input to a battery monitor  66 , whose output signal is converted to digital form by A/D converter  62 , and delivered back to the CPU electronics  60 . The location of battery monitor  66  in sensor electronics  60  is merely for convenience of using A/D converter  62 , and in other embodiments, battery monitor  66  could be part of CPU electronics  50 .  
         [0097]    CPU  51   a  can be programmed to execute various environmental data processing algorithms. For example, when monitor  10  is used to heat stress monitoring, known heat strain models can be used. For example, a model based on the WBGT index may be used.  
         [0098]    A feature of the invention is the incorporation of wind speed into heat strain models. As a result, the effect of evaporative cooling is considered in determining weather effects.  
         [0099]    Measured parameter data acquired from sensor module  10   b  can be combined with user input parameter data acquired via keypad  12  or other means. Such parameters might include, clothing type, work type, or work rate.  
         [0100]    As stated above, monitor  10  can be easily adapted for use with other or additional sensors. For example, one sensor might be an air quality sensor, such as one that measures oxygen content or one or more pollutants. Or, a sensor might measure noise. Other sensors might measure the user&#39;s physiological conditions, such as heart rate, blood pressure, or body temperature (skin or core). For physiological monitoring, sensors such as used by athletes could be used—for example, a heart rate monitor that attaches to the user&#39;s finger and provides input to the A/D converter  62  of sensor module  10   b  or directly to the processor  51  of the main body  10   a.    
         [0101]    Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.