BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention pertains to stack gas emissions monitoring systems using moveable gas differential pressure and temperature measurement devices whose readings are electronically recorded for analysis. 
     2. Description of the Related Art 
     Environmental standards require that gaseous emissions from smokestacks, particularly large stacks such as used by utility companies in the generation of electric power, meet predetermined emission standards. Periodic testing of the gaseous stack emissions is required and conducted, and reports are regularly submitted to the appropriate government environmental agencies. 
     In the past, gaseous stack emissions were determined by locating differential pressure and temperature measurement devices temporarily within the smokestack at predetermined locations, and the measurements were manually recorded. Such recording was accomplished by one individual placing the measurement devices into the flue gas stream within the smokestack, and another individual nearby recording the readings from analog instruments connected to the output of the measurement devices. 
     Usually, the stack gases are monitored at more than one horizontal location within the smokestack, and several ports, or openings in the stack wall to facilitate such measurements, are arranged along a horizontal plane around the circumference of the smokestack. This traditional system of flue gas flow measurement is expensive and time consuming (requiring two operators), and is subject to errors in the reading of the analog meters, data recording at the test location, and subsequent data transcription to computer spreadsheets for the final calculations and report. 
     A variety of sophisticated electronic systems and devices have been utilized in the analysis of emissions from various sources, and such devices are illustrated in U.S. Pat. Nos. 4,561,288, 4,786,472, 5,206,818, 5,415,025, 5,479,359, and 5,526,280. However, devices such as shown in these patents are not specifically designed for the measurement of volumetric flow of stack gas emissions. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to provide a method and apparatus for economically measuring the volumetric flow of flue gas emissions wherein such measurements require only a single operator and accurate readings are assured. 
     A further object of the invention is to provide a system for measuring volumetric flow of flue gas emissions which may be readily used by a technician with minimal training, is concise in its size and easily handled under difficult conditions and in cramped quarters, and wherein the readings of the measurement system are accurately recorded and stored for analysis purposes. 
     SUMMARY OF THE INVENTION 
     In the practice of the invention, an electronic data logger records the output of a temperature sensing thermocouple, and a pair of differential pressure transducers. The output of these transducers into the data logger is controlled by a remote control device hardwired to the data logger and operated by the same person that operates the probe on which the measurement devices are located. When the probe is properly positioned in the flue gas stream within the smokestack, a “read” pushbutton is actuated by the operator to read, and then store the output values of the transducers at that time. The operator will sequentially locate the probe at predetermined locations within the smokestack so that the data logger can measure and record temperature and differential pressures at the predetermined number of locations in the cross sectional area of the flue gas flow. In this manner, variations in the flue gas flow due to turbulence, wall friction, and the like, can be determined. 
     The remote control module also includes pushbuttons to “reverse” and “advance” the data logger measurement point, whereby the past measurement points can be remeasured if thought to be in error, and the data logger can then be advanced to the next position at which readings are to be taken. 
     In order to be assured that the data logger has received all of the necessary information at each position within the smokestack, a dual-colored red/green LED is located on the remote control device, and will display a green light if the correct measurements have been recorded. Conversely, if there is an error in the measurement due to unintelligible or spurious readings, the LED will display a red light, and the operator can then remeasure at that location. The remote control device also is equipped with a back lighted LCD, which displays the numerical location of the current measurement point, and the value of the temperature and differential pressure measurements. 
     The electronic data logger may be directly connected to a personal computer (PC), or may be connected to an electronic data storing device for later input into a PC. The data logger software installed on the PC allows the user to view and evaluate the readings taken within the smokestack. The apparatus used in the practice of the invention is conventional equipment commercially available, and the practice of the invention significantly improves the accuracy, speed and cost of flue gas volumetric flow measurement methods currently in use. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned objects and advantages of the invention will be appreciated from the following description and accompanying drawings wherein: 
     FIG. 1 is a schematic view of the apparatus used in the practice of the invention for the measurement of volumetric flow of stack gases, 
     FIG. 2 is a plan view of the remote control module, 
     FIG. 3 is a side elevation view of the remote control module, 
     FIG. 4 is an elevation view of a typical probe for insertion into the stack gas stream and to which the differential pressure transducers and thermocouple type temperature measurement devices are connected, and 
     FIG. 5 is a typical cross sectional view of a smokestack in which emission testing takes place, illustrating the positions of testing to achieve uniformity of testing across the gas flow. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 1, the apparatus of the invention includes an electronic data logger  10  which is capable of receiving electronic signals from temperature and differential pressure transducers and storing such signals. The data logger  10  may be of conventional construction such as sold by Campbell Scientific, Inc. Model CR10X. 
     The data logger  10  is connected to a remote control module  12  by hard wire  14 , and the wire  14  may be of a length of as much as fifty feet or more so that the data logger  10  may be securely supported on a firm surface in an environmentally friendly area, while the module  12  will be hand carried by the operator. If desired, the module  12  could include a wireless transmitter sending signals to a wireless receiver associated with data logger  10 . 
     Temperature and pressure transducers are connected to the data logger  10  providing the input signals thereto. A thermocouple  16 , FIG. 1, is connected to the data logger, and a pair of differential pressure transducers  18  and  20  also provide an electronic input into the data logger. The thermocouple  16  is of the type “E” while differential pressure transducer  18  is of the Omega PX655 series having a range of zero to one inch of water, and the differential pressure transducer  20  is also of the PX655 series having a measurement range between zero and twenty-five inches of water. 
     An electronic communications interface  22  such as made by Campbell Scientific, Inc. Model SC32A, may also be connected to the data logger  10  and the interface  22  may be connected to a personal computer (PC)  24 . A different communications interface  58  such as made by Campbell Scientific, Inc. Model SC532 may be connected to the data logger  10 , and then may be connected to a data storage module  60  such as made by Campbell Scientific, Inc. Model SM192. 
     The remote control module  12  is of a size as to be easily carried by the operator, and includes a Liquid Crystal Display (LCD)  26 , a “read” pushbutton switch  28 , a “go forward” pushbutton switch  30 , a “go back” pushbutton switch  32 , and an indicator  34  of the Light Emitting Diode (LED) type that may selectively glow red or green. The operation of the components of the remote control module  12  are described below. 
     The thermocouple  16  is mounted intermediate the arms  38  and  40  of a S-type pitot tube  36 , which in turn is affixed to a probe  62 . The thermocouple  16  is electrically connected to the data logger  10  by wire  46 . The differential pressure transducers  18  and  20  are mounted in a box along side the data logger  10 . The differential pressure transducers  18  and  20  are connected to the S-type pitot tube  36  by rubber tubing  42  and  44 . The probe  62  is usually of a rigid pipe design, but may take other forms. Both differential pressure transducers  18  and  20  are connected in parallel across the arms  38  and  40  of the S-type pitot tube  36 . The electronic output of the differential pressure transducers  18  and  20  are hardwired directly to the data logger  10 . 
     In FIG. 5, a cross section of a typical smokestack is illustrated. The method and apparatus of the invention is often practiced in very large smokestacks such as found in power plants, wherein the exhaust gases from fuel combustion to produce steam for electric generation passes through the smokestack  48 . The smokestack  48 , in a horizontal plane, has been divided into quadrants by imaginary lines  50  and imaginary circles  52  concentric to the stack axis locate the test points  54  which are the points at which testing of the stack gases are made. The test points  54  radially extend from the center of the stack  48  outwardly close to the stack walls, and the test points at equal locations from the center of the stack are each spaced in a different quadrant. In this manner, a fair representation of the characteristics of the gas within the stack  48  is made, and such readings will be relatively free of variations due to turbulence, stack wall friction, and other gas flow affecting characteristics. 
     In operation, the operator locates the data logger  10  on a firm supporting surface, and usually, the stack port  56  defined in the stack will be remote with respect to the location of the data logger. The operator will open the test port  56  and holds the probe  62  in his hand. As the S-type pitot tube  36  is connected through the inside of the probe  62  to the data logger  10  by flexible rubber tubing  42  and  44  and the thermocouple  16  is connected through the inside of the probe  62  to the data logger  10  by flexible wire  46 , the probe may be moved and located within the stack  48  as desired. The outer end of the S-type pitot tube  36  and thermocouple  16  will be positioned at one of the test points  54 . Thereupon, the operator will push the “read” pushbutton switch  28  wherein the output of the differential pressure transducers  18  and  20  and the thermocouple  16  will be recorded in the data logger  10 . The operator will then move the probe  62  to a different test point  54  and again push the “read” pushbutton switch  28  to record the temperature and differential pressure of the flue gas stream at that point. This procedure is repeated until all of the test point locations  54  reachable through the test port  56  have been measured. The operator will then carry the probe  62  to the next test port  56  and repeat the process. These steps will be repeated until all test point locations  54  within the stack  48  have been measured. 
     Each time the “read” switch  28  is actuated, the LED indicator  34  will glow either red or green. If the indicator is green, the data logger  10  has received sufficient and correct information from the differential pressure transducers  18  and  20  and from the thermocouple  16 , and the data logger  10  will advance its internal counter to the next measurement point. If the output of the thermocouple  16  or the pressure transducers  18  and  20  is incomplete, or outside a set of pre-programmed parameters, the signals will be considered in error, and the LED indicator  34  will glow red, and the operator will have to again push the “read” pushbutton  28  until the LED  34  glows green to indicate correct readings have been achieved. 
     If the operator desires to remeasure a previous point for any reason, the “go back” pushbutton switch  32  is actuated until the LCD  26  shows the proper numerical location for the test point  54  the operator wishes to remeasure. The “read” pushbutton  28  must be pushed until the LED indicator  34  glows green. The operator must then simultaneously push the “go back” pushbutton  32  and the “go forward” pushbutton  30  until the LCD  26  displays the proper numerical location for the next test point  54  to be measured. 
     Once the testing has been completed, the information stored within data logger  10  may be transferred directly to a PC  24 , via the communications interface  22 . Alternately, the information stored within the data logger  10  may be transferred to a data storage module  60  via communications interface  58 , and the data storage module  60  is then used as the input to the PC  24 . Either method of recovering the information stored within the data logger  10  allows the operator to view and evaluate the test results, and to permit printing of the test results. 
     From the above description, it will be appreciated that accurate monitoring of volumetric gas flow in a smokestack may be quickly and easily completed by a single operator, the accuracy of the readings are improved, and all operator error in the recording and transfer of test measurements is eliminated, and as each reading is checked for its completeness, a high degree of accuracy is achieved. The operator may proceed at his own desired rate of testing, and the apparatus of the invention provides many advantages over prior arrangements for measuring volumetric flow of flue gas emissions. 
     It is appreciated that various modifications to the inventive concepts may be apparent to those skilled in the art without departing from the spirit and scope of the invention.
A method and apparatus for monitoring stack gas emissions wherein a probe including temperature and pressure indicating transducers is sequentially located at predetermined positions within a smokestack and the output of such transducers is fed into an electronic data logger for retention therein. The data logger includes a light hand held module having a liquid crystal display and start/reverse/advance pushbutton switches whereby the data logger can be remotely controlled. The invention eliminates the necessity of using two operators to record the desired information and significantly reduces the cost of producing accurate evaluation of stack gas emissions.