Abstract:
A yield monitoring system for a grain harvesting combine includes a volume monitor, a moisture monitor, a test weight monitor, a ground speed monitor, and a computer which receives signals from each monitor and continuously derives harvested grain yield rates from those signals, displays the yield rates on a visual display and records the yield rate information for later recall and transfer to other computers. A GPS receiver linked to the system enables it to map yields geographically in the harvested field. The volume monitor receives all grain exiting the clean grain elevator of the combine and passes it through a paddlewheel, the angular displacement of which is monitored over time. The moisture monitor and test weight monitor are mounted to the exterior of the clean grain elevator and receive samples of grain from the lift side of the clean grain elevator.

Description:
BACKGROUND OF THE INVENTION 
     This invention pertains to yield monitors for grain harvesters. Increasing emphasis is being placed on determination of crop yields as harvesting is being accomplished, particularly when the crop yield data is integrated with precise mapping of fields through use of a global positioning satellite receiver. 
     In the existing onboard yield measurement systems available for grain harvesters, harvested grain weight is measured by use of a vertical impact plate positioned in the path of grain being discharged from an enclosed chain driven paddle conveyor commonly referred to as a clean grain elevator of the grain harvester or combine. Such a measurement device is described in U.S. Pat. No. 5,343,761. This system has shortcomings, namely baseline drift which occurs in the sampling must be corrected as described in U.S. Pat. No. 5,594,667. Also calibration is required at varying rates of flow, and inaccuracy cannot be eliminated because test weight measurements of the grain are not available on a real time basis. For example, with existing apparatus, the weight of corn harvested is presumed to be fifty-six pounds per bushel at fifteen percent moisture while the actual test weight of the corn may be much different. The condition and spacing of conveyor paddles, the varying slope of the combine as it traverses a field, and the speed of the clean grain elevator also can affect accuracy. A need exists for a yield measurement system which periodically samples test weight of grain being harvested and measures flow rate volume accurately at varying flow speeds, in order to provide accurate input data for real time calculation of yield rates within a field being harvested. 
     As part of the monitoring of crop yield, apparatus has been developed to measure crop moisture of samples of grain within the grain harvester or combine, including devices which mount to the exterior of the clean grain elevator of the grain harvester or combine. The clean grain elevator elevates grain from the separator of the combine to the onboard storage tank of the combine which is located at the top of the combine. Current moisture sensors collect a sample of grain from the lift side of the clean grain elevator through an opening in the elevator housing and pass the grain into a vertical chamber in which a moisture sensor has been mounted. Periodically the chamber is emptied by operation of a motor driven paddlewheel or auger which carries the grain from the chamber and drops it through an exhaust duct into the return side of the elevator housing so that a new sample can enter the chamber for moisture testing. Once the combine is shut down, the operator must remember to energize the paddlewheel or auger of the moisture test apparatus to empty it. If that is not done, grain will remain in the chamber and be subject to freezing or deterioration which may result in clogging of the moisture test apparatus. Downtime and inconvenience result from such clogging, along with the danger from manually removing clogged grain from the moisture test apparatus. A need exists for an elevator mount moisture sensor which resists clogging and which may be mounted on many different makes and models of harvester. 
     SUMMARY OF THE INVENTION 
     A yield monitoring system for a grain harvesting combine is disclosed. The system includes a volume monitor, a moisture monitor, a test weight monitor, a ground speed monitor, and a computer which receives signals from each monitor and continuously derives harvested grain yield rates from those signals, displays the yield rates on a visual display and records the yield rate information for later recall and transfer to other computers. A GPS receiver linked to the system enables it to map yields geographically in the harvested field. 
     A volume monitor is positioned at the exhaust spout at the top of the clean grain elevator. The volume monitor receives all grain exiting the clean grain elevator and passes it on to a fountain auger that delivers it to the on board storage tank of the grain harvester combine. The volume monitor includes a receiving hopper which collects grain exiting the clean grain elevator discharge port. An ultrasound level monitor is mounted above the hopper to detect and monitor the height of grain in the hopper. The hopper includes a lower discharge chute which directs grain onto a paddlewheel which may be driven at selectively varying rotational speeds. The speed of rotation at which the paddlewheel is driven is determined by a controller which causes the paddlewheel to turn sufficiently fast to maintain the grain at a steady level determined by the level monitor. Hence when grain in the hopper is below the level determined by the level monitor, the paddlewheel is stopped and when grain rises above the height determined by the level monitor, the paddlewheel is driven sufficiently rapidly so that grain in the hopper remains at the level determined by the level monitor. The angular displacement of the paddlewheel is measured and a signal is generated which is provided to the computer. Because the volume capacity of the paddlewheel to pass grain is predetermined, the angular displacement over time of the rotation of the paddlewheel provides information from which volume of harvested grain over a time interval may be calculated. 
     The length of time interval for volume measurement may be selected over any range but a convenient interval for effective measurement is from one to five seconds and in practice, the preferred interval is two seconds, that is, the volume monitor provides volume of grain exiting the clean grain elevator in two second increments, and the moisture and test weight data are polled by the computer every two seconds. 
     The moisture monitor mounts to the exterior of the clean grain elevator within the combine. A flexible entry duct which is open to the interior of the lift side of the grain elevator is joined to the upper end of a housing in which a moisture sensor is mounted. The housing is oriented vertically to hold a column of grain to be moisture tested. The lower end of the housing opens to a non-motorized, compartmented wheel preferably housing equally sized circumferential compartments of preselected size. The lower end of the housing is sized so that only one compartment of the wheel may receive grain from the housing at one time. Free rotation of the wheel is prevented by a stop mechanism which in practice may be a plunger which extends toward the wheel to prevent its rotation. Momentary retraction of the plunger is controlled by a signal from a level sensor which is mounted in the housing above the moisture sensor to sense when grain in the housing reaches the level of the level sensor. When grain is sensed by the level sensor, the plunger is momentarily de-energized and retracts from the wheel, allowing the wheel to turn an incremental one-quarter rotation. Immediately thereafter, the plunger is energized and extends to stop further rotation of the wheel. Rotation of the wheel allows a fixed volume of grain to exit the housing which may then be refilled by grain falling from the lift side of the elevator into the housing through the entry duct. The moisture sensor detects moisture content in the column of grain and when polled by the computer provides a signal indicative of the level of moisture in the grain. 
     After the grain passes the compartmented wheel, it may be exhausted into the return side of the elevator through a flexible exhaust duct, or it may be passed into a test weight measurement assembly which may be located below the wheel so that the grain from the wheel may fall into a container of known tare weight. The grain in the compartment of the compartmented wheel under the lower end of the housing is of a predetermined volume. This known volume of grain falls into the container of the test weight measurement assembly. The container is suspended from a load cell which determines the weight of the grain which is in the container of the test weight measurement assembly. 
     In order to improve accuracy of the test weight measurement, a second load cell is mounted near the first load cell with the second load cell suspending a known weight equal to the standard test weight of a preselected volume of the grain to be harvested plus the known tare weight of the empty container. Coupling the test weight load cell output with the inverse of the output of the second load cell suspending the known weight allows elimination of weighing errors due to vibration or jiggle of the load cells within the grain harvesting combine. Output of the combined load cells equals the difference in weight between the measured test weight and the standard test weight. 
     Once the weight of the known volume of grain is determined and grain is sensed by the level sensor, the container empties into the exhaust duct which returns the tested grain to the return side of the elevator. Emptying of the container may be done by providing the container with a trap door bottom which may be released to swing away and allow the grain to pass. After the container has been emptied, the trap door bottom closes so that the container may receive the next sample of grain to be weighed. The trap door of the container opens and closes each time before the compartmented wheel is released to turn a quarter turn. With the test weight monitor option, the control signal from the level sensor to the compartmented wheel is delayed until the container is emptied and the trap door closed. 
     The particular moisture monitor of the present invention has a vertically oriented housing for temporarily holding a column of grain to be moisture tested. The use of flexible ducting from the lift side of the clean grain elevator to the housing, and also from the discharge from the moisture monitor to the return side of the elevator allows the moisture monitor to be installed on many differing configurations of clean grain elevator which may be found in different makes and models of grain harvesting combines. The novel discharge mechanism of the moisture monitor additionally provides a moisture monitor housing which automatically is emptied upon equipment shut down because the stop mechanism plunger which restrains the wheel from rotation is retracted when it is de-energized, thereby permitting the wheel to rotate freely to empty the housing of its column of grain. The test weight unit also empties upon shut down and the grain falls into the return side of the clean grain elevator. 
     A global positioning system (GPS) receiver is stationed on the grain harvesting combine to receive and store position information as well as to receive change-in-position information from which to calculate direction and velocity information. The velocity information from the GPS receiver is transmitted to the computer to be used in the yield calculations. As an alternative, ground speed of the grain harvesting combine may be obtained from well known transducer means mounted in the drive gear of the combine. The electronic output of such a transducer would be delivered to the central computer to be used for the ground speed data. 
     As the computer receives the volume data, the moisture content data, the weight per bushel (test weight) data, the ground speed data, having been calibrated for the swath of the harvester cutting head, the computer can calculate the area harvested and the current yield in pounds (and bushels) per acre of dry grain equivalent, transfer the data to the display for display to the operator, and transmit the data to a non-volatile memory device such as magnetic media or optical media (CD-ROM). Because the system is preferably integrated with GPS data, mapping of fields by yield may be accomplished. 
     It is an object of the invention to provide a yield monitoring system for a grain harvester which provides real time yield information at a high level of accuracy independent of harvester variables. 
     It is a further object of the invention to provide a yield monitoring system which determines actual test weight in pounds per bushel of crop grain as it is harvested. 
     It is a further object of the invention to provide a yield monitoring system which provides an accurate measurement of volume of crop grain being harvested per unit of time. 
     It is yet a further object of the invention to provide a yield monitoring system which generates real time yield data at known field locations. 
     It is yet another object of the invention to provide a moisture monitor which mounts to many different combine clean grain elevators without substantial modification. 
     It is yet another object of the invention to provide a moisture monitor which prevents clogging of the moisture monitor when it is not in operation. 
     It is a further object of the invention to provide a weighing apparatus using two load cells to eliminate weighing errors due to vibration of the combine in which weighing of the grain is to be accomplished. 
     These and other objects of the invention will become apparent from examination of the detailed description and drawings included in this specification. 
    
    
     DESCRIPTION OF THE DRAWING FIGURES 
     FIG. 1 is a schematic diagram of the preferred embodiment system for calculating yield of grain harvested per acre on a real time basis. 
     FIG. 2 is a front elevation of a clean grain elevator of a grain harvesting combine equipped with an improved moisture and test weight monitor and an improved flow rate monitor with the case of the clean grain elevator partly cut away to illustrate the interior of the clean grain elevator. 
     FIG. 3 is a front elevation of the flow rate monitor of the invention mounted at the outlet of the clean grain elevator, with the cover removed to show the interior of the flow rate monitor. 
     FIG. 4 is a front elevation of the moisture monitor and test weight monitor of the preferred embodiment with the outer case cut away to show the interior features of the devices. 
     FIG. 5 is a side plan view of the paddlewheel of the flow rate monitor of the preferred embodiment of the invention. 
     FIG. 6 is a side plan view of the wheel of the moisture and test weight monitor component of the invention. 
     FIG. 7 is an enlarged side plan view of the paddlewheel and the grate of the flow rate monitor component showing interaction of a fin of the paddlewheel with the grate. 
     FIG. 8 is an electrical schematic of the preferred embodiment of the test weight measurement apparatus of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a yield monitoring system for a grain harvesting combine which allows real time determination and mapping of yield data as the combine passes through the field. FIG. 1 diagrams the system invention and illustrates that a central signal processor  2  is coupled to a moisture sensor  4 , a test weight monitor  6 , a grain flow meter  8 , and a DGPS receiver  10 , all of which provide input data to the signal processor  2 . The DGPS receiver  10  receives signals from an array of earth orbiting satellites from which coordinates on the surface of the earth can be determined, along with direction of movement and ground speed of the receiver. Signals from an earth based antenna at a precisely known location may also be received by the DGPS receiver to enhance accuracy of calculated location from coordinate data received from the earth orbiting satellites. The DGPS receiver  10  may provide to the signal processor the ground speed of the combine and it may provide position data which may be linked to yield data calculated by the signal processor from the moisture sensor  4 , the test weight monitor  6  and the flow rate meter  8 . Ground speed information may also or alternatively be provided to the signal processor  2  from a ground speed sensor  12  mounted to the transmission or other drive line component of the combine which counts revolutions of drive line components from which ground speed can be determined. 
     A keyboard  14  is coupled to the signal processor for operator data input, including for entering the width of the cutting head of the combine. The swath width is used with the ground speed data from the DGPS receiver  10  or the ground speed sensor  12  to calculate the area harvested over unit of time. A touch screen display  16  is coupled to the signal processor  2  and may be used both to receive operator inputs and selections and to visually display yield rate information. A non-volatile memory  18 , such as a storage device which will store data on magnetic or optical media, is coupled to signal processor  2  to receive and store yield data and location data for later use and for transmission or transport to other computing devices. 
     The moisture sensor  4  samples grain moving within the combine to determine the moisture content of the grain and provides this sampled data to the signal processor  2 . The test weight monitor  6  also takes samples of grain periodically and weighs a known volume of the sampled grain to determine the test weight of grain moving within the combine. The test weight data is transmitted to the signal processor  2  by the test weight monitor  6 . Grain flow data on a volume per time interval basis is collected by the flow rate meter  8  on a continuous basis and this grain flow data is provided to the signal processor  2  to be used to calculate pounds and/or bushels per acre corrected for moisture content and for test weight variance. For example, the standard test weight for corn (maize) is fifty-six pounds per bushel and the market moisture content is fifteen percent. Specifically, the moisture sensor  4  is periodically polled by the signal processor  2  for the moisture content of the last sample of grain tested by the moisture sensor  4 . The test weight monitor  6  is also periodically polled by the signal processor  2  for the last test weight determined for a specified volume sample of grain. The flow rate meter  8  provides an ongoing stream of data indicating the volume of grain exiting the clean grain elevator per unit of time. The DGPS receiver  10  or the ground speed sensor  12  provides an ongoing indication of the ground speed of the combine. From these data inputs the signal processor  2  may calculate the actual weight and volume per unit area (typically acres) of the grain being harvested and may correlate the yield data to geographic coordinates and cause display of such information on the display  16  and store it on the non-volatile memory  18 . 
     Referring now to FIG. 2, the moisture monitor  4 , test weight monitor  6  and flow rate meter  8  of the preferred embodiment may be seen mounted to the clean grain elevator  20  of a typical combine. The clean grain elevator  20  conveys grain  26  from the threshing machinery within the combine to the grain storage tank mounted at the top of the combine, as is well known in the art and not further illustrated in this disclosure. 
     A section of the case  22  of clean grain elevator  20  has been cut away in FIG. 2 to show the paddles  24  which elevate grain  26  on the lift side  28  of clean grain elevator  20 . Paddles  24  are carried by continuous chain  30  which also lowers paddles  24  on return side  32  of clean grain elevator  20 . A separating wall  34  is vertically disposed to separate lift side  28  from return side  32  of clean grain elevator  20 . The moisture sensor  4  includes housing  36  to which is coupled an intake duct  38  which is preferably a flexible or bendable tube with low friction inner surfaces which is in communication with the lift side  28  of clean grain elevator  20  such that some units of grain  26  may freely fall into intake duct  38  and pass into housing  36 . Stationed below moisture monitor  4  is test weight monitor  6  which may receive grain passed through housing  36  of moisture monitor  4 . Grain received in test weight monitor  6 , after weighing, may fall into funnel  40  and be returned to the return side  32  of clean grain elevator  20  via return duct  42  which is also a flexible tube which communicates through case  22  with the return side  32  of clean grain elevator  20 . The use of flexible tubes for intake duct  38  and return duct  42  allows the moisture monitor  4  and test weight monitor  6  combination to be mounted to the clean grain elevator of combines of various makes and models. 
     A level sensor  44  is mounted to housing  36  near intake duct  38 . Moisture sensing unit  46  is mounted to housing  36  below level sensor  44  and above wheel housing  50 . A solenoid unit  48  is mounted upon wheel housing  50  to selectively control passage of grain in housing  36  into test weight monitor  6 . 
     The flow rate meter  8  of the preferred embodiment system is positioned at the exit outlet  54  of the clean grain elevator  20  at upper end  56  thereof such that all grain leaving the clean grain  20  elevator passes into the flow rate meter  8 . Flow rate meter  8  includes an intake hopper  58  into which grain leaving the clean grain elevator is received. Grain  26  which has passed through flow meter  8  exits through discharge chute  60  and may pass to a fountain auger (not shown) which may be located within the grain storage tank of the combine. 
     A motor  64  is mounted near flow meter  8  for powering thereof. Rotation sensor  62  is mounted to flow meter  8  to measure the angular displacement of flow meter  8  and to provide such data to the signal processor  2 . 
     FIG. 3 illustrates the preferred embodiment flow rate meter  8  with its front cover removed so that internal components thereof may be understood. Flow rate meter  8  comprises a paddlewheel  66  having radially disposed multiple fins  68  which in the preferred embodiment are generally equally angularly spaced. Paddlewheel  66  is selectively driven in a clockwise direction by variable speed motor  64  which is preferably a DC motor powered by the electrical system of the combine. Variable speed motor  64  drives paddlewheel  66  at varying rates of rotation wherein the level of grain  26  in bin  70  is maintained generally constant. Grain  26  is allowed to fall freely through grate  72  into equal volume sectors  74  of paddlewheel  66  defined by adjacent fins  68 . Paddlewheel  66  is rotatively driven about an axis defined by drive shaft  76  thereof which in the preferred embodiment is disposed generally horizontally. Paddlewheel  66  is housed in cylindrical housing  78  which is provided with an opening into discharge  80 . The level of grain  26  present in bin  70  above paddlewheel  66  is sensed by a height detector  82  mounted within the top cover  86  of bin  70 , height detector  82  preferably being an ultrasound transducer  84  which detects the level of grain  26  in bin  70 . Other types of height detectors  82  may be used. When grain present in bin  70  rises above a predetermined level, height detector  82  transmits a control signal which causes the speed of variable speed motor  64  to increase, thereby driving paddlewheel  66  at an increased speed in order to more rapidly transfer grain  26  from bin  70  to discharge  80  in order to lower the level of grain  26  in bin  70 . When height detector  82  senses a lowering of the level of grain  26  in bin  70 , it signals variable speed motor  64  to drive paddlewheel  66  at a slower rate to slow passage of grain  26  from bin  70 . This feedback operation of motor  64  and height detector  82  thereby maintains the level of grain  26  in bin  70  above grate  72  at a consistent, predetermined level. 
     The rotational movement of paddlewheel  66  is measured by rotation sensor  62  and the angular displacement of paddlewheel  66  over time is transmitted by rotation sensor  62  to the signal processor  2  which may calculate the volume of grain exiting the clean grain elevator  20  as a function of time. Because the volume of each of sectors  74  of paddlewheel  66  is known, the volume of harvested grain  26  per unit of time exiting clean grain elevator  20  may be calculated. Any time increment may be utilized for such determination but it is found that a useful time interval is in the range of one to five seconds, and more preferably about two seconds, in which period the moisture and test weight of grain samples is collected. The volume per time calculation resulting from measurement of the rotation of paddlewheel  66  provides a grain yield result which must be corrected to a market moisture content and standard weight per bushel of the grain type being harvested. 
     Referring additionally to FIGS. 5 and 7, the features of paddlewheel  66  and its interaction with grate  72  may be visualized. Paddlewheel  66  may be driven by variable speed motor  64  by use of belt  90  or by gears which interconnect motor shaft  88  with drive shaft  76  of paddlewheel  66 . Rotation sensor  62  is coupled to drive shaft  76  such that the angular displacement of paddlewheel  66  may be measured and transmitted to the signal processor  2 . 
     Each of fins  68  of paddlewheel  66  has a free edge  92  which is provided with a multiplicity of spaced apart relatively stiff brushes  94  which may deflect slightly when an item of grain is caught between a brush  94  and the inside of cylindrical housing  78 . The placement of brushes  94  along edges  92  of fins  68  is prescribed by the spaces between bars  96  of grate  72 . Preferably bars  96  are triangular in cross section with the vertices  98  thereof oriented upwardly so that grain may be funneled through grate  72  and evenly deposited in sectors  74  of paddlewheel  66 . Brushes  94  are sized to extend from edges  92  such that brushes penetrate very slightly into the spaces between bars  96  of grate  72 , thereby serving to wipe grain units into sectors  74  without damage to the grain units. 
     Referring now to FIGS. 4 and 6, the moisture sensor  4  and test weight monitor  6  may be seen in more detail. Intake tube  38  feeds grain  26  from lift side  28  of clean grain elevator  20  into vertically oriented housing  36 . A moisture sensing unit  46  is mounted along housing  36  such that sensing probe  106  is exposed to grain  26  within housing  36 . Moisture in grain  26  causes moisture sensing unit  46  to respond with an electrical signal proportional to the percentage of moisture in the grain and this electronic signal is transmitted to the signal processor  2  during periodic polling by signal processor  2 . 
     Disposed partially in alignment below housing  36  is wheel  108  housed within wheel housing  50 . Wheel  108  is provided with a multiplicity of circumferential compartments  110  separated by blades  112  which radiate from central hub  102 . Blades  112  are angularly equidistant and number at least four and preferably a multiple of four such that the wheel  108  may be turned in one-quarter turn increments and convey the same volume of grain for each quarter turn. The compartments  110  are sized such that one-fourth rotation of wheel  108  will convey a known fraction of a bushel or other suitable volume measure of grain  26 . Wheel  108  is limited in its rotation by interaction of spoke wheel  104  with solenoid plunger  116  which extends to intercept one of spokes  114  when solenoid unit  48  is energized. Spoke wheel  104  is fixed to hub  102  such that rotation of spoke wheel  104  coincides with rotation of wheel  108 . Wheel housing  50  is open where it meets lower end  118  of housing  36  such that grain  26  in housing  36  will be stored in compartments  110  of wheel  108  while wheel  108  is prevented from rotating. When grain  26  rises in housing  36  to the level of level sensor  44 , level sensor  44  senses the grain and issues a signal to solenoid  48  to momentarily de-energize for sufficient duration for wheel  108  to rotate in a counterclockwise direction one-quarter turn thereby transferring a known volume of grain into open topped container  120 . Container  120  is fed by guide chute  122  disposed below wheel  108 . As wheel  108  rotates, the contents of filled compartments  110  are dumped into guide chute  122  and empty compartments  110  of wheel  108  are moved into position below housing  36  and fill by gravity with grain, thereby dropping the level of grain  26  below level sensor  44 . 
     When grain  26  drops from wheel  108  into container  120 , bottom  124  thereof is retained in its closed position by action of trap door controller  132 . While resting on bottom  124  of container  120 , grain  26  of known volume in container  120  may be weighed by first load cell  126 . Because of vibration and jiggle within the combine, and variations of slope or tilt of the combine as it travels over uneven ground, error in weighing may occur which is compensated for by comparative weighing of dummy weight  128  by second load cell  130 . Dummy weight  128  is preferably chosen to be equal to the standard test weight of a predetermined volume (equal to the known volume conveyed in one quarter turn of wheel  108 ) of the grain to be harvested plus the tare weight of container  120  when empty such that the measured weight from second load cell  130  may be compared with the measured weight of first load cell  126  to determine the test weight of the known volume of harvested grain  26  present in container  120 . This measured grain test weight is stored in associated circuitry and made available for polling by signal processor  2  until a new sample of grain  26  is placed in container  120  and its weight determined and stored. 
     When level sensor  44  detects grain, level sensor  44  first signals trap door controller  132  to extend prior to signaling solenoid  48  to de-energize, thereby permitting the bottom  124  of container  120  to swing downward allowing the contents of container  120  to fall into funnel  40  to thereafter fall through return duct  42  into return side  32  of clean grain elevator  20 . Trap door controller  132  promptly returns bottom  124  to its closed position and wheel  108  is then permitted to rotate to refill container  120  with a new grain sample. An interlock member intercoupling trap door controller  132  and solenoid unit  48  prevents solenoid plunger  116  from retracting while bottom  124  is not retained in a closed position by trap door controller  132 . 
     Once flow rate data has been generated by the signal processor  2  from the angular displacement per unit time of paddlewheel  66  as measured by rotation sensor  62  of flow rate meter  8 , the raw yield rate may be determined by dividing the flow rate by the product of ground speed of the combine and the swath of the combine cutter head. This raw yield data can then be corrected to a standard yield rate in pounds (and bushels) per acre of dry grain by adjusting the volume per unit area (bushels per acre) of wet grain to a standard market moisture and to a standard market weight (for example, the standard market weight for corn at fifteen percent moisture is fifty-six pounds per bushel) from the moisture data provided by the moisture sensor  4  and from the test weight data provided by the test weight monitor  6 . The resulting standard yield data may then be displayed on the display  16  for review by the combine operator and it may be integrated with coordinate data provided by the DGPS receiver  10  and stored on the non-volatile memory  18  for later review or for transfer to external computing and display devices. Hence the system invention may provide real time yield data with increased accuracy over other methods since approximation of grain test weight is avoided and calibration adjustments for speed and condition of the clean grain elevator  20 , and for variation of the grain flow rate, terrain slope, and grain quality, are not required. 
     FIG. 8 illustrates an electrical schematic for the test weight monitor  6  of the system invention. Voltage regulator  140  regulates the combine&#39;s onboard 12 VDC voltage to a convenient 10 VDC which is used as excitation voltage for first load cell  126  and for second load cell  130 . A satisfactory load cell unit for use for first load cell  126  and second load cell  130  may be an OMEGA™ LCL-454G full bridge load cell manufactured by OMEGA Engineering, Inc. of Stamford, Conn. The OMEGA™ LCL-454G load cell has a rated capacity of sixteen ounces and a rated output of two millivolts per volt of excitation voltage (twenty millivolts output at full scale deflection or 1.25 millivolts per ounce with 10 VDC excitation). Second load cell  130  suspends dummy weight  128  which is predetermined to be equal to the standard test weight of a predetermined volume of the grain to be harvested plus the tare weight of the container  120  when empty. Dummy weight  128  may be preset at nine ounces such that second load cell  130  will generate 11.25 millivolts referenced to ground at second terminal  138  when second load cell  130  is 3 excited with 10 VDC. If test container  120  holds seven ounces of grain precisely at standard test weight and market moisture content and container  120  weighs two ounces, then first load cell  126  will deliver 11.25 millivolts referenced to ground at first terminal  136  when first load cell  126  is excited by 10 VDC. Voltmeter  134  measures the potential difference between the output voltage of first load cell  126  at first terminal  136  and the output voltage of second load cell  130  at second terminal  138  and this voltage difference is directly related to the test weight of the predetermined volume of grain held in container  120  when its bottom  124  is closed. Because dummy weight  128  is preselected to be approximately the same mass as that of container  120  filled with a grain sample of known volume to be weighed, vibration and jiggle within the moving combine will be substantially offset and the potential difference detected by voltmeter  134  will represent the weight difference between filled container  120  and dummy weight  128  and this weight difference can be combined with the known weight of dummy weight  128  and the total reduced by the tare weight of the container  120  to obtain the test weight of the grain sample weighed.