Abstract:
This invention relates to a fluid flow control method that enables a self-propelled irrigation machine to apply varying amounts of fluid as might be required to suitably treat the surface area affected by each of the individual fluid application devices thereon. The control method regulates the total volume of fluid emitted by each application device to a predetermined value as it responds to a suitable control signal to permit or prevent fluid flow. This fluid flow control method involves time-based rapid cycling of the flow control apparatus to provide continuously variable fluid flow as is required to meet the desired average output of each emitting device as the flow requirement varies from time to time as needed to produce a selected, pre-determined application rate throughout the treated surface area.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Agricultural irrigation machines of the type known as center pivot machines have a main pipeline section supported at intervals on movable towers for rotation about an inner end of the pipeline. Water is supplied to the fixed, inner end of the pipeline and distributed through sprinklers or other fluid emitting devices placed along or supported from the pipeline. The movement of the main pipeline section about its central pivot point irrigates a circular portion of a field. The circular portion swept by the main pipeline is designated herein the primary field space. This leaves the corners of square or rectangular fields or other irregular perimeter areas without irrigation. In installations where the additional productive capacity of a field&#39;s corners or irregular perimeter areas warrants, the corners or irregular perimeter areas can be irrigated by adding an auxiliary span or spans near the outer end of the main pipeline for irrigating areas of the field outside of the circular area. These areas to be irrigated outside the primary field space are herein designated the secondary field space. The auxiliary span or spans are in fluid communication with and supplied by the outer end of the main pipeline section. Such an auxiliary structure is capable of moving as needed to extend into the corners or other irregular areas while also moving to keep up with the main pipeline section&#39;s rotation about the center pivot.  
           [0002]    A commonly-used motion control scheme for center pivot units causes the outermost tower on the main pipeline section to advance independently at a user-defined speed. All inboard towers advance as needed to keep the main pipeline straight. The auxiliary structure may be pivotally connected near the outer end of the main pipeline and supported on an auxiliary tower. The auxiliary tower may travel inside or outside of the main circle, following its own guide path. That path may be defined by various means, such as a buried cable. The guide path for the auxiliary tower extends at least partially into the corners or irregular perimeter areas of the fields, thereby causing the auxiliary structure to move out into any irregular area when the main pipeline is adjacent to such a feature. As the auxiliary structure moves into, through, and out of such secondary field space, the fluid emitting devices mounted thereon or supported therefrom are required to provide varying amounts of fluid as the field surface “area of responsibility” for each emitting device changes and as the velocity of each emitting device changes. When the main pipeline is adjacent the side of a field the auxiliary tower usually lags behind the main pipeline, thereby folding the auxiliary structure back in to a trailing position behind the main structure. With the auxiliary structure in this position the fluid emitting devices mounted thereon are required to provide very little if any contribution as the field surface area is effectively treated by the emitter devices on the main pipeline.  
           [0003]    The object of both the main pipeline span and the auxiliary span is to apply to the field a user-specified amount of fluid, typically expressed in inches, both in the primary field space and in the secondary field space to suitably treat the surface area affected by each of the individual fluid application devices thereon. Since the emitters on the main pipeline move in a relatively uniform way, adjustments in their size and spacing can readily accommodate their differences in area of responsibility arising from different radial locations on the main pipeline. However, such adjustments cannot be used to address the situation faced by the auxiliary span emitters. The movements of these emitters create irregularities in both the sizes of their zones of responsibility and the amount of time they spend in those zones. These irregularities make it difficult to apply the desired amount of irrigation in the secondary field spaces.  
           [0004]    In the past, controls for the emitters on the auxiliary span have relied primarily on a measurement of a control angle between the auxiliary span and the main pipeline. Different auxiliary span emitters, typically ganged into groups or banks of emitters, were successively turned on as the control angle increased beyond 85°. Eventually when the control angle became large enough, which meant the auxiliary span was well extended beyond the primary field space, all of the banks were turned on. As the auxiliary span folded back in and the control angle became smaller, the banks were successively turned off. The banks were set up such that a particular bank did not include any adjacent emitters. For example, every tenth emitter would be in a particular bank. Thus, the banks were fully interleaved.  
           [0005]    This prior art auxiliary emitter control method for the most part is able to prevent auxiliary emitters from irrigating the primary field space, which would otherwise over-irrigate the outer portions thereof. And the prior art control method generally assures that most of the secondary field space will receive water in some amount. That amount may be too much, it may be too little, or perhaps it may even be the desired amount. Whatever the case may be, the prior art control method can not uniformly vary the average amount of water which is emitted. At most it can turn an emitter on and achieve its full flow rate for a sustained period of time, or turn it off and have a zero flow rate.  
           [0006]    As mentioned above, the problem is that both the size of the area of responsibility of a particular emitter and the time available to that emitter in which it can apply water to that area are constantly changing. Furthermore, both of these parameters vary radically among the various emitters on the auxiliary span. The prior art control methods and apparatus are incapable of adequately dealing with these variations.  
         SUMMARY OF THE INVENTION  
         [0007]    This invention relates to a fluid flow control method that enables a self-propelled irrigation machine to apply varying amounts of fluid as might be required to suitably treat the surface area affected by each of the individual fluid application devices thereon as the surface area affected, and/or available exposure duration, vary from time to time as the machine travels along its path.  
           [0008]    The control method regulates the total volume of fluid emitted in a given time frame by each application device or emitter to a predetermined value as it responds to a suitable control signal to permit or prevent fluid flow.  
           [0009]    This fluid flow control method involves time-based rapid cycling of the flow control apparatus to provide continuously variable fluid flow as is required to meet the desired average output of each emitting device as that requirement changes from time to time.  
           [0010]    Flow control cycles are variable in frequency and duration.  
           [0011]    Flow control cycles are definable based upon the desired application for a specific area of responsibility.  
           [0012]    Rapid cycling causes the fluid emitting devices to emit brief bursts of fluid.  
           [0013]    This time-based rapid cycling is utilized to provide the desired output from each emitting device at any given time as the irrigation machine travels along its path.  
           [0014]    This fluid flow control method utilizing time-based rapid cycling of the flow control apparatus is capable of providing continuously variable average fluid flow as is necessary to meet the changing requirements as the field surface area of responsibility and/or available exposure duration for each emitting device changes.  
           [0015]    The preceding paragraphs illustrate the utilization of this control concept to control the flow of fluid emitted from devices mounted on or supported from an auxiliary span or spans added to the outer end of the main pipeline of a center pivot irrigation system to address the application of fluids to areas beyond the reach of the main structure. These are the features utilized to illustrate the control concept. It must be understood that the control concept claimed herein is not limited to this application, but rather that the control system can be beneficially utilized at any time that the fluid emitting devices are required to provide varying amounts of fluid as the field surface area of responsibility and/or available exposure duration for the various emitting devices changes. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a schematic plan view of a quadrant of a first field showing a main pipeline in one position and the auxiliary span in multiple positions.  
         [0017]    [0017]FIG. 2 is an enlarged schematic plan view, similar to FIG. 1, showing the details of an effective width W of an emitter.  
         [0018]    [0018]FIG. 3 is a schematic plan view of a second field showing where various programs might be used.  
         [0019]    [0019]FIG. 4 is a schematic elevation view of the banking configuration on the auxiliary span used in the specific field of FIG. 3.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    [0020]FIG. 1 schematically illustrates a center pivot irrigation machine according to the present invention. The machine includes a main pipeline  10  mounted on self-propelled towers  12 . The inner end  14  of the main pipeline is mechanically connected to a center pivot. Irrigation fluid, which may be water or water mixed with fertilizer, herbicide, insecticide or the like is supplied to the main pipeline at the center pivot. The outer end  16  of the main pipeline describes a circle  18  as it moves in the direction of arrow Z. The circle  18  defines the primary field space  20 . Emitters (not shown) are located along the main pipeline for distributing fluid to the primary field space.  
         [0021]    An auxiliary span  22  is mounted on an auxiliary tower  24  and connected near an outer end  16  of the main pipeline. The auxiliary span is a pipeline that receives fluid from the main pipeline for distribution through a plurality of auxiliary emitters spaced along the auxiliary span. Two such emitters are shown at  26  and  28 . The outer end of the auxiliary span describes an irregular outer boundary  30 . The area between boundary  30  and circle  18  is the secondary field space  32 . The auxiliary emitters distribute fluid primarily to the secondary field space. A nominal property boundary is illustrated at  34 . For clarity of the drawing the emitters  26  and  28  are shown on only one illustration of the auxiliary structure. Similarly, the auxiliary tower is shown on only the illustrations of the auxiliary structure. Obviously the auxiliary tower and emitters are present in each and every position of the auxiliary structure.  
         [0022]    [0022]FIG. 1 also illustrates a series of imaginary arcs  36 ,  38 ,  40 ,  42 ,  44  and  46 . These arcs are concentric with the center pivot of the irrigation machine. The arcs are equally spaced radially to define a plurality of swaths A-F outside of the primary field space  20 . It will be understood that while the main pipeline  10  is shown in only one position in FIG. 1, the auxiliary span  22  is shown in multiple positions. This shows how the auxiliary span moves from a tucked position to an extended position and back again. The tucked position occurs when the auxiliary span is opposite a point where the circle  18  and property boundary  34  converge. In other words, in the field of FIG. 1, the auxiliary span is tucked when it is adjacent to the twelve o&#39;clock position, as well as the three, six and nine o&#39;clock positions. The extended position occurs when the auxiliary span is opposite a corner of the property boundary, e.g., between the one and two o&#39;clock positions. FIG. 1 also illustrates an imaginary radial line (RL 1 ) projecting outwardly from the center pivot to the property boundary.  
         [0023]    The emitters can be connected to a control means such as a combined pressure regulator and shut-off valve, as shown in U.S. Pat. No. 6,374,853, the disclosure of which is incorporated herein by reference. Also, as used herein the term emitter can refer to a single device or to a group of devices given the same control signal. Each emitter includes either an internal or external valve that is controllable to start and stop fluid flow from the emitter, such as the valve in the referenced patent. An emitter could also include an end gun.  
         [0024]    On any radial line projected outwardly from the center pivot  14  to intercept the path of the auxiliary span, the center of the instantaneous area of responsibility of a given emitter (or bank of emitters) can be represented by the radial distance D beyond the central pivot  14  to the physical center point of the fluid application pattern of that specific emitter as it crosses that radial line. For a given emitter this radial distance obviously increases as the auxiliary span swings out into the secondary field space. Looking at FIG. 1, when the auxiliary span  22  is in position  1 , the control angle between the pipeline and auxiliary span is only slightly above 90 degrees and an emitter located such as  26  is so close to the primary field space that it may be shut off. An outer emitter such as at  28  maybe extending slightly into swath A and thus may be turned on. As the auxiliary span swings out to positions  2 ,  3  and  4 , outer emitter  28  has a greater distance D from the pivot point  14  and now takes on a portion of swath B as its area of responsibility. Other emitters closer to outer end  16  become responsible for swath A and are turned on. As the auxiliary span swings out to position  5 , the outer emitter becomes responsible for a portion of swath C and hands-off responsibility for inner swaths A and B to more inboard banks. It will also be noted that in order for the outer emitters to cover the greater distances needed to keep up with the main pipeline, the velocity of the auxiliary tower  24  will increase with a corresponding increase in the velocity V of the outer emitters. Once the auxiliary span gets to positions  5  or  6 , all of the banks may be required to turn on to cover swaths A-F.  
         [0025]    As illustrated in FIG. 2, the effective width W of the instantaneous area of responsibility of a given emitter at any given time extends radially both inwardly and outwardly from the center point of the fluid application pattern of that specific emitter to the area of responsibility of the adjacent emitters inboard and outboard. Depending upon the size and shape of the fluid application patterns of the various emitters utilized, the physical application of fluid by a specific emitter may overlap and be overlapped considerably (or not at all) by those of adjacent devices. At such-times as the fluid application patterns of proximate emitting devices adequately overlap, it is possible to combine the flow requirements of those devices into that of a single device or group of devices which is most appropriately located to serve the combined areas.  
         [0026]    When the fluid application patterns of adjacent emitters are of equal width, it might be presumed that the effective width of their instantaneous areas of responsibility would likewise be equal when crossing a specific radial line. That assumption, however, would likely be incorrect. Due to the fact that the emitters are spaced along the auxiliary span and that the auxiliary span is caused to change its angular disposition with regard to the main pipeline as it swings into, through, and out of a secondary space, the effective width of the area of responsibility of a given emitter is constantly changing. Further, while the auxiliary span may be at one angular disposition, such as position  4 , with respect to the main pipeline as the inboard emitters cross a specific radial line, such as that represented by line RL 1  on FIG. 1, it may be at a considerably different angular disposition such as position  5 , as the outboard emitters cross that same radial line. Therefore, the effective width W of the area of responsibility for a given emitter as it crosses a specific radial line can only be measured with respect to that of the next emitters inboard and outboard as they cross that same radial line.  
         [0027]    Determination of the effective width W of the instantaneous areas of responsibility, and the instantaneous velocities, for each of the respective application devices as they cross a specific radial can be readily calculated once the precise path of the machine, as it crosses that radial, is known. This is illustrated in FIG. 2. Here main pipeline  10  is at an angle α with respect to the auxiliary span  22 . An emitter  26  (or the center point CP of a bank of emitters) is shown in an instantaneous position crossing a fixed radial line RL 2 . Center point CP has a distance D from the pivot point  14  of the machine. Assume the spray pattern for this emitter is circular as shown by the dotted circle about point CP. The spray pattern has a width along the auxiliary span of Ws which, given the assumed circular spray pattern, is the diameter of the circular spray pattern. The center of the emitter CP has an instantaneous velocity vector V which is perpendicular to the auxiliary span  22 . This vector resolves into a radial velocity Vr, which is parallel to radial line RL 2 , and an angular velocity Va, which is perpendicular to the radial line RL 2 . The angle between the angular velocity vector Va and the auxiliary span is θ. It can be seen from the geometry involved that the effective width W of the instantaneous area of responsibility as it sweeps through a swath in the secondary field space is equal to Ws·sin θ. It will also be appreciated that by time the adjacent outboard emitter  26   a  reaches radial line RL 2 , angle α between the main pipeline and auxiliary span will have changed and therefore, θ for emitter  26   a  will be different than it was for emitter  26  at the time emitter  26  crossed radial line RL 2 .  
         [0028]    In a similar manner, the radial distance D to the physical center point of the fluid application patterns, the effective width W of the instantaneous areas of responsibility, and the instantaneous velocities V, for each of the respective application devices can likewise be determined at any specific point along the path of the machine.  
         [0029]    As discussed above it is the objective to maintain a pre-determined, user-selected application rate R, measured in inches, in both the primary and secondary field spaces. The factors in the application rate are: Q, the individual emitter average flow rate, in inches-cubed/second; W, the instantaneous effective width of the area of responsibility of the emitter in inches, and Va, the instantaneous angular velocity of the emitter along its path of movement, in inches/second. Thus, the desired condition is: R=Q/(W*Va) where R is the user-selected rate. Not only is this the desired condition at an individual emitter, it is also desired that all emitters perform together as necessary to suitably treat the surface area affected by each. Since W and Va are constantly changing for a particular emitter, as illustrated above, and W and Va vary among the total emitters, it follows that in order to maintain R accurately for all emitters, Q must be controlled at each emitter as dictated by W and Va at that emitter.  
         [0030]    Control of Q can be accomplished by selecting the appropriate percent “ON” time during a given cycle period. Thus, in a given situation, it may be determined from the above equation that Q should be, for example, about half of an emitter full flow rate. To meet that requirement, if a cycle period is chosen to be one minute, the desired average flow rate may be obtained by turning the emitter on for 30 seconds during that cycle time. It is preferable to stagger the on/off times of the various emitters during the cycle period to prevent an excessive number of the emitters from turning on or off at once.  
         [0031]    Actual control of Q can be achieved by a computer, typically mounted on the auxiliary tower, that monitors sensed values of W and Va and calculates the appropriate “ON” time percentage to achieve the desired Q. W is sensed by combining the known location of an emitter on the auxiliary span with a measurement of the control angle α between the auxiliary span and the main pipeline. W may also be sensed combining the known location of an emitter on the auxiliary span with a measurement of the angle between the auxiliary span and its travel path. V may be determined through a combination of the velocity of the auxiliary tower and the velocity of the end tower of the main pipeline. V may also be determined through other means. The end tower velocity may be obtained either through the percentage travel rate set by the operator, by the percent of standard rate set at the end tower drive motor or by other means. The auxiliary tower velocity may be determined directly or it may be determined because it is whatever velocity required along its path to maintain a constant distance between the end tower and the auxiliary tower. By combining the emitter location with the velocities of the end tower and auxiliary tower the velocity of the emitter can be derived. Once the computer determines what Q should be it can calculate the appropriate percent “ON” time needed to achieve Q. The percent “ON” time signal is sent to the valve controlling the emitter in question to produce the desired flow rate Q that will in turn produce the desired application rate R. Electrical, hydraulic or pneumatic systems could be used to connect the computer to the emitter&#39;s control valves.  
         [0032]    While continuous computer monitoring and adjustment of the percent on time is one way to achieve the results of the present invention, an alternate embodiment is contemplated which essentially calculates the percent on times in advance for a particular field. The results are then stored in one or more lookup tables that maintain instructions for each bank of emitters at a particular location on that specific field. Typically more than one lookup table (also known as a program) may be used for a particular field. That is, one lookup table may be appropriate when the pipeline is in one position while another lookup table is preferred as the pipeline makes its way into another position.  
         [0033]    [0033]FIG. 3 illustrates an example of a field having an irregular secondary field space  48 . Line  50  describes the path of the auxiliary tower. Line  52  defines the outer boundary of the secondary field space, i.e., the extent of the surface area that can be irrigated by the auxiliary span. As the main pipeline  10  approaches the four o&#39;clock position, indicated by arrow  54 , a look up table called “forward opening” may be selected for use. When the seven o&#39;clock position (arrow  56 ) is approached a second lookup table called “forward holding” may be used. As the eight o&#39;clock position (arrow  58 ) arrives the auxiliary span is going to be heading back to a tucked position and a third lookup table or program called “forward closing” may be preferred. These lookup tables or programs may vary further as the auxiliary span goes between tucked and extended positions.  
         [0034]    One alternate means of establishing in advance lookup tables with the percent “ON” times of the emitters to be controlled on the auxiliary span is by combining the known location and shape of the emitter fluid application pattern with a measurement of the control angle α between the auxiliary span and the main pipeline and the relative velocities of the end tower and auxiliary tower. In operation, once the computer determines the above angle and relative velocities, it can select from the appropriate table the percent “ON” time needed to control the various emitters. The percent “ON” time signals are sent to the valves controlling the emitters in question to produce the desired application.  
         [0035]    Another alternate means is by combining the known location and shape of the emitter fluid application pattern with a measurement of the control angle between the auxiliary span and the travel path of that span and the relative velocities of the end tower and auxiliary tower.  
         [0036]    A further alternate means is by combining the known location and shape of the emitter fluid application pattern with a measurement of the control angle α between the auxiliary span and the main pipeline, a measurement of the control angle between the auxiliary span and the travel path of that span, and the velocities of either or both of the end tower and auxiliary tower.  
         [0037]    Alternately, with the total path of the machine known and stored in a database, all necessary table information can be pre-determined and combined into a single table.  
         [0038]    [0038]FIG. 4 illustrates the banking configuration on the auxiliary span that may be appropriate for a field set up as in FIG. 3. A control computer  60  is mounted on the auxiliary tower  24 . The end or outermost tower of the main pipeline, that is, the one closest to the auxiliary span, is shown at  62 .  
         [0039]    The auxiliary span  22  has a total of forty emitters in banks of three, four and five. Each emitter is connected to one of the control lines  64 . Each control line  64  includes a quick exhaust valve. The quick exhaust valves are indicated schematically at  66 . The control lines are each successively connected to a plurality or bank of emitters. In the embodiment shown the emitters are daisy-chained to the control lines. In the illustration of FIG. 4, each intersection of one of the control lines  64  with the auxiliary span  22  represents an emitter. Note that the emitters in a particular bank are adjacent one another. There is no interleaving of emitters required within a bank. This is contrary to the banking configurations of prior irrigation machines and it allows simplified control apparatus, particularly where hydraulic or pneumatic controls are used.  
         [0040]    With the banking configuration of FIG. 4 operating on the field of FIG. 3, an example of a “forward opening” program or lookup table might be as shown in the following chart. At the top of the chart there is a conversion table for each bank as it relates to its corresponding output. The sequence of numbers in brackets { } is the rapid cycling programming. For example, the first line {7,8800,60,0} means that Output 7 (which is Bank 1, per the conversation table) at a control angle of 88.00 degrees between the auxiliary span and the main pipeline is ON 60% out of 60 seconds. The 0 is a time slot for the cycling to prevent all banks from shutting off at the same time.  
                                                                           Program: Opening           Forward Standard           Cycle Length: 60 seconds           (Potential Settings: 30           seconds to 600 seconds)           Bank to Output           Conversion Table (used to           derive data below                Bank   Output                        0   NA            1   7            2   2            3   4            4   1            5   9            6   6            7   3            8   8            9   0           10   5                { 7, 8800, 60, 0},           {2, 8800, 10, 60},           {0, 8800, 30, 70},           {3, 7700, 50, 50},           {8, 8800, 50, 0},           {1, 8800, 20, 70},           {5, 8800, 20, 10},           {9, 8800, 20, 30},           {9, 8800, 20, 50},           {4, 8800, 10, 0},           {2, 9100, 0, 0},           {1, 9100, 0, 0},           {7, 9100, 70, 0},           {6, 9100, 30, 70},           {3, 9100, 30, 0},           {5, 9100, 70, 30},           {8, 9100, 50, 0},           {0, 9100, 50, 50},           {9, 9100, 20, 60},           {4, 9100, 20, 80},           {7, 9600, 60, 0},           {3, 9600, 40, 60},           {8, 9600, 40, 0},           {5, 9600, 60, 40},           {0, 9600, 40, 0},           {2, 9600, 30, 40},           {4, 9600, 30, 70},           {6, 9600, 30, 10},           {9, 9600, 30, 40},           {1, 9600, 30, 70},           {5, 10100, 100, 0},           {7, 10100, 70, 0},           {1, 10100, 30, 70},           {8, 10100, 50, 0},           {2, 10100, 50, 50},           {0, 10100, 50, 0},           {4, 10100, 40, 50},           {6, 10100, 40, 20},           {9, 10100, 40, 60},           {3, 10100, 40, 0},           {7, 10600, 80, 0},           {6, 10600, 50, 0},           {4, 10600, 50, 50},           {3, 10600, 50, 0},           {8, 10600, 50, 50},           {2, 10600, 40, 10},           {0, 10600, 50, 50},           {9, 10600, 40, 0},           {1, 10600, 30, 40},           {7, 11100, 80, 0},           {2, 11100, 30, 0},           {4, 11100, 70, 30},           {1, 11100, 70, 0},           {9, 11100, 70, 30},           {6, 11100, 70, 30},           {3, 11100, 70, 30},           {8, 11100, 70, 0},           {0, 11100, 70, 30},           {8, 11200, 90, 0},           {0, 11200, 90, 10},           {7, 11200, 80, 0},           {6, 11200, 80, 20},           {4, 11200, 70, 0},           {2, 11200, 30, 70},           {1, 11200, 70, 30},           {9, 11200, 70, 0},           {3, 11200, 70, 30},           {7, 11600, 90, 0},           {1, 11600, 80, 20},           {6, 11600, 80, 0},           {8, 11600, 80, 20},           {0, 11600, 80, 0},           {4, 11600, 70, 30},           {3, 11600, 70, 0},           {2, 11600, 60, 40},           {9, 11600, 60, 0},           {9, 12100, 100, 0},           {3, 12100, 100, 0},           {8, 12100, 100, 0},           {0, 12100, 100, 0},           {1, 12100, 90, 0},           {7, 12100, 80, 20},           {6, 12100, 80, 0},           {2, 12100, 70, 30},           {4, 12100, 70, 0},           {1, 12600, 90, 0},           {7, 12600, 80, 20},           {4, 12600, 80, 0},           {9, 12600, 80, 20},           {6, 12600, 80, 0},           {8, 12600, 80, 20},           {0, 12600, 80, 0},           {2, 12600, 70, 30},           {3, 12600, 70, 0},           {8, 12900, 90, 0},           {0, 12900, 90, 10},           {7, 12900, 80, 0},           {4, 12900, 80, 20},           {2, 12900, 70, 0},           {1, 12900, 70, 30},           {9, 12900, 70, 0},           {6, 12900, 70, 30},           {3, 12900, 70, 0},           {7, 13100, 100, 0},           {1, 13100, 90, 0},           {3, 13100, 90, 10},           {4, 13100, 80, 0},           {8, 13100, 80, 20},           {0, 13100, 80, 0},           {2, 13100, 70, 30},           {6, 13100, 70, 0},           {9, 13100, 60, 40},           {2, 13300, 100, 0},           {4, 13300, 100, 0},           {1, 13300, 100, 0},           {9, 13300, 100, 0},           {6, 13300, 100, 0},           {3, 13300, 100, 0},           {8, 13300, 100, 0},           {0, 13300, 100, 0} },                      
 
         [0041]    Obviously the technique of developing one or more lookup tables that maintain instructions for each bank of emitters at a particular location on that specific field reduces the computer capability that has to be provided on the auxiliary tower or elsewhere, as opposed to an alternate embodiment wherein continuous computer monitoring and adjustment of the percent on time is accomplished as the machine follows its path. It will be understood that this lookup table shown is for purposes of example only and is not to be considered limiting in any way. Different fields will require different values. Further, different programs, such as a holding forward program, or a closing forward program would have different values for the percent on times. In addition, optional alternate programs could be provided wherein alternate desired application rates are provided.  
         [0042]    The values of the percent on times may be derived from pre-calculating Q/(W*Va)=R for each control angle and each bank at any location within the field. They may also be determined by means of trial and error analysis of the water application patterns of the various emitters and their interaction in order to obtain the optimum desired application for each specific area. They may also be determined by continuous computer monitoring of the machine and adjustment of the percent on time to meet the appropriate requirements as the machine follows its path.  
         [0043]    Another alternate means of determining the appropriate on and off cycling rates for the various emitters is as follows: With the total path of the machine and auxiliary span known and stored in a database, a series of initial computer simulations can be performed to determine the maximum volume of fluid applied by each of the various emitting devices to each of its affected areas as that specific device travels its full path of the field. The application volumes of the various emitting devices affecting any specific area can then be individually adjusted to provide the desired combined application to all affected areas. As previously stated, at such times as the fluid application patterns of proximate emitting devices adequately overlap, it is possible to combine the flow requirements of those devices into that of a single device or group of devices most appropriately located to serve the combined areas.  
         [0044]    While a preferred form of the invention has been shown and described, it will be realized that alterations and modifications may be made thereto without departing from the scope of the following claims. For example, while the auxiliary span can be a swing span on the outer end of center pivot, as shown in FIG. 1, alternatively it could be a Z-span on a center pivot as shown in U.S. Pat. No. 4,674,681, or it could be a Z-span on a lateral move machine. Also, the application rate R is a user-selected, desired rate. While a common choice might be to make the application rate R uniform throughout both the primary and secondary field spaces, this is not necessarily always the selected choice. Particular field conditions, e.g., varying soil types, varying elevations, local obstacles such as rocks or the like, may dictate that a particular spot on a field be irrigated at a rate that is different from rates in other locations. In the case of a local rocky zone that cannot grow any crops, the desired rate may even be zero. The present invention accommodates such variations and allows the secondary field space to receive variable application rates.