Remote fluid level detection system

[0001] This application claims the benefit of the filing date of U.S. Provisional Application No. 60/265,317.

[0002] This invention relates to a remote fluid level detection system. The system uses magnetic detection to determine the fluid level in a confined vessel. Suitably, the invention is utilized with anhydrous ammonia field tanks.

[0003] Anhydrous ammonia (NH₃) is a substance used in agriculture as a fertilizer because of its high nitrogen content. Typically, anhydrous ammonia is applied to fields in the fall after the crop has been harvested to replenish the nutrients for the next season. The application of anhydrous ammonia involves the use of a field tractor, a field implement that is pulled behind the tractor and a large anhydrous ammonia tank that is pulled behind the implement. This creates a relatively long, train-like configuration of machinery.

[0004] Anhydrous ammonia is a multi-phase chemical that, when stored under pressure in the field tank, is in the liquid phase. Upon application, the fertilizer is injected into the topsoil, and it undergoes a phase transformation while percolating through the soil in a gaseous state. Since anhydrous ammonia is a hazardous material, and needs to be stored under pressure, the field tanks are made of heavy gauge steel; much like propane tanks for remote residential use. As a result, fluid level inside the tank is not visible and a special measurement device is needed to indicate fluid level remaining in the tank.

[0005] Many existing fluid level sensing systems make use of a magnetic float gauge assembly. Such an assembly comprises an aluminum float-arm that pivots about the center of the tank (See U.S. Pat. No. 2,795,955, incorporated herein by reference). As fluid level changes within the tank, the buoyancy of the anhydrous ammonia affects the position of the internal float. The arm is mechanically coupled via bevel gears to a vertical shaft that runs to the top of the holding tank. Fluctuations in the position of the internal float translate to a small angular rotation of the vertical shaft. To keep the tank completely sealed, a permanent magnet is attached to the top of the vertical shaft. On the outside of the tank, a simple local compass, with fluid level markings, then tracks the position of the internal magnet. In this way, the fluid level of the anhydrous ammonia tank is made visible to the farmer without creating any opportunity for leaks since there are no through-holes or seals needed for the tank gauge to function.

[0006] This type of gauge system, however, has many shortcomings. When the farmer is applying the anhydrous ammonia, the fluid level inside the tank is not known because the size and orientation of the gauge face render it completely unreadable from the cab of the tractor. This situation makes it necessary for the farmer to periodically stop application of anhydrous ammonia, get out of the tractor, and walk forty feet back to the field tank to read the small dial on the top of the tank. A standard 1450 gallon anhydrous ammonia field tank is sufficient for only 40 acres of farmland, so this tedious task of determining the fluid level as the tank reaches empty is a recurring annoyance that results in degraded time efficiency.

[0007] Another shortcoming of the prior system, is that the total amount of dispensed ammonia is not accurately known until the tank has been emptied. When the tank has been emptied, the farmer can finally approximate the total acreage covered by one full tank, and thus the application rate per acre.

[0008] The need exists, therefore, for a means by which fluid level may be known to the farmer on a continuous basis from within the tractor cab during the application process.

[0009] The present invention relates to a remote fluid level detection system which provides information to the user, in a wireless fashion, on the fluid level of a towed tank. The present invention is suitably designed for use with a tank containing anhydrous ammonia, but can be practiced with any tank containing fluid and a magnetic float gauge assembly.

[0010] Fluid level information is available on a continuous basis as fluid application is occurring. This eliminates the current need to stop application to physically read the existing gauge mechanism on the field tank.

[0011] The invention is composed of two electronic modules, a tank module and a display module, that communicate with each other by wireless means, namely a radio frequency transmission.

[0012] The tank module is affixed atop the existing mechanical gauge mechanism on a towed field tank, and utilizes a magnetic detection scheme to sense the orientation of a local magnetic field produced by the embedded magnet of the float gauge assembly. The position of the embedded magnet corresponds with the fluid level within the tank.

[0013] Due to the hazardous nature of anhydrous ammonia, the application and storage of the fluid is a closely controlled process by various industrial and government agencies. Therefore, a fluid sensing means which would require any modifications to the existing tank would require lengthy testing and approval requirements. The present invention does not require any modifications or removal of any existing hardware and therefore is a completely safe and easy to use fluid level detecting system that does not adversely affect the performance and safety of the original system. The means by which magnetic detection is achieved in the present invention is sufficiently sensitive to eliminate the need for removal or modification of the existing gauge face on an anhydrous ammonia tank.

[0014] The tank module physically covers the existing gauge mechanism. A small liquid crystal display on the tank module indicates the percentage of fluid remaining. This liquid crystal display may be incorporated into the tank module at a vertical orientation, to provide much easier viewing of internal fluid level.

[0015] The tank module is quickly and easily installed to existing fluid measurement hardware on a tank by the use of a quick-release mechanical system, which captures the head of the existing gauge firmly and without the use of any tools. This allows for the tank module to easily be moved from tank to tank with very little effort and time.

[0016] The tank module is designed to accommodate a number of possible mechanical gauge configurations found on a tank, such that various bolt patterns and gauge head geometries will interface equally well with the tank module. The geometric constraints of the tank module limit the orientation by which the invention may be installed to two distinct orientations: an orientation aligned with the magnetic sensing element, and an orientation 180 degrees offset from the magnetic sensing element. In the event the tank module is installed on the existing gauge mechanism 180 degrees offset from the orientation of the internal magnetic sensing element, the control firmware identifies this misalignment and resets the internal origin to compensate for this misalignment, such that the invention will operate equally well in either one of the two mounting orientation possibilities.

[0017] Prior fluid level detection gauges utilizing magnetic fields often do so as a means to merely detect low fluid levels or to detect fluid levels at one of several discrete fluid levels. The present invention utilizes a magnetic detection scheme that permits much higher resolution and therefore a much more precise indication of internal fluid level over a continuum between full and empty. The capability of more precisely monitoring fluid levels using this magnetic detection scheme may then be used in conjunction with other inputs to output secondary information that would not have previously been possible.

[0018] Within the tank module, a microcontroller based electronic circuit detects the orientation of the magnetic field being generated by the permanent magnet inside the existing gauge mechanism. This magnetic orientation detection is accomplished by utilizing a magnetic sensor. The magnetic sensor is capable of interfacing with the microcontroller within the tank module and reports the orientation of the magnetic field to one degree of precision or better. This allows the microcontroller to locate precisely the position of the embedded tank magnet, and consequently the corresponding internal fluid level. Data stored in an internal look-up table within the tank module microcontroller is referenced to translate the magnetic field orientation reading to a usable fluid level value that corresponds with a percentage of fluid remaining in the tank.

[0019] The tank module is equipped with a radio frequency (RF) transmitter that encodes the resulting fluid level data, and transmits it in a wireless fashion to the display module mounted inside the tractor cab. The display module receives the signal from the tank module, decodes the information and utilizes this information for a number of purposes.

[0020] Information on the current fluid level can be directly conveyed to the user within the tractor cab via a visible liquid crystal display in the display module. Additionally, a tank low audible alert is included in the system to notify the user when fluid level has dropped beneath a certain threshold.

[0021] The display module includes a means by which it can interface with the tractor's electronic groundspeed indicator, thereby providing information to the display module on the tractor's rate of travel through the field. The display module also permits the user to input information on the size of the anhydrous ammonia field tank and the width of the field implement.

[0022] Information from the tank module on current fluid level is combined with information on the tractor's groundspeed, information on the anhydrous ammonia tank size, and information on the width of the field implement, to provide useful secondary information. The width of the field implement information is multiplied by the tractor's groundspeed on a time-basis to monitor and store total acreage covered for any given tank. Fluid level information is also monitored and stored on a time basis, such that a corresponding vector can be calculated which approximates the flow rate of anhydrous ammonia to the field. The flow rate is then divided by the corresponding acreage covered to yield a corresponding average application rate per acre.

[0023] Manipulating the same information in different ways, and with various conversion constants, allows the invention to display information on the time remaining until tank is empty, number of acres covered per tank and warnings if fluid level drops faster than a set threshold, which would indicate a burst hose or other catastrophic event. The present invention permits this calculation to occur much earlier in the application process, and thus allows the user to compensate for any error between desired application rate and actual application rate. Such displayed data allows the user to compensate for any error between the desired application rate and the actual application rate. The invention, therefore, can lead to significant material savings if these errors in over-application are caught earlier rather than later. Furthermore, the invention can catch under-application errors, which can lead to even greater adverse economic consequences than over-application due to the loss of crop yield.

[0024] Other features and advantages of the invention will become apparent to those skilled in the-art upon review of the following detailed description and drawings.

[0025] FIG. 1 is a side view of a typical agricultural set-up for the application of the fluid level detection system of the present invention for use with an anhydrous ammonia tank.

[0026] FIG. 2 is a cut-away side view of a tank showing detail of the existing internal float gauge mechanism.

[0027] FIG. 3. is a partial side view of the tank module of the present invention mounted on a tank.

[0028] FIG. 4 is a perspective view of the top side of the tank module.

[0029] FIG. 5 is a cutaway perspective view of the tank module.

[0030] FIG. 6 is a perspective view of the bottom of the tank module.

[0031] FIG. 7 is a top cutaway view of the tank module showing the positioning of one embodiment of the attachment band of the tank module.

[0032] FIG. 8 is a top cutaway view of the tank module showing the positioning of one embodiment of the attachment band of the tank module.

[0033] FIG. 9 is a top cutaway view of the tank module showing the positioning of one embodiment of the attachment band of the tank module.

[0034] FIG. 10 is a circuit block diagram showing the connections of the circuit of the tank module.

[0035] FIG. 11 is a dataflow diagram showing the process carried out by the tank module.

[0036] FIG. 12 is a top cutaway view of the tank module mounted on a gauge in a correct orientation, and showing the expected initial angular position of the embedded magnet of the existing gauge mechanism.

[0037] FIG. 13 is a top cutaway view of the tank module mounted on a gauge in an incorrect orientation, and showing the expected initial magnetic reading of the tank module.

[0038] FIG. 14 is a top cutaway view of the tank module mounted on a gauge in an incorrect orientation, and showing the corrected angular reading of the tank module.

[0039] FIG. 15 is a perspective view of the front of the display module.

[0040] FIG. 16 is a cutaway perspective view of the display module.

[0041] FIG. 17 is a perspective view of the back of the display module.

[0042] FIG. 18 is a circuit block diagram showing the connections of the circuit of the display module.

[0043] FIG. 19 is a dataflow diagram showing the process carried out by the display module.

[0044] FIG. 20 is a front, cutaway view of the display module.

[0045] FIG. 21 is a back, cutaway view of the display module.

[0046] FIG. 22 is a perspective cutaway view of the tank module.

[0047] FIG. 23 is a side, cutaway view of a tank at an incline.

[0048] Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of including and comprising and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof.

[0049] This invention relates to a remote fluid level detection system using magnetic detection to determine the fluid level from a confined tank. The present invention is suitably designed for use with a pressurized tank containing anhydrous ammonia, but can be practiced with any tank containing fluid and a magnetic float gauge assembly.

[0050] A typical agriculture set-up in which the present invention is utilized is depicted in FIGS. 1-2. A tractor 10 tows a pressurized tank 12 containing a fluid 14 to be applied to a field. The pressurized tank 12 contains a float gauge assembly 16. The float gauge assembly 161 is depicted in FIG. 2 and 3. The float gauge assembly 16 comprises a float 18, a float arm 20, a counterweight 21, bevel gears 22, a vertical shaft 24, a magnet 28, and a gauge 30. The float 18 is attached to a float arm 20 that pivots about the center of the tank. The arm 20 is mechanically coupled via bevel gears 22 to the vertical shaft 24 that runs to the top of the tank 12. As the fluid 14 level changes within the tank 12 the buoyancy of the fluid 14 affects the position of the float 18. Fluctuations in the position of the float 18 translate to a small angular rotation of the vertical shaft 24. The magnet 28 is attached to the top of the vertical shaft 24. On the outside of the tank 12, the gauge 30 is mounted by mounting bolts 32 which connect the gauge housing 34 to the tank 12. The face of the gauge 36 comprises a simple compass which tracks the position of the magnet 28.

[0051] The tank module 40 of the present invention is depicted in FIGS. 3-9 and 22. The tank module comprises a housing 42, a battery cover 43, battery units 44, a microcontroller 46, a circuit board 48, an RF transmitter 50, a magnetic sensor 52, an attachment band 54, electrical connection wires 56, a momentary switch 58, an electric inclinometer 60, a liquid crystal display 62, a clock oscillator 64, and a voltage regulator 66.

[0052] The housing 42 of the tank module 40 is dimensioned to fit over the pre-existing gauge 30 of a tank 12, and is secured to the gauge 30 by way of the attachment band 54. The housing 42 is suitably comprised of a durable metal such as aluminum. The attachment band 54 can be of many different configurations as depicted in FIGS. 7-9.

[0053] FIG. 7 depicts one embodiment of the attachment band 54. The tank module 40 is secured to the gauge 30 of the tank 12 by the attachment band 54. One side of the attachment band 54 is tapped to accommodate an attachment bolt 68 that screws into the attachment band 54. The other side of the attachment band 54 has a clearance hole 70 sufficiently large to allow clear passage of the attachment bolt 68 to pass through. The attachment bolt 68 contains a flange feature 72 which provides positive pressure to the attachment band 54 face as the attachment bolt 58 is tightened. The attachment band 54, when tightened, applies uniform pressure around the perimeter of the gauge 30 and secures the tank module 40.

[0054] FIG. 8 depicts another embodiment of the attachment band 54. The attachment band 54 is tightened by means of a lever actuated cam mechanism 74 that constricts the attachment band 54 upon a clamping motion by a lever 74. The cam features two flat surface positions, an open position 76, and a closed position 77. The distance from the flattened portion to the center of the cam is greater for the open cam face, which causes attachment faces to move closer together when the lever 74 is clamped in the closed position.

[0055] FIG. 9 depicts yet another embodiment of the attachment band 54 of the tank module 40. A compression spring 78 provides positive pressure to a pressure plunger 80 which in turn tightens the attachment band 54 around the gauge 30. User releases tension by depressing plunger 80 with thumb while pulling back with index finger on a finger flange 82.

[0056] The physical and circuit connections of the tank module 40 are detailed in FIGS. 3-10. The arrows in FIG. 10 indicate the input/output relationship between the circuit components of the tank module. The onboard battery 40, suitably a 9V or a number of AA batteries, is regulated to 3V by the voltage regulator 66, which provides power to all components on common 3V and ground connections. A 16-bit microcontroller 46 houses all system software and serves as the nerve center for the system. Suitable microcontrollers are readily commercially available. Suitable microcontrollers include Texas Instruments TI MSP430 or MSP430F435. The clock oscillator 64 outputs a 4 MHz square wave to the microcontroller 46 for timing reference. The momentary switch 58 is a switch that activates the system by grounding an input pin on the microcontroller 46. The inclinometer 60, magnetic sensor 52, liquid crystal display 62 and RF transmitter 50 incorporate an interface with the microcontroller. Suitable magnetic sensors are readily commercially available. Suitable magnetic sensors include a GMR AA002-02 magnetic sensor available from NVE Corporation. Suitable electronic inclinometers are also readily available, suitable inclinometers include the SPECTRON SP5003-A-000 inclinometer from Spectron Systems Technology.

[0057] The processes undertaken by the tank module 40 are detailed in FIG. 11. After the tank module 40 is mounted to the gauge 30 of the tank 12, the user depresses the momentary switch 58 to initiate operation and wake-up of the microcontroller 46. The microcontroller 46 goes through a start-up routine 84 which resets the input/output devices connected to the microcontroller 46. The microcontroller 46 then pauses momentarily for the circuit to stabilize. The magnetic field sensor 52 is then interrogated by the microcontroller 46 in an initial magnetic field reading process 86 which indicates to the microcontroller 46 the precise position of the fluid indicating needle on the face of the gauge 36. As the tank module 40 will be attached to anhydrous ammonia tank 12 most often at the beginning of the fertilizer process, when the tank 12 is freshly filled, the tank 12 should be filled to between 85-95% full. The microcontroller 46, therefore, is programmed to assume that the initial magnetic field measurement 86 will be within a pre-set boundary that correlates to a tank that is greater than 50% full. FIG. 12 displays the angular position of the gauge 36 with respect to such an assumed start fluid level. If the initial magnetic field reading is within these preset boundaries 88, the process continues with the original origin setting. However, if the initial magnetic field reading is not within preset boundaries, the microcontroller 46 concludes that the tank module has been inadvertently attached to the gauge mechanism exactly 180 degrees from the desired orientation and the microcontroller 46 then automatically moves 90 the origin point 180 degrees to be compatible with the relative orientation of the gauge 30. FIG. 13 shows the angular position of the gauge 36 when the tank module 40 is placed in the wrong orientation, and FIG. 14 shows the angular readings of the tank module after the realignment of the origin by the microcontroller 46.

[0058] The electronic inclinometer 60 is interrogated 92 by the microcontroller 46 to detect the tank module's pitch 94 and roll 96, which correlates with the anhydrous ammonia tank's 12 pitch and roll. The microcontroller 46 analyzes these tilt values to see if the field tank 12 is on sufficiently level ground to take fluid level measurements 98. If the pitch 94 values are above a preset threshold, suitably above a 10% grade or 5.7 degrees from level, the microcontroller 46 loops for a preset time, suitably 5 seconds 100, and then interrogates 92 the tilt sensor 60 again to see if the field tank 12 has moved sufficiently back to level ground as the fertilizing process is continuing. If the pitch 94 and roll 96 values are within preset thresholds, the microcontroller 46 interrogates the magnetic field sensor 52 to measure the immediate magnetic reading 104. This magnetic reading 104 is then cross-referenced with an internal look-up table 106 that correlates magnetic field orientation with an actual volumetric fluid level, based on preinstalled knowledge of the tank's geometry and gauge mechanism's behavior. The pitch 94 data is used again to compare 108 the field tank's 12 tilt to another pre-set threshold. If the pitch 94 values are above the threshold, suitably a 5% grade or 2.86 degrees from level, the microcontroller 46 compensates for the pitch and roll effects on perceived fluid level value 110 and stores 112 adjusted fluid level sub-sample accordingly. If the pitch 94 values are below the threshold 108, the process immediately stores 112 fluid level sub-sample without further compensation.

[0059] A procedure to compensate for the sloshing of liquid in the tank is then undertaken. The microcontroller 46 compares 114 the number of sub-samples stored 112 at this point to a preset threshold, suitably 100 or 1000 sub-samples. If there are insufficiently few sub-samples (number of sub-samples is below the preset threshold), the microcontroller 46 waits for a preset duration of time 116, suitably about 1 mS, before sampling again the immediate magnetic reading 104 and repeating the process. If there are sufficiently enough sub-samples (number of sub-samples is above the preset threshold), the microcontroller 46 averages the stored sub-samples 118 and then stores this averaged value as the current fluid level 120. The microcontroller 46 then updates 122 the liquid crystal display 62 on the tank module 40. The microcontroller 46 next compares 124 the number of current fluid level values to a preset threshold, suitably 100 or 1000 values. If the number of stored current fluid level values is above the set threshold, the oldest value within this data set is discarded 126, which has the affect of incrementally updating data set to reflect more current fluid level data.

[0060] Next, the microcontroller 46 calculates a weighted average of the fluid level values 128 and stores this as a final moving average parameter, which is the final approximation of the fluid-level within the field tank 12. The microcontroller 46 then sends 130 this singular fluid-level value 128 to the radio frequency transmitter 50 which transmits 132 the fluid level information to the radio frequency receiver 202 in the display module 200.

[0061] The tank module 40 circuitry automatically shuts down if both of two criteria are satisfied. If the fluid level information 128 has not changed beyond a preset threshold 134, suitably a 2% change in fluid level within 2 hours, and the momentary switch 58 has not been depressed within a preset threshold 136, suitably 2 hours, the tank module 40 circuitry shuts down 138.

[0062] Since the gauge 30 reading will change at a faster rate at the high and low portions of the tank volume relative to the mid-portions of the tank volume, the tank module 40 of the present invention allows the fluid level refresh rate to be optimized for both performance and power saving. If fluid level data has changed sufficiently within the preset threshold 134 or the momentary switch 58 has been activated within a preset period of time 136, the microcontroller 46 correlates averaged fluid level data 128 with a corresponding sleep time using another look-up table 140. The found sleep time value from the look-up table 140 defines the amount of time the tank module 40 will power down 142 until next fluid level value will be taken, and the process repeats itself by gathering current tilt data 92.

[0063] FIGS. 15-19 detail the display module 200. The display module 200 comprises a housing 203, a battery cover 201, a circuit board 225, an RF receiver 202, a microcontroller 204, input buttons 206, 208, 210, a liquid crystal display 212, an audio transducer 214, a power switch, a voltage regulator 218, a tractor groundspeed connector 220, and a clock oscillator 222. The display module 200 can be powered by an onboard battery 226 or by the power supply of a tractor, through a power supply input 224 in the display module 200. The display module 200 can be mounted within a tractor 10 cab. The display module 200 can be mechanically fastened either via suction cups to the windshield, a mounting holster within the cab or by magnetic means. The display module can also contain a T-slot attachment 227 to aid in mounting.

[0064] The physical and circuit connections of the display module 200 are detailed in FIGS. 15-18. The arrows in FIG. 8 indicate the input/output relationship between the components. A 16-bit microcontroller 204 is powered via 12V tractor supply or internal batteries 226 preferably 9V or AA batteries, within the display module housing 203. The power switch is a toggle or rocker switch which closes the circuit between the power supply and voltage regulator 218. The voltage regulator 218 regulates external voltage down to 3V for circuit components. The display module 200 can be connected to the tractor's onboard Doppler groundspeed instruments or other speed indicators to have access to the tractor's current speed for purposes of secondary calculations and features. The tractor's ground speed indicator is electronically interfaced with microcontroller 204 via a cable and appropriate connectors 220. The clock oscillator 222 supplies a square wave at 4 MHz for timing purposes to microcontroller 204. The liquid crystal display 212 is directly interfaced with microcontroller 204 to provide visual information to the user.

[0065] Three momentary input pushbutton switches 206, 208, 210 provide means by which the user may enter relevant information pertaining to tank size and field implement width, as well as select a display mode. The input buttons 206, 208, 210 are located directly beneath the liquid crystal display 212. The function of each input button 206, 208, 210 changes depending on the point in software flow.

[0066] The RF receiver 202 interfaces directly with microcontroller 204. The audio transducer 214 provides user with an audio alert and is powered by the 3V supply and signaled by microcontroller 204.

[0067] The processes carried out by the display module 200 are detailed in FIG. 19. The user initiates the display module 200 by pressing the power switch 216, at which time the display module microcontroller 204 ) and support circuitry go through a start-up algorithm 228 whereby the various components are reset, and an audible alert is made by the audio transducer 214. This indicates that the unit has power and the microcontroller 204 initiates a brief welcome message on the liquid crystal display 212. The user is then prompted with a request to input the total capacity of the anhydrous ammonia tank in gallons 230. The user may select one of several standard anhydrous ammonia field tank sizes: 1000, 1450, 1800 and 2000 gallon sizes, or may enter another size manually 232. Once an appropriate tank size has been entered, user is prompted with a request for the field implement width 234. User enters implement width 236 by selecting one of several common field implement widths or enters manually an implement width not offered as a choice. The anhydrous ammonia field tank volume input 232 and the application implement width 236 represent system constants and do not change during application period.

[0068] The microcontroller 204 then moves into a continuous data acquisition and processing mode 238 and outputs desired information to the user. This information is updated regularly. Periodic updates on current fluid level 128 are broadcasted to the display module via a radio frequency transmission 132 from the tank module's RF transmitter 50 and are received 240 by the RF receiver 202. Periodic fluid level information is stored within the microcontroller 204 memory banks along with an associated time that the fluid level data was acquired. Simultaneously, current groundspeed data 242 is gathered from the tractor's groundspeed electronics 244. Tractor groundspeed information 242 is combined with the width of the application field implement 236 to calculate total area covered by the application process by utilization of a simple multiplication algorithm:

[0069] Since it is presumed the tractor speed is not constant, and continuously varying with field conditions and operator circumstances, total acreage covered is an integral function that cumulatively adds acreage covered over each sample period. Rate of groundspeed sampling may occur at any frequency to increase or decrease the accuracy of calculation relating to total acres covered.

[0070] Current fluid level information 128 received 240 from the tank module is stored in another memory bank within the display module microcontroller 204. A table of fluid level values at various points in time is generated, and permits the calculation of the total quantity of fluid dispensed to farmland to be generated based on the microcontroller's 204 calculation of the difference between the fluid level at start of process and the current fluid level by the use of the following algorithm:

[0071] The display module microcontroller 204 also calculates the average application rate per acre using the following algorithm:

[0072] The fluid level tables contain information on the time each fluid level data point was taken. By calculating the difference between two fluid level values and comparing this difference to the corresponding difference in time, a ratio is found that corresponds to the rate of drain within the tank. Once the drain rate has been established, current fluid levels can be extrapolated to determine future fluid levels based on a constant rate of drain. Based on this data the microcontroller 204 can determine the estimated time at which the fluid level will reach zero.

[0073] Through the manipulation of the various inputs into the display module 200, the microcontroller 204 calculates continuous values for the following parameters: current fluid level 246, application rate per acre 248, acres covered 250, and time remaining until tank is empty 252. These four values may be displayed on the liquid crystal display 212 as the display control algorithm 254 receives information from user on the desired mode of display 256 by the input buttons 206, 208, 210.

[0074] Additionally, when the tank 12 reaches a predetermined low fluid level, suitably below 5%, the liquid crystal display 212 alerts user that fluid level is low 258 and is accompanied by an audible alert produced by the audio transducer 214. The audio alert may be disarmed by the user.

[0075] The display module 200 interfaces with the user via three general purpose input buttons 206, 208, 210. The input buttons 206, 208, 210 are located directly beneath the liquid crystal display 212. The function of each input button 206, 208, 210 changes depending on the point in software flow. Each button's 206, 208, 210 function is made known to the user by utilizing the bottom row of characters of the liquid crystal display 212 to print directly above each button 206, 208, 210 what the corresponding button will cause the display module 200 to do at various points in software flow.

[0076] The display module 200 initiates operation with a welcome screen to indicate power on status while the internal circuitry is reset and stabilized. The welcome screen allows user to select one of two options. The left button 206 is depressed if the user wants to input tank size, implement size, or groundspeed calibration information. The right button 210 is depressed if no further information is needed to be inputted or changed from the previous use.

[0077] If the left button 206 is depressed, corresponding to the word SETUP on the bottom row of the liquid crystal display 212 on the welcome screen, the display module 200 prompts user to input the current size of the anhydrous ammonia tank in gallons. The display module 200 displays the current value for the tank size. If the tank size that is displayed is correct, the user depresses the center button 208 to accept the current tank size. If, however, the tank size needs to be modified, the user may use the left 206 and right 210 buttons to decrease or increase the tank size respectively. When the correct tank size is being displayed, the user depresses the center button 208 to accept the newly modified tank size. This process is repeated in a similar fashion to input the width of the field implement.

[0078] The user may, at the conclusion of the tank size and implement size setup screens, enter a mode by which the groundspeed radar system may be calibrated. The user depresses the left button 206, which corresponds to START and then drives the tractor the distance specified on the display module 200, suitably 200 feet. Once the specified distance has been covered, the user depresses the right button 210, which corresponds with FINISH. The display module 200 now has an absolute distance by which it can calibrate its interface with the groundspeed electronics, and this calibration is stored for future use when display module is in monitoring mode. The user may cancel the calibration routine at any time by depressing the center button 208, which corresponds with CANCEL.

[0079] Once the display module 200 is suitably setup with proper tank size, field implement size and groundspeed calibration, the display module switches into the monitoring mode. The user may use the left 206 and the right 210 function keys to scroll through the various display screen options. Suitably, there may be four screens: a screen that simply displays fluid level with a corresponding numerical and bar graph output, a screen that displays the flow rate of fluid and the corresponding estimated time until tank is empty, a screen that indicates the application rate per acre, and a screen that verifies inputted tank size and the amount of fluid remaining in an absolute unit, such as gallons. The number of information screens in not limited to these, however, and may also include screens that indicate total acreage covered, the current ground speed of the tractor, the date and time, a plurality of error messages indicating status of tank module or other electronics, tank empty alerts, burst hose or other messages indicating excessive flow rates that are not anticipated, the internal battery level of either the display module or the tank module, the relative error associated with application rate per acre or other information presented, a summary screen showing all current constants such as current field implement width or current tank size, the total quantity dispensed using the system in current season, the total number of acres covered in the current season, and a total cumulative average application rate per acre in the current season.

[0080] The tank module 40 is capable of measuring both pitch and roll measurements of the tank's 12 angle of incidence relative to the ground plane by means of a 2-axis electronic inclinometer 60. Since most internal gauge mechanisms are mounted axially within the field tank 12, the pitch of the field tank 12 will have by far the largest effect on possible measurement errors associated with uneven terrain, as opposed to roll which would be encountered frequently in contour farming and does not have a significant effect on float position. The tank module 40 compensates for erroneous float positions due to pitch inclines or declines by combining the information from the electronic inclinometer 60 with the current averaged fluid level.

[0081] FIG. 23 details a fluid containing tank on an incline. As the tank goes up a hill, for instance, the inclinometer 60 will measure the angle of the field tank relative to the ground plane. This pitch angle angle X is proportional to the error in the float arm position angle cX. The relative effect a given incline or decline will have on the error in the float position is highly dependant upon the amount of fluid remaining in the tank. For an incline, for instance, any given incline angle will have a much more profound effect on float position error for a mostly empty tank than a mostly full tank. Fortunately, however, this behavior is perfectly consistent and predicable, and therefore, information in the form of a look-up table of conversion equation may be stored in the tank module's memory. The angle of tilt defines a coefficient, c that is multiplied by the inclinometer 60 reading angle X to compensate for the difference in float arm position. The angular difference in float arm position can then be directly correlated to the assumed error in the magnetic field reading using the preinstalled gear ratio information between float arm position and permanent magnet position. The resulting calculated error at the permanent magnet is then simply added or subtracted from the actual reading, and therefore, a compensated fluid level is found.

[0082] The microcontroller varies the amount of time it sleeps between fluid level samples depending on the amount of fluid remaining in the tank as a means to conserve battery power, while enhancing performance and accuracy of fluid level measurements.

[0083] It is known, based on the cylindrical geometry of the tank, that for any given flow rate of fluid from the field tank, that the rate of movement of the float arm will be greater at the upper and lower portions of the tank than it will be in the mid-section. This is because most of the volume of the tank is contained within the mid-section of the tank, so there is a smaller change in fluid level for any given quantity of fluid dispensed. The sampling rate, or duration of time that the microcontroller sleeps between samples, is selected from a look-up table within the tank module's onboard memory. Suitably, ten different sample periods are available to the microcontroller depending on the fluid level remaining within the tank. The sleep time periods utilized in the present invention are delineated in Table 1.

	TABLE 1
	Fluid Level	Sleep Time
	90-100%	5	sec
	80-90%	10	sec
	70-80%	15	sec
	60-70%	20	sec
	50-60%	25	sec
	40-50%	25	sec
	30-40%	20	sec
	20-30%	15	sec
	10-20%	10	sec
	0-10%	5	sec

[0084] While the present invention has now been described and exemplified with some specificity, those skilled in the art will appreciate the various modifications, including variations, additions, and omissions, that may be made in what has been described. Accordingly, it is intended that these modifications also be encompassed by the present invention and that the scope of the present invention be limited solely by the broadest interpretation that lawfully can be accorded the appended claims.