Patent Publication Number: US-2021187523-A1

Title: Drive circuit for estimating fluid flow based on valve closure time and fluid application system including same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 16/045,404, filed on Jul. 25, 2018, which is a continuation of U.S. patent application Ser. No. 14/926,901, filed on Oct. 29, 2015, the disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to fluid distribution systems and, more particularly, to diagnostic systems for use with fluid distribution systems and methods of diagnosing such systems. 
     In agricultural spraying, the flow rate through a spray nozzle is an important factor in delivering a specified amount of agrochemical to a specified area. Most agrochemicals such as crop protection agents and many fertilizers are applied as liquid solutions, suspensions, and emulsions that are sprayed onto the target fields. Certain agrochemicals, such as anhydrous ammonia, are dispensed into soil through dispensing tubes positioned behind knives or plows that prepare the soil for application. 
     Typically, the agrochemical liquid is supplied by powered pumps to simple or complex orifice nozzles that atomize the liquid stream into spray droplets. Nozzles are often selected primarily on the desired range of flow rates needed for the job and secondarily on the range of liquid droplet size spectra and spray distribution patterns they produce. 
     Increasing concerns over inefficient agrochemical use, the cost of agrochemicals and inadvertent spray drift or pesticide run-off have resulted in attempts to improve the quality, precision, accuracy and reliability of application of agrochemicals. This has led to increased use of electronic control systems and GPS-guided operations. Growth in these “precision agriculture” products and strategies has led to greater demand for “variable rate” technologies and the fluid handling means to alter spray liquid flow rates. 
     New sprayer models may have booms of 30 m (approximately 90 ft) widths and allow application at speeds up to 30 km/hr (20 mph) or higher. Faster ground speeds and wider spray booms can lead to application errors that are significant yet unavoidable with existing spray technology. For example, if the sprayer is traversing the edge of a field while scribing about a 100 m radius (actually, a very gentle turn), the outer nozzles are traveling 35% faster than the inner nozzles. At a 50 m radius, the difference in nozzle ground speeds is 85%. With sharp turns, such as at the end of a pass, the inner nozzles will travel backwards, thereby retracing and overdosing previously sprayed areas, while the outer nozzles will significantly accelerate giving their associated land areas sparse coverage of chemical. Unless the flow rate from each nozzle is individually adjusted to compensate for these differences in travel speeds, application errors may occur. 
     Individual control of spray nozzles or nozzle assemblies is of growing importance in agrochemical application. As individual control increases, the need for individual flow monitoring will increase since feedback is often needed for closed loop control. Even with a linear control strategy, such as the binary control of multiple nozzles or pulse width modulation, confirmation of proper flow is important. 
     As the spray application industry adopts larger liquid storage tanks on mobile equipment, operators are likely to make fewer stops for refilling and cover greater land area between stops. Consequently, clogged nozzles or other problems on the boom are unlikely to be detected while significant land areas are being treated. For example, assuming a 30 km/hr ground speed, a 30 m boom width and 50 l/ha (apprx. 5 gal/acre) application rate, a 4000 l (apprx. 1000 gal) tank will cover 200 acres in apprx. 1 hour. A single nozzle in this example would treat apprx. 3.5 acres per tank load and a single undetected nozzle malfunction would correspond to this 3.5 acre area receiving an incorrect, or perhaps zero, dose of agrochemical. 
     Additionally, wider boom widths, travel speeds and vehicle sizes increasingly restrict an operator&#39;s view of the boom and the opportunities to view the boom while driving. On modern agricultural spray vehicles, 30 to 50% of the spray boom may not be visible to the operator. 
     On some larger sprayers such as those typically used by custom applicators in the Midwest, Central Canada and the Plains, video cameras are sometimes mounted on the rear of the sprayer so that the operator can monitor, at least in theory, the spray boom out of his or her line of sight. However, at high travel speeds, the operator&#39;s attention is fully devoted to driving instead of monitoring the spray boom in the rear, either in the line of direct sight or shown on the video monitor. Due to poor overall visibility from the operator&#39;s station and the infrequency of stops and refillings, there is a need for individual nozzle monitoring to confirm that no clogging, pinched hoses, damaged nozzles or other problems may be present or developing on the spray boom. 
     A similar problem exists on shielded or shrouded sprayers sometimes used in the North American Plains and in urban and landscape applications. In farming areas in extreme southern and northern latitudes and in high value specialty crops, often grown in coastal areas, the agronomic time window for pesticide applications can be critically short and often occurs during windy periods. Shielded sprayers are often used in these conditions. Similarly, sprayers used in golf course, landscape and other urban conditions commonly use shrouds, curtains or shields to reduce spray drift and as a concession to public relations. However, the shields prevent the operator from visually inspecting the nozzle spray patterns to confirm proper operation. Improperly operating nozzles are not easily detected. Commercial systems for agricultural use often address this problem by routing individual liquid lines to each nozzle through a small rotameter (ball in tube) flow monitor that is mounted in the operator&#39;s line of sight. Such rotameters require cumbersome plumbing for each nozzle and require the operator visually monitor the bank of tubes. 
     One drawback of relying on visual inspection (either direct line of sight or video) or simple flow measurement (ball in tube) is that such methods do not assure proper nozzle operation. Nozzles can be partially clogged or have an obstruction in the flow path and appear to be operating correctly even if the flow rate is significantly affected. Conversely, the nozzle pattern and spray droplet size can be severely distorted by an obstruction or damage, yet the flow rate remains close to the original value. 
     Electronic spray rate control systems and application monitors typically use a single flowmeter and/or pressure transducer for feedback of the flow conditions on the entire spray boom. In systems with many nozzles, such as a 50-60 nozzle boom, failure of 1 or 2 nozzles would be unlikely to raise an alarm since the overall effect is only 2% of the expected flow rate; the system would compensate by maintaining the correct overall flow to the entire boom. So, if one nozzle became completely clogged, the system would simply increase the spray pressure and force an additional 2% flow through the remaining nozzles operating properly. Even with the electronic control or monitor system, the driver would likely remain unaware of the failure. 
     Additionally, when individual nozzle control is implemented, the need for individual nozzle monitoring increases. Pulse width modulation systems have electrical and mechanical components on each nozzle. Multiple nozzle manifolds have multiple tips and actuators at each boom location. The opportunity for failure is increased over that of a simple nozzle. These systems require not only flow monitoring but also monitoring of the control actuators used for flow or droplet size modulation. Moreover, individual nozzle control implies that individual nozzle feedback is required for closed loop operation. 
     Future systems may incorporate individual nozzle injection of multiple agrochemicals or adjuvants, individual control of droplet size spectra, droplet velocity or spray distribution. In each case, the need for monitoring and actuation on a single-nozzle or single manifold basis increases. 
     Thus, a need currently exists for a system and process for monitoring spray nozzle operation. Such a system and process is well suited for use in the agricultural field. It should be understood, however, that similar needs also exist in other fields. For example, on irrigation systems, there may be many small nozzles, often obscured from view or in areas that are difficult to access. Failure of a nozzle might not be detected until drought damage to a plant had occurred and symptoms were visible. Likewise, in industrial spray driers, malfunction of a nozzle might not be detected until significant amounts of product had been damaged. In spray humidification or cooling systems, nozzle failures might not be detected until excessive heating or drying had occurred. Specifically, a system that monitors nozzle operation may find wide applicability in any system, whether commercial, industrial or residential, that utilizes spray nozzles. 
     BRIEF DESCRIPTION 
     In one aspect, a drive circuit for a solenoid valve having a coil and a poppet configured to translate within the coil is provided. The drive circuit includes a drive switch operable to de-energize the coil to translate the poppet toward a closed position, a sensor configured to detect the poppet translating within the solenoid valve, and a drive circuit configured to energize and de-energize the coil of the solenoid valve to translate the poppet of the solenoid valve between an open position and a closed position. The drive circuit includes a controller configured to receive a closure signal from the sensor, determine a closing time of the solenoid valve based on the closure signal, determine a time delay between de-energizing the coil and the determined closing time, and determine a fluid flow value of fluid flowing through the solenoid valve based on the determined time delay. 
     In another aspect, a fluid application system includes a fluid dispensing outlet and a solenoid valve coupled in fluid communication with the fluid dispensing outlet and configured to regulate flow of fluid through the fluid dispensing outlet. The solenoid valve includes a coil and a poppet. The fluid application system also includes a drive circuit configured to energize and de-energize the coil of the solenoid valve to translate the poppet of the solenoid valve between an open position and a closed position. The drive circuit includes a controller configured to determine a closing time of the solenoid valve, determine a time delay between de-energizing the coil and the determined closing time of the solenoid valve, and determine a fluid flow value of fluid flowing through the solenoid valve based on the time delay. 
     These and other features, aspects and advantages of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of an agricultural spray system; 
         FIG. 2  is a perspective view of one embodiment of a nozzle assembly suitable for use with the agricultural spray system of  FIG. 1 ; 
         FIG. 3  is a sectional view of a portion of a valve assembly suitable for use in the nozzle assembly shown in  FIG. 2 ; 
         FIG. 4  is a sectional view of a portion of another valve assembly suitable for use in the nozzle assembly of  FIG. 2 ; 
         FIG. 5  is a schematic diagram of one embodiment of a drive circuit for controlling the valve assemblies shown in  FIG. 3  and  FIG. 4 ; 
         FIG. 6  is a flow diagram of one embodiment of a method of detecting nozzle flow in a spray system; 
         FIG. 7  is a flow diagram of another embodiment of a method of detecting nozzle flow in a spray system; 
         FIG. 8  is a plot showing times of peak coil current for variously sized nozzle assemblies; and 
         FIG. 9  is a plot showing nozzle flow versus time of peak coil current; 
         FIG. 10  is a perspective view of a fluid application system; and 
         FIG. 11  is a perspective view of a portion of the fluid application system shown in  FIG. 10 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Referring now to the Figures,  FIG. 1  is a perspective view of one embodiment of a spray system, indicated generally at  10 , operatively connected to a work vehicle  12 . As shown, work vehicle  12  includes a cab  14  and a plurality of wheels  16 . Work vehicle  12  may in certain embodiments be an agricultural tractor having any suitable configuration. However, it should be appreciated that in other embodiments, any other suitable aero or ground means may be provided for moving spray system  10 . For example, in other embodiments, work vehicle  12  may not include a cab, and instead may have any suitable operator station. Further, in some embodiments, work vehicle  12  and/or spray system  10  may include a global positioning system (e.g., a GPS receiver) for automated control of work vehicle  12  and/or spray system  10 . In some embodiments, the global positioning system is used to monitor a travel speed of vehicle  12  and/or spray system  10 , and/or to monitor a position of work vehicle  12  and/or spray system  10 . 
     In the example embodiment, spray system  10  includes at least one boom wheel  18  for engaging a section of ground with a crop, produce, product or the like (generally, P), a tank or reservoir  22 , and a spray boom  24 . Spray boom  24  includes a plurality of nozzle assemblies  34  attached thereto and in fluid communication with tank  22 . Tank  22  holds a product S, such as a liquid, a mixture of liquid and powder, or other product. Product S may be a quantity of water or an agrochemical such as a fertilizer or a pesticide, and may be sprayed from nozzle assemblies  34  onto, for example, a crop or produce or ground P itself, as shown in  FIG. 1  and described in greater detail below. It should be appreciated, however, that in other embodiments, system  10  may have any other suitable configuration. For example, in other embodiments, system  10  may not include boom wheel  18  or may alternatively include any suitable number of boom wheels  18 . Further, while work vehicle  12  is depicted as towing spray system  10  in the example embodiment, it should be appreciated that, in other embodiments, work vehicle  12  may transport spray system  10  in any suitable manner that enables spray system  10  to function as described herein. 
     The quantity of product S held in tank  22  generally flows through a conduit to nozzle assemblies  34 . More specifically, in the embodiment illustrated in  FIG. 1 , product S flows from tank  22 , through a pipe  30  to a boom pipe  32 , and from boom pipe  32  to nozzle assemblies  34 . In certain embodiments, nozzle assemblies  34  comprise direct acting solenoid valve equipped nozzles (see, e.g.,  FIGS. 2-4 ) and system  10  may include a pump, transducers to measure fluid pressure and fluid flow, sectional regulating valves, and a pressure and/or flow controller (not shown in  FIG. 1 ). If included, the pump may be positioned downstream from tank  22 , upstream from boom pipe  32  and nozzle assemblies  34 , and in operative communication with the controller. The pump may be a pulse width modulation controlled pump configured to provide a desired amount of product S flow through system  10 . The pressure or flow controller may be configured to vary certain operating parameters of the pump, such as the pump&#39;s pulse frequency and/or duty cycle, to obtain a desired product flow rate through system  10 . 
     Referring still to  FIG. 1 , product S flows through nozzle assemblies  34  and may be applied to ground P in various ways. For example, product S may flow from nozzle assemblies  34  in a pulsed pattern. It should be appreciated that terms “pipe” and “conduit,” as used herein, may mean any type of conduit or tube made of any suitable material such as metal or plastic, and moreover that any other suitable ground application devices can be added to provide varying effects of placement of product S on top or below a soil surface of ground P, such as via pipes, knives, coulters, and the like. 
       FIG. 2  is a perspective view of one embodiment of a nozzle assembly  34  suitable for use with spray system  10  of  FIG. 1 . As shown in  FIG. 2 , nozzle assembly  34  generally includes a valve assembly  36 , a nozzle body  37  configured to receive product S flowing through boom pipe  32  and a spray nozzle  39  mounted to and/or formed integrally with nozzle body  37  for expelling product S from nozzle assembly  34  onto crops, product and/or ground P. 
     In some embodiments, valve assembly  36  is a solenoid valve (see, e.g.,  FIGS. 3 and 4 ). Moreover, in some embodiments, valve assembly  36  may be configured to be mounted to and/or integrated with a portion of spray nozzle  39 . In some embodiments, for example, valve assembly  36  may be mounted to the exterior of nozzle body  37 , such as by being secured to nozzle body  37  through the nozzle&#39;s check valve port. Alternatively, valve assembly  36  may be integrated within a portion of nozzle body  37 . 
       FIG. 3  is a simplified, cross-sectional view of one embodiment of an electric solenoid valve  300  suitable for use in nozzle assembly  34  shown in  FIG. 2 . In general, valve  300  includes an inlet  302  and an outlet  304  for receiving and expelling fluid  306  from valve  300 . Valve  300  also includes a solenoid coil  308  (outlined by the dashed lines) located on and/or around a guide  310 . For instance, in one embodiment, solenoid coil  308  is wrapped around guide  310 . Additionally, an actuator or poppet  312  is movably disposed within guide  310 . In particular, poppet  312  may be configured to be linearly displaced within guide  310  relative to inlet  302  and/or outlet  304  of valve  300 . Moreover, as shown, valve  300  includes a spring  314  coupled between guide  310  and poppet  312  for applying a force against poppet  312  in the direction of outlet  304 . It should be appreciated that valve  300  may also include a valve body or other outer covering (not shown) disposed around coil  308 . 
     As shown in the illustrated embodiment, valve  300  is configured as an in-line valve. Thus, fluid  306  may enter and exit valve  300  through inlet  302  and outlet  304 , respectively, along a common axis  316 . In other words, the inlet  302  and outlet  304  may generally be aligned along axis  316 . Additionally, as shown in  FIG. 3 , in one embodiment, inlet  302  and outlet  304  may be concentrically aligned with both one another and the positioning of poppet  312  within guide  310 . As such, poppet  312  may be configured to be linearly displaced within guide  310  along axis  316  such that fluid  306  may generally be directed through valve  300  along axis  316  as the movement of poppet  312 . 
     In addition, solenoid coil  308  may be coupled to a controller  318  configured to regulate or control the current provided to coil  308 . Controller  318  may be enclosed within valve assembly  300 , may be enclosed within nozzle assembly  34 , as shown in  FIG. 2 , or may exist some distance away from nozzle assembly  34 . Controller  318  may generally comprise any suitable computer and/or other processing unit, including any suitable combination of computers, processing units and/or the like that may be communicatively coupled to one another (e.g., controller  318  may form all or part of a controller network). Thus, controller  318  may include one or more processor(s) and associated memory device(s) configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and/or the like disclosed herein). As used herein, the term “processor” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Additionally, the memory device(s) of controller  318  may generally comprise memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s) may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure controller  318  to perform various functions including, but not limited to, controlling the current supplied to solenoid coil  308 , monitoring inlet and/or outlet pressures of the disclosed valve(s), monitoring poppet operation of the disclosed valves, receiving operator inputs, performing the calculations, algorithms and/or methods described herein and various other suitable computer-implemented functions. 
     Coil  308  may be configured to receive a controlled electric current or electric signal from controller  318  such that poppet  312  may move within guide  310  relative to inlet  302  and/or outlet  304 . For example, in one embodiment, controller  318  includes a square wave generator, a coil drive circuit as shown in  FIG. 5 , or any other suitable device that is configured to apply a regulated current to coil  308 , thereby creating a magnetic field which biases (by attraction or repulsion) poppet  312  toward inlet  302 . As a result, poppet  312  may be moved to a proper throttling position for controlling the pressure drop across valve  300 . Additionally, the attraction between coil  308  and poppet  312  may also allow poppet  312  to be pulsated or continuously cyclically repositioned, thereby providing for control of the average flow rate through valve  300 . 
     In several embodiments, a modulated square wave may drive valve  300  to control the pressure and flow rate. The duty cycle of a high-frequency modulation (e.g., at a frequency greater than about 200 Hz) may be used to regulate coil current and partially open valve  300  by moving poppet  312  to a particular throttling position, thereby providing a means for manipulating the outlet pressure of fluid  306 . Additionally, the low-frequency pulse duty cycle (e.g., at a frequency of less than 30 Hz) may be used to meter the average flow rate by enabling/disabling the temporally-averaged flow rate that results from the outlet pressure. 
     In certain embodiments, the poppet position may be regulated by the forces acting on poppet  312 , with a steady throttling position resulting from equilibrium of the forces. For example, in the illustrated embodiment, forces from spring  314 , fluid  306  and coil  308  may act on poppet  312  simultaneously. Specifically, the forces from spring  314  and fluid  306 , tend to bias poppet  312  in the direction of outlet  304  while the force from coil  308  tends to bias poppet  312  in the direction of inlet  302 . 
     Thus, when valve  300  is unpowered (i.e., when a voltage is not applied across coil  308 ), spring  314  may force poppet  312  towards outlet  304  such that the increased system pressure has a tendency to force valve  300  into a sealed or closed position. In such an embodiment, poppet  312  may include a rubber disk or any other suitable sealing member  320  configured to press against an outlet seat  322  of outlet  304  to create a leak-free seal on valve  300  when valve  300  is in the closed position. Additionally, when valve  300  is powered (i.e., when a voltage is applied to coil  308 ), poppet  312  may be attracted by coil  308  toward inlet  302  such that poppet  312  is moved to the throttling position. Specifically, the current supplied to coil  308  may be controlled such that the force acting on poppet  312  by coil  308  is sufficient to position poppet  312  a predetermined distance  324  from an inlet seat  326  of inlet  302 , thereby allowing the pressure across valve  300  to be throttled. 
     The particular distance  324  from inlet seat  326  (also referred to herein as the “poppet displacement”) at which poppet  312  is positioned may generally vary depending on the desired outlet pressure for valve  300 . However, given the configuration of the disclosed valve  300 , distance  324  may always be less than total stroke of poppet  312  (defined as the summation of distance  324  and a distance  328  between poppet  312  and outlet seat  322 ). In several embodiments, distance  324  may be less than 60% of the total stroke of poppet  312 , such as less than 50% of the total stroke of poppet  312  or less than 40% of the total stroke of poppet  312 . 
     In several embodiments, when valve  300  is being pulsed, the movement of poppet  312  may be cycled between the throttling position and a sealed position, wherein poppet  312  is sealed against inlet  302 . Thus, as shown in  FIG. 3 , poppet  312  may also include a rubber disk or other suitable sealing member  330  that is configured to be pressed against inlet seat  326  of inlet  302  so as to create a leak-free seal when valve  300  is in the sealed position. In such an embodiment, in order to transition valve  300  from the closed position (wherein poppet  312  is sealed against outlet  304 ) to the sealed position (wherein the poppet  312  is sealed against inlet  302 ), the solenoid may be initially turned on with a 100% high frequency duty cycle so as to move poppet  312  from outlet  304  to inlet  302  as quickly as possible. Subsequently, the current supplied to coil  308  may be controlled such that poppet  312  may be cyclically pulsed between the sealed position and the throttling position. However, in alternative embodiments, valve  300  may be configured to be pulsed between the closed position (wherein poppet  312  is sealed against outlet  304 ) and the throttling position. 
     The sizes of inlet  302  and outlet  304  (e.g., diameter  332  and diameter  334 , respectively), as well as the geometry and/or configuration of poppet  312  and guide  310 , may be chosen such that the force acting on poppet  312  from coil  308  may overcome the fluid forces and spring forces for every throttling position within the total stroke of valve  300  when the coil is fully powered. Similarly, in one embodiment, spring  314  may be sized such that the spring force corresponds to the minimal amount of force required to maintain a drip-free valve  300  when valve  300  is unpowered. 
     In several embodiments, poppet  312  and/or guide  310  may include a tapered portion at and/or adjacent to inlet  302 . Specifically, as shown in  FIG. 3 , both poppet  312  and guide  310  include a tapered portion defining a taper angle  336  at and/or adjacent to inlet  302 . In several embodiments, taper angle(s)  336  may range from about 25 degrees to about 45 degrees, such as from about 25 degrees to about 40 degrees or from about 27 to about 35 degrees and all other subranges there between. However it is foreseeable that, in alternative embodiments, taper angle(s)  336  may be less than about 25 degrees or greater than about 45 degrees. 
     As indicated above, coil  308  may be driven with a complex pulsed voltage waveform. A “pulse” may correspond to a duration (e.g., a 100 millisecond cycle) in which a low frequency duty cycle value sets the amount of on/off time. The “on” time may correspond to a “coil discharging (or charging) period” in which the drive voltage is turned off (or on) continuously and a “modulated period” in which the voltage is turned on and off at a high frequency (e.g., at a frequency of greater than 200 Hz). The duration of the coil discharging (or charging) period may be determined by the amount of time for the coil current to reach the desired value. The coil current may be continuously measured and compared to a threshold in order to trigger switching of the drive voltage to a modulated signal. 
     In certain embodiments, movement of poppet  312  may be sensed by a poppet measurement device  338 . For example, in certain embodiments, measurement device  338  may be an accelerometer, a hall-effect sensor, a coil current sensor, or other suitable device capable of sensing when a poppet moves from an open position to a closed position. The measurement device  338  may be communicatively coupled to controller  318 , and may be disposed within valve assembly  300 , within nozzle assembly  34 , as shown in  FIG. 2 , or some distance away from nozzle assembly  34 . 
     Referring now to  FIG. 4 , a simplified, cross-sectional view of another embodiment of an electric solenoid valve  400  suitable for use in nozzle assembly  34  shown in  FIG. 2  is illustrated. In general, valve  400  may be configured similarly to valve  300  described above with reference to  FIG. 3  and, thus, may include many or all of the same components. For example, valve  400  may include an inlet  402  and an outlet  404  for receiving and expelling a fluid  406  from valve  400 . Additionally, valve  400  may include a solenoid coil  408  (outlined by dashed lines) located on and/or around a guide  410  and a poppet  412  movably disposed within guide  410 . Solenoid coil  408  may be configured to receive a controlled electric current or electric signal from a controller  414  such that poppet  412  may be moved within guide  410  relative to outlet  404 . Controller  414  may have the same configuration as controller  318  described above with reference to  FIG. 3 , and may be enclosed within the valve assembly  400 , may be enclosed within the nozzle assembly  34  as shown in  FIG. 2 , or may exist some distance away from nozzle assembly  34 . Valve  400  may also include a spring  416  coupled between guide  410  and poppet  412  for applying a force against the poppet  412  in the direction of outlet  404 . It should be appreciated that valve  400  may also include a valve body or other outer covering (not shown) disposed around solenoid coil  408 . 
     In some embodiments, valve  400  may also include a poppet measurement device  438  capable of sensing when a poppet moves from an open position to a closed position. For example, in certain embodiments, measurement device  438  may be an accelerometer, a hall-effect sensor, a coil current sensor, or other suitable device capable of sensing when a poppet moves from an open position to a closed position. The measurement device  438  may be communicatively coupled to controller  414 , and may be disposed within valve assembly  400 , within nozzle assembly  34 , as shown in  FIG. 2 , or some distance away from nozzle assembly  34 . 
     In contrast to the in-line valve  300  described above, valve  400 , illustrated in  FIG. 4 , is configured as a counter flow valve. Thus, fluid  406  may be configured to enter and exit valve  400  along different axes. For example, as shown, outlet  404  may generally be aligned with the axis of movement of poppet  412  and inlet  402  may be offset from such axis, such as by being disposed above outlet  404 . 
     Additionally, in one embodiment, poppet  412  may be configured to include a projection  418  (e.g., a section of poppet  412  being reduced in size) extending outwardly in the direction of outlet  404 . For example, as shown in  FIG. 4 , projection  418  may extend outwardly from the portion of poppet  412  configured to be sealed against an outlet seat  420  of outlet  404  (e.g., a rubber disk or any other suitable sealing member  422 ). 
     As described in U.S. patent application Ser. No. 13/410,589, the entirety of which is hereby incorporated by reference, projection  418  may be configured to be received within a portion of outlet  404  such that a partial opening of valve  400  generates a first constant flow coefficient, and fully opening valve  400  generates a second constant flow coefficient greater than the first constant flow coefficient. In alternative embodiments, the illustrated valve  400  may not include projection  418  shown in  FIG. 4 . 
     Similar to valve  300  described above, the partially open state may be achieved by controlling the forces acting on poppet  412 . For example, a regulated amount of voltage may be applied to solenoid coil  408  (generating a regulated amount of coil current through solenoid coil  408 ) such that the forces acting on poppet  412  by solenoid coil  408 , spring  416  and fluid  406  are in an equilibrium state when poppet  412  is located at the desired throttling position. In such an embodiment, a resulting distance  428  between sealing member  422  and outlet seat  420  may be chosen to position the volume of the outlet occupied by projection  418  to throttle the pressure across valve  400 . 
     Generally, the disclosed solenoid valves  300  and  400  may be utilized to control the instantaneous pressure drop across and the cyclic duration of flow through any suitable device. However, in several embodiments of the present disclosure, the solenoid valves  300  and  400  may be used to control the instantaneous pressure drop across and the cyclic duration of flow through an agricultural spray nozzle. In such embodiments, the disclosed solenoid valves  300  and  400  may be configured as part of a nozzle assembly for use with various agricultural spraying systems. 
       FIG. 5  is a schematic diagram of one embodiment of a drive circuit  500  for controlling valves  300  and  400  shown in  FIG. 3  and  FIG. 4 , or may form all or part of the disclosed controllers  318  or  414 . Drive circuit  500  may further include or interface with a poppet measurement device, such as poppet measurement devices  338  and  438 , shown in  FIGS. 3 and 4 , respectively. In general, circuit  500  may be configured to generate a waveform for a solenoid valve and may also be configured to measure the solenoid coil current. In one embodiment, circuit  500  includes a field-effect transistor (FET)  502  controlled by a control signal or waveform  504  to connect/disconnect a supply voltage  532  to a solenoid coil  508 , thereby energizing or de-energizing solenoid coil  508 . Solenoid coil  508  may be, for example, solenoid coil  308  or solenoid coil  408  of valves  300  and  400  shown in  FIGS. 3 and 4 . In addition, drive circuit  500  includes a current sense resistor  520  configured to generate a sense voltage  530  directly indicating the current through current sense resistor  520  and solenoid coil  508 . 
     While solenoid coil  508  is energized to open the solenoid valve, a fly-back switch  510  enables a fly-back diode  512  to allow current in solenoid coil  508  to remain nearly constant during a high frequency modulation of control signal  504 . Fly-back switch  510  may disable fly-back diode  512  at the beginning or end of a low-frequency pulse to force a more rapid coil current change. Fly-back switch  510  may be implemented as, for example, a field-effect transistor (FET), a silicon controlled rectifier (SCR), relay, or any other suitable switch. 
     FET  502  disconnects supply voltage  532  to de-energize solenoid coil  508  and to close the solenoid valve. During closing, current through solenoid coil  508  is dissipated to allow a poppet of the solenoid valve to translate toward the closed position. Fly-back switch  510  disables fly-back diode  512  by opening the fly-back circuit when FET  502  disconnects supply voltage  532 . Disabling fly-back diode  512  facilitates dissipating the current in solenoid coil  508  more quickly through a charge build up and resulting large potential across coil  508 . In certain embodiments, FET  502  may be protected from the voltage induced by coil  508  with a transient voltage suppressor diode  516  having a clamping voltage suitable to protect FET  502 . 
     As the current through solenoid coil  508  dissipates, the force exerted by solenoid coil  508  on the poppet decreases until the sum of forces acting on the poppet (e.g., spring forces, pressure differential forces, and magnetic force) cause the poppet to translate within solenoid coil  508  toward the closed position. As the poppet translates, an electromagnetic flux is generated and the poppet induces a coil current within solenoid coil  508 . Immediately before or as the poppet begins to translate to the closed position, fly-back diode  512  can be re-enabled by closing fly-back switch  510 , such that current may flow freely through the fly-back circuit and current sense resistor  520  detects the induced current, which manifests as sense voltage  530 . In this manner, current sense resistor  520  may serve as poppet measurement device  338  or  438 . 
     In certain embodiments, drive circuit  500  includes a processor  514 . Processor  514  receives current sense voltage  530  and determines a peak coil current after solenoid coil  508  has been de-energized. The time between de-energizing solenoid coil  508  and the peak coil current represents the closing time delay for the solenoid valve. The time required for the solenoid valve to close is related to a fluid flow through the solenoid valve. Generally, the greater the fluid flow through the solenoid valve, the greater the pressure drop that develops across the poppet; and the less time required for the poppet to translate to the closed position. This relationship is governed by the following equation: 
     
       
         
           
             
               
                 
                   
                     Q 
                     = 
                     
                       
                         C 
                         
                           V 
                            
                           
                               
                           
                            
                           1 
                         
                       
                       · 
                       
                         
                           
                             Δ 
                              
                             
                                 
                             
                              
                             p 
                              
                             
                                 
                             
                              
                             1 
                           
                           SG 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
     where, Q is fluid flow through the solenoid valve, C V1  is a flow coefficient of the valve metering orifice, Δp1 is a pressure drop across the valve metering orifice, and SG is the specific gravity of the fluid. Given the time at which the peak coil current occurs during closing of the solenoid valve and the relationship between peak coil current time and fluid flow, a fluid flow value representing fluid flow through the nozzle assembly may be determined. 
     In certain embodiments, processor  514  uses the time at which the peak coil current occurs to estimate flow through the solenoid valve based on experimental or statistical data gathered for close times for the solenoid valve. In one embodiment, for example, the flow is estimated by precomputed values in a look-up table. Additionally or alternatively, the flow may be computed using a “fit line” characterized by the experimental or statistical data, such as the data shown and described herein with reference to  FIGS. 8 and 9 . 
     In certain embodiments, processor  514  is further configured to compare the determined nozzle flow to a target nozzle flow for the nozzle assembly. For example, for a nozzle assembly having a given nozzle size and measured upstream pressure yielding a target nozzle flow of 1.0 gallons per minute, the determined nozzle flow is compared to the 1.0 gallons per minute. If the determined nozzle flow is less than 1.0 gallons per minute, the nozzle assembly may have a clog in the nozzle spray tip or elsewhere in the nozzle assembly that is impeding nozzle flow. Conversely, if the determined nozzle flow is greater than 1.0 gallons per minute, the nozzle assembly may be damaged and is not properly regulating flow through the nozzle assembly and nozzle spray tip. This may occur, for example, if the nozzle assembly strikes the ground or some other object and damages or shears off the nozzle spray tip. 
     In certain embodiments, processor  514  is further configured to generate control signal  504  to control FET  502 . In certain embodiments, processor  514  is further configured to generate a second control signal  518  for controlling fly-back switch  510 . Processor  514 , for example, may be configured to close fly-back switch  510  to enable fly-back diode  512  for a period of time after solenoid coil  508  is de-energized. In such an embodiment, current would dissipate from solenoid coil  508  more slowly if fly-back switch  510  were closed and fly-back diode  512  were enabled. Opening fly-back switch  510  permits the poppet to translate sooner, thereby closing the valve more quickly. In one embodiment, fly-back switch  510  is open for a period of 4.8 milliseconds, which is sufficient for current to dissipate in solenoid coil  508  and to allow the poppet to begin translating toward the closed position. The period of time may vary per embodiment, depending on the particular solenoid valve, nozzle, spray system, or fluid, for example. Processor  514  is further configured to generate second control signal  518  to close fly-back switch  510 . 
       FIG. 6  is a flow diagram of one embodiment of a method  600  of detecting nozzle flow in a spray system, such as spray system  10  of  FIG. 1 . Method  600  begins at a start step  610 . At a coil de-energizing step  620 , a voltage across a solenoid coil, such as solenoid coils  308  and  408  of  FIGS. 3 and 4 , is turned off. Referring to  FIGS. 4 and 6 , solenoid valve  400  is in fluid communication with a nozzle, such as nozzle  39  of  FIG. 2 . The solenoid valve regulates flow of a fluid through the valve and toward the nozzle. 
     As the solenoid coil current dissipates, poppet  412  translates toward valve outlet  404  to a closed position. In step  630 , poppet measurement device  438  senses the transition of poppet  412  to the closed position. Controller  414  detects the measurement device output at a step  640 , and determines a time delay between de-energizing the solenoid coil and the measured poppet closure. Controller  414  then determines the nozzle flow based on the time delay between de-energizing the solenoid coil and the measured poppet closure at a nozzle flow determination step  650 . In some embodiments, the time delay between de-energizing the solenoid coil and the measured poppet closure is determined based on a measured coil current, as described below with reference to  FIG. 7 . The method ends at an end step  660 . 
       FIG. 7  is a flow diagram of another embodiment of a method  700  of detecting nozzle flow in a spray system, such as spray system  10  of  FIG. 1 . Method  700  begins at a start step  710 . Referring to  FIGS. 4, 5, and 7 , at a de-energizing step  720 , solenoid coil  408  is de-energized by opening FET  502 . Fly-back diode  512  is disabled at a fly-back disabling step  730  by opening fly-back switch  510 . Opening FET  502  and fly-back switch  510  facilitates dissipation of coil current at a dissipation step  740  through a charge build up across coil  408 . 
     After a period of time, fly-back diode  512  is enabled at a fly-back enabling step  750  for the purpose of measuring coil current through current sense resistor  520 . A coil current induced by the poppet translating through solenoid coil  408  toward the closed position is detected at a detection step  760 . A controller, such as controllers  318  and  414  of  FIGS. 3 and 4 , receives the coil current measurement and determines, at a peak detection step  770 , a time of a peak coil current after solenoid coil  408  is de-energized. The controller then uses the time delay of the valve closure to determine nozzle flow at a determination step  780 . 
       FIG. 8  is a plot  800  showing times of peak coil current for variously sized nozzle assemblies, such as nozzle assembly  34  shown in  FIG. 2 . Plot  800  includes three different spray nozzles  39 : a nozzle assembly without a spray tip attached, a nozzle assembly with a small nozzle spray tip that permits a low nozzle flow relative to the nozzle assembly without a spray tip, and a nozzle assembly with a large nozzle spray tip that permits a large nozzle flow relative to the small nozzle spray tip, but still more restricted nozzle flow relative to the nozzle assembly without a nozzle spray tip. 
     For each of the nozzle spray tips, closing of the solenoid valve for the nozzle assembly was initiated at a time of 50 milliseconds by the opening of the drive switch. The opening of the solenoid valve for the nozzle assembly was some time before 50 milliseconds, e.g., at a time of 0.0 milliseconds. When solenoid valve closure is initiated, the solenoid coil is de-energized, which is illustrated by each of the coil current plots for the three different nozzle assemblies falling initially toward zero amps. After approximately 4 milliseconds, each of the coil current plots begin to rise toward respective peaks, which corresponds with movement of the solenoid valve poppet toward the closed position. The precise time of the peak coil currents correlates to a fluid flow value. 
     The nozzle assembly without a nozzle spray tip permits the largest nozzle flow. The nozzle flow corresponds to an earlier valve closure indicated by a peak coil current at a time  810  that occurs at slightly less than 58 milliseconds, or slightly less than 8 milliseconds after the drive switch opened and initiated the de-energizing of the solenoid coil. 
     The nozzle assembly having the large nozzle spray tip permits less nozzle flow than the nozzle assembly without any nozzle spray tip. The nozzle flow corresponds to a valve closure indicated by a peak coil current at a time  820  that occurs at slightly less than 59 milliseconds. 
     The nozzle assembly having the small nozzle spray tip permits the least nozzle flow among the three. The nozzle flow corresponds to a valve closure indicated by a peak coil current at a time  830  that occurs at slightly less than 61 milliseconds. 
       FIG. 9  is a plot  900  showing nozzle fluid flow in gallons per minute versus time of peak coil current in milliseconds. The data points on plot  900  represent various nozzle assemblies having variously sized nozzle spray tips. The solenoid valve for the nozzle assembly was closed at a time of 50 milliseconds. The solenoid valve for the nozzle assembly was opened at a time earlier than 50 milliseconds, e.g., at a time of 0.0 milliseconds. Each data point on plot  900  illustrates the relationship between nozzle flow and valve closure time as indicated by the time at which the peak coil current induced by the poppet translating to the closed position occurs. 
     In certain embodiments, nozzle flow is determined by the controller at determination step  780  based on experimental data for solenoid valve closing times, such as the data shown in  FIGS. 8 and 9 . In alternative embodiments, nozzle flow is determined according to a mathematical relationship characterized by Eq. 1 above. The method ends at an end step  790 . 
     Although systems and methods are described above with reference to an agricultural spray system, embodiments of the present disclosure are suitable for use with agricultural fluid application systems other than spray systems. In some embodiments, for example, the systems and methods of the present disclosure are implemented in a fluid application system that injects fluid, such as fertilizer, into the soil through dispensing tubes, rather than spray nozzles. 
       FIG. 10  is a perspective view of one embodiment of a fluid application system  1000 . Fluid application system  1000  includes a volatile liquid fertilizer application system for application of fertilizers such as, for example, anhydrous ammonia. Fluid application system  1000  includes a motorized vehicle  1002 , a fluid storage tank  1004 , and a distribution manifold  1006 . Motorized vehicle  1002  may be any machine that enables fluid application system  1000  to function as described herein. In suitable embodiments, one or more components of fluid application system  1000  may be incorporated into motorized vehicle  1002  without departing from some aspects of this disclosure. In the exemplary embodiment, fluid storage tank  1004  and distribution manifold  1006  are disposed on a wheeled chassis  1008  towed behind motorized vehicle  1002 . 
     During operation, fluid storage tank  1004  may contain any type of fluid for distribution by fluid application system  1000 . For example, fluid storage tank  1004  may store a volatile fluid intended to be applied to fields for agricultural purposes. A common fluid used for agricultural purposes is anhydrous ammonia, which is applied to fields primarily as a fertilizer to increase the nutrient level of soils. The anhydrous ammonia includes at least some gaseous substance and, therefore, is maintained at a carefully controlled pressure to control the gaseous properties. In the exemplary embodiment, fluid storage tank  1004  is configured to store and maintain the fluid at a desired pressure as fluid flows out of the fluid storage tank. Fluid application system  1000  includes at least one pump  1030  connected to fluid storage tank  1004  to facilitate maintaining the fluid in the fluid storage tank at the desired pressure. 
     In the exemplary embodiment, fluid storage tank  1004  is fluidly connected to a distribution manifold  1006  by a fluid line  1032 . Disposed between distribution manifold  1006  and fluid storage tank  1004  is a valve  1036  and quick connect  1034 . In suitable embodiments, quick connect  1034  and valve  1036  may be coupled to any portions of fluid application system  1000 . For example, in some suitable embodiments, any of quick connect  1034  and valve  1036  may be omitted without departing from some aspects of this disclosure. In the exemplary embodiment, quick connect  1034  facilitates fluid storage tank  1004  being connected to and removed from fluid line  1032 . Valve  1036  controls fluid flow through fluid line  1032 . For example, valve  1036  is positionable between a closed position where fluid is inhibited from flowing through fluid line  1032  and an open position where fluid is allowed to flow through fluid line  1032 . In certain embodiments, valve  1036  may be any valve that enables fluid application system  1000  to function as described herein. 
     The fluid is directed from fluid line  1032  through valve  1036  and into distribution manifold  1006 . As shown in  FIGS. 10 and 11 , distribution manifold  1006  includes a plurality of supply lines  1038  each connected to valve assemblies  36 . Each valve assembly  36  regulates flow of the fluid through a nozzle body  37  and into a dispensing tube  1040  for injecting the fluid into a soil. Distribution manifold  1006  distributes the fluid to valve assemblies  36  and dispensing tubes  1040  for emitting the fluid from fluid application system  1000 . 
     Each valve assembly  36  is controlled by a controller, such as controllers  318  or  414  described above with reference to  FIGS. 3 and 4 , respectively. The controller may be configured to determine or estimate fluid flow through dispensing tubes  1040  based on a valve closure time using the methods described above with reference to  FIGS. 6 and 7 . More specifically, the controller may be configured to determine or estimate fluid flow through dispensing tubes  1040  based on a time delay between de-energizing a solenoid coil within valve assembly  36  and a measured poppet closure time, as described in more detail herein with reference to  FIGS. 6 and 7 . 
     In suitable embodiments, fluid application system  1000  may include any number of dispensing tubes  1040 . In some embodiments, as the fluid is emitted from dispensing tubes  1040 , vehicle  1002  moves fluid application system  1000  along a desired path for fluid application, such as rows  1046  of a field  1048 . In the exemplary embodiment, dispensing tubes  1040  are connected to or positioned behind a soil preparation mechanism  1042 , such as a knife or plow, that contacts the soil as dispensing tubes  1040  dispense fluid onto the soil, as best seen in  FIG. 11 . Soil preparation mechanisms  1042  are connected to a boom  1043 , which is connected to and pulled behind vehicle  1002 . 
     The systems and methods described herein provide fluid flow measurements through a solenoid valve. For example, in spray systems within which the systems and methods may be embodied or carried out, fluid flow may be determined and presented to the operator. Additionally, determined fluid flow may be compared to a target fluid flow for the spray system or further compared to determined fluid flows from adjacent nozzle assemblies. The comparison of measured fluid flow to a target fluid flow facilitates determining whether a particular nozzle assembly is functioning properly. The determined fluid flow measurements facilitate determining, during operation, the state of the various nozzle assemblies on the spray system that are otherwise difficult to ascertain during operation. The systems described herein may include diagnostic capabilities derived from the determined fluid flow through the solenoid valve. For example, the system may be able to determine if valve  36  contains debris lodging it open or closed, if spray nozzle  39  is partially or fully clogged, if spray nozzle  39  has fallen off of nozzle body  37 , or if a spray boom section is failing to receive flow due to a conduit problem or section valve malfunction. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other and examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.