Abstract:
A distributed control system is provided wherein a master controller inductively delivers power and data to a plurality of remote slave modules or controllers via a plurality of coupling loops formed along a length of transmission line. Each of the remote slave modules, in turn, inductively delivers return data to the master controller via the plurality of coupling loops. The use of inductive coupling provides an advantage over the state of the art because no direct galvanic electrical connection is required between the transmission line and the remote slave modules which promise to simplify installation and enhance long-term reliability. Example applications for the control system described herein include agricultural irrigation systems where individual sprinkler and valve components may be controlled collectively, individually, or in groups or subsets, to vary application rates according to prescribed irrigation parameters.

Description:
Priority is hereby claimed from U.S. Provisional Application No. 61/302,841 filed Feb. 9, 2010, the entirety of which is incorporated herein by reference. 
    
    
     This invention relates generally to distributed controls technology and, more specifically, to the control of individual sprinkler or valve components in, for example, agricultural irrigation systems. 
     BACKGROUND 
     It is known to employ systems for distributing and transferring power and/or data to devices disposed along a transmission line or cable. Exemplary documentation in the U.S. patent literature includes the following: U.S. Pat. No. 7,176,589, discloses electrical devices such as inductive couplers, power conversion and modulation/demodulation circuits used in the distribution and/or transfer of power and/or data to electrical devices along an underwater cable; U.S. Pat. No. 6,624,745 discloses an inductively-coupled data communications system which distributes power and data along the same two-wire conductor between, e.g. network stations; U.S. Pat. No. 4,244,022 discloses a solid-state control system for large-scale irrigation that incorporates a central processing unit having a master clock and a central/syringe timing module system connected to a plurality of satellite controllers which are, in turn, connected to control irrigation solenoid valves. The listing above is by no means intended to be complete, but merely a sampling of patents relating to distributed power systems. 
     The invention described below is intended to simplify, ease installation and reliability, and potentially reduce cost in a distributed power system utilized in an exemplary but nonlimiting irrigation system. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary but nonlimiting embodiment, the invention provides a distributed control system wherein a master controller inductively delivers power and data to a plurality of remote slave modules or controllers via a plurality of coupling loops along a length of transmission line. In this exemplary embodiment, each of the remote slave modules, in turn, inductively delivers return data to the master controller via the plurality of coupling loops positioned along the length of transmission line. The use of inductive coupling provides an advantage over the state of the art because no direct galvanic electrical connection is required between the transmission line and the remote slave modules which promises to simplify installation and enhance long-term reliability. 
     Example applications for the control system described herein include agricultural irrigation systems where individual sprinkler components may be controlled collectively, individually, or in groups or subsets, to vary application rates according to prescribed irrigation parameters. 
     Accordingly, in one exemplary but nonlimiting aspect, there is provided a distributed control system comprising a master controller connected to a transmission line and adapted to deliver power and data to the transmission line and to receive data from the transmission line; the transmission line comprised of first and second conductors configured to carry differential data; and a plurality of couplers arranged along the transmission line, each coupler enclosing a pair of inductive coupling loops formed in the transmission line, and passing through an inductor or coil to thereby establish mutual coupling between the transmission line and the inductor, said inductor connected to one or more slave controllers; wherein said mutual coupling permits data transfer from the master controller to the one or more slave controllers and from the one or more slave controllers to the master controller. 
     In another exemplary but nonlimiting aspect, there is provided a coupler assembly for electrically coupling a transmission line and a slave controller where the coupler assembly comprises a housing including a lower body portion and an upper cover portion, and a split core, and wherein the upper cover portion is moveable between open and closed positions, and wherein a first half of the split core and inductive coupling loops formed in the transmission line are supported in the upper cover portion, and wherein a second half of the split core and a coil are supported in the lower body portion. 
     In still another exemplary but nonlimiting aspect, there is provided a method of controlling a plurality of sprinkler components in an irrigation system that includes a master controller for controlling a plurality of slave controllers operatively connected to one or more of the plurality of sprinkler components, the method comprising arranging a plurality of inductive coupling loops along a transmission line, and mutually coupling the transmission line to the plurality of slave controllers; and sending signals over the transmission line from the master controller to the plurality of slave controllers and receiving signals over the transmission line from the plurality of slave controllers to the master controller. 
     The invention will now be described in greater detail in connection with the drawings identified below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified schematic diagram showing the control system in accordance with an exemplary but nonlimiting embodiment; 
         FIG. 2  is a schematic diagram of a master controller taken from the control system of  FIG. 1 ; 
         FIG. 3  is an enlarged schematic of one of the slave controllers taken from the control system of  FIG. 1 ; 
         FIG. 4  is a more detailed schematic diagram of the slave controller shown in  FIG. 3 ; 
         FIG. 5  is a schematic diagram of the slave controller in an alternate embodiment; 
         FIG. 6  is a perspective view of a slave controller circuit board in accordance with the exemplary embodiment; 
         FIG. 7  is a front elevation view of the circuit board shown in  FIG. 6 ; 
         FIG. 8  is a plan view of the circuit board shown in  FIG. 6 ; 
         FIG. 9  is a side edge view of the circuit board shown in  FIG. 6 , rotated to a vertical orientation; 
         FIG. 10  is a perspective view of a slave controller circuit board mounted within a housing; 
         FIG. 11  is a perspective view of the slave controller shown in  FIG. 10  but shown here in cutaway form; 
         FIG. 12  shows an example embodiment where the master controller and slave controllers are mounted along a solid set irrigation line; 
         FIG. 13  is a perspective view of another application where the master controller is mounted at one end of a linear irrigation machine and slave controllers are mounted adjacent to individual sprinklers on drop hoses suspended from an overhead truss of the machine; 
         FIG. 14  is a schematic view of another application similar to  FIG. 13 , but where slave controllers are mounted along the top of the overhead truss; 
         FIG. 15  is a perspective view of yet another application where the master controller is mounted at the center pivot of a pivot irrigation machine and the slave controllers are mounted along the top of an overhead truss of the machine; and 
         FIGS. 16A and 16B  illustrate an alternative inductive coupler incorporating sine wave-shaped inductive coupling loops, the coupler shown in open and closed positions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An inductively coupled distributed control system  10  for use with, for example, irrigation machinery, is shown in  FIG. 1  in simplified form for ease of understanding. A master controller  12  is connected to a transmission line  14 . The master controller  12  is provided in the control system  10  to deliver power and command data to the transmission line  14 , and is further configured to receive status and sensory data delivered by the transmission line  14 . 
     The power delivered by the master controller  12  to the transmission line  14  is in a time multiplexed format, having a frequency less than about 200 kHz, and amplitude less than about 48 volts peak-to-peak. The data delivered by the master controller  12  to the transmission line  14  is specified as a command protocol wherein the data is modulated in continuous wave fashion, although other forms of modulation can be employed including frequency-shift keying, phase-shift keying, pulse-coded modulation, or other forms of modulation known in the art. 
     The data received by the master controller  12  from the transmission line  14  is specified as a status protocol wherein the data is demodulated from a continuous wave signal, although other forms of modulation can be employed including frequency-shift keying, phase-shift keying, pulse-coded modulation, or other forms of modulation known in the art. The modulation frequency of the transmitted signal and the received signal may be at the same or different frequencies, depending on the application. In a preferred embodiment, the received carrier frequency is less than about 1000 kHz. 
     The transmission line  14  is a balanced transmission line having two conductors (see conductors  92   a  and  92   b  in  FIG. 3 ) which are configured to carry differential signals. In this manner, the signals propagate along the length of the transmission line  14  with minimal attenuation because the field of each conductor effectively cancels to reduce radiated emissions. The transmission line  14  has a characteristic impedance value which is a function of its construction and environment. In a preferred embodiment, the characteristic impedance of the transmission line  14  is less than 200 ohms. The transmission line  14  can be twin-lead or twisted-pair-type of transmission line, and can be shielded or unshielded depending on the application. 
     Referring still to  FIG. 1 , along the transmission line  14 , the conductors are formed into a plurality of coupling loops  16 , wherein a portion of each coupling loop  16  is routed through a coupler  18 . The details of each of the coupling loops  16  and respective coupler  18  will be discussed in further detail below. Each coupler  18  is connected to a slave module or controller  20 , the details of which also will be discussed in further detail below. A line termination  22  is connected to an end of the transmission line  14 . In a preferred embodiment, the line termination  22  is a resistor having a resistance value that approximates the characteristic impedance of the transmission line  14 . One skilled in the art would recognize that other types of loads could be used as the line termination  22  such as inductive or capacitive loads without departing from the scope of this invention. 
     Referring now to  FIG. 2 , the master controller  12  includes a microcontroller  40  which is configured to power and communicate with each of the plurality of slave modules  20  ( FIG. 1 ). The microcontroller  40  is connected to a user interface  42  which enables an operator to configure and operate the distributed control system  10  ( FIG. 1 ). The microcontroller  40  is further linked to a communications port  44  to enable information exchange with other systems including other controllers. 
     A carrier signal  46  is generated by the microcontroller  40  to facilitate power and data transmission along the transmission line  14 . The carrier signal  46  can be in the form of a square wave or a sine wave depending on the application. The microcontroller  40  further generates a data signal  48  which reflects a protocol that is defined within the microcontroller  40 . An AND gate  50  is connected to each of the carrier signal  46  and data signal  48  to provide a modulated output signal generally designated by the numeral  52 . The signal  52  is passed through a signal filter  54  to remove unwanted spectral artifacts and a resultant signal is amplified by a transmit driver  56 . A transmit/receive switch  58  is connected in receiving relation to the signal provided by the transmit driver  56  and is connected to a balun transformer  62  and is configured to provide differential power and data signals to the transmission line  14  via connectors  64   a  and  64   b  in response to a switch control signal  60  provided by the microcontroller  40 . 
     Differential return data signals coming from the transmission line  14  are transferred through the balun transformer  62  as single-ended signals to the transmit/receive switch  58 . The microcontroller  40  is configured to provide a period when return data signals can be transferred from the slave modules  20  ( FIG. 1 ) by commanding the transmit/receive switch  58  into a receive mode, so that signals from the transmission line  14  are routed to the return signal amplifier  66  and return signal filter  55  and then to the return logic receiver  68 . Here the returned signals are conditioned to provide logic level data and are sent to the microcontroller  40  via the return data line  70 . 
     Referring now to  FIG. 3 , a slave controller  20  is shown in association with the coupling loop  16 . The slave controller  20  includes the coupler  18  that is connected to the slave control assembly  80 , described in further detail below. The slave control assembly  80  is connected to a solenoid  82 . The solenoid  82  is used to actuate a sprinkler component such as, for example, a valve (not shown), but may be used for other switching applications. In addition, other loads such as stepper motors could be used without departing from the scope of this invention. In a preferred embodiment, the solenoid  82  is a bi-stable latching solenoid. An alert switch  84  is connected to the slave control assembly  80  and is configured to provide a user request which may include initialization. The slave control assembly  80  may also be connected to a flow switch  86  that provides a contact closure when the flow rate of a fluid in a conduit exceeds a preset value. Other sensors could similarly be connected to the slave control assembly  80  without departing from the scope of the invention. 
     The coupler  18  is composed of a coupler inductor  88  and a coupler closure  90 . The combination forms a toroid type inductor which is characterized by its containment of the magnetic flux. When the coupling loop  16  and coupler inductor  88  are configured as shown in  FIG. 3 , and the coupler closure  90  is brought into close proximity and in mating relation to the coupler inductor  88 , a loose inductive or mutual couple is formed which enables transfer of energy and data as will be discussed in further detail below. 
     The transmission line  14  includes the first conductor  92   a  and second conductor  92   b  which, in combination, are configured to propagate differential signals over the length of the transmission line  14 . Since the signals in the respective conductors  92   a  and  92   b  are differential in nature, little useful energy can be coupled from and to the line since the field from each line will cancel. However, by arranging conductor  92   b  and forming a circular, 360° substantially closed loop generally designated by the numeral  94  referred herein as an in-phase loop, and further taking conductor  92   a  and twisting it, and then forming a loop generally designated by the numeral  96  (herein referred to as a counter-phase loop), the differential signals in the conductors provide a local region of in-phase fields so they add over the localized region of the coupling loop  16 . This localized region of in-phase fields found in the coupling loop  16  enables effective inductive coupling between the differential signals found in conductors  92   a  and  92   b  and the coupler inductor  88 . In a preferred embodiment, the core material used in the coupler  18  is composed of a powdered ferrite material, and wherein the inductance of the coupler inductor  88  is approximately 150 uH when the coupler closure  90  is mated with the coupler inductor  88  as described further below. Also, in a preferred embodiment, the inductance of the coupling loop is less than 1.4 uH, and the diameter of the coupling loop  16  is less than 50 mm. 
     It has been found that increasing the inductance of the coupling loop  16  improves the transfer of power from transmission line  14  to the coupler inductor  88  effectively changing a degree of coupling. For this reason, there is an optimum degree of coupling that exists for a given number of slave modules  20 , wherein as the number of slave modules  20  is increased, the degree of coupling should be decreased to ensure that the power requirement for all slave modules  20  is satisfied. 
     Referring now to  FIGS. 4 and 5 , the slave module  20  which includes the slave control assembly  80  is coupled to the transmission line  14  via the coupling loop  16 . The coupler inductor  88  is configured to extract and induce power into the transmission line  14  as discussed above. One lead of the coupler inductor  88  is connected to a common ground for the module, while another lead connects to the logic rectifier  100 . The logic rectifier  100  provides a positive pulsating direct current relative to common from the alternating current induced into the coupler inductor  88  from the coupling loop  16  and is smoothed by a capacitor  102 . The smoothed voltage at the capacitor  102  is fed to the input of a voltage regulator  104 . 
     The voltage regulator  104  provides a stabilized voltage output power supply for a microcontroller  106  and a nonvolatile memory  108 . The nonvolatile memory  108  includes an identity address which provides a unique identifier for the slave module  20 . The microcontroller  106  is also connected to the alert switch  84  and the flow switch  86  as discussed above. 
     The coupler inductor  88  is also connected to a data rectifier  110  that demodulates the signals from a coupling loop  16  into data signals. These signals are conditioned to a logic level suitable for connection to the microcontroller  106  via data series resistor  112  and data parallel resistor  114  that form a voltage divider. Herein, commands and data originating from the master controller  12  ( FIG. 1 ) are provided to the microcontroller  106  and are configured as time-sequenced, asynchronous, serialized data. One skilled in the art would recognize that other forms of data encoding could be used without departing from the scope of the invention. 
     The microcontroller  106  is configured to respond to only commands and data that are directed to match its embedded identity and stored in the nonvolatile memory  108 . This match can occur when a command includes an address that specifically matches the identity in the nonvolatile memory  108  relative to a synchronization phase, so that a plurality of slave modules  20  can respond to a single command in a time-synchronized manner. 
     The coupler inductor  88  is connected to solenoid drive voltage switch  116  that is controlled by solenoid drive voltage switch control line  118  that is controlled by the microcontroller  106 . The control of this line will be discussed in further detail below. When the voltage switch  116  is closed, alternating current induced from the transmission line  14  to the coupler inductor  88  is provided to a voltage multiplier  120 . This voltage multiplier rectifies and provides a passive step-up converter using a combination of diodes and capacitors. In a preferred embodiment, a half-wave series multiplier fashioned using a Villard cascade topology is utilized, although other types of multipliers known in the art could be used without departing from the scope of the invention. 
     Energy from the multiplier  120  is stored in the solenoid drive voltage capacitor  122 . A solenoid drive monitor line  124  is connected to the capacitor  122  and the microcontroller  106  to enable it to sense the voltage on the capacitor. In this manner, the microcontroller  106  can command the solenoid drive voltage switch  116  so that a specific target voltage can be maintained across the capacitor  122 . One skilled in the art would recognize other ways to maintain a specific target voltage, including holding the solenoid drive voltage switch  116  in a closed position with a zener diode connected in parallel with the capacitor  122  to maintain a target voltage. An H-bridge solenoid driver  126  is connected in supply-side relation to the capacitor  122 . The solenoid driver  126  is connected to the solenoid  82  in driving relation and is able to drive the solenoid  82  in both a forward and reverse manner in response to commands provided by the microcontroller  106  as it drives the H-bridge control line  128 . In a preferred embodiment, the solenoid drive voltage capacitor  122  is maintained in a fully charged state, so in the event of a power or transmission line failure, the solenoid  82  can be set to a default state previously determined by a user. Current delivered to the solenoid  82  is directed through an H-bridge current sense resistor  130 , wherein a voltage is provided that is proportional to the current traveling through the solenoid  82  and is made available to the microcontroller  106  by a current sense line  132 . In this manner, the microcontroller  106  can monitor the time-varying voltage along the sense line  132  during state changes of the solenoid  82  to determine its operational condition. 
     Referring exclusively to  FIG. 4 , the coupler inductor  88  is further connected to a data return rectifier  134  that rectifies negative-going pulses of the alternating current induced into the coupler inductor  88  from the transmission line  14 . The cathode of the rectifier  134  is connected to a data return storage capacitor  136  where a negative voltage relative to common is stored until it is needed for a data return transmission from the slave module  20  to the master controller  12 . The microcontroller  106  originates a return carrier signal  138 , and in a preferred embodiment, the frequency of the signal is less than 1000 kHz. 
     The microcontroller  106  further provides a data signal  140  which reflects a protocol that is defined within the microcontroller  106 . An AND gate  142  is connected to each of the return carrier signal  138  and the data signal  140  to provide a modulated output signal generally designated by the numeral  144 . A return voltage switch  146  is configured to respond to the modulated output signal  144  to switch the negative voltage present on the capacitor  136  back into the coupler inductor  88  at a rate that matches the signal  144 . In this manner, the negative voltage will induce a current into the coupler inductor  88 , creating a magnetic field in the coupling loop  16 , wherein a differential return data signal will be induced into the transmission line  14  which will propagate along the transmission line and back to the master controller  12  where it will be received and decoded as described above. 
     Referring now to the alternative configuration in  FIG. 5 , the modulated output signal generally designated by the numeral  144  is connected to a transmit-coupling capacitor  150 . A transmit coil or inductor  154  is wound or positioned adjacent to the coupler inductor  88 . A transmit coil tank capacitor  152  is connected in parallel with the transmit inductor  154  to provide an LC circuit with a resonant frequency that is approximately equal to the return carrier signal  140  frequency. In this manner, a current is provided to the transmit inductor  154 , creating a magnetic field in the coupling loop  16 , wherein a differential return data signal will be induced into the transmission line  14  which will propagate along the transmission line and back to the master controller  12  where it will be received and decoded as described above. One skilled in the art would recognize that there are other ways to couple the return data from the microcontroller  106  to the transmission line  14  including inserting a single or plurality of diodes in series connection to the inductor  154 . 
       FIGS. 6-9  illustrate an exemplary slave controller circuit board  156  supporting the coupler  18  formed by the inductor  88  and coupler closure  90 . The coupler inductor comprises a first, split ferrite core portion  158  and winding or coil  160  wrapped about the core. The coupler closure  90  is formed by the second, mating split ferrite core portion  162 .  FIGS. 10 and 11  illustrate the slave controller board  156  including the coupler inductor  88  and coupler closure  90  mounted within a slave controller housing  164  through which the conductors  92   a  and  92   b  pass in the looped configuration described above in connection with  FIG. 3 . The housing  164  may be configured to include a lower body portion  166  and an upper cover portion  168 ; with the upper cover portion  168  pivotally supported on the lower body portion  166  and moveable between closed and open positions, the open position shown in  FIG. 10 . By supporting the coupler closure  90  in the upper cover portion  168  of the housing  164 , easy access to the coupler  88  is provided upon opening the housing. 
     The control system described herein has many applications in, for example, various agricultural irrigation systems including solid-set, linear and pivot machinery where many individual sprinklers are carried on common water-supply conduits or trusses. In exemplary configurations, the master controller  12  may be secured at one end of the machine, with the slave controllers secured in proximity to respective individual sprinklers. Each slave controller may be connected to a solenoid, (see solenoid  82  in  FIG. 3 ), stepper motor or other suitable actuator device that operates a valve in proximity to the respective sprinkler inlet. 
     The distributed control system as described herein has many applications in (but is not limited to) agricultural irrigation. 
     With respect to agricultural irrigation,  FIG. 12  illustrates an exemplary but nonlimiting application for the subject invention, where the individual slave controllers  20  (connected to a master controller  12 ), are secured at the base of, for example, gun-type sprinkler components  169  including valves that are mounted along a fixed ground engaging conduit  170  in a solid-set irrigation system. 
       FIG. 13  illustrates another example application where the master controller  12  and individual slave controllers or modules  20  are mounted on a linear irrigation machine  172 . In this embodiment, the slave modules  20  are located on the drop hoses  174  associated with each of the individual sprinklers  175 , suspended from the overhead truss  176 . 
       FIG. 14  illustrates another example application similar to that shown in  FIG. 13  but where the slave controllers or modules  20  are mounted along the overhead truss  176  of a linear irrigation machine. 
       FIG. 15  illustrates yet another example application, similar to that shown in  FIG. 14  but wherein the irrigator is in the form of a pivot machine  178 , with the vertical conduit section  180  representing the center pivot of the machine. 
       FIGS. 16A and 16B  illustrate an alternative inductive coupler assembly similar to that shown in  FIGS. 6-10  but simplified for convenience and clarity. In this alternative configuration, the housing  164  is only partially shown, with the lower body portion  182  supporting the slave controller circuit board  184 , the split core inductor portion  186  and winding or coil  188 . The split core coupler closure  190  is supported in the upper cover portion of the housing (not shown). It will be appreciated, however, that the upper cover portion, like the upper cover portion  168  ( FIGS. 10-11 ), may be pivoted from an open position ( FIG. 16A ) to a closed position ( FIG. 16B ), so that, when closed, the split core inductor portion  186  and split core coupler closure  190  will close the inductor coupler about the transmission line conductors  192   a  and  192   b . In this alternative arrangement, the conductors  192   a  and  192   b  are arranged to form mirror-image loops having a shape in the form of a sine wave, herein referred to as sine loops, with a pair of loop portions  194 ,  196  in each loop arranged so that the ferrite split core coupler closure  190  passes through the loops. It will be understood that the electrical path including the inductive coupling is identical to the first-described embodiment. Only the loops are altered, from substantially closed 360° loops to “unfolded” loops extending generally in a linear path, where the bend radii at each loop are substantially identical. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements.