Two-wire power and communications for irrigation systems

A large number of irrigation system devices connected to a common two-wire cable can be powered and individually controlled from a central location by transmitting over the cable DC pulses of alternating polarity. Control information is conveyed by transmitting a command pulse train consisting of a series of pulses, separated by short no-power intervals, whose polarities indicate logic ones or zeros. Following a command pulse train, a selected watering station decoder acknowledges receipt of instructions by drawing current during a predetermined pulse of an alternating-polarity power pulse cycle, while a sensor decoder returns binary data by drawing current during one or the other of the alternating-polarity pulses of a series of power pulse cycles.

FIELD OF THE INVENTION

This invention relates to the combined powering, control and monitoring of sprinklers or other components of an irrigation system over a single set of two wires. More particularly, the apparatus of this invention transmits a square wave pulse train from a central location to remote components by alternating the polarity of the two wires with respect to each other. The pulses provide operating power to the components and at the same time can form a code which selects and operates a desired component. Operation of the component is monitored at the central location by sensing momentary current changes in the wires.

BACKGROUND OF THE INVENTION

Large commercial irrigation systems such as those used on golf courses or croplands use sprinklers, sensors or other components which are normally powered from 24 V AC power lines that can be several miles long and can serve many hundreds of components. Various schemes have been proposed for powering and controlling the components of such a system with just two wires. For example, U.S. Pat. No. 3,521,130 to Davis et al., U.S. Pat. No. 3,723,827 to Griswold et al., and U.S. Pat. No. 4,241,375 to Ruggles disclose systems in which sprinklers along a cable are turned on in sequence by momentarily interrupting the power or transmitting an advance signal from time to time.

A problem with this approach is that it does not allow the operator to freely turn on or off any selected sprinkler or set of sprinklers at different times. This problem is usually resolved by providing separate controllers in the field to operate groups of sprinklers in accordance with a program stored in them, or transmitted to them by radio or other means. Alternatively, it has been proposed, as for example in U.S. Pat. No. 3,578,245 to Brock, to operate individual sprinkler sets from a central location by superimposing a frequency-modulated signal or DC pulses onto the 24 V AC power line. All of these approaches are expensive, and the latter may cause electrolysis problems that can damage the system in the long run.

Finally, a system with hundreds of sprinklers stretched out over miles using conventional electric water valves requires expensive heavy wiring to accommodate the hold-open current drawn by a large number of valves that may be watering simultaneously.

It is therefore desirable to provide an irrigation system in which individual components connected to a two-wire cable can be turned on and off (or, in the case of a sensor component, read) from a central location at minimal cost, with a minimal expenditure of electrical power, and without causing any significant electrolysis problems in the system. It is also desirable to have the ability in such a system to monitor the successful execution of the on-off command, or to return data to the central location, without additional apparatus.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention provides a way to both power and control a large number of devices connected to a two-wire cable by energizing the cable with a square wave consisting of power pulses of alternating polarity. When a device operation is desired, the system transmits a command pulse train consisting of a series of pulses separated by short no-power intervals. The polarity of each pulse in that series indicates whether it is a 1 or a 0 in a binary device identification and/or action code. The DC power of one or the other polarity available on the cable during each power or command pulse powers the decoder circuitry of each device and powers the desired operation of the device. The presence of power on the cable allows the selected device to signal receipt of the instruction by drawing a burst of current during the first pulse following the end of a command train. Electrolysis problems are minimized by the fact that statistically, the number of pulses of one polarity is about equal to the number of pulses of the opposite polarity.

If the command is an interrogation of a sensor such as a flow, temperature, soil moisture or rain sensor, the sensor transmits data to the central location by drawing current during one of the pulses of each set of alternating-polarity pulses following the command train. Current draw during a pulse of a first polarity signifies a “1”, while current draw during a pulse of the other polarity signifies a “0”. The absence of any current draw following any command indicates a system or component failure and can be used to trigger an alarm.

The system of this invention is fail-safe in that a valve actuating capacitor is continuously charged except during the actual actuation of the associated water valve solenoid. If power is lost, the capacitor discharges through the solenoid and puts the valve into the “off” state. Additionally, the decoders of this invention can be set to predetermined run times by the command pulse train, whereupon they will automatically shut the watering station off upon expiration of the commanded time.

By using latching solenoids actuated by the discharge of an actuating capacitor, power consumption of the system is minimized, and wiring as small as 14 gauge can successfully be used for cable runs of several miles controlling hundreds of watering stations or other devices.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1aprovides a general overview of the system10of this invention. An RS232 or other communication system12transmits action commands from a PC or other control unit14to a gateway16, and receives acknowledgments or other device information from the gateway16for conveyance to the control unit14. The gateway16, which in the preferred embodiment contains a motherboard17and a pair of daughterboards19aand19b, receives power from a power source18. As explained in more detail in connection withFIGS. 1band1cbelow, the function of the daughterboards19a, bis to selectively apply, in the preferred embodiment, the following potentials to the wires A and B of their respective cables20: 1) +40 VDC on A with respect to B; 2) +40 VDC on B with respect to A; or 3) an equal potential on both A and B. The daughterboards19a,bare also equipped to detect current drawn by the decoders of the system, and to report that information to the control unit14through the motherboard17. Device decoders such as watering station decoders22and sensor decoders24are connected in parallel to the wires A and B, and are arranged to operate the system components (e.g. water valves26or sensors28) connected to them.

As best seen inFIG. 1b, the motherboard17is powered from a line transformer30that steps the commercial AC voltage down to 28 VAC. Following surge protection at21in the preferred embodiment, this is applied to a bridge rectifier32which converts the AC voltage to +40 VDC. This voltage is transmitted to the daughterboards19aand19bofFIG. 1cthrough connector23. The output of bridge rectifier32is also applied to an operational amplifier25which provides incoming voltage information to the microprocessor27. In addition, the output of bridge rectifier32is applied to three sets of voltage regulators29a-cand isolation circuits31a-cwhich provide isolated 5 VDC power to the microprocessor27, the daughterboards19a, b, and the two-way isolation circuitry33, respectively.

The microprocessor27receives information from the control unit14through RS232 connector35as well as through an external pump pressure sensor37and an external rain sensor39(FIG. 1a). Its outputs include a pump start signal41that controls the irrigation system's water pumps43, and a control signal45that operates the microprocessors47of the daughterboards19aand19bthrough the connector23. The microprocessor27may also provide appropriate outputs to operate LED indicators49to convey status information such as Watering In Progress, PC Connection Live, Power On, Transmitting Data, Receiving Data, Pump Pressure Normal, Rain Sensed, and Pump On. A communication line (Tx) connects the microprocessor47(FIG. 1c) to the RS232 connector35through connector23and two-way isolation circuitry33for the transmission of commands and response data as described below.

FIG. 1cshows the details of one of the two identical daughterboards19aand19bofFIG. 1a. The +40 VDC line of the connector23is applied through the current sensor38to a Four-transistor H bridge50which is switched by microprocessor47, through an isolation circuit51, into the three possible output states of A-positive-with-respect-to-B, B-positive-with-respect-to-A, and A-and-B-at-same-potential. These are the states required by the protocol described below. A status LED48may be provided to monitor the operation of the microprocessor47. The wires A and B are preferably connected to the decoder cable20through a surge protector57.

The sensing of current by the current sensor38is conveyed to the microprocessor47through an isolation circuit55. A current pulse is detected when the current (in either direction) sensed by current sensor38rises through a predetermined threshold. The microprocessor47interprets this and conveys the appropriate information to the control unit14(FIG. la) via the Tx line and the RS232 connector35.

A preferred protocol for the operation of the system of this invention is illustrated inFIGS. 2a-d. Normally, the daughterboards19a, bimpress a square wave53alternating between +40 V (A positive with respect to B) and −40 V (B positive with respect to A) across their respective outputs A and B at a 60 Hz rate. This provides a square-wave power supply (FIG. 2a) to all the decoders26,28along the cable20. As pointed out below, the decoders26,28can use power of either polarity. Because the time of the circuit at one polarity is equal to its time at the other polarity, no electrolysis problem is generated.

If it is now desired to actuate a specific sprinkler or sensor, the command pulse train52shown inFIG. 2bis transmitted. The command train begins with a no-power segment54in which the wires A and B are both grounded for 1/120 second. This is followed, in the preferred embodiment, by eight pulses56separated by similar no-power segments or delimiters54. The pulses56may be either +40 V (signifying a “1”) or −40 V (signifying a “0”). Taken together, the pulses56define the desired runtime (in minutes) of the device now to be selected.

The next twenty pulses58, again separated by no-power delimiters54, define the address of the desired device26or28. Next, the nature of the desired command is specified by the four pulses60. The command pulse train52illustrated inFIG. 2bmay, for example, convey the command “Turn Station3of decoder2873on for 25 minutes”. Upon completion of the command pulse train, the microprocessor ofFIG. 1breturns control of the wires A and B to the power relays. The output of gateway16thus resumes the square-wave format ofFIG. 2a.

If a selected decoder26has received and understood the command (seeFIG. 2c), it momentarily draws a high current burst62during the +40 V portion of the first square wave64following the command pulse train. This is detected by the current sensor38of gateway16and constitutes an acknowledgement that the decoder has received its instruction. If no current is detected during the first square wave64, a control failure is indicated, and the microprocessor46may transmit an alarm to the control device14.

If the addressed device was a sensor decoder28(seeFIG. 2d), the chosen decoder responds with current bursts66during the eight (in the preferred embodiment) square waves68following the command train. In each of these square waves, a current burst70during the +40 V portion transmits a “1” to the gateway16, while a current burst70during the −40 V portion transmits a “0”. As in the case of a station decoder26, the lack of any current burst during a square wave68indicates a system failure and may trigger an alarm.

An examination ofFIGS. 2a-dwill show that in the preferred embodiment, a complete command and response cycle requires a little more than one second. Consequently, the described system can execute about fifty commands per minute.

FIG. 3aillustrates a station decoder22used in the system of this invention. The power and communication signals from the gateway ofFIG. 1bappearing on wires A and B are applied to a bridge rectifier72that rectifies the incoming signals and conditions them to be interpreted by the microprocessor74. A power capacitor76is continually charged by the rectified power and communication signals in order to provide operating power to the microprocessor74through the no-power intervals54(FIG. 2b), and long enough to perform an orderly shutdown in the event of a power failure.

The microprocessor74includes three subprocessors: the power manager78, the communications manager80, and the control manager82. The power manager78controls the charging of the actuating capacitor84whose discharge, under the control of control manager82, operates the station (i.e. watering valve) solenoids86a-din the manner described below in connection withFIG. 3b. An A/D converter88converts the charge level of the actuating capacitor84into a digital signal to allow control manager82to monitor the charge level of capacitor84. The power manager78controls the charging of capacitor84from the bridge rectifier72through an on/off switch90under the guidance of control manager82.

The communications manager80interprets any communication signals that appear at the bridge rectifier72, enables the bridge rectifier72to provide power to the on/off switch90if it determines the decoder22to have been selected, and informs the control manager82of the desired action. The communications manager80also controls the current drawn from wires A and B by the bridge rectifier72so as to produce the above-mentioned current burst62(FIG. 2c) that acknowledges receipt of a command to the gateway16. The microprocessor74generates the current burst62by transmitting a pulse87(FIG. 3c) which causes the output of bridge rectifier72to be momentarily bridged by a low-impedance resistor89through the source-drain circuit of transistor91.

The control manager82, pursuant to instructions from the communications manager80, operates triac output stages92a-dto actuate the solenoids86a-dand determines whether the solenoids86a-dare to be turned on or off. Its function is shown in more detail inFIG. 3b, in which input100denotes the operating power from bridge rectifier72. Input102is the on/off signal from power manager78, with transistor104being driven by the on/off switch90. When switch90is on, power from input100can flow into the actuating capacitor84through transistor104. The voltage on capacitor84is monitored by the A/D converter88connected to output106.

When the solenoid86ais to be actuated, either by a received command or by the expiration of a runtime interval stored in the microprocessor74by pulses56(FIG. 2b), the control manager82causes power manager78to turn off switch90so as to block transistor104, and applies power to input108. At the same time, the control manager82uses input110to switch triac bridge92ato the desired output polarity for turning the water valve26on or off. The capacitor84now discharges through the transistor112and the solenoid86a, opening or closing the water valve26depending upon the polarity of the output of triac bridge92a. The triac bridge92aalso provides some degree of surge protection to the solenoid86a.

Following an actuation of the solenoid86a, the control manager82removes power from input108and directs the power manager78to turn switch90back on to recharge capacitor84. The control manager82will not execute an actuation command until the charge on capacitor84is back to a sufficient level. If a power failure occurs, the power manager, which continuously monitors the presence of power at the bridge rectifier72, causes the control manager82(which remains powered for a while by the power capacitor76) to immediately go through a closing routine of all the water valves26as described above.

FIG. 4illustrates a sensor decoder24according to the invention. The bridge rectifier72, microprocessor74, power capacitor76, power manager78and communications manager80serve the same functions as in the station decoder described above in connection withFIG. 3a. In the sensor decoder24, however, the control monitor82ofFIG. 3ais replaced by a sensor manager120. The sensor manager120, when so commanded by the communications manager80, causes a sensor read circuit122to read and condition the sensor data which is continuously transmitted by the sensor28to the interface124. The interface124preferably contains surge components and, if appropriate, A/D conversion circuitry.

The data received by the sensor manager120is conveyed to the communication manager80and is used by it to produce the current bursts66(FIG. 2d) that transmits the data to the gateway16.