GB2344707A - Surge-proof irrigation system controller - Google Patents

Abstract

The electronic control unit comprises a timer unit for providing system control signals in response to input data and a driver unit connected, via cables, to devices to be controlled, e.g. irrigation valves in an irrigation system. The timer unit and the driver unit are physically separated by an air gap and communicate only via a wireless link e.g. infrared. The sensitive electronics contained within the timer unit are thus protected against electrical surges occurring in the field wiring or driving part of the system. Surge suppression components are included in the drive unit circuit.

Description

SURGE-PROOF CONTROLLER The present invention relates to a control system which prevents damage due to electrical surges. The present invention is particularly, but not exclusively, useful for irrigation system control circuits.

Electrical surges caused by lightning can cause problems in many electronic or electrical systems, particularly systems with components located outside.

In the particular field of irrigation controllers, these electrical surges can damage the sensitive electronics, causing the system to fail. The problem is particularly acute in irrigation controllers for several reasons. In such systems, the field wiring can be up to many kilometers long and can run in many directions.

The field wiring generally has a low resistance and is terminated at the controller. The controller is normally located at a remote location and is normally connected to a high power electric pump. All of these conditions leave the system open to the damaging effects of electrical surges due to lightning.

Many systems have been developed for providing surge protection of electronic systems. The most common systems available operate by shorting the electrical surges to a common point which is connected to earth potential.

Such surge protection devices, however, are still not entirely effective due to the fact that lightning surges contain many high frequency components. Because of this, the inductance of the cable greatly increases the effective resistance of the earthing cable.

Furthermore, the inductance of a conductive track on a PCB greatly increases the effective resistance of the track.

In the particular field of irrigation controllers, such controllers have many inputs and outputs and the distances between the terminals can be great.

Furthermore, the surge energy can radiate and jump between the protection devices.

Because of these problems, it is difficult, particularly with irrigation controllers, to effectively short the high surge currents to a common point. It is also impossible to effectively short these currents to earth potential. The result is that the energy of the surge is likely to dissipate in some other way which risks damaging the controller and its sensitive electronics.

Other known techniques for surge protection use optical isolator chips to electrically isolate components. Again, however, these devices are not effective at high frequencies and are not reliable in the long term.

The present invention aims to provide a surge proof controller which overcomes the above problems.

Accordingly, the present invention provides an electronic control unit comprising a timer unit having data input means and a processor, connected to the data input means, for providing system control signals in response to input data; and a driver unit comprising means to receive the system control signals from the timer unit processor and to provide output signal to a device to be controlled, via a cable; wherein the timer unit and the driver unit are separated by an air gap and communicate only via a wireless link.

The timer unit and the driver unit preferably communicate via an infrared link.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings.

Figs. la and lb show conventional irrigation systems; Fig. 2 shows a surge-proof controller in accordance with the present invention; Fig. 3 shows an alternative embodiment of a surgeproof controller in accordance with the present invention; and Fig. 4 is a more detailed diagram of the timer and driver of a controller according to the present invention.

The present invention will be described particularly in relation to an irrigation system controller. However, it should be noted that the invention may also be applied to any other control system.

Fig. la shows a typical irrigation system with a decoder controller 1. The system includes a water tank 2 fed from a water supply. A pump 3 is connected to the water tank to pump water from the tank, into the irrigation system. The pump is controlled by means of the controller 1, via a contacter 4. The controller is powered by a mains or other power supply.

The pump 3 draws water from the water tank 2, through an irrigation pipe 5. Several branches 6 feed from the irrigation pipe to the areas to be irrigated.

Each branch is provided with a solenoid valve 7 which is again controlled by the decoder controller 1, via an individual decoder 8. Individual decoders are connected to the main decoder controller by means of a two-wire control cable 9. Each branch from the irrigation pipe is provided with a number of nozzles or sprinklers 10 disposed at suitable locations according to the area to be irrigated. Of course, any number of irrigation pipe branches may be provided, in any configuration, and these may be provided with any desired number of nozzles or sprinklers, according to the application to which the system is put.

Fig. lb shows a conventional multi-wire controller.

Such a controller has an individual output for each solenoid valve and each valve is connected directly, rather than via a decoder, to the irrigation controller.

In conventional controllers, all of the electronic circuitry within the main controller is connected by means of wires, cables and/or conductive tracks on PCBs, and is connected directly or indirectly to the field cables and valves. Thus, in attempting to dissipate an electrical surge, the conventional system will attempt to short all electrical components of the controller to a common earth potential. This gives rise to the problem mentioned above.

Instead, the present invention provides a new form of controller which is formed as two separate components, namely a timer 100 which includes the majority of the components for the human interface processor display, and a driver 200 which includes only the line drive components. This can be seen, for example, in Figs. 2 and 3. The timer unit 100 of the controller is completely isolated from the driver unit 200. The driver unit 200, which is connected to the field wiring may rise up with any surge voltage appearing on any of the cables attached to the driver.

The timer 100 is physically isolated from the driver 200 by a large air gap 110 of many centimeters.

Thus, electrical surges in the field wiring or driving part of the system will not induce any surge voltage in the timer which contains sensitive electronics. In particularly preferred arrangement, to further protect the timer, preventing it from being damaged by any surge voltage induced by its own mains supply input, the timer may be powered by its own completely isolated supply, e. g. a battery 120. This ensures that the timer and its associated sensitive electronics, are completely isolated from any possible electrical surges.

As regards the driver 200, it is only necessary that any differential surges generated across the wires connecting the driver to the mains power supply and the field wiring be shorted out. Suppression of such surges is practical in the driver since the total cable distances involved within the driver is smaller than the surge compression component itself.

Fig. 4 shows in more detail the timer and driver components.

The timer 100 is provided in a controller housing 300 similar to that shown in Fig. 1. The housing is provided with a keypad 130 and a display 140, providing the human interface with the timer. The operator uses the keypad to program the timer to open and close the various irrigation valves at the desired times.

The timer is preferably powered by a battery 120, as stated above, (via a voltage regulator 150), so that it is electrically isolated from the mains supply and the two-wire field cable. The driver 200, which is separated from the timer 100 by a large air gap 110 of many centimeters, is powered by 30 V AC derived from a mains supply, via a transformer 210. This 30 V AC supply is also fed, via the driver, to the individual decoders provided in the various branches of the irrigation system.

The timer communicates with the driver via a wireless link, preferably a infrared link. Of course, any other wireless communication can be used, but infrared is preferred because of its low cost.

The keypad 130 associated with the timer is connected to a main processor, preferably a microcontroller 160, in the timer. The valve opening and closing times input by the user, via the keypad 130, are processed by the microcontroller which sends signals via an infrared transmitter or transceiver 170, at the appropriate times, to the driver, via the wireless link.

A microcontroller 220 or processor is also provided in the driver. This receives the control signals from the timer microcontroller 160, via an infrared receiver or transceiver 230 and sends control signals to the appropriate individual decoder (s), via an output circuit 240 and the two-wire field cable, to open or close the respective solenoid valve (s). To ensure that the system is operating correctly, in a preferred embodiment, an acknowledgement signal is sent back to the timer from the driver, via the wireless link.

Although the system is described with reference to a decoder controller, the invention may also be used with a multi-wire irrigation controller.

In the system described, all of the solenoid valves of the different branches in the irrigation system are connected to the driver via a single two-wire field cable. In an alternative arrangement using a multi-wire controller as shown in Fig. lb, each solenoid irrigation valve for each irrigation branch may be connected to the driver via its own individual two-wire cable. In that case, additional drivers may be added in the controller, operating in the same way as the driver described above, and communicating with the timer, via a wireless link, preferably an infrared link. Further transmitters and receivers would then be required in the timer, for communication with the various drivers.

The arrangement of the present invention is also advantageous in that it allows the system to be expanded without any degradation in its surge handling performance.

In the embodiment shown in Fig. 4, the main pump 3, controlling the flow of water from the water tank 2, is controlled by the same driver that controls the field irrigation valves. The main irrigation pump is controlled via a relay 260.

In an alternative embodiment, a separate driver may be included to control the main irrigation pump directly, rather than via the relay. This would have the advantage that the field wiring and decoders would be completely isolated from the electrical supply for the pump.

The operation of the system is further improved by making the line driver physically small and by completely insulating it from external effects by encapsulating the driver in a plastic resin or the like.

These features improve the operation of the driver in rising up with the cable voltage surge.

In order to optimize suppression of the differential surges across the driver cables, the driver should be connected to the field decoders and valves by as few wires as possible. In the most preferred arrangement, the driver is connected to the various field cables by only three wires.

Claims (8)

1. CLAIMS 1. An electronic control unit comprising a timer unit having data input means and a processor, connected to the data input means, for providing system control signals in response to the input data; and a driver unit comprising means to receive the system control signals from the timer unit processor and to provide an output signal to a device to be controlled, via a cable; wherein the timer unit and the driver unit are separated by an air gap and communicate only via a wireless link.
2. 2. The control unit as claimed in claim 1 wherein the timer unit and the driver unit communicate by means of an infrared link.
3. 3. The electronic control unit of claim 1 or 2, wherein the timer unit is provided in a controller housing further provided with input means via which data or commands can be input to the timer and display means associated with said timer and said input means.
4. 4. The electronic control unit of any preceding claim, wherein the timer unit is powered by a battery and wherein the driver unit is powered by a main supply.
5. 5. The electronic control unit of any preceding claim, further comprising a microprocessor associated with the timer unit and a microprocessor associated with the driver unit.
6. 6. An irrigation system comprising one or more irrigation valves and an electronic control unit, as claimed in any preceding claim, to control the opening and closing of said valve (s).
7. 7. An electronic control unit substantially as hereinbefore described, with reference to Figs. 2 to 4.
8. 8. An irrigation system substantially as hereinbefore described, with reference to Figs. 2 to 4.