Remote supervision and control based on wireless technology to operation of central pivot irrigation machine

The availability of water resources in agriculture is a growing concern throughout the planet. The new technologies of automation and communications offer a set of solutions for the collection and analysis of information that make possible the decision making in the modern systems of agricultural irrigation. Important steps have been taken in the automation of irrigation systems, focused on the adequate determination of water requirements in crops, which has a positive effect on the saving of energy carriers, water resources, and agricultural productivity. In the present research we propose to perform a real-time control and monitoring system, allowing the operation and remote monitoring of irrigation machines of center pivot. For this, a programmable logic controller and wireless communication technology are used, according with the requirements and characteristics of the context of agricultural application.


I. Introduction
Agriculture is a decisive and strategic sector for the Cuban economy.The rational and efficient use of water and energy carriers in this branch is one of the most important items in the country's politics.Generally, in this sector, high consumption is generated due to excessive irrigation.Therefore, the correct operation of these systems allows a quality production and the saving of considerable volumes of this important natural resource (Jimenez, 2011).
Cuba has experienced increasingly prolonged periods of drought in recent years.There is a tendency of extensive droughts, as a result of climate change (González, 2016;Vázquez & Solano, 2013).Currently, although irrigation systems are implemented in several types of crops, exceptional attention is required to the cultivation of sugarcane, due to the high volumes of water it uses.Agricultural irrigation systems, which are generally used, are manually controlled, which causes, in many cases, the waste of water and electricity (Carranza, 2016).
Despite the efforts made, the control of irrigation systems in Cuba is not automated.Irrigation programming in many places remains empirical, and there are low irrigation efficiency rates reported.Hence, it is intended to increase the surfaces under irrigation, including the assembly of new electric center pivot machines, which are characterized by their high efficiency (Clavelo, & Seguí, 2012).Therefore, important investment programs have been developed for the manufacture and acquisition of modern equipment that integrates the new technologies of automation, control, and communications, with the aim of developing a sustainable and productive agriculture (Jimenez, 2011).
In this context, the current study aims to propose a control solution through a programmable automaton and remote supervision using wireless technology for the automated operation of center pivot irrigation machines.
As a contribution of the current research, thanks to the remote supervision of the operation of this type of irrigation machine, it is possible to control it remotely, as well as carry out operations to control its execution, such as the programming of the irrigation time, the direction of rotation, and the hours of work.It responds to the challenge imposed by the context of an agricultural application, proposing a communication solution based on wireless transmission.The architecture of the system and the control proposal have the necessary flexibility that the system can be applied in correspondence
En este contexto, el presente trabajo tiene como objetivo proponer una solución de control mediante un autómata programable y supervisión remota utilizando tecnología inalámbrica para la operación automatizada de máquinas de riego de pivote central.Como aporte de la investigación tenemos que, gracias a la supervisión remota de la operación de este tipo de máquina de riego, es posible gobernar a distancia la misma, así como efectuar las operaciones de control de su funcionamiento, entre ellas la programación del tiempo de riego, el sentido de giro y las horas de trabajo.Se responde al desafío que impone el contexto de aplicación agrícola, proponiendo una solución de comunicación basada en transmisión inalámbrica.La arquitectura del sistema y la propuesta de control poseen la flexibilidad necesaria para que el sistema pueda ser aplicado en correspondencia con las posibilidades de comunicación específicas del lugar donde se decida su implementación, así como de las necesidades del usuario.A su vez, la supervisión remota del funcionamiento de la máquina de riego permite a los directivos conocer, en tiempo real, el estado de su operación, las alarmas, los reportes y los históricos de los regímenes de riego, lo que representa la disponibilidad de la información de las variables with the specific communication possibilities of the place where its implementation is decided, as well as the user needs.At the same time, the remote supervision of the irrigation machine operation allows managers to know, in real time, the status of their functioning, alarms, reports, and historical irrigation schemes, which represents the information availability of the variables necessary for decision making.It can also be generalized to a set of irrigation machines.All the above impacts from the economic, social and environmental perspectives, by making more efficient use of water resources, making better use of energy carriers, improving production levels and reducing the costs of agricultural production.
The research applies the hypothetical-deductive method, when developing the research hypothesis based on the results derived from the bibliographic review, the theoretical framework preparation, and the problem approach.It also uses the systemic method, by relating several problems to obtain a broader issue and consequently propose the respective solutions; and the experimental method, when performing the experimental tests to check and evaluate the performance of the system as a whole.

II. Development
Irrigation can be defined as the science of the artificial application of water to land or soil (USDA, 1991, Pasha & Yogesha, 2014), its main objective is to supply the necessary moisture to the crop.It can be done to help growth of agricultural plantations or for the maintenance of landscapes or soil vegetation in dry areas and during periods of low rainfall.Irrigation has some other uses in crop production, which include: protecting plants against frost, suppressing weeds, and preventing soil consolidation (Kumar, Pramod, & Sravani, 2013).Regardless the irrigation method used, the purpose of irrigation is to periodically replenish the storage of soil moisture in the root zone of the plant (Camargo, 2013).
Irrigation methods and techniques are responsible for driving and applying water for irrigation, from the supply source and the conduction network, in order to achieve the necessary soil moisture status.Therefore, it is essential that they meet the irrigation regime defined for crops that benefit, guarantee adequate labor productivity and encourage the mechanization and automation of the irrigation process (Kumar et al., 2013).
tion (Santos, De Juan, Picornell, & Tarjuelo, 2010).This study focuses specifically on sprinkler irrigation using center pivot irrigation machines, which are characterized by their high efficiency.

A. Center pivot irrigation machines
The center pivot irrigation machines (Figure 1) use sprinkler irrigation technologies and guarantee irrigation efficiency of 80% (Rodríguez &López, 2014;Rodríguez & Puig, 2012).They consist of a tower center and a varied number of structural sections with their corresponding mobile towers.The machine irrigates in a circular way, in the process, the diffuser nozzles are selected appropriately for each section in question (Tarjuelo, 2005).As the flow rate of the pivot is constant, the water applied per unit area is smaller at higher rotational speed of the machine.Therefore, the amount of water to be applied is controlled according to the speed of the machine (Pérez, 2010).
Its advantages include: it is possible to apply frequent (daily) irrigations, which contributes to a better water and nutrients management.It allows fertilizers to be applied, in a process known as ferti-irrigation, which reduces the use of other external machineries.It is a system that works at low pressure; therefore, the energy expenditure is lower; and it is possible to modify rainfall, which allows the system to adapt to different types of soil and crops.
However, these machines also have some disadvantages such as: the high initial cost; the demand of qualified operators to obtain an efficient use of water.On the other hand, since it is a circular irrigation system, the land must be prepared in an appropriate way or irrigation surface can be lost in the corners (Pérez, 2010).
Currently, the standard irrigation machines have an elementary level of automation, very typical of their work functions, to be controlled by an operator; they have a control panel, from where their fundamental functions are governed, including starting and stopping the machine, selecting the operating mode (manual-automatic), and selecting the direction of rotation and speed of rotation (Figure 2).In automatic mode, the condition of not allowing the machine to work is conceived if the pumping station is not supplying water, which prevents it from turning dry.It also establishes that, in the case that the machine stops rotating, the pumping of water must be stopped, thus guaranteeing not to irrigate on the same point.The operating time is controlled by the percentage relay, which conforms the desired irrigation standard.There are other caudal del pivote es constante, a mayor velocidad de giro de la máquina, el agua aplicada por unidad de superficie es menor.Por consiguiente, la cantidad de agua a aplicar se controla en función de la velocidad de la máquina (Pérez, 2010).
There are several companies in the world that produce this type of technology.Its products include systems that control the total operation of the equipment from a panel center or through remote access.These companies have developed electronic sensors, controllers, and communication protocols to meet irrigation requirements.Such is the case of the firms "IRRIMEC", "Cuñat Agrocaja" and "Valley Irrigation" (Reductores CUÑAT S.A., 2017, Reinke Irrigation, 2017, Valley Irrigation, 2017).However, these technologies have a high cost.In Cuba, several of these machines have been imported, many of them destined for the sugarcane cultivation.In addition, they occur at the national level, with the aim of reducing imports and investment costs (Tornés et al., 2009).Therefore, the issue of implementing the operation and remote monitoring in the pivot machines constitutes a strategy to follow in the agricultural sector, in order to obtain important advantages from the economic, environmental, and energy points of view.

B. Wiireless technology in irrigation systems
Specifically, in center pivot irrigation machines, the selection of communication technology for remote operation and control is an important aspect to consider, since it guarantees better exploitation and machine supervision.
In the agricultural context, wireless communications play an increasingly important role, since they allow information transmission services over long distances, which are impossible to implement using cables (Kranz et al., 2010;Smith, Baillie, McCarthy, Raine, & Baillie, 2011).This is influenced by local and regional topography as well as the cost of the technology to be used, with the aim to guarantee the reliability of the supervision system (Pfitscher et al., 2011).Las técnicas modernas de riego utilizando pivotes posibilitan incluir herramientas para la recolección, el análisis y la transmisión de datos en tiempo real, con el objetivo de facilitar la toma de decisiones para desarrollar una agricultura de precisión (Capraro, Tosetti, & Vita-Serman, 2014;Kranz, Evans, Lamm, O'Shaughnessy, & Peters, 2010).En este contexto, se destacan las máquinas de pivote central, que cuentan con un alto grado de automatización, generado por los avances tecnológicos alcanzados en los últimos tiempos en el sector agrícola.
The sensor networks based on radiofrequency communication (RF, VHF, UHF) are among the different wireless transmission routes that are applied in agriculture.The VHF bands [Very High Frequency] and UHF [Ultra High Frequency] constitute a technology that offers higher data transmission speeds than most conventional radio modems, and also provides greater flexibility in terms of monitoring and control of radio frequency irrigation systems, which are located at great distances from the control points.Other methods of wireless transmission are: WiFi networks, Bluetooth, and GSM mobile networks [Global System for Mobile Communications] and GPRS [General Packet Radio Service].These types of mobile telecommunications enable the transfer of large volumes of data at high speeds.Communication systems based on mobile telephony allow the operator to consult the main control panel or the base computer from any location and at any time (Chávez, Pierce, Elliott, & Evans, 2010;Dong, Vuran, & Irmak, 2013;Pavithra & Srinath, 2014).

C. Supervision and control of irrigation systems
In recent years, the use of SCADA control and supervision systems (Supervisory Control and Data Acquisition) has increased in process automation (Gurban & Andreescu, 2011), in almost all types of industries where the monitoring and control of the variables associated to the process is required; mainly, when the decision making can be carried out remotely and in real time.
Regarding agricultural irrigation systems, the use of SCADA systems represents a global trend, due to its implementation, it is possible to control and supervise the irrigation system at a distance.In this way, the farmer can have full access to the process by viewing it on a computer screen, telephone or tablet.Therefore, he can obtain the information of the process and the state of the crop variables in real time.It also allows to store information in historical records, handle alarms and events, generate periodic reports and manage databases for information processing and decision making (Navarro, Martinez, Domingo, Soto, & Torres, 2016).
Another of its utilities is that the supervisor system can easily be integrated with other systems based on interactive platforms and web pages, through access to the history of the alarms in such a way that, if any system failure occurs, either electrical or communication, the supervisor can quickly stop the process and avoid major problems (Alghazali, Alkhaddar, & Hadi, 2013).
Generally, stock control and data acquisition irrigation system can be performed by programmable logic controllers or other control devices associated with the SCADA (Joshi, Bhujbal, & Kurkute, 2016).
In the literature, numerous publications are reported where programmable automatons are used for irrigation control.This technology is characterized by its high reliability and robustness, and accessibility to wired or wireless industrial communication (Maheshwari & Sindha, 2014).
The Schneider Electric company is one of these devices manufacturers, which produces and markets a whole range of automata for different control applications.The TM241CE40R automaton firm Schneider Electric is one of the hardware devices that have the features and functionality in its design to control center pivot irrigation machines (Schneider Electric, 2017).Therefore, this device is used in a suitable configuration of I / O to implement the proposed solution (Avello, Izaguirre, Martínez, & Hernández, 2017).

III. Results and discussion
Taking into account the availability of an integrated Ethernet port, which offers FTP services and a Web Server, in the TM241CE40R PLC, we propose the design (using the own device programming software) of a web display in HTML5 format, which guarantees the supervision and remote operation of the irrigation machine in real time.This type of web page format allows the easy integration of control systems with the machines remote supervision.The above through applications una gama de autómatas para disímiles aplicaciones de control.El autómata TM241CE40R de la firma Schneider Electric, se encuentra entre los dispositivos de hardware que poseen las características y funcionalidades en su diseño para controlar las máquinas de riego de pivote central (Schneider Electric, 2017).Por consiguiente, se toma la decisión del empleo de este dispositivo en una configuración adecuada de E/S para implementar la solución propuesta (Avello, Izaguirre, Martínez, & Hernández, 2017).

III. Resultados y discusión
Teniendo en cuenta la disponibilidad de un puerto Ethernet integrado, que ofrece servicios de FTP y un Servidor Web, en el autómata TM241CE40R, se propone el diseño (empleando el propio software de programación del dispositivo) de una visualización web en formato HTML5, que garantice la supervisión y operación remota de la máquina de riego en tiempo real.Este tipo de formato de páginas web permite la fácil integración de sistemas de control con la supervisión remota de maquinarias, mediante aplicaciones para teléfonos inteligentes, tabletas y computadoras, característica que lo hace ideal para su utilización en el contexto de aplicaciones agrícolas.
A. Soluciones de control y supervisión En este sentido, se propone como primer paso implementar la solución para el control y supervisión remota cuya arquitectura general se muestra en la Figura 3. Dadas las dificultades de comunicación mediante sistemas cableados en el contexto de aplicaciones agrícolas, se propone una solución de transmisión inalámbrica económicamente factible, aprovechando las posibilidades que brinda el autómata programable seleccionado de operar como servidor Web, y la disponibilidad de los recursos de hardware y software que son empleados.
for smartphones, tablets and computers, an important feature in the context of agricultural applications.

A. Control and supervision solution
As a first step, it is proposed to implement the solution for remote control and supervision whose general architecture is shown in Figure 3.Given the difficulties of communication through wired systems in the context of agricultural applications, a wireless transmission solution is proposed economically feasible, taking advantage of the possibilities offered by the programmable automaton selected to operate as a Web server, and the availability of hardware and software resources that are used.
The programmable automaton will be located as a local station, physically close to the control panel of the irrigation machine.It is also programmed to control the irrigation functions.The inputs and outputs are properly configured and connected to the control and drive devices, arranged in the control panel of the machine, which does not undergo substantial modifications with respect to its original design.
In the internal memory of the automaton can be stored the historical results of important variables related to irrigation, such as, for example: irrigation hours, machine speed, irrigation frequency, number of turns made by the machine, or others variables decided by the client.
A WiFi wireless access point connected to the PLC's Ethernet port will be used for the data transmission, using TCP / IP communication protocol.Subsequently, the control and supervision of irrigation parameters can be done from a remote station, using smart mobile devices, tablets or laptops, looking for flexibility, according to the possibilities and client needs.It can also operate from the local station itself, where it will have access to the PLC and its hardware configuration.Then, the information handled by itself, may be displayed on a web page that can be re-designed for each specific machine or for a set of them, providing the ability to process the irrigation data for decision making.The above, according to the characteristics and the application context (crop type, water resources availability, maintenance needs, etc.).

B. Web visualization
Depending on the proposed solution, the graphical user interface shown in Figure 4 is designed.The programming of its visual elements and dynamic links with the system variables is done using the SoMachine v4.1 SP2 software.riego; las entradas y salidas son debidamente configuradas y conectadas a los dispositivos de mando y accionamiento, dispuestos en el panel de control de la propia máquina, el cual no sufre modificaciones sustanciales respecto de su diseño original.
Entre las funcionalidades que brinda la interfaz se encuentran las siguientes: • Selección del tiempo de trabajo de la máquina: ajustable según la norma de riego establecida.• Registro de tiempo de funcionamiento: permite medir mediante un contador de horas el tiempo de operación de la máquina.The features provided by the interface are: • Selection of the machine working time: Adjustable according to the established irrigation norm.
• Operation time recording: It allows to measure the operation time of the machine by an hour counter.
• Selection of the work rate: It is done by selector buttons that allow distinguishing the manual-automatic mode of the machine operation.
• Selection of the machine rotation direction.
• Operation functionalities: It includes the machine start and stop buttons and a switch to turn on or off the interior light and others.
• Indicators: They allow to visualize the status of the operating parameters through indicator lamps.
The functionality of the supervisory system, the reports, the historical reports, the alarms and the information to be displayed, among other elements, are dependable of the user needs and the communication possibilities that exist in each sector where the system is implemented, which provides flexibility to the proposed solution.

IV. Conclusions
The proposal of automation and wireless control for center pivot irrigation machines ensure the monitoring of the operating status of these machines by managers and operators.It contributes to achieving greater efficiency in terms of water and energy savings in agricultural irrigation systems in Cuba.
The remote control solution based on wireless technology allows the visualization and operation of the machines through web pages, being able to get an access from various devices, such as cell phones, tablets, computers, etc.
Depending on the communication possibilities that may exist in the application place of our proposal, it can be adapted to the use of other technologies, for example GPRS service (in mobile telephony), information transmission in the UHF band and link via a radio modem.
The above provides a level of flexibility and applicability to the current research.

IV. Conclusiones
La propuesta de automatización y control inalámbrico para máquinas de riego de pivote central garantiza el seguimiento, por parte de directivos y operadores, del estado de funcionamiento de estas máquinas, lo que contribuye a lograr una mayor eficiencia en términos de ahorro del agua y de energía en los sistemas de irrigación agrícola en Cuba.

Figure 2 .
Figure 2. Central pivot irrigation machine: Example of control panel / Máquina de riego de pivote central: ejemplo de panel de control

Figure 3 .
Figure 3. Proposal of remote control and supervision applied to a central pivot irrigation machine/ Propuesta de control y supervisión remota aplicada a máquinas de riego de pivote central

Figure 4 .
Figure 4. Proposed Web interface for supervition and control of central pivot irrigation machines / Interfaz web propuesta para la supervisión y control de las máquinas de pivote central