Microirrigation Systems for Vineyards
Irrigation System Controllers
A controller is an integral part of an irrigation system. It is an essential tool to apply water in the necessary quantity and at the right time to sustain agricultural production and to achieve high levels of efficiency in water, energy, and chemical uses. Irrigation controllers have been available for many years in the form of mechanical and electromechanical irrigation timers. These devices have evolved into complex computer-based systems that allow accurate control of water, energy, and chemicals while responding to environmental changes and the development stages of the crop.
Basic Control Strategies
Two general types of controllers are used to control irrigation systems: Open control loop systems and closed control loop systems. The difference between these is that closed control loops have feedback from sensors, make decisions, and apply decisions to the irrigation system.
Open Control Loop Systems
In vineyards with no feedback system control (i.e., open loop system), irrigation scheduling is determined according to the grower’s perspective. Open loop control systems use irrigation duration or applied volume for control purposes. Open loop systems are also constructed in such a way that a timer is used to start irrigation and the application of a given volume to stop irrigation. The parameters set by the system operator are how often and the volume of water to be applied.
Closed Control Loop Systems
n a closed control loop, the operator sets up a general strategy for control. Once the general strategy is defined, the control system takes over and makes detailed decisions of when to apply water and how much water to apply. This type of system requires that feedback be given back to the controller by one or more sensors. Depending on the feedback of the sensors, irrigation decisions are made, and actions are carried out if necessary. It is important to note that in this type of system, the feedback and control of the system are done continuously.
Timer-Based Control Systems
A timer-based irrigation control system automates watering by using a central controller (timer/clock) to turn solenoid valves on and off at set times, durations, and frequencies. A timer-based irrigation system applies water on a fixed schedule (start time and duration) rather than responding to soil moisture or plant water status. Irrigation timers are simple controllers consisting of clock units that activate one or more subunits of the irrigation system at specified times. The two most common types of controller designs are electromechanical and electronic.
Electromechanical Controllers
Electromechanical controllers use an electrically driven clock and mechanical switching (gear arrays) to activate the irrigation stations. These types of controllers are generally very reliable and not too sensitive to the quality of the power available.
Electronic Controllers
Electronic controllers rely on solid state and integrated circuits to provide the clock/timer, memory, and control functions. These types of systems are more sensitive to power line quality than electromechanical controllers and may be affected by spikes, surges, and brownouts.
Advantages and Disadvantages
Irrigation systems where watering time is controlled by a timer have a simple design and are more reliable. The system is activated and deactivated automatically based on the programmed schedule. The main advantage of a timer-controlled irrigation system is its simple structure, which consists of water distribution pipes, a pump, a power source, and a clock controller (timer).
Computer-Based Control Systems
A computer-based control system consists of a combination of hardware and software that acts as a supervisor with the purpose of managing irrigation and other related practices, such as fertigation and maintenance. This is done by the use of a closed control loop. A closed control loop consists of (1) monitoring the state variables, (2) comparing the state variables with their desired or target state, (3) deciding what actions are necessary to change the state of the system, and (4) carrying out the necessary actions. Performing these functions requires a combination of hardware and software that must be implemented for each specific application.
Fuzzy Logic Control for Irrigation
Various types of automatic irrigation control systems have been designed where the frequency and duration of watering are controlled automatically based on weather conditions, time of day, and other parameters. Numerous irrigation systems are used, from the most straightforward clock-controlled systems to sophisticated computer-based control systems based on physical parameters such as ambient temperature, substrate moisture content, and time of day. However, these controllers and similar solutions are binary devices with only two states (0 or 1), and they are not always ideally suited for irrigation control.
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