If the soil at this field station is dry, the closer the circuit and the field at this station are irrigated for a specified duration.
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The suspended solids may finally clog or reduce the filtration efficiency. The automatic flushing valve is available for different types of filters.
The flushing is done by means of back flow of water [4, 8, 11], thus allowing the water to move through the filter in an opposite direction Fig. Normal flow b. In all these cases, digital flow meters can be used for the chemigation by allowing a known amount of chemicals in a known amount of water to maintain a constant concentration of chemicals-in-the-irrigation-water [8, 11]. Principles of Automation 13 1. The valves open and close based on the water pressure in the line.
The pressure arrives at the valve by means of a flexible hydraulic tube micro tube: polyethylene tube of small diameter to provide a required pressure. The diameter of the micro tube is generally between 6 and 12 mm and is connected to the hydraulic valve at one end and the other end is connected to the automatic control or the line of water. Some hydraulic systems can be connected to the main valve of the line or to the system that replaces the water.
Electrically operated automatic system activates the pump and deactivates the pump, when the irrigation cycle is over. The amount of water can be different for each valve and can be adjusted by a regulator mounted in same valve. The hydraulically sequential system can be used to water fruit orchards, gardens, green houses and nurseries, establishing low flow rates through tubes of small diameter and for flow rates in any diameter of tube. The system includes automatic metering valve, hydraulic valve and hydraulic tube.
For safety reasons, a current of V should not be used when the subsurface cables extend to the field valves.
The regular solenoid valves are mainly used for low flow rates. The control of the second valve is always hydraulic. In the hydraulic sequential system, the opening is controlled electrically by a timer mounted next to the main valve. In such cases, the current source is direct and not alternating. The irrigation programs are based on evapotranspiration estimations, complex water budgets in several dimensions or crop growth models.
Principles of Automation 15 Then the model incorporates the climatic information to calculate the evapo- transpiration rates and to adjust the water balance in the soil as the water is being used. The evapotranspiration model requires an irrigation criteria based on the allowable depletion or the irrigation interval. Actual field data after the irrigation can be helpful to compute the infiltration and immediate drainage for correction of estimated soil moisture.
- Management of Drip/Trickle or Micro Irrigation.
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The rate of computed ET can be used to indicate the required amount of irrigation or to specify the time for irrigation interval. This method is more practical for drip irrigation than for other irrigation methods. The records of field data are kept in the office files for the irrigation programming, so that the data can be used to-update-the-inputs-in-the-program. The solenoid valves can be used in the secondary or lateral lines to control the volume of water to the individual blocks. The primary function of a solenoid valve is to switch on or switch off the system.
However, these valves can be equipped with pressure regulators and check valves. Automatic valves require periodic maintenance to assure a satisfactory operation. The maintenance program depends on the use of the valve and the flushing operations. At least, it is recommended that all the diaphragm valves are disanned and cleaned at least once a year. It is important to clean the deposits on the stem of the valve. Almost all the manufacturers provide a service or fast replacement of most of the components. This can usually be done without removing the valve from the irrigation line.
A number of auxiliary controls can be adapted to the diaphragm valves to provide flexibility and convenience. A trouble in the operation can be caused by contamination, obstructions, incorrect assembly, and damages or worn out parts. It must be open during the normal operation.
Whenever the pressure exceeds a preset value, the valve releases the excess pressure. These regulate the speed of opening and closing of the main valve by blocking or strangling the flow that enters or leaves the casing. These can be subjected to obstructions by fine sediments if tightly fit. The controls with mechanical time clocks open and close only a single valve at one time. The controls are also available to diagnose operation and identify the troubles and to take remedial steps.
A timer uses a clock to program the beginning and sequence of irrigation. The control is a source of electric or hydraulic signal to activate by remotely located valves to allow or to stop the flow. The communication between the irrigation controller and the valves is by means of electrical wires, hydraulic lines or radio signals. The microprocessors and microcomputers also can be programmed using data of tensiometers, pan evaporation, thermocouples, soil moisture tension gages, anemometer, flow meter, pressure transducer, etc.
These controls are based on the climatic and soil sensors or according to the program specified by the irrigator. Principles of Automation 17 The data from the flow meters and pressure gages is used to determine the flushing time and to detect any troubles in the system. Most of the controllers can be programmed for 14 days, while others are only limited to seven days. Practically all-automatic controllers have a station selector on the outer surface of the panel Figs. This station selector shows a green light to show the station in operation. In addition, it can also be set manually so that the irrigation operator can start and put if off whenever desired.
A timer determines the duration of operation: 14 days and 24 h per day. Sensors based on tensiometers or pan evaporation can activate these.
Micro Irrigation Systems Design 3(2+1)
Although this type of system was developed mainly to water green houses, yet it can be used for the drip irrigation system. These nonsequential systems are controlled by hydraulic or electrical valves that can operate the valve in the desired block at random, and can supply known amount of water for a known duration to a desired block. Each unit can supply a known flow at different hours during the day, in response to soil moisture status in each block.
This system usually operates by a remote control system and is designed to provide feedback of field data, so that the automatic adjustment can be made and adjustments for changes in pressure and flow rates can be made to the discharge flow in the distribution lines. It consists of a programmed unit of irrigation, a unit for transmission of information, a unit for the control of flow in the laterals and a unit for warning signals.
The signals of the main panel are sent by an individual communication channel and these are transmitted to individual field panel. The field panel can collect the data on water meters, operating pressures and warning signals.
Then the data can be transmitted to the main panel control panel. Tensiometers and gypsum blocks are simple and economical to use. Another method is a neutron scattering method, but it is quite expensive and is used for research purpose only. There are two electrodes inserted in each block and the changes in the soil moisture are calibrated with variations in the resistance.
The precision of this method is based on the temperature, salt concentration in the soil solution, physical characteristics of the gypsum block and the electrical resistivity of the soil. For tensions of 80 cbars, a tensiometer is recommended instead of a gypsum block. Tensiometer Fig.
The main disadvantage of a tensiometer is a relatively low critical tension of 85 cbars after which the air enters the plastic stem of a tensiometer. The soil moisture by any method will show variations in the soil moisture within the same field. A sample of the soil in a given location represents only the soil condition of that location. Therefore, several observations of soil moisture at various locations in the field are desirable.
Neutrons travel through the soil medium, loose energy, and the speed is reduced when these hit the elements that are present in the soil.
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The hydrogen, a component of the water, is dominant in the reduction of the speed of fast neutrons. Due to other factors that can affect the reading, the calibration of this method is done in a location where the equipment will be installed and used. The use of the neutron scattering method requires the installation of access tubes at the beginning of planting and removal of these tubes after the last harvest. It is recommended to install one sensor at each 30 cm depth. Periodically the operator will obtain the readings of the tube at the desired depth. A minimum of three readings are taken: at shallow root depth, at middle depth, and at a deeper depth.
The water content of these readings is added and the water content at field capacity is deducted from the sum. The difference between these two estimates will be the amount of water that should be applied. The readings can be recorded automatically and are stored in the memory of the neutron scattering equipment. Then these can be downloaded on the computer of the Control Panel. With this information, the computer will give the necessary commands to the drip irrigation system so that the crop water requirements are met in the desired block.
Both are exposed to similar climatic conditions in the same field. This Principles of Automation 19 correlation can be used to schedule the irrigation. If electrodes in the tank can be installed at a depth based on previous experience , the irrigation can be controlled automatically. The irrigation will begin when the surface of the water in the class A pan lowers to a predetermined level and will stop when the level raises to certain level in the tank .
Clean the controllers, valves and sensors. Examine the condition of the control panel and store it well. Remove and store batteries. Flush and drain the hydraulic tubes. Disconnect the electrical wires in the field. Examine for possible breakage and defects in electrical conductors.