Agriculture Reference
In-Depth Information
hardware in this area. A majority of the instrumentation and hardware is commer-
cially available, and most products have developed into specialized standards with a
wide range of characteristics. Based on the basic functions, the hardware used in an
automated irrigation system may be grouped into four major categories: controllers,
control and monitoring devices, environmental sensors, and ancillary components.
An irrigation controller is the centerpiece of an automated irrigation system. The
basic function required for a controller is to be able to set the frequency of irrigation,
the start time, and the duration of watering (Miranda et al. 2005). Most control-
lers operate electronically or electromechanically with direct connection to solenoid
valves to control the on/off of each irrigation event. Commercially available off-the-
shelf controller products are generally used by urban and landscape irrigation. Some
of these controllers have additional features such as multiple programs to allow dif-
ferent watering frequencies for different types of plants, sensors to cut off irrigation
when it rains, and some ability for soil moisture and weather input. Sophisticated
professional controllers that allow irrigation schedules to be automatically adjusted
according to the weather or soil and plant water status are usually designed for more
demanding agricultural applications. Professional irrigation controllers can irrigate
based on volume; receive real-time feedback before, during, and after an irrigation
event; and react to actual events happening during the process such as shutting off
the system when a burst is occurring in the main line (a sudden pressure drop).
The control and monitoring devices in an automated system typically include
valves, pressure gauges, and flow meters. The basic function of the valves is to switch
water flow “on” or “off” on demand from the controller. Valves are often needed at
different places within a relatively complex system when different sections or blocks
of a large field need to be irrigated at different times with different volumes of water.
Common places for the valves include main line and laterals feeding different sub-
sections of an irrigated field. Pressure gauges are indicators of water availability or
potential system failures. Most sprinkler nozzles or drip emitters are designed to
operate at a fixed pressure range in order to achieve the desired discharge rate and
uniformity. Electronic transducers are used to convert hydraulic pressure to an elec-
tronic signal and subsequently transmit data to the irrigation controller. Flow meters
used in an automated irrigation system provide feedback on the volume of water
applied or the instantaneous rate of water flow in the irrigation pipes. In a closed-
loop system, this information is essential for the controller to determine when to shut
off the system. Two common types of flow meters are the propeller and turbine flow
meters.
Environmental sensors used in an automated irrigation system are generally
instruments for weather stations and for estimating soil water or plant water status.
Data generated from a weather station can be used to estimate ET, and thus used to
determine daily water deficit. Soil water or plant water measurements can be used to
assess water depletion from the soil profile or possible plant physiological responses
to water stress. When directly communicated (wired or wirelessly) with the irriga-
tion controller, these sensors provide information used for making irrigation sched-
uling decisions.
The ancillary components for an automated irrigation system include added
capabilities for chemical injection and site-specific water and chemical applications
