An irrigation system uses controllers to apply water, energy, and chemicals efficiently based on environmental conditions and crop needs. Controllers have evolved from mechanical timers to complex computer-based systems. There are two main types of control systems: open-loop and closed-loop. Open-loop systems rely on operator decisions for watering schedules, while closed-loop systems use feedback from sensors to automatically adjust watering based on soil moisture levels. Modern irrigation controllers integrate sensors and climate data to precisely control water distribution for optimal agricultural production.

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2. System- When a number of elements or components are connected in sequence to
perform a specific function, the group thus formed is called a system.
When the output quantity is controlled by varying the input quantity, the system is
called control system.
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A controller is an integral part of an irrigation system.
It is an essential tool to
Apply water in the necessary quantity and
At a right time to sustain agriculture production
To achieve high level of efficiency in water, energy and
chemical uses.

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Irrigation controller have been available for many years in the form of mechanical and
electromechanical irrigation timer.

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These devices have evolved into complex computer based system that allows
accurate control of water energy and chemical while responding to
environmental change and development stages of crop.

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1. Open Control Loop system
2. Closed Loop Control System
Difference
1. Open control loop system apply a present action, as is done by irrigation.
2. Closed control loops have feedback from sensor, make decision and apply decision to the irrigation
system.

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Open Control loop system
1. In an open control loop system, decision is made by operator.
2. The amount of water and the time at which water should be applied is decided
by the operator and set an irrigation controller according to desired schedule.
3. Open control loop system use irrigation duration or applied volume for
control purpose.
In this system, the output signal is not compared with the input signal which
means there is no feedback signal in this system. The open-loop control system
is also known as a non-feedback control system or control system without
feedback.

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In a open loop system, a clock is used to start irrigation and the application of the given volume to stop
irrigation.
In this type of controller the parameter set by the system operator are how often and the volume of
water to be applied.

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Advantages of open loop system Disadvantages of open loop system
1. Low cost 1. It does not respond automatically to changing
condition in the environment.
2. Readily Available 2. It require frequent resetting to achieve high level
of irrigation efficiency.
3.The devices are manufactured with different
degree of flexibility related to the number of
Station and schedule specification.
3. Recalibration is required time to time.

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Closed Loop Control System
Control Loop controller for irrigation system is based on the decision.
Direct Measurement of soil- moisture using sensor.
Calculation of water used by the plant based on climatic parameter.
Both soil moisture sensors and climate parameters measurement.
The simplest form of a closed loop control system is that of a high frequency irrigation
controller that is interrupted by a moisture sensor.

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Solenoid valves
1 Solenoid valves may have two or more ports.
2 In a two ports valves the flow is switched on or off.
3 In three port valves, the outflow is switched between the two outlet
ports.
4 Multiple solenoid valves can be placed together on a manifold.

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Sensor
The sensor operates as a switches that respond to soil moisture. When sufficient-
soil moistures is available in the soil, the sensor maintain the circuit diagram.
When soil-moisture drops below the certain threshold, the sensing devices closes
the circuit, allowing the controller to power the valves.
The controller can be set to irrigate at a very high frequency (4 or 5 times more
often required)
When the controller attempts to irrigate, irrigation will occur only if the soil sensor
allow it, which in turn occur only when soil-moisture has dropped below
acceptable levels.
The feedback system is very low cost and easy to install and maintain.

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Determining the best location of the sensor which requires
Knowledge of soil- water.
Root dynamics
Spatial variability of soil properties.

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Function of irrigation Timer
Clock/Timer:- Provides the basic time measurement by which schedules are executed.
Calendar selector:- This function allows definition of which days the system is to
operate.
Station time setting:- The function allows definition of start time and duration of each
station.
Master Switch:- The function prevents activation of any station connected to the timer.
Station Omission:- The function is used to omit any specified number of station from
the next irrigation cycle.
Master Valve Control:- Provides control to a master system valves.

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Types of controller Design
1. Electromechanical
2. Electronic

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