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4. Automation of Irrigation
System
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Automation
• Operation of the irrigation system with minimum or
without manual intervention.
• A well-controlled irrigation system is one which
controls the spatial and temporal distribution of soil
moisture to achieve maximum crop yield and benefit
cost ratio.
• The adoption of automated new micro irrigation makes
possible to grow advanced high value cropping system
with new technologies which are difficult to grow by
conventional means.
• Using automation one can control the irrigation valves,
pump and fertigation equipment.
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Features of automation irrigation
• It eliminates the manual opening and closing of
valves.
• It starts and stops pump exactly as and when
required thus optimizing the energy requirement.
• Irrigation system can be started at any desired
time. One need not worry to visit farm during
odd time (night).
• Possibility to change frequency of irrigation and
fertilizer application as per the crop need.
• Use of water from different sources and
increased water and fertilizer use efficiency.
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Merits
i. Reduced labour
ii. Improved life style
iii. More timely irrigation
iv. Assists in the management of higher flow
rates
v. More accurate cut-off
vi. Reduced runoff of water and nutrients
vii. Reduced costs for vehicles used for irrigation
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Demerits
i. Cost
ii. Reliability
iii. Increased channel maintenance
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Semi-automatic systems
• Semiautomatic systems and controls require manual
attention at each irrigation and are usually simpler and
less costlier than the fully automatic systems.
• Most semi-automated systems use mechanical or
electronic timers to activate control structures at
predetermined times.
• The irrigator usually determines when to begin
irrigation and its duration and manually resets or
returns the devices to their original positions or moves
them from one location to another before the next
irrigation.
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• The parts of given system may be automatic
while other parts are semiautomatic or
manually operated.
• Such systems require communication between
the controller and system components located
in the field.
• Communication may be by direct
interconnecting electrical wires, by hydraulic
or pneumatic conduits or by radio telemetry.
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Fully automatic systems
• Fully automatic systems normally operate without operator
attention except for periodic inspections and routine
maintenance.
• The irrigator may determine when and how long to irrigate
and turn water into the system or start programmed
controllers to initiate the automated functions.
• Fully automatic systems may use soil moisture sensors,
such as tensiometers or electrical resistance blocks to
activate electrical controls when soil water is depleted to
predetermined levels.
• Meteorological data using climate based sensors can also
be used to predict when to irrigate and the output from a
microprocessor controller can automatically begin
irrigation.
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• Once irrigation has been started water is diverted
into the farm distribution system and irrigation is
completed without operator intervention.
• Irrigation duration may be controlled by
programmed timers, soil moisture sensors or
surface water sensors.
• Fully automatic systems require a water supply
available on demand such as from wells or farm
reservoirs.
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Automatic Controllers
• Micro irrigation system use automatic controller,
• Can be simply mechanical clocks that open/close
a single valve on a pre-set time schedule to
microcomputers.
• These can be programmed to interrogate with:
– soil moisture and/or climate sensors,
– decide when to start and stop irrigation,
– start/stop pumps and open/close valves to accomplish
the irrigation and
– to apply exact amount of water and fertilizer to each
block within the field.
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Timer type controller
• A timer type controller uses a clock (either solid
state or motor driven electric) and programmed
for starting and to sequence the irrigation.
• The controllers supplies electrical or hydraulic
power to activate remote solenoid valves located
on individual laterals or sub-mains (manifolds).
• Electrical cables wires, hydraulic or pneumatic
conduit or radio telemetry are used for
communication between controller and valves.
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Microprocessor/microcomputer-based
controllers
• Microprocessor/microcomputer-based controllers can be
programmed to control:
– pumps,
– fertilizer injection equipment,
– filters, etc., as well as
– activate/deactivate solenoid valves using data from:
• tensiometers,
• pyranometers,
• evaporation pans,
• thermocouple,
• humidity meters,
• anemometers,
• flow meters,
• pressure transducers, and
• other sensors.
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• These controllers pull soil and/or climate sensors data
according to a schedule specified by the irrigator.
• The controller is programmed to use these data to determine
the need for irrigation in each field and block.
• It then operates:
– the pumps,
– filters,
– injection equipment, and
– valves needed to accomplish the irrigation.
• Data from flow meters and pressure sensors are used to
determine the need for such things as flushing and to detect
system malfunctions.
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Basic structure of irrigation control
system
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• The irrigation controller is an electronic
device to store and execute irrigation
scheduling program based on soil/plant water
content and using criteria of when and how
much water to supply.
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Decision making steps to execute
irrigation
1. Geospatial data are provided to the controller to generate
site specific water assessment or demand for water to
irrigate field crops.
2. Assessment of water demand using
a) soil moisture/plant water status sensors in-situ or remotely
located,
b) meteorological based soil-water balance estimation and
c) calendar based soil-water balance.
3. Direct continuous communication between these sensors
and irrigation controllers is essential, which can be
achieved by directly connecting the sensors output to the
analog interface panel for wired system or through
wireless transmitters/receivers.
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4. If irrigation is to be given after knowing soil-water
status, the irrigation is given using a pump attached
with source of water and network of pressurized
irrigation pipe lines. In case of additional pressure
requirement the booster pump can be operated
electrically or fossil fuel.
5. The set of control and monitoring devices are
deployed to execute irrigation command to complete
the irrigation. Solenoid valves are used to turn on/off
water flow with the amount of water monitored by
water meter. Sometimes timer is used to apply water
for set time.
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6. Fertigation or chemigation is important
process in micro-irrigation. This may be with
or without automation.
7. Sometimes filters cleaning and backwashing
are automated/manually operated. The last
step involves system monitoring to ensure
system maintenance. This is accomplished by
supervisory control and remote monitoring
to ensure optimal irrigation.
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Components of automated irrigation
system
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Automation Equipment
• The devices used for automation of micro-
irrigation (MI) system are:
– controller,
– control valves,
– metering pumps,
– flow transducers,
– sequencers systems,
– master relay,
– Sensors, etc.
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Controller
• PLC (Programmable Logic Controllers) is used
extensively for various industrial applications including
irrigation.
• These systems can be programmed to issue command
for operation of:
– solenoid valves,
– pumps,
– booster,
– fertilizer injectors,
– backwashing of filters etc. according to irrigation cycle
• Micro-processor, personal computers, laptops,
palmtops are also used as controllers.
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• The controller is programmed to run various
zones of an area for their required duration.
• In some cases moisture sensors are used with
it which give feed back to the controller about
field moisture level.
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2. Control Valves
• Control valves are activated:
– electrically,
– hydraulically or
– pneumatically
• They are also used to switch on or off:
– water supply,
– filter flushing,
– mains and laterals,
– sequence water from one field or segment to another.
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a) Solenoid valve
• Controllers are connected electrically operated valves
(solenoid valve).
• These valves are fitted in place of manual gate valve in
an automatic system.
• One valve controls one section.
• As soon as the signal is received from the controller the
solenoid gets activated and valve is turned on which
allows passing of water through it.
• After the signal is stopped the valve shuts off.
• These are normally two way open and close valves and
operate on 24 volt DC or 220 volt AC motor.
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b) Hydraulic valves
• These valves are operated on hydraulic pressure.
• The operation of a hydraulic valve depends on:
– the type of valve and
– whether it is NC (Normally closed) or NO (Normally
open) in principle.
• A command can be transmitted to these hydraulic
valves by means of control tubes and solenoid
coil.
• These solenoid coils are mounted on the main
line and connected to the valve by control tubing.
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c) Solenoid coil
• Solenoid coil is used to translate electric pulses into
hydraulic pulses which enable opening and closing of
specific hydraulic valve.
• These solenoid coils require 24V AC input for its operation.
• Solenoid coils mounted on the valves are connected to
controller electrically.
• The coil gets actuated after receiving required voltage.
• It pulls up the plunger and water passes from the lower
orifice port to control tubing towards the hydraulic valve.
• When operation time is over, the controller stops sending
signals to the solenoid coil to deactuate.
• Thus the plunger again seals the orifice port to close.
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d) Automatic metering valves
• These valves are used in volume based
irrigation system.
• The volume of water required for the
irrigation can be adjusted in these automatic
metering valves.
• It shuts itself off after a preset quantity of
water has flown through.
• These valves are available with different
capacity (10 L/h to 10 m3/h).
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3. Metering pumps
• These pumps are suitable for feeding of known quantity of
fertilizers/chemicals.
• The capacity of pumps varies from 1.5 to 3.5 L/h.
• These pumps are micro-processor based solenoid driven
diaphragm type.
• The control can be manual or remote.
• Peristaltic pumps:
– These are ideal system for accurate pumping of fluids at low
flow rates.
– These can be used for accurate dosing of chemicals as and when
desired.
– The flow rate is directly proportional to rotor speed and thus
dependent on motor drive voltage.
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4. Flow transducers
• These can be used for measuring flow rate and totalizing
the flow.
• The fluid passes through internal fluid flow straightners to
stabilize turbulence.
• Then the fluid impacts on the vaned turbine rotor, which
rotates at speed proportional to the flow rate.
• Each rotor blade has a stainless steel tip which is detected
by a sensor mounted externally to the glass tube.
• The pulse output which is proportional of flow rate, is
measured by the counter.
• Flow measuring feedback devices allow the computer to
determine the rate and volume of water applied for
estimating whether the irrigation scheduling algorithm and
recommendations are followed.
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5. Sequencer systems
• Electromechanical and electronic time driven
sequencer systems are available for use in
automatic micro-irrigation system.
• The electromechanical system consists of cam
sequencer assembly frame, gear box, gears and
synchronous motor.
• The cam shaft contains 2,4,6 or more adjustable
cams, to operate switches and SPDT contacts.
• The gears can be used to provide a variety of time
periods for a single revolution of cam shaft.
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6. Master relay
• This relay controls the function of pump
whenever any of the solenoid valve is
switched on,
• one pulse is sent to activate master relay
which in turn starts the pump through Pump
Starter.
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7. Sensors
• Sensor is defined as an element that senses a variation in
input energy to produce a variation in another or same
form of energy.
• Different types of sensors used to monitor soil and plant
parameters are as follows:
i) Electromagnetic
ii) Optical
iii) Mechanical
iv) Electrochemical
v) Airflow
vi) Infrared sensors for plants temperature and
vii) Climatological parameters monitoring
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Soil-plant water monitoring sensors
• Different types of devices used to monitor soil-plant
water status and to automate irrigation system are
listed below:
a) Tensiometer
b) Resistance block
c) Gypsum block
d) Granular matrix sensor
e) TDR based soil moisture sensor
f) Infrared sensors for leaf air temperature
g) High frequency capacitance type soil moisture sensor
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a) Tensiometer
• The tensiometer is a device, which provides
direct measure of tenacity with which water is
held by the soil.
• Any change in soil water causes corresponding
change in soil moisture tension.
• In automated irrigation controller, the
tensiometer is modified to read change in soil
moisture tension in terms of change in voltage or
resistance.
• it consists of electro tensiometer, an electronic
switching unit and a solenoid valve.
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b) Resistance Blocks
• In this type of sensor, the electrical resistance
between the electrodes varies with moisture
content of resistance block.
• The moisture of resistance block is in equilibrium
with the soil moisture.
• The presence of salt or salinity in irrigation water
or soil affects the observations.
• The gypsum block and granular matrix type
sensors are commonly used for soil moisture
sensing and irrigation automation.
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c) Gypsum Block
• It consists of two electrodes inserted in a solid
block of gypsum.
• Gypsum neutralizes the affect of salt content.
• Gypsum blocks are easy to use and
economical.
• The limitation of this type of sensor is gypsum
gets dissolved with water.
• Therefore, the calibration changes with the
passage of time.
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d) Granular Matrix
• The granular matrix sensor uses granular
matrix of standard size with uniform pore size.
• Two electrodes are inserted in granular matrix
fill material, above which gypsum wafer
supported with metallic or plastic screen.
• The gypsum wafer slowly neutralizes the
salinity of the soil solution hence electrical
resistance between the electrodes is
unaffected.
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• Particle size of the granular fill material and its
compression determines the pore size
distribution in sensor and their response
characteristics.
• Such sensors require little maintenance during
the growing season and suited for sensing soil
water potential and automatic control of
irrigation systems.
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• The electrodes are connected to controllers.
• As the soil moisture replaces the air present in
the voids of granular material, results in
reduction of electrical resistance between the
electrodes and vice versa.
• The sensor gives feedback to the central
processing unit of the personal computer to
automate micro-irrigation system.
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f) Infrared sensors for leaf air
temperature
• Plant canopy temperature measured from a distance with
an infrared thermometer can be used to detect plant water
stress.
• and signal irrigation needs before the crop exhibits any
visual symptoms of drought.
• This is because water-stressed plants have a tough time in
obtaining enough water from the soil to meet atmospheric
demand, and this reduces evaporative cooling of their
leaves.
• The Crop Water Stress Index (CWSI) method uses plant and
air temperature and vapor pressure deficit of the air to
determine whether a crop has adequate water (CWSI=0) or
under severe water stress (CWSI= 1).
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• Infrared thermometers can be hand held or
mounted on booms for continuous operation.
• Thermal scanners on board satellites or
aeroplanes, map crop temperatures across an
entire field or farm.
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g) High frequency capacitance type
soil moisture sensor
• The capacitance of electrodes inserted in to soil operating
at oscillation frequency (80-150 MHz) is dependent on the
dielectric properties of the soil.
• The probes consists of two stainless steel rods of 100 mm
long 6 mm diameter placed at 20 mm apart inserted in to
the soil.
• The relative permittivity of such sensors is related to soil
moisture content.
• Closer agreement between the observed soil water content
and estimated volumetric content by gravimetric method
for all types of soil has been reported for this type of
sensor.
• However, difference in bulk density affects the
performance of sensors.
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Types of Controls and Automation in
Micro Irrigation
1. Automation Controls
– Open loop control (OLC)
– Closed loop control (CLC)
2. Volume-Based Automated Irrigation System
3. Time Based Automated Irrigation System
4. Real Time Feedback System
5. Sequential and Non Sequential Automated
Irrigation System
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1. Open loop control (OLC)
• In an open loop control system, the operation
is pre-set and independent of any sensor input
with an operator making the decision.
• In irrigation scheduling program, two
decisions are used:
i) When to irrigate and
ii) how much to irrigate.
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2. Closed loop control (CLC)
• In this system, the input is directly dependent on the
output through a feedback mechanism from the output to
the input.
• By having closed to compare the output with some
reference input signal (pre-set value) so that the precise
control can be achieved.
• The crop evaporation (ETc) is measured directly by using
lysimeter using a sensor.
• and this information is used to adjust the irrigation volume
or time so that the depth of irrigation water (di) is
proportional to Etc such that
di = Etc/Ea
where, Ea = application efficiency of irrigation system
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2. Volume-Based Automated
Irrigation System
• In volume-based system, the preset amount of
water can be applied in the field segments by
using automatic volume controlled metering
valves.
• The volume of water required for each
segment can be programmed in the controller.
• Thus by counting the number of pulse
received by the controller, it can count the
volume of water passed through.
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3. Time Based Automated Irrigation
System
• In time based system, time is the basis of
irrigation.
• Time of operation is calculated according to
volume of water required and the average
flow rate of water.
• The first thing to perform before programming
for time-based system is to determine the
duration of irrigation required for each
section.
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4. Real Time Feedback System
• Real time feedback is the application of irrigation
based on actual dynamics demand of the plant itself,
plant root zone effectively reflecting all environmental
factors acting upon the plant.
• Operating within controlled parameters, the plant itself
determines the degree of irrigation required.
• Various sensors, viz. tensiometers, relative humidity
sensors, rain sensors, temperature sensors etc. control
the irrigation scheduling.
• These sensors provide feedback to the controller to
control its operation.
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5. Sequential and Non Sequential
Automated Irrigation System
• In sequential systems the field in divided in to
different sub-units, which is irrigated one after
the other in particular sequence.
• Whereas in the non-sequential systems the
sub-units are irrigated randomly based on the
plant water needs and operated electrically
with or without programming with possibility
of utilizing feedback information from the
field for remote control.
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Reference
• http://ecoursesonline.iasri.res.in/mod/page/vi
ew.php?id=226
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