This invention relates to Automated irrigation controller
for efficient water management for irrigation.
Water is recognized as a vital resource for life
human/social development and environmental sustainability.
India's water resources are good but the harnessable water is
about 115 mha-m which can irrigate only 1 30 to 140 mha. This
will be about 50-60% of the gross cultivable area.
Further agriculture draws about 90% of total water used
at present. It is likely to reduce to 75% in the next decade
due to increasing demand for the industry and municipal
purposes. Therefore it is necessary to economize the use of water
and at the same time increase the productivity from per unit
quantity of water. It is possible to economize water application
by using sprinkler and drip irrigation systems. These systems
could be further controlled by automating the irrigation system.
The most of the existing irrigation controller developed
in India, schedule irrigation based on time or volume or soil
moisture sensing. In the time-based schedule, the volume of
water applied is calculated depending on the average flow rate
of water through the pipe. As the flow rate in the pipe varies
due to various reasons it becomes difficult to calculate the
exact amount of water applied in a given time. In volumetric
concept per-set amount of water is applied without considering
the available soil moisture. In soil moisture sensing system
irrigation is controlled based on the available soil moisture.
Soil moisture based sensors are generally of resistance type
or mechanically operated (piston type tensiometers).
The resistance type sensors are affected by salt content
of water or of soil. On the other hand mechanical sensors are
not sensitive enough to respond to small changes in soil moisture
content, also they operate in very narrow range. Keeping this
view optical sensing based automated irrigation system has been
designed .
The object of the invention is that the developed instrument
senses the soil moisture through tensiometer. The tensiometers
are cheap and time-tested equipment for measuring soil moisture
potential. Tensiometers readings are not affected by salt content
of the soil or irrigation water.
Another object of the invention is that the change in the
soil moisture potential causes changes in suction value inside
the tensiometer, which is sensed by mercury manometer. The use
of manometer eliminates mechanical parts, which often tend to
fail or give incorrect reading in the field conditions.
Another object of the invention is that the optical sensors
used for sensing the mercury level for commencement and
culmination of irrigation make the system more reliable by
eliminating make and break type circuits used by some
researchers.
Yet another object of the invention is that the developed
instrument takes into account any effective rainfall during
and in between irrigation cycles as the starting and stopping
is done on the basis of actual moisture content of soil, as
against other instruments which use timers for shutting off
irrigation.
According to the present invention there is provided
an automated irrigation controller for measuring the soil
moisture potential comprising a manometer attached to a
tensiometer, said manometer is provided with a set sensor to
one of the capillary tube and one reset sensor to the other
capillary tube, each of said sensor housing is made of a 12mm
outer dia black PVC tube provided with a pair of pin holes and
a pair of 16mm outer dia black PVC tubes fixed to said 12mm
outer dia black PVC tube centrally opposite to each of said
pin holes and a light emitting diode is fitted in one of said
16mm outer dia black PVC tube with black drawing sheet packing
and a light dependant resistance is fitted in similar manner
to the other 16mm outer dia black PVC tube to provide signals
to automatically switching on and off the irrigation pump driven
by a motor.
The nature of the invention, its objective and further
advantages residing in the same will be apparent from the
following description made with reference to non-limiting
exemplary embodiments of the invention represented in the
accompanying drawings.
Fig. 1 shows the manometer with level of mercury for
saturated soil and position of sensors;
Fig. 2 showing the level of mercury and position of the
sensor at start of irrigation.
Fig. 3 shows the level of mercury and position of sensors
at end of irrigation ( at any desired soil moisture tension);
Fig. 4 shows the detail of sensor assembly.
DETAILED DESCRIPTION OF AUTOMATED
IRRIGATION CONTROLLER
The operation principle to automatically switching On and
Off of an irrigation pump driven by electrical motor is
illustrated through Figs. 1, 2 and 3.
The instrument developed, uses a manometer (1) attached
to a tensiometer for measuring the soil moisture potential.
The optical sensors ( 2,3) were used to switch On and Off the
electric motor to regulate the irrigation supply through pumps
based on the movement of mercury column (4) in the manometer
tube (5) resulting due to change in soil moisture tension.
The sensors ( 2,3) can be set to any desired soil water tension
range between 0 to 0.7 atmosphere to automate othe irrigation
system.
MATERIALS USED
Two Light Emitting Diode (LED) (6), two light Dependent
Resistance (LDR) (7), Sensor housing (8,9) made of 12mm and
16mm diameter low density poly ethylene (L.D.P.E.) pipe, mercury
manometer (1), telephone receiver cables for connecting sensors
(2,3) to the controller, 8-pin computer port, I.C., 12-volt
D.C. relay, 0.0l µF capacitor, two potentiometers of 470 kOhms,
two diodes.
DETAILS OF SENSORS FOR ACTUATING AND DEACTUATING
THE IRRIGATION PUMP
Two diametrically opposite pin holes ( 10) were drilled
at the centre of a 20 cm long piece of 12 mm diameter low density
polyethylene (LDPE) black pipe (8). The 12mm pipe (8) was
inserted in the hole ( 10) made at the centre of 16 cm long
and 16mm diameter black (LDPE) pipe "(9). On both the ends of
the 16 mm dia pipe (9), the light dependent resistance (7) and
light emitting diode (6) were placed just in front of the
pinholes (10) with black drawing sheet packing (11) for putting
On and Off the electric motor. The detail of sensor assembly
is shown in the Fig. 4. On a U-tube mercury manometer (1), two
sensors assemblies ( 2,3) were fitted in such a manner that
they can be slided to any desired position along the length
of capillary tube (5).
A circuit was designed using LDR and I.C. chip and a relay
for actuating and de-actuating the electric motor used in
irrigation pumps. The following prominent features were
considered for selection of I.C.
1. Ability to operate from a wide range of supply voltage.
2. Wide temperature stability.
3. Trigger and reset input are logic compatible.
4. Output can be operated normal on and normal off.
5. High current output on sink or source 200 mA.
6. Monostable and a stable operation.
7. An adjustable duty cycle.
The I.C. selected, operates satisfactorily over temperature
a range of 0-70 C with the power consumption of 600 m Watt and
maximum voltage rating of 18 volts. The I.C. was used as bi-
stable multivibrator with a provision to keep threshold value
of 2/3 Vcc and l/3Vcc respectively for set and re-set comparator.
The circuit, 12 volt relay and power supply unit were
assembled in a metallic box. The panel board of the instrument
has been provided with the controls such as power On-Off, reset
switch (3) to restart the pump in unprecedented conditions such
as the stopping of pump while in operation due to power failure
and three LEDs with two red LEDs for indicating the On and Off
position of the irrigation controller and electric motor
irrigation pump and green LED for indicating the off position
of irrigation pump.
The sensors ( 2,3) were connected to the controller circuit
through two coiled flexible cable. Each cable was provided with
four wire running through it, two each for connecting LED (6)
and LDR (7). Controller can be disconnected from sensor ( 2,3)
by 8-pin port similar to that used in computers.
The invention described hereinabove is in relation to non-
limiting embodiments and as defined by the accompanying claims.
WE CLAIM:
1. An automated irrigation controller for measuring the
soil moisture potential characterised in that comprises a manometer (1) attached
to a tensiometer, said manometer is provided with a set sensor
(2) to one of the capillary tube (5) and one reset sensor(3)
to the other capillary tube (5) each of said sensor housing
is made of a 12mm outer dia black PVC tube (8) provided with
a pair of pin holes (10) and a pair of 16mm outer dia black
PVC tubes (9) fixed to said 12mm outer dia black PVC tube
centrally opposite to each of said pin holes and a light emitting
diode (6) is fitted in one of said 16mm outer dia black PVC
tube with black drawing sheet packing (11) and a light dependent
resistance (7) is fitted in similar manner to ther other 16mm
outer dia black PVC tube to provide signals to automatically
switching on and off the irrigation pump driven by a motor.
2. An automated irrigation controller as claimed in claim
1 wherein the optical sensors ( 2,3) are connected to the
controller circuit through two coiled flexible cable to switch
ON and OFF the electric motor of the irrigation pump.
3. An automated irrigation controller as claimed in claim
1, wherein said sensors can be set to any desired soil water
tension range between 0 to 0.7 atmosphere to automate the
irrigation system.
4. An automated irrigation controller as claimed in claim
3 wherein said two sensors assemblies are fitted in such a manner
that they can be slided to any position along the length of
the capillary tube of the manometer (1) to set the desired soil
water tension.
5. An automated irrigation controller as claimed in claim
2 wherein said sensor assemblies comprises a pair of 16mm
diameter and 16cm long black PVC tube (9) placed opposite to
said pin hole having a light emitting diode (6) in one and a
light dependent resistance (7) in the other.
6. An automated irrigation controller as claimed in claim
1 wherein said controller comprises a light dependent resistance,
an I.C. chip and a 12V relay housed in a metallic box having
a panel board provided with the controls such as power ON-OFF
reset switch to restart the pump.
7. An automated irrigation controller as herein described
and illustrated in the accompanying drawings.

An automated irrigation controller for measuring the soil
moisture potential comprising a manometer (1) attached to a
tensiometer, said manometer is provided with a set sensor (2)
to one of the capillary tube (5) and one reset sensor (3) to
the other capillary tube (5) each of said sensor housing is
made of a 12mm outer dia black PVC tube (8) provided with a
pair of pin holes (10) and a pair of 16mm outer dia black PVC
tube (9) fixed to said 12mm outer dia black PVC tube centrally
opposite to each of said pin holes and a light emitting diode
(6) is fitted in one of said 16mm outer dia black PVC tube with
black drawing sheet packing(ll) and a light dependent resistance
(7) is fitted in similar manner to the other 16mm outer dia
black PVC tube to provide signals to automatically switching
on and off the irrigation pump driven by a motor.