ADAMA UNIVERSITYSCHOOL OF ENGINEERING AND INFORMATION TECHNOLOGY

DEPARTMENT OF ELECTRICAL ENGINEERING

SENIOR PROJECT REPORT FOR BSc THESIS ON PLC BASED IRRIGATION SYSTEM CONTROL

SUBMITTED TO: ATO KEMAL IBRAHIM

PREPARED BY GROUP # 1

1. ADUGNA BEKELE

2. DULLA MEKONNEN

3. EMEBET TADESE

4. MESKEREM TADESE

5. NEWAY MOGES

AUGUST, 2010

Abstract

New irrigation electrical control technologies could improve irrigation efficiency, promoting

water conservation and reducing the environmental impacts. The objectives of this project were

to avoid wastage of water and increase irrigation efficiency by using a PLC based irrigation

system with the help of soil moisture sensor. It also improves the traditional irrigation system in

Ethiopia enabling the irrigation system to have high efficiency and low water usage.The existing

irrigation system being tedious, time consuming and very wasteful in water usage. The PLC

based sprinkler irrigation system gives the best feature than the traditional one.

Acknowledgements

In order to successfully accomplish our senior project on PLC based

automation of irrigation system with case study on ADAMA UNIVERSITY garden

watering system the help of many people was very important and unforgettable.

So our kind and deep appreciation and thanks goes to our adviser Ato KEMAL

IBRAHIM for his advice, spending his golden time, knowledge and bringing materials

from different concerned bodies for the success of this project. Our next thanks goes to

M/r WOLFGANG, chief of GTZ/ECBP further training section, and all his subordinates

for their endless support and attempt to help us with any regards in their disposal. We

would like to tank AU water supply section and wood work sections for their kindly

cooperation and patience. Finally we would like to thanks all the teachers in ELT

department

Table of contents Page

Acknowledgement

Abstract

1. Introduction……………………………………………………………………….1.1Background of the project….………………………………………………….1.2Statement of the problem………………………………………………………1.3Objective of the Project……………………………………………………….1.4Scope of the Project……………………………………………………………

2. Description…………………………………………………………………………2.1Programmable Logic Controller (PLC)………………………………………...

2.1.1 History of PLC…………………………………………………………2.1.2 Basic functional sections of PLC……………………………………….2.1.3 Expansion module………………………………………………………2.1.4 Programming a PLC……………………………………………………2.1.5 PLC scan cycle………………………………………………………….2.1.6 Advantage of PLC……………………………………………………..

2.2Solenoid valve…………………………………………………………………..2.2.1 Definition……………………………………………………………….2.2.2 Function…………………………………………………………………2.2.3 Operation principle……………………………………………………....2.2.4 Types of solenoid valve………………………………………………….

2.3Soil moisture sensor……………………………………………………………...2.3.1 Types of soil moisture sensor……………………………………………

2.4Soil moisture sensor installation…………………………………………………2.5Level sensor………………………………………………………………………

2.5.1 Definition………………………………………………………………..2.5.2 Types of level sensor……………………………………………………2.5.3 Application of level sensor………………………………………………

2.6Description of the project………………………………………………………2.6.1 Design …………………………………………………………………..2.6.2 Implementation…………………………………………………………2.6.3 Test………………………………………………………………………

3. .Resources……………………………………………………………………4. Conclusion………………………………………………………………………5. Recommendation………………………………………………………………6. References…………………………………………………………………

6.1Appendix…………………………………………………………………

Introduction

1.1 Background of the project

Irrigation in Ethiopia has lasted for decades. Ethiopia covers 12 river basins with an

annual runoff volume of 122 billion m3 of water with an estimated 2.6 billion m3 of ground

water potential. This amounts to 1743 m3 of water per person per year: a relatively large

volume. But due to lack of water storage capacity and large spatial and temporal

variations in rainfall, there is not enough water for most farmers to produce more than

one crop per year with frequent crop failures due to dry spells and droughts. Moreover,

there is significant erosion, reducing the productivity of farmland. [Awulachew] So

irrigation being compulsory for Ethiopia; the government has recognized Ethiopia’s

irrigation potential and has identified the important role of irrigation development for

reducing vulnerability to inconsistent rain fall distribution and poverty reduction of the

people.

Traditional irrigation is very old in Ethiopia. The traditional small-scale schemes

are, in general, simple river diversions. The diversion structures are elementary and

subject to frequent damage by flood.

'Modern' irrigation was started at the beginning of the 1960s by private investors in

the middle Awash valley where big sugar estates, fruit and cotton farms are found. With

the 1975 rural land proclamation, the large irrigated farms were placed under the

responsibility of the Ministry of State Farms. Almost all small-scale irrigation schemes

built after 1975 were made into Producers' Cooperatives. [www.fao.org]

Ethiopia has an estimated irrigation potential of 3.5 up to 4 million hectares

(Awulachew et al. 2007b). During 2005/2006 the total estimated area of irrigated

agriculture in the country was 625,819 ha, which, in total, constitutes about 18% of the

potential (MoWR 2006); of which traditional irrigation accounts for 479,049 hectares

while 124,569 hectares of land was developed through medium and large scale

irrigation schemes ( MoFED, 2007).

According to the Ministry of Water Resource (2002), there are four broad

categories of irrigation systems in Ethiopia, namely; (i) traditional irrigation schemes; (ii)

modern small-scale irrigation schemes, (iii) medium- to large-sc irrigation schemes, and

(iv) large scale irrigation schemes.

About 75 percent of the developed irrigation is small-scale, about three-quarters of

which is traditional, and is mostly based on local practices and indigenous knowledge.

Given that the overwhelming majority of farming activities in Ethiopia is small-scale,

there could be a unique opportunity for positive interventions to stimulate agricultural

production, especially if certain fundamental conditions are met. Experience in many

parts of SSA has shown that with adequate community involvement in planning, design

and management, SSIs can be more viable and sustainable than conventional large-

scale schemes from a number of perspectives (Merry et al., 2002).

Sprinkler Irrigation is a method of supplying water for irrigation in a method similar

to rainfall. Water is distributed through a network of pipes spread out on a field. The

water from these pipes into the air and so irrigates the entire soil surface through many

sprinkler heads. Sprinklers provide better coverage for small to large areas and are

suitable for use on all types of fields. Total area to be irrigated is divided into small

segments called irrigation blocks or zones and these zones are irrigated in sequence

according to the flow of water. It is also adaptable nearly to all irrigable soils since

sprinklers are available in a wide range of discharge capacity. It is suitable for almost all

fields, crops as well as Vegetables and gardens: Residential, Industrial, Hotel, Resorts,

Public & Government Enterprises, Golf Links, Race Courses.

Water is a valuable resource and therefore its usage should be in an efficient manner.

Also, water scarcity is one of the most important factors driving growth in agriculture-

based industries in our country Ethiopia. For efficient use of water for irrigation, labor

cost, etc., drives the need for highly efficient automated sprinkler irrigation systems.

Automated sprinkler system has the following categories

(a)Time based system.

Time based automatic sprinkler systems is better to avoid being bothered with the

routine work of lawn watering, but tend to “set them and forget them”. This method of

watering accomplishes the task of keeping the lawn green, but over the growing season

uses significantly more water than the grass requires. This problem contribute to water

waste and are not often fixed because the lawn is unnoticed moist most of the time.

(b) Quantity based system.

In volume based system, the preset amount of water can be applied in the field

segments by using automatic volume controlled metering valves. Sequencing of

metering values can also be done automatically. Even though the amount of water

applied can be excess because the discharging of the moisture may vary in time.

(c) Moisture sensor based system

In the moisture sensing system the operation of irrigation valves are controlled by

a controller get values from the moisture sensors placed directly in to the root zone. If

there is sufficient moisture, then the sensor will prevent the sprinkler system from

activating and applying water. However, if it senses that the soil is dry, it allows irrigation

to take place.

Automatic sprinkler systems have the potential to save water if they are well

designed, installed and maintained and it will give a great advantage for the owners and

workers.[ Brent Q. Mecham] So, our project is a PLC based sprinkler irrigation system

using moisture sensor which can give the best feature in giving effective watering and

intense satisfaction of job well-done to bring an irrigation development in our country

Ethiopia.

1.2 Statement of the problem

Irrigation system has lasted years in Ethiopia which is traditional. Farmers are

traditionally accustomed to directing flood (surface) water for supplementing their crops

(spate irrigation).These irrigation systems have many drawbacks like wastage of water,

high labor cost, timing problem, uniformity of water supply, so that each plant will not get

the amount of water it needs, either too much or too little. Since the system is

uncontrolled the soil is soaked too much .These systems have low requirements for

infrastructure and technical equipment but need high labor inputs . So our project

comes up with a remedy to solve the above problem with high efficiency and low water

usage.

1.3 Objective of the Project

The general objective of the project is to design automated control system sprinkler

irrigation for the development of irrigation in our country.

Specific objective of the study are:

1. To design and implement a control system of sprinkler system for a

Garden of Adama University

2. To minimize human intervention in agricultural irrigation industry .

3. To improve automation, control, and distribution technology in irrigation system.

4. To increase irrigation water utilization efficiency.

5. To enhance the transfer of irrigation technologies and management alternatives

emphasizing economic and environmental benefits.

1.4. Scope of the project

Sprinkler irrigation system in this project takes water from Adama University of the existing garden water tap to irrigate a garden by automated control system and the principle can be extended to a higher to large scale farms and small scale ETHIOPIAN farmers land irrigation for farmers specially who live in a place where water is very scares and water can be stored in well and/or there is another water body like lake, river, ….etc but not suitable to surface irrigation system with the same control philosophy but pump- motor assembly instead of water tap with solenoid valve.

2. Project description

In working principle of automatic irrigation system there are three in put parameters to the controller:

1. Soil moisture sensor signal.2. Water balancing tank level signal.

3. Four push button signal.

The controller is programmable logic controller and the controlled variable in this system is electrically controlled solenoid valve mounted on tap end. The final elements are the PVC pipes and the sprinkler heads.

State of the valve is controlled and determined by statuses of the three PLC inputs,

1. The two moisture sensors are installed at two different depths under the plant root. The shallow moisture sensor is installed at 1/3 of the rooting depth to sense the moisture at 1/3 of the depth .The second moisture sensor installed at 2/3 of the rooting depth of the plant to senses wetness. When the system starts the irrigation the shallow moisture sensor senses first and irrigation continued until the second moisture senses. At this point the controller takes an action and the main valve will be closed.

2. The second input is a water level sensor in the balancing water tanker. When defective sprinkler head or any other problem clog the irrigation pipe network develops high pressure. The pressurized water is stored as a relief inside a balancing water tanker placed at elevated palace and its water level is detected by the level sensor to take action by the controller to avoid the over flow of water. So when the water in the balancing tank reaches at a pre determined set point it closes or opens solenoid valve accordingly.

3. Other inputs are start, stop, emergency stop and test buttons which send command according to programmed parameters. These input parameters to the controller sets high whenever the user want to start, stop and test the irrigation system irrespective of the status of the level sensor in the balancing tank and status of moisture sensors in the root zone of the plant.

Programmable logic controllers (PLC)

A PROGRAMMABLE LOGIC CONTROLLER is a solid state control system that

continuously monitors the status of devices connected as inputs. Based upon a user

written program, stored in memory, it controls the status of devices connected as

outputs.

History of PLC

The development of the industrial society led each manufacturing process to

become larger in scale, and more advanced and complex, requiring many different

forms of control systems. Up to now, control systems for automation were connected to

related electronic components, such as relay, contractor, timer, counter, etc, depending

on the circuit layout, which led to problems such as difficulty in the lining process and

the amount of space for sequence control, and the slow of operation.

Recognizing these problems, in 1968, General Motors, the American automobile

manufacturer, suggested 10 conditions for PLC, as shown in, which became the starting

point of PLC development. The chart is a brief history of PLC.

10 conditions suggested by General Motors

(1) Should be easy to implement and modify program and sequence system.

(2) Maintenance and repair must be easy and must be a plug-in type.

(3) Should be more reliable than relay controller.

(4) Output should be able to be connected to computer.

(5) Should be smaller in size than relay controller.

(6) Should be more cost effective than relay controller.

(7) Input should be supplied with AC 115[V].

(8) Output should be supplied with AC 115[V], 2[A].

(9) Should be expendable without making much modification of the entire system.

(10) Should be equipped with programmable memory, which is expandable to at

least 4K words.

History of PLC

Year Progress

1968 The birth of the concept of PLC

1970 Introduction of logic control, 1K memory capacity and 128 I/O score

handling

1974 Timer, counter, arithmetic operation, 12K memory capacity, and 1024I/O

score handling

1976 Introduction of remote I/O system (first standard created by the US)

1977 Introduction of microprocessor PLC

1980 Introduction of high performance I/O module, high performance

communication device high functional software; started to use

microcomputer as programming tool

1983 Introduction of inexpensive small-size PLC

1985 Standardization, distributed and hierarchical control made possible by

networking with computer

1991 Fuzzy logic implemented by fuzzy only package

Basic functional sections of PLC

Programmable logic controller has five basic functional sections to perform its intended

operation completely. These functional sections are:

1. Central processing unit (CPU).

2. Memory.

3. Input module.

4. Output module.

5. Power system.

Central processing unit

Central Processing Unit (CPU) is the brain of a PLC controller. CPU itself is usually one

of the microcontrollers. Aforetime these were 8-bit microcontrollers such as 8051, and

now these are 16- and 32-bit microcontrollers. CPU also takes care of communication,

interconnectedness among other parts of PLC controller, program execution, memory

operation, overseeing input and setting up of an output. PLC controllers have complex

routines for memory checkup in order to ensure that PLC memory was not damaged

(memory checkup is done for safety reasons). Generally speaking, CPU unit makes a

great number of check-ups of the PLC controller itself so eventual errors would be

discovered early. You can simply look at any PLC controller and see that there are

several indicators in the form of light diodes for error signalization.

Memory

System memory, today mostly implemented in FLASH technology, is used by a PLC for

a process control system. Aside from this operating system it also contains a user

program translated from a ladder diagram to a binary form. FLASH memory contents

can be changed only in case where user program is being changed. PLC controllers

were used earlier instead of FLASH memory and have had EPROM memory instead of

FLASH memory which had to be erased with UV lamp and programmed on

programmers. With the use of FLASH technology this process was greatly shortened.

Reprogramming a program memory is done through a serial cable in a program for

application development.

User memory is

divided into blocks having special functions. Some parts of a memory are used for

storing input and output status. The real status of an input is stored either as "1" or as

"0" in a specific memory bit.

Each input or output has one corresponding bit in memory. Other parts of memory are

used to store variable contents for variables used in user program. For example, timer

value, or counter value would be stored in this part of the memory.

PLC controller inputs

Intelligence of an automated system depends largely on the ability of a PLC controller to

read signals from different types of sensors and input devices. Keys, keyboards and by

functional switches are a basis for man versus machine relationship. On the other hand,

in order to detect a working piece, view a mechanism in motion, check pressure or fluid

level you need specific automatic devices such as proximity sensors, marginal switches,

photoelectric sensors, level sensors, etc. Thus, input signals can be logical (on/off) or

analogue. Smaller PLC controllers usually have only digital input lines while larger also

accept analogue inputs through special units attached to PLC controller. One of the

most frequent analogue signals are a current signal of 4 to 20 mA and milivolt voltage

signal generated by various sensors. Sensors are usually used as inputs for PLCs. You

can obtain sensors for different purposes. They can sense presence of some parts,

measure temperature, pressure, or some other physical dimension.

Other devices also can serve as inputs to PLC controller. Intelligent devices such as

robots, video systems, etc. often are capable of sending signals to PLC controller input

modules (robot, for instance, can send a signal to PLC controller input as information

when it has finished moving an object from one place to the other.)

Adjustment interface also called an interface is placed between input lines and a CPU

unit. The purpose of adjustment interface to protect a CPU from disproportionate signals

from an outside world. Input adjustment module turns a level of real logic to a level that

suits CPU unit (ex. input from a sensor which works on 24 VDC must be converted to a

signal of 5 VDC in order for a CPU to be able to process it). This is typically done

through opto-isolation, and this function you can view in the following picture. Opto-

isolation means that there is no electrical connection between external world and CPU

unit. They are "optically" separated, or in other words, signal is transmitted through light.

The way this works is simple. External device brings a signal which turns LED on,

whose light in turn incites photo transistor which in turn starts conducting, and a CPU

sees this as logic zero (supply between collector and transmitter falls under 1V). When

input signal stops LED diode turns off, transistor stops conducting, collector voltage

increases, and CPU receives logic 1 as information.

2.6 PLC controller output

Automated system is incomplete if it is not connected with some output devices. Some

of the most frequently used devices are motors, solenoids, relays, indicators, sound

signalization and similar. By starting a motor, or a relay, PLC can manage or control a

simple system such as system for sorting products all the way up to complex systems

such as service system for positioning head of CNC machine. Output can be of

analogue or digital type. Digital output signal works as a switch; it connects and

disconnects line. Analogue output is used to generate the analogue signal (ex. motor

whose speed is controlled by a voltage that corresponds to a desired speed).

Output interface is similar to input interface. CPU brings a signal to LED diode and turns

it on. Light incites a photo transistor which begins to conduct electricity, and thus the

voltage between collector and emitter falls to 0.7V, and a device attached to this output

sees this as a logic zero. Inversely it means that a signal at the output exists and is

interpreted as logic one. Photo transistor is not directly connected to a PLC controller

output. Between photo transistor and an output usually there is a relay or a stronger

transistor capable of interrupting stronger signals.

Power supply

Electrical supply is used in bringing electrical energy to central processing unit. Most

PLC controllers work either at 24 VDC or 220 VAC. On some PLC controllers you'll find

electrical supply as a separate module. Those are usually bigger PLC controllers, while

small and medium series already contain the supply module. User has to determine

how much current to take from I/O module to ensure that electrical supply provides

appropriate amount of current. Different types of modules use different amounts of

electrical current.

This electrical supply is usually not used to start external inputs or outputs. User has to

provide separate supplies in starting PLC controller inputs or outputs because then you

can ensure so called "pure" supply for the PLC controller. With pure supply we mean

supply where industrial environment can not affect it damagingly. Some of the smaller

PLC controllers supply their inputs with voltage from a small supply source already

incorporated into a PLC.

Extension modules

Every PLC controller has a limited number of input/output lines. If needed this number

can be increased through certain additional modules by system extension through

extension lines. Each module can contain extension both of input and output lines. Also,

extension modules can have inputs and outputs of a different nature from those on the

PLC controller (ex. in case relay outputs are on a controller, transistor outputs can be on

an extension module).

Programming a PLC controller

PLC controller can be reprogrammed through a computer (usual way), but also through

manual programmers (consoles). This practically means that each PLC controller can

programmed through a computer if you have the software needed for programming.

Today's transmission computers are ideal for reprogramming a PLC controller in factory

itself. This is of great importance to industry. Once the system is corrected, it is also

important to read the right program into a PLC again. It is also good to check from time

to time whether program in a PLC has not changed. This helps to avoid hazardous

situations in factory rooms (some automakers have established communication

networks which regularly check programs in PLC controllers to ensure execution only of

good programs).

Almost every program for programming a PLC controller possesses various useful

options such as: forced switching on and off of the system inputs/outputs (I/O lines),

program follow up in real time as well as documenting a diagram. This documenting is

necessary to understand and define failures and malfunctions. Programmer can add

remarks, names of input or output devices, and comments that can be useful when

finding errors, or with system maintenance. Adding comments and remarks enables any

technician (and not just a person who developed the system) to understand a ladder

diagram right away. Comments and remarks can even quote precisely part numbers if

replacements would be needed. This would speed up a repair of any problems that

come up due to bad parts. The old way was such that a person who developed a

system had protection on the program, so nobody aside from this person could

understand how it was done. Correctly documented ladder diagram allows any

technician to understand thoroughly how system functions by communicating the

programmer, computer, with the controller by means of RS 232 communication cable.

The following figure show price and functionality comparision of controllers.

PLC Scan Cycle

Self test | input scan |logic solve |output scan |Self test| input scan| logic solve |

output scan | Self test | input scan |logic solve

One scan cycle ranges from <1 to 100 ms are possible time.

SELF TEST

Checks to see if all cards error free, reset watch-dog timer, etc. (A watchdog timer will

cause an error, and shut down the PLC if not reset within a short period of time - this

would indicate that the ladder logic is not being scanned normally).

INPUT SCAN

Reads input values from the chips in the input cards, and copies their values to

memory. This makes the PLC operation faster, and avoids cases where an input

changes from the start to the end of the program (e.g., an emergency stop). There are

special PLC functions that read the inputs directly, and avoid the input tables.

LOGIC SOLVE/SCAN

Based on the input table in memory, the program is executed 1 step at a time, and

outputs are updated. Ladder logic programs are modeled after relay logic. In relay logic

each element in the ladder will switch as quickly as possible. But in a program elements

can only be examines one at a time in a fixed sequence. Consider the ladder logic, in

the ladder logic will be interpreted left-to-right, top-to-bottom. Ladder logic scan begins

at the top left rung and ends at bottom right of the rung.

OUTPUT SCAN

The output table is copied from memory to the output chips. These chips then drive the

output devices. Plc operation input scan takes a snapshot of the inputs, and solves the

logic. This prevents potential problems that might occur if an input that is used in

multiple places in the ladder logic program changed while half way through a ladder

scans. Thus changing the behaviors of half of the ladder logic program. This problem

could have severe effects on complex programs. One side effect of the input scan is

that if a change in input is too short in duration, it might fall between input scans and be

missed.

READ

EXCUTE

During its scan operation, the CPU completes three processes:

(1) It reads the input data from the field devices via the input interfaces,

(2) It executes, or performs, the control program stored in the memory system, and

(3) It writes, or updates, the output devices via the output interfaces.

This process of sequentially reading the inputs, executing the program in memory, and

updating the outputs is known as scanning. The input/output system forms the

interface by which field devices are connected to the controller. The main purpose of

the interface is to condition the various signals received from or sent to external field

devices. Incoming signals from sensors (e.g., push buttons, limit switches, analog

sensors, selector switches, and thumbwheel switches) are wired to terminals on the

WRITE

input interfaces. Devices that will be controlled, like motor starters, solenoid valves, pilot

lights, and position valves, are connected to the terminals of the output interfaces.

3.14 Advantages of PLC’S

The same programmable controller can be used for a very wide range of tasks.

The program can be changed without changing the wiring.

Once the program is created, we can copy it as many times as we like if a

number of similar controllers are required.

The program is the circuit diagram at the same time we can just connect up to a

printer and output date documentation after each program change without

technical drawing and without technical error.

PLC’S are economical even for applications that would otherwise need only five or ten

contactors and timing relays.

Description of system operation

The system has seven inputs these are:-

Emergency stop button

Start button

Two moisture sensors, M1 (shallow soil moisture sensor), M2 (deep soil

moisture).

Two level sensors, LL (low level sensor), HL (high level sensor).

Test button

The system has also six out puts:-

Main solenoid valve.

Tank solenoid valve.

“Dry” display.

“Saturated” display.

“Tank full” display.

“Need watering” display.

1. Condition to start the main valve

The main valve will turned on if either of the following condition is satisfied.

Start button is pressed and both moisture &level sensors must not sense.

If the valve is closed at the middle of the operation due to the statues of the level

sensors that means if the balancing tanker high level sensor sense water main

vale will be closed ,the main valve will be open if the following conditions are

fulfilled:

Moisture sensor 1 sense &moisture sensor 2 will not sense, both level sensors

will not sense.

1. To turn off the main valve either of the following condition must be satisfied.

Both level sensors sense water in the balancing tank.

Or

Both moisture sensors sense soil moisture in the garden.

Or

Emergency is pressed.

Or

Button is pressed.

2. The tank valve is open

When start button is pressed and it will be open until soil moisture sensor 2

senses.

3. The tank valve is closed

When soil moisture sensor 2 sense, or emergency stop button is press, or

stop button is pressed.

The program has real time displays which indicate the status of the system

operation.

4. “Dry” will be displayed

When both soil moisture sensors do not sense moisture.

5. “Saturated” will be displayed

When both soil moisture sensors sense moisture.

6. “Need watering” will be displayed

When soil moisture sensor 1 sense but soil moisture sensor 2 will not

sense.

7. “Tank full” will display

When both water level sensors sense water in the balancing tank.

8. The system has additional feature to operate the main valve manually if the

system fails to operate the normal operation due to electrical power cut off or/and

mechanical failures.

Solenoid valve

Definition

Solenoid control valves are electromagnetic valves that are used with both gas and

liquid are controlled by the starting and stopping of electrical current through a solenoid.

A solenoid is the coil in a wire that changes the state of the value. Solenoid control

valves dictate the flow of water or air, and are used in fluidics. Fluidics uses fluid to

perform both digital and analog operations. Solenoid valves may have two or more

ports: in the case of a two-port valve the flow is switched on or off; in the case of a

three-port valve, the outflow is switched between the two outlet ports. The inlet(s) and

outlet(s) are also known as "ports."

Function

Solenoid control valves are broken up into two main parts; they are the solenoid and

the valves. The solenoid works to convert electrical energy into mechanical energy. This

allows the valves to open and control mechanically. Solenoid control valves have metal

seals that allow the electrical interfaces to be easily controlled. When the valves are not

activated, a spring is used to hold the valve open or closed.

Operation Principle of solenoid valve

A solenoid valve is an electromechanical valve that is controlled by an electric current.

An electrical source can be either 220v AC or 24v DC. The electric current runs through

a solenoid, which is a wire coil wrapped around a metallic core. A solenoid creates a

controlled magnetic field when an electrical current is passed through it. This magnetic

field affects the state of the solenoid valve, causing the valve to open or close.

Each of the two ports on a two way valve is alternately used to permit flow as well as

close it off. A two way valve can be specified to be either “Normally Open" or “Normally

Closed” in its operation. With a normally open valve, the valve remains open until some

type of current is applied to close the valve. Suspension of the electrical power causes

the valve to automatically re-open to its normal state. A normally closed solenoid valve

is the most common, working in the opposite fashion, remaining closed until a power

source causes it to open.

Three way valves come with three ports. Three way valves are commonly used when

alternate pressure and exhaustive pressure are required for operation, such as in a

coffee machine or dishwasher.

Type of solenoid valve

All solenoid valves, no matter the design, are specified to be one of two general types:

either a direct acting valve or a pilot operated valves.

Direct Acting Valves

In a direct-acting solenoid valve, a coil magnetically opens the valve in a direct action,

lifting the shaft and the seat of the valve without depending on outside pressure.

Pilot-Operated Valves

In pilot-operated valves, the plunger opens up the pilot opening while built-up pressure

causes the valve to open and close.

Although piloted valves require less electrical energy to operate, they usually need to

maintain full power in order to remain in an open state, and they perform at a slower

rate than direct acting solenoids. Direct acting solenoid valves only need full power

when opening the valve, as they can hold their open position even when operating on

low power.

Application of solenoid valve

Solenoid valves are used to transport gases or liquids and have a wide variety of

applications; including automatic irrigation sprinkler systems use solenoid valves

with an automatic controller and industrial uses

Solenoids offer fast and safe switching, high reliability, long service life, good medium

compatibility of the materials used, low control power and compact design.

I n s t a l la t i o n a n d S e r v i c i n g I n s t r u c t i o n s

To insure peak performance, solenoid valves must be selected and applied correctly;

however, proper installation procedures are equally important. The following instructions

list the essential points for correct installation.

Soil moisture sensors

Definition

Soil moisture sensors measure the water content in soil.

Measuring soil moisture is important in agriculture to help farmers manage their

irrigation systems more efficiently. Not only are farmers able to generally use less water

to grow a crop, they are able to increase yields and the quality of the crop by better

management of soil moisture during critical plant growth stages.

Besides agriculture, there are many other disciplines using soil moisture sensors. Golf

courses are now using sensors to increase the efficiencies of their irrigation systems to

prevent over watering and leaching of fertilizers and other chemicals offsite. Connecting

a soil moisture sensor to a simple irrigation clock will convert it into a "smart" irrigation

controller that prevents an irrigation cycle when the soil is wet.

Moisture Sensor usage in urban landscape irrigation will only increase over the next

decade.

Types of moisture sensors

1. Capacitive moisture sensor

2. Pressure (tension meter) moisture sensor

3. Resistive moisture sensor

4. Electrical conductivity probes moisture sensor

1. Capacitive moisture sensor

Capacitance sensors contain two electrodes separated by a dielectric. The electrodes

are inserted into the soil or in an access tube in the soil and the

Soil becomes part of the dielectric.

Most soil moisture sensors are designed to estimate soil volumetric water content based on the

dielectric constant (soil bulk permittivity) of the soil. The dielectric constant can be thought of as

the soil's ability to transmit electricity. The dielectric constant of soil increases as the water

content of the soil increases. This response is due to the fact that the dielectric constant of water

is much larger than the other soil components, including air. Thus, measurement of the dielectric

constant gives a predictable estimation of water content.

A very high oscillating frequency is applied to the electrodes, which results in a resonant

frequency, the value of which depends upon the dielectric constant of the soil. The moisture

content of the soil will change the dielectric constant of the soil; therefore more moisture in the

soil will change the frequency. This change is converted into a soil moisture measurement. This

technology is very complex and quite expensive, but seems to provide high accuracy.

Disadvantages:

Long-term stability questionable

Costly

Advantages:

Theoretically, can provide absolute soil water content

Water content can be determined at any depth

Sensor configuration can vary in size so sphere of influence or measurement is adjustable

Relatively high level of precision when ionic concentration of soil does not change

Can be read by remote methods

2. Pressure (tensionmeter) moisture sensor

Tensiometers measure the soil moisture tension or suction. This device is a

Plastic tube with a porous ceramic tip attached at one end and a vacuum gauge on the

other end. The porous ceramic tip is installed into the soil at the depth where the

majority of the active root system is located.

The vacuum gauge measures the soil moisture tension or suction. It measures how

much effort the roots must put forth to extract water from the soil and is measured in

cent bars. The higher the reading, the less moisture that is available and the harder

roots must work to extract water. A lower reading indicates more available water. A

tensiometer can be used to take manual readings or a special model can be installed to

provide the capability for the tensiometer to be wired into the sprinkler system to provide

control.

Also the tensiometer needs routine maintenance to make sure enough liquid is in the

tensiometer and that it hasn’t broken tension because the soil has separated away from

the ceramic tip. In climates where the ground freezes, tensiometers must be removed

and stored for the winter months and re installed the following yea

Advantages:

1. Recommendation for irrigation policy develops with the tensiometers.

2. Inexpensive and easily constructed

Works well in the saturated range

3. Easy to install and maintain

4. Operates for long periods if properly maintained

5. Can be adapted to automatic measurement with pressure transducers

6. Can be used with positive or negative gauge to real water table elevation and/or

Soil water tension

Disadvantages:

1. Limit range of 0 to -0.8 bars not adequate for sandy soil.

2. Difficult to translate data to volume water content

Hysteresis

3. Requires regular (weekly or daily) maintenance depending on range of

measurements

4. Subject to breakage during installation and cultural practices

5. Automated systems costly and not electronically stable

6. Disturbs soil above measurement point and can allow infiltration of irrigation

water or rainfall along its stem

3. Resistive moisture sensor (general)

Description:

Electromagnetic techniques include methods that depend upon the effect of moisture on the

electrical properties of soil. Soil resistivity depends on moisture content; hence it can serve as the

basis for a sensor. It is possible either to measure the resistivity between electrodes in a soil or to

measure the resistivity of a gypsum block is that the calibration changes gradually with time,

limiting the life of the block

Resistive Sensor (Gypsum)

1. Description:

One of the most common methods of estimating matric potential is with gypsum or porous

blocks. The device consists of a porous block containing two electrodes connected to a wire lead.

The porous block is made of gypsum or fiberglass. When the device is buried in the soil, water

will move in or out of the block until the matric potential of the block and the soil are the same.

The electrical conductivity of the block is then read with an alternating current bridge. A

calibration curve is made to relate electrical conductivity to the matric potential for any particular

soil. Using a porous electrical resistance block system offers the advantage of low cost and the

possibility of measuring the same location in the field throughout the season. The blocks

function over the entire range of soil water availability. The disadvantage of the porous block

system is that each block has somewhat different characteristics and must be individually

calibrated. The main disadvantage of the

Electrical resistance blocks measure soil moisture tension with two electrodes

embedded in a porous material such as gypsum, or a sand-ceramic mixture. The block

allows moisture to move in and out of it as the soil dries or becomes moist. The

electrodes measure the resistance to electric current when electrical energy is applied.

The more moisture in the block, the lower the resistance reading indicating more

available moisture. The blocks use gypsum or similar material to be a buffer against

salts (such as fertilizer) that would also affect resistance readings. The sensors using a

granular matrix seem to work well and last for a longer time as compared to gypsum

blocks.

Disadvantages: Each block requires individual calibration

Calibration changes with time

Life of device limited

Provides inaccurate measurements

5. Advantages: Inexpensive

4. Electrical conductivity probes

Measure soil moisture in the soil by how well a current of electricity is passed between

two probes. In many ways the concept is similar to resistance blocks but the probes

(electrodes) have direct contact with the soil and are not buffered as in resistance

blocks. The more moisture in the soil the better the conductivity or the lower the

electrical resistance. This method is very sensitive to the spacing of the probes as well

as being influenced by soil type and salts that come primarily in the form of fertilizers

For our project we select Electrical conductivity probe type moisture sensor. This

type of moisture sensor works when electric current pass through the two probes or

when it conducts. We select this sensor because it is easily designed from the

materials that we have. It start to conduct when the resistance value reduces from

infinity to 6kΩ.. At this value it start to conduct and the controller takes an action.

The controller conceders the value from infinity to six kilo ohm as low (open) and

from six to zero resistance it conceders as high (closed). The sensors installed with

5cm separation and a depth of 8cm to 12cm depending on the type of the soil(sandy

loam).

This type of sensor has the following benefits, features, and applications which is

summarized as a table below.

Benefits Features Applications

Instantly measure soil moisture, electrical conductivity/salinity, and more

Optimize soil analysis and irrigation

Enables measurement of native (undisturbed) soil

Low risk: 10 years of field-proven science

Measure flow and movement of the wetting front through a soil profile

Performs well in high-salinity soils

Instantaneous sensor response time

Serial addressable: multiple units on one cable

Maintenance-free

No calibration for mineral soils

Compatible with most data logging systems

Digital or analog output

Compact & rugged for years of in-soil use

Long/short-term soil monitoring

Spot checking of soil

Golf & sports grass field management

Precision agriculture

Geotechnical measurement

Weather/climate studies

Agriculture research

Soil & ground water remediation

Flood control forecasting

Review real-time soil data and trends from the office

Soil moisture sensor Installation

To begin, sensor placement is very critical for proper function of soil moisture sensors.

The sensor should be placed in a “typical “spot of the land. It shouldn’t be the wettest

spot since it would inhibit the sprinklers from coming on and if it is in the driest spot,

then the sprinklers would be allowed to water too frequently. Choosing the

representative spot requires good site observations. The sensor should be in the middle

of the sprinkler pattern. Usually the sprinkler zone with the soil moisture sensor will

need to be wired into the controller as the last sprinkler zone. The sensors typically are

installed or wired to interrupt the common wire going to each of the valves of the system

to permit irrigation. How the sensor is actually placed in the soil takes care and

planning. For the sensor to work the best, the soil around the sensor needs to be

representative of the soil for the whole site.

After an installation hole is dug, some sensors can be easily installed into undisturbed

soil. This is the best because achieving the same bulk density of disturbed soil may take

weeks or months of time. Otherwise the sensor will be placed in a situation where the

disturbed soil will be replaced into the hole and tamped or compacted or watered in a

way that will make it different than the surrounding soil. This difference will affect how

well the sensor is sensing the soil moisture that is supposed to be representative.

For almost all soil moisture sensors, new wires will need to be installed from the sensor

location to the irrigation controller. This effort may take substantial time effort and

expense to achieve. But this will be necessary if only one sensor will be used for the

entire sprinkler system. Many times the cost of installing the additional wires will be

more than the sensor and its controls. If a new sprinkler system is being installed, run

additional wires from the field to the controller.

The cost of doing this is minimal and allows flexibility for the future. Usually five correctly

sized wires will be sufficient for even the more complicated sensors.

Another option would be to place a sensor and its control at each zone in the system.

This is a good alternative when valves are spaced far apart and eachsensor is only for a

particular zone.

Installation is easier, but costs increase because of the total number of sensors being

used. Where the sensor is placed in the root zone is also critical. Ideally the sensor

should be where the majority of feeder roots are growing. Typically the sensor will be

about 4-6 inches for grass. Again it is very important to place the sensor properly to gain

the best benefit for controlling irrigation. Another often overlooked aspect is to make

quality water-proof wire connections. If more wire is needed than supplied by the

manufacturer, make sure it is approved for underground burial.

Level sensor

Definition

Level sensors are used to determine the water level which is contained in the tank. A

means of measuring the level of water in the tank is accomplished by a variety of

sensors.

Level sensors may be categorized in several ways. One way is to determine if the level

is to be measured at a given set point, or if it's to be measured continuously from

minimum to maximum. The sensor that determines the level at a single point is called a

point-contact sensor, and the sensor that measures the level from minimum to

maximum is called a continuous level sensor. The substance to be measured can be

inside a container or can be in its natural form (e.g. a river or a lake).

There are many physical and application variables that affect the selection of the

optimal level monitoring method for industrial and commercial processes. The selection

criteria include the physical: phase (liquid, solid or slurry), temperature, pressure or

vacuum, chemistry, dielectric constant of medium, density (specific gravity) of medium,

agitation, acoustical or electrical noise, vibration, mechanical shock, tank or bin size and

shape. Also important are the application constraints: price, accuracy, appearance,

response rate, ease of calibration or programming, physical size and mounting of the

instrument, monitoring or control of continuous or discrete (point) levels.

Types of level sensor

Several level sensors are available. Most of these types of level sensors include a

switch that is activated when the level reaches a specific point. Each of these types of

level sensors are:-

1. Float-Level Sensor

2. Displacer-Level Sensor

3. Vibrating-Tines Level Sensor

4. Two-Wire, Conductance-Level Sensor

This section will explain the operation of the sensors used to determine the level of

water.

1. Float-Level Sensor

The float-level sensor is the simplest level sensor to understand. From the diagram in

Fig. 1 notice that a float is connected, to an arm, and the arm will activate a limit switch

when the arm is raised. The float will be lifted when the level of the liquid is high

enough. The limit switch can be adjusted so that the exact level where the switch is

activated can be set.

Above: Fig. 1: A float-level sensor that uses a float and arm to activate a limit switch

when the liquid level is high enough.

Another type of float switch uses a magnetic-activated switch. From the two diagrams

notice the float in this type of switch has a rod connected to it just like the previous type

float-level sensor. This type of sensor has a permanent magnet connected to the end of

the rod. Fig. 2b shows that when the float raises with the liquid level, the magnet is

moved into position so that it's near the magnetic-activated switch that is mounted in the

head of the sensor. When the permanent magnet on the rod is in the correct position, it

will pull the movable magnet that activates the switch. When the movable magnet is

pulled to the magnet on the rod, the switch contacts close. Notice in that when the liquid

level drops and the float allows the rod to be lowered, the magnet will no longer have

any attraction to the switch. Small springs will then cause the contacts to move to their

normally open position. (Notice that the switch has a single-pole. double-throw

configuration so that the common terminal can be connected for normally open or

normally closed operation.) .

Above: Fig. 2 (a) A float-level sensor that uses a magnetic-actuated switch. This figure

shows the sensor at low level. (b) The float-level sensor with the sensor at high level.

2. Displacer-Level Sensor

The displacer-level sensor has a displacer element located directly in the liquid. The

displacer element has a rod that connects it to a switch, and when the level increases,

the displacer element rises with the level and moves the rod so that it activates the

switch. The switch in this sensor is exactly like the magnetic switch explained in the

float-level sensor. Fig. 3 shows an image and Fig. 4 shows a diagram of this type of

sensor. Notice that when the rod moves up, the magnet on the rod moves to where it's

located close to the magnet that activates the switch. The magnet in the switch activator

is movable, and when it's pulled toward the magnet on the end of the rod, it will activate

its contacts. When the level drops and the displacer drops and the magnet on the rod

drops, the magnet on the rod will no longer have any effect on the switch magnet. Small

springs will cause the contacts to move back into their original position.

The major difference between the float and the displacer element is that the float is

totally supported by the surface of the liquid, and the displacer is partially submerged.

This is known as the buoyancy principle. The displacer element must be slightly denser

than the liquid that it's used in. Since the displacer element is partially submerged, it's

not subjected to the action on the surface of the liquid. Since pumps and agitators tend

to make the surface very rough, a float sensor may be subjected to false actuation, or it

may wear prematurely. If the surface is subject to floating debris or suspended solids,

an additional displacer may be used that is submerged further below the surface so that

it can activate safely.

Above: Fig. 3. A displacer-level sensor from Tempsonics.

Above: Fig. 4 (a) An example of a displacer-level sensor. The displacer element uses

the buoyancy principle to allow the sensing element to be partially submerged so that

action on the liquid surface does not interfere with the sensor's action. (b) The liquid-

level sensor is measuring liquid level at an intermediate level. (c) The liquid-level sensor

is measuring liquid level at a low level.

3. Vibrating-Tines Level Sensor

The vibrating-tines level sensor uses a set of tines that acts like a tuning fork to

determine when the level of material or liquid has exceeded the level set point. An

electronic circuit makes the tines oscillate at a specific frequency. When the level of

water rises and covers the tines, it stops them from oscillating. An electronic circuit

detects the change in the oscillating frequency and activates a switch. Fig. 3 shows an

example of this type of level sensor.

Above: Fig. 3 Example of vibrating tines used to determine the level of material. The

tines are oscillated at a specific frequency. When the level of water reaches a point

where it covers the tines, they will stop oscillating. The change of frequency is detected,

which activates a switch.

4. Two-Wire, Conductance-Level Sensor

Another way to determine the level of certain liquids is to mount two wires at different

heights in a tank where the level is measured. One wire is mounted near the bottom of

the tank, and the second one is mounted at the high level. When the liquid level rises to

a point where the second wire is covered, it conducted through the liquid between the

ground wire and two wires. This conduct to the electronic circuit activates a switch.

When the liquid level is below the second wire, the system will not conduct. Some

applications of this type of sensor use additional sets is of wires that are mounted at

several points along the side of the tank to detect the level of the liquid at more than one

point. It's also important that the liquid has the properties that make it a conductor.

Another version of this type of conductance-level sensor uses one or two probes

instead of the wires. If one probe is used, the side of a metal tank is used as the other

probe. When the liquid level increases to a point that it touches the tip of the probe, a

small current is conducted between the probe and the side of the tank. If the sensor has

two probes, a small current will flow through the liquid as it rises and touches both

probes. Provides a diagram that shows examples of the probes being used as level

sensors and for alarm points. Notice that one of the sensors has four separate probes of

different lengths to indicate when the tank is one-quarter, one-half, three-quarters full,

and completely full. Each probe is connected to an indicator lamp.

Above: Fig. 5 Example of conductance probes being used to sense the level of liquid in

a tank. The probes are shown as alarms to indicate high liquid levels and low liquid

levels.

APPLICATION OF LEVEL SENSOR

To determine the level of water in the tank two wires are mounted at different heights in

a tank where the level is measured. The first and the second plate are mounted at the

bottom and upper of the tank respectively. The third plate is mounted throughout the

internal body of the tank to act as a common ground. . When the water level rises to a

point where the first plate is covered, a small current is conducted through the water

between the first plate and the third plate which is called ground. This small current is

detected by the plc .When the water level rises to a point where the second plate is

covered; a small current is conducted through the water between the second plate and

the ground. This small current is detected by the plc to indicate the water tank is full .As

a result of this the plc program will shut down the solenoid valve which is used to control

the flow of water into the tank.

Resource used

Material Resources

no Item Unit rate amount

1 Solenoid valve 1inch 1 680

2 Solenoid valve ½ inch 1 1100

3 Reducer 1inch to ½ inch 2

4 Sprinkler head type1 2 195

5 Sprinkler head type2 2 60

6 PLC (Logo) 1

7 PLC expansion module 1

8 Galvanized pipe 1inch 1

9 Galvanized pipe ½ inch 3

10 Level sensor 2 650

11 Moisture sensor 2

12 Push button 4

13 Emergency switch 1

14 LED 4

15 Water tank 1

16 T-joints(Galvanized pipe)

17 Elbow(Galvanized pipe)

18 conduit

19 Wire

20 Relay 6

21 Breaker 16A

22 Socket 2 in 1

23 Wire 2.5mm 50m

24 Wire 1.5mm

25 connector 50

26 plug 1

27 Control Panel 40cmX60cm 1

28 Track 1

28 Fisher 4

29 Cable

Human resource

1. Plumbers with two labor workers to dig and find the source of 1 inch pipe and to

make all the plumbing installation

2. Carpenter to make a control panel

CONCLUSIONS

The selected PLC type for out project is logo PLC. We select the logo plc due to its

simplicity, easy to work on it, require less space etc. The logo we used is enough to

drive the loads we have and also when we compare with S7 It is cheap and does not

need large space, additionally it has in built timers like a weekly timer and yearly timers

which is easily programmed for a week and also for a year.

From this Project We got different knowledge and we developed our conference in order

t o do any parochial work with the help of the knowledge we have in future. This project

helps as to apply the different courses we took. After doing our project we are able to

achieve our objectives.

In this project we have shown the design and implementation of PLC based automated

irrigation system with programmable logic controller, sensors and actuators. With the

flexibility, simplicity, ease of troubleshooting and minimized cost per unit product in its

useful life time characteristics of PLC automated systems is possible to build a highly

safe, dependable and intelligent control system that would require minimum human

involvement to keep daily follow-up of its operation. Considering the availability of low

price PLCs, it would be profitable for many of Ethiopian large and small scale farms

irrigation system control and to have industries their control system automated by PLCs

to increase their profitability by decreasing down time and off set point operations,

increasing overall efficiency.

Recommendation

In doing our project, from starting day to the ending day we earn different knowledge

from theoretical as well as practical aspect. We also face many challenges since the

practical part of our project has mechanical parts which are out of our field like pipe

fitting etc; this needs people with that knowledge. The lack of materials also was one

of our problems in order to do this project which is supported by practical work; it

needs material to make it real. For this reason these types of problem will be solved

if the project is done in cooperation with mechanical department.

The other challenge was to have moisture sensors because it is not available in the market.

Even if it is available, the cost is too much there for it was not possible to have. This

problem leads as to search for the different types of moisture sensors from different web

site after this we decide to work it with material we have, after we see the conductive type

moisture sensor from website we decide to test whether it works or not in our specific

application, and we done it from the material that we have in hand after all when we

cheeked it, it works successfully. After these challenge we encourage people to tray different

possibilities rather than staying idle by looking for readymade instruments.

At the implementation stage the solenoid valve clogged by gravel and red ash

(gravel) that comes with water flow through galvanized pipe so this blocked the main

valve not to be closed. A mechanism to filter the water should be done to the pipe lines.

The pipe from which we tapped for our system is 1 inch besides the project garden

site but the pressure we get is not satisfactory. The pressure varies: decreases at the

day time because the line from which we tapped gives service and increases after dusk

when there is no service. So a mechanism to get a better and constant pressure should

be worked on.

The other case is during implementation we used DC 12/24V LOGO Controller having

DC 24V expansion module which needs an extra dc power source and 24V dc relays as

a switch between the LOGO and ac voltage working outputs. This made the circuit

complicated that should not be if the controller had been an AC V LOGO which

simplifies all these. On the other-hand two of outputs of the DC LOGO are not working

this hindered to implement all the displays. So AC V LOGO is mandatory.

Since this project is done on the control of an irrigation system, for a quantitative and

qualitative value for the irrigation system a further study of a hydraulics and irrigation

should be done. Not only this must an agronomic study also be included. So it needs an

intervention of who have the knowledge in these fields.

Even though we implement this project for the garden of this campus as a sample

having shortage finance, this PLC program can be implemented for small-scale and

large-scale farms. Generally, the poor farmers and entrepreneurs should use a

developed irrigation system for a better efficiency and yield so to implement this project

it needs the support of governmental and non-governmental organizations.

References

1. NEWNES- programmable controller an engineer guide.

2. Automation manufacturing system, version 4.2, April 2003, HUNG JACK.

3. Programmable controllers theory and implementation, second edition,

L.A. BRYAN

L.A. BRYAN

4. Siemens logo plc manual.

5. Different web sites.

Appendix

A. ladder diagram

B. Functionblock diagram