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Project design and management of programmable logic controllers for electrical technology.


PLCs are kind of Digital Computers (small scale) which run on a predefined logic. Further, 'Ladder Logic' and other programs languages are used to control different applications. PLC stands for Programmable Logic Controller. Basically it's like a small computer that uses simple logic to execute automated processes, like in a factory. Let's say there is a factory that test balls for color. The desired color is Green and any other color is discarded. With the help of sensors, the PLC will determine if the Ball is of Acceptable color and either trigger a sequence that transfers the ball to a different location, or kicks the balls of different colors out from the Passable balls. The use of programmable logic controllers or programmable controller began in 1968 and by 1969; the programmable controller had its first product offspring [1], when licensed from General Motors - GM, and since that time, research and studies focused on the use of these devices instead of the old traditional, use which depends on relays, contactors, timers and the other. The PLC has high efficiency, ease of use, responsiveness of the variables, and low costs [2]. Now there are more than 600 varieties of PLC working in similar areas and the difference lies in the method of programming, the number of inputs, outputs and the voltage used.

"Programmable Logic controllers are found in thousands of industrial applications. They are used to control chemical, petrochemical, food, pharmaceutical, wastewater treatment, water treatment, nuclear, natural gas, and mining processes. They are found in material transfer and storage systems that transport and store both the raw materials and the finished products. They are used with robots to perform hazardous industrial operations, thus promoting safer operations. Programmable Logic controllers are used in conjunction with other computers to perform process and machine data collection and reporting functions, including statistical process control, quality assurance, and online diagnostics, they are utilized in energy management systems to reduce costs and to improve the environmental control of industrial facilities and office buildings" [3].

The electrical switch is a very reliable and affordable means of switching electrical systems, like lights, off and on. These electrical switches have been a rounded since the invention of electricity many years ago and not much has changed in their design. These on/off switches have become a standard in many an electrical design, due to its simplicity and ease of operation. Recently these same switches are making a difficulty for electrical designers to solve some complex switching requirements like wall clutter, switching from multiple locations, flexibility to assign switches to other loads without major renovations, tie-in with security and other electrical systems and control from personnel computers to name a few. Electrical switching using a Programmable Logic Controller (PLC) will help to solve all these and future switching requirements. Programmable Logic Controllers are not a new product in the market place. These controllers have been used for over 50 years in the industrial world. They have proven to be a very reliable and affordable means of switching complex electrical systems in many manufacturing and large plant applications [9].

The PLC hardware is digital electronic devices with memory can be programmed to store commands or information and the implementation of various operations such as logical operations, arithmetic and timing. There are several companies (PLC's) devices such as Siemens who produced SIMATIC 200, SIMATIC 300, and SIMATIC 400. Allen Bradley Inc., Mitsubishi and many others. Each company has its own software, but all accomplish the required job of the (PLC's) [4].

Historically, process control of a single or a few related devices have been implemented through the use of banks of relays and relay logic for both the control of actuators and their sequencing [5]. Speed and accuracy are not available in electromechanical devices like relays, contactors and timers was used as controller before they were not precise or rapid in response this led to lack of speed and accuracy. Also any error in the circuit requires them to be reconnected correctly. A change in function or system expansion required extensive component changes and rewiring [4], any change in the requirements of the control system change in the coupling scheme control system consisting of a set of switches and relays and timers ... etc, or change some of the pieces cut off the other.

The advent of small, inexpensive microprocessors and single-chip computers, or microcontroller units [5], brought process control from the age of simple relay control to one of electronic digital control while neither losing traditional design methods such as relay ladder diagrams nor restricting their programming to that single paradigm

Therefore, PLC's provide many advantages over conventional types of control, these are [6,7]:

1- Flexible control, change any industrial process by modifying the program.

2- Maintenance and the discovery of faults in the PLC system are easily seen on the PLC screen.

3- Small size.

4- Has characteristics that are not available in ordinary computers.

5- Ability to be engaged with other PLC devices or other computers.

6- Instant monitoring system.

7- Low cost.

8- Durability, it is designed to withstand moisture, vibration and noise.

9- PLCs can be used in commercial and residential electrical designs to solve the complex switching requirements.


The PLC programs of two years level course in electrical technology institute have been built and designed based on the following main topics [8]:

1- Introduction

2- Technical terms

3- Number systems and codes

- Define the decimal, binary, octal, and hexadecimal numbering systems and demonstrate conversion from one numbering system to another.

- Perform basic addition, subtraction, multiplication, and division of binary numbers.

4- Definition of the terms bit, byte, word, least significant bit (LSB) and most significations bit (MSB) as they apply to binary memory locations.

5- Usage of the proper manual for programming or installation of an S7-200


6- Different types of PLC:

- Non- programmable controller

- Programmable controller

- Comparison between the programmable controller and electromagnetic control circuits

- Comparison between the programmable controller and the logic circuits

- Advantages of PLC's

7- Installation of PLC

- Describe the general classes and types of PLC memory.

- Describe the basic circuitry and applications or discrete and analog input and output (I/O) modules.

- Identify and explain PLC I/O addressing formats

- Describe the communication bus.

8- The principle of the work of PLC

9- Identification and explanation of programming languages. The three most common types of languages encountered in programmable Logic controller systems are as follows [3] :

- Ladder logic (LAD).

- Function block diagram (FBD).

- Statement list (STL).

10- Choice of PLC equipments.

11- Equipments associated with the programmable logic controllers - PLC

- Digital input devices

- Analog input devices

- Digital output devices

- Analog output devices

The load of theoretical lectures is about 48% which is equivalent to 30 theoretical contact hours, and about 52% dedicated to laboratory, this is equivalent to 64 contact hours. Students are also allowed to use the PLC equipments in their convenience at other times, while the assessments in the PLC course follows institution rules have been designed as following in Table 1.

While, the final exam concentrates on: how would you approach this problem, how would you structure this code, etc. This is very similar to problems given during the course, with the exception of (no) actual programming.


The PLC controls of the machines are various industrial processes, which are monitoring the inputs that take decisions based on the data, and the implementation of those decisions on the outputs to be presented through the following two models:

3.1 Counting and packaging bottles model using PLC

Electronic Circuit. This circuit controls the conduct belt of a motor; the signal is cut through water bottle. As the bottle passes, the light signal between the sender and receiver will be cut. The change in the optical resistance value will be compared to a reference; an electric signal comes out that causing an ignition to the transistor. The transistor controls a relay, which has an open reel; this will give pulses to a counter that is programmed in the PLC. This operation will be repeated with each passing bottle until the number of counter pulses reaches to the required limit. The counter operates the relay that controls the motor and the timer. The timer controls the period of belt return to its original place, putting the cartoon down back to its place and zeroing the counter to put the cycle back to start which is shown in figure (1) below.



Ladder Logic Diagram (LAD). Pulses passes through the key counter I0.0, and upon reaching of pulses to the calibration limit, the counter C0 closes the timer key T32 and the output key Q3.0. If a period of time determined by the timer operation, the timer switches off the key related to it which resets the counter to zero and separates the voltage from the timer and output Q3.0, then the cycle process is repeated which is presented by Figure 2.

Statement List (STL) and Method of Connections. The statement list is counting process and packages the water bottles on the conveyor belt by cutting the light signal using the PLC system. This can be seen through the figure 3 while figure 4, shows the method of connections to PLC.
Figure 3. Shows the behavior of STL for actions to count the
bottles and packaging of water on the conveyor belt by cutting the
reference using the system (PLC)

1 //


3 //

4 //Press Fl for help and example program

5 //


7 NETWORK 1   //NETWORK TITLE   (single line)


10 //

11 LD    10.0

12 LD    T32

13 CTU   CO,   +12



16 LD    CO

17 TON   T32, +5000



20 LD    CO

21 =     Q3.0



24       MEND


3.2 Control of agricultural land irrigation model using PLC

Electronic Circuit. The project consists of an electronic circuit with an optical resistance; upon sun rise the optical resistance will sense the incident light to send a command to the relay to close its open connections. The process of irrigation will start using ladder diagram program; this program was written to control the irrigation of 3 agricultural areas.

The system will stop its work till the next morning and irrigation will continue in the same way when the sun rises up. Knowing that the irrigation time is about 30 min per day for each agricultural area, it can be increased or decreased according to the need by PLC and this case have been presented and shown in figure (5) below.


Now, the optical resistance in the circuit shown in figure (5) has been used when the sun rises the optical resistance senses the light falling on it to give a command to a relay that closes the open contacts and the process of irrigation begins, as follows:

1- When closing the relay contacts, the timer (T1) and the electric valve (EV1) operate, then the system begins to irrigate the first agricultural area.

2- When the timing of the first timer (T1) ends, it opens its closed contacts and stops the electric valve (EV1), thus the irrigation process stops in the first agricultural area.

3- When the timer (T1) closes its contacts, the timer (T2) and the electric valve (EV2) operate, and then the irrigation of the second agricultural land begins.

4- When the timing of the timer (T2) ends, it opens its closed contacts and stops the electric valve (EV2), thus the irrigation process stops in the second agricultural area.

5- When the timer (T2) closes its contacts, the timer (T3) and the electric valve (EV3) operate, and then the irrigation of the third agricultural land begins.

6- When the timing of the timer (T3) ends, it opens its closed contacts and stops the electric valve (EV3), thus the irrigation process stops in the third agricultural area.

In addition to that and to get more precise model, the electrical circuit of the irrigation system has been shown in figure (6) below.


3.2.2 Ladder logic diagram (LAD)

The ladder logic diagram which is shown in figure (7) below can be described and analyzed through the following points:

1- When closing the relay contacts (I0.0), the counter (C0) operates.

2- When the counter closes its contacts (C0), the timer (T32) operates, which is represented by the timer (T1) in the electrical circuit shown in figure (6).

3- When the counter (C0) closes its contacts, the output (Q3.0) operates. The output (Q3.0) is an electric valve (EV1) of electrical circuit shown in figure (6).

4- When the timing of the timer (T32) ends, it closes its open contacts and operates the timer (T33). The timer (T32) is represented by timer (T2) and output (Q3.1) is represented by the electric valve (EV2) in the electrical circuit as shown in figure (6).

5- When the timing of the timer (T33) ends, it closes its open contacts and then the timer (T34) operates. The timer (T33) is represented by timer (T3) and output (Q3.2) is represented by the electric valve (EV2) in the electrical circuit as shown in figure (6).

6- When the timing of the timer (T34) ends, it closes its open contacts.and resets the counter to stop the operation of the cycle.

7- Then the system will stop to operate till the next morning, where the process of irrigation will resume in the same way described previously at the sun rise, knowing that the time of irrigation of one agricultural area is set for half an hour per day and can be increase or decreased as required by the programmable logic controller - PLC.


3.2.3 Statement List (STL) and Method of connections

The statement list and the method of connections to PLC for irrigation system have been presented and shown the figures (8) and (9) below.

Figure 9. Shows the statement list--STL for the irrigation system

1 //


3 //

4 //Press Fl for help and example program

5 //


7 NETWORK 1   //NETWORK TITLE   (single line)

8 //

9 //


10 //

11 LDN   10.0

12 LD    T34

13 CTU   CO, +1



16 LD    CO

17 TON   T32, + 3000



20 LD    CO

21 AN    T32

22 =     Q3.0



25 LD    T32

26 TON   T33, +800



29 LD    T32

30 AN    T33

31 =     Q3.1



34 LD    T33

35 TON   T34, +600



38 LD    T33

39 AN    T34

40 =     Q3.2





The Programmable Logic Controllers (PLC) course is a 3 credit hours course for electrical technology students. Fundamentals of PLC hardware (physical components) and software (control program), programming and diagnostic troubleshooting, are covered in lectures. Then the students are expected to design a PLC project based on the subjects covered in the lectures. The designing of a project afford the students an opportunity to apply the knowledge acquired from the theory part to solve any problems to be aced.

PLC design projects have been designed and analyzed to fulfill the requirements of reality and demand. In addition, few models have been built, analyzed, and discussed as a case study to be offered in the course syllabus. Moreover more applications might be performed in the designing of the course according to the requirements. At the end of the course the students will be more creative with developed abilities and skills in solving practical problems.

Also, course assessment can reflect an outstanding response of students to the design projects. Oral skills of the students can be enhanced through writing the final year reports.


I would like to express my appreciation and thanks to Mr. Abdulaziz Al-Naqeeb the ex-dean, Mr. Abdullah Othman Anaam the dean's deputy for educational affairs, Mr. Yaseen Mohammed Moqbel the dean's deputy for academic affairs; of the Technical Industrial Institute at Haddah - Sana'a - Yemen, for their guidance and encouragement during the time I spent at the institute.

I would like to express my sincere thanks to my two former students Abobker Al-Ghawil and Shoaib Al-Qdesi and to all of my students for accomplishing their graduation projects.


[1.] Bryan, L.A.; E.A. Bryan (1997). Programmable Controllers: theory and Implementation (2nd Edition) Industrial Text Company, U.S.A.

[2.] Guo, L. (2009) "Design Projects in a Programmable Logic Controller (PLC) Course in Electrical Engineering Technology" The Technology Interface Journal 10, (1).

[3.] Hughes, T. A. (2001). Programmable Controllers, Third Edition, the Instrumentation, Systems, and Automation Society--ISA, Volume EMC 64.01

[4.] Ahmad Fouad Alwan (2009). Fundamentals of Programmable Logic Controller--PLC (1st Edition)--Dar Al-Uns for Printing and Publishing and Distribution, Damascus, Syria.

[5.] PLC : Definition from

[6.] Siemens Technical Education Program - Basics of PLC's.

[7.] Bolton, W. (2006), Programmable Logic Controllers, Fourth Edition, Published by Elsevier Newnes.

[8.] Vocabulary curriculum for technical institutes - Electricity specialty--The Fundamentals of Programmable Logic Controller (PLC)--General Administration for Curriculum & Educational Facilities--Ministry of Technical Education and Vocational Training , Sana'a--Yemen.

[9.] Eugene Kowch (1996). Electrical switching using a Programmable Logic Controller.

Ahmad Fouad Alwan

Electronic Department, Technical Industrial Institute at Haddah Sana'a, Republic of Yemen (formerly)
Table 1. Shows, the ddistribution of semester course work.

Assessment         Percentage %   Due

Assignments for        30%        To be announced accordingly
Lab works
Mid-term exam -1       15%        To be announced accordingly
Mid-term exam-2        15%        To be announced accordingly
Final Exam             40%        To be announced accordingly
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Author:Alwan, Ahmad Fouad
Publication:International Journal of Emerging Sciences
Article Type:Report
Geographic Code:7YEME
Date:Sep 1, 2012
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