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Industrial System Automation and Control

Introduction to Programmable Logic Controller

Programmable logic controller is a well-known controlling device used to control the production process at industrial level where bundle of products are being manufactured in seconds. PLC is being used for the batch products. There are different manufacturing industries which are producing PLC units to control the large machines. These PLC are organized and trained using the ladder logic or other programming to perform different functions. PLC hardware basically consists of a computer in which the PLC is programmed using ladder logic or any other programming. The second part is the input output unit of the PLC in which the input is given to the controller and output is sent to the device to which the PLC is controlling. A PLC consists of number sensors including temperature, proximity and light sensor. The major function of these sensors is to get the run time data from the environment and thus help the PLC to operate according to that data. There is another important part of this PLC known as HMI which is human machine interface. This HMI consists of a screen which tells the helps the user to see the data regarding the functions of PLC and also this part of the PLC is customizable and the user can create button according to his requirements to control the process undergoing in this industrial area controlled by the PLC. We can divide a PLC in three basic modules which are power supply module, input/output module and CPU module.

"Programmable Logic Control" PLC Systems

After tackling the definition of PLC and the short history of its appearance on the industrial scene during the 70s it should be underlined that at a distance almost fifty years after its birth, having acquired significant processing skills and having over time drastically reduced the cost of hardware, this class of equipment, retains a significant importance in the field of automation. The factor that allows its constant diffusion concerns the ever increasing number of technicians specialized in dealing with the language that includes both the simplest (logic Boolean), is the most complex created using logics similar to those of the microcomputers. It should be emphasized that the adaptation of the training of technicians has enjoyed a strong impulse when, following the massive diffusion of this technology, both in professional institutes and in engineering faculties have been included special training courses on programmable logic, up to the point where the study of PLC programming languages has been fully included in the degree programs in Electronic Engineering at Automation address.

The Hardware of the PLC Systems

In the industrial field there are very different needs in the field of automation of continuous and discontinuous machines and processes. Consequently both hardware and applications of PLC software can be very different from each other. Since PLCs usually they operate at the cell level and at the command level, consequently there are various families of products dedicated to different applications. The following diagram proposes a simple characterization based on the type of hardware:

Compact and expandable PLCs mainly use Logic Languages (Ladder), while the modular PLCs the advanced languages, these languages have been identified and codified, as we will see, in the IEC 61131 standard.

Modular PLC

At the cell level and for highly complex commands, modular, based PLCs are used on open structures, with hardware very similar to PMC and of equivalent quality level. These are structures based on the use of multiple CPUs that operate simultaneously. In effects for the implementation of complex machine commands, functions of automation or process supervision, the boundary between modular PMC and PLC multiprocessor is very thin and is often limited to basic software. On microcomputers In fact, the basic software consists of a real-time multitasking operating system where the application software must be developed in high level language (Eg "C") by highly qualified personnel, as the system can often be excluded operational and have complete hardware control. In PLCs the operating system cannot be eliminated, its presence is essential on board CPU, which is detrimental to the performance time of the programs, but it benefits the reliability of the software Pseudo graphic programming by ladder or block diagram functional or list of macroinstructions and library macro functions is therefore much simpler reliable and can be referred to not highly qualified personnel. The simplicity of the application of the PLC software may be limiting with respect to application of a certain complexity, as happens in the case of modular PLCs. It therefore becomes necessary therefore resort to more powerful languages (eg IEC61131-3) but which require personnel qualified, just like industrial microcomputers.

In terms of performance, even the difference between the PLC and the PMC is not of great importance, given that the most recent and powerful modular PLCs allow a cycle time in the order of milliseconds. Cycle time and speed in program execution are parameters of considerable importance if the PLC is used for the realization of controls digital. Although historically the control functions assigned to the PLCs referred to slow processes (eg. temperature control), it is now possible to find PLC used for faster and faster process control (position control, high axis control speed,…). The modular PLCs are then essentially employed in critical applications in terms 55 processing time and multi-CPU architecture and they are very powerful systems used in centralized architectures. The limit of centralized architectures in many applications consists of the criticality of the wiring, so today it seems that powerful PLCs modular systems are giving way to distributed architectures made up of several smaller PLCs complexities placed where they are needed. This migration from centralized architectures towards distributed architecture is made possible by efficiency (determinism, very low jitter,) of the new industrial communication techniques.

 Expandable PLCs

 If the application does not require a centralized multi-CPU architecture, but for example if tasks can be divided among several PLCs communicating with each other on a high network efficiency (distributed architecture) or the tasks can be performed by a single CPU possibly supported by functional modules, expandable PLCs are used.

Operating Principle of the CPU

To better understand the structures of the 3 aforementioned architectures (compact PLCs, expandable, modular), it becomes necessary to describe the operating principle of generic PLC in its simplest sense, i.e. referring to a PLC consisting of a CPU and generic digital input / output points.

The CPU is a card based on a processor, memories, generation interfaces and bus management to peripheral modules and is equipped with a resident operating system. The operating system takes care of providing a structured, robust and real-time environment reliable for the execution of the application program. He also deals with the management of particular diagnostic functions (buffer battery status, initial check sum of the memories,), the management of internal timers and to implement the protocol for means of which, through the appropriate development package, it is possible to transfer and test the programs.

The CPU of a PLC can operate in two different ways:

  • STOP (also called PROG or TERM)
  • RUN

In STOP mode the CPU does not run the application program, but resides in its own operating system where it receives commands from a programming unit (typically a PC) for configuration, storage of the application program and diagnostics.

In RUN mode, the application program is instead executed under control of a resident operating system. The operating mode remains stored also following a power failure. When you start the mode RUN, the operating system performs initialization procedures, and then enters an operating mode with cyclic architecture, called the CPU operating cycle the figure shows the sequence of operations carried out in the case of normal CPU RUN operation (duty cycle or scan cycle). Reads him inputs (IPI) Executes the program Communicates Executes the self-diagnosis writes the outputs (IPU) from the cycle shown in the figure it is clear how the CPU performs, in addition to the program application, also other tasks. It follows that the cycle time depends on the length of the application program, but in any case it can never drop below a limit value which generally settles around the milliseconds.

In the case of very simple programs this value is dominant, given that the average time used by a recent PLC in carrying out an instruction is less than microsecond. The PLC is generally based on a CPU built around a microcontroller, or rather a microprocessor dedicated to peripheral management and more in general, I / O. Microcontrollers execute programs written in machine code while, as mentioned above, the operator builds the app programs To optimize the execution time of the application program, called "source" written in graphic language, it should be compiled up to obtain an "executable" in machine language to be stored and run by the microcontroller. This solution, however, severely limits diagnostics as it is lost correspondence between machine instruction and graphic instruction. In this way also, the entire program would be recompiled with each modification of the user program, making the system more vulnerable to programming errors.

The development system then processes the "source" in order to provide output a program written in an intermediate language, which the microcontroller interprets, which is decoding instruction by instruction.

The Application Software of the PLCs

Once the user program has been processed, the program is complete after commissioning it must be placed on non-volatile memories (usually EPROM or EEPROM) in such a way such that even if the buffer battery is discharged, the program is not lost. For 60 seconds as regards the data, these are stored in RAM, suitably supported from backup batteries (backup duration greater than 10h) to preserve data in case of power failure. Many PLC models allow dividing this data, in a fixed or settable way, in birds (or non-retentive) and non-volatile (or retentive). In the first case, the data is reset each time the program is restarted (for example when the PLC is restarted) while the rest are kept in the state they had before the arrest. For facilitate its management at the user program level, the data are structured in a way logical by dividing the space available in memory according to various types different size and operators.

  • Input process images (I)
  • Process images of the outputs (Q)
  • Variables (V –variable-)
  • Variables (L –local-)
  • Variables (M –merker-)
  • Variables (S –sequence-)
  • Variables (SM –special marker-)
  • Timers (T –timer-)
  • Counters (C –counter-)
  • Analog inputs (AI - analog input)
  • Analog outputs (AQ –analog output-)

Access to variables is typically byte-based; however bit-by-word access is provided (even addresses) and double word (addresses divisible by 4). Process images, as seen previously, these are the RAM images of the state of logical inputs and outputs. The inputs are sampled and stored in the process images of the inputs (IPI) before the execution of the application program cycle. The application program operates on IPI and IPU (process images of the outputs), therefore at the end of the cycle application program the IPUs are written on the outputs.

SCADA: Assistance Between Man and Machine

The acronym SCADA originates from the English definition; "Supervisory Control and Data Acquisition ”referring to distributed IT systems used for control and monitoring of industrial processes and infrastructure systems.

A SCADA system is able to make structures, machines and apparatuses also dialogue in different positions within a production plant, reporting to any state of the components and devices. This definition implies a system which is mainly responsible for carrying out the following homework:

a) Support a series of video pages that depict the plant / machine covered by the control and in certain pages allows the conduction through simple graphic commands and / or with specific instructions. As with recent Smart Phones, I latest generation SCADA systems can have a touchscreen graphic interface

b) Through specific hardware predispositions the SCADA has disks for the archiving of process data and for their management in the form of statistical trends.

This information is stored in a special data base that is normally standard type, i.e. it allows data exchange between the SCADA system and the MES system which we will see in the next paragraph

c) An essential feature of SCADA systems is that they are equipped with layered network connections. To communicate with the PLCs or with other devices present in the field, whether they are isolated computers and / or special machines equipped with proprietary automation, the mission of the SCADA is precisely to get in contact with all the components present in the manufacturing environment, helping to integrate all the information in a single point process / machine / system.

Configuration of SCADA Systems

From the hardware point of view, the most typical configuration of these solutions includes:

A Desktop or Touch Panel Personal Computer which, through specific software, is able to periodically collect data from programmable logic (PLC) and process them to then obtain useful information to be recorded on disk. The supervision PC allows you to view the processed data (real and historical values) on the screen, allowing the operator to monitor in real time the information of all the plants controlled by the SCADA system, thus allowing prompt intervention in the event of need. The system data are recorded in the database and allow you to monitor all system states and all alarms that have occurred.

One or more Programmable Logics (PLC) used to control and manage the system. Specifically, the PLCs read the status of the sensors and instruments in real time measure, to then process and implement all utilities according to the designed logic plant.

A communication system between the programmable logics and the supervision PC the PLC sends the data to the supervisory system through one or more communication lines (networks, LAN, WAN or fieldbus)

The integration of special equipment, equipped with microprocessor systems owners, because they are specific (see online scales, analysis tools, load cells for online weighing, etc. ...)

Functional Description of Code

The program that we write for the automation controlling through PLC should temporarily started in program without any conditions. We can also set and reset the program at any time while working on a station. Ladder logic is a sequential programmed which means that every next step is only executable once the previous step has executed successfully.

The first step in the program that we observed was the start and stop functions of the program. A latching circuit is used for this because the push button for starting the process is momentary. The code for the input handling is the part of code to start the program and defining the input ports and output ports which will play the essential role in the operation of the PLC based modular production system.


The code for handling is designed in such away H$ at pin one is connected with the indicator light that indicates the normal functionality of the machine. Timers are being set in such a way that it firs of the entire griper which is picking the object is jammed after it picks up the object and then the timers start running. If T5 is set to drop the object immediately and the in case of timer T6 T7 and T8 they leave the upstream and downstream timer and T9 is fast drop timer that drops the object at the place of it origin. After this process the push button is on and the timers T11 stops the downstream timer and timer T12 is operating for the purpose of pressuring the downstream leave timer.T14 is for the fast pick up of the object and the T15 and T16 are for the fast moving downstream of the machine.


This stage is the sorting of the products of objects picked and dropped by the machine. First of all the conveyer belt motor is turned on and switch 1 and 2 are extended. If the station on the belt is occupied by another object then the red indicator is turned on showing that the place is not right to drop the object. And light is reset after a small interval and when the space is available it will let the conveyer inform that the place is available. And the object is slides. For the purpose of observing this process if the work piece is not black the object is sided full and emergency stop button is unlocked which was normally closed and the sorting button is reset to its initial position successfully. Thus it completes the cycle of sorting and returns back to its original position.


In this step the program observes the lower lifting cylinder and then raises the cylinder. The ejecting cylinder is extended and indicator lights are tests if the free work piece is available or not and also the height of the work piece. If the height of lifting cylinder is correct then it is lifted then lowered and ejected. Then the downstream station is observed if it’s free and then the stop button and the manual switch are reset. A cycle is thus completed and testing station returns to its original position. In case of free downstream station lift is initialized and the slider is stopped. This is how the previous stages and their functions are tested.


In the stage of turning or processing the drilling motor is turned on and the indexing table motor is also turned on. Firstly the drilling unit is lowered and secondly it is raised up and then the work piece is fixed for the availability of space. If the station is occupied the indicator light is turned on and then reset once the station is free. If the work piece is out of order then the error message will be displayed by the indicator. After that the drilling part is lowered down and the drilling unit is kept in lower and upper drilling position. When the downstream station is free process is initialized to the station and then in the position of turn table it is counted for some time to process the commands. After this the work piece at start store is checked and polished and punch test is finished and the system is pushed back to its original position to start new processing.

Bill of Materials

A bill of materials for the up gradation of MPS system based on Allen Bradley Rockwell PLC technology is given below in which all the components and materials which are required for the up gradation are listed. For this purpose I did a market research in order to find the components having good performance and reasonable price. After comparing a number of components I decided the best one for this project which is listed below along with their price. In this bill of materials the name of title, its number of units used, price per unit and total price is given.

Part no

Part Name


Unit cost $

Cost $










































Total cost


Refrences for Industrial System Automation and Control

Zheng and J. Fang, "PLC Introduction," 2012 IEEE 26th International Parallel and Distributed Processing Symposium Workshops & PhD Forum, Shanghai, 2012, pp. 2347-2348, doi: 10.1109/IPDPSW.2012.356.

Sanver, E. Yavuz, C. Eyupoglu and T. Uzun, "Design and implementation of a programmable logic controller using PIC18F4580," 2018 IEEE Conference of Russian Young Researchers in Electrical and Electronic Engineering (EIConRus), Moscow, 2018, pp. 231-235, doi: 10.1109/EIConRus.2018.8317072.

Sheng Qiang, X. Z. Gao and Xianyi Zhuang, "PLC-based control systems for industrial production of fuel alcohol," 2002 IEEE International Conference on Industrial Technology, 2002. IEEE ICIT '02., Bankok, Thailand, 2002, pp. 827-832 vol.2, doi: 10.1109/ICIT.2002.1189274.

Moallim, J. Lee and D. Kim, "Wireless control and monitoring using Programmable Logic Controller (PLC)," 2017 17th International Conference on Control, Automation and Systems (ICCAS), Jeju, 2017, pp. 1763-1767, doi: 10.23919/ICCAS.2017.8204259.

G. Ioannides, "Design and implementation of PLC-based monitoring control system for induction motor," in IEEE Transactions on Energy Conversion, vol. 19, no. 3, pp. 469-476, Sept. 2004, doi: 10.1109/TEC.2003.822303.

Sapena-Banó et al., "Automatic translation of Programmable Logic Controllers (PLC) control programs in packaging machinery," 2014 9th International Microsystems, Packaging, Assembly and Circuits Technology Conference (IMPACT), Taipei, 2014, pp. 445-448, doi: 10.1109/IMPACT.2014.7048380.

Dong Yulin and Cui Wenchong, "The study on distributed control system based on PLC," 2010 2nd International Conference on Industrial and Information Systems, Dalian, 2010, pp. 188-191, doi: 10.1109/INDUSIS.2010.5565647.

Yong-Qiu, "Research on the PLC Technology Solutions in Four-Story Elevator Control and Renovation," 2015 8th International Conference on Intelligent Computation Technology and Automation (ICICTA), Nanchang, 2015, pp. 780-783, doi: 10.1109/ICICTA.2015.198.

Remember, at the center of any academic work, lies clarity and evidence. Should you need further assistance, do look up to our Computer Science Assignment Help

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