Detailed Explanation of Programmable Logic Controller Systems

This report offers a comprehensive overview of Programmable Logic Controllers (PLCs), essential devices in modern automation. It begins with an executive summary and table of contents, followed by an introduction highlighting the PLC's role in industrial automation. The report then delves into the different styles of PLCs, including unitary, modular, and rack-mounted systems, detailing their features, advantages, and disadvantages. It also explores switching voltages and the various sensors that can be connected to a PLC for industrial operations, such as human-machine interfaces, SCADA systems, and cyber security applications. The report further discusses switching voltage and opto-isolators in PLCs, along with explanations of programming, storage, and communication methods. Figures illustrating PLC types, mechanical, and electrical architectures are included to enhance understanding. Finally, the report concludes by summarizing the key findings and emphasizing the efficiency of PLCs in addressing circuit requirements, making it a valuable resource for electrical engineering students and professionals. The report includes references to support the information presented.

Running head: EXPLANATION OF THE PROGRAMMABLE LOGIC CONTROLLER
Explanation of the programmable logic controller
Name of the student
Name of the University
Author note

1EXPLANATION OF THE PROGRAMMABLE LOGIC CONTROLLER
Executive summary
This report includes a discussion of the PLC devices. The chosen country is United Kingdom.
The report includes a discussion of the three styles of the PLC devices. This report also includes
a discussion of the sensors corresponding to a PLC and the switching voltages. Moreover, this
report lists various sensor devices that can be used as a PLC. Moreover, the switching voltage of
the PLC is successfully described in this report. Furthermore, both the electrical and the
mechanical architecture corresponding to the electrical and mechanical format is shown in the
report.

2EXPLANATION OF THE PROGRAMMABLE LOGIC CONTROLLER
Table of Contents
Introduction......................................................................................................................................3
Discussion........................................................................................................................................3
Styles of plc.................................................................................................................................3
Switching voltages and sensors...................................................................................................5
Switching voltage and opto-isolators in PLC..............................................................................6
Explanation of programming and storage....................................................................................8
Communication..........................................................................................................................11
Conclusion.....................................................................................................................................12

3EXPLANATION OF THE PROGRAMMABLE LOGIC CONTROLLER
Introduction
In the modern industries, the use of a programmable logic controller is mainly adopted
for addressing needs of automation for the electronic and mechanical processes. These devices
are very specific and are used in the industries because of their special ability to withstand cold,
heat and dust. It is usually made using microprocessors that is programmed using the computer
languages. This program is made in a computer and is then transferred to the device using a
cable. This report includes a discussion of the three styles of the PLC devices. This report also
includes a discussion of the switching voltages and the sensors corresponding to a PLC.
Moreover, this report lists various devices that can be used as a PLC. Furthermore, this report
also includes a discussion about the processing of the information in PLC. Lastly, this report
discusses about communication of information aspects.
Discussion
This section of the report discusses about the main concepts of the plc devices.
Styles of plc
There are three different types of PLCs. They are the unitary, modular and the rack
mounted PLCs.
Unitary PLC
The unitary PLC consists of various features which are included in a basic system. These
features are the presence of a power supply and the presence of a main module. The main
module consists of a CPU (central processing unit) for processing of the instructions (Bolton

4EXPLANATION OF THE PROGRAMMABLE LOGIC CONTROLLER
2015). The PLC also consists of a input and an output module and the device is usually fitted to a
machine.
The major advantages of them are that they are compact and small. In spite of this, they
hold all the basic components in the unit. Another advantage is that they can give easy access
and is termed to be portable. Lastly, they are very cheap.
The main disadvantages of them are that the expansion of them is not possible. Another
disadvantage is that if any feature of the device fails then the whole device has to be replaced.
Modular PLC
The modular device can be slotted together for developing a system. The system of the
modular PLC is similar to the unitary PLC. With the core module, the device can use various
other modules of input and output for needed requirements.
The main advantages of the modular PLC is that the system can be expanded by
increasing the number of input and output modules (Khakhi, Salman and Shabir 2017). In
addition, if there is failure of any one portion of the device, it will not affect the functioning of
the whole device.
A major disadvantage of the modular PLC is that they are considered to be expensive
when compared to the unitary PLCs.
Rack-mounted PLC
The implementation and design of this PLC is similar to the modular system. These
modules are placed on standard cards which are then slotted in racks to form a control cabinet.
The modules communicate by using the rack.

5EXPLANATION OF THE PROGRAMMABLE LOGIC CONTROLLER
The first advantage of these types is that they can be easily modified and expanded. The
next advantage is that they have more ports for input and output operations than the other types
of PLC.
A major disadvantage of this type of PLC is that this is the most expensive among the
three different types of PLC.
Figure 1: Types of PLC
(Source: Stone, Temple and Baldwin 2015, pp 45)
Switching voltages and sensors
Almost all of the PLC units consist of their own power cards. This acts as an SMPS for
providing electricity to the rack associated. This in turn is used to send supply to the various
cards. The input required for a power module is considered to be 220V of ac current or 24V of dc

6EXPLANATION OF THE PROGRAMMABLE LOGIC CONTROLLER
current. This in turn is converted to the required voltages for the cards which are 12V dc, 24V dc
or 5V dc.
There are various sensors that can be connected to a plc for addressing industrial
operations. The first type of industrial activity is the human-machine interface (HMI) where
various sensors are attached to a plc for capturing gestures. The next process is the Supervisory
Control and Data Acquisition (SCADA) which utilizes the use of a plc for monitoring. The third
activity is the Object Linking and Embedding for Process Control (OPC) which is utilized for
data analysis and gathering (Stone, Temple and Baldwin 2015). The fourth sensor used is the
Prognostics and Health Management (PHM) framework which is mainly used in health related
industries. Lastly, for the cyber security industry, the Cyber-Physical Production Systems
(CPPS) is utilized which helps in future attack analysis against cyber threats.
Switching voltage and opto-isolators in PLC
The switching output voltage is usually considered to be in between the range of 0 to 10V
dc. Depending on the types of PLC, there can be other ranges of the output. These are -5 to 5V
dc, -10 to 10V dc, or 0-5V dc.
There are various types of sensors which can be connected to a PLC. This will be used
for addressing the requirements of an industry. The first type of sensor is the air flow sensor.
This helps in determining the speed of air flow and the property is utilized in aircraft industry.
The next type of sensor is the temperature sensor which is used for checking the temperature.
This is utilized in various industries. The next is the position sensor which helps in determining
the position of an object and is mainly utilized in automation industry. The fourth sensor is the

7EXPLANATION OF THE PROGRAMMABLE LOGIC CONTROLLER
vibration sensor which senses vibration or changes in the surrounding. This is heavily used in the
climate sensing department. The last type of sensor is the liquid level sensor which can be used
to determine the level of the liquid and is mainly deployed in underwater industry.
The opto-coupler is also known as a photo coupler which can be used to transfer
electrical signals among isolated network components. This is usually done by utilizing light.
This reduces the need of affecting circuits. The main purpose of the opto-coupler involves
utilizing a light source for electrical requirements. It is mainly done by utilizing LED equipment
which is done by converting electrical energy to light. Another requirement is the photo sensor
which is used to generate electricity or module electric current.
The main benefit of the opto-coupler equipment is to block the high voltage currents so
that any disruption in a part of the system may not be able to cause problems to other parts. It
converts an electrical signal to a light signal and then transmits it to the receiver where it is then
converted to electricity.
Figure 2: Opto-coupler

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(Source: Levenson, Nelson and Adegbege 2017, pp 14415)
Explanation of programming and storage
The plc operations are considered to be very simple. The most widely accepted logic is
the ladder logic. This is done by mainly communicating with various parts of a plc. There are
five different steps in the operation of a plc. This involves storing, execution and instruction. The
pressing of input switch is the first operation. After this, the input module is used to place 1 in
the data table. This results in putting of 1 in the output module. This causes in establishing of
connection among various data points. Lastly, the output module gets activated. This process is
followed by the scan cycle which involves input scan, execution of the program and output scan.
Lastly, this is followed by a logic scan.
CPU
This is used to check any errors in the PLC. The logic operations, arithmetic operations
and interface related operations are performed using the CPU.
ALU
This is the arithmetic and logical unit of the device. This is mainly utilized in the CPU
(central processing unit). This forms the building block of it. It utilizes a digital circuitry to
compute the necessary requirements.
ROM
This is termed as the read only memory. The ROM is mainly used for dynamic memory
allocation. When the power of the circuit goes off, any instructions stored in it also gets lost.
RAM

9EXPLANATION OF THE PROGRAMMABLE LOGIC CONTROLLER
This is termed as the random access memory. This is a non-volatile memory and aby
instruction stored in it does not get lost after power loss.
Registers
Registers are termed as data files which are used to store bits of information. They are
mainly utilized during the execution of a program.
Busses
These are termed as communication busses and are mainly used to communicate among
registers. This can also be termed as a signal for transfer.
Flags
These units of a PLC are used to denote the operations. It consists of a special bit which
determines the course of operation. It can store 1 or 0.

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Figure 2: PLC mechanical architecture
Source: Created by the author

11EXPLANATION OF THE PROGRAMMABLE LOGIC CONTROLLER
Figure 3: PLC electrical architecture
Source: Created by the author
Communication
The communication among the various components is usually done by utilizing four
methods. These are the twisted pair cables, coaxial cable, fiber optics and networks.
The twisted pair cables are the most widely used for electrical circuitry. The main
advantage of it is its simplicity. The disadvantage of it is the lack of security features. The
coaxial cables are upgraded and consist of a rounded sheath which helps in efficient
communication. The presence of complexity in installation is a disadvantage to it. The fiber