What is a PLC and How Does a PLC work with PLC Programming

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What is a plc.

In this article, you will get information about what is a PLC and how does it work with it’s programming.So, let us to start.

What is a PLC

PLC stands for “Programmable Logic Controller”.  A PLC is a computer especially designed to operate reliably under harsh industrial environments — such as extreme temperatures, moist, dry, or dusty conditions. It is used to automate industrial procedures such as a manufacturing plant assembly line, an ore processing plant, or a wastewater treatment plant. It shares many features of the personal computer you have at home. They both have a power source, a CPU (Central Processing Unit), inputs and outputs (I/O), memory, and operating applications (though it’s a different working applications ).

The biggest differences are that it can do different and constant functions a PC cannot do, and a PLC is much better suited to rough industrial environments. It can be thought of as a’ruggedized’ digital computer that manages the electromechanical processes of an industrial atmosphere.PLCs play a crucial part in the field of automation, using forming a portion of a bigger SCADA system. It can be programmed according to the operational necessity of the process.

In the manufacturing sector, there will be a demand for reprogramming due to the change in the nature of production. To overcome this difficulty, PLC-based control methods were introduced. We’ll first discuss PLC basics before looking at various applications of PLCs.If you would like to learn how to program PLCs, you need to have a look at a few of the different online PLC training courses. These classes can help jumpstart your livelihood in management engineering.

PLC Basics

PLCs were invented by Dick Morley at 1964. Since that time it has altered the industrial and manufacturing sectors. The main advantage of it’s over a”hard-wired” management system is that you may go back and alter a PLC after you’ve programmed it, at minimal cost (only the price of the developer’s time). In a hard-wired management system, you’re essentially needing to rip wires out and begin from scratch (that is much more expensive and takes longer).

Let us look at an example to understand this benefit.Imagine you have a light attached to a switch. In general, the light works under two conditions — ON and OFF. Now you’re given a job that if you turn ON the switch, the light should shine only after 30 seconds. With this hard-wired setup — we’re stuck. The only way to achieve this is to completely rewire our circuit to bring a time string. That’s a lot of hassle to get a little change.

How Does a PLC work?

The working of a PLC can be easily known as a cyclic scanning method called the scan cycle.

A PLC Scan Process includes the following steps

  • The operating system starts cycling and monitoring of time.
  • The CPU starts reading the data from the input module and checks the status of all the inputs.
  • The CPU starts executing the user or application program written in relay-ladder logic or any other PLC-programming language.
  • Next, the CPU performs all the internal diagnosis and communication tasks.
  • According to the program results, it writes the data into the output module so that all outputs are updated.
  • This process continues as long as in run mode.

Types of PLCs

The two main types of PLC are fixed / compact and modular.

Compact

Within a single case, there would be many modules. It has a fixed number of I/O modules and external I/O cards. So, it does not have the capability to expand the modules. Every input and output would be decided by the manufacturer.

Modular

This type of PLC permits multiple expansion through “modules”, hence referred to as Modular. I/O components can be increased. It is easier to use because each component is independent of each other.

It is divided into three types based on output namely Relay output, Transistor output and Triac Output . The relay output type is best suited for both AC and DC output devices. Transistor output type PLC uses switching operations and used inside microprocessors.

According to the physical size, it is divided into Mini, Micro, and Nano .

Some of the manufacturers of PLCs include:

PLC Applications

PLCs have a variety of applications and uses, including:

  1. Process Automation Plants (e.g. mining, oil &gas)
  2. Glass Industry
  3. Paper Industry
  4. Cement Manufacturing
  5. In boilers – Thermal Power Plants

PLC Programming

When using a PLC, it is very important to design and implement concepts depending on your individual use case.  To do this we first need to know more about the specifics of PLC programming.  This program is made up of set of instructions in textual or graphic form which reflects the logic that governs the process the PLC is controlling.  There are two main classifications of PLC programming languages that are further divided into several sub-classified types.

  1. Textual Language
    1. Instruction list
    1. Structured text
  2. Graphical Form
    1. Ladder Diagrams (LD) (i.e. Ladder Logic)
    1. Function Block Diagram (FBD)
    1. Sequential Function Chart (SFC)

Due to the simple and convenient features, graphical representation is much preferred to textual languages.

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