If you've wanted to work in industrial automation and have been looking for basic PLC training but aren't sure where to begin, this Beginner's Free PLC Training blog series has been developed for you.

After completing this course, you ought to be ready to begin studying PLC programming. If you have any questions about this post's content, feel free to leave a comment. Let's begin our introduction to PLCs straight away, therefore, without further ado.

PLC Training Series Outline

  1. Introduction to PLCs
  2. PLC Processors (CPU)
  3. PLC input and output (I/O)
  4. PLC Ladder Logic

A Programmable Logic Controller (PLC) is a solid-state control system that continually checks the status of the connected devices at the input and controls the connected devices at the output using a user- or programmer-written program stored in memory.

1.Introduction to PLC

PLC made its debut in the latter half of the 1960s. For General Motors, Dick Morley developed MODICON, the company's first popular and effective programmable logic controller. It was formerly a machine composed of many electronic parts. When the microprocessor became a reality in the late 1970s, the role of the PLC was significantly expanded, enabling it to advance from being a simple relay to the sophisticated system it is today. In the 1980s, efforts were made to standardize the manufacturing automation protocol's communication.

How Do PLCs Work?

PLCs are small industrial computers that may automate control processes by using modular elements. PLCs, which serve as controllers, power most industrial automation today. Although a PLC has many components, the majority of them belong to one of the following three categories:

  • Processor (CPU)
  • Inputs
  • Outputs

PLCs are powerful and complex computers. However, a PLC's operations may be summed up in a few simple terms. The PLC takes in inputs, processes them using CPU logic, and then regulates outputs by turning them on or off in line with that logic. We will go into more detail later, but for now, think about this:

  • The CPU maintains track of the inputs' statuses (ex. switch on, proximity sensor off, valve 40 percent open, etc.).
  • The information the CPU obtains from the inputs is used to process the inputs.
  • The output logic is managed by the CPU (ex. turn off the motor, open valve, etc.)

PLC or PAC?

  • Both mention computers used for industrial automation. A programmable automation controller (PAC) has a more complex programming interface than a programmable logic controller (PLC), which is a single microprocessor-based device (PAC). Compared to PLCs, PAC technology is more recent.
  • The PLC was developed by electrical engineer Richard "Dick" Morley for General Motors in 1968.
  • In 1972, Dr. Richard J. Steckel developed one of the first basic PACs.
  • Each machine or station in an automated system has a PAC or PLC installed to control it.

2.PLC Processors (CPU)

PLCs are electrical components built around microprocessors that serve as the programmable brains for simple or isolated applications. Additionally, integrated equipment and more intricate automation systems are being used more frequently.

PLCs and the Human Brain

The CPU is the PLC's brain. It can be compared to the human brain, despite not being quite as complex. So that we may better understand how the CPU works, we will use the human brain in this essay.

Logic
  • Similar to our dishwasher example, a PLC CPUs programmed logic differs depending on the application.
  • In the same manner that the brain receives input signals (sight, feel, smell, taste, and sound) and produces output actions (stepping, reaching, gripping, talking, etc.) in accordance with the brain's "programming," the logic of the PLC can be compared to that of the brain.
Memory
  • PLC programmes and data are frequently stored in the processor memory, which is normally found in the CPU, either temporarily or permanently. This resembles the memory of a computer (RAM or ROM).
  • This is similar to how our brains temporarily or permanently store knowledge, allowing us to carry out a variety of tasks, like riding a bike, "from memory."
Communications

Each PLC processor handles a certain type of communication. The communications handled by the PLC CPU frequently involve one or more of the following:

  • Through a serial or USB connector on the CPU module, communication with the programmer's computer is possible.
  • Input and output (I/O) modules are communicated using the chassis backplane.
  • PLCs and other industrial automation devices can connect with one another via Ethernet and other network types.

Allen-Bradley PLC/PAC Processors

The free PLC training courses on this site are designed to introduce you to PLCs and describe the operations of each of their component sections.

PLC-5 Controllers
  • Our PLC-5 control system is no longer available for purchase as it has been decommissioned.
  • With the aid of our tools and support, you may make the switch to our selection of ControlLogix control systems. Use our migration resources and advice.
SLC 500 Controllers
  • Our SLC 500 control platform, Bulletin 1747, has several uses.
  • Rockwell Automation has deprecated some SLC 500 Bulletin numbers, and they are no longer available.
  • Customers are advised to upgrade to our more modern CompactLogix 5370 or 5380 control solutions.
ControlLogix Controllers
  • Our ControlLogix® control solutions combine a common control engine with a common programming environment for excellent performance in a user-friendly environment.
  • By tightly integrating the programming software, the controller, and I/O modules, development time and costs are decreased during commissioning and regular operation.
CompactLogix Controllers
  • To help meet the growing demands of intelligent manufacturing machinery and equipment, we offer improved performance, more capacity, increased productivity, and enhanced security through our CompactLogix and Compact GuardLogix® controllers.
  • These controllers' development environment is well-known and approachable.

3.PLC Inputs and Outputs (I/O)

I/O refers to the interface between the controller and the object or process it is controlling.

I/O overview

  • PLC I/O is the part of the PLC that connects the CPU, the PLC's processing unit, to external machines.
  • In a PLC system, there will frequently be dedicated modules for inputs and outputs.

Discrete I/O

  • The majority of PLC I/O is made up of discrete I/O. Digital I/O is another name for discrete I/O.
  • The idea behind discrete I/O signals, which are ones that are either on or off, is simple.
  • Discrete input devices include things like light switches, proximity switches, and pushbuttons.

Industrial Communications

  • In most PLC systems, discrete and analogue I/O predominate.
  • One topic, though, I'd want to briefly touch on is communications, namely the I/O data that can be transmitted or received via industrial communication protocols to or from other controllers and devices.
  • Despite the fact that this is a very broad topic, I want to at least provide you with a brief overview of it in this piece.

4.PLC Ladder Logic

In the programming language known as ladder logic, a program is developed and represented using ladder diagrams, which are based on circuit diagrams. The main devices for which they are used to build programs or software are programmable logic controllers (PLCs), which are utilized in industrial applications.

Ladder Logic Instructions

  • Before you begin using ladder logic for programming, there are a few things you should know.
  • If you knew why ladder logic was invented, understanding it would be much easier for you. In particular if you have experience with electrical circuits, relays, or boolean logic.

Relay-Type Instructions

It is a problem that the PLC and electrical control systems behave differently in this scenario. The primary variances are as follows:

  • Before moving on to the next line of ladder logic, the PLC performs the first line (rung).
  • Electrical systems allow for the simultaneous activation of many lines (current routes). With these crucial contrasts in mind, let's get started. It's time to review ladder logic.