fbpx

PLC Hardware Explained

Learn about a typical PLC and its associated hardware.

In this article, we’re going to introduce you to a typical PLC and its associated hardware.

First of all, let’s start with the term PLC, and talk about what it means.

PLC is short for Programmable Logic Controller.

PLC industrial applications 

A PLC consists of a computer with several additional hardware pieces that are a part of it or can be attached to it at any time.

Before we go any further, this is probably a good place to discuss how and where a PLC has been included physically into industrial applications and what it has replaced.

PLC Components

Motor starter – 1960s

Let’s look at a typical motor starter schematic that could have originated in the 1960s perhaps.

Any electrician will tell you that when you push the Start button (stage 1), the M Relay will energize and the Motor will run assuming there are no overloads (stage 2).

The Motor will stay running after the Start button is released because a set of M contacts will seal in (stage 3).

Motor Starter Schematic - Start

The Motor is stopped by pressing the Stop button (stage 4) thus breaking the electrical circuit for the M Relay (stage 5).

Motor Starter Schematic - Stop-

Motor starter – today

In industrial applications today, much of the Motor Starter circuitry is replaced by a PLC. Interestingly, many of the original physical devices are connected to the PLC!

The Start and Stop switches, the OL (overload) contacts, and the M relay are hardwired to hardware modules that are part of the PLC…. More on the hardware modules later…

Motor Starter PLC Control

PLC Hardware components

Alright, now that we’ve got that out of the way, let’s look at what we mean by the term PLC Hardware. The Hardware components of a PLC include the following: 

Processor, Power Supply, Input/Output Modules, and a Programming Device.

Let’s look at each piece of hardware, or module one at a time.

1) Power Supply

The Power Supply is connected to AC mains for the supply voltage.

PLC Hardware

The output of the Power supply is a DC voltage used to power all of the other modules associated with the PLC.

The Power supply DOES NOT provide power for field devices.

PLC Power Supply

2) Input/output modules

The input/output modules are connected to digital or analog field devices.

Input field devices include switches, encoders, and transmitters for example.

Typical output field devices are relays, lamps, and proportional valves.

IO Modules

3) Processor

The Processor consists of the CPU (central processing unit) and memory.

The processor section makes decisions needed to observe and operate the field devices connected to the Input/Output modules.

PLC Processor

The decisions are based upon a user-created program saved in the memory. The memory also stores data representing the condition of all input field devices and contains the data telling the output field devices what to do.

PLC Memory

4) Programming Device

The Programming Device in today’s industrial applications is usually a laptop or a desktop computer that facilitates the creation of decision-making programs destined for the PLC.

Examples of the programming software residing on the laptop are Studio 5000 for Allen Bradley PLCs or SIMATIC Step 7 for Siemens PLC’s.

PLC Programming Software

Summary

OK, let’s review…

– A PLC consists of a computer with several additional hardware pieces that are a part of it or can be attached to it at any time.

– Today’s PLCs have replaced much of the old-style hardwired circuitry in industrial applications, but many of the original physical devices are connected to the PLC.

– The Hardware components of a PLC are the Processor, the Power Supply, the Input/Output Modules, and a Programming Device.

– The AC mains connected Power Supply provides DC power for the PLC modules but not for field devices.

– The input/output modules are connected to digital or analog field devices.

– The Processor consists of the CPU (central processing unit) and memory.

– The Programming Device in today’s industrial applications is usually a laptop or a desktop computer.

You might want to review one of our other articles:

PLC Basics | Programmable Logic Controller

Want to Learn More?

Newcomers to RealPars have free access to one of our online courses.

You can take advantage of this offer by downloading the RealPars app (iOS, Apple TV, Android, Android TV, FireTV, Rokuand selecting the first lesson of the PLC Hardware course. Just like the video, the lessons are all high-quality and also very easy-to-follow.

RealPars App

Also, for a low monthly fee, you’ll get full access to an exclusive library of courses on PLC programming and industrial automation topics as well as new fresh out of the oven videos each and every week. These courses are all member-exclusive and are not shared anywhere else on the internet.

If you would like to get additional training on a similar subject please let us know in the comment section.

Check back with us soon for more automation control topics.

Got a friend, client, or colleague who could use some of this information? Please share this article.

The RealPars Team
By Ted Mortenson

By Ted Mortenson

Automation Engineer

Posted on Aug 24, 2020

Ted Mortenson

By Ted Mortenson

Automation Engineer

Posted on Aug 24, 2020

5 Actionable Tips for Getting a PLC Programming Job with NO Experience

5 Actionable Tips for Getting a PLC Programming Job with NO Experience

In this blog post, you’ll learn about the mindset that helped me getting a PLC programming job with NO experience. This is my personal experience as someone who searched for a job in this field and as an employer who reviews resumes and interviews candidates for a variety of projects. So let’s get started!

Manometer Explained | Working Principle

Manometer Explained | Working Principle

In this article, we're going to introduce you to the manometer which is one of the oldest pressure measurement devices still in use today. A manometer is one of the most accurate devices for measuring pressure in the lower ranges. Since manometers are so accurate,...

What is the Industrial Internet of Things (IIoT)?

What is the Industrial Internet of Things (IIoT)?

Automation and Internet Cloud Computing are evolving and merging into a space allowing for Artificial Intelligence (AI) programming to facilitate improvements in productivity and efficiency with many economic benefits.Industry 4.0Along with Internet Cloud computing...

Learn how to program PLCs, install and wire industrial devices, and at the same time purchase them online.

Have questions? 

[email protected]

+31 10 316 6400

Mon - Fri  8:30 am to 5:30 pm (CET)

Rotterdam Science Tower, Marconistraat 16,
3029AK Rotterdam, Netherlands

COMPANY

About

Privacy

Cookies

LEARN

Courses

PLC Certificate

Blog

Search

Sign in

HELP

FAQ

Contact Us

© 2020 RealPars B.V. All rights reserved.

Created with coffee and tea in Rotterdam.