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.
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).
The Motor is stopped by pressing the Stop button (stage 4) thus breaking the electrical circuit for the M Relay (stage 5).
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…
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.
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.
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.
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.
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.
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.
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:
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, Roku) and 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.
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.
By Ted Mortenson
Posted on Aug 24, 2020
By Ted Mortenson
Posted on Aug 24, 2020
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!
In this article, we're going to introduce you to the NX and NJ series of Omron Controllers. The NX and NJ controllers are powerful as they combine both PLC and motion control functions into one package.PLC + Motion controlBefore we dive into the specifics of the...
There are many types of process flow meters. Coriolis mass flow meters; positive displacement flow meters, such as turbine meters; and volumetric flow meters, like the ultrasonic flow meter, just to name a few.In fact, there are at least eighteen different types of...
Learn how to program PLCs, install and wire industrial devices, and at the same time purchase them online.
+31 10 316 6400
Mon - Fri 8:30 am to 5:30 pm (CET)
Rotterdam Science Tower, Marconistraat 16,
3029AK Rotterdam, Netherlands
Help & Support
© 2021 RealPars B.V. All rights reserved.
Created with coffee and tea in Rotterdam.