A Beginner's Guide to PLC Programming using Ladder Diagram, Function Block, and C++

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⌚Timestamps:
00:00 - Intro
00:50 - Ladder Diagram programming
03:21 - Function Block programming
05:06 - C++ Programming
07:30 - Comparison of the 3 languages

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In this video, we're going to use 3 different PLC programming languages to solve one problem. We’re going to use 2 IEC 61131-3 languages and a higher-level language called C++.

The IEC 61131's five programming languages specified in the IEC 61131-3 Standard are Ladder Diagram, Instruction List, Function Block Diagram, Structured Text, and Sequential Function Chart. We are going to use Ladder Diagram and Function block in our exercise.

Ladder Diagram was the first language developed for PLC programming. The simple explanation for why Ladder Diagram programming became so popular was that it closely resembled traditional “Relay Logic Diagrams”.

Electricians and Engineers alike were familiar and comfortable with Relay Logic Diagrams and easily adapted to Ladder Diagrams.

Early Ladder Diagram programming involved entering typical relay-type symbols onto a rung via hand-held programming devices connected to a PLC. It wasn’t long before computers and Graphical User Interfaces made this process much easier.

This was all well and fine until more complex PLC hardware and I/O were developed and programming languages needed to advance thus spawning Function Block and other languages.

Now we are at a point in history where there is an overlap between the activities of IT programmers and PLC programmers.

More complex functions are not easily accomplished with traditional IEC 61131-3 languages and require higher-level languages such as C++ which is a familiar language in the world of IT programmers. 

For example, C++ programs can be easily created to produce “logged data” to assist with “Predictive Maintenance” (PdM). A program of that complexity cannot be easily created using Ladder Diagram.

We want an LED to turn on when two normally-open pushbutton switches are operated.

- The ladder diagram has 2 open contacts operated by SW1 and SW2 on the Starterkit. Operating the “coil” output will turn on LED1 on the digital output module. Operating SW1 and SW2 switches will close normally open contacts, energize the coil and cause LED1 to turn on.

- Basic blocks of FBD are based on “Logic Operators” such as AND, OR, and NOT. The FBD to solve our problem is built around an AND Function Block.

- Eclipse IDE can be used as C++ Editor. Because C++ is not an IEC 61131-3 language, it is not a programming choice available in PLCnext Engineer. With a few simple tools, a C++ project created in Eclipse can be imported into a PLCnext Engineer project.

Physically there's no difference in operation between any of the 3 programs we used to solve our problem.

What programming language should you use?

There’s really no single correct answer as there isn’t one best PLC programming language.

It’s apparent that we wouldn’t use C++ to solve the simple problem presented in this exercise as Ladder Diagram or Function Block are easier and more appropriate.

Each language has its strengths and weaknesses and degrees of suitability for specific applications and of course, the challenge is to choose the correct one.

@phoenixcontact1923

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If you're just starting out in the world of PLC programming, you can upgrade your skillset with a free course on PLCnext from RealPars!

Starting with the basics and working up to programming in ladder logic or C++, you'll have a handle on this exciting new technology when it's all said and done.

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[mosialive]

The Best PLC Teacher Out There... You made me fall in love with PLC's and automation. I am very thankful.

[automationpk]

I'm a plc programmer automation engineer from Pakistan I always use the ladder but I start with c++ insha'Allah thanks this is future of plc c++

[najateljaafari]

Thank you for your efforts. Personally, I benefit a lot from your channel

[syufrijal]

Amazing beginner's guide to PLC programming...very interesting

[JKTCGMV]

It surprises me C/C++ is referred to a higher level language. Coming from programming, C/C++ are some of the _lowest_ level languages. The other two would be considered higher level because they abstract away the technical bits of programming and just let you focus on the logic

[nikolaydubina]

makes me want to try to experiment it myself with this PLCnext thing! haha

[samalfellah]

Great video. Who else thinks that AI might take over in PLC programming and contribute to some job looses

[cck]

Good video....Is it possible to start a series for PLC programming for beginners (free) on this forum?
I think it's difficult...

[arvinmistry]

Excellent programming but we cannot see programming caractors and digits of programe which has been created, there for i will be apprisaite if proper magnifying can be done or, program can be created on larger Fonts.

[taktuscat]

And logic on C++ is denoted by two ampersand &&

[mohammedmahdi]

Hello
I need your help please, I need to know the difference between central commande and, décentralisée commande and combined commande,

[anushkakiranlamba]

Dear team, can you explain in simple terms about what is a profidrive exactly? Is it physical like profibus? What does it do? Is it a communication protocol

[ingbjellb]

Hi, thanks for all the high quality video you put out. A question regarding the PLC: does it support an integrated PID-controller, as part of the hardware and software in the starter kit model plc?

[buak]

I would like to get a grip on PLC/embeded, how should I start if I have never had experience with electronics? Any good courses out there on how to start? Udemy perhaps? I think starting off here might be not the best idea even though it says a BEGINNER's guide...But I think you need to have some knowledge about how this stuff works on prerequisite

[mboowashafiq]

Can plc be programmed with assembly code, ,,yes I understand it has a small CPU in it any way we can compile assembly code to much more low level code to be understood by this small CPU ?

[mathiasmortensen]

Why not just use Structured Text? In the given example its so close to C++ as the logic would bed LED1 := SW1 and SW2; given they all are Boolean datatypes.
Structured Text is already under the standard, and by that it will follow the same rules accors platforms, as long the stick to the standard. Most codesys programming platforms as an example.

[YEGODFIRST]

What is the best software for c++ programming for PLC ?

[alzubiaryousha]

Dear sir how can i be professional in plc and how can i get more informations about plc

[alikoohi]

Isn't python programming language related to PLC programming or industrial SCADA yet?if yes how can I find any tutorial on that?I think there is a big potential in connecting python to industrial information and adding much value to them by A.I and machin learning..

[ibrahimkavalci]

thanks, i have 10 years experience and hesitating to use IEC 61131-3 because it is closed to upload a program to your pc if you lost it. Is it same for this? There is another point that: Can we be online with plc while writing the program? I mean we need to see the status of all variables while programming. Is it possible?