There are 5 languages that are all a part of the IEC
or International Electrotechnical Commission
Section 61131-3 Standard.
This IEC Standard allows some ground rules
that standardize PLC’s and their languages.
Let’s take a deeper look into all these PLC Programming Languages.
Before we get started on today’s video,
if you love our videos,
be sure to click the like button below.
then, make sure to click subscribe
and the little bell to receive notifications of new RealPars videos.
This way you never miss another one!
The 5 PLC Programming Languages are Ladder Diagram (LD),
Sequential Function Charts (SFC),
Function Block Diagram (FBD),
Structured Text (ST), and Instruction List (IL).
Let’s show you a little bit about each of these.
I will start with Ladder Diagram
which is a graphical type of PLC Programming Language.
Ladder Diagram was originally modeled from relay logic
which used physical devices,
such as switches and mechanical relays to control processes.
Ladder Diagram utilizes internal logic to replace all,
except the physical devices
that need an electrical signal to activate them.
Ladder Diagram is built in the form of horizontal rungs
with two vertical rails that represent the electrical connection
on relay logic schematics.
You can program all the necessary input conditions
to affect the output conditions, whether logical or physical.
The main advantages of the Ladder Diagram language
are that the rungs allow it to be organized and easy to follow.
It also lets you document comments that are readily visible,
and it supports online editing very successfully.
The main disadvantage is that there are some instructions that are not available,
which might make it more difficult for programming such as motion or batching.
The next PLC Programming Language that I will talk to you about
is the Sequential Function Charts
which uses a graphical type of programming.
If you have any experience with flowcharts,
then this PLC Programming language will feel familiar to you.
In Sequential Function Charts,
you use steps and transitions to achieve your end results.
Steps act as a major function in your program.
These steps house the actions that occur when you program them to happen.
This decision can be based on timing,
a certain phase of the process, or a physical state of the equipment.
Transitions are the instructions that you use
to move from one step to another step to another step
by setting conditions of true or false.
Unlike traditional flowcharts,
the Sequential Function Charts can have multiple paths.
You can use branches to initiate multiple steps at one time.
A couple of the advantages of Sequential Function Charts are:
Processes can be broken into major steps
that can make it faster and easier troubleshooting.
You have direct access in the logic
to see where a piece of equipment faulted.
It can be faster to design and write the logic
due to the ability to use repeated executions of individual pieces of logic.
Even when you consider the advantages of the Sequential Function Charts,
this PLC Programming Language does not always fit every application.
Now we are on to our third PLC Programming Language.
The Function Block Diagram which is also a graphical type of language.
The Function Block Diagram describes a function between inputs and outputs
that are connected in blocks by connection lines.
Function Blocks were originally developed to create a system
that you could set up many of the common,
repeatable tasks, such as counters, timers, PID Loops, etc.
You program the blocks onto sheets
and then the PLC constantly scans the sheets in numerical order
or is determined by connections which you program between the blocks.
The code can get disorganized using this PLC Programming Language
because you can place the function blocks anywhere on the sheet.
This can also make it more difficult to troubleshoot.
The Function Block Diagram does work well with motion controls
and the visual method is easier for some users.
The biggest advantage of Function Block Diagram
is that you can take many lines of programming
and put it into one or several function blocks.
Our 4th PLC Programming Language that I am going to review is the Structured Text.
This language is a textual based language.
Structured Text is a high level language that is like Basic, Pascal and “C”.
It is a very powerful tool that can execute complex tasks
utilizing algorithms and mathematical functions along with repetitive tasks.
The code uses statements that are separated by semicolons
and then either inputs, outputs,
or variables are changed by these statements.
You must write out each line of code
and it uses functions such as FOR, WHILE, IF, ELSE, ELSEIF AND CASE.
If you have experience with Basic or C languages,
this PLC Programming Language will come easier
than some of the other languages.
Some of the advantages of Structured Text
are that is very organized and good at computing large mathematical calculations.
It will also enable you to cover some instructions
that are not available in some other languages like the Ladder Diagram.
The disadvantages are that the syntax can be difficult,
making it hard to debug and it is difficult to edit online.
I will now show you the 5th and final PLC Programming Language
which is Instruction List.
The Instruction List is also a textual based language.
The Instruction List language resembles Assembly Language.
When you use this PLC Programming Language,
you will use mnemonic codes such as LD (Load), AND, OR, etc.
The Instruction List contains instructions
with each instruction on a new line
with any comments you might want to annotate at the end of each line.
This Instruction List language is valuable for applications
that need code that is compact and time critical.
The main disadvantages of this PLC Programming Language
are that there are few structuring possibilities
with the "GOTO" command being one of them.
There can also be many errors
that are more difficult to deal with in comparison
to many of the other languages that I have previously reviewed.
So, have you decided which PLC Programming Language
you consider to be the most popular?
After reading many reviews and opinions and with my own experiences,
the Ladder Diagram language is by far the most popular.
The main reason for this is that the Ladder Diagram language
naturally followed the technology advancement
from a physical relay logic to a digital and logical one.
This allowed the engineers and skilled workers
to follow and troubleshoot and make that transition.
In summary, there is certainly a place for all the PLC Programming Languages
that I have discussed with you today.
Background, experience and the application you are working with
are really going to be the key to which PLC Programming Language you choose.
Want to learn PLC programming in an easy to understand format
and take your career to the next level?
Head on over to realpars.com