The theory is the same, regardless of manufacturer, but the method in programming it will be different. Ladder logic has been around for over 50 years. It is something that gets passed down from electrician to electrician. Ladder logic it is also an intuitive language. There are many things you can do with it. There are also many ways to program the same routine. There will always be the most efficient way to program a routine. It does have its weaknesses, such as higher level math.
Basic math 5 function being add, subtract, multiply, divide and compare can be done, but not in the most efficient manner for programming. Once you start addressing these areas, you then begin getting into the hardware, specifically the processor and its capabilities. You will also see hybrid packages that use the strengths of ladder logic with the strengths of another format to improve the weaknesses of the ladder logic format. Our electrician who does work for us at our factory, installed his first Entertron controller earlier this year.
He has for years wanted to get into automation, but didn't have the time. He finally made a commitment this year. His understanding of ladder logic was already there.
He had a bit of a learning curve due to how we handle some of the functions within our software. Once we taught him what was happening He had the theory part nailed down, but was questioning how we were doing it through our software.
For him, the learning curve was virtually nothing because of his existing knowledge. Hope this helps. God Bless,. As many have already stated. Ease of use is one of the main reasons latter logic is still used. Basically it makes you program look like your electrical drawings for a control circuit. This makes the program look more real world and makes it easier to explain and be understood by others.
You will however be limitied in what you can do as mentioned by others, especialy when dealing with higher level math. Many PLC manufacoturs get around this by creating special function blocks that will do this math PID function is the first that comes to mind that can be dropped directly into a ladder rung in the program. Once the program has been made and the machine is running the guy who will be working on the machine will probably NOT be a programer but hopefully he will have an electrical background and he will be reading the code to troubleshoot the machine.
So that makes ladder logic his best friend. DDHarrold, Our electrician who does work for us at our factory, installed his first Entertron controller earlier this year. God Bless, This about nails it. Ladder does the best job of eliminating the Am phone call than any other language.
Any sparky is already familiar with it! Now for the name and who you work for part. Many of the people on this forum do not care if you know who they are. Some do, very often this is reflected in their "handle" or signature. Some cannot tell you who their employer is, because of legal issues.
But bless their hearts they still want to help someone in need. Why not just mention this forum and their handle in the article? The quality of the forum member's post's stand on their own merit.
On-line programming. This is a must in many applications. I have had people that they would rather pay extra for a SlC than buy a MicroLogix because the SLC allows one to do on-line edits.
A graphical display is easier on the eyes than a bunch of text. It is easy to see why a rung doesn't activate a coil. This works because the ladder is executed every scan. A procedural language is not normally executed every scan.
Perhaps textual programming would gain more ground if the value of variable was displayed at run time. When the state of the coils or variables is chaning rapidly then none of the programming methods is very good without an event capture or logging capability.
The event capture or logging in not language dependent. Event logging will level the playing field between graphical and textual programming, just wait. There is a trend to textual programming. Not too long ago I had to generate a make file that would conditionally compile source code modules.
Then it would link the object code and then locate it so the code would run at a specific location. Now this is all done automatically in VB C Java etc. These languages actually to the compiling on-the-fly. When this technology reaches instruction list and structured text IDEs and compilers and they have the ability to download on-line then there will be a change. The new generation is exposed to VB, C etc.
Just wait and the preferred tools will change. I have seen a lot change in the last 5 years. Real-world events are defined as PLC inputs in ladder logic.
It is a type of digital logic circuit. We get High Output 1 only when all of its inputs are High 1. The Art of Cross-Referencing. How to Choose an Industrial Automation Controller.
When choosing an industrial automation read more. Recent Posts. Archives January 20 June 7 August 6. Popular Resources. It is sometimes referred to as reverse logic. Check out the truth table below…. If we translate a NOT function into a ladder logic diagram we express it symbolically in the form of a normally closed contact NC as seen in ladder logic truth table shown below….
In order to successfully read ladder logic we need a basic understanding of how a PLC works and how ladder logic is executed in a PLC. You see, the PLC follows a certain execution procedure and if not adhered to it can lead to the ladder logic being read incorrectly. Ladder logic works in a similar way to relay logic, but without all the laborious wiring.
It has supply rails, relay coils, relay contacts, counters, timers, PID loop controllers and much more. In simple terms, all the field input and output devices are wired to the PLC and the ladder logic program decides what outputs to trigger depending on the status of the input signals. In basic terms, PLCs execute ladder logic by first reading all the input states and storing them into memory.
Secondly, scanning through and evaluating each rung of ladder logic, from left to right and top to bottom. Lastly, at the end of the scan, the resultant logic is executed and the outputs are written to. On their own they cannot decide what action to take to automate something. Logic is the ability to decide what action needs to be taken depending on the state of one or more events.
We use the binary and logic concepts every day in our own lives. For example, if I feel cold then I put my sweater on, but if I feel hot then I take my sweater off. The binary and logic concepts are what makes ladder logic work. The hidden key to unlock your understanding of how ladder logic works is: The logic functions in ladder logic are are automatically built into the structure of the ladder diagram.
In ladder logic the real world events are defined as PLC inputs. In ladder logic the result of a rung logic function is defined as a PLC output. When we take these two fundamental elements and insert them into a rung in a ladder diagram we get your first line of code! Therefore it results in two possible logic iterations:. If we translate this into a ladder logic diagram we express it symbolically in the form of a normally open contact NO for the input and a relay coil for the output.
Remember the logic flow is from left to right and follows the same concept of current flow in an electric circuit. They are all connected in line, just like a series connection in an electric circuit. This time we have also highlighted the hidden AND function to illustrate the relationship between the ladder logic functions and the ladder diagram rung structure….
The inputs are placed in the rung in what is known as a branch. This is the equivalent of a parallel connection in an electric circuit. The output is then connected in line with the rung.
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