Ladder Logic or LL is
the primary PLC or Programmable Logic Controller programming language. It is
simple and represented graphically as coils and relay contacts. The biggest
question is, "How well can these ladder logics serve complex automation that
is needed by industries today or in the future, compared to other conventional
programming languages?" The answer to this question is pretty complicated
than just coils and contacts.
The
origin of ladder logic
Automation has been in
every industry way before Programmable Logic Controllers, usually using
networks of relays in the brain of individual applications. There was not a
programming role; these were engineers who design circuits and electricians to
assemble these systems. These circuits would be appropriately documented in
standard structures that resembled a ladder, hence the name ladder diagram.
When automated logic
controllers arrived, it promised a lot of benefits when it comes to the
automation industry, but nobody knew how to use them. Then, the experts got an
idea to program Programmable Logic Controllers with ladder diagrams. It allowed
the automation industry to repurpose existing skills for programming.
Electricians and
engineers could understand and read programming, and automation designs can
mostly follow the same patterns that were used with relays. Before the advent
of PLCs, the system relays took up most of the physical space in the cabinets.
It cost a lot of money to purchase and required a lot of time to wire and
setup.
These relays are also
limited to on and off functions without capabilities in math, data collection
or analog in relay logic (aside from some counting functions and sparse in
special relays). Even the most complex and most extensive automation systems
were limited by realities of physical relays, the language of LL did not have
to do that much.
Today, processor chips
inside PLCs can do more than relay information, at a lower cost of money,
space, or implementation time. In turn, these programming languages used PLCs
have grown to help reflect its increased capabilities. LL does a lot more in
today's world compared to what it used to be. Programmable Logic Controllers
are usually utilized for analog control, controlling motion, tracking part data
(test results, bar codes, calibration), as well as a plethora of other tasks.
A lot of experts still
considers ladder logic as the most dominant language in this industry. As
languages evolved and automation industry has become more complicated by the
minute programming Programmable Logic Controller has become a specialized job.
Ladder logic is no longer a convenient language for engineers or electricians
maintain and read, not it is a broadly existing skill set in the incoming
workforce.
Other
Programmable Logic Controller languages
Two communities
influence programming in the industrial world: standard International
Electrotechnical Commission 61131-3, or the industrial control standard used by
International Electrotechnical Commission; and the PC programming. Both are
usually seen as a complementary system to ladder logic, instead of directly
opposed.
International
Electrotechnical Commission 61131-3
As logic controllers
become pretty popular, companies found the need for standards to help guide the
programming industry. The International Electrotechnical Commission's committee
addressed the demand with a standard IEC 61131, and other codes in part three.
It defined the four codes
that usually were interchangeable: function block and ladder diagram,
instructional list, and Structured Text, as well as a program organization
language called the sequential function charts. Each language has its own
weakness and strengths, and all of them can be used together within one program
to support different functions.
There are certainly
debates on which language is suited to certain tasks. Generally speaking,
processes will operate as continue or discrete. The automation industry also
tends to lean towards analog Input and Output (I/O) or mostly digital Input and
Output.
PC
languages
Languages that are drawn
into automation from the PC industry tend to be used for peripheral/specialty
apps. That may include programming automation peripherals like robots and
cameras, as well as interfacing with databases. Structured Text or ST is very
similar to Pascal, one of the most common PC codes at the time International
Electrotechnical Commission 61131 was introduced.
Pascal has been out of
the game for many years now, but it is an excellent example of how the
automation world has borrowed from the PC industry. Current examples of these
languages in automation include Java, C#, and C++/ These systems are pretty
powerful but have not found a firm footing in the automation industry.
Common
questions
Before comparing LL to
other options, it is imperative to understand what programs really need to do.
These programs have to do automation work, which most of the systems can do,
but the world puts other demands from them as well. It boils down to the
program readability. Ask these critical questions about these programming
languages.
Can maintenance
technicians or programmers look at codes and understand what these codes do?
Can problems be found
immediately to help minimize downtime of systems?
When functionalities are
desired, how easy is it to extend programs?
There are features of
different codes that can affect a technician or programmer's ability to make a
good and readable program. There are areas, in particular, can influence the
selection of language.
Want to know more about
this topic, check out websites like https://onlineplcsupport.com/ladder-logic-tutorial-studio-5000 for
more details.
General
knowledge
LL is a widely used
system, which makes it a lot easier to find experts who can read the system.
Other International Electrotechnical Commission 61131 languages show some
preference within specific industries, but are not as widely understand or use.
The PC systems that are used in most automation businesses tend to be pretty
popular and have many support resources, but not always in industrial
communities which diminishes potential advantages and benefits.
Internal
documentation
Most, if not all, systems
available are a way for programmers to explain their intent in plain English.
In LL, it is mostly done with variables or tag comments and rung comments,
which work well for simple rung comments, but can be less helpful for more
extensive math or rungs. Other International Electrotechnical Commission 61131
languages differ but are usually excellent for documenting things they are good
at.
For instance, Structured
Text allows excellent documentations of loop structures and math. PC languages
used to have a lot of functionality available with a lot of options for
internal documentation. Sometimes even generate documentation automatically
from the source code, creating manuals for programmers and technicians to
understand and reference the big picture a lot quicker.
Loops
and decision structures
At simple levels,
programming comes down to "do these steps if, this situation
happens." This type of decision structure is called "if-then,"
and it is pretty easy to understand and use in every language discussed. But
what if the technician or programmer wants to do something multiple times?
These structures are not well supported by LL, resulting in codes with poor
readability. PC languages and Structured Text, on the other hand, used to be
pretty good at all loop structures and common decisions.
Math
Subtraction and addition
are very easy, and it works fine in any language, but what happens when complex
math is involved? LL supports arithmetic and essential functions like square
root or absolute value, but as math calculations include more pieces, it tends
to be less readable by users.
Comments get separated
from the things they are documenting, as well as doing the same mathematical
operation more than once is not good, since loops are not pretty. Structured
Text, as well as PC languages, used to be more graceful with more prominent
math functions.
0 Comments