Based on Google Trends, ladder diagram seems to be the most searched language. However, past PLC programming trends are no indicator of future requirements.
Each language has its pros and cons. With most 61131-3 compliant environments, the great thing is that each part of a PLC program can be written with a different language. This allows for the usage of the right language for the right purpose or application.
PLC’s continue to have more features, and applications are increasingly applying these new features. Examples: Data handling with arrays, sequencing state diagrams, more math, … A ladder diagram is not a good way to utilize or apply some of these functions. Fortunately, the alternative is not too difficult to pick up.
What are some of the underlying factors that keep the ladder diagram preference going?
- Ladder diagram is similar to a electrical control schematic with rails on each end. This makes it a easier for maintenance folks and electricians to troubleshoot it if the need arises.
- A large proportion( PLC count) of PLC’s sold go into ‘simpler’ applications. These applications are covered by the small and mid-range PLC market. The applications may be start/stop, sequencing and boolean logic based for the most part. These are great application grounds for ladder diagrams.
- Some PLC programming environments have a strong ladder editor. That combined with other features such as a live, animated view of the system when logged in with the ladder environment make it appealing. Other environments animate when logged in using any of the languages.
- We all like what worked before. Even when it doesn’t work well enough anymore. Until we have to do something different to stay in business. And then change is imminent and accelerated.
Why will the industrial control world need more than ladder diagram moving forward?
- Much more connectivity. PLC’s handle much more than just logic. They connect to other devices on the factory floor and at the plant level or even remotely.
- Data handling. PLC’s today have sufficient memory to track and control thousands of data points. The tools to handled these data points are best applied in non-ladder languages. Example: Arrays, file handlers, math functions..
Based on the above evolutions in industrial control, the following points need to be considered:
- Every language has its benefits, don’t get intimidated just based on familiarity.
- Consider what needs to be done before picking a language
- Stay open minded.
Ladder is good for viewing inputs and outputs and basic functions with triggers and timers. Structured text is good for math and data manipulation. Function block diagram is good for getting a graphical overview of a system. Sequential function chart is good for state based system organization. On larger PLC programs, all of them can be used for different parts.
The following Automation.com article covers the languages at a high level, with some details on pros and cons of each.
Going back to some of the other PLC programming trend observations
Interestingly, the term ‘structured text’ is strongly related to ‘CODESYS’ and ‘61131’ search terms. Note: The table embedded below shows the ‘Rising’ terms by default. Click on the ellipsis like button on the bottom right and select ‘Top’ to see the others.
Another interesting observation with regards to search cycles. July and December seems to be down-cycle parts on most years. Might it be tied to mid year and end year vacation times? Summer and winter breaks maybe?
On average, ladder diagram gets nearly double the search volume compared to structured text. This is followed by function block diagram which got about one third of the search volume relative to ladder diagram. Sequential function chart is a faraway fourth with about one tenth of the search volume relative to ladder diagram. Note, these are averages and there may be measurement errors due to exact search terms and various languages. Also, various vendors do have slightly different names for the languages compared to the IEC61131-3 names.
If you have a specific reason why you pick one language over another, leave a comment below.