PLC Programming

We’ve got the most complete list of PLC programming software online.  Find programming software from most of the major PLC manufacturers.  They’re all listed on the lower right column of this page.

Most PLCs are programmed using Ladder Logic, which is a set of electrical diagrams, showing open and closed contacts that allow or prevent electrical flow to outputs.  

Above is a very simple Ladder Logic Example.  Power comes in on the left side.  Some conditions must be met in the middle (in the form of contacts).  If they are met, power makes it to the Coil.  When talking about Ladder Logic, Function blocks are often mentioned, they add sophisticated functionality on top of Ladder Logic’s structure.  Function blocks may include ramp, filter and math functions among others.  Most major PLC makes including Siemens and Rockwell automation allow PLC programming using Ladder Logic with Function Blocks.  For further reading on how Ladder logic works, read some tutorials at PLCHowTo.com

Another popular, but not as common PLC programming language is Flow Charting.  They are sets of decision and processing blocks.  The decision blocks control which processing blocks are executed.

In the above example a decision block asks if “Heater” is on.  If it is, the “Turn ON Fan” block is executed, if not the “Turn OFF Fan” block is executed.  Some makers including Opto22 and Phoenix Contact feature flow charting.

Other PLC programming Languages include text based languages.  These are often more refined than assembly languages, but not as refined as a high level language like C.

The structure of PLC Languages is somewhat consistent between PLC manufacturers, but the specific implementation varies greatly between manufacturer (and often even between lines made by the same manufacturer).

Along you’re journey you may need to compare PLCs.  PLCCompare.com is a great place to start researching and comparing lines.