Methods of Programming
While using SIEMENS PLCs, Programs are written by using PGs (Programmers) and then transferred to the CPU module of PLC.
PGs are used to write the control programs for programmable controllers, and can also be used to test these programs when the system is put into operation.
Extensive user-friendly testing and debugging functions support troubleshooting and error recovery and a wide variety of documentation functions are available for adding program commentary, and documenting and printing out user programs.
Programming Languages:
The Programming languages serve as a mean of communication between the user and automation and are the language in which user formulates his control task.
There are four possible programming languages:
1. The Ladder diagram (LAD)
2. The control system flowchart (CSF) or Function Chart
3. The statement list (STL)
4. PLC Visual Script
1. Ladder Diagram:
Like a ladder, the diagram is made up of two vertical lines. The left one represents the connection to the voltage source, the right one the connection to the earth. The various current paths (rungs) run horizontally from left to right between the two Inputs are shown by these symbols:
-] [- : contact; normally open contact
-] / [- : negated contact; normally closed contact
AND-elements from inputs are actuated by the switching of contacts in series, OR-elements by parallel switching. In a ladder diagram, a negated input is designated by a normally closed contact.
Output has the symbols –( )– at the right-hand end of the current path in question. When programming, each symbol is accorded a real PLC address or a short form (symbolic address).
The ladder diagram (LAD) is suitable for some control tasks, particularly if a circuit diagram is available.
