S7-PLC

March 17th, 2010 by admin

Siemens Industry and Automation has a line of PLCs that includes the s7-300s, s7-400s, and the s7-1200. The s7-1200 is replacing their s7-200 model. They have the ability to communicate using several protocols including Profibus, MPI, As-I bus, and Ethernet.  They have a wide range of flexible I/O modules available as well that can be used in nearly any combination.

Simatic Step 7 engineering software is the software platform used for programming Siemens 300, 400, and 1200 level PLCs and is compliant with the “IEC 61131-3” standard. The most comprehensive version is called Step 7 Professional. It includes Step 7 Basic Software, S7- Graph, S7-SCL, and S7-PLCSIM. The programming environment, viewed using Simatic Manager, is powerful and has many advanced features that previously were not commonly found in PLC software. Several of the advantages are described below.

  • Symbol Based Programming- While address-based programming is still an option, the programming environment is also capable of the more powerful Symbol Based Programming methodology.  Using symbols instead of addresses allows for code that is more readable and is faster to troubleshoot.  It also allows for more structured code.  The programmer does not need to worry about adding values in the middle of a symbol list since the addresses will shift automatically and not affect the rest of what has already been programmed.
  • Function Blocks- Using function blocks allows the programmer to write reusable code blocks.  This removes the need to have repeated code in the same program as well as the need to reprogram common functionality in a subsequent project.  For example, if a system has several motors, the common code to control them only needs to be programmed and tested one time and then can be reused for all motors in the system. Any future updates to the control also will only need to be made one time.
  • Supports Several Programming Languages- The Step 7 software contains the option to program in several different programming languages. Some of the most common are Ladder (LD), Structured Text (ST), Structured Control Language (SCL), and Function Block Diagram (FBD).  Ladder programming is the most common form of PLC programming. It is designed to mimic relay logic.  SCL is a text based language based on Pascal that uses elements from high level programming languages. It allows for programming items such as arrays and indirect addressing yet it also includes the basic requirements of programming a PLC found in the ladder language such as addressing real inputs and outputs.  ST is a low level text language that is similar to an assembly language.  FBD is a flow chart like language.  It is built from a collection of blocks that are connected to one another with inputs and outputs.
  • Built-In Function Library- The S7 platform also comes with a large library of built in functions. This ranges from everything from simple math functions to PID loop control functions to basic motion control functions.