What Simatic programmable controllers are and how they work

What are and how do the Simatic family programmable controllers work?

Reading time: 6 minute

SIMATIC automation system

The SIMATIC automation system is represented by components coordinated with unitary methods of configuration, registration and data transmission. Family programmable controllers SIMATIC (S7) is the basis of the automation system.

The most common types mounted in systems are: S7-200 a small automaton used in automation of simpler processes (household objects for example); S7-300, an automation for medium automations, and S7-400, the solution for complex automations.

The structure of SIMATIC machines

Such an automaton consists of the central unit and the I / O modules. The central unit has loaded the user program while the I / O modules ensure communication with the process that is controlled.

The other components of the SIMATIC solution for automation, such as (C7, DP, C7, HMI, NET), complete the PLC representing a specialized programming console, distributed I / 0 modules - for a remote control, the module for connection in network etc.

The language of this concept of total automation is STEP7 which is used for SIMATIC component configuration, to assign parameters to them and last but not least to program them.

The central software tool for control is represented by SIMATIC Manager which keeps all the data of an automation project in a directory with a hierarchical structure and allows the reuse of user software through libraries.

The main activities performed by STEP7

  • hardware configuration - which is the arrangement of modules, assigning addresses, and setting their properties;
  • configuring the communication parameters as well as its properties;
  • writing user programs for the PLC in one of the 3 ways used: Ladder Logic (LAD), Function Block Diagram (FBD) or Statement List (STL), as well as their online automatic testing. The SIMATIC solution also provides optional software packages that can extend the operation of standard tools in STEP7.

Considerations regarding the choice of the automation solution

Choice of hardware

There are several criteria for choosing the type of PLC. For low level applications the most important criterion is represented by number of inputs and outputs as well as the size of the user program.

In the case of more complex processes, it must be considered whether the response in time is fast enough, whether the memory is sufficient for the volume of data to be stored. A machine tool will probably be controlled by a single programmable controller.

The solution for distributed automations

In the case of processes spread in several locations it is more useful to use distributed I / O modules, than of some modules arranged automatically. This not only reduces the length of some connection cables with the process, but can also indicate the response speed of the machine.

The solution of a distributed automation has other advantages: user programs for different parts of the process are shorter and can be (generally) run independently of the rest of the process.

At the same time, the necessary exchange of data between the automaton and the process is essentially easier if the network communication mode is used. (SIMATIC NET).

Choosing the programming language

The choice of programming language depends on the user as well as the complexity of the task to be performed. In the case of binary signal processing, LAD and FBD are easier to use, while in the case of tasks that require the handling of complex variables and indirect addressing, STL can be used.

We recommend using STL due to the fact that it is familiar to those who program at a higher level, as well as processing a large volume of data.

Creating a project

All the data that the automation solution offers are collected together in a project. It will be created using STEP7. The data are structured hierarchically.

The next level after the project is represented by "stations" that contain one or more central units with a user program. Menu commands can be used that insert new objects, these objects can be opened to be configured.

Writing, analyzing and saving a program

The user program contains all the instructions used by the programmer to process the signals for the control of the machine or the process to accomplish the required task.

The division of the program into instruction blocks can be process-oriented, in which case each function (function block) corresponds to a part of the process or machine, respectively functionally oriented, in which case the functions correspond to communication, modes of operation, etc.

The programs are edited and tested. Their testing can be done after loading them on the PLC or on PLCSIM testing software.

After testing the software it is loaded into an EPROM memory and the project documentation is generated using DOCPRO. The project can be saved as a compressed file.

Components of a SIMATIC automation station

We consider a SIMATIC automation "station" a programmable automaton in this family together with I / O modules.

The components of such a station are:

  • mounting rail - ensures the connection of individual modules. The S7-300 machines use a simple rail, its length being determined by the number of modules. S7-400 use a fixed length aluminum rail with bus connectors;
  • power supply - ensures the power supply of the entire automation station;
  • central unit - stores and executes the user program, assigns parameters to modules, performs communication between the programming device, modules, additional stations via the bus;
  • interface modules - connect the mounting rails together;
  • I / O modules - adapt the signals from the process or to the process;
  • functional modules - perform various functions that cannot be "covered" by the central unit (control);
  • communication processor - used when you want to connect to sub-networks;

Two types of buses are used: one for transmission to / from the I / O modules, respectively one for fast communication with a larger volume of data between the central unit and the other modules.

I / O modules can be local or distributed. The distributed ones can be of master or slave type if they are placed somewhere in the process field. And the distributed modules are seen as the local ones having allocated addresses and practically no differences between the 2 types from the point of view of the central unit.

SIMATIC central units

Central unit for S7-200 automations

  • programming language STEP7 Micro;
  • used for small automations, several expansion modules, network connection possibilities;
  • the number of I / O modules can be increased to meet the process requirements. A point-to-point interface allows several central units to be connected together (up to 31), as well as the connection with other machines from the SIMATIC family.

Central unit for S7-300 automations

  • medium automations, the same features as the S7-200 and in addition the possibility to install the source on the central rail;
  • the slots are numbered: 1 for source (even if missing), 2 for CPU, 3 for interface mode, 4-11 for I / O modules;
  • it is provided with modules for working in the environment with hostile conditions (very high or low temperatures, a high level of vibrations, a resistance to shocks).

Central unit for S7-400 automations

  • complex automations;
  • improves the performance of stations in the family of 300 having greater information processing capacity;
  • the possibility of connecting two central units to the same source, multiprocessing capacity;

The components of SIMATIC S7-300 / 400 standard allow a redundant automation system in case of slow processes, so that one station can take control of the process in case another station (master for example) fails.

During this period all signals in the process are "frozen". A complete C7 system involves in addition to the central unit and I / O modules and an operator panel through which the operator can interact with the automation system.

STEP7 programming language

The main requirement for the programming language of a PLC is to be easy to understand and use in process management applications.

This implies the need for high language to provide commands very close to the functions required by an automation engineer, but without being complex and requiring a long learning time.

There are several programming languages ​​and methods that can be used for programming the SIMATIC family of automata as they satisfy one of the programmers' requirements.

Three of them (LAD, FBD and STL) are included in the STEP7 package and others can be purchased as additional packages.

Download the attachments to this article to find out as programmed in LAD, FBD and STL:


https://www.youtube.com/ - SIEMENS S7-200 PLC Programming Tutorial Bangla | AC Motor on / off with signal lamp | Class 03


    1. The mentioned automata and the programming technique, respectively the software are still used. Indeed, new models such as the Logo, 1200 and 1500 have appeared, but they will have a separate article.

      1. I know they're used because I hit them too. By the way, I still hit both the S5 and the Coros.
        If you want to do it chronologically, you can start with some history (Siemens G, S3) and then go through the rest already mentioned.

Add a comment

Your email address will not be published. Required fields are marked with *

The maximum upload file size: 2 MB. you can upload: image, audio, video, document, spreadsheet, Interactive, text, archive, queues, Other. Links to YouTube, Facebook, Twitter and other services inserted in the comment text will be automatically embedded. Drop files here