Automating with STEP 7 in LAD and FBD: A Comprehensive Guide to Siemens SIMATIC S7-300/400 PLC Programming

byteckhme •May 01, 2023

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"Automating with STEP 7 in LAD and FBD: SIMATIC S7-300/400 Programmable Controllers" is a comprehensive guide to programming the Siemens SIMATIC S7-300 and S7-400 series of programmable logic controllers (PLCs) using two popular programming languages, Ladder Diagram (LAD) and Function Block Diagram (FBD).

The book covers a wide range of topics, from basic programming concepts and techniques to advanced programming features and functions. It provides detailed explanations of the LAD and FBD programming languages, as well as the STEP 7 programming environment.

Automation is the backbone of modern industries, and it has become a necessity to achieve high productivity, efficiency, and quality. The Siemens STEP 7 software is one of the most popular automation tools used by industries worldwide. With its user-friendly interface and powerful programming capabilities, it allows engineers to create and simulate programs in Ladder Diagram (LAD) and Function Block Diagram (FBD) programming languages. In this article, we will explore the basics of automating with STEP 7 in LAD and FBD and how to create efficient and reliable automation solutions.

Ladder Diagram (LAD) Programming

LAD programming is the most common language used for automation programming, and it's often used in conjunction with FBD programming. LAD programming is a graphical programming language that uses ladder-like diagrams to represent the logic of the program. The program logic is constructed by connecting relay symbols, which represent the input and output signals of the automation system.

To begin programming in LAD, the user has to select the LAD editor from the STEP 7 project tree. The LAD editor allows the user to drag and drop the required relay symbols from the toolbox onto the ladder diagram. The user can also modify the properties of the relay symbols to reflect the actual I/O devices that are being used.

After constructing the ladder diagram, the user has to set the program's operational mode, which determines how the program is executed. There are three operational modes available in STEP 7 LAD programming: continuous mode, cycle time mode, and single scan mode.

Function Block Diagram (FBD) Programming

FBD programming is a graphical programming language that is used to represent the program logic as a series of interconnected function blocks. The function blocks are similar to the relay symbols in LAD programming, and they represent the input and output signals of the automation system.

To begin programming in FBD, the user has to select the FBD editor from the STEP 7 project tree. The FBD editor allows the user to drag and drop the required function blocks from the toolbox onto the FBD diagram. The user can also modify the properties of the function blocks to reflect the actual I/O devices that are being used.

After constructing the FBD diagram, the user has to set the program's operational mode, which determines how the program is executed. There are three operational modes available in STEP 7 FBD programming: continuous mode, cycle time mode, and single scan mode.

Benefits of Automating with STEP 7 in LAD and FBD

Automating with STEP 7 in LAD and FBD programming languages offers several benefits, including:

Reduced development time: The user-friendly interface of the LAD and FBD editors makes it easy to create and simulate programs, reducing the time required for program development.
Improved reliability: The graphical representation of the program logic ensures that the program is easy to understand and debug. This leads to improved program reliability and reduced downtime.
Scalability: STEP 7 allows users to create scalable automation solutions that can be easily expanded as the automation system grows.
Reduced maintenance costs: The ease of program development and the improved reliability of the programs result in reduced maintenance costs.

details about automating with STEP 7 in LAD and FBD programming languages:

Simulating Programs: Before deploying a program to the actual automation system, it's recommended to simulate the program using the built-in simulation tools in STEP 7. This allows the user to identify and fix any errors in the program logic before it's deployed to the actual system.
Debugging Programs: Debugging is an essential part of program development. In STEP 7, the user can use the debugging tools to track the program's execution and identify any errors that occur during runtime.
Communication Protocols: STEP 7 supports various communication protocols, including PROFIBUS, PROFINET, and Ethernet/IP, which enables the automation system to communicate with other devices, such as sensors and actuators.
Data Storage: The STEP 7 software allows the user to store data in the form of data blocks. The data blocks can be used to store and retrieve data from the automation system, such as production data or alarm messages.
Programming Best Practices: To create efficient and reliable automation solutions, it's essential to follow programming best practices. Some best practices include creating modular programs, using descriptive naming conventions for variables and function blocks, and adding comments to the program code to make it easier to understand.
Integration with HMI: The Human Machine Interface (HMI) is an essential component of any automation system. STEP 7 allows the user to create an HMI using the WinCC software, which is fully integrated with STEP 7. This allows the user to create a user-friendly interface that can be used to monitor and control the automation system.
Security Features: In modern industries, security is a critical concern. The STEP 7 software offers several security features to protect the automation system from unauthorized access. For example, the user can set passwords for program access and modify the user privileges to restrict access to specific program functions.
Advanced Programming Capabilities: STEP 7 offers advanced programming capabilities, such as Structured Text (ST) and Sequential Function Chart (SFC). ST is a high-level programming language that allows the user to create complex programs using mathematical functions. SFC is a graphical programming language that allows the user to create programs using a flowchart-like interface.
Maintenance and Diagnostics: Maintenance and diagnostics are essential for ensuring that the automation system is running smoothly. STEP 7 offers several maintenance and diagnostic tools, such as the online/offline comparison tool, which allows the user to compare the online and offline versions of the program, and the diagnostics tool, which allows the user to monitor the status of the automation system and identify any issues.
Advanced Communication Capabilities: STEP 7 supports several advanced communication protocols, such as OPC UA and MQTT, which allow the automation system to communicate with other systems, such as enterprise resource planning (ERP) systems, and cloud-based services.
Modular Programming: In STEP 7, modular programming is a best practice that involves breaking down the program logic into smaller, more manageable modules. This makes the program easier to understand, maintain, and modify. The user can create function blocks and call them from other parts of the program, which helps to reduce the complexity of the code.
Online Monitoring: STEP 7 offers online monitoring capabilities, which allows the user to monitor the status of the automation system in real-time. The user can view the status of the inputs and outputs, program variables, and other system parameters, which makes it easier to troubleshoot any issues that occur during runtime.
Time-Based Programming: In modern industries, time-based programming is becoming increasingly important. This involves programming the automation system to perform specific tasks at certain times or intervals. STEP 7 offers several features that support time-based programming, such as the high-speed counter module and the real-time clock module.
Custom Libraries: STEP 7 allows the user to create custom libraries that contain reusable function blocks, data types, and other program components. This makes it easier to develop and maintain programs, especially in larger automation systems. The user can create their own libraries or use third-party libraries that are available online.
Remote Access: Remote access is a critical feature in modern industries, as it allows engineers and technicians to access the automation system from a remote location. STEP 7 offers several remote access features, such as the ability to connect to the automation system over the internet, and the ability to use a mobile device to monitor and control the automation system.
Simulation: Simulation is an essential tool in the development of automation systems, as it allows the user to test the program logic without the need for physical hardware. STEP 7 offers a simulation environment that allows the user to simulate the behavior of the automation system and test the program logic in a virtual environment. This helps to reduce development time and costs.
Data Logging: Data logging is an important feature in modern automation systems, as it allows the user to log and analyze data from the automation system. STEP 7 offers several data logging features, such as the ability to log data to a local database or a remote server, and the ability to analyze the data using tools such as Microsoft Excel.
Redundancy: Redundancy is an important feature in critical automation systems, as it helps to ensure that the system continues to operate even if a component fails. STEP 7 offers several redundancy options, such as the ability to use redundant controllers and power supplies, and the ability to switch to a backup system if the primary system fails.
Motion Control: Motion control is becoming increasingly important in modern automation systems, especially in industries such as robotics and manufacturing. STEP 7 offers several motion control features, such as the ability to control servo motors, stepper motors, and other types of motion control devices.
PID Control: Proportional-Integral-Derivative (PID) control is an essential feature in modern automation systems, as it allows the user to control the system's behavior based on feedback from sensors. STEP 7 offers several PID control features, such as the ability to tune the PID control parameters and the ability to implement PID control algorithms in the program logic.

SIMATIC S7-300400 Programmable Controllers

SIMATIC S7-300/400 are programmable logic controllers (PLCs) developed by Siemens AG. These controllers are designed for industrial automation applications and are widely used in various industries, such as manufacturing, automotive, energy, and many more.

The SIMATIC S7-300/400 controllers offer a wide range of modules, such as CPU modules, communication modules, digital and analog input/output modules, power supply modules, and many more. These modules can be combined to create a customized automation system that meets specific requirements.

The programming language used for the SIMATIC S7-300/400 controllers is Step 7, which is a ladder diagram (LAD) based programming language. Additionally, other programming languages, such as Function Block Diagram (FBD), Structured Text (ST), and Sequential Function Chart (SFC), can also be used.

The SIMATIC S7-300/400 controllers offer various advanced features, such as high processing speed, large memory capacity, redundancy, hot swapping of modules, and many more. These features make the controllers suitable for complex automation systems that require high reliability, availability, and flexibility.

Some of the topics covered in the book include:

The basics of programming with LAD and FBD
The STEP 7 programming environment
Data types and data blocks
Logic operations and branching
Analog signal processing
PID control
Communication between PLCs
Diagnostics and troubleshooting

The book also includes a number of practical examples and exercises, which are designed to help readers develop their programming skills and apply the concepts they have learned to real-world automation tasks.

You can download it in below link :

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Conclusion

Automating with STEP 7 in LAD and FBD programming languages is an efficient and reliable way to create automation solutions. The user-friendly interface of the LAD and FBD editors, coupled with the powerful programming capabilities of the STEP 7 software, makes it easy to create scalable automation solutions that improve productivity, efficiency, and quality. Whether you are a seasoned automation engineer or a beginner, STEP 7 is an excellent choice for your automation needs.

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