Hello! Welcome to the first lesson in your journey to becoming a controls and robotics engineer.
This course is designed to build your skills from the ground up, focusing on practical knowledge that will be valuable for your portfolio and future career, especially as you aim for a work-study program in Germany.
In this introductory lesson, we will focus on the physical building blocks of an automation system. The learning outcome for this session is to identify the components of Siemens S7-1200 and S7-1500 PLC systems, specifically the CPU, I/O modules, and power supply.
Understanding the hardware is the essential first step before we can dive into programming. Just like an electrical engineer first learns about resistors and capacitors, a controls engineer must be able to identify and understand the function of each piece of hardware in a control cabinet.
We'll start with the fundamental components common to all PLCs and then explore the specific architectures of the S7-1200 and S7-1500 series, which are two of the most common families you'll encounter in the industry.
The Core of an Automation System
At its heart, a Programmable Logic Controller (PLC) is a ruggedized industrial computer designed to withstand harsh factory environments. Its job is to execute a user-written program to control machines and processes. Regardless of the brand or model, nearly every PLC system is built from three essential types of components:
- Power Supply (PS): This component takes the main electrical supply (e.g., 120/230V AC) and converts it into the low-voltage DC (typically 24V DC) required by the PLC's electronic components. It's the heart of the system, providing the energy for everything to operate.
- Central Processing Unit (CPU): This is the brain of the PLC. It runs the control program you write, processes inputs from the field, makes decisions based on the program's logic, and sends commands to the outputs.
- Input/Output (I/O) Modules: These are the PLC's senses and hands, connecting the CPU to the real world.
- Input modules receive signals from devices like pushbuttons, sensors, and switches.
- Output modules send signals to control devices like motors, indicator lights, and solenoid valves.
Now, let's see how these components are implemented in the Siemens S7-1200 family.
The Siemens S7-1200: The Compact Controller
The SIMATIC S7-1200 series is known as a "compact controller." This means the CPU, a basic power supply, and a set of digital inputs and outputs are often integrated into a single, compact housing. This design is cost-effective and ideal for controlling smaller, standalone machines or simple processes.
To get a clear picture of the S7-1200 hardware, please watch the following video from RealPars. It provides an excellent overview of the different components and CPU variations.
S7-1200 PLC 101: A Step by Step Introduction for Beginners
This video introduces the S7-1200 PLC, its main hardware components, and the different CPU models available, giving you a sense of its capabilities and typical applications.
Please watch the following segments: 00:27 - 01:16: This part introduces the main hardware components. 01:16 - 05:13: Focus on how the different CPU models (1211C, 1212C, etc.) scale in capability and are suited for different applications. 06:51 - 08:29: This segment explains the 'C' for compact design and how communication modules can be added.
As you saw in the video, the S7-1200's key features are:
- Compact Design: The CPU, power input, and some I/O are all in one unit. The "C" in models like "1214C" stands for Compact.
- Onboard I/O: Most S7-1200 CPUs come with a set of built-in digital inputs and outputs, making them ready to use out of the box for simple tasks.
- Expandability: Even though it's a compact controller, you can expand its capabilities. You can add:
- Signal Boards (SB): Small boards that snap directly onto the front of the CPU to add a few extra I/O points without increasing the physical footprint.
- Signal Modules (SM): Full-size modules that are attached to the side of the CPU to add a larger number of digital or analog I/O channels.
- Communication Modules (CM): Added to the side of the CPU to enable communication over different network protocols like PROFIBUS or for serial communication.
To see how these components are wired together in a practical application, have a look at the following diagram.
The Siemens S7-1500: The Modular Powerhouse
Next, we'll look at the SIMATIC S7-1500. This is an "advanced controller" designed for larger, more complex, and higher-performance applications. The key difference from the S7-1200 is its fully modular design.
In an S7-1500 system, each component (CPU, power supply, I/O modules) is a separate module that you select and assemble on a mounting rail. This provides immense flexibility and scalability.
The following video provides a great hands-on look at how an S7-1500 rack is assembled.
Siemens S7-1500 PLC hardware assembly, CPU HMI walkthrough, IP address configuration, CPU1513-1. Eng
This video demonstrates the physical assembly of an S7-1500 rack. Pay close attention to how the different modules—CPU, I/O, and communication—are individual components that plug into a backplane.
Please watch these two key segments: 01:54 - 05:56: Watch the presenter physically install the CPU, a Profibus communication module, and various digital and analog I/O modules onto the mounting rail. 05:56 - 07:59: This part discusses the power supply for the CPU and modules, and the critical role of the Siemens Memory Card (SMC), which is mandatory for S7-1500 operation.
The video clearly shows the modularity of the S7-1500. Here is a summary of the components you saw, which form a typical S7-1500 rack:
To get a more structured overview of these components, we'll use a technical summary document. You don't need to memorize everything, but reading these specific sections will solidify your understanding of the S7-1500 architecture.
This document, 'S7-1500 In a nutshell,' provides a concise technical reference. We will use it to understand the function of each module type in more detail.
Please read the following sections from the PDF: Section 5.1 Structure (Page 10): Look at the 'Sample configuration of SIMATIC S7-1500 system' diagram. This section explains how modules are installed on a mounting rail and connected via 'U connectors' which form the backplane bus. Section 7 Controller (Pages 13-14): Read the first page of this section ('What can you do with the CPU?'). This explains the central role of the CPU and introduces different types, such as standard, fail-safe (F-CPU), and technology (T-CPU) for motion control. Section 9 Inputs/outputs (Page 21): Read the first page of this section. It explains that I/O modules are the interface to the process and introduces different performance classes (High Feature, Standard, Basic). Section 12 Power supply (Page 40): Read the first page of this section. This is important as it distinguishes between the Load Power Supply (PM), which powers the whole system including sensors/actuators, and the System Power Supply (PS), which specifically powers the backplane bus for the module electronics.
Based on the video and the document, the key takeaways for the S7-1500 are:
- Modular Design: The system is built by combining separate modules on a mounting rail with a backplane bus.
- System Power Supply (PS): In larger configurations, the CPU's integrated power might not be enough for all the modules on the rack. A separate PS module is added to supply power to the internal electronics of the modules via the backplane bus.
- Load Power Supply (PM): This is the main 24V DC power supply that provides power to the CPU, the PS modules, and the input/output circuits, including external sensors and actuators. It is often mounted to the left of the CPU.
- Wide Range of Modules: You can choose from a vast catalog of modules to precisely match the application's needs, including:
- CPUs: Ranging from standard CPUs to high-performance, fail-safe (F-CPU), and technology (T-CPU) versions.
- Signal Modules (SM): For digital (DI/DQ) and analog (AI/AQ) inputs and outputs.
- Communication Modules (CM): To connect to various industrial networks.
- Technology Modules (TM): For special tasks like high-speed counting or motion control.
Conclusion
In this lesson, we have identified the fundamental hardware components that make up a Siemens PLC system. You are now equipped to distinguish between the two major families and their design philosophies.
Key Takeaways:
- All PLC systems consist of a Power Supply, a CPU, and I/O Modules.
- The S7-1200 is a compact controller family, best for smaller applications. It integrates the CPU, power, and some I/O into one unit but can be expanded with signal boards and modules.
- The S7-1500 is an advanced, modular controller family for larger and more demanding applications. All components are separate modules that are assembled on a rack, offering maximum flexibility and scalability.
- Common module abbreviations include PS (System Power Supply), PM (Load Power Module), DI (Digital Input), DQ (Digital Output), AI (Analog Input), and AQ (Analog Output).
Preview of the Next Lesson:
Now that you can identify the physical hardware, our next step is to explore the software environment used to bring it to life. In the next lesson, we will begin our dive into the TIA Portal (Totally Integrated Automation Portal), the engineering software used to configure, program, and diagnose all modern Siemens automation devices. We will focus on navigating the interface and creating your very first project.