Introduction
When considering EtherCAT for your industrial network, one fundamental decision involves choosing the right EtherCAT Master. Should you go for a lightweight, software-based solution running on general-purpose hardware, or opt for a traditional, dedicated PLC with built-in EtherCAT Master capabilities? In this article, we explore the technical advantages and disadvantages of using a software-based EtherCAT Master, such as SOEM (Simple Open EtherCAT Master), compared to a dedicated PLC, helping you make the right choice for your application.
PLC vs. Software-Based EtherCAT Master
Both dedicated PLCs and software-based EtherCAT Masters have distinct characteristics that can make them more suitable for different types of applications. To better understand these differences, let’s break down the workflow involved in each approach.
Workflow with a Dedicated PLC
When using a dedicated PLC as an EtherCAT Master, the process is straightforward and highly standardized. The engineer starts by selecting a suitable PLC model that supports EtherCAT as a native communication protocol. With the PLC and its development environment (typically an integrated IDE provided by the PLC vendor), the engineer configures the EtherCAT network, adding slaves and mapping process data. The PLC’s integrated tools make it easy to set up network parameters and handle I/O, reducing the need for low-level programming.
Since PLCs come with extensive support and libraries, the focus remains primarily on developing the control logic using function blocks or ladder diagrams, and the real-time communication is handled by the PLC firmware.
Once the control logic is programmed, the system is tested, and any necessary adjustments are made through the vendor’s development tools. Since PLCs are built to operate reliably in industrial settings, maintenance involves regular updates from the vendor.
Workflow with a Software-Based EtherCAT Master
In contrast, the workflow with SOEM requires more hands-on development. First, the developer selects general-purpose hardware, such as a PC or embedded controller, to run the SOEM stack. Since SOEM is an open-source EtherCAT Master stack, the developer must create their own master application around the stack. This involves writing custom software that will handle network configuration, data processing, and task scheduling. This step requires an in-depth understanding and experience with low-level programming.
The developer must also ensure that the system can meet real-time requirements. This often involves choosing a suitable operating system, such as Linux with real-time patches (PREEMPT-RT) or an RTOS, such as RT-Kernel from RT-Labs, and carefully configuring the hardware and software to minimize latency and jitter. Once the master application is developed, the network setup is defined programmatically, with the developer specifying slave devices and their configurations directly in the code.
Advantages of a Software-Based EtherCAT Master
Software-based EtherCAT Masters, such as once built around SOEM, offer several unique advantages over traditional PLC-based solutions. These advantages make them an attractive option for certain types of applications, particularly those that require flexibility around hardware choices.
Another benefit is the cost-effectiveness of SOEM. Being open-source and dual licensed, it significantly reduces upfront costs, making it particularly attractive for applications with limited budgets or those in the prototyping phase. Developers can begin working on their application without waiting for specialized hardware, as SOEM can be run on a standard x86 machine, which speeds up the prototyping process and allows for quick iterations.
Using SOEM also provides complete control over the software stack. This is especially beneficial when an application has unique timing, functionality, or communication requirements that a standard PLC may not be able to fulfill without extensive customization.
Challenges with Software-Based EtherCAT Masters
However, there are notable challenges when using software-based EtherCAT Masters. Real-time performance can be a concern when using SOEM, but with proper hardware selection and configuration, it is possible to achieve the necessary deterministic control for critical industrial systems. With SOEM, achieving real-time performance depends heavily on the hardware and operating system. While it is possible to use real-time operating systems like Linux with PREEMPT-RT, it often requires careful tuning to ensure the necessary timing is met.
Development complexity can be higher with SOEM due to the need for a deeper understanding of the EtherCAT protocol and the underlying network stack. However, this also provides developers with greater flexibility to tailor their system to specific needs, which can be a significant advantage for certain applications. Developers must address issues like jitter, task scheduling, and network interface tuning—tasks that are largely simplified in a PLC environment. While PLCs come with vendor-provided support that reduces the technical burden on the development team, SOEM users have access to RT-Labs’ support, which provides extensive training, consulting, and maintenance options, helping bridge the gap and offering significant assistance in implementation.
When to Choose a Software-Based EtherCAT Master
A software-based EtherCAT Master is ideal for projects requiring custom hardware or specific communication approaches, as it offers greater flexibility and control. It also provides significant advantages for implementing advanced control loops and optimizing them for timing, as programming is done in C rather than traditional ladder logic or other PLC programming languages.
In educational and research environments, SOEM’s dual license nature and adaptability make it a popular choice for training and experimentation.
When to Choose a Dedicated PLC
PLCs can be advantageous when there are no specific hardware requirements, or when there are no special requirements for surrounding systems. Furthermore, when safety standards are involved, PLCs with integrated safety capabilities simplify the development process.
Conclusion
Choosing between a dedicated PLC and a software-based EtherCAT Master depends on the specific requirements of your application. Software-based solutions like SOEM offer flexibility, cost savings, and adaptability, and can be customized to meet unique requirements that may be difficult for PLCs to accommodate. Dedicated PLCs provide a reliable, standardized solution that may be preferable for applications needing minimal setup and where specific hardware requirements are less important.
By understanding these trade-offs, you can make an informed decision that aligns with your project’s technical requirements and budget—whether you’re developing a mission-critical industrial automation system or an experimental research setup.
