Foreword
When it comes to industrial real-time Ethernet, EtherCAT is currently the most popular and successful. EtherCAT is an open bus, and thanks to its excellent Ethernet characteristics and hard real-time capabilities, major industrial control manufacturers have successively developed products based on EtherCAT technology. Of course, EtherCAT is not the only industrial real-time Ethernet technology; mainstream options include Siemens Profinet, B&R PowerLink, and others such as SERCOS, Ethernet/IP, and EPA. Today, we will mainly discuss a comparison between BECKHOFF's EtherCAT and Siemens' Profinet, two typical real-time Ethernet buses.
(a) Profinet
The image below shows the TIA Portal hardware catalog with SIPLUS extreme components. First, let's look at Profinet. As you can see from the image, Profinet is divided into three versions:
Profinet CbA
Profinet RT
Profinet IRT
These three different versions correspond to three different real-time characteristics of Profinet. CbA refers to component-based automation, with a real-time response time of 100ms, typically used in general industrial control applications where high real-time requirements are not critical. RT refers to soft real-time, used for PLC-level control in factory automation, with a response time of 10ms. IRT refers to synchronous real-time, also known as hardware real-time, with a response time of less than 1ms, meeting the real-time and synchronous requirements of most motion control applications. Profinet's RT and IRT can be illustrated vividly with the following diagram:
To ensure absolute real-time performance, Profinet IRT isolates its data transmission channel from ordinary Ethernet. This isolation means that IRT does not use the TCP/IP protocol to transmit real-time data, similar to EtherCAT.
(II) EtherCAT
EtherCAT was developed by Beckhoff and launched to the market in 2003, and is currently operated through ETG (EtherCAT Technology Group). EtherCAT is a high-speed, real-time Ethernet standard, with no version distinctions. It directly competes with Profinet IRT, also ensuring its real-time performance through hardware chips. EtherCAT bus boasts superior performance, with response times reaching the microsecond level.
By employing distributed clocking, EtherCAT bus clock synchronization can achieve nanosecond-level accuracy, which is precisely why major motion control manufacturers are so eager to adopt EtherCAT technology. EtherCAT Distributed Clock Applications:
(III) EtherCAT and Profinet IRT
(1) Operating principle
EtherCAT employs a technology that can be figuratively called "on the fly," optimizing the Ethernet packet structure for distributed I/O. Communication is entirely supported by hardware chips to ensure maximum performance. In a pure EtherCAT network, there is no need for a switch at all, and the diagnostic functions are very powerful.
Profinet employs time-slicing technology, achieving hard real-time performance through a specific switch chip built into the device. The loop time ranges from 250 microseconds to 4 milliseconds, with a jitter of approximately 1 microsecond. The following diagram illustrates how IRT data is guaranteed in real-time during the loop:
(2) Topology
EtherCAT offers highly flexible topologies, including linear, star, tree, and hybrid types, making it suitable for virtually any connection method. Furthermore, EtherCAT supports cable redundancy, and each EtherCAT network can theoretically support 65,535 nodes, unaffected by the topology.
Profinet supports linear, tree, and other structures. The maximum number of nodes in each Profinet network is 60, and specific Profinet IRT switches must be used. There is also a limit to the number of switches that can be cascaded, which cannot exceed 20-25. This means that, whether you like it or not, star connection is the most common design, which ensures performance and reduces costs, but its topology is obviously not flexible enough. (3) Ease of use
EtherCAT is unaffected by slave devices and network topology, offering flexible network deployment. There's no need to manually configure slave addresses or manage IP or MAC addresses. Slave addresses are automatically generated, and new slave devices don't require manual address updates, eliminating address conflicts and providing a superior user experience.
Profinet requires manual configuration of the address of each slave station, and the insertion of a new slave station will affect the addresses of all slave stations in the network. Address management is complex and requires professional personnel, which is usually beyond the capabilities of equipment vendors. If certain non-Profinet networks experience situations such as high-intensity ARP requests, the Profinet network will become vulnerable. To address this, the PI organization has specifically released recommendations on Profinet IO network load to help users manage the load limits of their networks, which is clearly not user-friendly. (4) Stability
Since EtherCAT first drafted the IEC 61158 standard in 2005, it has undergone 46 technical changes, most of which were errata. Each change can be traced using an errata sheet, which can be downloaded from the ETG website. Maintenance and testing tools have been continuously improved, but no fundamental changes have occurred. EtherCAT has undergone some parameter changes, but its technical version has remained unchanged since its release.
Profinet does not provide a detailed errata, and there are three versions of Profinet, with its IRT version constantly changing. Because Profinet is not an open bus, it's understandable that it doesn't provide detailed documentation to users when parameters change or technology evolves. However, from a technical stability perspective, an open bus is more user-friendly.
(IV) Summary
Due to differences in bus technology and application background, we cannot say that one bus performs better than another. Generally speaking, market users can provide the evidence. EtherCAT has gained a large number of users due to its openness. From this perspective, Profinet is unlikely to achieve the same success as PROFIBUS in the near future. As a traditional fieldbus, PROFIBUS is also open. EtherCAT's rapidly growing user base:
In line with current trends, EtherCAT has also begun to integrate with IoT technology. Conceptually, EtherCAT has incorporated itself into IoT technology; ETG even claims that EtherCAT itself is IoT. The future of industrial Ethernet buses is very bright, as traditional fieldbuses have fallen far behind industrial Ethernet in terms of data volume and transmission speed. For example, CAN is commonly used in the automotive industry. As the automotive industry develops, cars are increasingly seen as mobile internet terminals. Can CAN still meet the requirements for high-speed and high-volume data transmission? Some automakers are already at the forefront of this technology; for example, Toyota has begun using EtherCAT. The traditional bus competition in the field of industrial automation will undergo fundamental changes with the advancement of internet technology.
