What are the differences between two popular industrial real-time Ethernet networks: EtherCAT and Profinet?

[Introduction] Comparison of industrial real-time Ethernet EtherCAT and Profinet.

 

Foreword

When it comes to industrial real-time Ethernet, the most popular and popular one currently is EtherCAT. EtherCAT is an open bus. With its good Ethernet characteristics and hard real-time functions, all major industrial control manufacturers have successively developed products based on EtherCAT technology. Of course, there is more than one type of industrial real-time Ethernet: EtherCAT. The mainstream ones include Siemens Profinet, B&R's PowerLink, and others such as SERCOS, Ethernet/IP, EPA, etc. Today we will mainly discuss EtherCAT from BECKHOFF and Profinet from Siemens. Comparison of typical real-time Ethernet buses.

 

 

 

(一)Profinet

The figure below shows the TIA Portal hardware catalog with SIPLUS extreme components. First, let’s take a look at Profinet. As can be seen from the figure below, Profinet is divided into three versions:

Profinet CbA

Profinet RT

Profinet IRT

 

 

 

These three different versions correspond to the three different real-time characteristics of Profinet. CbA refers to component-based automation. Its real-time response time is 100ms. It is usually used in general industrial control situations where real-time requirements are not high. RT refers to Soft real-time is used for PLC-level control of factory automation. The response time reaches 10ms. IRT refers to synchronous real-time, which can also be said to be hardware real-time. The response time is less than 1ms, which can meet the real-time and synchronization requirements in most motion control fields. Require. Profinet's RT and IRT can be vividly illustrated by the following figure:

 

 

 

In order to ensure absolute real-time performance, Profinet IRT is isolated from ordinary Ethernet on the data transmission channel. The so-called isolation means that IRT does not use TCP/IP protocol to transmit real-time data, which is similar to EtherCAT.

 

(二)EtherCAT

EtherCAT was developed by BECKHOFF and launched to the market in 2003. It is currently organized and operated through ETG (EtherCAT Technology Group). EtherCAT is a high-speed real-time Ethernet, regardless of different versions. It directly benchmarks Profinet IRT, and also uses hardware chips to ensure its real-time performance. The EtherCAT bus has excellent performance and the response time reaches microsecond level:

 

 

 

Through the use of distributed clocks, the clock synchronization of the EtherCAT bus can be achieved at the nanosecond level. This is why major motion control manufacturers are flocking to EtherCAT technology. EtherCAT distributed clock applications:

 

 

 

(三)EtherCAT and Profinet IRT

(1)Operating principle

EtherCAT adopts a technology that can be vividly called "on the fly". It optimizes the message structure of Ethernet to be suitable for distributed IO. Communication is completely supported by hardware chips to ensure maximum performance. If It is a pure EtherCAT network, no switches are needed at all, and the diagnostic function is very powerful.

Profinet uses time slice technology to achieve hard real-time through a specific switch chip built into the device. The cycle time is 250 microseconds to 4 milliseconds, and the jitter is about 1 microsecond. The following figure illustrates how the IRT data is guaranteed to be real-time in the loop:

 

 

 

(2)Topology

EtherCAT的拓扑结构非常灵活，可以是线性、星型、树型、混合型等等，几乎可以用于任何一种连接方式，同时EtherCAT支持线缆冗余，每个EtherCAT网络理论上可以支持65535个节点，而且不受拓扑结构的影响。

Profinet supports linear, tree and other structures. The maximum number of nodes in each Profinet network is 60, and a specific Profinet IRT switch must be used. The number of cascaded switches is also limited and cannot exceed 20-25, which means that whether you like it or not, star connection is the most conventional design, which not only ensures performance but also reduces costs, but obviously its topology is not flexible enough.

(3)Ease of use

EtherCAT is not affected by slave stations and topology structures, and the network deployment is flexible. There is no need to manually set the slave address, nor do you need to manage IP or MAC addresses. Slave addresses are automatically generated, and if a new slave joins, there is no need to manually update the address. In this way, address conflicts are out of the question, and EtherCAT therefore has a good user experience.

Profinet needs to manually set the address of each slave station, and if a new slave station is inserted, it will have an impact on the slave station addresses of the entire network. Address management is complicated and requires professionals to operate. Usually, machine equipment suppliers cannot complete it. . If situations such as high-intensity ARP requests occur on some non-Porfinet networks, the Profinet network will become vulnerable. For this reason, the PI organization has also specially issued a recommendation for Profinet IO network load so that users can grasp the load limits of their own networks. , which is obviously not very user-friendly.

(4)Stability

Since EtherCAT first drafted the IEC61158 standard in 2005, a total of 46 technical changes have been made, most of which are errata. Every change can be traced using an errata sheet, and the document can be downloaded from the ETG official website. Maintenance testing tools have been enhanced but have not fundamentally changed. EtherCAT has undergone some parameter changes, but its technical version has not changed since its release.

Profinet does not provide detailed errata. At the same time, Profinet has three versions, and its IRT version is constantly changing. Because Profinet is not an open bus, it is understandable not to provide detailed information to users when parameter changes or technological changes occur. But in terms of technical stability, the open bus is more user-friendly.

 

(四)Summarize

Due to differences in bus technology and application background, we cannot say that the performance of one bus is better than another. Generally speaking, market users can explain the problem.

EtherCAT has won the favor of a large number of users due to its openness. From this perspective, Profinet is unlikely to achieve the same glory as Profibus for the time being. As a traditional fieldbus, Profibus is also open. EtherCAT’s rapidly growing number of users:

 

 

 

In line with current trends, EtherCAT has also begun to be combined with IoT technology. Conceptually, EtherCAT has integrated itself into IoT technology, and ETG even claims that EtherCAT itself is IoT. The future of the industrial Ethernet bus is very bright. The traditional fieldbus has lagged far behind industrial Ethernet in terms of data volume and data transmission speed. For example, CAN is usually used in the automobile industry. With the development of the automobile industry, the automobile is increasingly regarded as a mobile Internet terminal. Can CAN still meet the high-speed and large-scale data transmission requirements? Some automobile manufacturers are already leading the way. At the forefront of technology, Toyota, for example, has begun to adopt EtherCAT technology. The traditional bus battle in the field of industrial automation will undergo fundamental changes with the advancement of Internet technology.

 

Source: Industrial Control Library. If there is any mistake or infringement, it will be deleted.

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