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Topics: Ethercat vs. Sercos - Benefits and deciding factors on Automation Technologies
Start by
Melvin Foo
10-21-2013 02:00 AM

Ethercat vs. Sercos - Benefits and deciding factors

What are the benefits of Ethercat and what are the deciding factors that make people choose sercos over Ethercat
10-21-2013 04:35 AM
Top #2
John Kowal
10-21-2013 04:35 AM
Ethercat is similar in performance to Ethernet Powerlink, both are open and well supported in the marketplace for all industrial networking purposes, including motion. SERCOS was originally intended for motion and typically is run over optical fiber but is in transition. The new SERCOS III will go over Ethernet, therefore will have broader application. However, Ethernet Powerlink and Ethercat are supported and stable today, whereas SERCOS II will go away and SERCOS III products are just appearing.
10-21-2013 07:32 AM
Top #3
William Grissom
10-21-2013 07:32 AM
John may be optimistic in stating that B&R's Ethernet Powerlink is similar to Beckhoff's EtherCAT. I considered both before deciding on EtherCAT. Ethernet Powerlink is slower, though much faster than legacy field busses and sufficient for many applications. It also requires special ethernet hubs. National Instruments recently selected EtherCAT for remote I/O in their CompactRIO. I haven't used Sercos III, but Beckhoff uses it in their motor drives because it has features that make it preferable to EtherCAT there, particularly in configuration control.
10-21-2013 10:25 AM
Top #4
Marc Ostertag
10-21-2013 10:25 AM
Hi William, thanks for your sharing of your evaluation. I'd love to hear what convinced you that Ethernet Powerlink would be slower than EtherCAT since that is not what we are seeing on any practical applications. EPL also does not need special hubs as far as I can tell whereas EtherCAT requires specific ASICs on its nodes. If you are interested, I'd love to hear more of your thoughts on EPL's performance.
10-21-2013 01:19 PM
Top #5
William Grissom
10-21-2013 01:19 PM
A disclaimer. I am an automation user and don't represent any manufacturer or vendor.

A B&R rep displayed the X20 system in 2006, which uses EPL. I recall he estimated response times from analog input to digital output ~2 ms. That is our main concern, to quickly kill a test if an analog reading goes out of limits. We prefer <1 ms in some tests with tiny rocket engines. In our EtherCAT system, I measure a 0.4 ms response. That is not the full-up system since still awaiting parts, but with 16 chans (2 chan analog modules), at 0.1 ms cycle time. Performance was not the only concern with B&R. At that time, they used 3rd-party reps and didn't appear fully committed to the U.S. market. We had also started with EtherCAT in 2004, but wanted to keep considering alternatives (still do). Indeed, some in-house engineers kept asking "why not Allen-Bradley?" (still do).

Other impressions have come from plots in Beckhoff or National Instruments seminars and magazine articles. I have never seen measurements that show EPL faster than EtherCAT, and most show it many factors slower. I recall a statement at a seminar (Beckhoff or NI, don't recall) that EPL requires old-fashion hubs that are uncommon today, since based on an earlier ethernet standard. I don't have hard-copies to quote, only memory, and am no ethernet expert. Perhaps a Beckhoff tech guy will chime in (after proper legal guidance).

EtherCAT does need special chips at the sensor/module end, but Beckhoff makes them affordable. A few transducer vendors have jumped on-board, but I am sure they would like more. They also offer an IP core, which is easy if the device has an FPGA, which I understand is the way National Instruments implements EtherCAT in CompactRIO. The PC/controller end originally required certain Intel NIC ethernet chipsets to run the drivers, but I think they eliminated those restrictions. I use Beckhoff PC's, so no issue.

Anyway, the original post asked for comparisons between EtherCAT and SERCOS. You B&R guys jumped in with EPL. I think Beckhoff agrees that SERCOS III has advantages in motor control since they use it there, but better that they chime in.
10-21-2013 04:04 PM
Top #6
A. Steinhoff
10-21-2013 04:04 PM
The performance of EtherCAT, SERCOSIII and Ethernet Powerlink is defined by the transmission performance of the 100Mb/s Ethernet media. As long as the packet size is small and the number of stations are also small, there are no remarkable speed differences. The ring topologies of of SERCOSIII and EtherCAT has speed advantages if the number of slaves are huge.
But this ring topology has a lot of disadvantages ... but this is an other issue.
10-21-2013 06:28 PM
Top #7
Shawn Nelson
10-21-2013 06:28 PM
Melvin - I don't think your question was "Ether" specific............possibly it was.

Since SERCOS II (Fiber) and SERCOS III (Ether) are both current and valid in the market place you have many SERCOS products to choose from (50 control?? 30 drives?? 3-4 IO). It's not my impression that SERCOS II is going away.

From a practical application standpoint – SERCOS, EtherCat and Powelink handle majority of applications with the exaction of a few very unique requirements. All have strengths and weaknesses – being clear about the intended application is key.

You could find white paper after white paper touting the bullet points for each if you were to Google it example: http://www.sercos.com/technology/advantages.htm

If you have a real application I’m not sure I’d base my decision on the “communication bus”……. What I have been asking the following when this question comes up:
1. How is the infrastructure for supporting the hardware and software?

1. Does the organization have distributors or contacts local for me ….not on a plane?

1. Can the vendor repair/service their products in my country or when I ship machines?

1. Does the contact I’m working with have working knowledge of the application attempting to be done?

1. How stable are the contacts at the organization - are they new?

Hopefully this helps - happy engineering!!
10-21-2013 09:02 PM
Top #8
Melvin Foo
10-21-2013 09:02 PM
Thanks for the answers guys... the question actually came from our etherwire forum (http://snipr.com/u531t) from a guy that wanted to discuss the more about this. I was hoping that it would be answered there as this question is more publicly/ directly accessible rather than buried in a group from within linkedin (which inturn is only accessible to guys that have linkedin accounts and subscribe to this group).
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