Fieldbus openness – Critical Considerations for Selecting Your Next Fieldbus

Ultimately, any user of industrial technology must place a certain level of trust in the organization acting as the driving force behind the technology. If this vendor or organization has a tradition of openness, their technologies deserve a higher level of trust. But it appears as though everyone has a different definition of openness. Hence, some technologies are more “open” than others.

For example, with one particular industrial Ethernet solution, the key technology to enable compatibility is hidden in the highly complex optimization algorithm of the configuration tool, which happens to be excluded from the specification and is not disclosed or made available to third party manufacturers.

The networking world has a history of fieldbus representatives telling users that a particular feature cannot be made accessible for competitive reasons. The configuration tools offered by some companies only support their own devices and often have a range of undocumented features. Some suppliers even pronounce their proprietary implementation, which was incompatible with the rest of the world, as Version 1 of a new standard and refuse to support Version 2 (which was developed by the user organization), because it would mean competition for their devices from partner companies.

Safety over EtherCAT protocol has been certified as a protocol for transferring process data between Safety over EtherCAT devices up to SIL 3 according to IEC 61508. The transport medium is regarded as a “black channel” and not included in safety considerations. A safety frame containing the safe process data and the required data guard is included in the EtherCAT process data.

Then you have the development of renowned, but competitive, suppliers entering into strategic partnerships that start waving their alliance under shared banners. There are several examples of archenemies from the fieldbus wars suddenly becoming partners. And still, those fieldbuses are not as open as users would like. What good are “flavor of the month” fieldbuses to the long term planning of technology companies when the door to openness can be suddenly slammed in your face after a collapse in multi-vendor support?

So how do you secure the necessary insurance against being stranded with a fieldbus that has fallen out of favor (assuming you are not hamstrung with legacy requirements or management or customer dictates)? The key is to understand the most important considerations when selecting an “open” fieldbus.

We submit that the specific criteria a technology must meet to be regarded as truly open are: Standardization, Free Access to Technology and Open Implementation. To help put these into perspective, we will use EtherCAT, a leading industrial Ethernet technology, as an open fieldbus example.

Standardization
EtherCAT in and of itself is an open standard and uses other open standards. The EtherCAT Technology Group (ETG) is recognized as an official IEC partner organization and EtherCAT is an IEC, SEMI and ISO Standard. It uses Ethernet frames according to IEEE 802.3 and supports the use of other Ethernet protocols (including non-IP-based protocols) in the same network.

Free Access to Technology
Other network technologies have similar organizations and are based on IEEE standards. Just because a technology is a “standard” as described above, however, does not necessarily mean that it can be implemented in master or slave devices by any other company that wishes to. If the company that invents the technology doesn’t allow third party manufacturers of master or slave devices, the system can ultimately be a ‘standard,’ but it is a ‘closed’ or proprietary solution.

Using EtherCAT as an example, any company or user (competitor or not) may join the ETG and obtain insider access to EtherCAT technology.

The EL7201 for the EtherCAT I/O system is a full-featured servo drive for the direct connection of servomotors up to 200 W. The integrated, fast EtherCAT control technology with field-oriented current and PI speed control supports highly dynamic positioning tasks.

Open Implementation
Standardization and access to the technology in and of itself does not fully facilitate an open technology. If the configuration tools for the network (typically associated with the master software of the IP holder) do not allow configuration of all devices equally, or worse yet exclude some or all third party devices, the technology can be effectively closed off. And there are many implementations of so-called open network technologies where the configuration tools do not support devices from third-party manufacturers, or that only provide rudimentary support.

An example of open third-party support is shown by the EtherCAT Configurator. It is a tool from the EtherCAT Technology Group that treats devices from any and all manufacturers in the same way. You simply copy the third-part device description into the associated directory in the form of an XML file. Any future devices will be supported without requiring modification of the tool.

Benefits of open technologies to the market
Open technologies deliver a number of benefits, five of which we will discuss here. Again, we will use EtherCAT as an example of an open fieldbus technology.

• Openness means lower costs
Some organizations charge membership fees, some do not. Some organizations charge fees for acquiring software development kits and support; some do not. In some cases, the charges are necessary to recoup development costs. In other cases, they can be a way of limiting participation.

In general though, an open fieldbus should be able to use a variety of components with a range of costs, enabling the developers to decide the most cost-efficient way to design a network.

• Openness means interoperability
Interoperability is only possible if technology discontinuities are avoided. Usually, the supporting organization ensures that incompatible versions do not exist, and they see to it that no manufacturer has the right to change the underlying technology. Both the ETG organization and the Profinet organization ensure a high degree of interoperability because chips from different suppliers are tested thoroughly or use the same code basis. The ETG, for example, organizes interoperability validation events (“Plug Fests”) as well as conformance and interoperability tests.

• Openness means multi-vendor capability
From a user point of view, perhaps the most important aspect is that multi-vendor systems ensure competition, lower costs, optimum availability, and quality.

• Openness means a choice of implementation technologies
Choices are needed for the real-time platforms that can support a given technology. EtherCAT, for example, has master software stacks for almost 30 different OS platforms.

• Openness means future-proof technology
Due to its openness, EtherCAT is a future-proof technology. Its associated features and performance ensures that future requirements can be met without a change in technology.

Beyond standard
Thus, there is more to being “open” than simply claiming that a certain technology is a “standard.” The truly open characteristics of a technology address the fundamental need to fully support competitors in the successful implementation of the technology. This represents a realization that this decision will have consequences in the market, both beneficial to the inventor of the technology and at times potentially harmful consequences to that company’s sales. This is especially true if a competitor develops a better, more competitive product using the open technology.

From a user’s perspective, however, this attitude toward open solutions enables the unrestricted choice of master controllers and supported operating systems and field devices from a variety of vendors that are targeted to a wide range of industries. This applies not just for the short term, but for the long term too. Besides getting rid of proprietary solution headaches, this also results in better implementations, better machines and better end products.

EtherCAT Technology Group
www.ethercat.org

::Design World::