Why PROFINET? And, Why Now?
“Bandwidth.” When asked what the major advantage of PROFINET over traditional Fieldbus technologies is for industrial automation, Carl Henning says it starts with bandwidth. Henning is the Deputy Director of PROFIBUS & PROFINET International, an industry group dedicated to providing PROFIBUS and PROFINET education and training.
“Fieldbus has been around for 20 years, so it’s nothing new,” he adds. “Based on RS 485 it can move 244 bytes at up to 12 MBaud. PROFINET, on the other hand is Ethernet-based networking. It’s less than a decade old and can move 1440 bytes of data at 200MBaud. So it can give you much more information at a much higher speed which can be really important in industrial applications.”
PROFINET is an open Industrial Ethernet standard that uses TCP/IP and IT standards to provide real-time Ethernet communications all the way to the lowest level of the factory – the sensors, actuators, drives, switches and valves. Fieldbus refers to a set of industrial network protocols for real-time distributed control (now standardized as IEC 61158).
Fieldbus links PLC layer of the plant control system to those same devices at the bottom of the control chain. In both cases the PLCs are in turn connected to an HMI system which provides human input and ultimate control.
“The more complex your process the more robust you want you network to be,” says Henning. “In addition to speed PROFINET is orders of magnitude more scalable than Fieldbus. PROFINET has an address space of 2048 nodes while Fieldbus can only go to 126 nodes, making PROFINET vastly superior in architectures where you have to connect a lot of nodes to the same network.”
PROFINET also leverages some familiar IT-type Ethernet techniques that make it easier to diagnose and trouble shoot maintenance issues, especially remotely. For example, PROFINET uses Ethernet standards that are familiar to the IT world such as SNMP; a simple network management protocol that provides a standard method of getting diagnostic information out of Ethernet switches. With this you can get access to data points like the number of retries before a communication is successful. If the number is high that may indicate the presence of electromagnetic interference or connection problems. This data can then be reported to your HMI or enterprise asset management application where it can be analyzed and addressed.
“Since you can monitor that kind of information you can take action automatically, you can be proactive and that helps increase network uptime which then helps increase your overall equipment efficiency (OEE) and ultimately plant uptime,” says Henning.
The other benefit you get with PROFINET over Fieldbus is simplified remote access to the devices. This is a key benefit for machinery OEMs who want to avoid expensive service calls by networking into the customer’s installation remotely.
“Remote access is the key piece that makes follow-the-sun monitoring and maintenance possible. This feature makes it possible for an engineer in Shanghai to log in and troubleshoot a problem in your Chicago plant in the middle of the American night when your local experts are unavailable,” says Henning. “Sure, you could wake up the local engineer and have him come all the way into the plant from wherever he lives, but that will take time and disrupt his life. It’s actually faster to have the guy at your overseas plant do it because he is already on hand. All he has to do is log into the problem device through the network.”
This feature, which has spawned numerous services offerings from vendors including Siemens Industry Inc., is possible because many of the devices and PLCs have built in web servers, making it possible to access it from anywhere with a web browser (given the appropriate security and access), figure out what’s wrong and fix it.
“PROFINET allows for more intelligence and monitoring and thus affords the opportunity for improved operations.”
Henning has identified a set of five criteria for selecting an Industrial Ethernet network.
Criterion #1: Performance; literally which network technology is fastest and will convey the information you need when you need it? Where is the determinism? PROFINET delivers increasing levels of determinism through four stages.
Step 1 – TCP/IP. PROFINET uses TCP/IP for non-time-critical data like configuration and diagnostics.
Step 2 – Layer 2. For time-critical data, PROFINET skips the TCP and IP layers to move data directly from Ethernet to the application.
Step 3 – Bandwidth Reservation. While the first two steps are sufficient for 90 percent of applications, there are still times – like motion control systems – when you need guarantees of sufficient bandwidth for data delivery regardless of other network traffic. To meet this need, PROFINET reserves bandwidth on the network.
Step 4 – Scheduling. The PROFINET configuration tool ensures that the data to the device farthest away is sent first.
Criterion #2: Scope; ideally you don’t want to have a mishmash of protocols and technologies that require integration engineering and then separate maintenance and training. “Because it is so robust with a lot of bandwidth, PROFINET is a great platform for multitasking,” says Henning. “So we can put IO, motion control, functional safety, peer-to-peer integration, vertical integration, and the integration of PROFIBUS and many other fieldbuses on the network simultaneously, giving it what I think is the best scope of any such protocol in the market,” says Henning.
Criterion #3: Adoption; put simply, how popular is it? The more deployments a given technology has, the more people who are using it, the more secure your investment is, and the more options you will have in the future as more development and technological advances become available. According to research by IMS Research and published in The Industrial Ethernet Book, PROFINET and Ethernet/IP are the market share leaders with about one-third of the market each.
Criterion #4: global support; as the saying goes, the world is flat. Whatever technology you select you want to make sure you can get technical support wherever you need it around the globe.
Criterion #5: Third party certification is a requirement for PROFINET products, ensuring interoperability in real world installations.
“These elements provide a good guide for what people should ask about when selecting a networking technology,” says Henning.
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