Inside the industrial Ethernet

UK Industry Automation expert and trainer, Peter Thomas, will visit Australia in November to conduct Profibus Association of Australia's 3-day Certified PROFINET Engineer course.

Here he sheds light on common industrial Ethernet misconceptions. He also discusses network security requirements and controlling process applications through industrial Ethernet.

What is PROFINET and how does it differ from PROFIBUS?

PROFINET is the Industrial Ethernet standard developed and supported worldwide by PROFIBUS and PROFINET International or PI for short. At the end of 2013, 7.6 million PROFINET devices, from a wide range of vendors, had been installed and the number continues to grow.

Most manufacturing sites are used to using fieldbus technology like PROFIBUS and Ethernet side by side. PROFINET merges the two together with obvious benefits.

PROFINET is based on established, well-proven, Ethernet technology but with the added robustness demanded for use in an industrial automation environment.

Unlike PROFIBUS, it is not a multi-drop network but uses four-core, twisted pair screened cable to connect one device to another using switches. Termination, to prevent reflections, is no longer an issue as the resistors are already installed in each device.

Again, unlike PROFIBUS, PROFINET is not a master-slave protocol but uses full duplex communication at 100 Mbit/sec which means that devices can read and write at the same time. It makes use of existing IT standards, but unlike IT systems, PROFINET is a real time, deterministic protocol capable of achieving guaranteed cycle times. 

There are two implementations of PROFINET that can work side by side. These are PROFINET RT for the most common automation applications where cycle times of 10mS are more than acceptable and PROFINET IRT, standing for Isochronous, for use in high-speed applications such as multi-axis drives where cycle times as low as 31.25µS can be achieved.

Although PROFINET is not PROFIBUS over Ethernet, there are many similarities with this fieldbus technology and many of the features have been enhanced.

Those people used to developing and supporting PROFIBUS systems will feel quite comfortable with the new technology although PROFINET-specific training is recommended. A Certified PROFINET Engineers course with world-wide recognition is now available.

Most importantly, PROFINET does not make your existing PROFIBUS installation redundant. PROFIBUS will continue to play an important role but a gradual migration over to PROFINET will allow you to benefit from features only available using 21st century technology.

Is is possible to integrate PROFINET with an existing PROFIBUS installation?

Because PROFINET uses standard Ethernet technology as well as the enhancements required for use in an Industrial Automation environment, it offers several benefits that cannot be achieved with PROFIBUS.

These include:
· High-speed, deterministic, cycle times as fast as 31.25µS
· Automatic compatibility with existing Ethernet standards such as SNMP, LLDP, DHCP and HTTP
· More flexible topology options including star, tree, line and ring
· The use of user-friendly, application-specific, device names instead of numeric addresses
· Automatic neighbour recognition allowing devices to be replaced with a minimum of technical expertise
· More detailed diagnostics about the network
· IO Devices with integrated switch capability
· The ability to communicate wirelessly
· Access to web-based functionality
· Safety and Redundancy functionality when required
· One cable for all applications

Collectively, these make better use of your resources, increase your productivity and allow more scope when developing innovative solutions.

Integration with existing PROFIBUS installations, and many other older technologies, is catered for by use of a device known as a PROXY. These devices are available from a wide range of suppliers and provide a low-cost option for protecting your investment in these older technologies.

What about security?

In the past, automation networks were normally isolated from other IT networks. In addition they used specialist protocols and operating systems that helped to create a protected and secure environment. With the widespread use of Industrial Ethernet the situation has dramatically changed. 

Highly interconnected systems using standard operating systems and protocols are becoming the norm. As a consequence security is now an essential consideration in automation systems such as PROFINET. 

Security systems can help protect your plant from malicious and accidental damage but It is not just a matter of locking things down.

Threats must be identified, responsibilities need to be established and security policies need to be implemented and maintained. Industrial-grade firewalls are recommended on all PROFINET installations.

These firewalls will:
· Control access to the protected network and its devices.
· Only allow authorised traffic to and from a protected network.
· Conceal the network and devices from outside the protected area.
· Record information useful for traffic monitoring and intrusion detection.
· Restrict access for firewall setup and maintenance.

Virtual Private Networks, or VPNs, are another method of improving the security of your network, especially when remote access is required.

Is it a good idea to control an industrial process using Ethernet?

Well, whilst it is perfectly possible to get a PROINET-enabled PLC to communicate with remote IO using conventional CAT5 cables and off-the-shelf switches, this is not going to be suitable for an industrial automation environment.

We are all aware of the annoying delays experienced in file opening times, file transfer times or the time taken for web pages to open. 

Clearly, these are completely unacceptable for industrial automation and to overcome this, PROFINET defines the required specifications for cables, connectors and switches.

It also uses a dedicated, prioritised communications channel that by-passes several of the time-delaying layers of the 7-layer OSI model to transmit IO data in real time. 

It is these enhancements that allow PROFINET to be classed as a real-time, deterministic Industrial Ethernet solution that can be used with complete confidence. It is also the reason why so many organisations are now using the technology.

What skills and tools will I require to configure and support a PROFINET system?

The line between industrial automation and the IT world is becoming blurred and automation engineers now need to be conversant with a lot more IT-related functionality than was the case in the past.

So a working knowledge of things like MAC addresses, IP addresses, Ethernet protocols and the ability to configure Ethernet switches are just some of the tools that a 21st century automation engineer will require.

In terms of support, there are free tools that allow you to go as in-depth as monitoring the Ethernet frames passing back and too along a cable. However on a day to day basis it will not be necessary to go down to this level.

This is because PROFINET is a diagnostic-rich protocol that builds upon the capabilities of PROFIBUS in this area. 

As well as giving access to device-related diagnostics down to the module and channel level, PROFINET makes use of the SNMP protocol to allow you to monitor the health of the network components like switches. 

SNMP stands for Simple Network Management Protocol and is a protocol that will be familiar to people working in the IT world. This information could be used to produce a SCADA page showing the status of the network with disconnected cables changing colour.

Many of the organisations that produce tools for PROFIBUS are doing the same for PROFINET and these range from software tools for use on a conventional laptop to permanently installed diagnostic monitoring devices with web interfaces.

In a series of six audio recordings uploaded to Youtube, Thomas addresses a variety of Industrial Ethernet issues and misconceptions relative to PROFINET and its working relationship with Profibus.

Also addressed in the series of Q&A interviews are the benefits & best practices of Profibus & PROFINET integration in Process & Factory Automation; important Network Security requirement; controlling Process applications through Industrial Ethernet; and reviews on the contents of PROFINET Engineer Course syllabus.

More information: Profibus Association of Australia

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