PROFINET

Based on its experiences with PROFIBUS, a real time fieldbus that is the most popular automation networking solution in automation today, PI Working Groups comprising more than 500 experts from major automation suppliers spent many years creating a comprehensive real time Ethernet solution for automation: PROFINET.

This solution is able to operate in the difficult industrial environments and is capable of delivering the speed and precision required by manufacturing plants. It can also provide additional functions – for example, Safety, Energy Management, and IT Integration. These can be used in combination with the control and monitoring functions. Users have a choice on which services they would like to utilize.

Here are some other advantages of working with PROFINET at the I/O level:

• Lower costs for production/quality data monitoring
• Highly scalable architectures
• Access to field devices over the network
• Maintenance and servicing from anywhere (even over the internet)
• Best in class diagnostics

All three communication channels can be used simultaneously. Bandwidth sharing ensures that at least 50% of every I/O cycle remains available for TCP/IP communications. Combined with ruggedized cabling, connectors, and Ethernet switches, PROFINET can meet all the needs of automation. Further below you can read about PROFINET’s features, which make it the world’s most advanced Industrial Ethernet.

It’s important to understand that PROFINET is fully compliant with internationally-accepted Ethernet standards. Some Industrial Ethernets break Ethernet conventions and are not truly compatible with office-based systems. These cannot interoperate as easily within enterprise architectures, or indeed alongside those Industrial Ethernets which are fully compliant.

Actually, Ethernet has been used on the factory floor almost as long as it has been used in the office, though mainly for inter-cell communications and not for IO. There has never been a standardized way to implement it, installations have tended to be proprietary. In addition, there are practical difficulties, including:

• Office Ethernet cannot deliver the real time performance needed for industrial IO.
• Office Ethernet cannot meet the high precision determinism needed for advanced motion control.
• Office Ethernet is unable to withstand the physical conditions found in manufacturing environments (dusty, hot, humid, corrosive, EMI, etc).

Fortunately, all these difficulties can be overcome, leading to what we now know as ‘Industrial Ethernet’.

The advantages of a fieldbus include its ability to connect multiple devices over a single cable or ‘bus’. This factor alone can cut design, engineering, commissioning, and maintenance costs by up to 40%. The greater accuracy of ‘digital’ also means big improvements in production speeds and quality, while better diagnostics allow fieldbus-connected production lines to benefit from advanced asset management techniques. Fieldbuses can also deliver the real-time performance demanded by current automation environments.

PROFIBUS, the world’s most widely used fieldbus, was introduced in 1989 and is standardized under IEC61158. It is supported by more than 1500 equipment vendors around the world. The single standardized approach means users have a wide choice of vendors and products –factors that encourage higher performance and lower costs. A fieldbus-enabled plant also delivers more and better data to supervisory systems, to support improved management strategies across the enterprise.

The vast field experience gained from PROFIBUS is embedded deeply in the PROFINET solutions available today.

However, ‘coexistence’ does not mean different systems are ‘interoperable’. It means only that it is possible to use the same network infrastructure to support multiple Industrial Ethernets. Protocol differences mean that Industrial Ethernets cannot communicate with each other except by using additional hardware such as protocol converters.

It’s also important to recognize that some Industrial Ethernets do not conform with the international Ethernet standard and that these require deployment on a closed network. Although these are not necessarily ‘proprietary’, they are non-standard from an Ethernet point of view.

PROFINET delivers a rich set of specialized features that sit on top of other communications. They are aimed at automation applications of all types and designed to make life easier for the designer, engineer, maintenance staff, and manager. You don’t have to use all the features at once – just choose what you need to meet your particular circumstances. Some features are listed below:

• iPar Server: Individual Parameter Server for automatic parameter assignment of devices
• Dynamic Reconfiguration: Allows a device to be configured and set up even with the controller in run
• Shared Device: Distribution of device functions to various controllers
• Application Profiles: Safety, energy management, motion control, etc
• Redundancy: Device, controller, media, and network redundancy options
• Simple Device Replacement: Allows a controller to automatically name a replaced IO device in case of device failure and replacement
• Tool Calling Interface: Used to call up a device-specific engineering tool

Think of PROFINET as a modular solution, offering the flexibility to start simple and add functionality as required.

The I/O Devices are structured hierarchically as Device, Module, and Channel. Inputs and Outputs are exchanged between the controller and I/O Device as ‘cyclic’ data. The controller sets the update cycle time.  Additional information such as diagnostic data that is not required as frequently is communicated as ‘acyclic’ data.

In Process Control

PI is a primary supporter of the WirelessHART protocol (ISA 100.11a). A standard adapter interface for WirelessHART has been agreed by PI in conjunction with other process automation organizations including the FieldComm Group. Therefore, users benefit from a single technology offer from multiple vendors.

In Factory Automation

Factory Automation differs from process in many respects. For example, bandwidth requirements are greater and network resilience, security, and redundancy are critical. As with the enterprise, WiFi and Bluetooth solutions are already used in factory situations. In addition, a set of standards is currently being developed by PI Working Groups for sensor/actuator communications in conjunction with both PROFIBUS and PROFINET. Bluetooth has been selected as the communications medium, complemented by IO-Link as the interface to end devices.

Diagnostic overviews provide levels of detail according to your needs, showing device, module, channel and interrupt activity. Current fault events can be acknowledged and PROFINET’s I&M (Identification and Maintenance) functions are facilitated at the same time. Comprehensible naming conventions mean you don’t have to look up obscure tag names or numbers before getting down to business. Even topology layouts showing the geography of your plant network become possible with PROFINET.

Integrated web servers are incorporated in automation devices and these mean that a standard Internet browser can be used to access diagnostic displays. It also means that engineers don’t necessarily have to be on site in order to diagnose a fault as access to plant networks can easily be facilitated over an intranet or even the internet. Automated, event-driven messages can be dispatched by SMS or e-mail to your engineering staff.

Cable diagnostics are just as simple. Again, displays are standardized to give accurate topology views of the network for fast location of faults. Standard Ethernet tools such as SNMP and Ethereal can be utilized. There’s also easy access to vendor-specific tools for complex devices.

With PROFINET, production data can be made available to supervisory staff in real time from almost anywhere in the enterprise. This can provide better management of plant, skills, and assets and lead to improved production scheduling and order processing. PROFINET can even deliver full Internet connectivity, enabling global enterprises to operate more efficiently across the globe.

By defining a standardized open profile, PI has made it possible for vendors and users to collaborate on intelligent energy management strategies using PROFIenergy.

User Benefits

• Energy and cost savings
• Fulfill laws/regulations for environmental protection

OEM Benefits

• Easy to program – using loadable function blocks
• Competitive Advantage

Device Maker Benefits

• Unique selling proposition and competitive advantage
• Builds on existing PROFINET protocol

PROFINET transmits standardized PROFIenergy commands to end devices and receives back status information and energy consumption data. PROFIenergy data uses the acyclic slots of the PROFINET communications protocol and it does not interfere with normal PROFINET processes. PROFIenergy can, therefore, be fully integrated into existing automation architectures.

PROFIenergy can be used to balance energy demand and match peak load conditions to avoid costly penalties.

In car body production, the total cycle time for a single robot cell can be as low as 45 seconds (including the delay for tool change). Many Industrial Ethernets suffer from slow start up, typically in the range of seconds compared with 100 ms range for fieldbuses, and this can be too slow for many production needs. By optimizing the PROFINET protocol and how data is utilized by end devices it is possible to reduce start up times dramatically.

PROFINET FSU defines the time between ‘power on’ and receipt of the first cyclic input data to be less than 500 ms. The protocol optimizations needed to achieve this are standardized in the PROFINET specification as follows:

• Use of fixed transmission parameters (only for copper wires), instead of automatic detection, which reduces start up by up to three seconds.
• The network address is not passed to the IO device on every cycle, but only at first start up. Parameters are stored in the IO device memory and re-used. This may save several seconds.
• IO Devices announce their readiness to establish communication instead of waiting for the IO Controller to search. It is possible to save up to one second this way.

From the OEM/end-user point of view, a number of other optimizations are possible. For example, start up can also be reduced through the use of suitable hardware. Wireless may also help, either by keeping communication up all the time or by establishing communication in advance of ‘power on’.

PROFINET addresses these sometimes critical security issues in various ways, as defined in a special security specification:

• By guarding against errors and improper operation
• By preventing unauthorized access that could lead to network manipulation or espionage
• By using proven and certified security standards (e.g. firewalls and VPN)

With these measures, the integrity of a PROFINET control network can be fully protected, without presenting any restrictions to personnel who rightfully needs access.

PROFIsafe

PROFIsafe is an additional software layer that provides functional safety over the bus on top of existing PROFIBUS and PROFINET protocols. PROFIsafe ensures the integrity of failsafe signals transmitted between safety devices and a safety controller meeting the relevant safety standards. It works independently of any automation functions even though it is running on the same network. It can be used with either PROFINET or PROFIBUS, in combination if required, in factory and process automation applications.

PROFIsafe has been available since 2001 and nearly 9 million PROFIsafe devices are operational. PROFIsafe is approved for wireless transmission channels such as WLAN and Bluetooth. It can even be used on open Industrial Ethernet backbones.

Please note: Safety is a sensitive area of automation. The dissemination, implementation, and deployment of PROFIsafe technology must be treated seriously. All companies and institutions involved with PROFIsafe conduct themselves according to the PROFIsafe Policy.

If a device fails, the failed device can be replaced with a new device, without any user configuration. When the user manually replaces the failed device for a new one, the controller detects the new device and assigns the respective IP address, name, and related configuration. There is no need to use engineering tools or reconfigure the network.

There are three requirements for using this feature:

1. The replacement device must be the same as the device it is replacing
2. The replacement device must have a blank name
3. The controller must support Simple Device Replacement

Users can bypass the second requirement by using a controller function. Controllers give the option to allow for name overwrite. If that option is enabled, then the replacement device can have an existing name.

PROFINET provides a high-speed, high-bandwidth, backbone for PROFIBUS PA (and other fieldbus networks) similar to the way that PROFIBUS DP does! It differs slightly however by using a ‘proxy’ interface – a module that sits between PROFINET and the underlying bus. The data path via the proxy is fully transparent, instruments on the fieldbus appear directly connected to the PROFINET controller as remote IO. This makes configuration, maintenance, and management of an automation system very simple from any part of the enterprise. Proxies exist for PROFIBUS PA and for many other bus technologies including Foundation Fieldbus and WirelessHART. The great advantage of the proxy approach is that existing field networks do not have to be replaced when upgrading a plant to PROFINET, investments in skills and inventory are protected as the migration to Industrial Ethernet architectures occurs.

Moreover, the PROFINET backbone can be used to connect other field devices typically found in process applications – for example, drives and discrete IO. Since most process plants are ‘hybrid’ (they include both process and discrete automation elements) only one network – PROFINET – is needed to cover the entire plant.

Three key additional needs of process automation are also supported by PROFINET:

• Dynamic Reconfiguration: The ability to make changes to an application program without stopping the controller.
• Time Sync / Time Stamping: The ability to record the actions, alarms and status messages to a sequence of events.
• Fieldbus Integration: Investment protection through the integration of plant units using proxies.
• Scalable Redundancy: PROFINET already has media redundancy but needs to support system redundancy as well for process applications.

Remember, PROFINET offers a modular approach to automation. That means it’s flexible and versatile. Not everything needs to be utilized so, ‘start slowly and build’.

Like office networks, PROFINET uses Ethernet switches to connect devices. PROFINET switches can be external infrastructure components or integrated switches. In general, the only requirement for Ethernet switches in a PROFINET network is 100 Mbps full duplex transmission. Most Commercial Off-The-Shelf (COTS) switches can work in a PROFINET network. However, there are many factors to consider when selecting a device, such as the installation environment (harsh manufacturing environments) and requirements for specific PROFINET features. The following section on Selecting will give further details.

In addition, specialized ASIC-based switches are now being fitted into many end devices. Both 2 and 4 port versions are available. Onboard 2-port switches allow easy ‘daisy-chaining’ of devices to enable bus-like line networks to be created. Design considerations here include taking into account accumulated switching delays. In linear networks, 10 switches in a line are usually the desirable maximum.

If HMI traffic and data-intensive signals (e.g. vision) are required, it’s worth paying attention to overall bandwidth requirements. PROFINET’s ability to reserve bandwidth for particular functions means that limitations rarely occur. It also means that multiple-functionality can exist on a single network.

For high integrity systems, PROFINET supports media redundancy with ring topologies. If a cable or device fails, then the system automatically segments itself into a ‘line’ topology to keep the rest of the system active.

Remember, PROFINET offers a modular approach to automation. That means it’s flexible and versatile. Not everything needs to be utilized so, ‘start slowly and build’.

• Remember that the environment you are planning for may be dirty, dusty, electrically noisy and generally unfriendly to data transmissions and infrastructure components of all types.
• Normal twisted pair cabling is suitable for PROFINET. TCP/IP has methods in place to resend telegrams when lost but the timing is not acceptable for industrial use! In other words, electrically noisy environments can easily interrupt your data flows and may cause control malfunctions. In these situations, always use Shielded Twisted Pair cabling.
• Grounding at both ends is best. However, it’s not always applicable due to ground loops.
• The need for shielding is independent of the protocol used. All Industrial Ethernet protocols – and indeed fieldbuses – need protection in noisy environments. If you used shielded cable with DeviceNet or PROFIBUS, use shielded cable with PROFINET as well.
• Use PROFINET-rated cable.
• Always use rugged connectors too. Field installable RJ-45 types are available, as illustrated.

• A PROFINET Commissioning Guideline is available, together with a separate Word file, which provides protocols and checklists for individual adaptations. The commissioning guideline explains setting IP addresses, PROFINET device names and typical steps to configure real time IO devices with their GSD files, and proper network measurements.
• Excellent engineering and test tools designed for use with Industrial Ethernet in general – and PROFINET in particular – are available from many sources. Such tools can investigate full Ethernet and PROFINET activity, provide a detailed analysis of parameters such as delays and jitter, and time stamp frames for later assessment.
• General-purpose Ethernet tools include the Wireshark software analyzer which uses the Ethernet ports on a PC as the analyzer hardware. Wireshark is license free and acts as a sniffer to analyze the Ethernet traffic.

Standard Ethernet protocol tools

The use of familiar Ethernet protocols means that browser based access to individual devices is possible from any PC in any location – even over the internet. Many PROFINET devices incorporate a web server for this purpose. A browser can also read out information such as device status and configure a device either locally or from a remote site.

IT protocols familiar from the industrial world include SNMP (for managing components such as switches and reading statistics and diagnostics). Again these can be used from anywhere in the network. Another familiar protocol is LLDP which is used for mapping network topologies for making device replacement easy.

PROFINET-specific tools

The PROFINET specifications also include a set of specific diagnostic tools which operate at the application layer level. These provide more advanced diagnostics capabilities in standardized formats. Some allow for remote monitoring of networks, and some are intended for on-site use.

Simple Device Replacement

Many devices can be replaced in the field without the need for configuration – no computer is required; you just take the new device out of the box and install it in place of a failed unit.

The migration process to PROFINET was made simple not only for PROFIBUS but also from many other existing protocols. PROFINET achieves this through the use of the unique ‘proxy’ concept, which is covered in detail in this section. Proxies are part of the PROFINET specification and perform consistently across all protocols. PROFINET proxies are defined for the following protocols:

• CC-Link
• PROFIBUS DP
• PROFIBUS PA
• HART
• INTERBUS
• DEVICENET
• Foundation Fieldbus
• CANopen
• Modbus
• IO-Link
• AS-i

PROFINET is alone in being able to integrate many popular fieldbuses, making it the ideal way to move to Industrial Ethernet architectures.

Special Note: In addition to the proxy migration option, a wide range of gateway devices exists for connecting legacy protocols to PROFINET from various vendors.

With proxies, investments in the skills, equipment, and software associated with the sub-network can be retained. No changes to automation systems at the fieldbus level are required; fieldbus networks can simply be connected into the PROFINET architecture and utilized as before. Therefore, PROFINET can greatly assist in the expansion and deployment of distributed automation architectures. It also simplifies greater vertical integration, moving manufacturing closer to enterprise IT networks.

PROFINET is also highly scalable and modular in concept, not every feature needs to be deployed at once. New users can start simple and build as required. Migration can happen in steps, allowing plant and personnel to build experience while improving productivity and profitability.

• Simple device replacement: Just physically replace a device when it fails. There are no switches to set and no computer is needed.
• Device names: Meaningful names can be allocated by the user which contributes to much simpler replacement procedures. The PLC assigns an IP address to the node.
• Standard wireless: Familiar WLAN and Bluetooth protocols are used.
• More topology options: Ethernet offers many more topology options, including star, ring and tree structures which make it easier to design and commission according to the layout and functions of a plant, especially where redundancy, long distance, and remote connections are needed.
• Shared Device/i-Device: One device can be accessed by more than one controller. This flexible assignment of modules to different controllers suits many applications, for example, a single sensor that participates in a safety function and needs to communicate with a failsafe PLC. An IO-controller can also operate in a so-called i-Device mode, in which it combines the IO-Device functionality with an IO-Controller function on the same interface (see diagram).

• Unlimited scalability
• Unlimited address space
• Larger message size (1440 bytes vs. 244)
• Machine to Machine (M2M) communication
• Vertical integration capabilities
• The possibility to coordinates more drive axes (32 axes vs. >150) – with IRT cycle times <1 ms and jitter <1 μs
• It’s faster too, which means more application potential and fewer interfaces