PROFINET – a solution platform for process automation?
04 November 2015
A recent Whitepaper from PROFIBUS and PROFINET International (PI) details the functions and capabilities of PROFINET that meet the demands of the process automation industry, and highlights work being undertaken to a create a solution platform for process automation.
Industrial communication is a key technology for modern automation – to control and monitor machines and systems in manufacturing and production processes. It also interconnects production islands and integrates adjacent tasks like logistics, quality assurance, and system maintenance business systems. In the future world of Industry 4.0, the Industrial Internet of Things, and Big Data, industrial communication is of even greater importance. Easy-to-handle solutions with high performance capability for real-time, availability, flexible topologies, and integration – even over long distances – are needed to take advantage of the possibilities of the digital world.
Ethernet technology and IP-based communication are the current driving force behind interconnectivity and factory automation-related industries are already benefiting from this, with better products that can be produced in more quickly and at lower cost.
Process-related systems, however, are typically complex in structure, consisting of different sub-systems with numerous devices and differing topologies, manufacturers and technologies. It is important to harmonise this complexity and to fully integrate data and information systems to improve operational reliability. According to PI, PROFINET meets these demands. It is 100% Ethernet, providing an environment for interoperability at all levels of a plant, including IT. It is also precisely defined in its specifications, which is a requirement for full interoperability.
As a uniform technology in a plant, PROFINET can also affect personnel costs. There is less training expense, fewer specialists are needed, and plant operation is more transparent. Like PROFIBUS, PROFINET has a selection of application-oriented profiles for solving tasks. PROFIenergy, for example, enables energy-saving during process-related standby periods of plant segments.
Security is also an increasingly important consideration, particularly in the process industry. PROFINET already features a multi-level security concept and, because it is 100% Ethernet, it is able to share in future security developments from the IT world.
As an Industrial Ethernet standard, PROFINET offers plant operators and owners of process automation-related plants a step forward in terms of standardisation, integration, ease of use, security, and cost reduction. PI is also working intensively on the development of a comprehensive solution for process automation that includes existing and new PI technologies. The goal is for PROFINET to offer a complete solution platform for process automation. To this end, a working group has carried out a study to compare the range of demands of the process industry on communication technology with the performance offered by PROFINET. Based on this research, a gap analysis identified the needed developments of the technologies and specifications. Special emphasis was put on the explicit specification of all functions needed to ensure interoperability between products of different manufacturers.
A new Whitepaper looks at the findings of the working group and goes into detail about existing functions and capabilities of PROFINET which already meet the demands of the process automation industry, as well as providing guidance as to specifications that are published, or under development, and which could be implemented and utilised in future products.
Special properties of Industrial Ethernet over and above standard Ethernet include robust, industrial-grade components and products and the development of protocols which fulfill industrial requirements, such as real-time capability.
PROFINET is standardised in IEC 61158 and IEC 61784 and, as a universal communication technology, covers all requirements of automation technology. PROFINET is 100% Switched Ethernet, according to IEEE 802.3, so is open for application of all Ethernet technologies and parallel operation of multiple Ethernet protocols.
Compared to factory automation, process automation places additional demands on communication technology. Process plants, can extend over wide areas and have lifespans of up to 40 years. These often consist of continuous production processes where interruption or disturbance can pose a hazard for people and the environment. Unplanned stoppages can also result in large financial loss.
Plant owners want to achieve an integrated data and information flow both horizontally and vertically. This yields clear specifications for the communication technology, including:
• Installation technology and field devices can be handled easily and by skilled staff.
• Application in hazardous areas, including intrinsically safe ignition protection.
• Long cable distances (up to 1,000m).
• Flexible topology design.
• Robust connection technology.
• Redundancy concepts for critical components.
PROFIBUS PA already enables long cable distances and explosion protection for the harsh environments of process automation and offers complete digital integration of field instrumentation in control and asset management systems. The connection is made using a link/coupler, typically via PROFIBUS DP.
The fieldbus combination of PROFIBUS DP with connected PA segment is found in many installations worldwide today. Specifications and guidelines, such as the PA 3.02 device profile, provide the needed standardisation, while the many field devices from various manufacturers provide users with choice when selecting instrumentation for their plants.
However, to date, some requirements have not been tackled, especially in connection with device replacement and device integration. Version 3.02 of the PA profile standardised the compatibility of devices to make device replacement, independent of manufacturer and software version, possible. Duplication of integration tools will also soon end with the newly completed joint industry standard FDI (Field Device Integration), which also supports PROFIBUS PA.
Process applications with PROFINET do already exist, especially in areas where PROFIBUS DP was previously used and Remote I/Os or motor management systems were connected. However, this use case is subject to certain limitations because PROFINET functions, such as system-redundancy and configuration-in-run, are not yet implemented in all products.
Proven PROFINET functions and technologies of importance to process automation and especially with field devices include network configuration, connection technology, network diagnostics, topology display, detection of neighbouring devices, device replacement and diagnostics. These functions enable automatic address configuration during device replacement, as well as the display of a plant, which can be used, for example, to ensure that a replacement device was connected at the correct port. The replacement device receives the same name and parameters as the replaced device. In addition, the topology display is used for diagnostic purposes and shows, for example, a wire break graphically at the corresponding location.
The network configuration of PROFINET can be designed flexibly, and reflects the plant conditions. It supports line, star, ring and tree topologies. Connection of devices is carried out exclusively using switches as network components, which are often already integrated in the device.
PROFINET field devices use the LLDP (Link Layer Discovery Protocol), according to IEEE 802.1AB, to exchange the available addressing information via each port. This allows the respective port neighbour to be explicitly identified and the physical structure of the network to be determined.
Status-oriented maintenance is also important for operation and maintenance of plants. It is based on the capability of devices and components to determine their status and to communicate using standardised mechanisms. PROFINET provides a system for signalling alarms and status messages from the devices to the controller. To ensure a uniform display of the different diagnostic messages, the results of the PROFINET diagnosis model have been assigned to the diagnostic display according to NAMUR NE 107, which ensures a uniform display for all devices in a plant.
Replacement of field devices can be performed easily and reliably, according to PI. The basis for this is the cyclic exchange of neighbourhood information of the devices. If a device fails, its neighbourhood is known. A replacement device that is ‘nameless’ is inserted, and the controller searches for the explicitly identifiable neighbour device of the defective device. The replacement device can therefore be assigned the same position in the network, the same address, and the same parameter set as the failed device.
For secure networking within a large factory or over the Internet, PROFINET provides a graduated security concept which can be adapted to the application through configurable upstream security zones. This frees devices from being overloaded with security mechanisms. The concept can also be adapted to meet changing security requirements.
For safety-relevant applications a consistent communication path is vital. One possibility for this already exists today in the form of Safety with 4-20mA HART using Remote I/O or Proxy. A future solution is based on PROFIsafe, which is defined in IEC 61784-3-3 for implementing functional safety. PROFIsafe can be used with both PROFIBUS and PROFINET. Elements of a fail-safe controller can be transferred directly with the process control data on the same network without the need for additional wiring.
Important and already released specifications for using PROFINET in process automation Include ‘Configuration in Run’ for disturbance-free changes during operation, ‘Media and system redundancy’ for very high system availability, ‘Proxy technology’ for investment protection through transparent integration of existing systems such as PROFIBUS PA and other communication technologies in PROFINET as well as exact ‘Time stamping’.
Configuration in Run refers to the feature based on redundant communication connections that enables problem-free interventions in the plant without affecting the communication in the network. This applies to actions taken on or with compact devices as well as to modular devices and proxies. Examples include change of device configuration, device replacement, addition or repair of components, and change of parameters.
High system availability is ensured through PROFINET redundancy solutions. Developed by PI, these include media and system redundancy, and have been standardised to ensure interoperable behaviour of devices from different manufacturers. In the case of media redundancy the PROFINET device has more than one physical connection path to the controller. If one communication path fails the second path is automatically used, so communication with the connected devices continues. In the case of system redundancy a PROFINET device establishes more than one communication relation with a redundant controller. A distinction is made between different ways of implementing system redundancy. S2 system redundancy describes a compact PROFINET device, such as a field device, that can be operated on a system with high availability with no need of additional hardware. R1 and R2 system redundancy refers to the redundant realisation of the communication interface of a modular PROFINET device for example, with a Remote I/O. R2 system redundancy achieves maximum plant availability through its four paths between the controller and device.
With proxy technology, existing plant sections can be integrated into a PROFINET infrastructure. For process automation, this incorporates the existing fieldbus systems PROFIBUS DP/PROFIBUS PA, FOUNDATION Fieldbus H1, HART and others.
Proxies are gateways that represent devices in a structured manner in the PROFINET network. The control systems can use them to access the field devices cyclically as well as acyclically.
PA Profile 4.0
The current PA Profile – version PA 3.02 – is the generic device profile of PI for process field devices which ensures uniform behaviour of devices of various types and from different manufacturers.
Requirements and expertise of manufacturers and users, including consideration of core parameters for easy device commissioning and replacement, are currently being incorporated into a revised profile version which will contain all useful elements of Version 3.02 and will, additionally, be independent of physical layer and protocol. The result will be a PA 4.0 device profile that can be used uniformly with PROFIBUS and PROFINET systems.
This, says PI, will result in significantly easier and uniform processes for engineering, installation, commissioning, and replacement of devices. Profile devices, for example, will be commissioned according to a uniform procedure.
For vendor-neutral configuration of field devices in the control system, devices with the PA profile offer a standard interface in the form of the ‘neutral channel’, which represents the combined functions of the devices and provides these in an expanded GSD file for device integration. NAMUR NE 107-based diagnosis model is retained and is being revised and adapted in dialogue with all industry participants.
The transmission of large quantities of data made possible by Industrial Ethernet, expands the former data exchange into an information exchange. As a result, not only data and keywords but also meaningful information from the entire plant is made available to the operator.
In the short- and medium-terms, PI sees two technologies as keys for process automation – PROFIBUS PA for plants with long cable distances and hazardous areas and PROFINET devices with currently available interfaces in compact plants and selected industry sectors.
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