PROFINET – broadly positioned


Discussion on PROFINET in the context of Process Automation

Dr. Peter Wenzel, PI (PROFIBUS & PROFINET International)

Market penetration of PROFINET

The move to Ethernet-based communication systems is in full swing. This is true especially for PROFINET as proven by the latest figures on installed PROFINET devices. With 1.3 million new PROFINET devices sold on the market in 2011, the total installed base has now risen to 4.3 million devices. Factory automation projects account for almost all of these figures. It is the goal of PROFIBUS & PROFINET International (PI) to make PROFINET up the task for the full range of industrial automation applications.

In order to optimize PROFINET for the wide range of requirements of factory and process automation applications, the new PROFINET V2.3 version has been supplemented in two respects. First, advanced functions for integration and parameter assignment of devices (for Configuration in Run), scalable redundancy, and time stamping (for determining Sequences of Events) have been added that open up the market for PROFINET to process automation applications. Second, a performance upgrade has been implemented with the addition of the Fast Forwarding, Dynamic Frame Packing, and Fragmentation functions that extends the market for PROFINET all the way to high-end motion control applications, while still ensuring its coexistence of with IT applications.

Innovation of PROFINET for process automation

Innovations of PROFINET

In its quest to make PROFINET fit for use in process automation, PI collaborated with users to develop a set of requirements. In addition to user-friendly operation, protection of investment for the end user is an essential requirement because instrumentation in a process control system typically has a life cycle of several decades. This ensures that plant owners using PROFIBUS today can rely on a future-proof system and can change to PROFINET at any time.

The requirements that apply to PROFINET for process automation mainly include the functions for cyclic and acyclic data exchange, integration of fieldbuses, integration and parameter assignment of devices (Configuration in Run), diagnostics and maintenance, redundancy, and time stamping (Sequence of Events).

Fieldbus integration in PROFINET

For two-wire conductor systems used both in standard applications and in applications involving energy-limited bus feed of devices in hazardous areas, PI is continuing to rely on its thoroughly proven PROFIBUS PA solution. The question then arises as to the optimal gateway from PROFIBUS PA to PROFINET. A proxy concept for the integration of fieldbuses in PROFINET, which was specified several years ago, is available for this. This concept can be used to integrate the three communication systems used in the process industry, namely PROFIBUS PA, HART, and Foundation Fieldbus. It is based on standardized mechanisms for mapping the fieldbus-specific properties onto PROFINET. The bus systems are integrated using gateways (proxies) that link the higher-level PROFINET network to the fieldbus system to be integrated. The proxy becomes responsible for implementing the physics and protocol and ensures the exchange of all I/O and diagnostic data as well as alarms with the field devices.

The availability of automation systems is of critical importance in continuous processes in particular because, for reasons that are known, plant operation often must not be interrupted under any circumstances. To avoid automation failures caused by wire breaks, short circuits, and the like in these types of plants, a scalable redundancy concept was developed for PROFINET, in which the redundancy solution can be structured optimally to meet the specific requirements of the application.

Some applications require a time stamp for digital and analog measured values and alarms that is accurate to the millisecond. A precondition for this is an exact time synchronisation of the components involved. The purpose of this is to ensure that I/O devices can provide real-time information about alarms and other important events with a time stamp that is based on a network-wide standardized time of day. The time recording of events is the basis for determining the Sequence of Events, thereby enabling an exact description and analysis of a possible error case, for example.

Like redundancy, uninterrupted plant operation – including when reconfiguring devices and networks and when inserting, removing, or replacing devices or individual modules while the plant is operating – plays an important role (Configuration in Run). The actions are performed in PROFINET without causing any interruption or adversely affecting network communication. This ensures that plant repairs, modifications, or expansions can be performed without a plant shutdown in continuous production processes, as well.

Fieldbus and Ethernet systems provide extensive possibilities for diagnostics, e.g., for maintenance. These include, for example, the provision and transmission of identification and maintenance (I&M) data, as is familiar from PROFIBUS and PROFINET applications, or the communication of events and transmission of device status according to NAMUR Recommendation 107. Manual changes made directly on the device or via external parameter assignment tools are signaled to the control system via PROFINET as parameter change events. This allows the control system to detect deviations from the central data management, notify the user, and perform updates, if necessary.

Performance upgrade for machine building
With the latest PROFINET V2.3 specification, a performance upgrade is available to users. This was made possible by the incorporation of intelligent functions in the new version of the specification, namely Dynamic Frame Packing, Fast Forwarding, and Fragmentation.

Functionality of Dynamic Frame Packing

PROFINET real-time communication (RT) uses the prioritization methods of Ethernet and can therefore be implemented on standard Ethernet controllers. The accuracy of the firmware implementation determines the jitter of the transmitter clock, just like on other Ethernet systems. With a data rate of 100 Mbps and full-duplex transmission, bus update times that are faster by several factors compared to today’s fieldbuses are possible. As a result, RT is usually fully sufficient for typical factory automation applications. For applications whose requirements include the need to synchronize nodes to within 100 µs or less or to form a highly dynamic control loop via the bus, additional measures become necessary. The highly accurate isochronous real-time (IRT) synchronization process of PROFINET eliminates Ethernet transmission delay times of differing and fluctuating lengths.

PROFINET enables parallel TCP/IP communication for standard data, diagnostics, or parameter assignment purposes alongside both RT and IRT communication, without the need for additional modules or firmware measures. This is made possible by a free time slot in the update cycle. Data access, diagnostics, and parameter assignment are the same with RT and IRT communication. The user only has to specify when configuring whether RT or IRT communication will be used.

PROFINET V2.2 meets the real-time requirements of more than 95% of applications. Only applications involving specific configurations in which many nodes with few bytes are connected in a line topology may have more stringent performance requirements. For example, the possible bandwidth utilization is not optimal when padding is used, i.e., filling of frames to the minimum 64 byte length in compliance with standards. Additional measures have been taken in the PROFINET V2.3 specification for this case. These measures at different starting points produce high-performance communication with exact deterministic behavior at update rates as fast as 31.25 μs, without affecting the openness for TCP/IP communication.

The decision whether to forward a frame in the integrated switch of a device requires address information in the frame header. With Fast Forwarding, the FrameID (FID) address information is integrated once at the start of the frame header so that instead of having to wait for a large number of bytes it is possible for forwarding to take place early on. As a result, the current standard delay times of 3-6 µs per node can be reduced to 1.2 µs.

To optimise the ratio of frame to user data, the Dynamic Frame Packing function was defined. For this, improvements were made to the summation frame method already used in several fieldbuses in which the I/O data for several nodes on the network are integrated in one frame, thus requiring only one frame header and trailer (FCS). In contrast to ring bus systems, PROFINET uses the full-duplex principle of data transmission common in Ethernet systems. Here, input and output data are sent simultaneously on the 2-pair cable. When a single summation frame is used, this complete frame is sent, received, and checked all the way to the last node, including the checksums. With Dynamic Frame Packing, the data of the first nodes in the line, which are not relevant for the nodes placed further at the end, are removed during the passage. As a result the frame becomes shorter when passing through each node.

Time scheduling ensures the unlimited openness of PROFINET for TCP/IP frame transmission alongside IRT communication. Specifically, it ensures that the network is reserved for TCP/IP frames rather than user data during a defined time phase. With Fast Ethernet, the transmission of one TCP/IP frame can take up to 125 μs, which defines the minimum cycle time. The Fragmentation function defined in PROFINET V2.3 takes large TCP/IP frames in the individual nodes and, if necessary, divides them into smaller individual parts prior to sending. These fragments are then sent in consecutive cycles. The counterpart then reassembles the fragments into a complete TCP/IP frame. In this way, it is possible to configure bus cycles of 31.25 μs with shared user data and TCP/IP communication.

With Version V2.3, PROFINET now meets all requirements for automation applications, ranging from process automation and factory automation to high-performance motion control applications. This technology development paves the way for developing cost-optimized automation solutions and is especially important for meeting the demand for investment protection, both for existing plants and expansions to existing plants. PROFIBUS and PROFINET are not competing solutions but rather are complementary solutions. While PROFIBUS is used in continuous processes and hazardous areas, PROFINET is primarily of interest in applications requiring integration all the way to the corporate management level or whose real-time communication requirements cannot be met by conventional fieldbuses.

Open to new ways!


New prospects with PROFINET for the process industry

by Dr. Peter Wenzel, PI (PROFIBUS & PROFINET International) Support Center

With over three million installed nodes, PROFINET has long since become a familiar feature of production automation and drive engineering applications. But what about the process automation sector? Although this sector traditionally reacts cautiously to new technologies, users have expressed heightened interest in PROFINET.

Food and beverage industry sector

In particular, the food and beverage industry sector is interested in PROFINET because of its large number of upstream and downstream processes. The chemical, oil and gas, and pharmaceutical industries have recently expressed considerable interest in the technology, as well. PROFIBUS PA is already widely used by facilities in these industry sectors. However, an integrated communication system such as PROFINET is essential to enable complete integration of centralized process-related operations of a plant with downstream applications involving mostly discrete processes, such as filling and packaging.

For this reason, PI (PROFIBUS & PROFINET International) established a working group of manufacturing companies (ABB, Emerson, Endress+Hauser, Pepperl+Fuchs, Siemens, Softing, Stahl, and Yokogawa) whose initial task was to define the particular characteristics of process industries. Additional consideration was given to the requirements of NAMUR (an international user association of automation technology in process industries). Besides the extended cycle times, continuous plant operation, and complex actuators and sensors, another major challenge is the sheer quantity of devices (up to 100,000 I/O signals). Moreover, life cycles in the process industry are often very long. It is not unusual to find 20-year old control systems, and many plants are even older than that.

These specific characteristics have always been an impediment to the introduction of new technologies in the past. In spite of this, PROFINET holds interesting prospects for process-related applications and the process industry sector, based in large part on its flexibility. In order to establish PROFINET on a widespread basis, however, the specific requirements of this sector had to be implemented. This effort focused on four main areas:
Investment protection

In order to protect investments, seamless integration into existing fieldbuses must be possible. Many process industry plants have been in operation for several decades and have a large installed base of field devices, controllers, and communication systems. Continued use of this installed base is the aim. How can this be ensured? By means of a proxy concept, the three communication systems encountered in process industries – PROFIBUS PA, Hart, and Foundation Fieldbus – can be integrated into the higher-level PROFINET network. The proxy assumes responsibility for implementing the physics and protocol and ensures the exchange of all I/O, diagnostic, and parameter assignment data as well as alarms with the field devices.

Configuration in Run

Chemical industry

The chemical industry, whose plants operate continuously in most cases, places top priority on plant availability. It is inconceivable that a column would have to be shut down before making a parameter change or replacing a device. It must be possible to reconfigure devices and networks and to add, remove, or replace devices or individual modules during operation. Thanks to the auto-sense and topology detection features, devices are identified automatically and their locations pinpointed. This enables convenient, reliable solutions to be developed for device/spare part replacement scenarios, in which the replacement device parameters are assigned automatically by the control system. All of these “Configuration in Run” measures (CiR) are carried out in PROFINET without any interruption and without adversely affecting network communication. This ensures that plant repairs, modifications, or expansions can be performed without a plant shutdown in continuous production processes, as well.

Time synchronization and time stamping

Power plant

In power plant automation, an especially high value is placed on time-correct tracking of individual process signals. This is especially critical when it comes to malfunctions in individual automation areas. Afterwards, the plant operator wants accurate information on the order in which signals were sent and at what time. He is then able to perform a detailed “root cause” analysis. An accuracy of 1 ms is critical for this purpose.

This requires a time stamp for digital and analog measured values and alarms that is accurate to the millisecond. A precondition for this is an exact time synchronization of the components involved: By means of a central system master clock (e.g., based on GPS or DCF77), a master selected specifically for this purpose transmits a cyclic equidistant clock signal to all bus nodes, thereby synchronizing them. This ensures that I/O devices can provide real-time information about alarms and other important events with a time stamp that is based on a network-wide standardized time of day. By acquiring events at a comparable time, an exact description and analysis of a possible fault can occur. Because not every field device has such a time stamp, a hybrid operation must also be possible. This is guaranteed.

Scalable redundancy
To avoid automation failures caused by conditions such as wire breaks or short circuits, redundancy concepts were developed for PROFINET, which can be structured differently depending on the application (“scalable redundancy”). The basis for these concepts is the automatic switchover of communication paths to intact paths in the event of a fault, along with communication of status information regarding the cause of the communication interruption. The user can decide whether he wants to use controller redundancy, network redundancy, device redundancy, or device interface redundancy. Moreover, the recovery time of a communication system must be fast enough to prevent process disturbances. All redundant elements must have a diagnostic capability so that faults can be detected and faulty elements replaced.

Uniform concept
Many users express the desire for an integrated communication system down to the field level. PROFINET enables a direct path to MES and ERP systems, while at the same time facilitating the use of Internet services for things like remote maintenance, integration of wireless communication, or intelligent network management. New architectures can be realized with PROFINET. The flexible signal allocation allows signals to be assigned to controllers in the PROFINET network without any rewiring. This aids in future plant expansions, even when continuous processes are involved. Over the long-term, this could also make planning of automation systems easier since individual lines can still be expanded even during the commissioning phase. Entirely new paths are also possible: if, up to now, architectures have been based on the layer model of the conventional automation pyramid, flatter and thus more cost-effective architectures are now conceivable, especially for smaller applications.

With completion of the “PROFINET for Process Automation” application profile, PI (PROFIBUS & PROFINET International) has taken an important step towards a uniform communication concept for process and production industries. The preconditions for this have been put in place with the implementation of process-specific requirements. What remains now are a few housekeeping tasks, such as the review of security concepts, coordination with FDI, development of test specifications for devices, and certification of devices that meet the PROFINET requirements. Starting in 2011 work can commence on implementing PROFINET products for process automation, thereby opening up whole new prospects for this industry sector.

ProfiBus seminar


In what is hoped to be a biennial affair the first ProfiBus Ireland seminar was hosted by Limerick University’s Automation Research Centre (ARC) on January20th 2010. Hassan Kaghazchi of ProfiBus Ireland and the Limerick University was responsible for the organisation of this very successful event.

Speakers and Organisers: From left: Joost Van der Nat, Hassan Kaghazchi, Conal O'Reilly, Steve Dickinson, David Maher, Joachim Lauer, Nigel DeHaas, Eric Gory, Jorg Freitag.

Conal O'Reilly

It was very well attended and over 50 people attended. The progamme comprised of a morning with eight short presentations from a truly international group of speakers including Profibus International (PI) Chairman Jörg Freitag. There were many opportunities for hands-on demonstrations. The demonstartions panels constructed by ProfiBus Ireland members under David Maher of Elmar Engineering, The afternoon was an optional tour of the Bulmers, state of the art cider making facility in Clonmel where many of the ProfiBus techniques, discussed in the morning were seen in an actual plant. This part of the day was organised by Matt Wilhite of molex with the cooperation of the Bulmers plant engineers.

The seminar programme

Introduction, HassanKaghazchi (IR), ARC Limerick University
Present and Future, Jörg Freitag (D), PI Germany
HART over PROFIBUS, Nigel DeHaas (ZA), DH Controls
Wireless HART, Joachim Lauer (CH), Endress+Hauser
Diagnosing PROFIBUS, Joost Van derNat (NL), Procentric
Industrial Wireless , Conal O’Reilly (IRL), Phoenix Contact
PROFINET, Eric Gory (F), molex
Redundant PA, Steve Dickinson (GB), Pepperl & Fuchs

A pdf version of each presentation is available to download from the Profibus Ireland site.

The tour of the Bulmers Clonmel plant took place in the afternoon. This plant manufactures the traditional Bulmers range for Ireland and Magners Irish Cider for the export market. As part of the C&C Group it also produces Carolan’s Irish Cream, Tullamore Dew and other products at the site. The tour was fascinating as it concentrated on the technical aspects of control especially in the very impressive bottling plant and then in the manufacturing of the cider itself from the simple apple to the finished refreshing brew. The tour also emphasised the complete use of the raw materials and its minimum impact on the environment. For instance the pulp left after the extraction of the apple juice is used for anamal feed – primarily for deer.

Part of the attendance at the seminar

Group for plant tour at Bulmers Clonmel

PROFIBUS: A Pocket Guide by Ron Mitchell is a pocket guide provides a basic overview of PROFIBUS operations, installation and configuration, wiring schemes, troubleshooting, and tips and tricks. Also useful for engineering management seeking a summary understanding of PROFIBUS. Illustrative figures and technical tips are provided for quick reference. It is published by the International Society of Automation.