Fieldbus integration for PROFINET I/O

By Hans-Werner Auberg Woodhead Industries, Inc.

PROFINET allows critical communication between the industrial network and the IT network. A proxy server keeps communications flowing in real time. This article briefly describes the key elements of a proxy server and configuration into the network.

In today’s automation world, communication between different networks can be a challenge. In addition to the already installed base of more than 50 different fieldbus systems with more than 20 Mio nodes, industrial Ethernet solutions are becoming an international standard. Since 2003, the industrial Ethernet solution PROFINET has been part of the IEC 61158 and IEC 61784 standards. PROFINET provides a component-based machine modeling interface (PROFINET CBA) as well as real-time direct access to sensors and actuators (PROFINET I/O). 

Like other industrial automation systems, the PROFINET I/O system consists of three components:

1. The I/O controller – typically a PLC where the automation program runs
2. The I/O supervisor – a PC or a device with commissioning and diagnostic functions
3. The I/O device – a remotely assigned field device connected to an I/O controller

PROFINET resides on top of standard Ethernet as a scalable communication service and uses TCP/UDP and IP for nontiming critical data exchange, such as configuration and diagnostic information. Time-critical data exchange between the I/O controller and the I/O device is realized using a prioritized real-time channel (IEEE 802.1Q) on top of standard Ethernet (layer2). The Ethernet layer itself has not changed. In this manner, PROFINET allows factory automation applications to exchange data on standard office networks. 

Protecting the fieldbus investment
One of the key aspects of the development of PROFINET was to protect the existing investments on the plant floor. A seamless transition from existing fieldbus solutions such as PROFIBUS, Interbus, or DeviceNet to Ethernet-based PROFINET was needed. PROFINET uses a “proxy” concept for the integration of a device or an entire fieldbus application as shown in the applicom PROFINET I/O Proxy (Figure 1). In general, a proxy server is a computer network service that allows clients to make an indirect network connection to other network services. The server provides the source either by direct connection or by serving it from a cache.

Figure 1

In the case of PROFINET I/O, proxies offer a fully transparent transition from existing to newly installed devices.

The I/O devices are described by the Generic Station Description (GSD) in XML format. The PROFINET proxy is also an I/O device, which means that Interbus or PROFIBUS devices linked to a proxy server are described in the same way. In the engineering tool of the PROFINET I/O controller, they appear like PROFINET I/O devices.

There are proxy devices available on the market today providing this functionality (see Figure 2). The applicom PROFINET I/O Proxy is a good example, and is currently the only multiprotocol proxy server that provides a real-time connection between a PROFINET I/O controller and more than 10 different networks, all from a single device.

Figure 2

More precisely, the applicom PROFINET I/O Proxy enables cross communication through its internal database. The information transfer is simply based on cyclic data exchange between the industrial equipment and the proxy. Parts of the internal database can be mapped as input or output modules to permit I/O exchange with the PROFINET I/O controller. This solution enables the user to configure the proxy without being worried about the difficulties associated with the different fieldbus protocols. Each cyclic function stores the last automation status automatically and provides this information to remote devices such as the PROFINET Supervisory Station.

The configuration process is fully supported by the Woodhead Console installed on a PC running Windows 2000 or Windows XP (see Figure 3). Functions provided by the console include:

• Configuration support for integrated fieldbus systems
• Extended diagnostics to validate the fieldbus and Ethernet networks
• Internal diagnostic tools to analyze the PROFINET I/O behavior

Figure 3 (click to zoom)

I/O controller configuration
In order to configure the I/O controller (for example, the PLC system), the applicom I/O Proxy provides a GSD file in XML format. The appearance of the I/O device is similar to the appearance of a PROFIBUS device. Once the GSD file for the applicom PROFINET I/O Proxy is imported, it appears in the PLC system’s I/O browser providing access to different types of I/O modules including analog input, analog output, and digital variables in multiple formats. Upon completion of the application, the program is then downloaded to the PLC and the system goes online. 

Summary
With the industrial Ethernet system PROFINET, users have access to an open and scalable system. With PROFINET, synchronized motion control applications can be executed on the same Ethernet network as office applications. Investments are protected as PROFINET supports the Ethernet standard IEEE 802.3 as well as TCP/IP and UDP. Current systems using DeviceNet, PROFIBUS, or EtherNet/IP can be integrated easily using a PROFINET I/O Proxy server.With the applicom PROFINET I/O Proxy, duplication is not required, and special tools for each legacy network are not required as all protocols are integrated into one consistent set of tools.

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Hans-Werner Auberg is product marketing manager for Woodhead Industries, Inc., responsible for European network solutions since 2003. His career in industrial automation began in 1990 as a sales and marketing engineer for industrial communication and PLC programming environment, and in 1997 he moved to sales manager and managing director for the SCADA business.

To learn more, contact Woodhead Industries at www.woodhead.com.

PROFINET and PROFIBUS are registered trademarks of PROFIBUS International in the United States and other countries. applicom is a registered trademark of Woodhead Industries in the United States and other countries. DeviceNet is a trademark of Open DeviceNet Vendor Association, Inc., in the United States and other countries. Windows is a registered trademark of Microsoft in the United States and other countries. EtherNet/IP is a trademark used under license by ODVA in the United States and other countries. Other company product and service names may be the trademarks or service marks of others.