The new Profinet FL Switch IRT real-time switches from Phoenix Contact enable the configuration of the Profinet network using fibre optic technology so that the application can be reliably operated even in plant areas having high EMC interference.

Reliable real-time transmission even under difficult industrial conditions

Profinet provides integrated communication to support the growing trend toward modularisation in plant engineering. Locally installed switches are being used to integrate plant components and machine groups into an optimised network topology that can be customised to the plant structure. Two important criteria when selecting suitable switches are ensuring the required real-time capability and high plant availability. On the other hand, economical engineering and service features are also important.

The new Profinet FL Switch IRT real-time switches from Phoenix Contact enable the configuration of the Profinet network using fibre optic technology so that the application can be reliably operated even in plant areas having high EMC interference. The combination of four-port switches and two-port terminal devices can be used to implement flexible topology types such as star, tree, line, or redundant ring topologies.

Hardware support ensures preferred processing

The Profinet technology offers scalable real-time features ranging from real-time file exchange in conventional production automation to synchronous communication in highly dynamic motion control devices. The Profinet RT (real-time) model is the primary model used in plant automation. Profinet IO describes the cyclical data transmission between the controller and the field devices, in which the bus cycle times are just a few milliseconds long.

The Profinet real-time switches have hardware support in the form of the ERTEC (enhanced real-time Ethernet controller) ASIC, which ensures optimum real-time operation in Profinet applications. By implementing the Profinet module in the real-time switches, incoming Profinet IO-type data packets are identified and are always processed preferentially, independently of the priority in their VLAN tag.

Competing applications that potentially have the same level of priority in the VLAN tag, such as camera applications with video streaming, thus do not affect the Profinet communication. The hardware support in the switches thus facilitates project planning and makes it easier to guarantee the required real-time features during operation, since there is an automatic separation from the priorities of all non-Profinet telegrams.

On the basis of the transmission processes defined in IEEE 802, the Profinet real-time switches combine the “cut through” and “store and forward” switching mechanisms. The cut-through technology makes it possible to shorten the latency times when forwarding data packets. Profinet packets can thus quickly reach their target even via multiple switches in a longer linear structure, which is typical in large plants.

Fibre optic communication ensures high availability

The Profinet real-time switches from Phoenix Contact provide two or three diagnostics-capable POF interfaces. The fibre optic interfaces with SC-RJ connectors can be used to connect both polymer and HCS fibers, which then connect the switches to each other. These optical fibres are user-friendly and easy to assemble in the field. Since no crimping, gluing, or polishing is required, the fibre optic plugs can be connected on site in less than two minutes. It is possible to span a range of up to 250m when using the gradient index HCS (GI HCS) fibre.

Using fibre optic technology increases ruggedness and thus also increases the reliability of the entire plant. Any additional costs incurred in procuring optical components are offset by the additional functionality and operational savings. Furthermore, using fibre optic cables makes the application immune to EMC interference. Implementing the Profinet network in an optical ring structure also substantially increases the availability of the automation solution. This pays off if a cable in the ring should be destroyed, since all coupled participants are still accessible. If problems with the POF or HCS fibres should nonetheless arise, the faults can be quickly localised using optical diagnostics.

Cable length measurement provides early indication of the need for maintenance

The Profinet real-time switches provide integrated fibre optics diagnostics to support users during predictive proactive maintenance. The device continuously measures the reception power of the fibre optic transceiver. The optical system reserve for the port is then available as information in the Web-based management either through an SNMP object or via the Profinet communication. Gradual changes in the cable or coupling attenuation potentially resulting from mechanical stress or contamination will thus be detected even during operation. The operator can thus arrange for service before critical system threshold values are reached and there is an imminent risk of transmission route failure.

The Phoenix Contact switches report required maintenance via a Profinet “POF-SCRJ” diagnostics alarm. If the device exceeds the 2dB reserve, a service request is sent to the controller as a Profinet alarm. If the system reserve falls to 0dB, the switch generates another Profinet alarm, which then indicates the need for urgent maintenance to the controller.

The FL Switch IRT series provides a cable length measurement on the Ethernet ports as a special feature. The signal propagation times on the connection cables determined using the Precision Time Control Protocol (PTCP) is used. The Profinet real-time switches combine the power budget from the fibre optic transceivers with the automatically measured cable length for conducting preventive evaluation of the fibre optic lines. The cable length is used to provide a qualitative assessment of the signals on POF lines. In addition to evaluating fibre optic lines during optical system installation and acceptance, it is possible to plan predictive maintenance measures at an early stage during operation.

Device diagnostics provided by Profinet

The FL Switch IRT series can be fully configured via the Profinet controller. The integrated Profinet I/O device also reads the real-time switch diagnostics information during operation and forwards it to the controller via Profinet. The port-related diagnostics information is thus available in the control technology software tools. The Link Layer Discovery Protocol (LLDP), which has been incorporated into the Profinet standard, supports fast device swapping in the event of failure as well as monitoring of the network topology. The topology can also be checked with LLDP via a network management tool.

In addition to the normal port LED, each SC-RJ port in the FL Switch IRT series has a diagnostics LED that provides an early indication of attenuation changes occurring on the POF fibre, thus making it possible to replace the fibre optic line during non-productive periods. The real-time switches from Phoenix Contact can also be diagnosed using Simple Network Management Protocol (SNMP) and the integrated web interface.