Thursday 31 January 2013

Real-time communication for industrial WLAN

Using a new Key-Plug, the Scalance W product family from the Siemens Industry Automation Division can now be equipped for integrated real-time transmission over Industrial Wireless LAN(IWLAN) in compliance with the IEEE 802.11n standard.

The Key-Plug, a swap medium similar to the proven C-Plug, can be used to enable so-called iFeatures – in other words supplementary functions specifically for industrial use – which offer the deterministic data communication needed for real-time requirements. The iPCF(industrial Point Coordination Function) activated in this way can be realized using Profinet IO from minimal cycle times of 16 ms and over. With this function, it is even possible to trigger a Profisafe emergency stop command over IWLAN, meaning that data communication over WLAN can now be used in applications such as passenger transport. The Key-Plug is available in two different versions: Key-Plug W780 iFeatures for Scalance W Access Points and Key-Plug W740 iFeatures for Scalance W Client Modules. As well as enabling iFeatures, the Key-Plug also offers facility for saving configuration data.

This allows a device to be exchanged without loss of time in case of failure – without the need for intermediate connection of a PC or programming device. Additional functions are planned for the Key-Plug in 2013 which will extend the scope of feature sets capable of being enabled.

Background: the WLAN standard IEEE 802.11n does not define specific methods either for rapid roaming between several access points or deterministic data communication. The key requirements for real-time transmission over WLAN can be selectively upgraded using iPCF. Under these conditions, seamless real-time transmission over Industrial Wireless LAN(IWLAN) offers an alternative to wired networks. Areas of application include uses in which the laying of cables would be excessively laborious or expensive, or where cables would be subject to rapid wear.

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