Fieldbus & Industrial Networking


Industrial communication

September 2010 Fieldbus & Industrial Networking

Ethernet is becoming popular for industrial communication systems due to its flexibility and use throughout the world for different applications. Ethernet originated as a 10 Mbs half duplex shared environment with resultant collisions and delays in traffic. Getting the job done, but with nowhere near the timing accuracy needed for automation systems. This is a thing of the past and now 10/100 Mbs and even 1 Gbs network speeds are available in full duplex switched environments giving the speeds for automation to take place in a predictable and reliable manner.

Ethernet is built from the 7 Layer OSI model. What makes it diverse is that at the top, or application layer, different protocols can be applied for different purposes, to name a few:

* HTTP for web browsing or IP CCTV viewing.

* FTP for file transfers.

* SIP for VoIP telephony.

* Modbus TCP for industrial communication.

* DNP3 for serial encapsulation.

The Ethernet layer is made up of the physical (medium) and data link (MAC) layers. The IP layer has already started changing from IPv4 to IPv6 for specified applications (not typically used in automation networks) and the application layer has continuous growth of new protocols as different needs arise.

Substation automation has also adopted industrial Ethernet automation networks as part of the automation and protection strategy. For some applications however, fast response in harsh environmental conditions was a concern. The 61850 standard was born to cater for this adding in a 61850 protocol in the application layer. Another adaptation was not to use an IP address for certain messaging; these messages are addressed to the end devices using the hardware address known as the MAC. PTP (Precision Time Protocol) is also used in conjunction with this to ensure timing accuracy of nanosends.

As can be see from these examples Ethernet is diverse and in almost every location from the household to large industrial plants. The keys to a successful implementation of an Ethernet-based automation system in a plant include the following:

* Network design with IP Layout to cater for future expansion (incorrect design can drastically degrade performance).

* The right equipment for throughput and the environment (no fans, high temperature and robust power supplies).

* If possible additional cable (fibre) runs for redundant mesh topology for automated network recovery.

* Network management system for pro-active on alerts on the network.

Once these are in place users are ready to enjoy the versatility and reliability of a communication backbone that can cater for the following applications using individual VLAN’s (virtual local area networks):

* Scada.

* PLC.

* Seismic detection.

* VoIP.

* IP CCTV.

* Fire detection.



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