When we introduced the lesson on the evolution of buses in Automation Evolutionary Trends we showed control connectivity evolving from manual to pneumatic to 4-20mA to fieldbus to Industrial Ethernet. Each step improved manufacturers’ ability to install, commission, operate, and maintain their production lines.
The step to fieldbuses provided the benefits of reduced wiring, additional information, and faster diagnostics. It was also a step-change from the analog world to the digital world. PROFIBUS, the world’s best-selling fieldbus, uses the RS485 standard to transmit messages up to 244 bytes long, at speeds up to 12Mbit/sec. PROFIBUS has limits on the number of devices that can connect on one segment (32) and a limit on the total number of devices that can be connected (128). PROFIBUS requires termination resistors, and repeaters between RS485 segments. In the decades since PROFIBUS’ rise to popularity in the 1990’s, tens of millions of PROFIBUS nodes have been installed on countless networks. In those rare instances where there is an issue with a PROFIBUS network, 9 times out of 10 it’s due to an electrician’s faulty wiring or RS485 bus segmentation during installation.
Ethernet incorporates and improves on the benefits of fieldbuses. PROFINET provides faster updates, more bandwidth, larger messages, an unlimited address space, and more diagnostics than PROFIBUS. It leverages standard Ethernet and therefore eliminates the installation errors that can crop up with an RS485 network.
For further study:
“Why industrial Ethernet?” in the May 2006 issue of Control Engineering magazine.
PROFIblog post: The Difference between PROFIBUS and PROFINET