Fieldbus

Profibus offers a complete family of fieldbus versions: Profibus PA for process automation, Profinet for data transmission based on Ethernet and Profibus DP for automating plants, power plants and machines. Due to its simple and robust data transmission physical layer principle (RS-485) and the different service levels DP-V0 (fast cyclic and deterministic data exchange), DP-V1 (acyclic access to device parameters and diagnostic data) as well as DP-V2 (further functions such as time stamp or redundancy), Profibus DP is the ideal solution for plant automation.

• Internationally standardised (www.profibus.com)
• Worldwide distribution
• Large installation base
• Standardised integration within the DCS (FDT, EDD). Large selection of devices
• Typical applications: Power plants, sewage treatment plants, water treatment plants, tank farms

In comparison with other fieldbus technologies, Modbus is simple but has a multi-functional fieldbus protocol. It offers all services required for plant automation, e.g. exchange of simple binary information, analogue values, device parameters or diagnostic data.

For plant automation and similar to Profibus, the simple and robust physical layer RS-485 is often used.

On the basis of this physical layer, Modbus supports various telegram formats, e.g. Modbus RTU or Modbus ASCII. Using the Modbus TCP/IP version based on Ethernet, vertical integration into a host automation system is often implemented.

• International standard (www.modbus.org)
• Simple protocol
• Worldwide distribution
• Largely sufficient for many simple automation tasks
• Typical applications: Water and wastewater treatment plants, pumping stations, tank farms

Foundation Fieldbus (FF) was explicitly adapted to the requirements of process automation. Transmission physics of the FF H1 protocol used at field level is based on IEC 61158-2 and ISA SP 50.02. These standards define the framework conditions for data transmission and energy supply of simple field devices using the same cable pair. FF H1 supports various topologies. In combination with junction boxes or segment barriers, extremely flexible cable installations are possible. Apart from conventional line and tree structures, FF H1 supports point-to-point topology or other structures with one trunk combined with individual spurs leading to the field devices.

Foundation Fieldbus data interfaces are based on standardised function blocks, for example AI (Analog Input), or AO (Analog Output) whereby their inputs and outputs can be linked.

Therefore, FF field devices can directly communicate with each other provided that the segment is equipped with a Link Active Scheduler (LAS) to coordinate FF communication.