15a - Foundation Fieldbus overview

Abstract

This chapter provides an insight into the Foundation Fieldbus (FF). The FF aims to preserve the desirable features of the present 4-20 mA standard (such as a standardized interface to the communications link, bus power derived from the link and intrinsic safety options) while taking advantage of the new digital technologies. FF takes full advantage of the emerging “smart” field devices and modem digital communications technology, allowing end-user benefits such as reduced wiring, communications of multiple process variables from a single instrument, advanced diagnostics, interoperability between devices of different manufacturers, enhanced field level control, reduced start-up time, and simpler integration. FF consists of four layers. Three of them correspond to OSI layers 1, 2, and 7. The fourth is the so-called “user layer” that sits on top of layer 7 and is often said to represent OSI “layer 8”, although the OSI model does not include such a layer. The user layer provides a standardized interface between the application software and the actual field device. High-speed Ethernet (HSE) is the FF's backbone network running at 100 Mbits/second. HSE field devices are connected to the backbone via HSE-linking devices.