Installing Fieldbus

June 4, 2008
Many automation engineers are coming face to face with real fieldbus applications for the first time. Fieldbus (the use of digital communications networks for distributed instrumentation and control) is a wonderful technology with many benefits, but fieldbus installation requires some additional considerations over and above normal 4-20mA projects. In this article, we will discuss some of those issues, and show you how to deal with them.

Don’t get hung up on which fieldbus to choose. Fieldbus is a generic term for a variety of communications protocols using various media, but all are simply a means to an end. What you want at the end of the project is a satisfactory and functional control system, and practically every installation will use multiple fieldbuses to accomplish the many tasks required. For example, you may use FOUNDATION™ fieldbus in the process plant, DeviceNet for a PLC network, and PROFIdrive to run motor drives. Every DCS can easily integrate all these functional plant buses into the Ethernet-based control room bus.

In process control engineering, “fieldbus” normally means FOUNDATION fieldbus H1 (H1) or PROFIBUS PA (PA); both fieldbuses are perfectly adequate and widely used around the world in refineries and process plants as modern day enhancements to 4-20mA, 2-wire devices. This article focuses on H1 and PA physical layer implementation.