PCT No. PCT/US97/17983 Sec. 371 Date Dec. 30, 1997 Sec. 102(e) Date Dec. 30, 1997 PCT Filed Oct. 3, 1997 PCT Pub. No. WO96/12993 PCT Pub. Date May 2, 1996Functional elements within a two-wire, loop-powered, two-way digital communications environment are interconnected using selective redundant connections and selective redundant functional elements. The redundant functional elements and redundant connections provide a smooth transition from operation of a primary process loop element to a secondary process loop element in the event of a failure of the primary process loop element. Redundancy is selectively implemented using a redundant pair of field devices or a redundant bus pair having a primary bus and a redundant bus. In a first case, redundancy is selectively implemented using a single set of communication media, such as a single communication loop, but implementing redundant functional elements, such as field devices, so that recovery is achieved upon failure of a functional element but not upon failure of the communication media. In a second case, redundancy is selectively implemented using a redundant set of communication media in addition to use of redundant devices so that recovery is attained both for a failing device and a failing communication media. In a third case, redundancy is selectively implemented using a redundant set of communication media but using a single device so that recovery is attained for a failing communication media but not for a failing device.
