| 摘要 |
Functional 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, rcdundancey is selectively implemented using a single set of communication media (202 in fig. 6), such as a single communication loop, but implementing redundant functional elements (204, 206), 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 (302, 303 in fig. 7) in addition to use of redundant devices (304, 306) so chat 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 (402, 403 in fig. 8) but using a single device (404) so that recovery is attained for a failing communication media but not for a failing device.
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