The easy, seamless integration of DCS and PLC/PAC control platforms plays a larger and larger role in industrial applications. Such integration capability was a key requirement of a thermal power station implementing flue gas desulphurization for emissions reduction. Since no disruption of the DCS control system in place could be sustained, the plant required a high-availability stand-alone control solution that could be implemented with no disruption to operations and then be fully integrated with the DCS.
This Emerson case study describes how Emerson RX3i controllers fit the requirements perfectly -- take a look.