Retrofitting distributed process control systems

When an older process control facility using conventional analog instrumentation is in need of a control system upgrade, the conventional method would be to replace the analog instruments on a one-for-one basis with new analog instruments. An alternative method for the control system upgrade would be to retrofit a distributed control system into the existing control room and utilize the existing field wiring. This paper presents the considerations involved in the decision to implement distributed control on a retrofit basis and the practical considerations involved in implementation of that decision, including specification preparation, installation considerations, configuration considerations, and operating considerations. Background for this paper comes from experience gained in retrofitting distributed control systems into nuclear fuel reprocessing facilities at the Idaho National Engineering Laboratory (INEL), near Idaho Falls, Idaho