With the wide range of RTU (Remote Terminal Units) and PLC (Programmable Logic Controllers) currently on the market, SCADA system engineers and decision makers face several challenges. Which classes of units provide the optimal functionality, expandability, and cost effectiveness for a given SCADA application? What type of unit will serve the mission not just today, but years into the future?
As implemented, RTUs and PLCs serve overlapping application niches and share some design details. To combat industry confusion, the discussion that follows provides a background of RTU and PLC units, and compares the various technical aspects for specifying the units including environmental ruggedness, modularity and scalability, and CPU performance. With remote applications for PLCs and RTUs continuing to expand, the discussion also helps the reader understand crucial remote system communication requirements including store and forward, report by exception, support for multiple protocols, and two-way communication with acknowledgements.