13 - Special-Purpose Controllers

Abstract

This chapter discuss the standardization of controllers to address the specific needs of localized and distributed processes. The localized and distributed processes need functionally different and diversified types of controllers. The variants of general-purpose controllers for the localized processes are: programmable logic controller (PLC), loop controller, and programmable controller (Controller). The PLC supports limited continuous process automation while according highest priority and speed to its basic functions. The importance of the loop controller is its ability to handle the analog data with accuracy. Hence, the hardware and software are specifically designed to address the accuracy requirement. The programmable controller is technically a functional combination of a PLC and loop controller that implements both discrete sequential control with interlocks and continuous control, which facilitates both discrete and continuous process automation. Remote terminal units (RTU) are primarily designed and optimized for data acquisition from the process and transmission to the remote control center and receipt of command from remote control center and transfer to process. They also support local automation in a limited way.