2 - Automation System Structure

Abstract

This chapter discusses the structure of the overall automation system and the functions of its subsystems. The automation system is broadly divided into three subsystems, namely, instrumentation subsystem, control subsystem, and human interface subsystem. An instrumentation subsystem acquires information on the behavior of the process and sends this to the control subsystem in an acceptable form. In the other direction, the instrumentation subsystem sends the information to the process in an acceptable form to change the behavior of the process. The human interface subsystem, also called human–machine interface (HMI) or man–machine interface (MMI) or human–system interface (HSI), allows the operator to manually interact with the process. There is no need for any interface devices between the control subsystem and human interface subsystem. The signals between the control and human interface subsystems are electronic in both directions and therefore compatible. Control subsystem is the core of automation system and it manages the information flow to and from the instrumentation subsystem for process monitoring and control, and to and from the human interface subsystem for manual interaction with the process.