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Test Measurement and Control >> SCADA System

SCADA stands for Supervisory Control And Data Acquisition. As the name suggests, it is not a full control system, but rather focuses on the supervisory level. As such, it is a purely software package that is positioned on top of hardware to which it is interfaced, in general via Programmable Logic Controllers (PLCs),Remote Terminal Unit (RTUs) or other commercial hardware modules
Generally speaking, a SCADA system usually refers to a system that coordinates, but does not control processes in real time. It is a centralized system which monitors and control entire sites, or complex systems spread out over large areas (anything between an industrial plant and on a globe).In short it gives overview of large system at single location.

A SCADA System usually consists of the following subsystems:
  • Supervisory Station: The term "Supervisory Station" refers to the servers and software responsible for communicating with the field equipment (RTUs, PLCs, etc), and then to the HMI software running on workstations in the control room, or elsewhere. In smaller SCADA systems, the master station may be composed of a single PC.
    A Human-Machine Interface or HMI is the apparatus which presents process data to a human operator, and through this, the human operator monitors and controls the process. The HMI system usually presents the information to the operating personnel graphically, in the form of a mimic diagram. This means that the operator can see a schematic representation of the plant being controlled.
    A supervisory (computer) system, gathering (acquiring) data of the process parameters and sending command (control) signal to the process.

  • Field equipment :
    • Remote Terminal Units (RTUs) connecting to sensors in the process, converting sensor signals to digital data and sending digital data to the supervisory system.
    • Programmable Logic Controller (PLCs) used as field devices because they are more economical, rugged, versatile, flexible, and configurable than special-purpose RTUs.
    Most control actions are performed automatically by Remote Terminal Units ("RTUs") or by programmable logic controllers ("PLCs").

An important part of most SCADA implementations is alarm and event handling. The system monitors whether certain alarm conditions are satisfied, to determine when an alarm event has occurred. Once an alarm event has been detected, one or more control actions are taken such as the activation of one or more alarm indicators, buzzers etc.

Events are nothing but the occurrence of some user defined conditions which may not be dangerous conditions as alarm conditions but are necessary to keep track of system. E.g. in case of manual and auto mode, user may be interested in knowing about the time at which operator switched from auto to manual mode. An alarm and Event conditions can be set by user. Alarm and event logging is possible in software. This information helps user to analyze system status and data.

Salient Features:
  • Access Control
  • Process Visualization (Schematic representation)
  • Real Time & Historical trending
  • Supervisory control
  • Report Generation
  • Set and log alarm & Events conditions.
  • Connectivity to Third Party PLCs, Remote terminal units( RTUs) & I/O
  • Event Driven processing
  • Database connectivity e.g. Mysql, MS Access.
Application:
  • SCADA system for a Waste Water Treatment Plant
  • SCADA system for a Building Management System (BMS).
  • SCADA system for Furnace Control.
Application Note:
  • SCADA system for a Building Management System (BMS).