Types of Scada Systems

by Christopher Donahue

Most modern manufacturing, utility or processing plants are unable to run without their Supervisory Control And Data Acquisition (SCADA) system, which is a computer-based control scheme allowing a single operator or small group of operators to oversee a variety of processes. SCADA is a "force-multiplier." By using distributed electronic controls and sensors to perform batch or repetitive tasks, SCADA only alerts the operator if something needs attention or has exceeded pre-set parameters. Several types of SCADA systems are in use. The main differences are generational. Early systems vary greatly from more modern systems as well differences between modern systems themselves. Modern SCADA systems tend to use a "Mix and Match" variety of components and software.

Early or Monolithic SCADA systems

The first SCADA systems held all operations in one, usually a mainframe, computer. There was little control exercised, and most early SCADA functions were limited to monitoring sensors and flagging any operations which exceeded programmed alarm levels. These systems were all vendor-proprietary software and usually limited to a single plant or facility. Like the software, SCADA hardware from one vendor was rarely usable in another vendor's SCADA system.

Distributed SCADA Systems

Later SCADA systems became known as Distributed systems since they often shared control functions across multiple smaller (usually PC) computers connected by Local Area Networks (LAN). Using LAN, these individual stations shared Real Time information and often performed small control tasks in addition to alerting operators of possible problems or tripped alarm levels.

Networked SCADA systems

Current SCADA systems are usually networked. They communicate through Wide Area Networks (WAN) systems, over phone or data lines and often transmit data between nodes through Ethernet or Fiber Optic connections. Networked SCADA systems make heavy use of Programmable Logic Controllers (PLC) to monitor and make routine process adjustments, only flagging Operators when major decisions are required. Unlike earlier SCADA systems, which primarily used vendor-proprietary software and sometimes hardware, current systems are based on more general use software. The hardware tends to be more interchangeable as PLC and other sub-unit vendors have standardized communications and other protocols to allow the user to choose the best component for their needs rather than being tied to one vendor's line of products. While earlier SCADA systems were limited to single building or sometimes single site networks, many current SCADA systems connect to the Internet, which raises security risks not seen with older or "sealed" systems.

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About the Author

Chris Donahue is an electrical engineer living in the Dallas area. He has worked on defense projects, semiconductor process equipment, instrumentation and is currently in water utilities. He earned his Registered Massage Therapist (RMT) standing in Texas in 1999.

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