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SCADA OPERATOR WORKSTATION AND SOFTWARE COMPONENTS

SCADA OPERATOR WORKSTATION AND SOFTWARE COMPONENTS
What are the roles of an operator workstation in a SCADA system?

Operator workstations are most often computer terminals that are networked with the SCADA central host computer. The central host computer acts as a server for the SCADA application, and the operator terminals are clients that request and send information to the central host computer based on the request and action of the operators.

An important aspect of every SCADA system is the computer software used within the system. The most obvious software component is the operator interface or Man Machine Interface/Human Machine Interface (MMI/HMI) package; however, software of some form pervades all levels of a SCADA system. Depending on the size and nature of the SCADA application, software can be a significant cost item when developing, maintaining, and expanding a SCADA system. When software is well defined, designed, written, checked, and tested, a successful SCADA system will likely be produced. Poor performances in any of these project phases will very easily cause a SCADA project to fail.

Many SCADA systems employ commercial proprietary software upon which the SCADA system is developed. The proprietary software often is configured for a specific hardware platform and may not interface with the software or hardware produced by competing vendors. A wide range of commercial off-the-shelf (COTS) software products also are available, some of which may suit the required application. COTS software usually is more flexible, and will interface with different types of hardware and software. Generally, the focus of proprietary software is on processes and control functionality, while COTS software emphasizes compatibility with a variety of equipment and instrumentation. It is therefore important to ensure that adequate planning is undertaken to select the software systems appropriate to any new SCADA system.

Software products typically used within a SCADA system are as follows:

• Central host computer operating system: Software used to control the central host computer hardware. The software can be based on UNIX or other popular operating systems.

• Operator terminal operating system: Software used to control the central host computer hardware. The software is usually the same as the central host computer operating system. This software, along with that for the central host computer, usually contributes to the networking of the central host and the operator terminals.

• Central host computer application: Software that handles the transmittal and reception of data to and from the RTUs and the central host. The software also provides the graphical user interface which offers site mimic screens, alarm pages, trend pages, and control functions.

• Operator terminal application: Application that enables users to access information available on the central host computer application. It is usually a subset of the software used on the central host computers.

• Communications protocol drivers: Software that is usually based within the central host and the RTUs, and is required to control the translation and interpretation of the data between ends of the communications links in the system. The protocol drivers prepare the data for use either at the field devices or the central host end of the system.

• Communications network management software: Software required to control the communications network and to allow the communications networks themselves to be monitored for performance and failures.

• RTU automation software: Software that allows engineering staff to configure and maintain the application housed within the RTUs (or PLCs). Most often this includes the local automation application and any data processing tasks that are performed within the RTU.

The preceding software products provide the building blocks for the application-specific software, which must be defined, designed, written, tested, and deployed for each SCADA system.


source: National Communication System, Technical Information Bulletin 04-1
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