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Wednesday, January 26, 2011

SCADA : What?, Why?

              The acronym SCADA stands for Supervisory Control And Data Acquisition.  In reality, the primary purpose of SCADA is to monitor, control and alarm plant or regional operating systems from a central location.  While override control is possible, it is infrequently utilized; however control set points are quite regularly changed by SCADA.

In a municipal context, "plant" systems are typically water and wastewater treatment facilities, while "regional" systems include intake and/or effluent structures, pumping stations, chlorination stations, control valve stations and the like.

What makes up a SCADA system?

There are three main elements to a SCADA system, various RTU's (Remote Telemetry Units), communications and an HMI (Human Machine Interface).

Each RTU effectively collects information at a site, while communications bring that information from the various plant or regional RTU sites to a central location, and occasionally returns instructions to the RTU.

The HMI displays this information in an easily understood graphics form, archives the data received, transmits alarms and permits operator control as required.

Communication within a plant will be by data cable, wire or fiber-optic, while regional systems most commonly utilize radio.  The HMI is essentially a PC system running powerful graphic and alarm software programs.

Why is SCADA so popular?

The major attraction of SCADA to a municipality is the ability to significantly reduce operating labor costs, while at the same time actually improve plant or regional system performance and reliability.  Information gathering within a plant no longer requires personnel to spend time wandering all over the site, and correspondingly the frequency of field site inspections required in a regional system can be minimized.

Costly after-hours alarm call-outs can often be avoided since a SCADA system will indicate the nature and degree of a problem, while the ability to remotely control site equipment may permit an operator at home to postpone a site visit till working hours.  SCADA based alarming is also very reliable since it is in-house and tied directly to process control.

A significant feature of a SCADA system, often not fully appreciated, is the trending of data and nothing comes close for speed and ease of operation. When graphically displayed, accumulated operating data often will indicate a developing problem, or an area for process improvement. Reports can easily be generated from this data utilizing other common software programs.
It should be appreciated that while a SCADA system is often complex to configure - it is extremely easy to operate!

What is involved?

There are five phases to creating a functional SCADA system:

Phase 1 
The DESIGN of the system architecture. This includes the all-important communication system, and with a regional system utilizing radio communication often involves a radio path survey. Also involved will be any site instrumentation that is not presently in existence, but will be required to monitor desired parameters.
Phase 2
The SUPPLY of RTU, communication and HMI equipment, the latter consisting of a PC system and the necessary powerful graphic and alarm software programs.

Phase 3
The PROGRAMMING of the communication equipment and the powerful HMI graphic and alarm software programs.

Phase 4
The INSTALLATION of the communication equipment and the PC system. The former task is typically much more involved.

Phase 5
The COMMISSIONING of the system, during which communication and HMI programming problems are solved, the system is proven to the client, operator training and system documentation is provided.

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