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.
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.
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.
There are five phases to creating a functional SCADA system: