How SCADA Systems Work

Section 2: How SCADA Systems Work

A SCADA system performs four functions:

1. Data acquisition; the collection of data frequently involves some kind of analog to digital conversion. Temperature is converted to degrees Celcius. Transmit signal strength is converted to dBm. Channel quality is measured in errored seconds.

2. Networked data communication; the collected data is transmitted either spontaneously or in response to a request for data to some kind of upstream consolidator or master. The communication channel can be analog (T202, POTS) or digital (RS485, TCP/IP). Contemporary channels typically include some kind of transport validation independent of any content validation.

3. Data presentation; the collected data is processed, organized and presented for system operators to make appropriate response and control decisions. The presentation can vary from tabular presentation of logged events to graphical presentation against mapping or image backgrounds.

4. Control; if control decisions are warranted and the system supports output, appropriate commands can be dispatched to affect specific operational or configuration changes.

SCADA Diagram

These functions are performed by four kinds of SCADA components:

1.Inputs (either digital or analog) and output relays or electrical signals that directly interface with managed elements.

2. Remote telemetry units (RTUs). These are small computerized units deployed in the field at specific sites and locations. RTUs (Remote Telemetry Units) serve as local collection points for gathering reports from sensors and delivering commands to control relays.

3. SCADA master units. These are larger computer consoles that serve as the central processor for the SCADA system. Master units provide a human interface to the system and automatically regulate the managed system in response to sensor inputs.

4. The communications network that connects the SCADA master unit to the RTUs in the field.