Data Communication

In our simple model of the widget fabricator, the "network" is just the wire leading from the switch to the panel light. In real life, you want to be able to monitor multiple systems from a central location, so you need a communications network to transport all the data collected from your sensors.

Early SCADA networks communicated over radio, modem or dedicated serial lines. Today the trend is to put SCADA data on Ethernet and IP over SONET. For security reasons, SCADA data should be kept on closed LAN/WANs without exposing sensitive data to the open Internet.

Real SCADA systems don't communicate with just simple electrical signals, either. SCADA data is encoded in protocol format. Older SCADA systems depended on closed proprietary protocols, but today the trend is to open, standard protocols and protocol mediation.

Sensors and control relays are very simple electric devices that can't generate or interpret protocol communication on their own. Therefore the remote telemetry unit (RTU) is needed to provide an interface between the sensors and the SCADA network. The RTU (Remote Telemetry Unit) encodes sensor inputs into protocol format and forwards them to the SCADA master; in turn, the RTU (Remote Telemetry Unit) receives control commands in protocol format from the master and transmits electrical signals to the appropriate control relays.

 

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