Introduction to SCADA

What is SCADA ?

SCADA is an abbreviation for "Supervisory Control and Data Aquisition"

It is a mechanism for remotely monitoring and controlling anything that needs monitoring and controlling - chemical processes, oil refineries, electricity networks, gas pipelines, dams, lighthouses, etc.

It has a fairly long history, and a basic SCADA system could contain the following building blocks :-

remote digital devices such as proximity sensors, level switches, thermostats - they provide a two-state signal - hi/low, on/off, etc
remote analogue devices such as transducers that measure voltage or temperature or pressure - they provide an analogue signal that provides a measure of the item being monitored
remote control devices such as a door lock, a valve, a relay that switches on an electric motor
one or more remote terminal units - an RTU is a "box" that receives a data stream from a central control room or computer, breaks up the data stream and sends or receives an individual signal to or from each of the various remote devices
some kind of communication network that carries the data stream between the remote terminal unit and the control computer
a master terminal unit - the central facility end of the communication network
the control room or control computer - the control rooms for early SCADA systems were often quite large wall-mounted displays, with physical switches and meters that were used by the operators. Nowadays, they are usually computer based, running on standard pc`s using SCADA application software.

One of the developments that is taking place is the integration or migration of building energy management systems into full SCADA systems - and increasingly not just the energy side of building management, but security, access control, CCTV, building related micro energy generation, are all becoming part of the whole building management system.

Another development which is affecting SCADA is the collection, retention, and processing of data - not just for the real-time use of that data for controlling equipment, but for security auditing - ie, who did what, when - also for long term performance auditing in order to confirm that systems are meeting long term performance targets. There is also an increasing need to transfer that data outwith the SCADA environment and into the wider corporate environment. SCADA therefore has an increasing dependency on IT technology - such as desktops, servers, web servers, and networks.

A bit on the telemetry side

SCADA systems require both communication protocols suitable for the kind of data to be transferred, and various forms of data telemetry to carry the status data back to the servers and control operators, and to send the control signals out to the remote sites.

Traditional industrial SCADA protocols like IEC 60870, DNP3, and Modbus are now being joined by building management related protocols like Profibus/Profinet, BACnet, LonTalk/LonWorks, plus a few more.

The data telemetry systems used in SCADA can be based on quite a few different technologies - including RS232, RS 422, RS485, GSM, GPRS, 3G, satellite, IP networks, and fibre optics - as well as the good old fashioned telephone system. There is a separate set of web pages on this website about data telemetry, so it is not included in this set of pages.

The convergence of SCADA technology and IT technology is resulting in an emphasis on the reliance on networking. In addition, the increasing importance of SCADA data storage and transfer into the wider corporate environment is also driving an increased dependency on IP networks - so there is a growing tendency to carry both SCADA data and SCADA control traffic on the corporate IP networks - this is a security issue, as it exposes the incoming data or outgoing control signals to various kinds of attack which would be much less likely on a closed SCADA or telemetry network.

The pages that follow have various bits of information about some specific SCADA protocols, and about security in relation to carrying SCADA data and control signals on the corporate network.

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