SCADA Definition: Supervisory Control And Data Acquisition

The Basics of SCADA

SCADA programs are used in industrial process control applications for centralised monitoring and recording of pumps, tank levels, switches, temperatures etc. SCADA systems are also referred to as HMI (Human Machine Interfaces), or the less politically correct MMI (Man Machine Interfaces).

A SCADA program normally runs on a PC and communicates with external instrumentation and control devices. Communications methods can be via direct serial link, radio, modem, fieldbus or Ethernet links. If a mixture of instruments with differing communication interfaces and protocols need to be connected, then converters can be used. SCADA is often used on remote data acquisition systems where the data is viewed and recorded centrally.

The SCADA program has a user configured database which tells the software about the connected instrumentation and which parameters within the instruments are to be accessed. The database may also hold information on how often the parameters of the instruments are accessed and if a parameter is a read only value (e.g. a measured value) or read / write, allowing the operator to change a value (e.g. an alarm setpoint).

The parameters of the instrument being accessed are normally split between analogue (numeric) or logic (digital). When running, the SCADA software continuously updates its own database with the latest analogue and digital values collected from the instrumentation. Some SCADA systems also allow real time calculations to be made on the received data and the results would be available as a "virtual" value.

The real time values can then be used by the SCADA software for:

Real Time Display and Operator Interactions (Supervisory Control)
And
Recording (Data Acquisition)

Most SCADA PC software include a drawing package for the configuration of the operator screens; these allow for the animation of objects dependant on the real time data. The SCADA screen designer can create and graphically display bar-graphs, valve positions, tank levels etc. The operator may be allowed to alter an instruments parameters or send batch recipe values to instruments by use of a mouse / keyboard or a touch screen.

More sophisticated SCADA PC software can provide messaging modules for SMS or E-mail; these enable plant conditions to be reported to external personal. Modern SCADA programs can provide better access to plant information through a web interface; the only requirement for the remote PC is an internet browser.

If a SCADA software solution is not suitable for an application, then stand alone operator interfaces are also available. More commonly refered to as HMI, these panel mounted devices combine a micro processor, communication interfaces and LCD touch screen. Like SCADA software, configuration and screen designs are created on a computer but then downloaded to the HMI for use in real time.