What is scada? Definition and Details paessler com/it-explained/scada it explained: scada back to index Content

Supervisory control center
The main functions of the supervisory control center, also called a SCADA host platform,
are to poll field devices like sensors via field device controllers like RTUs and PLCs for
data, send setpoints to field devices like actuators, and monitor alerts. Field devices are
located at numerous substations. A typical SCADA system comprises several substations
that are linked to several higher-level control and monitoring points, like PLCs. The
supervisory control server communicates between field device controllers and the HMI
software which is located at a central control hub.
Central control hub

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The central control hub is manned by people who monitor a SCADA system through
HMIs.
SCADA and PLC programming
SCADA programming takes place at different levels and involves the coding of different
functions, for example converting data collected from RTUs to signals, creating responses
for trigger events, storing data, creating reports, and designing graphical illustrations of
the system for display on HMI screens. 
Because SCADA systems are customized for disparate solutions in different sectors, the
programming languages used in SCADA systems depend on the hardware being
programmed or application requirements. For example, SQL may be used for managing a
SCADA database and a visualization language like Visual C# may be used to code HMI
features. Most modern SCADA systems use standard programming interfaces and APIs.
RTU and PLC programming is based on the IEC 61131-3 standard and supported by
PLCopen. IEC 61131-3 is a standard set by the International Electrotechnical
Commission (IEC) to specify the semantics and syntax of control programming
languages. Common control programming languages include ladder logic, sequential
function charts, function block diagram, structured text, and instruction lists.
PLCopen is an organization that provides support, code libraries, and coding guidelines
for PLC programmers.