The word SCADA means “Supervisory Control and Data Acquisition”. The definition clearly explains what are the functions and objectives of a SCADA system, namely supervision, control and data acquisition.

A SCADA system is part of an architecture that includes:

  • One or more computers, connected to each other, that perform the supervisory functions and implement the human-machine interface (HMI)
  • A series of peripheral devices (RTUs, i/o Modules, PLCs) that interface to the process (machinery, plant, etc.) through sensors and actuators
  • A communication network, with a variety of transmission media and communication protocols, able to ensure the correct exchange of data between peripheral devices and supervisory computers

A SCADA software is an integrated development environment, which provides all the tools necessary to create SCADA applications, designed to run on supervisory computers and perform the functions that are typical of a SCADA system: supervision, control and data acquisition.




Supervision is the function that allows the operator to have an immediate view of the process status and to control how the process evolves over time by analyzing the sequence of operating states.

The main task of the supervision is to realize the human-machine interface (HMI). To be effective, the HMI must provide the operator with a prompt and complete image of the whole process, highlighting the status, the evolution and the unexpected deviations (alarms).

For an effective HMI, the graphic representation is of great importance, since it translates information relevant to the process into a visual language of easy understanding for the operator.

For example, you can display the status of a pump through a graphic symbol with different colors, the change of the value of a pressure through a graphical trend, the occurrence of an alarm through a pop-up window.

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The control function of a SCADA system consists in the ability of the control system to interact with the controlled process, in order to modify its evolution according to pre-established rules or decisions taken by the operator.

It is important to underline that, with “control of a SCADA system, we do not mean “real time process control”, usually the prerogative of the PLC, but rather the ability to modify the evolution of the process, for example by sending a different work recipe.

To better clarify the concept, we can say that, with reference to a particular process temperature, the task of a real time control is to keep this temperature unchanged (by acting on the appropriate actuators), while the task of the SCADA control is to fix the temperature at which the process should work (by sending the appropriate set point).

Data Acquisition


Data acquisition not only means transfer of information from peripheral devices to supervisory computers, but also transfer of information in the opposite direction, in order to allow the supervisory system to control the process, that is to direct its evolution by modifying the values of the variables that condition its operation.

We can say that data acquisition is the main function among those performed by SCADA systems. In fact, by putting the process in communication with the supervision, data acquisition makes it possible for the supervisory system to get all the information on the process status that are necessary to allow the observation of the process itself.

The task of data acquisition is to ensure the error-free transfer of information between process and supervision, in a context characterized by a variety of transmission media and different communication protocols.

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