4.1 Statement of the Problem

4.1.1 Tasks of the SCADA system

In the present days, when constructing the automated process control systems of the technological processes (ACS TP) the user interface with the control system are implemented using computer systems. This approach is due to several reasons: the compactness (in the physical and energetic sense) of modern computer technics, maturity of the methods of presentation the information, great functionality and variability of control systems.

The application of computer technology in the "ACS TP" in general, and in the workplaces of the operators in particular, has led to the origin of class of software (SW), known as SCADA (Supervisory control and data acquisition) and HMI (Human Machine Interface).

Thus, the key purpose of SCADA and HMI is to provide the interface between the operator and control system of the TP. Often, SCADA and HMI also implements the following tasks: the formation of alarm about the violation in TP, making the parameters' archives of TP and protocols of events.

Therefore, SCADA and HMI software can be regarded as a set of subsystems: the database of the parameters of TP and connections with the control systems of TP (controllers), the formation of alarms about the violations of TP, archiving, logging, visualization of the operational and archival data.

In addition to the above problems it can be included the separation of access rights for read-modify those or other parameters of TP, implemented in the security subsystem.

Thus modern SCADA and HMI systems are fairly complex software systems.

The subject of this subproject is to develop the concept of visualization and control are (VCA) and implementations of VCA's on the basic ways of representation for SCADA system OpenSCADA.

Visualization means the next set of tasks:

• Providing the operator with current information about the parameters of TP (sensors' data, the positions of the mechanisms, actuators). Much attention is paid to alarm about deviations (violations) of TP.
• Display the archive information about the parameters of TP and the events that occurred.
• Reception and transmission of operator's commands to the controlled system.

VCA must operate in two modes - editing (development) and execution. The first phase is planned to implement the development mode only for the Qt-version of the VCA!

In the operation process the VCA must use data from other subsystems:

• Subsystem "Data acquisition (DAQ)":
  • "Development" — when you connect the dynamics to the frame (widget).
  • "Execution" — at the time of formation of the dynamics of the frame (to access the current values of the parameters of its history, as well as violations of the parameters).
• Subsystem "Archives":
  • "Development" — when setting up the dynamics of the frame.
  • "Execution" — at the time of formation of the dynamics of the frame (access to archival values of the parameters).
• Subsystem "Security":
  • "Development" — when setting up access to the widgets.
  • "Execution" — when forming the image of the widget, and control capabilities.
• Subsystem "DB": access for loading and saving data for widgets, frames, library of the frames and projects as in the development mode, and in the execution also.

An image on the screen should be formed from the limited set of basic widgets (primitives). Presentation and interface of the basic widgets for each VCA should be done separately. This is done to optimize performance and simplify the task of creating the library of basic widgets. With the purpose of compatibility between different implementations of the VCA is planned the creation of the general description of the library of basic widgets (data model) with the subsequent implementation of its interface in each VCA.

Basic widgets are to be grouped and form derivatives of widgets, with the further accumulation of them in the user's widget library/frame.

4.1.2 Tasks of monitoring system

Given the purpose of the OpenSCADA system, as a system for monitoring data in many related fields, it is necessary to formulate the tasks for such systems in general.

In the monitoring systems, as a rule, there is no control possibility, but the interactive elements must be present.

The primary objective of such systems is the continuous provision of information in an accessible form and on the background of the basic work.