A SCADA (Supervision, Control and Data Acquisition) system is a software application, designed with the purpose of controlling and supervising remote processes.
It is based on the acquisition of data from remote processes and is designed primarily to operate on computers in production control, providing communication with field devices (autonomous controllers, PLCs, etc.) and controlling the process automatically from a computer. In addition, it sends the information generated in the production process to various users, both at the same level and to other supervisors within the company, i.e. it allows the participation of other areas such as: quality control, supervision, maintenance.
There are different types of SCADA systems depending on the manufacturer and above all on the purpose for which the system will be used, so before deciding which is the most appropriate you must bear in mind whether or not it meets certain requirements:
Every system must have an open architecture, that is to say, it must allow its growth and expansion, as well as be able to adapt to the future needs of the process and the plant.
Programming and installation should not be more difficult, it should have graphical interfaces that show a basic and real scheme of the process.
They must allow the acquisition of data from all equipment, as well as internal and external communication (local and management networks).
Programs should be simple to install, without excessive hardware requirements, and easy to use, with user-friendly interfaces.
Open Loop Systems
In non-feedback or open-loop systems, the controlled variable is not compared to a reference input. Each input setting determines a fixed operating position in the control elements.
Closed Loop Systems
Feedback or closed loop systems operate in such a way that makes the system feed back, the output goes back to the beginning to analyze the difference and in a second option adjust further, so until the error is 0. Any basic concept that has as its nature a controlled quantity such as temperature, speed, pressure, flow, force, position, and couplings, etc. are closed loop control parameters.
A SCADA software must be able to offer the system:
Possibility of creating alarm panels, which require the presence of the operator to recognize a stop or alarm situation, with recording of incidents.
Generation of historical data of the plant signal, which can be dumped for processing on a spreadsheet.
Execution of programs that modify the control law, or even cancel or modify the tasks associated with the automaton, under certain conditions.
Possibility of numerical programming, which allows arithmetic calculations of high resolution on the CPU of the computer.
Remote Terminal Unit (RTU)
The RTU is physically connected to the equipment and reads status data such as open/closed status from a valve or switch, reads measurements such as pressure, flow, voltage or current. Through the equipment the RTU can send signals that can control it: open it, close it, exchange the valve or configure the pump speed, start it, stop it.
The term "Master Station" refers to the servers and the software responsible for communicating with the field equipment (RTUs, PLCs, etc.) where the HMI (Human Machine Interface) software is running for the workstations in the control room, or elsewhere. In a small SCADA system, the master station can be on a single computer. On a large scale, in SCADA systems the master station can include many servers, distributed software applications, and disaster recovery sites.
Infrastructure and Communication Methods
SCADA systems traditionally have a combination of radios and direct serial signals or modem connections to meet communications requirements, even Ethernet and IP over SONET (fiber optics) is also frequently used in very large sites such as railways and power stations. Moreover, the methods of connection between systems may even be through wireless communication, is deir, if you want to send the signal to a mobile phone without using cables.
To develop a SCADA system is necessary a Development Environment in which to design, among other things:
What SCADA will look like
The functions and events you must execute when interacting with your HMI interface
The operations and calculations you must perform with the acquired data.
Type of Architecture: Centralized.
Predominant control type: Supervisory - Control loops closed by the operator. Additionally: sequential and regulatory control.
Types of Variables: Decoupled.
Area of action: Geographically distributed areas.
Data acquisition and control units: Remote, PLCs.
Media: Radio, satellite, telephone lines, direct connection, LAN, WAN.
Functions of a SCADA System
The basic functions of a SCADA system are described below:
- Remote Supervision of Installations
- Remote Control of Installations
- Information Processing
- Presentation of Dynamic Graphics
- Report Generation
- Presentation of Alarms
- Historical Information Storage
- Presentation of Trend Graphs
- Event Programming
Modules of a SCADA System
The modules or software blocks that allow the activities of acquisition, supervision and control are the following ones:
Configuration: allows the user to define the working environment of his SCADA, adapting it to the particular application to be developed.
Graphical operator interface: provides the operator with the functions of control and supervision of the plant. The process is represented by synoptic graphics stored in the process computer and generated from the editor incorporated in the SCADA or imported from another application during the configuration of the package.
Process module: executes the pre-programmed control actions from the current values of read variables.
Data management and archiving: takes care of the storage and orderly processing of data, so that another application or device can have access to them.
Communications: is responsible for the transfer of information between the plant and the hardware architecture that supports the SCADA, and between it and the rest of computer management elements.
This concludes another installment that I leave for you with much affection hoping that I can be of use to you and sincerely thanking you for the time you have taken to read my article.
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