SCADA is Supervisory Control And Data Acquisition is a software application program for process control, which refers to do both Data acquisition and Communication interface.
SCADA is a central control system which consists of controller network interfaces, input or output communication equipment and software. SCADA system control and monitor the industrial process.
SCADA system collects the data from one or more distant facilities as well as sending basic control operations to the facilities and it makes unnecessary for a human operator to be permanently present at the site of the facilities for normal operations.
SCADA is combination of telemetry and data acquisition
Data Acquisition:
Data acquisition refers to the method used to collect or send data/information from/to the equipment being controlled and monitor. The data accessed are then forwarded to a telemetry system ready for transfer to the different sites.
The data can be digital or analogue gathered from sensors, actuators, relays, valves, motor etc.
Telemetry:
Telemetry is simply the communication system. Telemetry is the technique used in transmitting and receiving information or data over a medium. The information can be any measurement value. The information is transmitted through cable, telephones or radio information. Information is reached from different locations.
Architecture of SCADA:
Basic components of SCADA system are:
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Field instrumentation
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Remote station (RTU)
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Communication network
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Master station (MTU)
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Commercial Data processing computer (client)
RTU:
The Field instruments are connected to the RTUs and connected to the control loop. The RTU collects data from the field instruments about process parameter, alarm status. It keeps the information until the MTU asks for it. And the MTU commands the RTU to change the setpoint and to change the Process variable through control action, such as closing or opening valves, Turning on/off the output etc,
RTU sends any type of control action to the field device such as 4-20mA analogue control, contact closure control and serial message to field equipment. RTU sends alarm, equipment status, field analogue signal, equipment message etc to the MTU.
RTU receives all analogue signals, equipment status signal pulse train meter signals from field devices. And receives discrete control orders, analogue setting instructions, order response from MTU.
Commonly RTU can be PLCs, DCS.
MTU:
MTUs read and write data from/to the RTU, handle communication errors and retries, scheduled scanning of the RTU’s. The MTU read and scan the information from the communication interfaces and check the deviation from the set point in the process variable and produce control action, alarm status.
MTU execute an action according to a specified time, event or condition e.g. print a report at the end of every shift, display values in a spreadsheet at a specified time.
MTU connects the process with the HMI station, MTU’s action and information include, on setpoint, process variable, alarm acknowledgement, control setpoint, etc, The data obtained are processed to form charts and spreadsheets, Printers and scanners can be connected to the HMI.
Data transmission:
RTUs in the field are connected together through a controller network. Each RTU has a unique address and the network is connected to a modem. The transmission of data from RTUs to MTU can be through wireless or wired using specific kinds of wires.
The MTU unit contains the receivers to decode the information at the HMI end.
Applicaions od SCADA:
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Traffic light control system
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Generators and Tribune
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Water distribution and reservoir system
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Electrical heating and cooling system.
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Power generation
