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It refers to the computer and software responsible for communicating with the field connection controllers, which are RTUs and PLCs, and includes the HMI software running on operator workstations. In smaller SCADA systems, the supervisory computer may be composed of a single PC, in which case the HMI is a part of this computer.
PLCs use built-in ports, such as USB, Ethernet, RS-232, RS-485, or RS-422 to communicate with external devices (sensors, actuators) and systems (programming software, SCADA, user interface). Communication is carried over various industrial network protocols, like Modbus, or EtherNet/IP. Many of these protocols are vendor specific.
DF-1 - used by Allen-Bradley ControlLogix, CompactLogix, PLC-5, SLC-500, and MicroLogix class devices; DNP3 - a protocol used to communicate by industrial control and utility SCADA systems; DirectNet – Koyo / Automation Direct proprietary, yet documented PLC interface; EtherCAT; Ethernet Global Data (EGD) – GE Fanuc PLCs (see also SRTP)
A feedback control loop is directly controlled by the RTU or PLC, but the SCADA software monitors the overall performance of the loop. For example, a PLC may control the flow of cooling water through part of an industrial process to a set point level, but the SCADA system software will allow operators to change the set points for the flow.
The DNP3 protocol is also referenced in IEEE Std. IEEE 1379-2000, which recommends a set of best practices for implementing modern SCADA Master-RTU/IED communication links. These include not just encryption but other practices that enhance security against well known intrusion methods.
OPC servers provide a method for different software packages (as long as it is an OPC client) to access data from a process control device, such as a programmable logic controller (PLC) or distributed control system (DCS). Traditionally, any time a package needed access to data from a device, a custom interface or driver had to be written.
A remote terminal unit (RTU) is a microprocessor-controlled electronic device that interfaces objects in the physical world to a distributed control system or SCADA (supervisory control and data acquisition) system by transmitting telemetry data to a master system, and by using messages from the master supervisory system to control connected objects. [1]
The HMI/SCADA Module Layer contains mainstay products of the Ignition Platform. Vision is the main visualization module, SQL Bridge is a bidirectional OPC to SQL database historian and transaction manager, Reporting generates dynamic Pdf reports, and Mobile allows access to HTML 5 compatible devices such as iPads, iPods, Android, Smartphone ...
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