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PACs are deployed in SCADA systems to provide RTU and PLC functions. In many electrical substation SCADA applications, "distributed RTUs" use information processors or station computers to communicate with digital protective relays, PACs, and other devices for I/O, and communicate with the SCADA master in lieu of a traditional RTU.
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.
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
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.
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]
A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis.
These could be distributed around plant, and communicate with the graphic display in the control room or rooms. The distributed control system was born. The introduction of DCSs allowed easy interconnection and re-configuration of plant controls such as cascaded loops and interlocks, and easy interfacing with other production computer systems.
The OPC Data Access Specification is the first of a group of specifications known as the OPC Classic Specifications. [1]OPC Data Access is a group of client–server standards that provides specifications for communicating real-time data from data acquisition devices such as PLCs to display and interface devices like Human–Machine Interfaces (HMI), SCADA systems [2] and also ERP/MES systems. [3]