Remote Terminal Unit (RTU) is a device of electronic which controlled by microprocessor that interfaces things in the actual to a SCADA (supervisory control and data acquisition system) or DCS (distributed control system) by sending out data telemetry to the system, and with messages from the system supervisory to control linked objects.
An RTU observes the field analog and digital parameters and sends out data to the CMS (Central Monitoring Station). An RTU can be connected with the Central Station with different media of communication for example serial RS232, RS485, RS422 or Ethernet. RTU can support standard protocols to connect any third party software. RTUs make high current to a digital output (DO) board to turn power on and off to tools in the field in several control applications. The board of DO changes voltage to the coil in the relay, which closes the contacts of high current, which completes the circuit power to the tool. An RTU can supervise inputs of analog of different types with 4–20 mA, 1–5 V etc.; the host system or RTU then converts this raw data into the suitable units for instance gallons of water left or temperature before showing the data to the user through the HMI.
Recent RTUs are generally capable of performing simple programs autonomously with no involving the computers host of the system of SCADA or DCS to make simpler deployment, and to give redundancy for safety causes. An RTU in a recent system of water management will characteristically have code to adjust its behavior when physical supersede switches on the RTU are toggled when maintenance by maintenance personnel. This is prepared for safety considerations; a misunderstanding between the maintenance personnel and for example the system operators could impact to system operators to wrongly allow power to a pump of water when it is being substituted.
PLCs, DCS, and RTUs are more and more beginning to partly cover in responsibilities, and many manufacturers trade RTUs with PLC-like vice versa and feature. The language of functional block for making programs to operate on PLCs and RTUs, the industry has standardized on the IEC 61131-3, even though nearly all manufacturers also present proprietary options and related development environments.
Additionally, some manufacturers currently provide RTUs with wide-ranging functionality pre-defined, occasionally with extensions and/or interfaces of PLC for configuration.
Some manufacturers of RTUs have produced simple GUI (graphical user interfaces) to allow users to organize their RTUs easily. Some instances are MoxGRAF from Products of MOX for their Field Controller of MX602 and PC-Link RTU-1, RTU-3 and RTU-8from Promosys Technology.
A PAC (programmable automation controller) is a solid controller that merges the capabilities and features of a control system PC-based with that of a characteristic PLC. PACs are arranged in systems of SCADA to supply the functions of RTU and PLC. Distributed RTUs utilize station computers or information processors to correspond with relays of digital protective, PACS, and devices for I/O, and correspond with the master of SCADA in a traditional RTU in many electrical substation SCADA applications.