Remote Terminal Unit (RTU)

Remote Terminal Unit (RTU)

The Remote Terminal Unit is usually defined as a communication satellite within the SCADA system and is located at the remote site. The RTU gathers data from field devices (pumps, valves, alarms, etc.) in memory until the MTU initiates a send command. Some RTUs are designed with microcomputers and programmable logic controllers (PLCs) that can perform functions at the remote site without any direction from the MTU. In addition, PLCs can be modular and expandable for the purpose of monitoring and controlling additional field devices. Within the RTU is the central processing unit (CPU) that receives a data stream from the protocol that the communication equipment uses. The protocol can be open like Modbus, Transmission Control Protocol and Internet Protocol (TCP/IP) or a proprietary closed protocol. When the RTU sees its node address embedded in the protocol, data is interpreted and the CPU directs the specified action to take.

During the sixties, many manufacturers developed RTUs with communicative functions that performed a few specific tasks such as monitor and control digital and analog field devices. These all-in-one RTUs needed constant communication with the MTU in order to operate. A wide variety of programming languages were used that were not well known or supported. In the eighties the first micro PLCs were introduced as the first Open Architecture technology which has evolved and gained acceptance as todays preferred alternative to closed, proprietary systems.

Some manufacturers, like EPGs SCADA division NBT, now make Remote Access PLCs (RAPLC) specifically designed for SCADA and Data Acquisition applications. With NBTs PLC system, you can:

* Perform control
* Check site conditions
* Re-program anytime from anywhere
* Have any alarm or event trigger a call to your personal computer

This can all be done from a single, master site and the system can control one or multiple sites. Both industry representatives and customers welcome these smart PLCs because they provide remote programmable functionality while retaining the communications capability of an RTU.