A remote terminal unit (RTU), also called a remote telemetry unit or a remote telecontrol, is an industrial device that can collect and process data from sensors, actuators, and other devices. It may have a built-in microprocessor or a programmable logic controller (opens in new tab) (PLC) that can be programmed like a computer.
A remote terminal unit is used in many industries to control and monitor industrial equipment. It can be used to monitor the operation of machines, record data from them and send commands to them. They are a vital component of a supervisory control and data acquisition (opens in new tab) (SCADA) system. Here are a few examples of where RTUs are used:
A remote terminal unit (RTU) is a computer, while a programmable logic controller (PLC) is not. An RTU can be used to perform process monitoring and control functions and collect data from sensors within a plant or facility. A PLC has no operating system or display; it only accepts instructions from another device, which tells the PLC what to do based on those instructions.
Below is a graph to illustrate more differences between the two and how they interact with other systems and processes:
The illustration below highlights how a RTU and PLC work from the plant level (i.e., factory floor), up to the production scheduling (i.e., SCADA computer).
In the example above the primary level is the field level, which has a series of sensors and actuators. A sensor converts a physical attribute to an electrical signal. An actuator changes an electrical signal to a physical action. From here the next level (level 1) has the sensors speak to RTUs and actuators to the PLCs. Both then feed their data information to a SCADA computer (level 2).
In level 2 the SCADA computer feeds information to the systemwide SCADA supervisory computer, and vice versa. But what is the difference between these two systems?
A SCADA computer refers to a facility or a collection of computers (a server room or data center) that houses multiple computers and servers dedicated to running SCADA software and managing data storage and processing. A systemwide SCADA supervisory computer is typically a single, central computer that oversees and coordinates the entire SCADA system across a wide area, potentially encompassing multiple facilities or regions.
Lastly, the final level (level 4) is when the systemwide SCADA supervisory computer feeds its information into the SCADA computer center. The computer center is a dedicated facility or a collection of computing resources that support a SCADA system's operation, management, and maintenance. This center is critical for ensuring the reliability, efficiency, and security of the SCADA system.
Let's take an example of an RTU at a water treatment plant. The RTU is installed at different points within the treatment plant and throughout the distribution network. For instance, an RTU may be installed at a pumping station. The RTU interfaces with various sensors and actuators at the station. It collects data from the sensors, which might measure parameters like water flow rate, pressure, and water quality. It can also control the actuators by turning pumps on or off or adjusting valve positions.
If, for instance, the pressure in a section of the distribution network drops below a certain level, the RTU at the corresponding pumping station can be commanded to turn on a pump to increase the pressure. Sensors connected to the RTU could include flow meters, pressure sensors, and water quality sensors that measure parameters like pH, turbidity (cloudiness), and disinfectant levels.
Remote terminal units (RTUs) offer several benefits, especially for industries where monitoring and controlling operations at remote or distributed sites are critical. Here are some of the key benefits:
Remote terminal units can monitor and control various physical processes, such as temperature, flow rate, and pressure. They're incredibly beneficial for remote control monitoring and help improve safety when someone cannot physically visit a site to operate and check equipment.
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