What is Remote Terminal Unit(RTU)? Block Diagram, Application

A Remote Terminal Unit or RTU is basically a type of computing, programming, controlling, and networking device that connects different types of physical world sensors, transducers from remote locations to a central processing system. So, the Remote Terminal Unit is a specially designed multipurpose device mainly used in automation systems such as SCADA(Supervisory Control and Data Acquisition), IoT(Internet of Things), etc. The Remote Terminal Unit is also known as the Remote Telemetry Unit or Remote Telecontrol Unit.

Remote Terminal Unit(RTU) Function

The main functions of a Remote Terminal Unit are,

• Connecting - It connects multiple devices of an automation system that actually interacts with the physical world such as sensors, transducers, actuators, etc. In this layer, they are mostly connected through wire connection.
• Converting - It can converts signals from analog to digital or digital to analog.
• Controlling - It can control all the devices connected to it as per given instructions.
• Processing - It process all the signal coming from the devices connected to it, then sends to the central or master control system.
• Networking - RTU supports different types of network protocols and ways such as wearable or wireless to send the data from a remote place to a central control system.

Remote Terminal Unit(RTU) Block Diagram

Here, you can see the block diagram of RTU or Remote Terminal Unit to better understand its working and function.

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Remote Terminal Unit(RTU) Architecture

The RTU can be called a powerful mini-computer also because it also has hardware, software, and firmware like a computer. It also has a powerful processor, Drivers, peripherals, ports. In a computer we can do multiple task by installing different softwares. The RTU also designed and programmed as per the requirement.

An RTU allows multiple inputs at the same time in different forms such as analog inputs, digital inputs, mixed signals, etc. An RTU has all the controlling, converting, and filtering circuits. When it receives data or signals from the physical world devices connected to it, first it filters, converts(if required), and amplifies before processing. 

RTU circuit is designed to operate with a DC power supply, so it has a AC to DC converter circuit or an external AC to DC power adapter is uses to power up the RTU. RTU is also embedded with a battery and charger circuit for uninterruptable operation when the main power supply is not available.

An RTU has both Analog and Digital outputs. Its outputs are connected through a high current carrying relays. So, an RTU can operate high current carrying loads, actuators, etc. 

The communication system of the RTU is also very powerful and stronger. It supports different types of protocols(RS232, RS485, RS 422, etc) and different communication mediums such as Ethernet wireable connection, Radio Frequency wireless connection, etc.

How RTU Works?

The working principle of an RTU is very simple. Basically, it is installed in different plants and machinery stations. All the field devices such as sensors and actuators are directly connected to this RTU. RTU makes communication with those field devices through wire connections. But when it communicates with the master SCADA station it uses a wireless system. It has an inbuilt modem and antenna system so it transmits a signal through radio signals. For example, when a command is given from the master station, the instruction signals come from the master station to RTU wirelessly. After that, the RTU decodes the signal and generates the output signal for field devices to operate. Then the output signal reaches to the connected field device through a wire connection and the field device(e.g. actuator) will operate.

Also, remember that an RTU can be interfaced with multiple master stations with different communication protocols. If you think a single RTU interfaced with a single master station only, that is wrong. Sometimes, the RTU is designed to support the standard protocol to interface with any third-party software. During data transmission between an RTU and a Master Station different factors are considered such as proper synchronization, minimum traffic, Low Data Delay, eliminating data stealing, etc. 

Applications of RTU(Remote Terminal Unit)

The main function of an RTU is to connect the sensing and controlling devices from a remote place to a central master station in an automation system. So, RTU is used for,

1. Environmental Monitoring System to monitor weather status, and air pollution monitoring of different remote places from a central control center.
2. In oil plants and gas plants, to monitor the status of level, environmental conditions, and to operate or control different types of valves, switches, machines, etc.
3. In electrical power transmission and distribution system to monitor power, voltage, current and to operate circuit breakers, switches, etc.
4. In water treatment and supply plants to monitor treatment status, water flow, consumption, etc.
5. RTU is also used in chemical plants, automobile industries, sewage treatment plants, food processing industries, agriculture, nuclear power plants, etc.
6. RTU can be used in manufacturing planta to control the assembly line or to gather the production details.

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