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The Basics of SCADA RTU Protocols and Communication

Imagine the simplest possible Supervisory Control and Data Acquisition (SCADA) system would be a single circuit that processes data and notifies you of one event. Imagine a fabrication machine that produces widgets. In this SCADA application, every time the machine finishes a widget, it activates a switch. The switch turns on a light on a panel, which tells a human operator that a widget has been completed.

In our simple industrial process of the widget fabricator, the "network" is just the wire leading from the switch to the panel light. In real life, you want to be able to monitor and control a lot of systems in remote sites from a central location, so you need a communication network. This a special kind of network used to transport all the real-time data collected from your sensors by PLCs or RTUs. This data will ultimately reach your Human Machine Interface (HMI) software.

SCADA Protocols

Early, native SCADA communication protocols communicated over radio, modem, or dedicated serial communication lines. Today the trend is to put SCADA data on Ethernet and IP over SONET. For security reasons, SCADA protocols are frequently restricted to closed LAN/WANs to avoid exposing sensitive data to the open Internet.

Real supervisory systems don't talk with just simple electrical signals, either. SCADA data is encoded in protocol format. Older SCADA systems depended on closed proprietary protocols, but today the trend is to open standard protocols and protocol mediation.

This kind of protocol allows the SCADA connection of electronic devices from different vendors, making it possible for them to communicate with one another. This means these manufacturers want to achieve superior compatibility when they design their equipment's functionality and capabilities.

Using an open standard protocol is a very important decision that leads to cost reduction and maximized flexibility. The open standard has many benefits over the proprietary protocol, such as:

Examples of open protocols include SNMP, DNP3 and Modbus.

SCADA Diagram

RTU Communication

Sensors and control relays are very simple electric field devices that can't generate or interpret communication protocols on their own. Therefore the remote terminal unit (RTU) is needed to provide an interface between the sensors (data acquisition) and the SCADA network.

An RTU will connect to your monitored equipment and encodes sensor inputs into protocol format and forwards them to the SCADA Human Machine Interface (HMI) - also called master station. A human-machine a software that gives you an interface to connect a person to a machine, system, or device.

The communication of information from an RTU to the HMI user interface is called telemetry.

HMI SCADA allows technicians to improve their situational awareness, while also have the capacity to check on their network anytime and anywhere. The best SCADA HMIs will present information graphically, in the form of a map or pictures. Also, they allow users to remotely control devices and processes from its interface.

The best practice is to have a SCADA software that supports what HMI communication protocol you have, such as DNP3 (distributed network protocol) and Modbus TCP/IP.

The exchange of data can be asynchronous with events reported by the RTU as they occur. It can also be exchanged using a command and response protocol that is generally controlled by the SCADA master - this is called polling.

If the RTU is designed with outputs, it can also receive control system commands in protocol format from the master and translate them to the appropriate physical or communication outputs.

How SCADA RTU Communication Can Be Valuable To You

Like any other technology, SCADA is only beneficial if it can help you. SCADA systems are very important for remote monitoring and controlling many different types of equipment and processes in various networks. So, if you need to manage a system that is not located within your office or facility, SCADA will be valuable to you as well.

This is because through alarm notification features, you can get alerts anytime one of your set parameters goes above or beyond the thresholds that you configured. Protocols and overall SCADA communication is the main key to visibility over these parameters, allowing you to keep your network working efficiently.

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