Hanjalka Csabai at April 14, 2021

Let’s start at the beginning. What the RTU is, where it is used, and why it is needed. Why it is more appropriate than, for example, a Logger or as a field data collection and communication device with multiple inputs and outputs.

Definition of RTU (Balsom, 2019)

An RTU (Remote Terminal Unit) is a device used to monitor and control various devices. As for the meaning of the „remote” word RTU, this simply means that due to its location, it is impractical to wire the unit to a central processing computer. The unit can be placed in a neighboring room or even in an off-shore oil rig. Most units can be considered stand-alone computers because of the way the microprocessors are built.

Different, but in what?

The simplest is to take the method and place of use as a basis for comparison. If we consider that telemetry or control tasks need to be performed in remote, isolated locations, they could even be replaced by a PLC. However, it is its autonomy, energy supply/consumption, and operating environment that distinguishes it from PLC. It can be scaled in the number of inputs and outputs, it can be easily modified to suit the task/environment to be solved (eg with a spark-free input isolator).


RTU was born of technological demand. A device was needed that could receive and send digital and analog signals to the connected devices, transmit data and status signals to the central processing unit.

And here’s the point! He remained an intelligent member of a larger system. The software running on it can set the initial values ​​of the variable data, interpret the protocols of the incoming data and solve problems, to change the reading frequency of the data as they approach the extreme values.

The Cason DW RTU is designed to be flexibly adapted to monitor and control the level of reservoirs or to monitor pumps, sensitive, complex systems at sewage lifting stations, or even to remotely operate gas pressure regulating stations. It can be used almost everywhere, even in cooperation with a PLC system.

The complexity of the units can vary from small control cabinets with a single module to larger units with different sections with multiple modules. In addition to the communication interface, the cards usually provide one or more of the following functions:

• Analog input (AI)
• Digital input and output (DI / DO)
• Digital or control relay output (DO / CO)
• Analog output (AO / CO)


As an active member of a larger system, it must be able to communicate with the central data processing system in any environmental conditions, between -40 and + 60 °C.

It must support at least two serial communication protocols, depending on the connected devices (RS-232, RS-422, or RS-485), complete with a wireless connection. The way energy is used can, of course, be adapted to your needs.

The DW RTU is a true “Always On” device. However, it is open to the possibility of several types of communication, which can take place via Cellular and/or TCP / IP protocols. In Central and Eastern Europe, there is no point in Satellite communication, there is no buyer who would be willing to pay for it.

It should be mentioned that both TCP / IP and RS-485 are generally accepted internal bus systems, their interoperability is provided by an extra protocol conversion module for the Cason DW RTU.

Energy supply

Typically, RTUs operate on AC mains power because each module and circuit breaker requires it. When designing, Cason has moved in the direction of design so that this feature does not limit the scope of use. Our users prefer functionality that requires remote field, autonomous placement. That is why they are designed primarily with solar and battery power, but of course, the power supply unit is designed to be suitable for mains power as well. The total energy demand is designed to ensure 72-96 hours of battery operation even in case of adverse weather conditions or solar cell failure, of course in this case the system sends an alarm signal to the central control room.

Analog and digital outputs and inputs

Keeping a wide range of usability in the basic design of the Cason DW RTU, the analog inputs are made to 0-1 mA and 4-20 mA according to industry standards. This is made possible by an explosion in a hazardous environment with an isolating module free of ignition sparks. If analog control is required, the analog outputs will be available after current and voltage stabilization.

Digital inputs and outputs are commonly used for status signals, switches, circuit breakers, valve position indicators, or alarms. For example, pulse-based meters and tamper indicators are connected to a digital input. At the same time, an RS232 line is used to read a gas corrector value, while the flow meters are connected to an RS485 or RS232 input. The Outputs can also be used to control functions via relays or transistors. This allows you to work with the PLC.

The software

The CPU and the software running on it make the RTU truly autonomous. This is essential because, for example, GSM service is not always provided for a pressure regulating station located in a remote, isolated agricultural area. The lack of possible field strength must not limit the operation of the RTU, the entry and reading of data, and the initiation of controls in the event of alarm values. The software should also ensure that, once communication is restored, the activity performed and logged is forwarded to the central system.