In every point of the automation system where data have to collected and control has to be applied a Peripheral Control Station is installed. At the core of the station is the Remote Terminal Unit - RTU

Every such unit includes:

• Controller.Where the main CPU, RAM and program ROM are located.
• Real Time Clock-RTC. It is mainly used for time stamping every measurement.
• Digital Inputs. Every input can accept a two state condition.
• Digital Outputs. Outputs can emulate a two state switch.
• Analog Inputs.They can be connected to analog sensors, which usually operate under the 4-20mA or 0-10V prototype. These can measure values such as water pressure or water level in a tank.
• Analog Outputs. They can regulate the value of a parameter that takes constant values within a certain range (ex. motor speed regulation).
• Communication Ports & Modems.They handle the communication links with other RTUs and/or PCs.
• Power Supply Unit. Responsible for the power supply of every electronic and electrical unit. It usually has the ability to supply power even when there is a power failure (UPS).

The purpose of every Remote Terminal Unit is:

• To read the inputs of the unit
• To alter output state according to changes at inputs and to stored program control.
• To store in memory any measurements taken
• To communicate with the Central Terminal Unit in fixed intervals, in order to transmit all the measurements taken and to receive the relative commands.