The level 2 includes all devices that interact directly with the sensors and the actuators implementing so the control and the safe functionalities both for a single equipment and for working cells and entire production lines; they are the followings:
- Remote terminal unit (RTU) is an electronic device that is controlled by a microprocessor. It acts as an interface for sensors, actuators, and intelligent devices by transmitting data and receiving command messages from a master system. It is basically used to centralize the input and output to and from the sensors and actuators by reducing the complexity of their cabling and wiring.
- Embedded controller is generally a single chip or board that includes all the necessary components to carry out the required control tasks. They are usually designed for a specific application and are built on top of a specific or custom hardware.
- Computer Numerical Controls (CNCs) are machine tools that are controlled by an electronic device integrated into the machine. Movements and functions of CNC machines are predefined and set through a specific software. They are used for performing high-precision machining that requires long processing times without any interaction with the external environment.
- PLC is an industrial controller that is dedicated to the control of industrial processes. The PLC executes a program in a cyclical fashion, processing the signals coming as input from the sensors and sending the output values to the actuators to control the physical process. The reading of the inputs, their processing, and finally the writing of the outputs, takes place within a predefined maximum time, called a scan cycle. This typically takes between 10 and 100 milliseconds.
- DCSes are typically used in continuous processes such as in refineries, energy production, or chemical plants. They integrate both the control function implemented in the PLC and the supervision of the SCADA system. While the PLC and the SCADA are two separate systems, each with their own variables and data structures, in the DCS, the control and the supervision of their processing tasks share the same variables and data structures.