Input and output (I/O) module

The I/O modules, both digital and analogic, are the modules through which the PLCs communicate with the physical process, detecting events and data from the sensors and ordering actions to the actuators. From an electrical point of view, they act as an interface between the voltage levels (TTL or CMOS) of the PLC circuits and the voltages (or currents) used for the transmission of the signals to the actuators. These signals are in a range of between a few tens and hundreds of volts. In most cases, this allows us to connect the PLCs directly to the various devices that are present in the field, minimizing the need for further signal conditioning. The analog I/O modules also carry out the digital to analogical or analogical to digital conversions that are required to directly interface the analog signals, which are continuous in time and in value with the PLC. Being a calculator, the PLC works with strings of bits of a fixed length in discrete time intervals.