The PLC system consists of various modules. The Central Processing Unit (CPU) performs the main controller functions like scanning data and running control sequences. The power supply unit converts line power to 24 volts. The I/O modules typically run off 5 to 7 volts logic supply. These PLC-I/O modules are part of a modular industrial machine control system. They interface between the CPU and the outside world. Devices which interface to the I/O modules are input devices like proximity switches, temperature/pressure sensors and output devices like motors, solenoids, relays and valves. As shown in the previous slide, the types of I/O modules are digital, analog, intelligent I/O modules and communication interface modules. These modules can be complex with a high amount of analog components.