The second DC represents the DC input (24V DC).
The third DC represents the DC output (24V DC, transistor), and if RLY, the relay output.
CPU
The central processing unit (CPU) is the control center of PLC and the core component of PLC, and its performance determines the performance of PLC.
The central processor is composed of a controller, an arithmetic device and a register. These circuits are concentrated on a chip, and are connected to the input\/output interface circuit of the memory through the address bus and the control bus. The role of the central processing unit is to process and run user programs, perform logical and mathematical operations, and control the entire system to make it coordinated.
input unit
The input unit is the input interface connected between the PLC and the controlled device, and is the bridge for the signal to enter the PLC. Its role is to receive the signal from the master component and the detection component. Input types include DC input, AC input, and AC-DC input.
output device
The output unit is also the connection part between the PLC and the controlled device, its role is to transmit the output signal of the PLC to the controlled device, that is, the weak current signal sent by the central processor is converted into a level signal, and the executive element of the controlled device is driven. The output types are relay output, transistor output, and gate output.