The hardware of a PLC mainly consists of several parts: the Central Processing Unit (CPU), memory, input units, output units, communication interfaces, expansion interfaces, and power supply.The CPU is the core of the PLC, while the input and output units serve as the interface circuits connecting field input/output devices to the CPU. The communication interface is used to connect with programming devices, host computers, and other peripheral devices.
1. Central Processing Unit (CPU) is the core of the PLC.
★Microprocessor: Performs logical operations and mathematical calculations, coordinating the operation of various parts of the control system.
★ Operates according to the tasks assigned by the system program.
★ Tasks:
1) Control the reception and storage of user programs and data.
2) Perform self-diagnosis.
3) Execute user programs.
★Control interface circuits
are components that connect the microprocessor with other units inside the host..
2.Memory
System program memory
Stores:
•System monitoring programs
•User instruction interpretation
•Standard program modules
•System call management programs
•Various system parameters
The system program relates to the performance of the PLC and cannot be accessed or modified by users.
User program memory
3. Input and Output Units
•PLC’s CPU connects with field I/O devices or other external devices through interface (unit) circuits.
1) Input Unit
DC input interface
AC input interface
2) Output Unit
Relay output method4. Power Supply Unit
◆ Converts external power into the power required by each unit inside the system.
◆ Uses a switching power supply.
◆ The performance of the power supply directly affects the PLC’s anti-interference capability.
◆ Power failure protection circuit.
◆ Backup battery power supply.
