Answer: Power supply, central processing unit (CPU), memory, input/output (I/O) unit.
Answer analysis: The 4 main components of PLC (Programmable Logic Controller) usually include:
1. Power supply:
- Function: The power supply is an important part of PLC. It is responsible for converting the external input AC power into the DC power required by PLC.
- Characteristics: Most PLCs are powered by switching regulated power supplies to ensure the stability and reliability of the system voltage.
- Importance: The stability of the power supply is crucial to the normal operation of PLC.
2. Central Processing Unit (CPU):
- Composition: The CPU consists of a controller, an arithmetic unit, and registers, all of which are concentrated on a chip.
- Function: The CPU is the control center and core component of the PLC, responsible for processing and running user programs, performing logical and mathematical operations, and controlling the coordinated work of the entire system.
- Function: The CPU continuously collects input signals, executes user programs, and refreshes the output status of the system.
3. Memory:
- Classification: Memory usually includes system memory and user memory. The system memory stores system programs, which are written by the PLC manufacturer and fixed in the read-only memory (ROM), and cannot be accessed by users. The user memory includes the user program storage area and the working data storage area, which are used to store the control programs and data written by users.
- Function: The memory has a memory function and is used to store system programs, user programs, logical variables and some other information.
4. Input/output (I/O) unit:
- Input interface: responsible for receiving signals from external sensors, buttons and other devices, and converting them into digital signals that can be recognized by the CPU.
- Output interface: Convert the digital signal processed by the CPU into a signal that can drive external actuators, such as controlling the on and off of the contactor coil.
- Function: The I/O unit is a bridge for data exchange between the PLC and external devices, realizing the control of the PLC over external devices.
In summary, the four main components of the PLC are the power supply, central processing unit (CPU), memory and input/output (I/O) unit. These components work together to complete the control tasks of the PLC.