PLC (Programmable Logic Controller) is an industrial automation control device, and its components and functions are crucial to the realization of automation control.
The following is a detailed introduction to the main components of PLC and their functions:
1. Central Processing Unit (CPU)
Function:
* The CPU is the core component of PLC, which is responsible for the entire control process, including the acquisition of input signals, logical operations, and the control of output signals.
* It translates the user program into a user-compiled program recognized by the PLC, and performs data processing and logical judgment according to the program.
* The CPU is connected to the I/O interface circuit through the address bus and data bus to realize data exchange with various components.
Composition:
* The CPU consists of a controller, an arithmetic unit, and registers, which are integrated on a chip.
* The controller is responsible for controlling the entire CPU working process, including the reading, decoding, and execution of instructions.
* The arithmetic unit is responsible for arithmetic and logical operations.
* Registers are used to store data and instructions.
2. Memory
Function:
* The memory is used to store control programs and data written by users.
* It includes system program memory and user memory. The system program memory is used to store system programs, including management programs, monitoring programs, and interpretive compilers that compile user programs.
* The user memory is divided into a user program storage area and a working data storage area, which are used to store user-written control programs and various data required for work.
Type:
* The system program memory is usually composed of a read-only memory (ROM), the content of which cannot be changed and does not disappear when the power is off.
* The user memory is composed of a random access memory (RAM), the content of which will disappear after a power outage, but can be maintained using a backup power supply.
3. Input/output (I/O) module
Function:
* The I/O module is the interface between the PLC and external devices, responsible for the input and output of signals.
* The input module receives signals from external sensors, buttons and other devices, and converts them into digital signals that the CPU can recognize.
* The output module converts the digital signals processed by the CPU into signals that can drive external actuators, such as controlling the on and off of devices such as contactors and solenoid valves.
Type:
* Input modules include digital input modules (DI) and analog input modules (AI), which are used to receive digital and analog signals respectively.
* Output modules include digital output modules (DO) and analog output modules (AO), which are used to output digital and analog signals respectively.
4. Other auxiliary components
In addition to the three main components mentioned above, PLC may also include other auxiliary components, such as programming devices, network communication modules, power modules, etc.
* Programming devices: used to program and debug PLCs, usually including handheld programmers and computers.
* Network communication modules: realize data transmission and interactive control between PLCs and other automation equipment and computers.
* Power modules: provide stable and reliable power supply for PLCs to ensure the normal operation of PLCs.
These components work together to form a complete PLC system and realize precise control of industrial automation equipment.