Working principle of PLC Basic structure of PLC

PLC is the abbreviation of "Programmable Logic Controller", which is an industrial automation control device that can automatically control the operation of machines or production equipment. The programmable controller is composed of CPU, instruction and data memory, input/output interface, power supply, digital analog conversion and other functional units. PLC controls the output signal by writing programs. With the continuous upgrading of technology, the functions of PLC are becoming more and more perfect, and it has been widely used in machinery manufacturing, electric power, petrochemical, transportation, water conservancy and hydropower and other fields.

The working principle of PLC is based on input, output and program logic. PLC transmits input signals from various sensors to the processor. These input signals include temperature, pressure, flow, switches, buttons, etc. PLC processes these input signals and controls output signals such as motors, valves, lights, etc. according to pre-written program logic to control machines or processes.

The operation of a PLC is controlled by a program that can be written by a programmer and then downloaded to the PLC controller. PLC programs are usually written in ladder diagrams, a programming language that is similar to a simplified electrical circuit diagram. The PLC can detect and respond to input signals according to the instructions of the program, which can improve efficiency and reduce human error.

When the input signals change, the PLC's processor will quickly read and process these signals and execute predefined program logic to determine the state of the output signals. In this way, the PLC achieves fast and precise control, thereby supporting the control of automated production lines and other processes.

The basic structure of PLC mainly includes the following parts:

1. Central Processing Unit (CPU): The CPU is the core component of the PLC. It is responsible for the entire control process of the PLC, including the acquisition of input signals, logical operations, control of output signals, etc. The CPU usually includes components such as a microprocessor, memory, and clock.

2. Input/output module (I/O module): The I/O module is the interface between the PLC and external devices. It collects signals from external sensors, actuators and other devices to provide input information to the CPU, and outputs the control signals processed by the CPU to external actuators and other devices.

3. Memory: The memory in PLC usually includes program memory, data memory, etc. The program memory is used to store the control program written by the user, and the data memory is used to store various data required during operation.

4. Programming equipment: Programming equipment usually uses computers and other devices to program and debug PLCs through specific programming software to enable users to control the automation system. Programming equipment needs to support relevant programming languages ​​and protocols.

5. Communication interface: The communication interface of PLC can connect PLC with other automation equipment, computers, etc. to realize data transmission and interactive control. Communication interfaces usually include serial ports, Ethernet ports, etc.

These components work together to form the basic structure of PLC. In the process of realizing automatic control, PLC can provide strong support for engineering projects and production by using its stable, reliable and flexible control characteristics.