What is PLC? You will understand after reading this

What is PLC?

PLC (Programmable Logic Controller) is a new type of industrial control device based on microprocessors, integrating computer technology, automation technology and communication technology. It realizes networking communication, human-computer interaction, process control, logic programming and other functions in industrial automation control, and has the characteristics of simple operation, reliability and stability. The PLC control system consists of processors, memory, I/O interfaces, communication modules, external devices and other parts. Unlike general-purpose computers, PLCs are specially designed for multiple input and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and shock. Programs that control machine operations are usually stored in backup power support or non-volatile memory. PLC is an example of a hard real-time system because it must respond to input conditions and produce output results within a certain period of time, otherwise it will cause unexpected operations. As shown in the figure below, it is a factory automation control system, and PLC is mainly in the control layer of the entire system.

What is the main structure of PLC?

The figure below shows the main functional modules included in the PLC structure.

1. The processor, the brain of the PLC, executes the program and controls input and output.

2. Power module, which realizes 110V/230V AC power conversion and supplies power to all functional modules on the PLC.

3. Analog input module (AI), receives analog input and converts it into digital signal for CPU.

4. Analog output module (AO), converts CPU instructions into analog output.

5. Digital input module (DI), receives digital input and converts it into digital signal for CPU.

6. Digital output module (DO), converts CPU instructions into digital output.

Classification of PLC?

Small PLC I/O points less than 256 points

Small size, low price, mainly switch control function, relatively simple. Suitable for controlling a single device or developing mechatronic products. Low market entry threshold, serious product homogeneity, high degree of localization, mainly for OEM market.

Medium-sized PLC I/O points: 256~2048 points

Based on the functions of small PLC, it has strong communication function, digital computing ability and analog processing ability. It is suitable for more complex logic control production system and continuous production process control. The technical barrier is high, mainly facing the project market, and is currently dominated by foreign manufacturers.

Large PLC I/O points more than 2048 points

It has calculation, control and coordination functions and a powerful network structure. The monitoring system uses CRT display to display dynamic processes. It is suitable for equipment automation, process automation control and process monitoring systems, etc. It has high technical barriers and is mainly oriented to the project market. It is currently mainly monopolized by foreign manufacturers.