What is PLC?

Longzhong PLC Programmable Logic Controller

What is PLC?


PLC」full name is Programmable Logic Controller,It has the characteristics of strong versatility, convenient use, wide adaptability, high reliability, strong anti-interference ability, and simple programming. It is a digital electronic device with a microprocessor, a digital logic controller for automatic control, and can load control instructions into the memory for storage and execution at any time.

PLC is a modular combination of internal CPU, instruction and data memory, input and output unit, power supply module, digital analog and other units, which can receive (input) and send (output) various types of electrical or electronic signals. And use them to control or supervise almost all kinds of mechanical and electrical systems.


The parts are likened to organs in the human body: the input function is like the nervous system, responsible for receiving instructions; the CPU is like the brain, coordinating work distribution; the output function is like muscle cells, executing the completed instruction requirements…… and many more. Through the program to set the instructions to make each part operate, so that the PLC can achieve the functions we need.


In 1968, General Motors of the United States proposed the famous "General Ten" bidding indicators, which are also the characteristics of the current PLC:

1. Easy to program, the program can be modified on site
2. Easy maintenance and modular structure
3. The reliability is higher than that of the relay control device
4. The volume is smaller than the relay control device
5. The data can be directly sent to the computer
6. Cost can be competitive with relay control devices
7. The input can be AC ​​115V
8. The output is AC 115V, above 2A, which can directly drive solenoid valves, contactors, etc.
9. When expanding, the original system only needs minor changes
10. User program memory capacity can be expanded


PLC is widely used in various industries because of its high flexibility. The annual growth rate of PLC usage around the world remains at 20% to 30%. With the continuous improvement of factory automation, the PLC market capacity base is also expanding.
There are quite a few PLC brands on the market now, and the logic of the programs that each brand needs to write is not the same. Different brands and models will be used to match the needs of different situations.

Longzhong has a very good team, whether it is SIEMENS、MITSUBISHI、OMRON、Schneider、DELTA、AB PLC(Allen-Bradley)......etc., For the PLC Longzhong of major brands, there are engineering staff responsible for writing.


Have any PLC programming requirements and questions
Longzhong provides Technical Advisory Services | Tel: 06-243-7822

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