PLC logic control refers to the use of programmable logic controllers (PLCs) to control various logical relationships in industrial production processes or equipment. The following is a detailed explanation of its meaning, working principle, application, etc.:
Basic meaning
PLC logic control is mainly based on logical operations to process input signals and generate output signals to achieve automatic control of equipment or systems. It digitizes and programs the traditional relay control logic, and implements various logical functions such as AND, OR, NOT logical operations, as well as timers, counters, etc. through software programming, thereby replacing a large number of hardware relays and complex wiring, and improving the reliability, flexibility and scalability of the control system.
Working principle
Input sampling stage: PLC collects various signals from field devices through input modules, such as status signals of buttons, switches, sensors, etc. These signals are converted into digital signals and stored in input image registers.
Program execution stage: PLC reads data from input image registers and other internal registers according to the control program written by the user, performs logical operations, data processing and other operations, and updates the data in the output image register according to the logical relationship and operation results in the program.
Output refresh phase: After the program is executed, the PLC converts the data in the output image register into actual physical signals through the output module to control the actions of external devices such as contactors, solenoid valves, indicator lights, etc., thereby realizing the control of the production process or equipment.
Programming language
Ladder diagram (LAD): It is a graphical programming language similar to a relay circuit diagram. It uses graphic symbols such as contacts, coils, and instruction boxes to represent logical relationships. It is intuitive and easy to understand, and it is easy for engineers familiar with electrical control circuits to get started.
Instruction list (IL): Similar to assembly language, it consists of instruction mnemonics and operands. It realizes logical control by arranging instructions in sequence. It is suitable for programmers who are familiar with the internal working principles of PLC and has the characteristics of high programming efficiency.
Function block diagram (FBD): With function blocks as the basic unit, the logical relationship is represented by connecting the input and output ends of the function blocks. It is similar to the logic block diagram in digital circuits and is suitable for implementing complex logic control and algorithms.
Application areas
Industrial automation production line: In production lines such as automobile manufacturing and electronic equipment production, PLC logic control can achieve precise control of the start and stop of conveyor belts, the handling of workpieces, the movement of assembly robots, etc., to ensure efficient and stable operation of the production process.
Elevator control system: responsible for controlling the up and down movement, floor parking, door opening and closing of elevators, etc., and monitoring and judging various states of elevators through logic control to ensure the safe operation of elevators and the comfortable experience of passengers.
Smart home system: can realize intelligent control of lights, curtains, air conditioners, security equipment, etc., through preset logic rules, such as automatic control of the switch and operation status of equipment according to time, light, human body sensing and other conditions, to provide people with a more convenient and comfortable living environment.
