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PLC

PLC is a digital operation controller with a microprocessor for automatic control. It can load control instructions into the memory at any time for storage and execution. It has the characteristics of high reliability, easy programming, flexible configuration, and fast running speed.

Material

Programmable logic controller is a kind of digital operation electronic system specially designed for application in industrial environment. It uses a programmable memory that stores instructions for performing logical operations, sequence control, timing, counting, and arithmetic operations within it. It controls various types of mechanical equipment or production through digital or analog input and output. process.

Programmable Logic Controller, PLC, a digital operation controller with a microprocessor for automatic control. It can load control instructions into memory for storage and execution at any time. Programmable controller is composed of CPU, instruction and data memory, input / output interface, power supply, digital analog conversion and other functional units.

Features

(1) High reliability. Because most PLCs use a single-chip microcomputer, they have a high degree of integration, coupled with corresponding protection circuits and self-diagnostic functions, which improve the reliability of the system.

(2) Easy programming. Most of the PLC programming uses relays to control ladder diagrams and command statements. The number is much smaller than that of microcomputer instructions. Except for medium and high-end PLCs, there are only about 16 small PLCs in general. Because the ladder diagram is simple and simple, it is easy to grasp and easy to use, and it can be programmed without even requiring computer expertise.

(3) Flexible configuration. Because PLC adopts the building block structure, users only need to simply combine to flexibly change the function and scale of the control system, so it can be applied to any control system.

(4) The input / output function modules are complete. One of the biggest advantages of PLC is that for different field signals (such as DC or AC, switching, digital or analog, voltage or current, etc.), there are corresponding templates to connect with industrial field devices (such as buttons, switches , Sensor current transmitter, motor starter or control valve, etc.) directly connected, and connected to the CPU motherboard through the bus.

(5) Easy installation. Compared with computer systems, the installation of a PLC requires neither a dedicated machine room nor strict shielding measures. When using, you only need to properly connect the detection device with the I / O interface terminals of the actuator and the PLC, and then it can work normally.

(6) Fast running speed. Because PLC control is performed by program control, relay logic control is incomparable regardless of its reliability or operating speed.

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Application

Open loop control
Open-loop control of switching value is the most basic control function of PLC. The PLC’s instruction system has powerful logic operation capabilities, and it is easy to implement various logic control methods such as timing, counting, sequence (stepping). Most PLCs are used to replace traditional relay contactor control systems.

Analog closed loop
For the analog closed-loop control system, in addition to the digital input and output, there must be analog input and output points in order to sample the input and adjust the output to achieve continuous adjustment of temperature, flow, pressure, displacement, speed and other parameters And control. Current PLCs not only have this function for large and medium-sized machines, but also some small machines.

Digital control
When the control system has a rotary encoder and a pulse servo device (such as a stepping motor), it can use PLC to realize the function of receiving and outputting high-speed pulses to achieve digital control. The more advanced PLC has also developed a digital control module to achieve the curve. The interpolation function has recently introduced a new type of motion unit module, which can also provide a programming language for digital control technology, making PLC’s digital control easier.

Data acquisition monitoring
Since PLC is mainly used for field control, collecting field data is a very necessary function. On this basis, connect the PLC to a host computer or touch screen. You can observe the current values ​​of these data and perform statistical analysis in time. Some The PLC has a data recording unit, which can be inserted into the unit with a memory card of a general personal computer to save the collected data. Another feature of PLC is that there are many self-test signals. With this feature, the PLC control system can implement white diagnostic monitoring, reduce system failures, and improve system reliability.

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