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PLC is a specialized in industrial environments for applications designed to operate electronic digital computing device. It uses the memory can be programmed to store in its internal implementation logic operations, the order of operations, timing, counting and arithmetic operations, such as operating instructions, and can be digital or analog input and output, control of various types of machinery or the production process. PLC and its associated peripheral equipment should be in accordance with the industrial control system is easy to form a whole, easy to extend the principle of its design features. PLC features: 1,high reliability, strong anti-interference ability: high-reliability electrical control equipment is the key to performance. PLC as a result of the use of modern large-scale integrated circuit technology, strict production process, the internal circuit to take an advanced anti-jamming technology, with high reliability. For example, the production of the Mitsubishi F series PLC MTBF of up to 300,000 hours. Some use of the PLC's CPU redundancy MTBF longer working hours. From the PLC circuit of the machine, the use of PLC control system constitutes, and the same size of the relay contact system, electrical wiring and the switch contact has been reduced to a few hundreds or even thousandths, fault will be greatly reduced. In addition, PLC hardware failure with self-detection, failure alarm information in time. In the application software, the application also can be incorporated into the external device fault self-diagnosis procedure, the system in addition to the circuit outside the PLC and equipment has also been the protection Fault self-diagnosis. In this way, the entire system with extremely high reliability is not strange. 2 matching complete, fully functional, applicability: PLC to develop until today, has formed a large, medium and small series products of all sizes. Of all sizes can be used for industrial control occasions. In addition to the logical processing functions, the most modern PLC equipped with a sophisticated computing power data can be used in a variety of digital control. PLC in recent years a large number of functional units, so that penetration to the position of PLC control, temperature control, CNC and other industrial control. Coupled with enhanced communications capabilities PLC and human-machine interface technology, the use of PLC control system composed of a variety of very easily. 3 easy to learn and use by engineering and technical personnel welcome: PLC as a general-purpose industrial control computer, is the industrial control equipment for industrial and mining enterprises. It interfaces easily, easy programming language for engineering and technical staff. Ladder language graphic symbols and expressions, and very close to the relay circuit, only a small amount of PLC logic control command switch can easily achieve the functions of the relay circuit. Is not familiar with electronic circuits, computer principles and do not use assembly language to engage in industrial control computer and opened the door. 4 system, design, construction work in small, easy maintenance, easy to transform: PLC logic with storage in place of logical connection, greatly reducing the wiring and external control equipment to control system design and construction of the cycle is much shorter, has become at the same time safeguard easy. More importantly, the equipment have been changed so that the same procedure to change the production process possible. It is suitable for multi-variety, small batch production of occasions. 5 small size, light weight, low energy consumption: for example in ultra-small PLC, the newly produced species at the bottom of size less than 100mm, weight less than 150g, just a few watts power consumption. Due to small size easily into the internal machinery to achieve the ideal of mechanical and electrical control equipment integration. At present, PLC at home and abroad, has been widely used in iron and steel, petroleum, chemical, electric power, building materials, machinery manufacturing, automobile, textile, transportation, environmental protection and cultural entertainment and other industries, the use can be broadly divided into the following categories: 1 The logic control switch: This is the most basic PLC, the most wide-ranging applications, which relay to replace the traditional circuits, the realization of the logic of control, order control, equipment can be used for a single control can also be used for multi-aircraft control and automated assembly line. Such as injection molding machines, printing presses, Protocol machinery, modular machine tools, grinding machines, packaging production line, assembly line, such as electroplating. 2 analog control: in the industrial production process, there are many changes in the amount of continuous, such as temperature, pressure, flow, level and speed are all analog. In order to deal with analog programmable controller, the need for analog (Analog) and Digital (Digital) between the A / D conversion and D / A conversion. PLC manufacturers are supporting the production of the A / D and D / A converter module, so that the programmable controller used to simulate the volume control. 3 Motion Control: PLC can be used in a circular motion or linear motion control. From the control configuration, the early switch directly to I / O modules to connect the location of sensors and the executing agency, is now generally use a dedicated motion control module. Such as stepper motor or servo-driven single-axis or multi-axis motor control module location. PLC world's major manufacturers of products that almost every motion control functions, a wide variety of machinery, machine tools, robots, elevators and so on. 4 Process Control: Process control refers to the temperature, pressure, flow volume of the closed-loop control simulation. For industrial control computer, PLC to the preparation of a wide range of process control algorithm to complete the closed-loop control. PID regulation of a general closed-loop control system with a lot of adjustment methods. PLC have a large and medium-sized PID modules, many small PLC module also has this feature. PID operation processing is PID-specific subroutines. Process control in metallurgy, chemical industry, heat treatment, boilers, control and so on have a very wide range of applications. 5 Data processing: the modern PLC has a mathematical (including matrix operations, function operations, logic operations), data transfer, data conversion, sorting, look-up table, bit operation functions, you can complete the data collection, analysis and processing. These data can be stored in the memory of the reference value of comparison, the complete control of certain operations, can also be used to send communication to other intelligent devices, or to print them tabulation. Generally used in large-scale data processing control systems, no control, such as flexible manufacturing systems; also can be used for process control systems, such as paper making, metallurgy, food industry in a number of large-scale control system. 6, communications and networking: PLC communication with the communication between PLC and the PLC and other communications between intelligent devices. With the development of computer control, factory automation networks have developed rapidly, the PLC manufacturers have attached great importance to PLC communication functions, have launched their own network systems. PLC recently have produced communication interface, communication is very convenient.
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