PLC overall composition and characteristics

This section of the PLC of the structure and characteristics of the hot issues of the solution, so that beginners PLC has an overall knowledge.
Q: what is a PLC (programmable logic controller)?
Answer: PLC can series program device (Programmable Logical Controller) is a digital operation operation of electronic system, designed for industrial environment Xia application and design of industrial computer; it used a can programming of memory, for its internal storage program, implementation logic operation, and order control, and timing, and count and arithmetic operation, oriented user of instruction; and through digital type or simulation type entered/output control various type of mechanical or production process. Is easy with industrial control systems as a whole, easy to expand the principle of functional design, universal automatic control device based on the microprocessor, PLC is now towards the rapid expansion of other industries.
Second, ask: what PLC made?
A: the PLC consists of hardware (the equivalent of the human body) and software (the equivalent of human thought). Its core is a single board computer (CPU boards), single board computer peripheral configuration of interface circuits (hardware) is configured in the single board computer monitoring program (software). SBC’s role is to control the work of the PLC, its work is divided into two parts: the first is to manage the system, such as diagnosis, error checking, such information, count, flush; the second is the detection field input, program the user program execution, output operations, and so on.
Third, ask: what is the unique advantages of PLC?
A: the PLC’s unique advantages:
1, high reliability, high reliability of PLC, average trouble-free run time than the IEC (International Electrotechnical Commission) provides 100,000 hours. Such as Japan’s Mitsubishi FX series PLC can be run continuously for more than 30 years of trouble.
2, easy to program, easy to use
Software: for general electric control lines, use the ladder diagram programming, intuitive and easy to understand;
Specific issues for more complex designs such as step ladder instruction, flow chart (SFC) instruction set.
Hardware: using PLC, both wiring and configuration are very convenient, only with a screwdriver to complete all wiring work.
Typically, is control by PLC system programming, simulation and debugging in laboratory after the site will soon be able to install successfully.
3, the environments requiring low PLC to temperature and humidity changes within the larger scope of work; its good anti-vibration, anti-impact properties; on the stability of power supply voltage low; anti-electromagnetic interference ability, suitable for harsh working environments.
4, interface with other devices, configure the connected PLC principle: for external wiring, level shift as little as possible.
PLC inputs are analog, digital output driving external circuits with relays, SCR (SSR), several different forms such as transistors, can be connected directly to a variety of different types of load. In the area of data communication, only used coaxial cables and ordinary PS232 or RS422 interface, users don’t need to worry about technical issues in data communications. (J) (Not to be continued)

Problems in PLC described in the application and use of
First, brief
For many years, PLC (hereinafter referred to as PLC) from its origin to the present, realized the connection to storage logical leap of logic; its function from weak to strong, realizing logic control to control progress; its applications from small to large, realize a single simple device control to qualified motion control, process control and distributed control of a variety of tasks, such as across. PLC today in dealing with analog and digital operation, all aspects of the human-machine interface and network capacity has increased significantly, becoming the mainstream of industrial control field control equipment, in all walks of life play an increasingly large role.
Second, PLC application
At present, the PLC has been widely used in iron and steel, petroleum, chemical industry, electric power, building materials, machinery manufacturing, automobile, textile, transportation, environmental protection and cultural and entertainment industries, usage can be divided into the following categories:
1. Switch logic control
Instead of the traditional relay circuits, logic control, order, control, and can be used for device control, can also be used for fleet control and automation lines. Injection molding machine, printing machine, book machine, combination machines, grinding machines, packaging line, plating lines and so on.
2. Industrial process control
In the industrial production process, there are things such as temperature, pressure, flow, liquid level and speed continuous variation (analog), the PLC using the corresponding a/d and d/a conversion module and various control algorithms to handle analog signals, complete closed loop

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