Wear anti-static clothing and anti-static shoes when fixing the wiring of the transmission control system.
In all areas of industrial production, both process control systems and transmission control systems contain a large number of switching and analog quantities. Switching quantity is also called digital quantity, such as starting and stopping of motor, turning on and off of electric light, opening and closing of valve, setting and resetting of electronic circuit, timing, counting, etc.; analog quantity is also called continuous quantity, such as changing temperature and pressure , speed, flow, liquid level, etc.
From the perspective of electrical appliances and control methods used in production machinery, some manual electrical appliances were used to control the execution of electrical appliances. This type of manual control is suitable for some occasions with small capacity and single operation. Subsequently, it developed into a relay-controlled anti-static shoe with an automatic control appliance, and an anti-static clothing system. This kind of control system is mainly composed of some relays, contactors, buttons, travel switches, etc. It is characterized by simple structure, low price, convenient maintenance and strong anti-interference, so it is widely used in various types of mechanical equipment. The relay-contactor control system not only facilitates the automation of the production process, but also enables centralized control and remote control. At present, relay-contactor control is still one of the most basic forms of electrical control. However, since the control form is a fixed wiring, the versatility and flexibility are poor, and the switching operation is performed by using a contact, the operating frequency is low, the contact is easily damaged, and the reliability is poor.
With the development of productivity and the advancement of science and technology, people are constantly putting forward new requirements for the control equipment used. In actual production, due to the existence of a large number of program control processes controlled by switching quantity, and the production process and process often change, the application of anti-static shoes and anti-static clothing to the aforementioned relay-contactor control circuit cannot satisfy this kind. need. Then, a sequence controller composed of an integrated circuit emerges as the times require. It has the advantages of easy program change, large program storage, and high versatility.
In the 1960s, the plate sequential controller SC (SeqtJence (; ontr011er) appeared. The so-called sequential control is based on a predetermined time or condition, and sequentially controls each stage of the control process according to a predetermined sequence of actions. Carry out
Switching-based automatic control. There are three main types of sequential controllers that have been popular: basic logic, conditional stepping, and time stepping. Its characteristics are: versatility and flexibility, it can be easily adapted to the frequently changed control requirements by changing the program, and it is easy to control large and complex systems, but the implementation and modification of the program does not change in essence, still Make settings and changes to the hardware.
In 1969, the programmable logic controller PLC (Progi'ammable Logic (; ontroller) appeared, which is a combination of computer technology and relay contact control technology, with logic control, timing, counting and other functions, and replaced Electric anti-static shoes, anti-static clothing one-piece control. PLC uses computer storage program and sequential execution principle; programming language uses intuitive ladder-like language similar to relay-contactor control circuit diagram, which makes the control site staff It can be easily learned and used. Control Cheng Heng's changes can be realized by directly changing the application software in the memory. Because the software changes are easy to implement, there is an essential leap in the way of implementation, its versatility and flexibility. The nature is further enhanced.
In the 1970s, a programmable controller with a microprocessor as its core appeared, also known as the Industrial Control Unit (ICU). It is based on the working principle and purpose of the logic and step-by-step sequence controller. It is specially applied to the microprocessor of industrial logic control and constitutes the programmable sequential controller with ICU as the core. It turns out the programming and execution of the program in the original sequential controller by computer software, and becomes a new type of industrial control device, which opens up a new way in the field of sequential control.
Around 1980, the programmable controller PC (:Progl'ammable(;ontroller) appeared, which was further developed on the basis of programmable logic controller PLC. It is composed of central microprocessor (CPU), large A dedicated micro-computer consisting of a large-scale integrated circuit, an electronic switch, and a power output device not only inherits the original functions of the PLC, but also has more powerful functions such as sequential control, arithmetic operation, data conversion and communication, and has a rich command system. The program structure is flexible, it can replace a large number of relays, and has low power consumption and small volume, and has been widely used in electrical automatic control. CPU technology is used to make the operation of the motor from intermittent control into continuous control.
In order to distinguish it from a personal computer (Personal Computer), people often still use the programmable controller (PC) as a PLC. Although the programmable controller is extremely powerful, it can realize both switching (digital) control and continuous quantity (analog) control, but it was originally designed to replace the relay one contactor in digital control. The design concept generated by the control system is derived from the relay-contactor, which has many similarities and similarities. Therefore, after familiar with the relay-contactor control technology, it is easy to accept the programming language of the programmable controller, laying the foundation for further learning of the programmable controller. On the other hand, relay contacts are still being used in many applications where control requirements are less complex. When the motor is dragged, the on/off of the main circuit is still completed by the contactor. In addition, machine tools, power equipment and industrial power distribution equipment are still dominated by relays and contactors.
Relay one contactor control and PLC control have their own characteristics, not because of PI. C's high performance completely replaces traditional devices such as relay-contactors. It is foreseeable that in the future, conventional devices such as PLC and relay one contactor will still be the main components of the electrical automatic control device.
At present, PLC is mainly developed in the direction of miniaturization, low cost, standardization, high speed, intelligence, large capacity, and network, and combined with computer technology to form industrial control system and distributed control system. (DistributedControlSystem) Fieldbus Control System (FCS), which will make PLC more powerful, more reliable, more convenient to use, and more applicable.