Exploring the application features of PLC

1, high reliability, strong anti-interference ability

High reliability is the key performance of electrical control equipment. PLC adopts modern large-scale integrated circuit

Integrated circuits use semiconductor manufacturing processes to fabricate many transistors and resistors, capacitors, and other components on a single monocrystalline silicon wafer, and combine the components into complete electronic devices according to the method of multilayer wiring or ramp wiring. Circuit. It is represented in the circuit by the letters "IC" (also with the text symbol "N", etc.).

The technology is manufactured using a strict manufacturing process. The internal circuit adopts advanced anti-jamming technology and has high reliability. Using a PLC to form a control system and relay contacts of the same size

The contactor is a widely used switching device. The contactor is mainly used to frequently turn on or off the AC and DC main circuit and the large-capacity control circuit. It can be operated from a long distance. It can realize timing operation, interlocking control, various quantitative control, and loss and undervoltage protection. Widely used in automatic control circuit, the main control object is the motor, can also be used to control other electrical loads, such as electric heaters, lighting, welding machine, capacitor bank and so on. [full text]

Compared to the system, the electrical wiring and switch contacts have been reduced to hundreds or even thousands of times, and the failure has been greatly reduced. In addition, the PLC has a hardware fault self-detection function, which can promptly issue an alarm message when a fault occurs. In the application software, the user can also program the fault self-diagnosis program of the peripheral device, so that the circuit and equipment other than the PLC can also obtain fault self-diagnosis protection. In this way, the reliability of the entire system is extremely high.

2, complete supporting, perfect function, strong applicability

PLC has developed into a series of products of various scales and can be used for industrial control applications of various scales. In addition to the logic processing functions, most PLCs have perfect data computing capabilities and can be used in various digital control fields. A large number of various functional units emerged, which allowed PLC to penetrate into various industrial controls such as position control, temperature control, and CNC. With the enhancement of PLC communication capabilities and the development of human-machine interface technology, it has become very easy to use PLC to form various control systems.

3, easy to learn and use, welcomed by engineering and technical personnel

PLC is an industrial control equipment for industrial and mining companies. Its interface is easy, and the programming language is easy for engineers and technicians to accept. Ladder language graphics symbols and expressions and relay circuit diagram is quite close to open the door for industrial control of people who are not familiar with electronic circuits, do not understand computer principles and assembly language.

4, the system design of the workload is small, easy maintenance, easy to transform

(1) Design and Maintenance

PLC replaces the wiring logic with storage logic, which greatly reduces the external wiring of the control equipment, greatly shortens the design and construction cycle of the control system, and also makes routine maintenance easier. More importantly, the same equipment is changed through changing programs. The production process becomes possible. It is especially suitable for production occasions with many varieties and small batches.

(2) Installation and wiring

Power line, control line, and PLC power cord

A power cord is used as a connecting wire for an electrical component or device and a power source. Generally, it refers to a group of plugs or tail plugs that are connected to one end of a power cord, and is one of the basic components of an electrical product. The power cord is divided into two parts: wire and plug.

The I/O lines should be wired separately. Twisted pair connection should be used between the isolation transformer and the PLC and I/O. Separate the PLC's I/O line from the high-power line. If it is necessary to separate the AC line and the DC line in the same slot, if the conditions permit, the sub-slot alignment is best. This not only makes it possible to make it as much as possible. Large space distance, and can minimize interference.

PLCs should be kept away from strong sources of interference such as welders, high-power silicon rectifiers, and large power equipment. They must not be installed in the same switchgear with high-voltage appliances. The PLC should be far away from the power line in the cabinet (the distance between the two should be greater than 200 mm). Inductive loads that are installed in the same cabinet as the PLC, such as relays with large power and coils of contactors, should be connected in parallel with the RC arc suppression circuit.

The input and output of the PLC are preferably routed separately, and the switch quantity and analog quantity are also laid separately. The transmission of analog signals should be shielded. The shield should be grounded at one or both ends. Grounding resistance

Resistance, the material's resistance to current is called the resistance of the material. A material with a small electrical resistance is called an electrical conductor, or a conductor for short. The material with a large electrical resistance is called an electrical insulator, or an insulator for short. Should be less than 1/10 of the shield resistance.

Do not use the same cable for AC output line and DC output line

A cable is a wire product used to transmit electrical energy information and achieve electromagnetic energy conversion. Existing conductors and insulation layers, sometimes with tight inner sheathing to prevent moisture intrusion, or outer sheaths with large mechanical strength, are complex structures, and products with large cross-sectional areas are called cables.

The output line should be as far away from the high voltage line and the power line as possible to avoid parallelism.

(3) I/O terminal wiring

Input wiring: input wiring is generally not too long. However, if the environmental interference is small and the voltage drop is not large, the input wiring can be longer; the input/output cable cannot use the same cable, and the input/output lines should be separated; as far as possible, the input/output cable should be connected to the input terminal. Make the ladder diagram and the relay schematic consistent, easy to read.

Output Connection: The output wiring is divided into independent output and common output. In different groups, output voltages of different types and voltage levels can be used, but the output in the same group can only use the same type, the same voltage level power supply. Since the output element of the PLC is packaged on a printed circuit board and connected to the terminals

The terminal usually refers to a connector contact that is stamped from a copper material or the like. Terminals are commonly used components for connecting electrical circuits. They mainly act as electrical connections and signal transmissions between devices and components, components and cabinets, systems and subsystems, and try to keep signal distortion and energy loss between the system and the system. Variety.

If the board is shorted to the load connected to the output element, the printed circuit board will be burned. When relay output is used, the size of the inductive load that is subjected to it will affect the service life of the relay. Therefore, when using inductive load, it should be reasonably selected, or add isolation relay. The output load of the PLC may cause interference, so measures must be taken to control it, such as the freewheeling protection of the DC output, the RC output absorption circuit of the AC output, and the transistor

The transistor is a device composed of three impurity semiconductors and has three electrodes. Therefore, it is also called a semiconductor transistor, a crystal transistor, and the like, and can be used for detection, rectification, amplification, switching, voltage stabilization, signal modulation, and many other functions.

Thyristor is the abbreviation of thyristor. It can also be called silicon controlled rectifier. It was previously called thyristor. In 1957, General Electric of the United States developed the world's first thyristor product and it will be developed in 1958. Its commercialization; thyristor is PNPN four-layer semiconductor structure, it has three poles: anode, cathode and gate; thyristor has the characteristics of silicon rectifier devices, can work under high voltage, high current conditions, and its working process can be controlled, It is widely used in electronic circuits such as controlled rectifiers, AC voltage regulators, contactless electronic switches, inverters, and inverters.