Proximity switch
What is a proximity switch? It is a position switch that can be operated without direct mechanical contact with moving parts. When an object is close to the sensing surface of the switch to the action distance, it can make the switch act without mechanical contact and applying any pressure, so as to drive DC electrical appliances or provide control instructions to computer (plc) devices. Proximity switch is a kind of switch type sensor (i.e. contactless switch), which has the characteristics of travel switch and microswitch, as well as sensing performance, reliable action, stable performance, fast frequency response, long service life, strong anti-interference ability, waterproof, shockproof, corrosion resistant and other characteristics. The products are inductive, capacitive, Hall, AC and DC. Proximity switch, also called contactless proximity switch, is an ideal electronic switch sensor. When the metal detection body is close to the sensing area of the switch, the switch can quickly send out electrical commands without contact, pressure and spark, and accurately reflect the position and travel of the moving mechanism. Even if it is used for general travel control, its positioning accuracy, operating frequency, service life, ease of installation and adjustment, and adaptability to harsh environments, It is incomparable with general mechanical travel switch. It is widely used in machine tools, metallurgy, chemical industry, textile and printing industries. In the automatic control system, it can be used as a limiting, counting, positioning control and automatic protection link. Proximity switch wiring diagram 1) Proximity switch has two wire system and three wire system. Three wire system proximity switch is divided into NPN type and PNP type, and their wiring is different. 2) The wiring of the two-wire proximity switch is relatively simple. The proximity switch is connected in series with the load and then connected to the power supply. 3) Wiring of three wire proximity switch: red (brown) wire is connected to the positive end of power supply; The blue wire is connected to the 0V end of the power supply; The yellow (black) line is a signal and should be connected to the load. The other end of the load is connected as follows: for the NPN type proximity switch, it should be connected to the positive end of the power supply; For PNP type proximity switch, it shall be connected to the 0V end of the power supply. 4) The load of proximity switch can be signal lamp, relay coil or digital input module of PLC. 5) Special attention shall be paid to the type selection of three wire proximity switch connected to PLC digital input module. PLC digital input modules can generally be divided into two categories: the public input terminal of the first category is the negative pole of the power supply, and the current flows from the input module. At this time, PNP proximity switch must be selected; The common input terminal of the other type is the positive pole of the power supply, and the current flows into the input module. At this time, the NPN proximity switch must be selected. Don't make a mistake. 6) The two-wire proximity switch is limited by the working conditions. When it is turned on, the switch itself produces a certain voltage drop, and when it is turned off, there is a certain residual current flowing through, which should be considered when selecting. Although the three wire proximity switch has one more wire, it is not troubled by such adverse factors as residual current, and its operation is more reliable. 7) Some manufacturers lead out the "normally open" and "normally closed" signals of the proximity switch at the same time, or add other functions. In this case, please connect the wires according to the product specification. Main applications of proximity switches: They are widely used in aviation, aerospace technology and industrial production. In daily life, such as the automatic doors of hotels, restaurants, garages, and automatic hot air fans, they are all used. In terms of security and anti-theft, such as data files, accounting, finance, museums, vaults and other important places, anti-theft devices consisting of various proximity switches are usually installed. In measurement technology, such as length and position measurement; In control technology, such as the measurement and control of displacement, speed and acceleration, a large number of proximity switches are also used.