Please ask the magnetic induction switch has a three-wire PNP tube type, there are two-wire spring tube type, what is the difference between the two choices?

Magnetic switch means that through the magnet to sense, this "magnetic" is the magnet, the magnet also has several kinds of magnets, the market above the commonly used magnets are rubber magnets, permanent ferrite, sintered neodymium-iron-boron and so on. Switch is the reed switch. Reed switch is the dry reed switch is short for, is a contact passive electronic switching elements, with a simple structure, small size and easy to control, etc., its shell is generally a sealed glass tube, the tube is equipped with two ferrous elastic reeds electric plate, but also filled with a kind of inert gas called metal rhodium. Normally, the glass tube in the two reeds made of special materials are separated. When a magnetic material close to the glass tube, under the action of the magnetic field lines of force, the two reeds in the tube are magnetized and attracted to contact each other, the reeds will be suction together, so that the junction connected to the circuit connected. When the external magnetic force disappears, the two reeds separate due to their own elasticity and the circuit is disconnected. Therefore, as a use of magnetic field signals to control the line switching device, reed switch can be used as a sensor, for counting, limit and so on (in the security system is mainly used for door magnets, window magnets, the production), but also widely used in a variety of communication equipment. In practice, usually with a permanent magnet to control the two metal pieces of the connection or not, so it is also known as "magnetron". Reed switch, also known as magnetron, it is almost the same as Hall components, but the principle of nature is different, is the use of magnetic signals to control a switching element, non-magnetic disconnect, can be used to detect the state of the circuit or mechanical movement, another magnetic switch is what the market said the proximity of the switch, the door magnetic switch, also known as the inductive switch, which is a dry one to open a good mold and the standard size of the plastic case, the reed switch is encapsulated in the black Inside the shell wire lead out the other half of the plastic shell with a magnet is fixed at the other end when the magnet is close to the switch with a wire, send out a switch signal! General signal distance of 10mm connection, this product is widely quoted to the security doors, home doors, printers, fax machines, telephones, and other electronic equipment above. There is a magnetic switch is in a closed metal or plastic tube, set up a point or more points of the reed switch, and then the tube through one or more, hollow and internally fitted with a ring-type magnet float, and the use of fixed ring, control the float and reed switch in the relevant position, so that the float in a certain range up and down. The magnet inside the float is used to attract the contact point of the reed switch to produce the opening and closing action. Features PP, PVDF material can be applied to strong acid and alkali places; SUS 304/316 metal material is suitable for high temperature and high pressure barrel tank. The most complete specifications of the junction box, plastic, aluminum alloy, stainless steel explosion-proof type, protection level IP-65 or more. The contact capacity is 50W/250VAC SPST or 30W/200VDC SPDT. The connection flange has JIS, DIN, ANSI specifications; the tooth mouth has NPT, PF, BSP and other specifications. With ABS, GL, CR international ship registration certification and Ex explosion-proof certification. Multi-point control, easy installation and cost saving.