Magnetic switch sensors are a type of circuit switch that uses magnetic field signals to control the switch, also known as magnetically controlled switch. It is a switch device induced by a magnet and commonly used magnets include sintered neodymium iron boron, rubber magnets, and permanent magnet ferrites. Its air cylinder reed switch is a reed switch, a passive electronic switch element with contacts, usually encapsulated in a sealed glass tube filled with inert gas and equipped with two ferromagnetic elastic spring plate electrodes. Similar to an electromagnet, a magnetic switch is activated when the coil is powered, creating a magnetic field that attracts the reed to make contact and close the switch. When the power is turned off, the magnetic field disappears and the switch opens. It is mainly induced by a magnet and is convenient and belongs to the sensor category.
The working principle of magnetic switch sensors
The dry reed pipe in the magnetic switch, also called a magnetic control tube, is a switch element that controls the magnetic field signal. The reed switch sensor working principle is that when there is no magnet, the circuit is open and can be used to detect mechanical motion or circuit status. When magnetic switch sensors are not in operation, the two spring plates in the glass tube do not come into contact. If a magnetic substance is brought close to the glass tube, the two spring plates will be magnetized and attracted to each other under the action of the magnetic field, thus making the circuit conductive. When the magnetic substance disappears, the two spring plates will separate due to their own elasticity and the circuit will open again.
There is a type of magnetic switch with multi-point or one-point magnetic reed switches set in a sealed plastic or metal tube. The entire container is hollow and there is a floating ball with a ring-shaped magnet inside. The magnetic reed switch and floating ball are controlled and fixed in a relevant position by a circular ring. The opening and closing actions of the switch are generated by the magnetic reed switch contact attracted by the magnet inside the floating ball. Another type of magnetic switch is commonly known as a proximity switch, also called a door magnet switch or an induction switch. It has a standard size plastic shell that seals the reed switch in a black enclosure. The wires are led out from it, and another half of the plastic shell with a magnet is fixed at the other end. When a magnetic substance approaches the switch at a distance of about 10mm, the switch will send a signal.
Wiring method of magnetic switch sensors
There is a difference between a two-wire proximity switch and a three-wire proximity switch. The three-wire proximity switch is further divided into NPN type and PNP type, and their wiring is different.
The wiring of a two-wire proximity switch is relatively simple. The proximity switch is connected in series with the load and connected to the power supply.
The wiring of a three-wire proximity switch: the red (brown) wire is connected to the positive pole of the power supply; the blue wire is connected to the 0V end of the power supply; the yellow (black) wire is the 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 pole of the power supply; for the PNP-type proximity switch, it should be connected to the 0V end of the power supply.
The load of the proximity switch can be a signal light, a relay coil, or a digital input module of a programmable controller PLC.
It is necessary to pay special attention to the type selection of the three-wire proximity switch when connecting it to the digital input module of the PLC. The PLC digital input module can generally be divided into two types: one type has a common input terminal for the power supply 0V, and the current flows out from the input module (Japanese model). At this time, an NPN type proximity switch must be used; the other type has a common input terminal for the positive pole of the power supply, and the current flows into the input module, that is, the well-type input (European model). At this time, a PNP type proximity switch must be used. Never select the wrong type.
Although the two-wire proximity switch of the magnetic cylinder position sensor has limitations on the working conditions, as it generates a certain voltage drop when it is turned on and a certain residual current flows through it when it is cut off, it should be considered when selecting it. The three-wire proximity switch has an additional wire, but is not affected by unfavorable factors such as residual current and is more reliable in operation.
Some manufacturers simultaneously lead out the "normally open" and "normally closed" signals of magnetic switch sensors, or add other functions. In this case, please refer to the specific wiring in the product manual.
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