In a wide variety of electrical and electronic circuits, a radio component with the beautiful name "reed switch" is used. What is it and how does it work?
Name and meaning
The name really sounds poetic, it is worthy of a beautiful flower. But the origin of the word is very prosaic, it stands for "hermetic contact." It is the absence of air or its replacement with an inert gas that determines the advantages of the device compared to conventional contact groups. The principle of its operation is extremely simple, and is explained briefly by the other name of the part: “magnetized electrical connection”. Inside a small glass cone, two elastic metal plates are fixed, one of which is equipped with a ferromagnetic lining. Sealing is achieved by a tight fit of the amorphous body material at the time of manufacture, in other words, the leads are simply fused on both sides.
Device device
So, a mechanical system is inserted into the glass tube, consisting of two springy plates, magnetic material and contact groups deposited or soldered on them. In the normal state, the right and left components can be in galvanic contact, providingthe possibility of passing an electric current (such reed switches are called normally closed), or, on the contrary, they can be open (closing reed switch). Then a vacuum is created inside the tube or an inert (chemically passive) gas is pumped into it. This is done to increase the life of the part. When the current passes, the contacts heat up and the oxidation process, that is, the connection with oxygen, accelerates. If the metal is surrounded by an inert medium, then such a reaction will not occur. Now the tube can be soldered, and the device is ready.
The operation of the device, its advantages and disadvantages
To change the state of the contacts (opening or closing), act on the reed switch. What it is, what exactly the effect is expressed in, is clear from the second name of the device and from its device. You need to bring a magnet to the cone, and one of the plates will begin to move, bending or bending away from the second. As a result, switching of the desired direction will occur. The simplicity and reliability of the part, low cost (there is no need to use silver or gold for contact groups) - these are its main advantages. But there are also disadvantages that the reed switch has. What's this? Such a glorious invention suffers from the so-called "bounce" (due to the elastic properties of the metal), susceptibility to parasitic magnetic fields, which are enough in any production, mechanical inertia and excessive fragility.
Application
And yet, despite the constructive fundamental flaws, completely eliminate whichalmost impossible, the characteristics of reed switches make it possible to use them in many areas of human activity, in which the disadvantages are not so important, and the advantages prevail. For example, in a conventional computer keyboard, in which the so-called "bounce" can be de alt with by including damping filters in the circuit, and then not worrying about the cleanliness of the contacts. These devices are also indispensable in alarm systems. There is nothing easier than installing a sensor, which is based on a reed switch included in the circuit. The doors are closed - the contact is closed, and when they are opened, the magnet attached to the jamb moves away, the magnetic field strength decreases, the circuit opens, which serves as a signal for the activation of the electronic warning circuit. To determine the position of the elevator car, reed switches are also most often used. Divers' lighting equipment is also easy to control using magnets, without fear of s alty sea water flowing into electric lights through openings in the switching fixtures. In the circuits of electric meters, both single-phase and three-phase, reed switches are also present.
Hercotrons
When studying high-voltage circuits, students and specialists sometimes come across the term "reed switch", while it is clear from the context that, in terms of its fundamental design, this is the same reed switch. What is it and what is the difference? In the characteristics, namely in the voltage (up to 100 kV) and the current that can go through the contacts. The ability of the insulation to withstand the possibility of breakdown and the cross section of the conductor, as well as the areacontact - that's what distinguishes the reed switch from the reed switch. In all other respects, and most importantly, in principle, these devices are identical.
