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?
Title and its 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 "sealed contact." It is the absence of air or the replacement of it 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 briefly explained by a different name for the part: “magnetically controlled electrical connection”. Inside the small glass cone, two elastic metal plates are fixed, one of which is equipped with a ferromagnetic plate. Sealing is achieved by tightly fitting the amorphous material of the case at the time of manufacture, in other words, the conclusions are simply fused from two sides.
Device device
So, a mechanical system consisting of two springy plates, magnetic material and contact groups deposited or soldered onto them is inserted into the glass tube. In the normal state, the right and left components can be in galvanic contact, providing the possibility of electric current (these reed switches are called normally closed), or, on the contrary, can be open (the reed switch is closed). 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. With the passage of current, the contacts are heated and the oxidation process, i.e., compounds with oxygen, is accelerated. If the metal is surrounded by an inert medium, then such a reaction will not occur. Now the tube can be sealed, and the device is ready.
The operation of the device, its advantages and disadvantages
To change the state of the contacts (opening or closing) it is necessary to 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 move, leaning or bending from the second. As a result, the necessary direction will be switched. 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 is it? Such a glorious invention suffers from the so-called "bounce" (due to the elastic properties of the metal), susceptibility to spurious magnetic fields, which are enough for any production, mechanical inertness and excessive fragility.
Application
And yet, despite constructive fundamental flaws, which are almost impossible to completely eliminate, the characteristics of reed switches allow them to be used in many areas of human activity, in which shortcomings are not so important, and virtues prevail. For example, in a conventional computer keyboard, in which the so-called "bounce" can be fought by including damping filters in the circuit, and then not worry about the cleanliness of the contacts. These devices are irreplaceable 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 open, the magnet attached to the jamb moves away, the magnetic field decreases, the circuit opens, which serves as a signal for the electronic notification circuit. To determine the position of the elevator car, reed switches are also most often used. Diving equipment is also easy to control with magnets, without fear of salt water flowing into electric lights through openings in the switchgear. In the circuits of electric meters, both single-phase and three-phase, reed switches are also present.
Gerkotrons
When studying high-voltage circuits, students and specialists sometimes come across the term “reed switch”, and it’s clear from the context that this is the same reed switch in principle. 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 contact area, are what distinguishes the reed switch from the reed switch. In everything else, and most importantly, in the basic structure, these devices are identical.