Reed, what it is, how they work, and arranged

Today I want to tell you about such a switching device as a reed, about their history and applications in today's realities.

History of creation

Without contact is impossible to imagine any electronics or power and to increase performance contact characteristics were created magnetically sealed contacts, which subsequently became cited as reed switches.

The very first such product collected Soviet scientists V. Kovalenkov in 1922

And he worked very first reed switch as follows:

By core "3" through specialized dielectric spacers were fixed contacts "1" and "2". Moreover, all these elements have been implemented from magnetically permeable material.

Once the coil "4" starts to pass the current in the core of the magnetizing magnetic field formed fixed contacts, causing mutual attraction and subsequent closure. At the time when the movement of electrical charge on the coil ceased, the contact opens.

This reed switch, but still without watertight case. In a sealed envelope placed this design already learned W. B. Ellwood in 1936

The greatest development of reed switches obtained in the 70s and used almost everywhere. But as they say, progress is not in place, and these products have given way to the Hall sensor. However, reed switches, and is now quite actively used in many circuits, and all because they are cheap to produce and very reliable.

types of reed switches

Reed switches, in principle, as well as the most simple contacts, divided as follows:

functional differences:

1. Closing. In the present structure 1 normally open contact.

2. Switching. In the present structure 1 make contact.

3. NC. The design of the present normally closed contact.

Constructive - technological differences:

1. Reed dry contact. This simple contact with their shortcomings. In particular, when triggered, there is often contact bounce. Called contact bounce bounce after closing and opening that the unit of switching products is multiple switching of the transmitting signal.

This is an extremely undesirable effect, which are fighting in every possible way.

2. Mercury reed. Structurally these reed switches are characterized in that inside the sealed bulb is present a small drop of mercury. And it is intended to wet the contacts when triggered, thereby removing jitter and reducing the contact resistance at the contact location.

construction of reed switches

There are four types of reed switches

Absolutely all reed switches represent a hermetically sealed glass flask inside thereof is located a pair of contacts. Moreover, they are implemented permalloy rod of diameter 0.5 to 1.3 mm

The internal parts of the contacts are designed for opening and closing the circuit and to increase the reliability can be coated with various deposition of precious metals.

Outer ends of the contacts (beyond the glass bulb) need to connect the product to the chain.

The inner space of the glass bulb filled with an inert gas, or simply evacuated. This action also increases the life of the product by increasing the corrosion resistance of the contacts.

On what basis are working reed

To make the work on the reed switch circuit, it is necessary to form around the reed switch magnetic field strength required. it does not matter in principle, which will be the source of the magnetic field: permanent magnet or an electromagnet.

In this case the lines of force of the external magnetic field and magnetize the internal contacts as a result of this exposure, contacts are attracted to each other, overcoming the elastic force close an electrical chain.

In the closed state of the reed switch contacts will remain as long as the effect will not be lost of the magnetic field.

As soon as the external action to cease contact immediately opened.

It turns out that the contacts in the apparatus operate just three functions: springs, magnetic and conductive contacts.

A little different work reed, functioning on the opening. The magnetic system is arranged so that when exposed to an external magnetic field is performed simultaneous magnetization of the contact group, and they start to repel each other and thus break the chain.

In this open position, the contacts will remain until it comes off the impact of the external field.

In the case of switching the reed switch in the flask was still present one contact (NC) which implemented by a non-magnetic material, and the other two normally open contacts of magnetically material.

It turns out that when exposed to a magnetic field on a normally open reed switch contacts closed and nonmagnetic normally closed, is opened, so it remains in a fixed position.

About reed switches control methods and their application in modern electronics, we will talk in the next section. Therefore, in order not to miss the new releases, do not forget to subscribe and Like this article! Thank you for your valuable time!