Reed relay: principle of operation of the switch, description, scope of application of the disconnecting switch

In electronic units and radio engineering, switching devices and contacts are actively used. But such parts are considered unreliable, as frequent use of the equipment wears them out. Because of this, specialists often use a reed switch, which is presented in the form of a magnetically controlled hermetic contact. For longer operation, high-quality switches are installed on them.

Short description

In the modern world, reed switches are practically not used, since more universal Hall sensors have entered the mass market. But still, there are situations when you simply cannot do without such a relay. And the thing is that the device is easy to control, and it can be installed in the circuit of any equipment. When the master needs to achieve a high degree of reliability and durability from the unit, then one simply cannot do without a reed switch.

Today, such a relay can be found in various sensors and similar devices. Functionality is customary to share into three main categories:

1. Switching.
2. Closure.
3. Opening.

Dry and mercury contact can be distinguished among the main technical features. In the latter case, metal drops are contained in the glass case, which are especially important during the operation of the relay, since the quality of the contact is improved.

In addition, mercury helps to avoid unwanted vibration, thereby increasing the response time of the installation. That is why experts always recommend using this type of contact.

Device characteristics

The high quality reed switch consists of two contacts made of a specific ferromagnetic alloy. They are installed in a sturdy flask, so that the user can always control their work. If a permanent magnet enters the contacts, then a closure occurs with the formation of a continuous circuit. Because of this specificity, the reed switch began to be called the limit switch.

Industrial manufacturers label such units in strict accordance with the final scope of application. For example: if the abbreviation KEM is applied to the relay, then it belongs to the category of electrical switching mechanisms. The large letter "A" means that the device can be used in all weather conditions, but the parts marked "B" are intended exclusively for indoor use. The abbreviation MCA can often be seen, which means that this magnetic switch is ideal for all conditions of use.

For a standard changeover unit, the resistance level is within 0.2 ohm. A high-quality reed switch for opening differs in that this indicator is 1 kOhm. This data allows technicians to significantly speed up switching between existing circuits. All magnetic switches of this type are used for power voltage networks, since they have higher performance. The magnetic disconnecting reed switch is actively used in various circuits, in the computer and security industry, as well as in contact sensors.

Varieties of models

High-quality reed relays are usually divided into several categories, which differ from each other in the device of the contact group. Each variety has numerous positive characteristics that are highly valued by both professionals and home craftsmen. There are several types of reed switches on sale:

• With changeover type of contacts.
• Traditional open-loop installations.
• Specific elements with closed contacts.

In addition to the main functional features, specialists also distinguish technological parameters that divide the switching sealed units into dry and mercury.

Design differences

The multifunctional reed switch is presented in the form of a sealed glass cylinder, inside which there are sensitive contacts. These elements are magnetic cores welded from the end sides of the product. All external parts are connected to the existing power supply.

The most popular today are reed relays for closing. Contacts are made of high quality rectangular ferromagnetic wire. The cores are made of permalloy, a material where power and reed switch size play a major role. If necessary, the coating can be replaced with silver, gold, rhodium.

The finished flask is evacuated or an inert gas is introduced into it, which prevents the development of corrosion in the switch. In the manufacturing process, specialists also take into account the fact that there is a gap of a certain diameter between the cores.

Principle of operation

The changeover reed switch with closing contacts is equipped with two cores, which are distinguished by increased magnetic permeability. These two elements are located in a sealed glass bottle filled with an inert gas or a gas mixture. In the flask itself, there is a pressure of 50 kPa. The special inert environment does not allow the contacts to oxidize.

The reed switch cylinder is placed in the inner compartment of the control winding, which is connected to a DC power source. At the moment the power is turned on, the required magnetic field is formed on the responsible relay, which passes through the cores of the contacts, and then along the gap and closes on the control coil. The working energy flow creates a pulling force that connects the contacts together.

Additional plating of contacts with silver, gold, palladium or radium helps to reduce contact resistance. After turning on the power in the coil of the electromagnet, the force disappears, and the springs themselves work according to the principle of opening. It is worth noting that in the reed relay there are completely no surfaces where the parts would be subject to friction with each other. The contacts themselves are distinguished by a variety of functions, since they can do all the work of a conductor, magnetic circuit and springs.

Increasing the current density helps to reduce the size of the magnet coil several times. Enamel wire is actively used for winding. All reed switch assemblies go through stamping, and connections are made by welding or soldering. These units actively use magnetic shields, which help to reduce the zones of the on state.

The well-coordinated operation of the relay is due to the fact that all springs are installed without additional tension, due to which the device is ready for operation immediately after starting. Instead of the usual electromagnets, permanent magnets can be used, which is why reed switches are called polarized. To press the relay contacts, a certain force is required, which is due to the presence of a magnetic coil. This effect cannot be found in conventional electromagnetic units, where the entire force depends on the spring.

The principle of operation of a reed relay for opening differs in that the relay system, under the influence of an electromagnet, magnetizes the cores, which are gradually repelled among themselves and open the circuit. Those models that belong to the closed type are equipped with three contacts, one of them is covered with metal, and the rest are ferromagnetic.

Advantages and disadvantages

Each unit has both positive and negative characteristics. If the user knows all the strengths and weaknesses of the purchased product, he can choose the most suitable application for him. That is why before buying a reed switch you need to study its benefits:

1. High degree of switching reliability. This parameter is almost twice as high as those typical for open contact groups. This effect is achieved due to the high resistance between open contacts (can amount to tens of Mohm).
2. Ease of use. This parameter is due to the fact that all contacts are isolated from the external environment, so that the user does not need to worry about their cleanliness. In addition, there is no mechanical attachment to the permanent magnet.
3. Long service life. The number of relay operations is in the billions, no contact group can match this figure.
4. High-speed performance. Many models have a switching frequency close to 1 kHz.
5. The equipment can be controlled without the help of electricity.
6. This type of switch is completely undemanding to the choice of load.

When all the positive aspects have been studied, you can familiarize yourself with the disadvantages. If the master has the necessary work experience, then he will be able to eliminate minor flaws. Among the main disadvantages of a reed switch can be distinguished the following characteristics:

• Relatively small number of contacts.
• Large dimensions that do not fit well with a modern radio base.
• Quite low rates of switching power.
• Vibration when triggered (this parameter does not apply to those models where mercury drops are filled into the capsule).
• Hypersensitivity to external magnetic fields.
• The glass bulb can be easily damaged by improper handling.

Despite the significant predominance of positive characteristics, the reed relay is gradually being replaced by other analogs of the semiconductor type (for example, a Hall sensor). The higher structural strength, the complete absence of rattle, and also the small size played a decisive role.

Applications

High quality and multifunctional reed switches are considered to be in demand in security systems where they are used as relays. Such devices are also mounted in special sensors. Do not forget about other areas of application:

• Powerful snorkeling equipment.
• Synthesizers and keyboards.
• Specialized equipment for automation and safety.
• Narrow-profile equipment in medical institutions.
• Switching devices.
• Measuring and testing devices.

Reed switch control rules

Due to the fact that such equipment is used not only in everyday life, but also in many other industries, each user should know how to handle it. Only in this case, you can count on the high-quality operation of the relay. Moreover, you can control a sealed switch in two main ways:

1. Using a permanent type magnet.
2. By acting on a coil that is connected to a constant current source.

In the first version, the user can use the angular or linear movement of the permanent magnet. In addition, there is often a way when a special curtain covers the working area. This option can be found in universal level and position sensors, as well as in burglar alarms.

The second method allows specialists to build a powerful relay based on a reed switch. Unlike well-known traditional designs, such a unit will be more reliable, high-quality and durable, since there will be no moving elements in its circuit. But as for a small number of contact groups, this small disadvantage can be easily eliminated by using several reed switches at once.

An example of the application of this control method is a current relay. This unit is presented in the form of a powerful coil, which is wrapped with a strong wire of large cross-section. A sealed switch is always located in the inner compartment.

The versatility of this device can be used as a reliable overload protection system in DC circuits. In addition, the master can adjust the sensitivity of the device by linearly moving the switch inside the coil.