The principle of operation of the microwave transformer. Microwave oven magnetron device. Thermal fuse and why is it needed

Microwave oven (microwave oven), at present, is very popular, it is the most demanded kitchen appliance. Using a microwave oven, you can not only reheat or cook food, but also defrost food and even disinfect some metal-free kitchen utensils. This device has become quite common today.

A microwave oven is a household electrical appliance that is mainly intended for cooking or heating food in fast mode... Microwaves are also used in some industries where you need to heat up the necessary materials.

Unlike conventional ovens, heating different foods in this device happens quite quickly, since radio waves are able to penetrate deep into the food. This drastically reduces the heating of any product and contributes to the preservation of all the nutrients in it.

The device of all microwave ovens consists, as a rule, of the same components. The design of microwave ovens has main and auxiliary elements. Appearance these devices can be very diverse. Sizes, colors and functions may vary, for each individual stove, they may be different.

Microwave oven structure:

• Camera equipped with a rotating podium;
• The magnetron is the main element - the microwave emitter;
• Transformer;
• Metal case with a door that locks when the device is in operation;
• Control and communication scheme;
• Waveguide.

Also inside the microwave must be equipped with a fan. Its purpose is very large, since the device itself will not work without it. Such a device provides excellent magnetron performance and cools the electronic circuits.

How a microwave oven works: its varieties

The operation of a microwave oven is very simple, it is based on microwave radiation. The heart of every microwave is a magnetron. He is the source of radiation. The frequency of microwaves is approximately 2450 MHz, and the power of modern microwave ovens can be equal to 700 - 1000 W. This oven is powered by electricity.

To make the magnetron work well and not overheat, a fan is installed next to it. He is also engaged in the circulation of air inside the oven itself and contributes to uniform heating of food or products.

Microwaves enter the oven through a waveguide, and then the walls, which are made of metal, reflect the magnetic radiation itself. Radiation, penetrating deep into products, makes their molecules move very quickly. These actions contribute to friction, as a result of which heat is released (physics is present). This is warm and will keep the food warm.

Varieties of electrical appliances:

• With grill;
• Convection oven;
• Inverter controlled device;
• Appliance with microwaves that are evenly distributed;
• Mini microwave.

The main advantage of all microwaves is design. The market provides a huge selection of devices, you can choose both a stylish and ergonomic model. The description of these models will allow you to choose the model you like, which will become not just a decoration of the kitchen, but also its highlight. An example is Samsung's microwave oven.

Control unit: how the microwave works

Each microwave oven has such an important element as a control unit. It, in turn, performs two main functions: maintains the set power and turns off the device when set time expired. To date, technology has developed a new type of this element - electronic.

Today, the electronic unit can support not only its basic functions, but also some additional ones. Some of them are necessary, while others are not needed at all. Many modern models have a grill, it is also controlled by a control unit.

Today, the command block is equipped with different microprocessors, which, in turn, support the functionality of other programs. Therefore, the power supply unit can be responsible for the operation of additional functions.

Additional service functions:

• Built-in clock;
• Power indicator;
• Automatic defrosting;
• An audible signal that indicates the completed operation.

The electronic unit is closely related to the display panel and keyboard. The most important part of such a block is relay box... He is responsible for the operation of the fan, convector, built-in lamp and even a magnetron.

Microwave frequency: magnetron and its components

The principle of operation of the microwave oven is that the magnetron, when the microwave is turned on, begins to release energy, and then it is already converted into heat. This heat is used to heat the food. The magnetron translates as an electric vacuum diode, which consists of a copper anode. This is the most expensive detail ovens.

The heating of food inside the microwave occurs under the influence electromagnetic radiation, that is, microwave radio waves. Due to the fact that radio waves penetrate deeply into the heated product, it is heated very quickly and efficiently.

Deciphering a magnetron is a device that produces a huge amount of heat due to the radiation frequency. The radiation frequency is 2.4 GHz. The efficiency (efficiency) of the magnetron is 80%, and the power consumption of this type of furnace during radiation can be 1100 W.

The magnetron device consists of the following parts:

• The cylindrical anode is its base, consisting of 10 sectors, each of which is made of copper;
• In the center there is a cathode with a filament;
• The end parts are occupied by magnets, they create the magnetic field necessary for radiation;
• Lead out to an antenna that emits energy, a wire loop.

With the help of a radiating antenna, energy first enters the waveguide and then into the furnace chamber. The voltage supplied to the anode is 4 thousand watts, the filament is 3 thousand watts. The magnetron body is located in a plastic heatsink, where a built-in fan blows air over it, and a special fuse is responsible for overheating it.

The device and principle of operation of the microwave oven (video)

WITH of English language such a saying Microwave oven can be deciphered as a microwave oven. This design is a household appliance that runs on electricity and differs in that it defrosts or reheats food very quickly. This is due to microwave radiation.

Heating food in the microwave is carried out by radiation, the frequency of which is equal to 2450 MHz, generated by a magnetron. If, after turning on the oven, the plate is spinning, the light in the chamber is on, the fan is on, and the food remains cold or heats up indecently for a long time, then something is wrong with this lamp. If you know how to test a magnetron in the microwave, then you can do without going to the workshop. Moreover, some auxiliary part in the magnetron circuit may be faulty.

What the microwave is capable of. What is magnetron and magnetron microwave energy? A magnetron is a zelectro-vacuum lamp that performs the functions of a diode and consists of several parts:

1. A cylindrical copper anode, divided into 10 parts.
2. In the center there is a cathode with a built-in filament. Its task is to create a flow of electrons.
3. Ring magnets are placed at the ends, which are necessary to create a magnetic field, due to which microwave radiation is created.
4. Radiation is captured by a wire loop connected to the cathode and is removed from the magnetron using a radiating antenna, directed along a waveguide into the chamber.

During operation, the magnetron gets very hot, so its case is equipped with a plate radiator blown by a fan. To protect against overheating, a thermal fuse is included in the power circuit.

How the magnetron works, diagram.

A malfunction of the magnetron may occur for the following reasons:

• The protective cap is burnt out and therefore sparks during operation. Replaced with any integer, since they are the same for all magnetrons.
• Filament burnout.
• Depressurization of the magnetron due to overheating.
• Breakdown of a high-voltage diode.
• High voltage fuse blown.
• There is no contact in the thermal fuse.
• High voltage capacitor broken.

For all malfunctions, except for depressurization, do-it-yourself repair is possible.

Resistance measurement with an ohmmeter.

Fault definition

To find out why the oven does not work, you need to unplug it from the outlet and remove the lid.

1. The inside is carefully examined for melting, burning, and soldered wires. The state of the high-voltage fuse is visible to the naked eye. The fuse with a broken thread changes to a whole one, and if it blows out again when testing the furnace, the search continues.
2. For further diagnostics, you will need a multimeter or tester. Verification starts with printed circuit board, on which the magnetron power circuit is assembled, consisting of resistors, diodes, capacitors, varistors. Parts can be called locally, without soldering.
3. Then the thermal fuse is checked with a tester. With normal contacts, the resistance is zero.
4. Checking the high-voltage capacitor with a multimeter is possible only for breakdown. If the device shows a short circuit, the part is replaced. Since some types of capacitors have built-in resistors for discharging, a good capacity will show a resistance of 1 MΩ instead of infinity.
5. The tester is not suitable for testing a high-voltage diode, since it has a small resistance measurement range. To correctly assess the state of the diode, a megohmmeter with a scale of up to 200 megohms is required. But he is unlikely to be found in the home workshop. Therefore, a diagnostic method is used using a two-wire home electrical network with mandatory compliance with safety rules. One pin of the diode is connected to the mains wire. A multimeter is connected between the second and another conductor of the network to measure DC voltage in the range up to 250 V. If the diode is intact, the device will show the presence of a rectified voltage. In case of breakdown or breakage, the arrow will remain at zero. Any high-voltage diode with an operating voltage of 5 kV and a current of 0.7 A.
6. The magnetron test begins with a continuity of the filament. For this, the resistance between its terminals is measured, which for a working heat is several ohms. If the tester shows infinity, this does not mean that the thread is burnt out. For complete confidence, it is checked, after removing the cover, the integrity of the connections of the chokes with the terminals of the magnetron.
   Some craftsmen recommend removing the throttle. In no case should this be done, since the operating mode of the transformer is disrupted, which is why a fire is possible.
   After measuring the resistance between the terminals and the case, you can judge the state of the feed-through capacitors. At infinity, everything is normal, at zero, they are broken, and in the presence of resistance, with a current leak. Defective capacitors are bitten off with nippers and new ones with a capacity of at least 2000 pF are soldered in their place.
7. If all the elements are intact, but the magnetron radiation is not enough to fully heat the food, then the cathode has lost emission. This malfunction can only be eliminated by replacement. When replacing capacitors, you cannot use ordinary solder, refractory grades or a compact resistance welding machine are required.

In the video, a story for dummies on how to check a magnetron is very clear:

Replacing the magnetron

Since the repair of the magnetron is not carried out even in well-equipped workshops, you will have to purchase a new one. Before removing the magnetron from the microwave, it is necessary to mark the connector pins so as not to confuse them when installing a new part. If the leads are connected incorrectly, the magnetron will not work.

The replacement can be done independently, if at least once used a screwdriver for its intended purpose and a couple of diodes rang. This does not require special skills and knowledge of how the magnetron works. If it is impossible to find a specific magnetron for the microwave, you will have to use a suitable analogue.

Its power must be equal to or greater than that of the original, and the mounting and location of the connector must match. The device of the magnetron is the same for manufacturers, and the design may differ, so you need to make sure that the analogue to the waveguide is tight. If the heat-conducting paste on the thermal fuse is dry, it is replaced with fresh one.

When buying a new magnetron, it is necessary that the power matches, the contacts and mounting holes match. If at least one of the conditions does not match, you purchased a part that is not suitable for you.

• If something cracks and sparks in the microwave when you turn it on, you need to stop using the oven and find out the reason. Troubleshooting is cheaper than buying a new part. In this case, the culprit is usually the burning of the cap, because of this, the microwave oven sparks.
• It is necessary to constantly monitor the condition of the mica pad, which protects the exit of the waveguide into the chamber from the ingress of fat and food crumbs. If the cap is faulty, the mica may be burnt out, which leads to the failure of their magnetron system. The cover should be kept clean, as the grease that gets on it is charred by the temperature and becomes electrically conductive. Interacting with radiation, it causes sparks in the chamber.
• If the voltage is unstable, it is better to connect the microwave through a stabilizer, since even a slight drop will negatively affect the operation of the oven. The power decreases and the wear of the magnetron cathode accelerates. For example, with a mains voltage of 200 V, the power is halved.
• The microwave has many uses, so if it malfunctions, the usual order of things is disrupted. The reason for the failure is not necessarily the magnetron or its power supply circuit. First, you should check the voltage at the place where the oven is connected to the network and the condition of the mica plate.

He was the first to publish the results of theoretical and experimental studies of the device's operation in a static mode and proposed a number of magnetron designs. The generation of electromagnetic oscillations in the decimeter wavelength range by means of a magnetron was discovered and patented by the Czechoslovak physicist A. Zhachek.

Operating magnetron generators of radio waves were created independently and almost simultaneously in three countries: in Czechoslovakia (Zhachek, 1924), in the USSR (A.A.Slutskin and D.S.Steinberg, 1925), in Japan (Okabe and Yagi , 1927).

The French scientist Maurice Pont with colleagues from the Parisian firm "KSF" in 1935 created an electron tube with a tungsten cathode surrounded by resonator anode segments. It was the forerunner of resonator chamber magnetrons.

The design of the Alekseev-Malyarov multi-resonator magnetron, which provides 300-watt radiation at a wave of 10 centimeters, created in 1936-39, became known to the world community thanks to the publication of 1940 (Alexeev N.F., Malyarov D.E. Getting powerful vibrations of magnetrons in centimeter wavelength range // Magazine of Technical Physics. 1940. Vol. 10. No. 15, P. 1297-1300.)

The Alekseev-Malyarov multi-cavity magnetron was born due to radar. Radar work was launched in the USSR almost simultaneously with the start of radar work in England and the United States. According to foreign authors, by the beginning of 1934 the USSR had advanced in these works more than the USA and England. (Brown, Louis. A Radar History of World War II. Technical and Military Imperatives. Bristol: Institute of Physics Publishing, 1999. ISBN 0-7503-0659-9.)

In 1940 British physicists John Randall (eng. John randall) and Harry Booth (eng. Harry boot) invented resonant magnetron New magnetron gave impulses high power, which made it possible to develop a centimeter-range radar. The short wavelength radar made it possible to detect smaller objects. In addition, the compact size of the magnetron led to a sharp decrease in the size of the radar equipment, which made it possible to install it on airplanes.

The phenomenon of voltage tuning of the magnetron frequency was first discovered in 1949 by the American engineers D. Wilbur and F. Peters. A voltage-tuned magnetron or mitron is a magnetron-type generator device, the operating frequency of which varies in a wide range in proportion to the anode voltage.

Magnetrons are either non-tunable or tunable in a small frequency range (usually less than 10%). For slow frequency restructuring, hand-driven mechanisms are used, for fast (up to several thousand restructuring per second) - rotary and vibration mechanisms.

Magnetrons as microwave generators are widely used in modern radar technology.

Design

Magnetron in longitudinal section

Resonant magnetron consists of an anode block, which is, as a rule, a thick-walled metal cylinder with cavities cut in the walls, which act as volume resonators. The resonators form a ring oscillating system. A cylindrical cathode is attached to the anode block. A heater is fixed inside the cathode. The magnetic field, parallel to the axis of the device, is created by external magnets or an electromagnet.

To output microwave energy, as a rule, a wire loop fixed in one of the resonators or a hole from the resonator to the outside of the cylinder is used.

The resonators of the magnetron form an annular oscillatory system, around them there is an interaction of an electron beam and an electromagnetic wave. Since this system, as a result of the ring structure, is closed on itself, it can be excited only on certain modes of vibration, of which π -view. Such a system has not one, but several resonant frequencies, at which an integer number of standing waves from 1 to N / 2 (N is the number of resonators) fits on the ring oscillatory system. The most advantageous is the mode of oscillation, in which the number of half-waves is equal to the number of resonators (the so-called π-mode of oscillation). This type of oscillation is so named because the microwave voltages across two adjacent resonators are phase-shifted by π .

For stable operation of the magnetron (in order to avoid jumps during operation to other modes of vibration, accompanied by changes in frequency and output power), it is necessary that the nearest resonant frequency the oscillatory system significantly differed from the operating frequency (by about 10%). Since in a magnetron with identical resonators the difference of these frequencies is insufficient, it is increased either by introducing ligaments in the form of metal rings, one of which connects all even and the other all odd lamellas of the anode block, or by using a multi-resonator oscillatory system (even resonators have the same size, odd - other).

Individual models of magnetrons can have different designs. So, the resonator system is made in the form of several types of resonators: slot-hole, blade, slot, etc.

Principle of operation

Electrons are emitted from the cathode into the interaction space, where they are affected by a constant anode-cathode electric field, a constant magnetic field and an electromagnetic wave field. If there was no field of an electromagnetic wave, electrons would move in crossed electric and magnetic fields along relatively simple curves: epicycloids (a curve that is described by a point on a circle rolling along the outer surface of a circle of larger diameter, in a specific case, along the outer surface of the cathode). With a sufficiently high magnetic field (parallel to the magnetron axis), an electron moving along this curve cannot reach the anode (due to the action of the Lorentz force on it from this magnetic field), while it is said that the diode is magnetically blocked. In the magnetic blocking mode, some of the electrons move along the epicycloids in the anode-cathode space. Under the influence of the intrinsic field of electrons, as well as statistical effects (shot noise), instabilities arise in this electron cloud, which lead to the generation of electromagnetic oscillations, these oscillations are amplified by resonators. The electric field of the generated electromagnetic wave can slow down or accelerate electrons. If the electron is accelerated by the wave field, then the radius of its cyclotron motion decreases and it deviates in the direction of the cathode. In this case, energy is transferred from the wave to the electron. If the electron is decelerated by the field of the wave, then its energy is transferred to the wave, while the cyclotron radius of the electron increases and it gets the opportunity to reach the anode. Since the anode-cathode electric field does positive work only if the electron reaches the anode, energy is always transferred mainly from the electrons to the electromagnetic wave. However, if the speed of rotation of electrons around the cathode does not coincide with the phase speed of the electromagnetic wave, the same electron will alternately be accelerated and decelerated by the wave, as a result, the efficiency of energy transfer to the wave will be low. If the average speed of rotation of the electron around the cathode coincides with the phase speed of the wave, the electron can be continuously in the decelerating region, while the transfer of energy from the electron to the wave is most efficient. Such electrons are grouped into bunches (the so-called "spokes") that rotate with the field. Multiple, over a number of periods, the interaction of electrons with the HF field and phase focusing in the magnetron provide a high efficiency and the possibility of obtaining high powers.

Application

In radar devices, the waveguide is connected to an antenna, which can be either a slotted waveguide or a conical feed horn paired with a parabolic reflector (the so-called "dish"). The magnetron is driven by short, high-intensity pulses of applied voltage, resulting in a short pulse of microwave energy being emitted. A small portion of this energy is reflected back to the antenna and waveguide, where it is directed to the sensitive receiver. After further processing the signal, it eventually appears on a cathode ray tube (CRT) in the form of a radar map A1.

In microwave ovens, the waveguide ends with a hole that is transparent to radio frequencies (directly in the cooking chamber). It is important that there is food in the oven during operation. The microwaves are then absorbed instead of being reflected back into the waveguide, where the intensity of the standing waves can cause arcing. Long enough sparking can damage the magnetron. If you are cooking a small amount of food in the microwave, it is best to put a glass of water in the cooking chamber to absorb the microwaves.

Sources of

Magnetrons are used to obtain partial and high vibrations. Electric and magnetic fields are very strong. As a result, high frequency vibrations occur. A commonly used type of device is the multi-cavity one. In such a magnetron, electrons are affected by three fields at once:

• electric;
• magnetic;

Magnetron: what it is and how it appeared

This term was first used in 1921 by the American physicist A. Hull. His research and experiments were continued further, which led to the emergence of many types of magnetrons, which began to be used in radio electronics.

A. Jacquet received a patent for this invention in 1924. It was he who invented the modern magnetron, the principle of which is based on the interaction of two fields.

In the next decade, the development of magnetrons for the generation of microwave waves was carried out. The main task was to increase the frequency of oscillations, which only Soviet scientists managed to do. They doubled the original value using copper as the anode material.

Device

The heart of the magnetron is an anode block consisting of a copper cylinder with a void inside. There are cavities in its center; they are a ring system of cavity resonators. There is a hole in the middle of the anode, it is through it that the power is connected.

Also from it the anode is connected to the cathode. This is the filament, it is heated and runs through the entire middle of the anode. To provide an output of high-frequency oscillations, such an output is installed in one of the resonators. There is a vacuum inside the anode block. To cool it, finned radiators are installed on the surface.

Place this block so that it is between the magnets that create a magnetic field of sufficient strength.

Set the voltage between and so that the positively charged pole is at the anode. Electrons from the cathode begin to move due to the action of the electric field. They should move to the anode, and the magnetron, the principle of which is to return it figuratively to the cathode.

It is possible to achieve the effect when the electrons move along the circumscribed circle and are at the same time close to the anode, but return back, if certain conditions are met in two coupled fields. In this state, only a small fraction of all electrons emitted from the cathode remain at the anode.

Returning to the cathode, some of the electrons are replaced. This process continues, forming a ring-shaped charge near the anode. Such a charge begins to form near each resonator, and persistent high-frequency oscillations appear. Such vibrations can be brought out by turns of wires, placing them in any of the resonators. These vibrations are then transmitted to the waveguide (or coaxial line).

A magnetron can be called a microwave device, it is a generator, vacuum, the movement of electrons in it occurs in two fields: electronic and magnetic. The magnetron is created by the principle of operation of these two fields, which form the third - microwave.

Application

They can be used in radio engineering. For example, when drawing up radar maps. For this, the magnetron must consist not only of a feed horn, but also of a parabolic reflector. By controlling the high intensity pulses, a short pulse of microwave radiation is generated. Some of the energy is reflected back to the waveguide and antenna, which are directed to the receiver.

After processing, the data appears on the radar map.

Household use

In ovens based on microwaves, the principle of operation is slightly different. The microwave magnetron has a transparent hole at the end of the waveguide for radio frequencies that are generated in the cooking compartment. Therefore, it is important to turn on such an oven only with the presence of food in it. Without this condition standing waves sparks because the magnetic waves are not absorbed but are returned. If it lasts long time, the magnetron will just break. The speed at which food is cooked in the microwave depends directly on the power of the magnetron.

Most have a wattage of 700 to 850 watts. This is enough to boil a glass of water in just 2-3 minutes. Microwave magnetron "Saturn", depending on the model, may have different power. The choice of a microwave from this company can be started with a comparison of magnetrons, and then additional functions.

Buying a microwave

When buying, you should know how it works. Many are wary of this technique, mistakenly believing that it is a source of radiation. In fact, the microwave principle operates in it, which follows from the name itself. Microwave is nothing more than "ultra-high frequencies". It does not emit radiation, of course, but such equipment must be handled with care.

The microwave itself is already initially protected from microwave radiation. This oven is equipped with a special sensor that will turn off the magnetron if the door is open. The magnetron, whose principle of operation is to generate microwave waves, cannot complete its work if the operating rules are violated. If you put, for example, a metal bowl in the oven, it will simply disable the entire appliance.

Waves from a microwave oven can go out no further than five meters.

Therefore, while she is working, it is better to stay away. However, the layout of the kitchens of most apartments does not allow this, because you have to go to another room.

The electromagnetic field non-contact heats food placed in the microwave. Moreover, the heating process takes place directly within the product, which reduces the cooking time to several minutes. It is not necessary to preheat the dishes containing the food.

For the best cooking result, you need to know the culinary tricks for preparing certain products. Taking into account the fact that time passes, and the device of microwave ovens does not change, it can be assumed that they will be further and permanently assigned to the kitchens of many consumers.

Buying a magnetron for microwave

When buying a magnetron yourself, you need to know the marking. In order not to make a mistake, when buying a magnetron, you do not need to familiarize yourself with what they are. The weakest power is at the 2M213 magnetron. Its output power under load and typical are 700 and 600 W, respectively, the anode value is 3.95 kVp, and the frequency is 2460 MHz.

There are several magnetrons with average values. The main one: 2M214. This model has the same frequency, the anode value is slightly higher - 4.20 kVp. output power under load and typical - 1000 and 850 W, respectively.

The maximum values ​​of indicators for the magnetron of the brand 2M246.

At the same frequency, the anode value is higher - 4.40 kVp, average output power at load - 1150 W, typical - 1000 W.

Is it possible to replace with your own hands

Any type of magnetron for LG microwaves can be replaced with a similar one for another company, for example, Samsung. Similarly, you can replace the Samsung microwave magnetron with a suitable power element from another company. If the model of a household microwave oven was released a long time ago, then it is very difficult to find a part of the corresponding brand. Perhaps the manufacturer has already discontinued this species.

But even if you know how a magnetron works, you should not repair such equipment at home on your own.

You can purchase a 2M218 JF Daewoo magnetron on your own by ordering in specialized stores or directly from the manufacturer. It costs about 2 thousand rubles.

The basis of the microwave

Heating food in the microwave is as follows: any food contains water molecules, which, in turn, consists of positively and negatively charged particles. Such molecules act as a dipole because they are good at conducting waves of electricity.

Conclusion

Frequent breakdown of microwave ovens - failure of the magnetron. Buy a magnetron for an LG microwave (as well as other manufacturers of data household appliances) and replacing it yourself will be quite problematic. Even if a suitable element is found, only a master can install it.

Before buying a device, you should compare its price with the cost of the microwave itself. It often happens that repairs will cost more than a purchase. Always consider this factor.

So, we found out what an element such as a magnetron is for, and in what areas it is used.