Microwave oven device operating principle. How does a microwave oven work? Microwave oven electrical circuit

Service maintenance household microwave ovens (microwaves) are a vivid example of the ideology of consumer society in action: the warranty period is assigned a relatively long time, but after it expires, repairs often turn out to be more expensive than buying a new product. The impact on the environment and the economy of the fact that industry “threshes for the landfill” is fully understood by a narrow circle of well-trained experts, candidates for which are carefully filtered. Therefore, for the average citizen the question: how to repair a microwave oven with your own hands is obviously important economically, because... technically quite feasible at home.

However, the microwave oven is an equally clear illustration of another consumer-ideological problem, when the qualities of a product that contribute to the demand for it are emphasized in every possible way, truly useful, but not so spectacular, are mentioned in passing, and the potential danger is obscured by streamlined expressions. The last one from the microwave is quite large and treacherous, so repair microwave oven it is necessary to produce with a clear idea of ​​what and how can be done, what cannot be done, what should be avoided and feared. The purpose of this publication is precisely to give readers such an idea.

What is visible from the outside

Let’s take a closer look at our “micro” again, see fig. We immediately draw your attention to the fact that the latch mustaches different configurations: they are not just locks, but also parts of the electromechanical locking system (EMB, see below). We also remember the output window of the waveguide, which is usually not noticeable. Repair of a microwave oven will most often be associated with the units marked with letters; For the programmer and power regulator, their external controls are marked. In “digital” microwave ovens with full touch control, the electromechanical programmer and power regulator are replaced by electronic ones. Repairing them requires special knowledge, but everything else in the digital devices works the same way.

Note: The programmer is often called a timer, even in proprietary manuals. In fact, the timer is only one of the functional units of the programmer.

What is inside

If you remove the outer casing of the microwave, a picture of its structure is shown in more detail, see fig. In newer furnaces (on the right in the figure), components critical for reliability (high-voltage unit, EMB and programmer) are covered with protective covers and a high-voltage fuse is necessarily added; The first microwaves didn't have it.

On the 2nd prev. rice. The backlight lamps, grill and table rotation mechanism are not visible. This is no accident: getting to them without removing the working chamber or without completely disassembling the stove is possible in most modern models (yellow arrow on the right in the figure), and in some old ones. This complicates independent repairs, because in order to fix a generally simple problem, you most often have to remove the magnetron, which is bad, see below.

What does it mean?

All this filling is needed to immediately heat up the entire load of food products with ultra-high frequency (microwave) radiation. Gives it a powerful compact generator Microwave – magnetron. What is a magnetron, how it works and how it works, see video:

Video: about the structure of a microwave oven magnetron

Microwaves penetrate into partially electrically conductive media to a depth of approx. equal to its wavelength and is absorbed by the medium, releasing thermal energy. The microwave wavelength of the standard frequency for microwaves, 2.45 GHz (sometimes 2.85 GHz), just ensures complete microwave absorption by the product load. This shows most useful property Microwave heating: thanks to heating in the mass, the temperature of the product does not rise to values ​​at which hydrolysis of fats begins, producing toxins and carcinogens. This is especially important for heating food, because if it is done on a flame or from a heating element, then the hydrolysis of the fats remaining in the food continues, and its existing products decompose deeper, into even more harmful substances.

Note: Microwaves almost do not penetrate into metals, because their conductivity is caused not by individual charge carriers, but by the so-called. degenerate electron gas. It also gives a metallic shine and malleability. Therefore, it is strictly forbidden to place metal objects in the microwave chamber - all the microwave energy will concentrate on their surface, causing excessive heating, arc discharges, etc., after which all that remains is to throw away the stove. Unless the magnetron power transformer is suitable for .

However, for the same reason, the physiological effect of microwaves on living organisms is strong, harmful and may not be noticeable at first. This requires the use of special safety measures during the design, production, ongoing operation and repair of microwave ovens, see below.

The functional diagram of a microwave oven is shown in Fig. The configuration of the waveguide and microwave flow are shown conventionally; more or less corresponding real circuit is given in the inset at the bottom right.

1a – mains current pulses with a voltage of 220 V. The radiation power of the magnetron is not smoothly adjustable, so to control it it is necessary to use pulse width modulation (PWM, see below). 4a and 5a – internal control signals. 6a – high constant supply voltage of the cathode (emitter) of the magnetron – 4000V; 6b – power supply to the magnetron filament circuit 6.3V 50/60Hz.

Modern microwave ovens are built according to the so-called. circuit with a shortened microwave path, increasing the efficiency of the furnace. In this case, the chamber is tuned to resonance, which is why, firstly, without absorbing microwave energy, the stove will burn itself with its radiation. Which is what is indicated and the instructions for it.

Secondly, the magnetron produces coherent radiation, therefore, due to the interference of reflected waves in the chamber, the product is illuminated unevenly by the microwave. To ensure that the load is baked properly, it is placed on a turntable. As a consequence, a malfunction of its mechanism can lead to more serious problems, see below. Just like a malfunction of the internal convection system in the chamber, which modern microwave ovens are equipped with for completely uniform heating of food.

Safety regulations

Already by functional diagram A household microwave oven can be divided into units and modules that require compliance with the corresponding requirements when repairing. safety precautions:

• External 220V power supply circuits and the control module are general safety measures for class I electrical installations in terms of the degree of danger created by electric shock.
• Power source (IP or power supply unit) of the magnetron - safety measures for electrical installations over 1000V, capable of short circuit(short circuit) output power of more than 60 W for more than 1 s.
• Magnetron and microwave path - special safety measures for high-power microwave installations.

I class

Look at the back of your microwave. You'll see a contact pad down there with a metal threaded pin and a nut on it - unless someone has already screwed it on. This means that the microwave oven belongs to electrical installations of hazard class I, which must be connected to a separate protective grounding circuit with a current flow resistance of up to 4 Ohms tightly, i.e. permanent connection. A detachable connection to a grounding conductor through a Euro socket is not considered to be tightly grounded. Such requirements for a microwave oven are determined by the coincidence in it, formally speaking, of more than 2 hazard factors:

1. The presence of electrical voltage over 1000V;
2. Availability of a microwave radiation source;
3. The air temperature is above 30 degrees Celsius, its relative humidity is more than 85% and the presence of volatile substances in the air in the form of evaporation from heated food.

About grounding

In countries with a metal-efficient power supply system with a solidly grounded neutral TN-C, incl. In the Russian Federation, it is technically not possible to provide all residential buildings with protective grounding circuits, and a global solution to this problem is not expected in the foreseeable future. Safety guidelines take the reader from paragraph to paragraph and from point to point, without providing general guidance suitable for each specific case. General meaning: saving drowning people is the work of the drowning people themselves. Look for every opportunity to arrange a protective grounding circuit, at least an individual one of a simplified design. If there is none - regularly check the microwave for the quality of shielding and the microwave “siphon”, see below. Although formally this would be a gross violation of the safety rules and regulations and it would be useless to sue even a helpless homeless person for damage caused by a microwave oven. True, there is no need to fear a fine for violation; Due to the widespread use of microwave ovens, this is no longer legally feasible.

High voltage

The degree of influence of electric current on a person depends on the state of his body, the strength of the current, the time of its exposure and the amount of electrical energy released in the body. Therefore, for example, a TV with a picture tube and a stun gun (up to 25 kV at the 3rd anode of the picture tube and 35 kV at the output, respectively) do not belong to class I: the high-voltage rectifier of the first is not capable of producing a dangerous current even in normal operation, and the portion the energy at the output of the second is precisely dosed. Although, if you put your hand into the line scan of the TV, the sensations will be disgusting. The defining parameters of the impact of electric current on a person are as follows:

• The electrical resistance of a healthy body is 100 kOhm; in a state of intoxication, sick, steamed, tired - 1 kOhm.
• The dangerous current from the point of view of possible long-term consequences is 1 mA.
• The non-releasing current causing muscle cramps is 10 mA.
• Instantly (within 1s) killing current – ​​100 mA.
• The maximum permissible energy release in the body for 1 s is 60 J, i.e. power – 60 W.

This follows the division of electrical installations into 2 broad categories: up to 1000V and over 1000V. The former may still be safe; the latter are certainly dangerous. By the way, TV and stun guns are also dangerous, but their degree of danger is not the highest, because due to one factor.

One more point must be taken into account: a person’s individual susceptibility to electric current varies within very wide limits. This is especially true for the permissible discharge power; frankly speaking, it is “lightweight”. Taken on the basis that a person under normal conditions excretes approx. 60 W of heat, but there is no reliable physiological justification. 60-watt pulses are sometimes used to treat severe and dangerous mental patients, but it is better to avoid pulsed current discharges through yourself altogether, because They are the ones that most often produce long-term consequences. The microwave is especially dangerous in this regard, because... power is supplied to the magnetron in pulses. Therefore, before repairing it, you must strictly perform the following preparatory procedures:

1. Completely disconnect from the power supply by unplugging the plug from the socket;
2. Wait for the standard time for discharging high-voltage capacitors through a standard resistor - 20 minutes;
3. Disconnect the grounding conductor (if any);
4. Wait 3 more discharge times, i.e. 1 hour;
5. Only now can you remove the outer casing and start working;
6. All work should be carried out only with the microwave oven completely turned off (with the plug removed from the socket and the ground wire disconnected);
7. In the process of self-repair - no trial starts! If replacing the suspicious element does not help, we leave everything as is and contact a certified specialist. Or we are looking for funds for a new stove, having found out the cost of repairs.

Note: perform a forced discharge of high-voltage capacitors by any means (for example, shorting the terminals with a screwdriver) outside a special laboratory extremely dangerous! Remember - the energy accumulated in a capacitor is proportional to the square of the voltage across it!

High voltage is especially dangerous for electrical installations if handled incorrectly. For example, grasp a high-voltage wire with your fingers. Completely safe, de-energized and discharged. When working under the influence of an electric field, grease diffuses quite quickly (as they say now, it migrates) into the insulation, which will soon lead to its breakdown. Therefore, when working with high-voltage components, you need to wear clean latex gloves, if possible, handle parts only with a tool, and upon completion of work, wipe with 96% technical ethyl alcohol. Not a medical distillation! Technical alcohol leaves small streaks of salts, because... Sulfation is used in its production. When the part is completely dry, drips are removed with a clean, dry, washed flannel rag or, better yet, a microfiber cloth for cleaning glasses.

Microwave

Microwave effect on human body is in many ways similar to that of penetrating radiation:

• A single exposure to a large dose can immediately cause irreversible health problems, of which the loss of reproductive abilities is not the most severe.
• There is a certain threshold value of microwave energy flux density (EFD), below which its effect on the body does not affect the body either immediately or in the long term.
• Within the limits of the PES value from the threshold of susceptibility to a noticeable physiological effect, microwave irradiation has a cumulative effect - it may be completely imperceptible at first, but later it will manifest itself in the most dangerous way. Typical after-effects are genomic disruption, leukemia and skin cancer.

From ionizing radiation The microwave also differs in bad side: it easily leaks out of the volume allocated to it and through cracks and along electrical conductors protruding outward. Experts say that microwave siphons very well. Therefore, it is better not to undertake the repair of the microwave path of a microwave oven, from the power input to the magnetron to the output window of the waveguide, without deep special knowledge and equipment: if, according to the test results (see below), it does not siphon immediately after the repair, it will siphon later.

The matter is further complicated by the fact that the limits of individual susceptibility to microwave radiation are even wider than to electric current. The threshold of perception is so blurred that, for example, in the USA they accepted the monstrous value of PES as the maximum permissible value - 1 (W*s)/sq. m. A person directly feels such radiation and must immediately leave the danger zone, because Microwave PPE of this magnitude causes plasmolysis of body cells. Long-term consequences - you have health insurance at the expense of the company. Is medicine powerless in your case? Sorry, you were immediately warned about the possible consequences.

In the USSR they went to the other extreme, accepting the permissible PES a million times less - 1 (μW*s)/sq. m; this is approximately 5 times lower than the natural microwave background in mid-latitude areas with infrequent and mild thunderstorms. Everything would be fine, but it turned out to be technically impossible to provide shielding to the required degree for microwave installations. Although, by the way, the frequency of occupational diseases among personnel working with microwaves in the USSR was approximately three times lower than in America.

A new or immediately after repair microwave oven must be checked, firstly, for the quality of shielding; secondly, whether the microwave is siphoning from it during operation. Exactly in this order: if the shielding is good, then the microwave dose that you receive within an hour at a distance of more than 1 m from the stove will not exceed one time permissible for the most sensitive person.

Shielding

To check the microwave for shielding quality, firstly, you need to completely de-energize the apartment/house by turning off the main circuit breaker at the input switchboard or unscrewing the plugs on the electricity meter. Leave the RCD, if any, on. This is necessary to make sure that the microwave does not siphon through the network and grounding wires.

Next, we put the turned on mobile phone in the microwave, close the door and try to call it from another one. It doesn’t matter where it’s from, even from Antarctica. It is important for us to make sure that the nearest cell does not pick up the marker signal of what is in the oven. As is known, Cell Phones, even when turned off, respond once a minute like “I’m online,” and the impulse from the phone’s transmitter is quite powerful.

So, if the call did not go through and a message arrived like “The called party’s phone is out of network coverage or turned off,” then everything is OK, the furnace shielding is in order and it can be tested more deeply. If the message was “Subscriber unavailable” or “Call failed”, then it means that the control phone marker reached the cell, but speech channel It was not possible to fix it, the furnace shielding is bad. What to do next with such a stove is at your discretion, in the American way: “You have been warned of the possible consequences.”

Siphon

Mobile phones operate in the 900 or 1800 MHz frequency range, and the phone's transmitter is much weaker than the magnetron. Therefore, you also need to check whether the microwave’s shielding from its own radiation is reliable enough. To do this, you will need 2 disposable plastic cups of water, an aluminum pan with a lid and a load of not very wet product that you don’t mind overbaking, for example, boiled jacket potatoes. The water in the cups should be the same temperature, equal to room temperature. Therefore, if the experiment is planned in advance, tap water needs to be poured into any clean container about 24 hours in advance, and water that is already in thermodynamic equilibrium with the environment must be poured into glasses: in order for a filled 200-ml container to arrive, it will take at least 2 -3 hours.

For the experiment, the product is loaded into the oven and the door is closed without starting the timer yet. Glasses of water are placed 10-40 cm in front of the oven door: one “naked”, the other in a covered pan. Water is measured into glasses using a beaker equally in the amount of 100-500 ml with an accuracy of no worse than 0.5 ml. We set the oven power regulator to maximum without grilling. If possible, it is better to turn off the camera backlight. The room should be as dark as possible and certainly there should be no direct light, incl. and from light bulbs. Now turn the timer knob to maximum time(usually 30 minutes) and get out of harm’s way. The magnitude of the PES decreases with the square of the distance from the source, so it will be completely safe to go to another room.

As soon as the microwave bell rings, we return, turn on the light (you can now), remove the lid from the pan and, without touching the cups with your hands (!), measure the temperature of the water in them, carefully stirring with a temperature probe. If the temperature difference in the containers is less than 1 degree (this is double the intrinsic error of the temperature probe, although the tester shows the temperature in gradations of 0.1 degrees), then everything is OK - for an hour and a half a day, this microwave can be used according to Soviet standards. If it’s more, everything is again at your discretion, American style.

Checking the door

If a seemingly working microwave is siphoning, then most likely the gap between the closed door and the oven body is more than 0.15 mm. In RuNet they correctly write that you can check it with a sheet of writing paper with a density of 90-110 g/cubic. dm, it is just the right thickness, but the testing method they give is incorrect. It would be correct to cut a strip of paper 5-7 cm wide and place it under the door 6 times before closing: at the top and bottom at the hinges, then in the middle and at the latches. Each time the paper should not be pulled out from under the buried door. In this way, the door will be checked for distortion both horizontally and vertically, and it can be eliminated due to the play of the hinge fastening bolts in the mounting holes.

How does a microwave work?

Well, now you know enough about microwaves and microwave ovens to decide whether it’s worth taking on the repairs yourself. If such a desire remains, then in order to finally understand how a microwave oven works, where things can break in it, and where what degree of care needs to be taken when repairing it, you will have to turn to the circuit diagram of the microwave oven. Its typical structure, used in many models from Samsung and other manufacturers, is shown on the left in Fig. Highlighted in green is a surge protector designed to prevent microwave power from being released onto the microwave power wires (see below). Blue – control module with EMB system. Gorchichny - a device for generating power supply pulses to a magnetron (UFI). Formally, the UFI is included in the control module; their components are located on one printed circuit board. But UFI malfunctions are specific, so functionally it should be considered separately. The power supply for the BPM magnetron is indicated in pink.

What is happening there

The mains filter contains a common fuse F1, which can blow in many cases, see below. If the fault that caused its burnout is eliminated, the new F1 must be set to the same rating (for the same current, time and response temperature) as the “native” one. F1 provides general protection for the oven against current overloads, so if the thought of a “bug” flashes through your mind, it is better to immediately switch it to a new microwave oven.

The thermal fuse (thermal fuse) is installed on the body of the hottest component - the magnetron - and is triggered many times: it is restored when it cools down. If the microwave oven turns off due to overheating before the programmer turns it off, it is a sign that the magnetron cooling exhaust fan, its outlet grille, or the inlet pipe are clogged. If the fan motor operates with knocking, creaking, or a lot of noise, its mechanical wear is likely, which requires replacing the motor.

EMB

Microswitches SWA, SWB and SWC make up the electromechanical interlock system. SWA and SWB are activated by the upper door latch, SWC by the lower. Since the microwave is a hazard class I device and is often operated abnormally (without grounding), it is used a complex system EMB: double for opening with control for short circuit. One of the principles of TB is implemented here: if it is impossible to avoid an invisible danger 100%, you need to at least make it visible. Invisible danger in this case - microwave radiation through a loosely closed door, and visible - combustion of F1.

In view of the importance of the EMB for the safety of the oven and its susceptibility to breakdowns due to the sedimentation of fumes (see below), it is necessary to consider the EMB circuit in more detail separately from the general one already in the state with the door closed (see figure on the right). As you can see, if the SWA gets stuck when the door is open, the SWC will short-circuit the common power circuit, causing F1 to burn out. To avoid false alarms of the EMB, it is necessary for the SWC to switch a little slower than the SWA. Therefore, firstly, faulty SWA and SWC need to be replaced only with ones of the same type.

Secondly, a situation is possible when all the EMB mics ring normally both when the door is open and when the door is closed, but F1 burns out immediately when it is opened. This means that the fumes from the products penetrated into the mikriki, their response times “floated” and the EMB became unbalanced in time. There is only one way out - change SWA, SWB and SWC at once, because They are non-removable and cannot be repaired.

Note: The same microswitches for the electromechanical door lock must first be checked if the oven does not turn on when the door is closed. Very often their contacts simply do not close/switch due to the child adhering to them.

Fat and fumes

We immediately encountered the role of fat and its fumes in causing microwave malfunctions, and there will be even more troubles from it in the future. The fat in foods does not boil in the microwave, like in a frying pan, but evaporates, and its vapors settle anywhere, forming a film of fumes. It disrupts the mechanics, causing complex problems (see below). A slightly damp smoke film has noticeable conductivity, “confusing” the control automation, and a dry film breaks through with a voltage of less than 500V, which is dangerous for the high-voltage part. It is especially undesirable for children to get into the microwave path - repairing a microwave oven in this case turns out to be the most difficult and expensive.

To verify the ubiquity of fat vapors, you can do an experiment that requires a completely new frying pan with a lid. For now, keep the lid away, and melt any cooking fat in a frying pan until it spreads. Then they let it completely harden in the frying pan, cover it with a lid and keep it at room temperature for a day or more. After this, the lid turns out to be sticky to the touch - fatty fumes have settled on it. What happens to fat in the oven chamber at a temperature of 100 degrees or more is a rhetorical question. Fat in the microwave is not dark, burnt, like kitchen fat, but almost transparent and therefore difficult to notice, but no less harmful.

Automatic control

Let's say our stove is still working. Product loaded and door closed. The power control (see below) is set correctly. Turn the timer knob to right time– SW1 will immediately close, turning on the backlight, table rotation, magnetron blowing and convector. When they “accelerate”, SW2 will work and turn on the magnetron power pulse generation device (UVI), the furnace will begin to heat. When the timer returns to zero, SW1 and SW2 will open, turning everything off, and the bell will ring. In simple microwave ovens, its spring is charged mechanically when the door is closed, and released by a lever that pushes the timer cam.

Timer

The microwave timer is an electromechanical cam programmer driven by the timer itself: a coil spring with a clock mechanism or a micromotor with a gearbox. Several disks with cams are mounted on the timer shaft, closing and opening contact groups.

Malfunctions of the timer (we will call it that for brevity) are most often caused by fatty children. Less often - breakdown of mechanical parts. Even less common, if the timer is completely mechanical, is by weakening the spring. Typical signs of timer failure are as follows:

• After turning the control knob, the oven does not work at all, the knob does not rotate back - the mechanics are completely clogged or the micromotor or its gearbox has failed. Repair in the first case is overhaul and cleaning, in the second - replacement.
• End functions do not work. For example, the backlight, table, magnetron blower and convector turn on, but the oven does not heat. Either the contacts (in this case SW2) are clogged, or its cam has broken off. Repair - as before. case.
• The knob rotates back, goes to zero in the allotted time, the bell rings, but nothing turns on electrically. The same, only with SW1.
• Everything works as it should, but slowly - real time return the handle to zero more than specified. It rarely happens, and only with timers with a clock mechanism - its spring has weakened. Repair - wind it by 0.5-2 turns; Timers with clocks have this feature. In some, without disassembly: under the back cover there is a slot for a screwdriver for winding.

Oh, those “skis”...

In some old LG microwaves, due to fumes in the timer, a completely exotic breakdown occasionally occurs: the stove turns on spontaneously and “threshes” until it goes into a heat stop. When the FU cools down, it turns on again. Dangerous failure, because If the chamber is empty, the magnetron soon breaks down, and replacement turns out to be more expensive than a new furnace. It is most often observed in the off-season before turning on the heating, but only with the door closed. The reason, as it turns out, is that SW1 is stuck due to fumes and, at the same time, a lump of fumes between the contacts of SW2. Its resistance in damp air turned out to be commensurate with that of the timing resistors of the UVI (see below), the storage capacitor slowly charged and started the relay that supplied power to the magnetron.

Camera mechanics

The sedimentation of the child in the table rotation mechanism and the convector acts as a pumping action: due to uneven heating of the load, the release of fat vapors from overheated places intensifies. Eventually, the cover of the waveguide output window burns out, which means complex and expensive repairs to the microwave path. Therefore, if you notice uneven rotation of the table or the child is tightening the convector grates, you need, without waiting for the worst, to disassemble the stove and clean the mechanics. With the condition: do not touch the magnetron and microwave path, if the design of the furnace allows this. Otherwise, it is better to contact a service center; prices for such repairs are reasonable.

UVI and power

The device for generating magnetron power pulses operates in this way: through the low-power rectifier diode D1 and resistors R2/R3, the high-capacity electrolytic capacitor C4 is charged. Zener diode D2 is designed to protect low voltage C4 and RY relays from overvoltage. When the voltage on C4 reaches the trigger voltage RY, it will supply 220V 50/60Hz to the primary winding of the magnetron power transformer, which will output a microwave pulse into the chamber. Later a short time C4 will discharge through the RY winding, it will release, then the cycle will repeat until the timer opens SW2 or FU fires. Thus, microwave pulses are supplied to the chamber (inset in the bottom center in the figure with the diagram).

In the simplest case, power adjustment is carried out by switching R2/R3. In this case, the charging time of C4 changes, but its discharge time remains unchanged. Accordingly, the ratio of the pulse repetition period to the pulse duration changes, the so-called. duty cycle of the pulse sequence. This is pulse width modulation (PWM), which, as we see, is by no means the prerogative of “digital” microwaves. The average power delivered by the magnetron, which the product load, due to its thermal inertia, perceives as constant, depends on the duty cycle of the pulses.

So that during a sudden power outage, the magnetron, due to the energy accumulated in the windings of the transformer, does not give a large surge of microwave frequencies that can siphon through any screen, the primary winding of the transformer is not completely disconnected from zero 220V, but remains connected to it through high resistance resistors R4. If they are removed, an otherwise serviceable stove will stubbornly siphon to any grounding. If the R4 soldering on the board becomes contaminated, the magnetron will process each pulse longer than it should, overheat, and the heater will shut down due to heat. So remember these “cutters” well.

A number of microwave oven models use double PWM, which ensures greater stability of the average magnetron power. To do this, additional disks with different amounts cams and their contact groups. Power adjustment is carried out by switching the UFI power supply from group to group. In this case, a series of power pulses comes in packets, following each other less frequently or more often (positions a and b in the figure), and the duty cycle of the pulses within the packet remains unchanged.

In UFI, the relay most often fails (see figure on the right) - its contacts need to switch a large current. The magnetron does not turn on and the oven does not heat, although everything else is fine. To check, the terminals of the RY winding are connected to an regulated power source, and a multimeter turned on in ohmmeter mode is connected to the terminals of the closing contacts. If, when the voltage on the winding increases from 3 to 24V, the tester does not show a short circuit, RY needs to be changed, regardless of whether the click of the triggered contacts was heard or not.

Another typical malfunction is that the stove heats less than what is set by the regulator knob. It develops gradually: to obtain the same heat, you need to turn the handle further and further. A possible reason is loss of capacity C4; it is replaced with a known good one of the same type.

Note: other possible reason a drop in microwave power - the magnetron has exhausted its lifespan. Characteristic signs are that the furnace is more than 5 years old, it has been used intensively, and the drop in power develops much more slowly, not in days and weeks, as with the loss of capacity of a timing capacitor, but over the course of months. Accurate diagnosis - in service center or a production laboratory with appropriate equipment.

Finally, every now and then there is a sudden bang and the oven stops heating. Upon opening, it turns out that the C4 body is swollen and cracked. The reason is that D1 is broken or D2 is out of order. In addition to replacing both of them at once and C4, you must definitely check RY, as described above - its winding could very well burn out.

High voltage stand

During the repair of the high-voltage part (magnetron IP), it will be necessary to ring its components. A regular tester “does not pick up” them; its battery voltage is not enough. In RuNet it is advised to check high-voltage (HV) components using a 15-25 W 220V incandescent test light. “Ringing” a circuit using a “control” is, firstly, directly prohibited by the PTB. Secondly, the method is very rough and 100% reliable result does not give.

A homemade stand for testing explosive components (see figure on the right) is, first of all, completely safe: the input impedance of the multitester at the measurement limit of 750V AC is several megohms. If you accidentally touch the blue end of the wire according to the diagram, the sensations will be no greater than when using a phase indicator. You just need to mark on the body of the socket where the phase is (determined by the same phase indicator), on the plug - which pin the red wire in the diagram goes to, and insert the plug into the socket so that the marks match.

In addition, this stand is much more sensitive and allows you to find even potentially faulty elements that cause intermittent malfunctions in the operation of the furnace:

• The tester shows almost full network voltage - the component is short-circuited.
• The voltage is incomplete, but quite high (tens of volts) - breakdown under operating voltage; the control “catches” him uncertainly.
• The voltage is low, a few volts - leakage under operating voltage. The component is still half-dead, but it will break through soon. The control system will respond to this as if it is working properly.

Note: However, remember - any manipulations with the component being tested (connection, disconnection, switching) can only be performed by removing the plug from the socket!

Magnetron power supply

Due to the pulsed mode of its operation, the high-voltage power supply of the magnetron is made using a half-wave circuit with doubling the voltage. Do not try to build one like this for your needs - its transformer must be designed to operate in short-circuit mode secondary winding within 5 min.

The positive half-wave from the secondary winding of the transformer, closing through the high-voltage diode D, charges the high-voltage capacitor C to its amplitude voltage of 2000 V. The negative half-wave through the same diode charges it to 4 kV, as in the voltage booster of old TVs. The magnetron under such an emitter voltage (negative relative to the common wire) begins to generate microwave frequencies, C is discharged and everything repeats all over again.

High-voltage fuse F and discharge resistor R are protective. The first one turns off the magnetron when it is instantly overloaded to the point of overheating (for example, when the chamber is empty or overloaded, there are metal objects or unsuitable products in it, or when a high-voltage diode breaks down). Through R, the capacitor quickly discharges, which saves the microwave from “splashing out” when the door is suddenly opened while the oven is running.

In this circuit, when F burns out, a microwave splash outward is possible in case of poor-quality shielding and/or grounding, because An electric arc burns in a blown fuse for several milliseconds. Therefore, a number of microwave oven models use a magnetron power supply circuit with a protective diode (see figure on the right). Microwave bursts are excluded in it, but the bad thing is that the protective diode is as disposable as a fuse, breaks more often, and costs the same as a high-voltage capacitor. The protective diode is checked on the stand described above, just like the high-voltage one: when you turn it on in both the forward and reverse directions, the tester should show approx. half the mains voltage. If the difference is more than 20%, it is faulty, although “scrolling” with an induction megger and a control test will pass normally.

Any malfunction of the HV IP leads to the fact that the oven does not heat, although all its other functions are operational. In this case, F necessarily burns out. This is basically the same fuse, only with a spring-loaded thread for faster opening. Called by a regular tester. The high-voltage capacitor is tested on the stand described above; the tester should show 10-70 V in both directions, depending on the capacity of this sample (indicated on the case).

Transformer

After checking as many as 4 explosive components, you need to check the magnetron power transformer. The microwave may not heat due to an interturn short circuit in its windings (turn short circuit). It is not determined by the continuity tester, because has almost no effect on the active resistance of the windings. It is best to have a suspicious transformer checked by a company specializing in electrical measurements (not electrical installation work!) or to the electrical measuring laboratory of the Distribution Zone or Consumer Supervision. The prices for such a service are divine everywhere.

If it is not possible to get to the laboratory, then with a high degree of confidence you can check the transformer at home. The technique is based on the fact that in the presence of a turn short circuit, the no-load current of the transformer increases several times. Here you will have to commit a violation by using the same control lamp at 220V 15-25 W. You can’t determine it on the bench: the current through the tester in voltmeter mode is too small, and measuring in ammeter mode is very dangerous.

The control is connected in series with the high-voltage winding. It is with high voltage, but on the other hand it is extremely dangerous! Finding the high-voltage winding is not difficult; it is heavily insulated and, together with the filament winding, is wrapped in additional insulation, see fig. on right. The assembled circuit is briefly connected to the network, for no more than 5-10 s. If the transformer is working properly, the light bulb will either not light up at all, or its filament will heat up to a dull red. If there is a noticeable glow, there is also a turn short circuit.

Without experience, it can be difficult to determine: what does “dull red” and “noticeable glow” mean? To be sure, we will arrange an artificial orbital one. Let's disconnect the circuit from the network (!!!), short-circuit the filament winding and briefly plug it into the network again. The light bulb should flash much brighter than in the first case. If the glow has not changed or changed only slightly, the transformer “twists” and is unusable.

Magnetron

If all high-voltage components are checked, but there is still no microwave generation, then the problem is probably in the magnetron. Without removing it or disassembling the microwave path, you can use a regular tester to check the magnetron for internal short circuit. It occurs due to peeling of the cathode coating, which closes the gap between it and the anode.

Almost as often as an internal short circuit, a breakdown of the cathode filter occurs in the magnetron (shown by the red arrow on the left in the figure). This is not just a connector, but a pair of high-voltage feed-through capacitors. It is impossible to pick out the filling of the capacitors (in the center in the figure), this, firstly, is unlikely to show anything; secondly, its crumbs and, especially, dust are toxic. First of all, you need to measure the resistance between the terminals with a regular tester. It should be close to zero: the terminals are connected to the filament, and its current is approx. 10A at 6.3V.

You need to carefully unscrew the clip with feed-through capacitors; in many cases this can be done without removing the magnetron and without touching the microwave path. Most likely, the breakdown will be visible immediately (on the right in the figure); if not, carefully bite the clip off the filter inductances and ring each terminal on the flange on the bench. If the “passes” are working properly, the tester will show zero in each case. If there is at least a couple of volts, there is a hidden breakdown or voltage leak. If everything seems to be in order, but the oven still does not heat, the cathode has suddenly completely lost emission and the magnetron is unusable. This happens with magnetrons, high-power generator klystrons and traveling wave tubes (TWTs); the reason is depressurization of the housing, which should have a deep vacuum. What else is possible with a magnetron - the magnets become demagnetized due to overheating. In this case, when turned on, the high-voltage fuse will immediately burn out.

Camera

According to the logic of the presentation, the microwave chamber is the last one, but because of it, it is where the most breakdowns occur. A disaster like the one in pos. 1 Fig., may not be as scary as the eyes see: the camera coating is generally designed for such cases. Unless you tried to cook eggs in the microwave, the boiled denatured protein eats firmly into the coating, which means a new oven. You need to carefully remove debris from the camera, wash it with a detergent recommended by the manufacturer and inspect for scratches deeper than the eye, 0.1 mm. After this, we check by hand the smooth rotation of the table and do a shielding and “siphon” test. The probability that the furnace will be suitable for further use, not small. If the coating burns through (item 2), the problem is at seams - a new stove is needed. No matter how you repair it, the siphoning will be “direct fire right through.”

Perhaps the most common malfunction of household microwave ovens is that everything works as it should, everything is loaded as it should be and what was previously heated without problems, but there is sparking in the chamber. Then, with clean hands in a clean, dry room, carefully remove the protective cover of the waveguide output window - if it is removed from the outside, without disassembling the microwave path. The lid is made of muscovite mica or mica cloth and is quite fragile. The outer side of the cover may appear clean or have subtle damage, but on the waveguide side a completely different picture is revealed, pos. 3 and 4. It was the evaporation of fat and fat fumes that worked.

The cover needs to be replaced with exactly the same one. Homemade kulibins vying with each other to offer: I cut them out of 1.5 mm material! The resource is four times longer - proprietary 0.4 mm! In fact, mica is not ideally transparent for the microwave; a thick lid will heat up, strongly absorb fat vapors and will last less than the original one. But the main thing is that the furnace will lose its mode and start siphoning “almost at a run.”

If the microwave has a short path, then under the cover the inside of the waveguide (more precisely, the output resonator) and the antenna (emitter) of the magnetron will be visible. The resonator, if its coating is not swollen, cracked or discolored, can be cleaned with alcohol as described above. The darkened emitter needs to be replaced with a new branded one; it is simply removed from the magnetron. To do this, the old emitter stuck in the socket is very carefully swung with small pliers, and the new one must be placed with a latex glove so as not to get dirty or scratched.

There are three subtleties here. First, never remove the magnetron yourself. Second, do not try to extend the life of a punctured (burnt out) emitter by turning it over. In both cases, the oven goes out of order and the “siphon” cannot be eliminated. Third, after any repair during which you even touched the microwave path with your finger, be sure to check the microwave for shielding and microwave leakage, as described above.

Finally

A completely legitimate question after reading: is it worth keeping a device that is so dangerous at home? There is no absolute evil, just like there is no absolute good. At the pace of modern life, it is sometimes very difficult to do without a microwave oven, and the absence of fat hydrolysis is a strong argument in its favor.

The author has worked professionally with microwaves for many years. There were no health consequences: I was always extremely careful, and individual sensitivity turned out to be low. There is a microwave on the farm, it’s inexpensive. It stands mostly with the plug removed; It turns on very rarely and irregularly, when it is impossible to do without it.

This is how you should treat household microwave ovens: as an inevitable, but sometimes useful evil. Like a can of dichlorvos or a propane torch - sometimes you need it and there is no replacement, but these are not things for pampering and amateurish experiments. And most importantly, check the microwave at least once every six months for the quality of shielding and microwave leakage.

All microwave ovens, depending on their functional content, can be divided into the following types:

Solo– conventional microwave ovens are only capable of defrosting and heating food. These models use microwaves only. There are no other functions.

Microwave ovens with grill– in addition to the basic functions of defrosting and heating food, it also has a built-in heating element and a spit for cooking dishes in grill mode (grilled chicken, grilled meat, etc.). The heating element grill can be movable, that is, change the inclination.

Microwave ovens with convention– has the function of circulating hot air around the prepared product. In such a microwave you can cook many different dishes, just like in a traditional electric oven.

Multifunctional microwave ovens - in addition to standard functions, they have many more additional modes, which make the cooking process safer, more comfortable and varied.

For our safety, manufacturers implement the following protective functions in their models:

• Blocking the operation of the device if the door is opened during the cooking process;
• Child lock – eliminates the possibility of accidental activation;
• A radiation shield is a protective device that should be in every model.

It is clear that it is the versatility of the model that makes its operation especially comfortable for us. A variety of modes and additional tools allow you to prepare complex dishes and help reveal your culinary abilities. In expensive multifunctional models of microwave ovens, the following functions are most often found:

I have listed the most popular functions of microwave ovens, but this is probably not full list. IN different models these functions are combined in different ways.

Types of microwave ovens by control method

Based on the control method, all microwave ovens can be divided into three types:

Mechanical adjustment- this is the simplest and cheap way control equipment, which is inherent in budget solo models. Using two round knobs, the radiation power is set and the timer is turned on (time for heating or defrosting food). For models where there are several different modes, two switch knobs are not enough. Therefore, in other types of microwave ovens it is used electronic control.

Push button control– this is a more convenient electronic control of equipment. Push-button control is represented by a set of buttons on the instrument panel and is used in models that have different modes.

Touch control– essentially these are the same buttons, only touch ones. Such models, as a rule, have a display that shows the time, programs used, and the degree of readiness of the dish. Touch control is the best in terms of programming. It also allows you to set more precise parameters for the equipment.

Unfortunately, of this type The controls have one drawback: the touch buttons are very sensitive to voltage changes in the electrical network. When there are strong changes, they stop functioning normally.

Microwave oven chamber volume

The volumes of microwave ovens range from 9 to 41 liters. For a small family, it is enough to have a microwave oven with a volume of 17-23 liters. For a family of three or four people – from 23 liters or more. Almost all models of microwave ovens are equipped with a timer and illumination of the working chamber.

The larger the volume of the microwave chamber, the greater its power. The speed of cooking also depends on the power.

Types of internal coating of the chamber in microwave ovens

The interior of the camera is most often coated with highly durable enamel, which is easy to keep clean.

Ceramic coating is also quite common. Some manufacturers call it "bio-coating". It is also very durable. It is difficult to scratch, which prevents the growth of microbes in the oven. Fat does not linger on the perfectly smooth ceramic surface and slides down the walls of the chamber, so the device is easy to care for.

The inner lining of the chamber is made of stainless steel. Stainless steel can withstand any temperature, but it is somewhat more difficult to care for.

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Microwave ovens have become so integral to our daily life that today it is difficult to imagine an apartment or house in the kitchen of which there would not be this useful device. The functionality of microwave ovens allows you to perform a wide range of work related to the thermal processing of food: defrosting, heating and even preparation. You may not know this, but they can also be used to disinfect rags and sponges that do not contain metal. In this article we will look at how microwave ovens are designed and what the principle of their operation is.

As is often the case with useful and ingenious inventions of mankind, the benefits of microwave waves for domestic use were discovered completely by accident. This happened in 1942 at the Raytheon company, where physicist Percy Spencer was studying the properties of devices with microwave radiation.

According to one version, the scientist accidentally placed a sandwich on the installation and discovered after a couple of minutes that it had warmed up throughout its entire thickness. Another version says that a chocolate bar melted in Spencer’s pocket and he, happy with his discovery, immediately ran to the store; after some time, the scientist observed how microwave waves turned the fresh corn he bought into popcorn in a couple of seconds.

In 1945, Percy Spencer patented the technology for using ultrahigh-frequency waves in the food industry, and two years later the first devices similar to modern microwaves appeared in American military hospitals and canteens. It is worth mentioning separately that these units, unlike modern ones, really resembled stoves, since they weighed about 340 kg.

Further development and launch of microwave ovens on the market household appliances Sharp took over, it is they who own the main revolutionary achievements in this industry:

• in 1962 they released in mass production the first household microwave;
• in 1966 - they began to equip the stoves with a rotating stand-table;
• in 1979 - released the first microprocessor-controlled device;
• in 1999 - they created the first model of a microwave oven with the ability to connect to the Internet.

Today, the household appliances market offers a huge variety of microwave ovens with a wide variety of functionality, but all of them are simple, economical and safe for health.

How it works?

Surely many of us, at least once in our lives, have been interested in what the operating principle of a microwave oven is based on and how it turns out that food placed in it warms up quite quickly.

The fact is that the products we use for cooking contain water, fat, mineral components, and sugar in various proportions. All of these substances contain dipolar molecules in their structure, which means that one of their ends is positively charged and the other negatively charged. Meat, grains, vegetables and any food product in general contain great amount such molecules.

Let's remember physics - in the absence of an electric field, dipolar molecules are in a disordered position. As soon as a substance is exposed to an electric field, the molecules are rearranged and “stacked” according to the direction of the lines of force: the positively charged ends are towards the “plus” pole, and the negative ends are towards the “minus”. Accordingly, when the polarity of the electric field changes, the molecules will begin to “unfold” 180˚. The operating principle of a microwave oven is based on this phenomenon.

So, on average, the operating frequency of a microwave oven is 2.45 gigahertz. This means that 1,000,000 oscillations (switchings) occur in one second. During one such switching, the polarity of the electric field inside the microwave changes twice - from “plus” to “minus” and back. A simple mathematical calculation tells us that in one second, the electric field into which we place food changes polarity 4.9 million times. That is why these devices are called microwave ovens - the decoding of the abbreviation reveals the word “ultra-high frequency”. In fact, we make the molecules rotate with very high speed, as a result of friction from each other, heat is released. The upper 1-3 cm of the substance is exposed to the electric field, from which heat spreads deeper. That is why, when cooking some products in a microwave oven, it is recommended not to turn it on “full”, but to select medium power and increase the processing time.

How does a microwave oven work?

A household microwave oven consists of the following functional parts:

• a metal chamber with a metal door into which food is placed to be heated;
• magnetron - a device that emits microwave waves;
• transformer for powering the magnetron;
• control and switching circuits;
• a waveguide that transmits the radiation generated by the magnetron into the chamber.

In addition, the design of the furnace includes the following components that do not affect the heating process itself, but serve to improve the operation of the device:

• rotating stand for uniform wave exposure;
• circuit that ensures the operation of the timer;
• a security circuit that blocks the operation of the device in different situations(for example, when opening the door);
• a fan necessary to ventilate the stone and cool the magnetron.

How does a magnetron work?

The magnetron is the main device of a microwave oven, which emits the microwave waves necessary for heating. In fact, it is a high-frequency vacuum diode with a cylindrical copper anode. From the inner wall, this anode is divided into several sectors with copper walls.

The cathode, made in the form of a rod, forms the center of this structure (check out the picture). Thanks to the filament placed inside it, electrons are emitted. At the end sides of the device there are powerful ring-shaped magnets. By using magnetic field, created by them inside the magnetron, microwave radiation is generated.

During operation, a voltage of 4 kV is applied to the anode, and only 3 V to the filament. This provokes the emission of electrons, picked up by a high-tension electric field. The magnetron generation frequency is determined by the anode voltage and the geometry of the resonator chambers.

To remove energy, a special wire loop is used, running from the cathode to the emitter in the form of an antenna. From it, through the waveguide, microwave waves enter the main chamber. The output power of magnetrons installed in household microwave ovens is typically 800 watts.

To reduce the intensity of operation of the magnetron, the control circuit turns it on for short periods of time, with pauses between them. So, for example, in order for the output power of the magnetron to be 50% (400 W), it is necessary to alternately turn it on and off every 5 seconds. This control principle is called pulse width modulation.

The operation of the magnetron is accompanied by the release of a large amount of heat, therefore, to prevent overheating, it is equipped with a plate radiator, to which air is constantly supplied from a fan.

Thermal fuse

Temperature overload (overheating) is the most common cause of magnetron failure, which is why thermal fuses or thermal relays are installed on them. It is of particular importance for microwave ovens with functions that require long-term operation of the magnetron, for example, grills.

A specific device is selected based on the nominal temperature indicators, which are applied to their body.

The principle of their operation is quite simple:

• The thermostat has aluminium case and is installed at the location whose temperature needs to be controlled using a flange connection, providing direct thermal contact.
• The bimetallic plate located inside the fuse is pre-set to operate at a given temperature.
• As soon as the device heats up to the specified limit, the plate bends and, with the help of a pusher, breaks the connection on the contact group plates, as a result of which the power to the microwave oven is cut off.
• As the device cools, the bimetallic plate takes its previous shape, the pusher returns to starting position and the contact group closes again, supplying power.

The importance of the ventilator

One of the most important parts of any microwave oven is the built-in fan. Thanks to it, not only the magnetron is cooled, but also the rest of the circuit.

Using the thermostat alone to prevent microwave components from overheating is not enough. Firstly, this will lead to constant operation of the thermal fuse and the magnetron turning on and off, which will negatively affect not only it, but also other devices. Secondly, in some microwave ovens the thermostat simply cannot cope with the heat - in appliances with a grill function you cannot do without a fan.

While the microwave is operating a large number of heat is released not only by the components included in its design, but also by the heated products. And since the main “target” of microwave waves is water, heating is also accompanied by the release of steam. The fan allows you to get rid of excess humid air by pumping fresh air into the chamber. Thanks to this, the released steam escapes through the ventilation holes to the outside.

In microwave ovens with one fan located at the back of the device, special air ducts come from it, carrying fresh air first to the magnetron and then inside the chamber.

Protection system

Powerful high-frequency radiation from a magnetron can cause irreparable damage to human (and not only) health, so modern models of microwave ovens pay special attention to preventing this danger.

To protect the user and other living beings from harmful radiation Microwave oven chambers are made of shielded metal. And since the camera itself is also placed in a metal case, there is actually two-level isolation of microwave radiation.

You may ask a completely reasonable question: is the glass door through which we observe the readiness of the dish dangerous? Isn't she a "hole" in this defense? Rest assured - the glass is covered with a special fine-mesh metal mesh that reflects radiation emitted by the magnetron with a frequency of up to 2.45 GHz (with a wavelength of up to 122 mm) back into the camera.

Of no small importance is how tightly the door closes and fits against the body. The gap between its groove and the body is specially measured at the factory (it is equal to ¼ wavelength, for example, 122/4 = 30.5 mm) and must be maintained throughout the entire service life. This distance contributes to the formation of a standing electromagnetic wave, which does not extend beyond the device due to the fact that the amplitude value at the point of contact between the body and the door is zero. Such a simple and effective radiation protection scheme is known as a microwave choke.

What happens when the door is opened?

There is an opinion that when the microwave door is opened during operation, dangerous high-frequency radiation hits the user, causing great harm on the body. In reality, this is just a myth - the magnetron control circuit includes several switches that respond to the state of the door. Their number depends on the specific model, but usually there are at least three. One is responsible for turning off the magnetron when the door is opened, the second is for the backlight, and the third transmits information to the microprocessor about the position of the door. The operation of these switches is organized in such a way that the magnetron can only operate when the microwave door is tightly closed.

Control block

The control unit plays the most important role in the operation of any microwave oven. In fact, it is the brain of the furnace, performing two basic functions:

• maintains the power value at a given level;
• stops the operation of the device after a specified period of time.

The control unit circuit of older models was a design of two switches, one of which served to set the timer, and the other to select the processing intensity. As technology developed, the “filling” of microwaves also improved - electromechanical control units were replaced by electronic ones, which today have already been replaced by microprocessor ones. Their advantage lies not only in compactness, but also in broader functionality, including:

• power adjustment using touch or push-button keyboard;
• display of current power on the display;
• built-in clock;
• numerous presets for preparing various dishes and performing specific tasks (several defrosting modes for different types of products);
• automatic calculations - for example, you enter only the weight of the piece of meat to be defrosted, and the oven itself selects the power for it;
• a large selection of sound signals for completing the work cycle.

A separate power supply is used to power the control circuit. A relay unit is used to transmit signals and commands between the unit, keyboard, magnetron, grill, lamp and fan. To connect other components (display, keyboard) to the circuit, cables are used.

Inverter technology

When choosing a microwave oven, many consumers try to find a model with a large chamber volume to ensure maximum versatility. Unfortunately, functional elements often occupy most of the total volume of the device; accordingly, the size of the oven is large, but its useful volume is small. This problem was one of the main ones before the advent of inverter furnaces.

This technology can significantly reduce the space occupied by the magnetron through the use of smaller components. This allows you to create cameras bigger size, keeping the dimensions of the entire microwave within accepted standards.

Inverter technology is fundamentally distinguished by the fact that in such microwave ovens the emitter does not have to constantly operate at maximum power, unlike classic magnetrons. The intensity of processing is regulated by pulses, so that the food is not exposed to powerful surges of microwave energy, which affects its quality. Studies have confirmed that cabbage processed in an inverter microwave retains one third more vitamin C, and pork retains 41% more vitamin B1.

In addition to being compact and useful, inverter microwave ovens are also more economical devices, thanks to the use of only the amount of electricity that is necessary to maintain the selected power. Fine pulse adjustment of the operating mode also serves to speed up the defrosting of food.

Today, the flagship company in the use of this technology is Panasonic, which released the first inverter microwave bake.

Myths about microwave radiation

There are several well-established misconceptions about the harmfulness and danger of using microwave ovens. In fact, most (usually all) are wrong. Listed below are common myths about microwave ovens that are actually not worth your trouble.

1. A microwave can electrically damage appliances located a few meters away from it if left on. long time. In fact, modern microwave ovens are completely protected from radiation escaping outside the chamber. The minimum radiation, which may be in the immediate vicinity of the device, does not exceed the radiation of a computer system unit.
2. Microwave ovens may cause the user to become allergic to electromagnetic waves. This is simply impossible. There are only a few people in the world with such a rare disease and its causes are in no way related to the use of microwaves. In general, no household appliance creates such dangerous radiation, since all models undergo safety certification.
3. Products become radioactive when exposed to microwave waves. This is also incorrect. Microwave microwave radiation is non-ionizing and therefore does not change the properties of food. The statement about the carcinogenicity of products exposed to microwave processing is also incorrect - microwaves have a completely different operating principle than X-rays and, once again, cannot in any way affect the properties of products.
4. Microwaves pose a high health hazard. This has already been partially said - direct exposure to microwave radiation is really detrimental to tissues, but if you follow the rules for using a microwave, you will never be exposed to such effects. In fact, radiation from a microwave oven represents only a small fraction of the total electromagnetic field in which we find ourselves while using numerous other household appliances.

Just remember that the oven door must close tightly and the body must be intact, and also do not touch the operating microwave with your hands or other parts of the body and you can rest assured that at a distance of half a meter from the device you are exposed to no more electromagnetic radiation than when watching TV.

October 8th marks 65 years since microwave oven technology was patented.

A microwave oven (microwave oven, microwave oven) is one of the most popular household electrical appliances and is designed for quick cooking, heating food and defrosting food. Its creator, Massachusetts resident Percy Spencer, patented his invention on October 8, 1945.

According to legend, the idea of ​​​​creating a microwave oven came to his mind after he stood near a magnetron ( electric lamp, generating microwave electromagnetic radiation), discovered that the chocolate bar in his pocket had melted. According to another version, he noticed that a sandwich placed on the switched-on magnetron became hot.

The first microwave ovens, intended for army canteens and large restaurants, were cabinets 175 cm high and weighing 340 kg. More compact home stoves began to be produced in 1955.

The first mass-produced household microwave oven was released by the Japanese company Sharp in 1962. Initially, the demand for the new product was low. In the USSR, microwave ovens were produced by the ZIL plant.

The operating principle of a microwave oven is based on the processing of a product placed inside the device with microwaves (microwave radiation). These waves heat the food.

Microwaves are a form of electromagnetic energy, like light waves or radio waves. These are very short electromagnetic waves that travel at the speed of light (299.79 km/s).

Food contains many substances: mineral salts, fats, sugar, water. To heat food using microwaves, it must contain dipole molecules, that is, molecules that have a positive electrical charge at one end and a negative one at the other. There are plenty of similar molecules in food - these are molecules of both fats and sugars, but the main thing is that the dipole is a molecule of water - the most common substance in nature. Every piece of vegetables, meat, fish, and fruit contains millions of dipole molecules.

In the absence of an electric field, the molecules are arranged randomly. In an electric field, they line up strictly in the direction of the field lines, “plus” in one direction, “minus” in the other. As soon as the field changes direction to the opposite, the molecules immediately turn over 180 degrees.

The magnetron that every microwave oven contains converts electrical energy into an ultra-high-frequency electric field of 2,450 megahertz (MHz) or 2.45 gigahertz (GHz), which interacts with water molecules in food.

Microwaves bomb water molecules in food, causing them to spin millions of times per second, creating molecular friction that heats the food.

This friction causes significant damage to food molecules, breaking or deforming them. Simply put, microwaves cause breakdown and changes in the molecular structure of food through the process of radiation.

Microwaves operate only in a relatively small surface layer of food, without penetrating deeper than 1-3 cm. Therefore, heating of products occurs due to two physical mechanisms - heating of the surface layer by microwaves and subsequent penetration of heat into the depth of the product due to thermal conductivity.

When choosing a microwave oven, you should focus on its main characteristics, including chamber volume, type of control, presence of a grill, power and some others. The volume of the chamber is determined by the number of products that fit into the microwave oven.

There are three types of controls in microwave ovens - mechanical (the simplest type of control), push-button and touch.

Depending on the functions they perform, microwave ovens are divided into three types: microwave ovens, grill ovens, and grill and convection microwave ovens.

As for the additional functions of microwave ovens, the most common ones include the functions of double radiation (for uniform cooking of the product by volume) and auto-weight, which means that electronic sensors will weigh the product and select the cooking time.

Some models of microwave ovens have an interactive mode, when recommendations are displayed on the display while cooking a dish.

There may also be a microwave oven with built-in cooking recipes. To start the cooking process, you need to specify the type of product, quantity, and recipe. Ready-made programs make it possible to choose the optimal mode and exact cooking time.

Some models are equipped with a communication port for Internet access. This makes it possible to download new recipes and receive information about its calorie content.

Microwave oven accessories may include a multi-level plate rack, which allows you to heat several dishes at the same time, and a grill rack.

The material was prepared based on information from open sources

Microwave oven is one of the irreplaceable devices in the kitchen, without which housewives today have a difficult time. Everyone knows perfectly well how to use it: place the dish, press 1-2 buttons and wait 2-3 minutes, after which all that remains is to take out the already heated food. However, few people understand the principle of operation of a microwave oven, that is, how its main elements work. Let's try to understand this issue.

How does a microwave oven work?

All microwave ovens operate on the same principle, and the main element is the magnetron - special device, capable of emitting short waves with a frequency of 2450 MHz. In modern devices its power is 700-1000 W. Note that during operation it gets very hot, so a fan is installed near it, which performs several functions at once: first of all, it removes heat from the magnetron, and secondly, it ensures air circulation in the microwave oven chamber. In turn, this ensures even heating of the food.

Actually, the entire principle of operation of a microwave oven is based on this: the magnetron supplies short waves With high frequency, which act on food and heat it. Of course, such an explanation is primitive, but it also makes it possible to understand the essence of the process.

More detailed explanation

Microwaves emitted by the magnetron pass into the oven chamber through a special waveguide - a channel with metal walls that reflect magnetic radiation. Once these waves enter the chamber, they affect the food, or more precisely, the water molecules that are contained in any food product. As a result, dipoles (molecules) under the influence of microwaves begin to move quickly and rub against each other, which contributes to the release of thermal energy. This is how food is heated.

The peculiarity of microwaves is that they can penetrate up to 3 centimeters deep. The remaining volume of the product is heated from the top layer. This principle of operation of the magnetron in a microwave explains why, after heating, food can be hot on top and at the same time cold inside. Heat penetrates deeper due to natural thermal conductivity.

If you have used a similar device before, you could not help but notice that it rotates during the heating process. This is necessary to ensure that the microwaves reach all areas of the food being heated.

Microwave protection

Considering the principle of operation of a microwave oven, it is logical to think about its harm to human health. Of course, microwaves emitted by a magnetron are harmful to humans. However, after opening the door, the magnetron stops working, so a person physically cannot feel their influence. And to ensure that they do not go beyond the heating chamber, special protection is provided. All its walls are made of metal, which reflects waves, and they cannot leave the device. As for the glass door (it simply must be there so that the user can see the heating or cooking process), it is covered with a special mesh that reflects microwaves. If this grid is removed, then the waves can leave the chamber space, and this can really harm a person. It is unacceptable to use the microwave oven if there is damage, for example, to the door seal or its mesh.

By the way, given the fact that metal reflects microwaves, it is unacceptable to use metal utensils.

Device design

All microwave ovens work the same way, therefore, they have the same composition of parts. In particular, the following structural elements can be distinguished:

1. Magnetron is the main unit that is the source of microwaves.
2. A chamber with a rotating podium and metal walls that reflect radio waves.
3. Transformer for increasing voltage.
4. Door with protective mesh and transparent glass.
5. Communications and control circuit.
6. Waveguide.
7. Fan for cooling the magnetron.

All these elements take part in one way or another in the operation of the furnace.

Magnetron operation

As already mentioned, the magnetron is the heart of the microwave oven. It is an electric vacuum diode made of a large cylindrical anode. The anode itself is copper; it combines 10 sectors of the copper wall.

In the center of the device there is a rod cathode, inside the channel of which there is a filament. It is designed to emit electrons. In order for the device to generate microwaves, a magnetic field must be created in the cavity. Ring magnets are used for this purpose. high power- they are located at the ends of the part. And to create emission, a voltage of four thousand volts is applied to the anode. To achieve this voltage, a transformer in the microwave comes into play. The operating principle of any model presupposes its presence.

There are also wire loops inside the device that connect to the cathode, which is connected to the radiating antenna. It is from this element that the microwaves enter directly into the waveguide itself, from where they exit and enter the chamber with food.

Power control

If less power is needed to cook food, the magnetron can be cycled on or off. In science similar technology called pulse width modulation.

In order for a 400 W device to produce half of it within 20 seconds, it is activated for 10 seconds, after which the power is turned off for the same 10 seconds. Of course, all this happens with full automation.

Magnetron cooling

Note that during operation the device generates a large amount of heat, therefore, it needs to be cooled. To do this, the device itself is installed in a plate radiator, and a cooler is placed next to it. It blows on the radiator and removes heat from the magnetron. If the fan does not work, the device may simply overheat during operation and simply fail. But to prevent this from happening, it is additionally equipped with a special thermal fuse - a protective device.

Purpose of the fuse

To prevent the grill and magnetron from overheating, some models install special thermal fuses (thermal relays). They may be different. Specifically, the main difference is the amount of heat they are able to withstand.

This device is quite simple in terms of its operation. It is made of aluminum alloy and is attached using a flange connection, ensuring reliable contact with the area where the temperature is measured. There is a bimetallic plate installed inside the case, which can resist a certain temperature. And if the temperature value goes beyond a certain limit, then the plate compresses and activates the pusher, and it opens the circuit of the contact group. The supply of electricity to the unit then stops, the magnetron turns off and gradually cools down, the plate returns to its initial position as the magnetron cools. Through certain time the contacts close again.

This is the simple principle of operation of a microwave oven, in particular the overheating fuse. Note that in cheap models this element may be absent, since it is completely unnecessary for normal functioning devices. This is only a protection element that increases the reliability and service life of the stove, nothing more.

The role of the cooler

When talking about how a microwave oven works, the principle of operation must be explained taking into account all structural elements, which can be used in it. Cooler is one of them. Of course, this is an important component of the system, without which the device and operation of the microwave will not be complete.

His tasks:

1. Magnetron cooling. This is the most important task, without which the magnetron would burn out on the very first day of using the furnace.
2. Cooling other components that generate heat during operation. In particular, we're talking about about microcircuits.
3. In models with a grill, the cooler cools the thermostat.
4. Creating excess pressure in the chamber where the food is located. Because of this, vapors and air are removed through the ventilation ducts.

Most often, just one fan is enough to perform all these functions. Due to the presence of air duct holes in the chamber, the air itself is distributed evenly.

Camera device

In principle, the physics of how a microwave operates is not complicated, because it has been known since school that strong electromagnetic radiation is dangerous for humans. It is this that comes from the magnetron and enters the chamber with food, so this device requires a strong multi-level protection system.

All working chamber The inside is covered with enamel, which blocks electromagnetic radiation. There is a metal casing on top that prevents waves from penetrating into the room. And to protect the glass door, a steel mesh with small cells is provided - it blocks radiation with a frequency of up to 2450 Hz and a wavelength of up to 12 cm.

Note that the door is the most weakness, through which microwaves can leak, so it should fit as tightly as possible to the housing and have no gaps. If there is a gap, the operation of the device is prohibited. In this case, it is necessary to adjust the door hinges and return it to its original position.

In addition, the microwave operating algorithm provides for the use of a special protective device against switching on door open. Similar system can be implemented in different ways, most often microswitches are used to control the position of the door. These switches can turn off the magnetron and transmit information about the door position to the control unit.

Control Panel

It is available on any model. In older devices, the control panel is represented by just two (or even one) mechanical switches. One sets the operating mode (heating, defrosting, etc.), the other sets the time. The scheme is primitive, but working and simple.

However modern models equipped with a large touch panel. Such control panels provide the user with great functionality and even the ability to program the mode. For example, you can set a specific start time for heating food, the duration of the process, you can even specify the food or dishes that will be heated. And although it seems that such devices are more advanced, in technically there are few differences. The electronic control panel does not change how the microwave operates.

Control block

There is a command device in every device (not only in microwave ovens), where at a certain moment one or another action must be performed. Thanks to it, various functions are provided. In particular, the device can use it to maintain a given temperature, turn the oven on or off after a given operation.

In older microwave ovens, this device is presented in the form of two electromechanical switches - they are responsible for the functions described above and play an important role in the overall structure of the microwave. Of course, over time, electronics evolved, and as a result, completely electronic components management. Nowadays, microwave ovens (and not only them) use microprocessors and special programs, according to which the device can perform one or another function:

1. Built-in clock.
2. Defrosting food.
3. Sound signal when defrosting, cooking or heating food is complete.

Conclusion

Now you have a more precise understanding of how a microwave works. The operating principle of this device is relatively simple. It is based on the elementary laws of physics.

Let's consolidate what we have learned: the magnetron (the main element of a microwave oven) emits very short radio waves with a high frequency. They affect water molecules, causing them to begin to actively move. This process is accompanied by the release of heat. Considering the fact that the waves penetrate shallowly into the food, only the surface of the food is heated, and then, due to natural thermal conductivity, the heat moves deeper.

This is the basic principle of operation of a microwave oven. We also reviewed the device and main elements in this article. All of them are classic and are used in absolutely all models from any manufacturer. On this moment the working scheme described above is the only one, although different manufacturers can use modules that differ in some parameters. For example, one model may use a more powerful magnetron, which can heat food much faster. In other compact models, this element may have low power, which allows you to create a small device. Similar differences hundreds, but the principle of operation does not change at all. Of course, a stronger magnetron determines how long the microwave operates to heat food of the same volume. Therefore, if you don’t like to wait, then it is better to choose a more powerful model.

That's all. We have completely disassembled the structure of this piece of household appliance and answered most of the questions related to it.