How a microwave oven works - a household electrical appliance for quickly heating and defrosting foods, not all of its owners know. This often causes breakdowns and even accidents. Knowing the device of the microwave oven, the user will be warned of possible malfunctions and the dangers that await him during self-repair.
Microwave principle
The principle of operation of the microwave radically differs from conventional ovens. Products penetrated by microwave waves are heated throughout the entire volume, and not on the surface, as during thermal exposure. That is why the warm-up / defrost process is so short.
The heating of food occurs due to a physical phenomenon - electromagnetic microwave fields are converted into heat. In the microwave oven, only the product itself is heated, energy is not wasted on heating the camera itself, which means that energy is saved.
Microwave action is able to raise the temperature of the object in minutes to the value needed by the user. This is especially convenient when defrosting: a huge piece of frozen meat can be heated in a matter of minutes without changing its properties.
Food heating is triggered by the action of high-frequency waves, their frequency is 2,450 MHz. These microwaves, passing inside an object, polarize water molecules. Under the influence of radiation, molecules are built along the lines of force of the electromagnetic field.
The directed movement of molecules causes an increase in the temperature of the product throughout the volume. Microwaves, penetrating the depth of the object by 2.5–3 cm, heat the water molecules, and the heated sections of the object transfer heat further - in this way the entire volume is heated.
How is the microwave
Components of a microwave oven:
- Camera. Made of metal. Equipped with a metallized door. Microwave radiation is concentrated here. Here they put food for warming up. Requires care.
- Magnetron. High frequency microwave emitter.
- Transformer. Magnetron power source.
- Communications and management system.
- Waveguide. Transmits microwaves from the emitter to the camera.
Additional details:
- Pallet. Rotating, it contributes to uniform heating of cooking objects.
- Fan. For airing the chamber and cooling the magnetron.
The operation of a microwave oven is reduced to the release of energy by a magnetron, which is converted into heat. The device is connected to a stabilizer transformer. Once this device was the most expensive in a microwave oven, today its cost has decreased and microwaves have become much more affordable.
The circuit diagram for all microwave ovens is almost the same, they only have different characteristics, capabilities and design.
What is a magnetron?
Its purpose is the generation of radiation of a given frequency. In fact, this is an electrovacuum diode. Its structure:
- It has a cylinder shaped anode. It has a circular cross section and ten sectors with copper walls.
- In the center of the diode is the cathode. Inside it is an incandescent thread. The function of the cathode is the emission of electrons.
- Along the edges of the magnetron are magnetic elements of a ring-shaped form. Their task is to create a magnetic field in the emitter. This field is a generator of high-frequency waves.
- The voltage applied to the anode is 4,000 V, and to the cathode filament is 3 V.
Due to the voltage difference, the cathode emits electrons, which catches the electric field with high tension. The generation frequency depends on the configuration of the resonator chambers and on the voltage of the anode.
Energy is removed through a loop of wire that connects to the cathode and is output to a radiating antenna. The radiation from the antenna is directed to the waveguide, through which it passes into the microwave oven.
In conventional microwaves, 0.8 kW magnetrons are used. It happens that to cook a dish, you need power less than 0.8 kW, then the device turns on for short periods of time, interspersed with pauses.
This principle of operation is known as pulse width modulation. Since the magnetron, while working, heats up, it is placed in a plate-type radiator, which constantly blows the fan. Overheating can cause damage. To prevent this, install a special thermal fuse.
What a thermal fuse consists of
These devices are also known as thermal relays. They are produced for different nominal temperatures.
The thermal relay consists of an aluminum case, which is attached to the temperature control point by a flange connection, and a bimetallic plate tuned to a specific temperature value. When the heating exceeds the permissible threshold, the plate, bending, starts the element opening the contacts - the power to the stove is stopped.
When the magnetron cools down, the bimetallic plate will take its original shape and the contacts will close - the oven will turn on.
Fan Description
Without a fan, operation is not possible. Its functions:
- Blowing a radiation source and other components of an electronic circuit that produce heat.
- If there is a grill, then the fan blows it too.
- In the chamber, during cooking, a lot of heat and steam is generated. Thanks to the fan, increased pressure is created, squeezing warm air and steam through the ventilation holes.
The fan is located near the rear wall of the device. Sucking in air from the room, it directs the air flow through the air ducts to the magnetron plates, and then into the chamber. The fan blades are driven by an AC induction motor.
How the door works
Thanks to the lock that works when the door is opened, users are protected from exposure. The door device is quite complicated - the owner’s safety depends on the serviceability of its operation. The door design provides security measures:
- Tight fit to the body. A stove with large gaps cannot be used. Radiation can go beyond the chamber through the gaps. The metal casing of the apparatus and the special groove of the door must be separated by a gap whose width is equal to ¼ of the length of the microwave. In this gap, an electromagnetic wave of a standing type is formed, which has zero amplitude at the place where the door adjoins the case, which is why it does not go beyond the camera. This method of protection - from waves using the waves themselves - is called a microwave choke.
- Along the perimeter of the door there is a high-frequency throttle damper, which reduces radiation to a safe level.
- When casting the door casing, various additives are used, due to which the metal absorbs radiation better. They do not provide 100% absorption, but attenuated waves definitely do not pose a danger to humans.
- To prevent the stove from turning on when the door is open, the device has a system of switches that control its position. As a rule, there are three switches - to turn off the magnetron, to turn on the backlight and to transmit a signal to the control unit. The setting and arrangement of microswitches does not allow them to operate with the door open.
Protection system
Every microwave is a source of powerful radiation that can cause great damage to the human body and all living things. To protect others from exposure, the device is shielded by a metal casing through which high-frequency radiation cannot pass.
The door is equipped with transparent glass so that the user can observe the processes of heating, cooking, defrosting. Glass is also shielded - it has a fine-mesh metal mesh that prevents the penetration of microwaves.
Control unit design
The tasks of the control unit - the “brain” of the microwave oven:
- Maintain set power.
- Turn off the oven at the end of the process.
In earlier versions, control was carried out by two mechanical switches: one set the power, the other - time. Today, the devices are equipped with electronic and microprocessor control units that control, in addition to the two named, many functions - important and unimportant. For example:
- built-in clock;
- sound signal about the end of the process;
- power display;
- cooking according to special programs “sewn” into the memory of the block.
Types of Microwaves
Consider the main types of stoves you can buy.
With grill
These devices have a heating element - heating or quartz. The first is placed in different places of the camera and in a different position, it is quite reliable and inexpensive. Quartz is installed only at the top. It is more powerful than heating oil, but costs more.
In grilled stoves, you can easily cook kebabs or bake chicken with a crispy crust.
An example of a microwave with a grill is the LG MH6022D. This model is equipped with a 600 W quartz grill and has mechanical control. Her characteristics:
Capacity, l | 20 |
Dimensions (WxHxD), mm | 455x284x347 |
Weight, kg | 13,5 |
Colour | white |
Power, W | 700 |
Cost, rubles | 6 000-7 000 |
With convection
It will be useful to those who like to bake. Thanks to convection, you can cook using warm air. This allows you to get delicious homemade cakes. Heated air, circulating around the cooked dish, bakes it evenly.
The device operates in a combined mode - microwave plus convection. This mode allows you to cook dishes faster than in a conventional oven, which means that more vitamins are stored. The oven, equipped with both grill and convection, replaces the stove and oven. Here you can cook everything - from compote to barbecue.
A striking example of a microwave oven with grill and convection is the Samsung MC28H5013AW. Her characteristics:
Capacity, l | 28 |
Dimensions (WxHxD), mm | 517x310x475 |
Weight, kg | 17,5 |
Colour | white |
Power, W | 900 |
Cost, rubles | 14 000 |
With inverter
In traditional devices, the power is regulated by switching the radiation - on / off. Because of this, food is often overdried. Thanks to inverter control, power is regulated smoothly. Built-in inverters allow you to save the texture and usefulness of the cooked products.
Such models, having recently appeared on the market of microwave ovens, have already become popular.
An example of an inverter model is the Panasonic NN-GD371M. Parameters:
Capacity, l | 23 |
Dimensions (WxHxD), mm | 488x279x395 |
Weight, kg | 10 |
Colour | silver |
Power, W | 950 |
Cost, rubles | 15 000–16 000 |
Small microwave ovens
Mini-microwave ovens are usually designed only for heating and defrosting. These are budget models without grilling and convection. They have a small capacity and size. They do not have a rotating pan.
They are chosen for cramped kitchens. Dainties are not cooked in them - they only heat and thaw foods.
An example of an inexpensive but durable model is the Daewoo KOR-5A0. Her characteristics:
Capacity, l | 15 |
Dimensions (WxHxD), mm | 230x430x310 |
Weight, kg | 9 |
Colour | white |
Power, W | 500 |
Cost, rubles | 4 000 |
Uniform distribution of microwaves
A major drawback of conventional microwave ovens is the uneven distribution of microwaves. Result: in one place the food is too hot, in another it is barely warm. The reason for this phenomenon is the concentration of microwaves in one area. To eliminate this defect, manufacturers instead of one emitter install three at once.
One of the currently popular technologies is I-wave. In devices with this solution, the waves propagate in a spiral.
An example of such a device is the LG MS2043HS. Specifications:
Capacity, l | 20 |
Dimensions (WxHxD), mm | 260x450x330 |
Weight, kg | 11,5 |
Colour | white |
Power, W | 700 |
Cost, rubles | 6 000 |
Useful Tips
- For networks with frequent voltage drops, a voltage stabilization device is required. If the mains voltage surges, the first touchscreen LCD screen will fail.
- Do not forget to buy a care product in a specialized store.
- Check the warranty card. The store where the goods are purchased should cooperate with a specific service center - from the manufacturer.
- The pallet is usually made of glass. Check for chips and other defects.
- Be sure to inspect the goods and check the equipment.
What precautions are important to know
- Do not cook in metal utensils. Firstly, the waves do not pass through the metal, and secondly, metal objects placed in the stove can cause damage to the furnace.
- It is forbidden to heat liquid products in a closed container. Inshell birds cannot be cooked - a mini-explosion may occur. This also applies to sausages in a plastic film.
- Use caution when heating water - it may heat up above the boiling point. Such water can instantly boil when moving. This is especially the case with water placed on smooth-walled dishes. From dishes with a narrow neck, water can simply spill out and burn your hands.
- Do not place cookware with metal spraying. A thin layer of metal heated by eddy currents can cause cracking of dishes.
When choosing a microwave oven, often the consumer pays attention only to the brand, design and cost. As a result, a thing is acquired that does not meet the needs and expectations of the consumer.
Knowing the device and the principle of microwave operation, you will not only easily buy the right model, but also protect yourself from harmful effects.