A microwave works in almost every modern apartment. This convenient household appliance can heat, defrost, bake. Some models are capable of grilling and complex programs for cooking inside ready meals. The principle of operation of the microwave has not changed since its invention. But thanks to the achievements of technological progress, the safety of the equipment has increased, and the electrical circuit is able to carry out comprehensive control and precise control of operation parameters.
General principle of the microwave oven
The physics of the process of heating the contents of a microwave oven is quite simple. Microwave radiation affects the molecules of products, and due to their mutual friction, heat is released. But this is too simple an explanation.
In fact, fluctuations are only water molecules. But if you put a perfectly clean glass of distilled liquid in the microwave, then its temperature will change quite a bit during the standard operating time of the oven. So why do foods get hot? This is due to the friction of molecules at the interface between media, that is, different substances. And since the structure of any material, be it an edible product or a piece of wood, is large and necessarily has water in its structure, fluctuations of different amplitudes arise.
Important! The frequency of the microwave oven is designed to have the maximum impact on the molecules of the liquid. It is they, with their intense vibration and friction against their neighbors, that contribute to the release of a large amount of heat. Dry and chemically pure materials heat up very slowly, but there are few of them in nature.
Do not put metals in the microwave. When exposed to microwave radiation, surface currents are formed and spark, arc breakdowns occur on the walls of the inner compartment of the furnace. However, technological progress has found a way out. Today, many companies, such as Daewoo, produce microwave ovens that you can put metal objects. Also, in many models, the use of closed contours is allowed, in particular, plates with foil stamping along the edge or decorative dishes with a metal border.
What elements are in the design of the microwave
The device of a microwave oven only at first glance seems complicated. The owner of this device is misled by the number of buttons, indicators, programming tools. In fact, any oven, with mechanical control, touch panel, remote control, hybrid electronic control, consists of the same functional blocks:
- microwave radiation generation unit, magnetron and waveguides;
- voltage conversion system, the main module is a step-up high-voltage transformer;
- control means as part of a group of sensors;
- secondary protection system;
- microwave control circuit.
Important! Depending on the complexity of the furnace model, a variety of options may be included in it. For example, a grill, secondary wave diffusers, additional microwave generation units.
It is worth considering the operation of each unit separately, in the order in which they are used in the standard scheme for using a microwave.
The main electrical circuit of the microwave that the user is dealing with is the control unit. In it, with the help of buttons, mechanical switches, regulators, boundary parameters are set. That is, operating power or mode, program execution time, and so on.
The control scheme can be arbitrarily complex. The simplest option is circular controls, one of which is a timer relay. With their help, the power of the mode and the operating time are set. Another option familiar to users is hybrid, with buttons. In fact, its functionality is not much wider than mechanical adjustment.
Touchpad, in most cases, does not differ in principle from buttons. It is simply more reliable and requires no maintenance. Advanced electronic control schemes include programming, that is, switching according to a given algorithm for the radiation power and the time of its issuance.
Voltage conversion system
The microwave oven consists of a group of nodes that are very dangerous for humans. Chief among them – step-up transformer. When the control circuit gives a command to turn on the mode, it produces up to 4 kV of voltage. In this case, the operating current can reach 10A and above. Such parameters of the electrical network pose a huge danger to humans.
Important! The step-up transformer is the key and most expensive node of the voltage conversion system. It powers the magnetron, the element without which it is impossible to implement the basic principle of the microwave oven.
Microwave radiation generation unit
The magnetron is the heart of the microwave. In essence, this is a common vacuum lamp, similar to those used in kinescopes of old televisions. Only the magnetron generates an intense electromagnetic wave of high frequency, formed when electrons pass through a magnetic field.
The radiation generation unit does not consist of a single microwave source. For, so to speak, the supply of waves to the working zone of the furnace are installed waveguides. It is they who are behind the mica plate that everyone saw on the side wall of the microwave when they put a plate of breakfast in it.
Primary and secondary protection systems
The role of control sensors is quite clear. They make sure that none of the key elements of the electronic and hardware part goes into a critical mode of operation. Sensors guarantee trouble-free operation of the device and prevent dangerous malfunctions. But the microwave has protection systems designed for humans. Their functions will be described in detail below.
So, the control system initializes the start of the magnetron. It also sets operation parameters, counts time intervals, changes power, and so on. There is also feedback between security and control systems. According to the signals of the first, the operation of the furnace can be completely stopped, the mode is changed, a service message or sound alerts are issued.
Schemes of distribution of microwave waves
First, it is worth dwelling on the operation of the microwave generation unit. The structure of the magnetron is a radiating element and a winding that generates a magnetic field. This lamp, roughly speaking, constantly wears out. Everyone was faced with a situation where, with the course of operation, the microwave heats up weaker and weaker. This is a normal phenomenon, each model sooner or later requires magnetron replacement.
In furnaces of different manufacturers (or levels of complexity), different schemes for distributing microwave waves can be used. In the standard solution, which uses LG and many other manufacturers, only one waveguide goes from the magnetron to the product area. It is covered with a mica plate to prevent debris and steam from entering.
Important! Models with a single waveguide, which radiates a fairly localized wave stream, use a reflector on the opposite side of the product compartment. This is the concave zone of the wall. It helps to more evenly distribute microwave radiation over the working volume.
Some microwaves Samsung a different principle is used: the main waveguide and several slot antennas are installed. This allows you to evenly distribute the flow of energy, to form the so-called 3D radiation. In addition, the oven, by varying the power of the magnetron, achieves smooth heating of products throughout the volume.
But the most important thing in the generation of microwave waves is their parameters. The radiation frequency of the magnetron in the microwave is 2.45 GHz – it is this value that is resonant for water molecules, causing them to oscillate with a large amplitude. The product is heating up. Heat from the surface layers gradually spreads throughout the entire volume of the product.
There are some solutions that allow you to speed up the heating of food in the working area of \u200b\u200bthe oven. These are the so-called dissectors. In appearance, such a structural element is similar to a fan on the ceiling of a microwave chamber. However, it does a different job, namely it scatters microwave waves.
Other functional elements of the furnace have a completely understandable purpose. For example, a microwave with a grill acts on food not only microwave, but also infrared radiation. It allows you to achieve a beautiful baked crust on products. Some models of furnaces can be equipped with additional fans for heat dissipation.
How the protection system works
It is also worth highlighting in detail the functioning of security systems. They fall into two significant groups.
- Control of hardware parameters. These are the magnetron temperature sensor, fuses, cooling fans. They solve the problem of blocking potentially emergency situations and maintaining the normalized performance of electronics.
- Human protection from electric shock and microwave radiation.
Anyone who has ever taken apart the body of their microwave oven has encountered electric current protection systems. Microswitches are located at key mounting points. After removing the cover, the oven can no longer be turned on. This simply will not allow the protection system.
But more interesting is the scheme for neutralizing microwave waves. It should be understood that radiation, even theoretically, cannot be localized inside the furnace chamber. Waves are reflected, including from products. Therefore, on the front door is installed glass with a thin metal grating applied to it. This is an antenna module. It is connected to a spark gap, which gives off the accumulated energy by surges to the main power supply of the device.
Important! The microwave generates wiring noise. In some houses, this can be fixed by the operation of other devices (in particular, Wi-Fi routers), especially if a frankly cheap stove with poor noise suppression is used.
Microwave circuit diagram
Based on the foregoing, it is not difficult to understand how a microwave oven is arranged, simply by looking at it from the outside, looking into the camera and to the rear. But if you want to fix something, it is useful to understand in general terms how the nodes interact with each other. A circuit diagram of a microwave oven will help with this. Its structure only at first glance seems complicated. However, any scheme consists of basic blocks. As an example, it is worth looking at the device of a model with mechanical analog control.
The diagram clearly shows how energy is converted and security systems work. One of the very first contours is always squelch (NOISE FILTER). It is he who dampens the vibrations that the energy arrester forms in the door, protecting a person from high-frequency radiation.
Then comes basic security system. This is a block of contacts in the door, one monitors the fit to the body, the second is the position of the latch, the third is the position of the handle. If any of them is open, the oven will not work.
Third functional block − drives and lights. Everything is simple here. A constant voltage is applied to the motor that turns the dish, to the fan and the lamp. The timer opens the circuit at the end of the set time interval.
Last working circuit – step-up transformer, magnetron temperature control sensor, its breakdown protection system and fuse. And it always ends the same way. The main working body of the furnace, the magnetron.
As a conclusion
Despite the fact that the microwave may seem an extremely complicated and even dangerous device, it is recommended. service regularly. It’s safe and easy. Opening the case to remove dust from the hardware is not worth it. It is enough to keep clean the surface of the walls of the food compartment, the door glass. Periodically carefully remove and wipe the mica plate covering the waveguide. And then the microwave will maintain stable parameters for the entire period declared by the manufacturer.