- Home >> Solution >> Appliances >> cookers
Microwave Solution
Microwave oven is a product of the development of electronic and electrical technology. It has the advantages of convenient use, energy saving and time saving, less pollution and the ability to maintain the original color and taste of food. Because the microwave oven works under the condition of high pressure, high heat and high humidity, failures such as failure to start, no heating, insufficient firepower, intermittent operation, fire in the furnace and frequent burning of fuses often occur, and some failures are difficult to repair. A thorough understanding of its basic structure and principles is required.
1. What is microwave?
The wavelength is in the range of 10mm to 1m. The frequency between 300MHz and 300GHz is called microwave, and the modern cooker that uses high-frequency electromagnetic waves with an oscillation frequency higher than 24.6GHz as heating to cook food is called microwave oven. It was discovered by American radar engineers in an accidental experiment. In the 1940s, people used the characteristics of microwave heat to manufacture the world's first microwave oven. It was originally used in industry and commerce. family, become the best in cookware.
Microwaves, radio waves, infrared waves, etc. all belong to electromagnetic waves. When they interact with other substances, they will be absorbed and generate heat inside them. Various substances have different absorption abilities to microwaves. For example, metal materials such as gold, silver, copper, and iron are conductors. Microwaves are reflected on the surface of these good conductors and are rarely absorbed. They cannot be heated by microwaves; glass, ceramics, Although plastics and other media are insulating materials, due to their weak ability to absorb microwaves, the thermal effect produced is also very small; water molecules are polarized molecules that can strongly absorb microwaves, so water-containing substances can be heated by microwaves. The remarkable feature of microwave is that it can penetrate the surface and reach the inside of the object, so as to obtain the ideal effect of cooking food. Using microwave ovens to process food saves electricity and time and has little damage to the nutritional value of food. The dishes cooked with it can basically maintain the natural color, fragrance and nutritional content.
2.Types of microwave ovens
There are a wide variety of microwave ovens of various brands on the market. Microwave ovens can be divided into two categories: ordinary electromechanical type and microcomputer (chip) control type according to the control and operation methods.
For ordinary electromechanical microwave ovens, its structure and operation are relatively simple, and the control part adopts electromechanical type, which is operated by mechanical knobs, which is intuitive and easy to grasp. The function of popular type microwave oven in this class product is single, only microwave energy is not used to heat food by other means, and its structure is the simplest in all varieties.
Microcomputer-controlled microwave ovens refer to models that use microcomputer chips to control heating time and methods. Most of these microwave ovens have two heating functions of microwave and grill at the same time. The operation panel is mostly light-touch key switches. Users can press different keys according to the type and quantity of food to be heated, and input operating data such as heating time and power. Thanks to the microcomputer, the microwave oven will work as required until the cooking is done.
3. The working principle of the microwave oven solution
The basic principle of the microwave oven is shown in Figure l. When the microwave oven is powered on, the magnetron M A G (Magnetron) in the furnace will generate microwaves with a frequency of about 2450MHz, and then a microwave stirrer will send the microwaves to various parts of the furnace (or turn the food through the turntable to rotate the microwave). And accept microwaves more uniformly). The oven door is usually made of two layers of transparent glass sandwiching a layer of metal mesh that can shield microwaves, so the microwaves cannot leak out, and will be reflected inwards on the metal walls of the oven, and will be continuously absorbed by the food. When the microwave penetrates and acts on the food in the oven, the polar molecules in the food vibrate at a very high frequency of 2450M Hz, and the heat generated by the vibration makes the food heated. However, the penetrating power of microwaves is only 2.5-3.9 cm. If the food is too thick, the part that has not been penetrated can only be cooked by means of heat conduction.
The grilling function of microwave ovens is usually realized with quartz heating tubes. The quartz heating tube is installed on the outer wall of the oven cavity. After power on, it emits infrared and far-infrared heat energy and radiates into the oven cavity, making the surface of the food get heat radiation energy and turn yellow and become brittle. ability.
4. The structure principle of microwave oven
The physical schematic diagram of the microcomputer-controlled microwave oven is shown in Figure 2. From Figure 2, you can clearly see the appearance of the microwave oven and the main structure in the oven cavity. In the picture:
① It is a safety interlock switch for the furnace door, which is used to ensure that the microwave oven cannot work when the door is opened, and the microwave will not leak, so as to ensure the safety of the operator.
② It is a screen window with a metal shielding layer, which is used to shield microwaves, and at the same time, it is convenient for operators to observe the cooking status of food in the furnace.
③ is a vent, used to maintain good ventilation.
④ is the turntable support frame, the effect is to support the glass turntable, and make it rotate according to its orbit.
⑤ is the rotating shaft that drives the glass turntable to rotate.
⑥It is a glass turntable for holding food, which can heat the food evenly when turning.
⑦ is the operation control panel, which mainly includes light touch key switches and digital displays.
⑧ is the furnace door switch button. Except for the two knobs of the timer and the fire regulator on the control panel of the ordinary electromechanical microwave oven, the others are similar to those in Figure 2.
The grilling function of microwave ovens is usually realized with quartz heating tubes. The quartz heating tube is installed on the outer wall of the oven cavity. After power on, it emits infrared and far-infrared heat energy and radiates into the oven cavity, making the surface of the food get heat radiation energy and turn yellow and become brittle. ability.
4. The structure principle of microwave oven
The physical schematic diagram of the microcomputer-controlled microwave oven is shown in Figure 2. From Figure 2, you can clearly see the appearance of the microwave oven and the main structure in the oven cavity. In the picture:
① It is a safety interlock switch for the furnace door, which is used to ensure that the microwave oven cannot work when the door is opened, and the microwave will not leak, so as to ensure the safety of the operator.
② It is a screen window with a metal shielding layer, which is used to shield microwaves, and at the same time, it is convenient for operators to observe the cooking status of food in the furnace.
③ is a vent, used to maintain good ventilation.
④ is the turntable support frame, the effect is to support the glass turntable, and make it rotate according to its orbit.
The basic circuit block diagram of a microwave oven is shown in Figure 3. It can be seen from the figure that the common electromechanical microwave oven can be divided into three major parts, namely: the furnace cavity (furnace body), the magnetron and the power regulation circuit (the circuit in the dotted line box in Fig. 3). Microcomputer-controlled microwave ovens have more microcomputer control parts than ordinary electromechanical microwave ovens, which are mainly composed of computer control circuits and control panels. The cavity of the microwave oven is the place where food is accommodated, and is used to receive microwave energy and heat the food; the magnetron is used to generate microwave energy, which is the "heart" of the microwave oven; the power supply and power regulation circuit in the dotted line box in Figure 2 contains A number of circuits are used to supply power to the magnetron, blow and cool the magnetron, adjust timing and power (firepower), illuminate the oven cavity, and rotate the turntable, etc. Obviously, the core device of the microwave oven is the magnetron , the furnace body and food are the service objects of the magnetron, the power supply and power regulation circuit are the necessary equipment to ensure the normal operation of the magnetron, etc., and the microcomputer control part mainly uses several relays controlled by the micro-processing chip circuit to replace the ordinary microwave oven. The timer and power controller and other components can be used to increase and enhance the function of the microwave oven and facilitate operation.
5.Microwave oven circuit design principle
The electrical schematic diagram of a typical ordinary electromechanical microwave oven is shown in Figure 4. The working state of the microwave oven shown in the figure is the stop state, that is, the oven door is opened and the timer is in the off position. At this time, the main interlock (safety) switch s 1, the sub interlock (safety) switch s 2 and the timing switch s 4 that are linked with the oven door or controlled by the oven door switch are all in the off state, so the power supply of the microwave oven is cut off , the stove doesn't work.
When we use a microwave oven and need it to work, we usually first adjust the power (firepower) size and position according to the type and amount of processed food, then open the oven door, put the food and then close the oven door. When the oven door is opened, the microwave oven is in the above stop state; when the oven door is closed, the interlock monitoring switch s3 linked with the oven door turns from closed to off, and then the main and auxiliary interlock switches s1 and s2 are turned off. Open to close. At this time, the working time is set for the timer, and its switch s4 is turned on. At the same time, the power control switch s5 of the power regulator in the adjusted state is also in the intermittent conduction state, and the on-off time ratio is determined by the set power It depends on the value, and it is fully on when the output power is full. In this way, the power circuit of each component of the microwave oven is connected, and the 220V power is supplied to the motor M I through the fuse tube F1, the overheat protector ST and s4, sl, s5, s2, etc. M 3. On parts such as high-voltage transformer T and lighting lamp L H, the furnace starts to work. Among them, the lighting lamp LH in the furnace lights up to illuminate the furnace cavity, so that the operator can observe the cooking and working conditions of the food in the furnace and the turntable; the timer motor M1 rotates, and the timer starts to time the microwave oven. ． The turntable motor M 2 is energized to rotate, driving the glass turntable and food to rotate; the fan (cooling) motor M 3 drives the fan blades to rotate. Air-cool the magnetron M A G to prevent it from being damaged due to overheating. At the same time, it also has the effect of cooling and ventilating the high-voltage transformer T and the furnace cavity. If it is set to the maximum, the power switch s5 is normally on.
At the same time, the primary winding L1 of the high-voltage transformer T is energized to work, and a corresponding voltage is induced in the secondary winding, and its secondary low-voltage winding L3 outputs an AC voltage of about 3.3V, which is used as the filament (cathode) voltage of the magnetron MAG , so that the cathode of M A G is heated and emits electrons. The other secondary winding L2 is a high-voltage winding, and the output is an AC voltage of more than 2000 volts. Through a half-wave voltage doubler rectifier circuit composed of a high-voltage diode V D and a high-voltage capacitor c, it outputs a DC high voltage of about 4000V, which is applied to both ends of the magnetron. , so that a high-voltage electric field is formed between the anode and the cathode of the magnetron, so the magnetron starts to work, and converts the electric field energy into microwave energy with a frequency of about 2450MHz, and emits (sends) it to the furnace cavity: the microwave is reflected back and forth in the furnace cavity , constantly penetrating the food in the oven cavity, making the molecules of the food vibrate violently at an ultra-high frequency of 2450M Hz and quickly heat up, so that the food is quickly heated and then cooked, achieving the purpose of microwave heating and cooking.
When reaching the set timing time, the food heating is completed, the timing switch s 4 is switched from on to off, the high-voltage transformer of the microwave oven, each motor and the lighting lamps in the oven are all cut off, and the oven stops working. If the furnace door button is pressed for reasons such as flipping food before the preset timing time, at this time, at the moment the furnace door is opened, the chain safety switches S1 and S2 are also disconnected successively, and the same is true. The power supply of each part of the microwave oven is cut off, so the stove stops working. At this time, operations such as flipping food or taking out food can be safely performed, and then the microwave oven can continue to work or stop working according to the cooking situation.
The important chain protection safety device of the microwave oven is composed of the main chain (safety) switch S1, the secondary chain (safety) switch S2 and the monitoring (safety) switch S3, etc., and its function is to prevent microwave leakage. When the furnace door button is pressed and the furnace door will be opened, the interlock switches S1 and S2 are disconnected to cut off the power supply of the microwave oven to ensure that the microwave oven stops working at the moment the furnace door is opened, thus ensuring that the microwave oven cannot work when the door is opened. Microwaves will not leak to ensure the safety of operators.
Because the interlock switches S1 and S2 may fail or be damaged, the microwave oven may still be working after opening the oven door, and the microwave will leak and hurt people. Although the probability of this situation is not high, it is very dangerous once it happens , so the monitoring (safety) switch is generally set in the microwave oven, which is s 3 in Fig. 4 . s 3 is linked with the oven door and closes when the oven door is opened. If S 1 is not disconnected due to failure and the power is still on, then s3 will short-circuit the power circuit of the microwave oven and blow out the fuse tube in the oven. F l, forcibly cut off the power of the microwave oven, thereby ensuring the safety of the operator. The setting of s3 is necessary, and its function is also clear. It adds a safety barrier to the microwave oven. When the monitoring switch s3 has a short circuit or malfunction, it may cause the fuse tube of the microwave oven to be blown repeatedly. At this time, if you disconnect or disassemble s3, the fuse tube will not be burned again, but do not mistakenly think that it has no effect and turn it on casually. It is very wrong to remove s3 or change its position, or even subjectively assume that setting s3 is a defect in the circuit design. The correct way should be to replace it with a good switch in time and ensure its reliable operation before using the microwave oven.
The working temperature rise of the microwave oven magnetron MAG is relatively high, so a fan should be used to blow and dissipate heat to prevent it from being damaged due to overheating. The blades of the radiating fan are driven by the motor M3, and the fan also plays a ventilation and cooling effect on the high-voltage transformer and the furnace chamber. Although there is a fan for heat dissipation, the magnetron may still be overheated and damaged due to fan failure and other reasons during work. Therefore, a magnetron self-recovery overheat protector is usually installed in the microwave oven. ST in Figure 4 is the magnetron overheating protector. It is installed on the shell of the magnetron tube, and its action temperature is the limit temperature allowed by the shell of the magnetron tube or slightly lower. When the temperature rise of the magnetron tube is too high for some reason and reaches this value, the ST acts to cut off the power supply, thereby Prevent the magnetron from overheating and burning out. The action temperature of the overheat protector is generally 125-150°C, and the self-recovery temperature is 20-40°C lower than the action temperature. In addition to setting an overheating protector on the magnetron, some microwave ovens also set up an overheating protector on other parts that generate more heat, such as the furnace wall, to prevent related parts from being damaged due to abnormal overheating.
A typical electromechanical microwave oven circuit with barbecue function is shown in Figure 5. This is a product produced by Japan's Sharp. The names and representations of its components are quite different from those in Figure 4. You may wish to familiarize yourself with them, which will be beneficial to maintenance work. There are many brands and varieties of microwave ovens nowadays. Due to various reasons, there are many differences in the circuit diagrams and components of many domestic and imported microwave ovens, which brings inconvenience to some maintenance personnel and enthusiasts. As far as components are concerned, the main interlock switch s 1 in Figure 4 can also have the following titles in other circuit diagrams: first interlock switch, door bolt switch, snap key switch (up and down), interlock safety switch wait.
Figure 5 shows a typical circuit of a microcomputer-controlled microwave oven. Compared with Fig. 4, Fig. 5 has more microcomputer control circuits, except that timing and power regulation control circuits are performed by microcomputers, and other circuit structures and principles are basically the same as those of ordinary electromechanical microwave ovens. The essence of this circuit is to replace the timer and power controller in Figure 1 with the relays RY1 and RY2 controlled by the microprocessor chip circuit, so the electromechanical timer and power controller in Figure 4 are not needed here up. If you don't look at the microcomputer control part, the main circuit structure of the two is similar. The function of the high-voltage fuse (H.V.F U SE) in Figure 5 is to protect the components of the high-voltage circuit. The microcomputer control circuit is usually composed of a computer control board and a control panel circuit, and the control panel is mostly composed of membrane switch keys, time, digital display devices and other components. The microcomputer control circuit is generally powered by a dedicated low-voltage power supply circuit. The maintenance practice shows that the failure rate of the microcomputer control circuit of the microwave oven is low, and the failure rate of the relay, the membrane switch keyboard circuit and the power circuit are more common.
6. Design of new intelligent microwave oven
1. Definition of Smart Microwave Oven
Smart microwave ovens can also be called Internet of Things microwave ovens, which are implanted with new technologies such as sensor technology, microprocessors, and network communication technologies in traditional microwave ovens. Controls query functionality. Such a microwave oven is an intelligent modern microwave oven.
2. The main components of the smart microwave oven
Smart microwave ovens get rid of the single individual form of traditional microwave ovens and exist in the form of a system. The system includes four parts: IoT smart microwave ovens, cloud, control terminals, and other home appliances. In the recipe query stage, the IoT microwave oven needs to obtain the existing ingredients information of the refrigerator, and at the same time, it needs to obtain the working information of other home appliances during the working process. Therefore, the Internet of Things microwave oven needs to exchange information with other household appliances in a timely manner.
(1) Smart IoT microwave ovens and the cloud: IoT microwave ovens can store certain recipes locally, but the storage space is limited. The cloud has a huge database, which can store a large number of recipes, and at the same time obtain the latest recipe information, update the original recipes, and inform users in time. In addition, the cloud can record the user's operations on the IoT microwave oven, and after classifying the information, generate the user's favorite setting mode in the smart microwave oven, and make timely changes according to the user's living habits.
(2) Smart IoT microwave ovens and control terminals: Control terminal devices mainly include mobile devices such as mobile phones and tablet computers and computers. Users can receive recipes recommended by others and experts at any time through the control terminal. For recipes with complex processing procedures, users do not have to frequently go to the smart microwave oven to operate, and can easily switch to the next step of the program through their mobile phones. At the same time, the mobile phone and the Internet of Things microwave oven maintain a synchronous working state, and the user can also turn on the mobile phone to watch the processing status of the food at any time.
(3) Cloud and control terminal: The cloud pushes the latest version and recipes to the user's control terminal in time for users to view. At the same time, the operation information on the terminal will also be recorded by the cloud, so there is also information communication between the cloud and the control terminal.
Summarize
The above are the details of the microwave oven solution introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. We have rich experience in customized development of electronic products, and can evaluate the development cycle and PCBA price of microwave ovens as soon as possible. We are a number of chip agents at home and abroad, including MCU, voice IC, Bluetooth IC and modules, wifi modules. Our development capabilities cover PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development and other hardware and software design. It can also undertake the research and development of smart electronic products, household appliances scheme design, beauty equipment development, Internet of Things application development, smart home scheme design, TWS scheme development, Bluetooth audio development, children's toy scheme development, and electronic education product development.
- TOP