China Neodymium And Ferrite Magnets Manufacturer & Supplier 
A rice cooker is one of the essential appliances in a household. It is very convenient to use—simply add rice and the appropriate amount of water to the rice cooker, and it will be ready in no time. The switch will automatically pop up, disconnecting the power or switching to a keep-warm mode. How does this work? This is where a particular material comes into play: temperature-sensitive ferrite.
Thermally sensitive ferrite is made by sintering a mixture of manganese oxide, zinc oxide, and iron oxide powder. At room temperature, it is ferromagnetic, meaning it has strong magnetic properties. However, when the temperature rises to approximately 103 degrees Celsius, it becomes paramagnetic, at which point its magnetic properties become very weak. The temperature at which this magnetic transition occurs is called the “Curie point.”
Magnets (magnetic steel) in rice cookers - temperature-sensitive ferrite
When we start cooking, we press the switch, and under the action of the lever, the small magnet on the left end rises and attaches to the temperature-sensitive ferrite on the inner pot of the rice cooker. At this point, the elastic copper plate in the circuit comes into contact with the contact point, connecting the circuit. Current flows through the heating coil, heating the rice cooker. During the cooking process, since there is water inside the pot, the temperature inside the pot remains below the boiling point of water (100°C), so the temperature-sensitive ferrite on the inner pot retains its magnetic properties, attracting the permanent magnet and ensuring the circuit remains closed.
Once the rice is cooked, the water is absorbed by the rice, causing the temperature inside the pot to exceed 100°C and continue rising. When the temperature rises above 103°C, the temperature-sensitive ferrite on the inner pot loses its magnetic properties. At this point, under the action of the spring, the left end of the lever drops, causing the insulating plate to push open the elastic copper plate, thereby stopping the heating process. Therefore, when the rice cooker emits a “pop” sound and the switch springs up, it indicates that the rice is cooked. If we immediately press the switch again at this point, we will find that the switch pops up again. This is because the temperature inside the pot is still very high, and the ferrite has lost its magnetic properties.
In other words: the temperature-sensitive ferrite can detect changes in temperature and convert these changes into changes in current (on/off). This device that converts temperature into an electrical quantity is called a temperature sensor. The rice cooker uses a temperature sensor to automatically shut off the power after the rice is cooked.
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