Thermistors made of semiconductor materials and metal thermistors can be made into temperature sensors, which can convert thermal signals into electrical signals for automatic control.

1. Electric iron

(1) Sensitive element of electric iron -- bimetallic sheet

Two kinds of metal sheets with different thermal expansion coefficients are bonded together to make a bimetallic sheet The thermal expansion coefficient of the upper metal of the bimetallic sheet is greater than that of the lower metal. When the temperature rises, the upper metal sheet bends downward due to large elongation to disconnect the contact, so as to disconnect the circuit. The function of the bimetallic sheet temperature sensor is to control the on-off of the electrical metal base plate circuit.

(2) Working principle of electric iron

A bimetallic sheet temperature sensor is installed inside the electric iron. Under normal temperature, the upper and lower contacts are in contact, but when the temperature changes, the bimetallic sheet bends due to the different thermal expansion coefficients of the upper metal and the lower metal of the bimetallic sheet, so as to control the on-off of the circuit The height of the lifting screw is adjusted through the temperature adjusting knob, so as to realize the setting of different temperatures. If the temperature to be set is high, lower the lifting screw; Conversely, increase

2. Electric rice cooker

(1) Temperature sensing ferrite, a sensitive element of electric rice cooker

Temperature sensitive ferrite is characterized by ferromagnetism at room temperature and can be attracted by magnets. However, when the temperature rises to about 103 ° C (called the "Curie temperature" or "Curie point" of the material), it loses ferromagnetism and cannot be attracted by magnets.

(2) Working principle of electric rice cooker

① When the switch is pressed by hand, the permanent magnet and the temperature sensing magnet attract each other. After the hand is released, the button will no longer return to the state shown in the figure, then the contact will be connected, powered on for heating and start cooking;

② When water boils during cooking, the temperature remains unchanged;

③ When the rice is cooked, the water is absorbed by the rice and the temperature at the bottom of the pot rises. When the temperature at the bottom of the pot reaches 103 ° C, the ferrite loses its magnetism, loses its attraction with the permanent magnet, and is bounced off by the spring, so as to push the lever to disconnect the contact switch and restore the button to the state shown in the figure.