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Whether it is electrical or electronic equipment，Even the electric motor、Transformer electromagnetic conversion equipment often has abnormal temperature when it is about to fail.。For example, when an electric motor or transformer is overloaded or short-circuited, its winding temperature will rise sharply;/ Transistor components will also experience abnormal temperature rise before breakdown; contactor/relay coils burned due to overvoltage or inter-turn short circuit or long-term use in a closed environmentwait. It can be seen that，Temperature protection for the above equipment has become a very necessary preventive protection measure, so today we will talk about some knowledge in this regard.

First, let's look at an irreversible temperature protection device——Thermal fuse. Unlike current fuses that use lead-antimony alloys/silver-copper alloys with higher melting points and focus on protecting circuit current values, temperature fuses are made of alloy materials that are more sensitive to temperature. Temperature fuses will not only operate when the current value flowing through them rises to a certain value, but will also melt when the temperature of the protected object rises to a certain value, thereby playing a preventive protection function. At present, temperature fuses are often seen in household appliances such as hair dryers and rice cookers; handheld power tools, small and medium-capacity transformers and other devices.

At present, the common temperature fuses are: cylindrical porcelain tube type (mostly seen in rice cookers, electric pressure cookers and other cookers) and plastic-sealed sheet temperature fuses (mostly embedded in the primary winding of transformers and windings of small power motors). At present, the two most commonly used action temperature values ​​of temperature fuses are92℃ and 98℃. It should be emphasized that, since the temperature fuse focuses on preventive protection at the temperature level, if the temperature fuse is found to be blown in actual work, the protected electrical appliance should be carefully checked first. Usually, the temperature fuse should be 80℃ or above.~In 90% of cases, the protected electrical appliances will be intact, which is completely different from the situation after the current fuse blows!

Next, considering that the temperature fuse is a one-time protection device and has to be replaced after damage, a reusable temperature protection device was born for the convenience of maintenance and use.——Temperature switch. The temperature switch is a protective device that uses a bimetallic strip as a temperature sensing element. When the load is working normally, the bimetallic strip remains in the on/off state; when the temperature of the protected object rises to the bimetallic strip's action value, the bimetallic strip is heated to generate internal stress and quickly acts. When the temperature of the protected object drops back to normal, the bimetallic strip returns to its original state. In terms of its protective action mechanism, the temperature switch is almost the same as the traditional overload protection device - the thermal relay.

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The rated current value of the temperature switch (the current value flowing between the bimetal strips) is generallyThere are three levels: 1A, 2A, and 5A. Common packaging forms of temperature switches include plastic-sealed sheets and metal-shell strips. They are widely used in electric cooking utensils such as electric frying pans, electric baking pans, and electric ovens. In industrial control equipment such as soft starters, frequency converters, and inverter welding machines, temperature switches are mostly fixed on the aluminum heat sink behind high-power components (thyristors, IGBTs). In addition, temperature switches are also implanted in motors and large-capacity transformer windings to serve as over-temperature warning and temperature protection components.

Thermistors and thermocouples are two types of temperature detection elements. They both need to be equipped with corresponding electronic circuits to play the corresponding temperature measurement, over-temperature protection and other functions. Thermocouples are voltage output temperature sensors (mV level output), its output end has polarity, its temperature measurement range is wide, and its detection accuracy is average, and it is mostly used in temperature detection of industrial heating equipment. Thermistor is a resistance value output type temperature sensor (mostly 10KΩ and 100KΩ resistance levels), its temperature measurement range is narrow, but the accuracy is high, and it is mostly used for general temperature measurement, and is often used in induction cookers, light wave ovens, electronic thermometers and other devices.

As for the above four temperature protection and measurement devices, temperature fuses and temperature switches are more common in electrical equipment. Because they have a certain current carrying capacity, they can directly participate in circuit control; thermistors and thermocouples are more common in temperature measurement.In electronic equipment with temperature protection, they are only used as temperature sensing elements and cannot be directly connected to the main circuit or control circuit.