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    Shenzhen Nixi Technology Co., Ltd.


    Address: No. 1221 Guangguan Road, Guanlan Street, Longhua District, Shenzhen City, Guangdong Province


    Contact: Mr. Li

    Tel: 13798455373, 13798433058


    Website: www.nixikj.com

    Email: lzf@nixi-cap.com


How NTC Thermistors Work Technical Support

How NTC Thermistors Work

Time:2022-01-04

1 The working principle of semiconductor thermistor

The thermistor can be divided into two categories according to the temperature characteristics. The resistance increases with the temperature rise is the positive temperature coefficient thermistor, and vice versa is the negative temperature coefficient thermistor.

⑴ The working principle of the positive temperature coefficient thermistor

This kind of thermistor is made of barium titanate (BaTio3) as the basic material, and then mixed with an appropriate amount of rare earth elements, and is sintered at high temperature by ceramic technology. Pure barium titanate is an insulating material, but after being doped with an appropriate amount of rare earth elements such as lanthanum (La) and niobium (Nb), it becomes a semiconductor material, which is called semiconducting barium titanate. It is a polycrystalline material with a grain interface between the grains, which acts as a potential barrier for conducting electrons. When the temperature is low, due to the action of the electric field in the semiconducting barium titanate, the conductive electrons can easily cross the potential barrier, so the resistance value is small; when the temperature rises to the Curie point temperature (ie the critical temperature, the 'temperature of this element Control point' When the Curie point of barium titanate is generally 120°C), the internal electric field is destroyed and cannot help conductive electrons to cross the potential barrier, so the resistance value increases sharply. Because this kind of element has a very slow change of resistance with temperature before reaching the Curie point, it has the functions of constant temperature, temperature adjustment and automatic temperature control. Yes, it has a long service life and is very suitable for overheating detection of electrical devices such as motors.

⑵ The working principle of negative temperature coefficient thermistor

Negative temperature coefficient thermistors are made of metal oxides such as manganese oxide, cobalt oxide, nickel oxide, copper oxide and aluminum oxide as the main raw materials, and are manufactured by ceramic technology. These metal oxide materials have semiconductor properties, which are completely similar to germanium and silicon crystalline materials. The number of carriers (electrons and holes) in the body is small, and the resistance is high; the temperature increases, the number of carriers in the body increases, and the natural resistance value decreases. There are many types of negative temperature coefficient thermistors, which are divided into three types: low temperature (-60 ~ 300 ° C), medium temperature (300 ~ 600 ° C), and high temperature (> 600 ° C), with high sensitivity, good stability, fast response and long life. , low price and other advantages, it is widely used in temperature automatic control circuits that require fixed-point temperature measurement, such as temperature control systems for refrigerators, air conditioners, and greenhouses.

The thermistor can be combined with a simple amplifier circuit to detect the temperature change of one thousandth of a degree, so it can form a thermometer with an electronic instrument to complete high-precision temperature measurement. The working temperature of general purpose thermistor is -55℃~+315℃, and the working temperature of special low temperature thermistor is lower than -55℃ and can reach -273℃.

2 Types of thermistors

The thermistor made in China is modeled according to the ministerial standard SJ1155-82, which consists of four parts.

The first part: the main name, with the letter 'M' indicating the sensitive element.

Part II: Category, using the letter 'Z' for positive temperature coefficient thermistors, or the letter 'F' for negative temperature coefficient thermistors.

Part 3: Purpose or feature, represented by a single digit (0-9). The general number '1' indicates general purpose, '2' indicates voltage stabilization purpose (negative temperature coefficient thermistor), '3' indicates microwave measurement purpose (negative temperature coefficient thermistor), and '4' indicates bypass heating (negative temperature coefficient thermistor), '5' for temperature measurement, '6' for temperature control, '7' for degaussing (positive temperature coefficient thermistor), '8' for linear (negative temperature coefficient thermistor) temperature coefficient thermistor), '9' means constant temperature type (positive temperature coefficient thermistor), '0' means special type (negative temperature coefficient thermistor)

The fourth part: serial number, also represented by numbers, representing specifications and performance.

Manufacturers often add a 'derived serial number' after the serial number for the special needs of distinguishing this series of products, which is a combination of letters, numbers and a '-' sign.

Example: M Z 1 1

serial number

general purpose

Positive Temperature Coefficient Thermistor

sensitive components

3 The main parameters of the thermistor

The working conditions of various thermistors must be within the allowable range of their factory parameters. There are more than ten main parameters of thermistor: nominal resistance value, ambient temperature (maximum working temperature), measurement power, rated power, nominal voltage (maximum working voltage), working current, temperature coefficient, material constant, time constants etc. The nominal resistance value is the resistance value at zero power at 25°C. In fact, there is always a certain error, which should be within ±10%. The operating temperature range of ordinary thermistors is large, which can be selected from -55°C to +315°C according to needs. It is worth noting that the maximum operating temperature of different types of thermistors varies greatly, such as MF11 sheet negative temperature coefficient heat. The varistor is +125℃, while the MF53-1 is only +70℃. Students should pay attention to it when experimenting (generally, it should not exceed 50℃).


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    Shenzhen Nixi Technology Co., Ltd.


    Address: No. 1221 Guangguan Road, Guanlan Street, Longhua District, Shenzhen City, Guangdong Province


    Contact: Mr. Li

    Tel: 13798455373, 13798433058


    Website: www.nixikj.com

    Email: lzf@nixi-cap.com


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