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Selection method of thermistor temperature sensor
Date：2019-12-28 11:38:41 From：JPET
Select the type according to the sensitivity required in the working environment. Different applications require different response speeds of NTC thermistor temperature sensors. Different materials have different thermal conductivity, and there are several factors that affect the response speed of NTC thermistor temperature sensors:
1. Thermal time constant of thermistor chip. The thermal time constant is small and the response speed is fast.
2. The thermal conductivity of the material of the temperature sensing head shell. The metal shell conducts heat faster than the plastic shell. The thermal conductivity of different metal materials is also different. Generally, a zinc-copper shell is used.
3. The influence of the size and structure of the temperature sensing head. The size of the temperature sensing head is small, the heat conduction time will be correspondingly short, and the reaction speed will be faster.
4. Thermal adhesive filled inside the temperature sensing head. The thermal head filled with thermally conductive silicone grease with a high thermal conductivity will react faster than thermally filled silicone grease with no or only thermal conductivity.
Select according to the measurement object and the measurement environment. For example, in a high temperature and water environment, a temperature-resistant waterproof structure is required. The temperature-sensitive head must be waterproof, anti-fog, and high-temperature resistant. The thermal conductive silica gel must have a small coefficient of thermal expansion and contraction. There will be no significant change in volume over time. The most common filling and sealing materials for temperature sensors are epoxy resins. Epoxy resins have good sealing and adhesion, and can withstand temperatures up to 200 degrees. However, its adhesion to the metal shell is weaker than that of the plastic material. Compared to the adhesion with the wire, the combination of epoxy resin and PVC wire has the best compactness, followed by irradiated wire, and Teflon wire has the worst. . Therefore, when selecting a wire, it is not necessarily a material with a higher temperature resistance, as long as it is a material that satisfies the operating temperature range and has a good adhesion to the filler material, it is the most suitable.
Temperature sensor stability. Any product has a service life. The ability of the sensor to maintain its performance after a period of use is called stability. The factors that affect the long-term stability of the sensor include the stability and reliability of the NTC thermistor chip, the sensor itself and the structure, and the environment in which the sensor is used. For the sensor to have good stability, the sensor must have strong environmental adaptability. The main considerations for stability are the following:
1. The highly reliable thermistor chip is selected as the core. The NTC thermistor chip is fired at high temperature. The production process of different manufacturers has a great impact on the quality of the product.
2. The structure of the appropriate shell is selected, and the mechanical strength of the shell of different structures is different.
3. For different use environments, choose different filled thermal grease.
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