When using the NTC thermistor to collect the temperature in the lithium power battery module, the factors that should be considered when selecting the NTC thermistor are:
1) The shell of NTC thermistor should be smooth, uniform in color, free of cracks, deformation, and serious scratches. The color of each batch of products (including lead wires) should be the same without any corrosion. There should be a permanent model and serial number on the surface of each NTC thermistor shell.
2) Temperature range. Choose NTC thermistors of different materials according to the working temperature range of the application. NTC thermistors are generally composed of a temperature sensor (metal or plastic shell), wires, terminals, connectors, epoxy resin or other filling materials, etc. When choosing, choose NTC thermistors of different materials according to different working environment temperatures.
3) Accuracy (the whole measurement error is within ±2℃). NTC thermistor has good linearity in the entire temperature detection range, and the characteristics of NTC thermistor conform to the entire parameter range. And to consider the influence of NTC thermistor resistance accuracy on temperature detection accuracy; the influence of NTC thermistor B constant accuracy on temperature detection accuracy; the influence of NTC thermistor thermal diffusion constant C on temperature detection accuracy.
Precision NTC thermistor is an important performance index, which is an important link related to the measurement accuracy of the entire measurement system. The higher the accuracy of the NTC thermistor, the more expensive it is. Therefore, the accuracy of the NTC thermistor only needs to meet the accuracy requirements of the entire measurement system. The factors that determine the accuracy of NTC thermistors are:
The error of NTC thermistor itself. The smaller the resistance error and B value error of NTC thermistor, the higher the measurement accuracy.
The contact method between the temperature sensing head of the NTC thermistor and the temperature measurement object. The measurement accuracy of direct contact is higher than that of indirect contact. In addition, because the R-T curve of NTC thermistor is non-linear, it is impossible to guarantee the same accuracy in a wide operating temperature range. Therefore, in order to obtain higher measurement accuracy, select the central operating temperature point of the workplace (generally the central operating temperature point has the highest accuracy. According to the discreteness of the RT curve, the further the temperature point away from the central operating temperature point, the accuracy error will gradually Increase).
4) During the measurement, the NTC thermistor has a fast response speed, and the time to reach the closest temperature should be as short as possible, not more than 10 seconds, otherwise the efficiency requirements will not be met in practicality. Different applications require NTC thermistors to have different response speeds, and different materials have different thermal conductivity. The factors that affect the response speed of NTC thermistor are:
Thermal time constant of NTC thermistor chip. The thermal time constant is small and the response speed is fast.
The thermal conductivity of the NTC thermistor temperature sensor housing material, and the material with high thermal conductivity has excellent thermal conductivity.
The size of the NTC thermistor temperature sensor head is smaller, the heat conduction time will be correspondingly short, and the response speed will be faster.
The thermal conductive glue filled in the NTC thermistor thermal head, the thermal head filled with high thermal conductivity silicone grease will react faster than the unfilled\filled thermal conductive silicone grease with low thermal conductivity.
5) If self-heating is within a certain range, the value of resistance needs to consider its own heating, so as not to cause heating. Otherwise, the heating of the NTC thermistor itself will affect the temperature measurement, and it should have high reliability (superior thermal shock performance), and the thermal time constant should be small (fast response speed).
6) Stability. The ability of NTC thermistors to remain unchanged after a period of use is called stability. The factors affecting the long-term stability of the NTC thermistor include the stability and reliability of the NTC thermistor chip, the sensor itself and its structure, and the use environment of the NTC thermistor. To make NTC thermistor have good stability, NTC thermistor must have strong environmental adaptability. The selection elements of NTC thermistor stability are:
Choose highly reliable NTC thermistor.
Choose NTC thermistor with reasonable structure and strong mechanical strength.
It is reasonable to choose different filling materials for different use environments.
7) Life: not less than 6 years, including a storage period of 2 years.
8) The NTC temperature sensor is impacted three times in the environment of -55℃～70℃, and there should be no mechanical damage and any looseness.
9) Insulation resistance: greater than 10MΩ/500V.