Detailed explanation of B value/resistance ratio of ntc thermistor

　　The NTC thermistor resistance ratio, also known as the B value, material constant and thermal index, refers to the ratio of the zero-power resistance values measured by the thermistor under specified operations at 25° and 85°. It is the material constant of the thermistor, that is, the chip of the thermistor (a semiconductor ceramic) is sintered at high temperature to form a material with a certain resistivity, and there is only one B value for each formula and sintering temperature. is the material constant. NTC thermistors can be widely used in temperature measurement, temperature compensation, suppression of surge current and other occasions.

　　The purpose of NTC thermistor B value test

　　The temperature coefficient of the thermistor is determined by testing the B value of the thermistor. The larger the B value, the larger the temperature coefficient and the higher the sensitivity of the product.

　　NTC thermistor resistance ratio test method

　　1. Use the LCR tester to measure the resistance value of the NTC thermistor at the oil tank temperature of 25° with zero power resistance, which is the manufacturer's nominal resistance value.

　　2. Raise the temperature of the oil tank to 85°, and measure its zero-power resistance value, record and save it.

　　3. Use the data to calculate the thermal index, that is, the B value.

　　Calculate the B value with the following formula:

　　B=[(Ta×Tb)/(Tb-Ta)]×In(Ra/Rb) or B=2.303×[(Ta×Tb)/(Tb-Ta)]×log(Ra/Rb)

　　Formula description:

　　B: constant (unit is K);

　　Ra: zero-power resistance value (unit: Ω) measured at temperature Ta (unit: K)

　　Rb: zero-power resistance value (unit: Ω) measured at temperature Tb (unit: K).

　　Ta=298.15K1)

　　Tb=358.15K1)

　　NOTE: If the detail specification specifies that the B value is to be determined at other temperatures, the values of Ta and Tb (in K) in place of the preferred numbers shall be specified, and this B value shall be described as "B."

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