High-precision NTC temperature measurement circuit design and resistance value calculation.SMD Thermistor Processor

　　There are two types of thermistors, one is negative temperature coefficient resistor (NTC), the resistance value decreases when the temperature increases, and the other is positive temperature coefficient resistor (PTC), the resistance value increases when the temperature increases.

　　Calculation of resistance value of thermistor

　　The relationship between the resistance value R of the NTC and the temperature can be approximately expressed as:

　　Equation 1, Resistance as a function of temperature. where T is the absolute temperature in degrees Celsius + 273.15 in K (Kelvin). R0 generally takes the resistance value when the temperature is 25°C, i.e. 298.15K, and the corresponding T0 takes 25°C, i.e. 298.15K. B is the material constant. Different village materials or production processes can cause the value of B to change, and even within the working range of the thermistor, the value of B may change, rather than a strict constant;

　　Because the resistance of the NTC has a nonlinear relationship with temperature, and there is an increase in temperature, the rate of change of temperature with temperature changes is smaller.

　　Therefore, as the temperature increases, the accuracy of NTC temperature measurement changes; so it is more suitable for use scenarios with a small temperature change range, such as ambient temperature (about -20°C-50°C) or water temperature detection (0°C-100°C ).

　　The NTC searched can have different specifications such as 5KΩ and 10KΩ according to the resistance value at 25°C, and the material coefficient B value is fixed at 3950.

　　We choose the specification of 10K. According to formula 1, the relationship between the resistance and temperature of this NTC can be obtained as:

　　Equation 2, Resistance as a Function of Temperature

　　Through the formula in the excel sheet, enter the temperature in the first column of the excel worksheet, and enter the formula in the second column to get the resistance value at different temperatures, for example, 0°C is 33.6 KΩ

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