ntc thermistor temperature measurement circuit nonlinear serious capacitance

　　NTC negative temperature coefficient thermistor sensor is that its resistance value will increase when the temperature drops. The thermistor has the highest sensitivity (that is, the change in resistance per 1°C change in temperature) of all passive temperature sensors, but the thermistor's resistance-temperature curve is non-linear.

　　Methods and precautions for improving NTC thermistor nonlinearity

　　NTC thermistors have a nonlinear relationship with temperature and must be linearized. The specific method is to connect a suitable external resistor RExt in series with RT, then connect it to the 1.24V reference voltage URef, and then use the MAX6691 to measure the voltage on RExt, so that the nonlinearity of the NTC thermistor can be changed within the selected temperature range. minimized.

　　The steps to calculate RExt are as follows:

　　(1) Determine the temperature range to be measured (eg 0°C~+70°C);

　　(2) Determine the minimum value Rmin of the thermistor (corresponding to the highest temperature, such as +70°C), the maximum value Rmax (corresponding to the lowest temperature, such as 0°C) and the intermediate value Rmid (corresponding to the lowest temperature, such as 0°C) within this temperature range Intermediate temperature, here +35°C);

　　(3) Finally, use the following formula to calculate the RExt value [3]

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