NTC calibration and multiple temperature sensors

Introduction

Calibration of NTC sensors and different

NTC

Note that the temperature of the sensor rises when the current supplies through the resistor. The NTC is nonlinear; see below Calibration.

Negative Temperature Coefficient, NTCLE100E3101JB0 or similar (MF52B NTC Thermistor). The NTC is connected in series with a "shunt" resistor $R_{1}$, see Measurement of resistors: voltage divider. Usually $R_{1}=10kOhms$ is used. The total resistance of the circuit is $R=R_{1}+R_{NTC}$, which gives

${\begin{aligned}R_{NTC}&={\frac {U_{\text{measured}}}{U-U_{\text{measured}}}}R_{1}\\\end{aligned}}$

${\begin{aligned}V(R_{1}+R_{n})=V_{in}R_{n}\end{aligned}}$

Calibrating: Steinhart-Hart Equation

A nonlinear Steinhart-Hart equation is widely used

${\frac {1}{T}}=A+B\ln(Rt)+C(\ln(Rt))^{3}$

The parameters $A$, $B$ and $C$ can be obtained, if the resistance of three (3) temperatures is known.

Calibrating using known datapoints

Though the NTC sensor is nonlinear, locally it will be linear. Thus by using some known datapoints the temperature can be estimated.