I am using an ADS1115 as an analog to digital converter to measure temperature. I am using an RTD100 temperature sensor to measure a temperature range of -40 to 150 degree celsius but the resistance vs. temperature table of the temperature sensor is non linear.

How can I convert the temperature range of -40 to 150 degree celsius to a proportional voltage of 0-5V so that I can measure it with an ADS1115?

Temperature vs. resistance table of RTD100:

This is a reference circuit to which an RTD100 is connected. It converts the temperature range of 0-200 degrees celsius to 0-5V but I want to design a circuit that converts (-40)-150 degree celsius to 0-5V.

How should I calculate the resistance values connected to the opamp?

• Use R-divider. R1 - is RTD100 connected to grownd and measured point. R2 - const resistor, connect to Vdd and measured point. R = R1 + R2. I=Vdd / (R1+R2). U=I*R. Umeasured= R1 * Vdd / (R1+R2) Sep 14, 2020 at 10:15
• If the power supply 5v, Umeasured-max can be not highter then 2,5 (cause Divider use). 5 volts at the output is possible if there is an additional power supply with a voltage of 10V or highter. Sep 14, 2020 at 10:24
• but how can i get linear relationship with resistance and voltage?@nick_n_a Sep 14, 2020 at 13:04
• When R2 greater then R1 many times - the value R1+R2 - is roughly equal R2. And U= R1*Vdd/R2(roughly) Sep 14, 2020 at 13:34
• @nick_n_a i am actually not clear with the circuit diagram Sep 14, 2020 at 15:00