I would like to build a circuit to read the signal from a thermopile temperature sensor which has build-in RTD temperature sensor for cold-junction compensation. The datasheet of the sensor is here. I need to know the resistance value of the built-in Ni-RTD at some particular temperature to build the circuit. I search the web to check how can I calculate the resistance value but all I could find is the formula for a platinum RTD. Could you guide me how to calculate the resistance value for a Ni-RTD?

Thank you very much.


I have used the Temperature Coeficient Resistance (TCR) to calculate the resistance at temperature T: Rt = R0[1+(TCR)T] However as I know the real temperature-resistance curve is not linear, is there a similar formula like the Callendar-Van Dusen equation to fix the curve?


Updated with a better calculator

Use an online calculator like this with R = 1000 ohm, there is a NI-RTD with a temperature coefficient of 0.00618 that I think it is an approximation of the 0.006178 that you have, it should be the same material.

If you need a polynomial approximation use together with this tool

For samples at 0, 40, 80, 120 degrees the formula is: R = 1000(1 + 0.00549577t + 0.000006156t^2 + 0.000000006732t^3)

Or use the values from the table to find A, B and C in the CALLENDAR-VAN DUSEN formula.

Choose the sample points close to your interest area

It's true that there are errors of a few percents with the linearized formula, the maximum error is somewhere around 40 degrees.


You can use these formulas:

enter image description here

Which are derived from this similar sensor datasheet.

It's fairly close to linear for this particular purpose, especially over the relatively narrow temperature range in which the sensor would likely operate.


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