Pt100 sensors (platinum 100 Ω (PRTD)) are more linear than thermocouples:

Figure 6 Change in the coefficient of linearity of a type S TC and a Pt100

Figure 6 Change in the coefficient of linearity of a type S TC and a Pt100 The relationship between the temperature and the ohm value of the RTDs was calculated by Callendar, then later refined by Van Dusen, which is why it is known as the Callendar-Van Dusen (CVD) equation.
$${R_T} = {R_0} + {R_0}\alpha \left[ {T – \delta \left( {\frac{T}{{100}} – 1} \right)\left( {\frac{T}{{100}}} \right) – \beta \left( {\frac{T}{{100}} – 1} \right)\left( {\frac{{{T^3}}}{{100}}} \right)} \right]$$

Where RT = resistance at T°C, R0 = resistance at 0°C, α = temperature coefficient at 0°C in Ω/Ω/°C, δ = coefficient of linearisation, β = second coefficient of linearisation for negative temperature values (β = 0 for T > 0°C).

This equation has been converted to enable it to be used more easily with the coefficients A, B and C given by the standard DIN 43760 (IEC 751) and the data sheets of the components:
$${R_T} = {R_0}\left[ {1 + AT + B{T^2} – C\left( {T – 100} \right){T^3}} \right]$$

C=0 for T>0°C.

These three α values represent the three main specifications for RTDs.

• 0.03850 Ω/Ω/°C: Standards DIN 43760, IEC 751 and other international specifications, called the European Standard.
• 0.003926 Ω/Ω/°C: Requires platinum of 99.999% purity or better, called the American Standard.
• 0.3911 Ω/Ω/°C: Often called the US Industrial Standard.