What is RTD temperature sensor sensitivity?

The RTD temperature sensor is a temperature sensitive resistor. Therefore, the indication of its "sensitivity" should indicate the amount that the resistance changes with temperature.
Some discussions on RTD temperature sensor sensitivity simply use the alpha value of the element to represent the sensitivity of RTD temperature sensor element, which may be misleading, because it does not directly represent the amount of resistance change of 1 degree.
However, if we check how alpha is calculated, α =  [(R100 ° C – R0 ° C)/R0 ° C]/100 ° C, we can see that alpha really represents the increase of resistance score at 100 ° C.
In other words, for α= 0.00385, the resistance increases by 38.5% from 0-100 ° C, or 0.385% per ° C.
Therefore, we can use 0.385%/° C to express the sensitivity of the sensor, or we can convert it to its original measurement unit and use Ω/° C instead.

More simply, we can calculate the sensitivity of the resistance thermometer by multiplying the resistance of the RTD temperature sensor at the reference temperature R0 (its calibration temperature) by the resistance temperature coefficient (TCR, or alpha value), as follows: sensitivity=KRTD=R0* α。

For α= For a 100 Ω platinum RTD temperature sensor with 0.00385 Ω/Ω/° C and R0=100 Ω, the sensitivity coefficient is calculated by the expression 100 Ω * 0.000385 Ω/Ω/° C=0.385 Ω/° C.
Therefore, a 100 Ω sensor at 0 ° C will increase its resistance by 0.385 Ω or 0.385 Ω/° C at 1 ° C.
Referring to the previous table, we can see that the higher the alpha value, the more sensitive the sensor is.
Therefore, nickel RTD（ α= 0.00672 Ω/Ω/° C, R0=120 Ω) is more sensitive to temperature change than platinum RTD temperature sensor, because its resistance will change by 120 Ω * 0.00672 Ω/Ω/° C=0.8064 Ω/° C, which is greater than 0.385 Ω/° C of Platinum sensor, making its sensitivity more than twice.
Sometimes a multiple of the nominal resistance R0=100 Ω is used to produce a sensor with higher sensitivity.
For example, the sensitivity of 500 Ω Pt RTD (Pt500) is 5 times that of 100 Ω Pt RTD (Pt100).
Similarly, the sensitivity of 1000 Ω Pt RTD (Pt1000) is ten times that of 100 Ω Pt RTD. Their resistance changes as follows:
Pt100 0.385Ω /°C
1.925 Ω/° C for Pt500
Pt1000 is 3.850 Ω/° C
In a word, the sensitivity of RTD temperature sensor refers to its resistance change per temperature change. It is a function of its base resistance and resistance temperature coefficient (TCR).
A sensor with higher sensitivity may not be more accurate, but the larger the signal it generates, the less susceptible it is to lead wire effects and electrical noise, because it usually improves the signal-to-noise ratio of the sensor interface.
A larger resistance also produces the same output voltage with a smaller excitation current, which helps to reduce the self heating effect in the sensor element by allowing a lower current to excite the sensor element.