All metals produce a positive change in resistance in response to a positive change in temperature, which is the main function of an RTD. System error is minimised where the RTD’s resistance nominal value is large; this means using a metal wire with high resistivity.

Resistivity of the metals used in RTDs
MetalSymbolResistivity Ω·cm/fResistivity Ω·mm²/mResistivity siemens
GoldAu132,1612e-24,6272e+7
SilverAg8,81,4629e-26,8356e+7
CopperCu9,261,5394e-26,496e+7
PlatinumPt599,8083e-21,0195e+7
TungstenW304,9873e-22,0051e+7
NickelNi365,9847e-21,6709e+7

Due to their low resistivity, gold and silver are rarely used in RTDs.

Le tungstène a une résistivité relativement élevée, mais est réservé pour des applications à très hautes températures parce qu’il est extrêmement fragile et difficile à travailler.

Tungsten has a relatively high resistivity, but is reserved for applications at very high temperatures because it is extremely fragile and difficult to work. Its upper temperature limit is only around 120 °C.

The most common RTDs are made of platinum, nickel or nickel alloys. Wires in nickel alloy are economic and used in a restricted temperature range, but they are non-linear and tend to drift over time.

Platinum is the obvious choice for all measurements.