The measurement is based on variation of resistance from metallic wires (resistors) against variations of temperature.
Materials most often used are platinum and nickel.
Platinum offers a large temperature range and a good linearity. His pureness and chemical inertia guarantee a high stability
of sensor itself.

Relation between platinum resistance and temperature according Standard CEI 751 is as following formula (restricted):

Rt = Ro [ 1 + At + Bt² + Ct³ (t - 100)]

• Rt : Sensor resistance at temperature t
• Ro : Sensor resistance at 0°C
• t : Temperature in °C
• A B C : coefficients according to previous calibration ( C = 0 for positive temperature in °C)

Industrial probes and boards are based on:

• Ro = 100 Ohm at 0°C
• R100 = 138.5 Ohm at 100°C

• France: NFC 42330
• Germany: DIN 43760
• Great Britain BS 1904
• International CEI 751