Platinum Properties

The function of the Pt temperature sensor or heating element is based on the temperature dependence of the electrical resistance of the platinum metal. The relationship can be described by the following characteristic polynomial:

R_T = R_o (1+αt+βt²)

R_T = Measured resistance

R_o = Nominal resistance at 0°C

The constants are defined in the international standards for Pt temperature sensors.

α = 3.9083 x 10^-3 °C^-1

β = -5.775 x 10^-7 °C²

β is so small that for most applications a linear relationship between R_T and the temperature can be assumed.

Pt temperature sensors with high nominal resistances have a higher sensitivity than those with lower nominal resistances, because the slope of the characteristic is directly proportional to R_o.

Depending on the substances and processes used in the manufacture of the Pt temperature sensors, slight specific deviations from the ideal constants and the optimum characteristic can occur. These deviations define the working temperature range and the accuracy tolerance class for each sensor type. The product range from Heraeus Sensor Technology is designed for a temperature range from

-196°C to +1.000°C.

The temperature coefficient (T_C or α) is positive and defined as:

T_C = (R100-R_o)/(100 * R_o).

This represents the slope of the linear approximation of the characteristic polynomial between 0°C and 100°C. The standard DIN EN 60751 for Pt temperature sensors specifies a T_C of 0.003850/°C. This T_C value applies to all the products described here.

In addition, customised sensors with temperature coefficients of 0.003750/°C and 0.003500/°C as well as other intermediate T_C values are available, e.g. according to the JIS standard.