Pt temperature sensors operate on the basis of the temperature-dependent change in the electrical platinum metal resistance. This relationship can be described using the following characteristic polynomial:

RT = Ro (1+at+ßt2)

RT = Measured resistance
Ro = Normal resistance at 0°C

The constants are specified in the international standards for Pt temperature sensors. ß is so small that for the most applications, a linear dependence between RT and the temperature can be assumed.

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

Depending on the materials and processes used for the manufacture of Pt temperature sensors, slight deviations from the ideal constants and the optimum characteristic may occur. These deviations determine the working temperature range and the precision tolerance classes for every sensor type. Heraeus Sensor Technology product spectrum is designed to cover a temperature range of -200°C to +1,100°C.

The temperature coefficient (TC or a) is positive and defined as:

TC = (R100-Ro)/(100 * Ro).

It is the increase in the linear exposure of the characteristic polynomial between 0°C and 100°C. The standard IEC 751 for Pt temperature sensors specifies a TC of 0.003850/°C. This TC value applies to all products described here.

In addition, customer-specific sensors with temperature coefficient of 0.003920/°C as well as other intermediate TC values are available e.g. in accordance with the JIS standard (0.003916/°C).