Resistance Temperature Detector (Pt100)

What are the equations of an Pt100?

The relationship between resistance (R) and temperature (t) of platinum resistance thermometers (RTD, Pt100) is described by The Callendar-Van Dusen equation.

It is also used in the international standard DIN EN 60 751 (IEC751). For a more accurate relationship, the ITS-90 is used.

For the range between -200 °C to 0 °C the equation is :

R(t) = R(0)[1 + A * t + B * t^2 + (t − 100)C * t^3]

For the range between 0 °C to 661 °C the equation is

R(t) = R(0)(1 + A * t + B * t^2)

These equations are listed as the basis for the temperature/resistance tables for platinum resistance thermometers. The coefficient A, B and C are temperature dependent and can be determined using calibration in our metrology laboratory.

The equation was found by British physicist Hugh Longbourne Callendar, and refined by M. S. Van Dusen.

As an example, the table below shows both sets of coefficients for a Pt100 resistor
according to the IEC751 and ITS90 scale: 

R0 = 100 Ohm
A=3,908 x 10^-3
B=-5,775 x 10^-7
C=-4,183 x 10^-12

A=3,908 x 10^-3
B=-5,775 x 10^-7
C=-4,183 x 10^-12

At last, the coefficient alpha (α) is a linear parameter determined as the normalised slope between 0 and 100 °C:

α=(R100-R0)/100xR0

The more used Pt100 have an alpha coefficient equals to 0.00385 following DIN IEC751.

Click here to use our on-line calculator to convert °C<==>Ohm for a Pt100.

Contact us