Pt100 Sensors - Measurement with resistance thermometers

Resistance of Pt100 temperature sensors

The name Pt100 is composed of the chemical symbol for platinum (Pt) and the resistance value of 100 ohms specified at 0°C.
The Pt100 sensor is based on the principle that the electrical resistance of an electrical conductor changes with a change in changes in temperature.
So actually almost all electrically conductive materials can be used.
For practical use in temperature measurement, however, they must meet certain conditions.

Long-term stability / low aging
Chemical resistance
Usable large resistance change
Linear change in resistance over the widest possible temperature range

In practice, in addition to nickel (Ni100), copper (Cu10) and silicon, the use of platinum as a resistive element has mainly proved successful.
Platinum has a high melting temperature and high chemical resistance, which allows precise measurements, with high stability and accuracy, even under adverse conditions.
Like all metals, the Pt100 sensor has a temperature-dependent resistance that increases with rising temperature. (PTC = Positive Temperature Coefficient). A useful change in resistance already occurs at low temperatures.

In addition to metal temperature sensors, sensors made of a wide variety of metal oxides are also used in mass applications. These often provide a usable change in resistance only at higher temperatures.
The resistance decreases when the temperature increases (NTC = Negative Temperature Coefficient).
The advantage of these sensors is the low-cost production and the small design with high response sensitivity.
On the other hand, the lower accuracy, the restricted measuring span, sensor-specific resistance values and a non-linear change in resistance, which make an adaptation of the downstream evaluation electronics necessary.

Resistance values according to DIN EN 60751

Calculating of the Pt100 resistance value

Please enter a temperature value in °C and press the "Calculate" button.
The right window then displays the resistance in ohms calculated for the Pt100 resistance sensor.

t= °C

resistance (t) = Ohm

Calculation formulas for Pt100 resistor

The resistance of the Pt100 sensor is calculated according to DIN EN 60751 using the following 2 formulas:

Temperature range: -200 to 0°C:
R_t = R₀ * (1 + A * t + B * t² + C * (t-100) * t³)
Temperature range: 0 to 850°C:
R_t = R₀ * (1 + A * t + B * t²)

R_t=Resistance [Ohm] at desired temperature
R₀=Nominal resistance Pt100 at 0°C = 100 Ohm
t= desired temperature [°C]
A= 3,9083 * 10^-3
B= -5,775 * 10^-7
C= -4,183 * 10^-12

Please note:
The constant "A" for spectrally pure platinum is 3,925*10^-3.
As the production of spectrally pure platinum was complex and therefore expensive, the constant "A" was defined as the value for platinum contaminated with other substances.
A further advantage of "defined impurity" platinum is that it is less sensitive to additional external impurities, making the sensor more stable over the long term.
The value of 3,9083 * 10^-3 specified in DIN EN IEC 60751:2023-06 is used as the usual value for constant "A".
For high-precision measurements or when recalibrating a Pt temperature sensor, it is important to know which platinum the sensor was made of and which value of constant "A" is used to calculate the temperature.
Especially with older Pt temperature sensors or with Pt sensors manufactured in non-European countries, different platinum based on other standards (DIN 43760-1980, ASTME, JIS, Gost, etc.) is sometimes used. There may be deviations from the values specified in DIN EN IEC 60751:2023-06.