Rtd (Pt100) Sensors - Intab PC-Logger 2100 User Manual

3.4.4. RTD (Pt100) sensors

Using the built-in (I-Out) constant current source (0.500mA) and "four wire technique"
it is easy to measure resistance. In a Pt100, resistance varies with temperature. The
relationship between temperature and resistance is very nearly linear.
Several Pt100 sensors can be connected in series to the same current source. See figure
below.
Channels that are to measure temperature using Pt100 sensors should be set to
FS=100mV.
Resistance is calculated from read voltage by R = U / 0.5mA. (This is a linear
transformation that is extremely easy to realise using the "transform" function of the
software)
A Pt100 has a nominal resistance of 100Ω at 0°C. Resistance then increases by
approximately 0.39Ω/°C. The Pt100 is slightly non-linear so for more accurate readings
the linear transform should be applied around the temperature-points of interest.
For large swing readings with great accuracy, a polynomial (e.g. the Callendar-van
Dusen equation) for calculation of temperature from resistance should be employed.
Page 17
3 CONNECTIONS