RTD measurement circuits The two most common methods to measure an RTD are constant current excitation (Figure 1 ) and constant voltage excitation (Figure 2 ).

The circuit uses the popular Pt100 RTD, which has a resistance of 100 Ω at 0°C. Its temperature coefficient of 0.00385 Ω/Ω/ºC produces a 38.5-Ω increase in resistance from 0°C to 100°C.

An RTD is a temperature sensor that operates on the measurement principle that a material’s electrical resistance changes with temperature.

In a typical resistance temperature detector (RTD) measurement application, the delta-sigma converter often is configured in a ratiometric topology using a constant current excitation source.