Note: A versatile, stable, high-resolution readout system for RTD and thermistor sensors

A readout system for resistance temperature detectors and thermistors is described featuring temperature resolution better than 1 mK and capability to fit sensors having different resistance or requiring different excitation current. For instance, with a sensor equivalent to an ideal 100 Pt, an excitation current of 0.7 mA, and reading @ 1Hz, the system resolution corresponds to 0.38 mK and its temperature coefficient (TC) to 0.26 mK/K. The system, however, can control its own temperature accurately enough to make its TC negligible. When thermostated, the overall stability of the system was better than 10 ppm for 230 h.