Long-term relative stability of thermistors

The relative stability of four glass-bead thermistors has been analyzed for 44 months to determine if thermistors have sufficient relative stability to be used as feedback sensors for milliKelvin levels of temperature control. The thermistors were measured at 20 ± 0.1 °C using commercial two-wire instrumentation. The thermistors have a nominal resistance of 12.5 kΩ and sensitivity of −4.5%/°C at 20°C. They are nested together inside several layers of thermal resistance and capacitance, which are held at nominal 20°C with a temperature-controlled, recirculating air chamber. After correction for instrumentation drift with two high-stability reference resistors, the average relative rms drift of the thermistors is 50 ± 15 μK, with an rms fitted drift rate of 0.26 ± 0.16 μK/week.