Thermistor based ultra-sensitive thermal probe and its signal processing methods suitable for solution calorimeter

Abstract

A sensitive thermometric probe to measure a minute change in temperature of the order of mK, is designed and developed as a prerequisite for the in-house development of solution calorimetry system to study the heat of solutions of the compounds containing alkali metals. A measurement range of 2 K is considered in commensurate with the volume of the solution and the sample size. In this paper, construction of the probe using a thermistor, a linear signal-conditioning scheme, and calibration procedure using the PT100 are discussed. The inexpensive electronics scheme with a lock-in-amplifier and an integrating type ADC is prudently adapted for measuring a change of thermistor resistance of the order 0.1 W in 10,000 W. An adaptive procedure of the signal conditioning scheme to measure temperature over a wider range and also at a suitable base temperature is also discussed. The versatile measurement technique realizes a measurement of minimum change in temperature 2.127 x10^–4 oC over the base temperature of 25 ^oC. The probe is successfully adapted in out solution calorimetry system as well.

Keywords: Thermistor, lock in amplifier, integrating type ADC, solution calorimeter, Dewar Vessel