Modeling a self-calibrating thermocouple for use in a smart temperature measurement system

Abstract

A smart temperature measurement system that consists of a commercially available self-calibrating thermocouple connected to a data-acquisition system with a specially designed algorithm capable of automatically detecting the calibration temperature of the self-calibrating thermocouple was developed. The self-calibrating thermocouple has a high-purity, low-melting-point metal encapsulated near its thermojunction. The time-temperature record of the thermocouple forms a plateau at the phase transition temperature of the encapsulated metal, providing a single-point calibration. Since the plateau is usually not horizontal, a major effort of the work reported was to determine which point of the phase transition plateau is the actual phase transition temperature. A finite-difference computer simulation program was written to explain the thermodynamic behavior of the system. On the basis of a literature review and simulation analysis, a method was developed to recognize which point on the melting or freezing plateau curve is the actual phase transition temperature of the encapsulated metal. The known phase transition temperature is compared with the reported melting or freezing point of the encapsulated metal to determine the magnitude of error in the thermocouple output. >