Implementation of cold junction compensation in a thermocouple using a temperature sensing capacitor

Abstract

Thermocouples are widely used for temperature measurement, however they, need linearization and cold-junction compensation. This paper proposes an embedded system for a K-type thermocouple with cold junction compensation using a temperature sensing capacitor. Even though capacitive sensors are widely used for measuring various parameters, using them for measuring temperature is a recent research area. The proposed system has a minimal signal conditioning circuit for linearization and cold-junction compensation. Linearization was achieved using the NIST standard polynomial and cold-junction compensation was accomplished using a Class 1 U2J/N750 ceramic capacitor. The capacitance of this ceramic capacitor varies linearly as a function of temperature. Maximum error for the temperature sensing capacitive sensor was 0.25 ^°C. A K-type thermocouple without any signal conditioning circuit possesses 2.03 % nonlinearity over the range -100 ^°C to 1372 °C. Maximum error after linearization and cold junction compensation was found to be 0.52 ^°C. The proposed embedded system is simple and cost efficient.