DEVELOPMENT OF AN ONLINE TEMPERATURE MEASUREMENT SYSTEM IMPLEMENTING THERMOEMF TO DIGITAL CONVERSION TECHNIQUE *Manash Protim Goswami, Debashis Saikia and Utpal Sarma Dept. of Instrumentation & USIC Gauhati University, Assam-781014 *Corresponding author : manashgoswami@gauhati.ac.in ABSTRACT Development of an online temperature measurement system implementing thermoemf to digital conversion technique is explained in this paper. In this work, a class-I, K-type thermocouple is used as the temperature sensor. The thermoemf generated by the thermocouple is applied to a cold junction compensated K-type thermoemf to digital converter with resolution of 0.25 0 C. This is a 12-bit analog to digital converter with a temperature sensing diode for cold junction compensation. The internal circuitry of the converter provides the diode voltage (sensing ambient temperature) and the thermocouple voltage to the conversion function stored in the analog to digital converter to calculate the thermocouple hot junction temperature. The 12-bit output of the SPI compatible converter is read by an 8-bit microcontroller. A firmware has been developed to read digital data from the converter, for doing necessary data conversion of the digital data to temperature and to communicate with the PC via RS232 network for data logging and monitoring. Calibration method and performance of the system are described in the paper. Key words: Microcontroller, K-Type Thermocouple, RS232 communication, Reference junction, Thermoemf J. Assam Sc. Soc. Vo. 56, No.2 ISSN 0587-1921 December 2015; PP. 29-38 J. Assam Sc. Soc. Vo. 56, No.2 December 2015  29