Masters Theses

Date of Award

5-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Nuclear Engineering

Major Professor

Belle R. Upadhyaya

Committee Members

E. M. Katz, L. F. Miller

Abstract

This thesis describes research concerning the characteristics of long-term aging of resistance temperature detectors and the development of life estimation techniques performed at The University of Tennessee. The objectives included the study of long term thermal aging of resistance temperature detectors (RTDs) and the study of changes in several RTD parameters throughout the aging and degradation process. The study of long-term aging of thin-film design and wire wound element construction RTDs was performed at elevated and constant temperatures and with thermal cycling at elevated temperatures. A single manufacturer provided all of the RTDs used in this study.Variations in calibration parameters (α, δ and Ro from the Callendar-Van DusenEquation), loop resistance, insulation resistance, sheath to lead voltage, compensating loop resistance, open circuit voltage, self-heating index, drift rates and life prediction ofRTDs were periodically and continuously monitored. Relationships among these parameters were identified and established.The RTD aging facility used was designed and constructed to include four hightemperaturefiunaces. These furnaces were used to carry out several RTD tests. All the RTD measurements were performed automatically using a data acquisition system with an expanded capability to acquire resistance measurements from up to eighty RTDs.One of the tasks during this phase of the project was to establish the maximum temperatures at which the RTDs completely fail (either in the fail open mode or by indication of a non-physical behavior). These temperatures are in the range 600-700 ° C for thin film RTDs and 800-900 ° C for wire wound RTDs. Thermal cycling at elevated temperatures indicated a stronger drift rate in resistance and a faster failure of RTDs. As The aging progressed, a strong correlation between the calibration parameter δ (of the Callendar-Van Dusen equation) and the self-heating index (SHI) was also observed. Thiswas further confirmed by an excellent linear fit between the two parameters with a small least-squares error variance. As the aging progressed, the drift rates changed with the temperature, and the resistance drift changed its rate of change to a negative value. The Life prediction of RTDs was continued until the resistance value reached preset alarm and failure levels.The possible correlation between the calibration parameter α and the self-heating index, when fully established may be used for on-line calibration verification of RTDs.This intelligence can be built into the transmitter for periodic and non-intrusive monitoring of industrial platinum resistance thermometers.

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