Development of a smart temperature measurement system based on the multi-lead thermocouple concept

A smart temperature measurement system (STMS) based on the concept of multi-lead thermocouples (MTC) was developed and tested. The system consists of a MTC, an interface, and a knowledge base. The MTC is comprised of five thermo-elements sharing a single measuring junction that provides up to ten estimates of the temperature. The interface is controlled by a microprocessor. It facilitates signal transmission between the MTC and the microprocessor and provides the reference junction temperature. The knowledge base is interactive, user friendly, and menu driven. It is equipped with on-line signal validation methods that represents the core of the STMS and allows the system to perform the "intelligent" duties of communication, computation, and self-checking. The system worked, but two of the ten possible measurements were not useful because the corresponding wire pairs showed low sensitivity to temperature. Long term drift tests were performed on five groups of MTCs. The MTCs in each group were made of a unique set of five thermo-elements. Effects of exposure to high temperatures, calibration temperature, type of environment, and frequency of sensor removal from the process for testing purposes on the sensor drift rates were investigated. All the groups showed typical thermocouple behavior (no excess drifts due to the close proximity of several wires in the same sheath). A set of weight factors were developed that drastically reduced the average error, resulting in high overall system accuracy.