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Aug 25, 2015

Thermocouples: Simple Temperature Measuring Devices – or Are They? A Placement Exploration With JMP®

In engineering science, thermocouples are considered to be a simple and effective method for assessing local temperature fluctuations in often difficult to reach places. They consist of two wires of different metals, and a voltage is induced when the end of the wires is at different temperatures. There is a significant assumption when used currently that the temperature at the measurement end of the wires is the same as the desired object temperature. As a result, there are some factors that impact the performance, namely, that measurement itself impacts the local temperatureand the actual temperature field, and that the surroundings influence the measurements, e.g., conduction through the wires. Hence, in the use of thermocouples, appropriate corrections are often not taken into account, largely because there is no closed-form solution available
to predict the error; only a numerical approach exists presently. A practical experimental investigation will be outlined in this paper. The measurement errors related to
use and placement of thermocouples which should be known when utilizing these devices, in terms of errors, will be discussed. An approach that can be used to mitigate and reduce systemic errors will be described. This paper will effectively focus on placement design exploration. It is based on known physics/chemistry of the problem which is enhanced by applying a thorough analysis through the use of JMP and its ability to track experimental results cohesively and
comprehensively from the screening stage, and right though add-on designs to the final predictive/tolerance step.

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