Obtaining the Sensed Temperatures from a Detailed Model of a Welded Thermocouple
Jonathan W. Woolley, Michael A. Bestor, Mark L. Weaver, and Keith A. Woodbury
International Mechanical Engineering Congress and Exposition
Boston, Massachusetts, October 31 - November 6, 2008
ABSTRACT
When imbedded in
dissimilar materials subject to large temperature gradients, thermocouples are
known to yield erroneous (bias) temperature measurements.It has been established that the bias error
may be accounted for with an appropriate computational model and the measured
temperatures may be corrected with an appropriate kernel function.In this work, a thermocouple with a welded bead is
considered.Early two-dimensional models
considered the thermocouple to be a single wire with effective thermal properties.The model in the current investigation is
three-dimensional and represents the sensor as two wires, each with unique
thermal properties.The welded bead is
represented as a separate entity with properties distinct from those of the
wires.
The problem of determining what location in the
three-dimensional model corresponds to the measured temperature is
considered.Earlier models have
considered the sensed temperature to be the temperature at the tip of the two-dimensional
thermocouple or, in three-dimensional models, the temperature at the center of
the volume of the welded bead.In the
current work, a theory is set forth for identifying the location at which the
temperature is sensed by a thermocouple.This theory is in line with traditional thermoelectric theory and is
supported with experimental evaluation with thermal imaging as well as
examination of thermocouples by scanning electron microscopy and energy
dispersive X-ray analysis.The
significance of accurate modeling of the sensed temperatures is demonstrated
with a numerical experiment.
