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| Titel |
Calibration of non-ideal thermal conductivity sensors |
| VerfasserIn |
N. I. Kömle, W. Macher, G. Kargl, M. S. Bentley |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2193-0856
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Instrumentation, Methods and Data Systems ; 2, no. 1 ; Nr. 2, no. 1 (2013-04-12), S.151-156 |
| Datensatznummer |
250017760
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| Publikation (Nr.) |
 copernicus.org/gi-2-151-2013.pdf |
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| Zusammenfassung |
A popular method for measuring the thermal conductivity of solid materials is
the transient hot needle method. It allows the thermal conductivity of a
solid or granular material to be evaluated simply by combining a temperature
measurement with a well-defined electrical current flowing through a
resistance wire enclosed in a long and thin needle. Standard laboratory
sensors that are typically used in laboratory work consist of very thin steel
needles with a large length-to-diameter ratio. This type of needle is
convenient since it is mathematically easy to derive the thermal conductivity
of a soft granular material from a simple temperature measurement. However,
such a geometry often results in a mechanically weak sensor, which can bend
or fail when inserted into a material that is harder than expected. For
deploying such a sensor on a planetary surface, with often unknown soil
properties, it is necessary to construct more rugged sensors. These
requirements can lead to a design which differs substantially from the ideal
geometry, and additional care must be taken in the calibration and
data analysis.
In this paper we present the performance of a prototype thermal conductivity
sensor designed for planetary missions. The thermal conductivity of a suite
of solid and granular materials was measured both by a standard needle sensor
and by several customized sensors with non-ideal geometry. We thus obtained a
calibration curve for the non-ideal sensors. The theory describing the
temperature response of a sensor with such unfavorable length-to-diameter
ratio is complicated and highly nonlinear. However, our measurements reveal
that over a wide range of thermal conductivities there is an almost linear
relationship between the result obtained by the standard sensor and the
result derived from the customized, non-ideal sensors. This allows for the
measurement of
thermal conductivity values for harder soils, which are not easily accessible
when using standard needle sensors. |
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