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Assessment of Uncertainties for the NIST 1016 MM Guarded-Hot-Plate Apparatus

Volume 115, Number 1, January-February 2010
Journal of Research of the National Institute of Standards and Technology
[J. Res. Natl. Inst. Stand. Technol. 115, 23-59 (2010)]
Assessment of Uncertainties for the
NIST 1016 mm Guarded-Hot-Plate Apparatus:
Extended Analysis for Low-Density
Fibrous-Glass Thermal Insulation
Author’s Note: This paper is based on NIST Technical Note 1606, Assessment of Uncertainties for the NIST 1016 mm Guarded-Hot-Plate
Apparatus: Extended Analysis for Low-Density Fibrous-Glass Thermal Insulation, February 2009. Most of the content remains the same; the
uncertainty analysis has been updated to reflect recent modifications in the heat flow imbalance study (p. 44).
Volume 115
Number 1
January-February 2010
Robert R. Zarr
An assessment of uncertainties for the
National Institute of Standards and
Technology (NIST) 1016 mm Guarded-
Hot-Plate apparatus is presented. The
uncertainties are reported in a format
consistent with current NIST policy on the
expression of measurement uncertainty. The
report describes a procedure for determina-
tion of component uncertainties for thermal
conductivity and thermal resistance for the
apparatus under operation in either the
double-sided or single-sided mode of
operation. An extensive example for com-
putation of uncertainties for the single-sided
mode of operation is provided for a
low-density fibrous-glass blanket thermal
insulation. For this material, the relative
expanded uncertainty for thermal resistance
increases from 1 % for a thickness of
25.4 mm to 3 % for a thickness of
228.6 mm. Although these uncertainties
have been developed for a particular
insulation material, the procedure and, to a
lesser extent, the results are applicable to
other insulation materials measured at a
mean temperature close to 297 K (23.9 °C,
75 °F). The analysis identifies dominant
components of uncertainty and, thus,
potential areas for future improvement in
the measurement process. For the NIST
1016 mm Guarded-Hot-Plate apparatus,
considerable improvement, especially at
higher values of thermal resistance, may be
realized by developing better control strate-
gies for guarding that include better meas-
urement techniques for the guard gap ther-
mopile voltage and the temperature sensors.
National Institute of Standards
and Technology,
Gaithersburg, MD 20899-8632
robert.zarr@nist.gov
Key words: building technology; fibrous
glass blanket; guarded hot plate; thermal
conductivity; thermal insulation; thermal
resistance; uncertainty.
Accepted: November 3, 2009
Available online: http://www.nist.gov/jres
1. Introduction
uncertainties for the NIST 1016 mm Guarded-Hot-
Plate apparatus and expresses the uncertainties in a
manner consistent with NIST policy. The uncertainty
assessment presented herein elaborates on a previous
effort [3] presented in 1997 for the production of NIST
Standard Reference Material (SRM) 1450c and super-
sedes the previous error analysis prepared by Rennex in
1983 [4]. Technical details of the apparatus design and
fabrication have been described previously [5-6] and,
therefore, are only briefly presented here.
The guarded-hot-plate method was standardized in
1945 after many years of effort and designated ASTM
Test Method C 177 [7]. Essentially, the method estab-
lishes steady-state heat flow through flat homogeneous
slabs—the surfaces of which are in contact with ad-
In October 1992, NIST officially adopted a new
policy [1] for the expression of measurement uncertain-
ty consistent with international practices. The NIST
policy is based on recommendations by the Comité
International des Poids et Mesures (CIPM) given in the
Guide to the Expression of Uncertainty in Measurement
[2] hereafter, called the GUM.1 This report assesses the
1 Certain commercial entities, equipment, or materials may be iden-
tified in this document in order to describe an experimental proce-
dure or concept adequately. Such identification is not intended to
imply recommendation or endorsement by the National Institute of
Standards and Technology, nor is it intended to imply that the enti-
ties, materials, or equipment are necessarily the best available for the
purpose.
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