CEN/TS 15548-1:2014

Thermal insulation products for building equipment and industrial installations - Determination of thermal resistance by means of the guarded hot plate method - Part 1: Measurements at elevated temperatures from 100 °C to 850 °C

This Technical Specification provides additional information to that given in EN 12667, EN 12664, EN 12939 and ISO 8302 on the design of apparatus and operational procedures required to determine the thermal resistance of thermal insulation products in the temperature range 100 °C to 850 °C using the guarded hot plate method.

Wärmedämmstoffe für die Haustechnik und für betriebstechnische Anlagen - Bestimmung des Wärmedurchlasswiderstandes nach dem Verfahren mit dem Plattengerät - Teil 1: Messungen bei erhöhten Temperaturen von 100 °C bis 850 °C

Diese Technische Spezifikation stellt zusätzliche Informationen zu den in EN 12667, EN 12664, EN 12939 und ISO 8302 enthaltenen Angaben zur Konstruktion des Prüfgeräts und zu den Arbeitsabläufen zur Verfügung, die für die Bestimmung des Wärmedurchlasswiderstandes von Wärmedämmstoffen im Temperaturbereich von 100 °C bis 850 °C bei Anwendung des Verfahrens mit dem Plattengerät erforderlich sind.

Produits isolants thermiques pour les équipements de bâtiments et les installations industrielles - Détermination de la résistance thermique par la méthode de la plaque chaude gardée - Partie 1: Mesurages à haute témperature entre 100 °C et 850 °C

Le présent document fournit des informations supplémentaires par rapport à celles données dans l’EN 12667, l’EN 12664, l’EN 12939 et l’ISO 8302 sur la conception de l’appareillage et les modes opératoires de fonctionnement nécessaires pour déterminer la résistance thermique des produits isolants thermiques dans la plage de températures allant de 100 °C à 850 °C par la méthode de la plaque chaude gardée.

Toplotnoizolacijski proizvodi za opremo stavb in industrijske inštalacije - Določevanje toplotne upornosti z zaščiteno vročo ploščo - 1. del: Meritve pri povišani temperaturi od 100 °C do 850 °C

Standard CEN/TS 15548-1 vsebuje dodatne informacije za standarde EN 12667, EN 12664, EN 12939 in ISO 8302 o načrtovanju naprav in delovnih postopkov za ugotavljanje toplotne upornosti toplotnoizolacijskih proizvodov v temperaturnem območju od 100 °C do 850 °C z zaščiteno vročo ploščo.

General Information

• Status: Published
• Publication Date: 05-Aug-2014
• ICS: 91.100.60 - Thermal and sound insulating materials
• Technical Committee: CEN/TC 89 - Thermal performance of buildings and building components
• Drafting Committee: CEN/TC 89/WG 11 - Thermal testing of materials
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 06-Aug-2014
• Due Date: 05-Mar-2015
• Completion Date: 06-Aug-2014
• Ref Project: SIST-TS CEN/TS 15548-1:2014 - Thermal insulation products for building equipment and industrial installations - Determination of thermal resistance by means of the guarded hot plate method - Part 1: Measurements at elevated temperatures from 100 °C to 850 °C

Relations

• Replaces: CEN/TS 15548-1:2011 - Thermal insulation products for building equipment and industrial installations - Determination of thermal resistance by means of the guarded hot plate method - Part 1: Measurements at elevated temperatures from 100 °C to 850 °C
• Effective Date: 13-Aug-2014

Overview

CEN/TS 15548-1:2014 is a Technical Specification from CEN that supplements EN 12667, EN 12664, EN 12939 and ISO 8302 for measuring the thermal resistance of thermal insulation products at elevated temperatures (100 °C to 850 °C). It focuses on the guarded hot plate method, offering detailed guidance on apparatus design, operational procedures and limits specific to high‑temperature testing where standard ambient‑temperature methods are insufficient.

Key topics and requirements

• Scope & purpose
  • Extends guarded hot plate testing practice into the 100–850 °C range and documents practical adaptations needed for reliable results.
• Apparatus design
  • Detailed requirements for main heating units, metering area, edge insulation/auxiliary guards, cold plates and plate materials to withstand high temperatures.
• Measurement practice
  • Procedures for measuring heat flow density, temperature difference across specimens, specimen thickness and deriving thermal resistance, transfer factor and, where appropriate, mean thermal conductivity/transmissivity.
• Performance limits & uncertainty
  • Realistic uncertainty expectations are provided: typically ±5% up to 450 °C and ±7% above 450 °C, reflecting material stability, sensor degradation and heat‑loss challenges at high temperatures.
• Specimen handling
  • Guidance on specimen selection, size, preparation and allowances for expansion/shrinkage and inhomogeneity at elevated temperatures.
• Quality & calibration
  • Emphasises sensor calibration, equipment performance checks, stability, uniformity and repeatability requirements; includes normative annex with apparatus limits and suggested sizes.

Applications and who uses this standard

• Testing laboratories conducting steady‑state thermal tests at elevated temperatures to determine material R‑values and thermal conductivity.
• Manufacturers of thermal insulation for building services and industrial installations who need validated high‑temperature properties for product data sheets and compliance.
• Design engineers and specifiers for building equipment, process piping, furnaces and industrial plant where insulation performance above 100 °C matters.
• Certification bodies and regulatory authorities that evaluate thermal performance claims for high‑temperature insulation products.

Related standards

• EN 12667, EN 12664, EN 12939 - complementary guarded hot plate and heat flow meter methods
• ISO 8302 - general guarded hot plate apparatus principles
• EN ISO 7345 / 9288 - definitions for thermal quantities and radiation

This Technical Specification is practical guidance for implementing the guarded hot plate method at elevated temperatures, improving test reliability and supporting accurate thermal performance data for high‑temperature insulation applications. Keywords: guarded hot plate method, thermal resistance, thermal conductivity, elevated temperatures, CEN/TS 15548-1:2014, thermal insulation testing.

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2014
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SIST-TS CEN/TS 15548-1:2012
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'RORþHYDQMHWRSORWQHXSRUQRVWL]]DãþLWHQRYURþRSORãþRGHO0HULWYHSUL
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Thermal insulation products for building equipment and industrial installations -
Determination of thermal resistance by means of the guarded hot plate method - Part 1:
Measurements at elevated temperatures from 100 °C to 850 °C
Wärmedämmstoffe für die Haustechnik und für betriebstechnische Anlagen -
Bestimmung des Wärmedurchlasswiderstandes nach dem Verfahren mit dem
Plattengerät - Teil 1: Messungen bei erhöhten Temperaturen von 100 °C bis 850 °C
Produits isolants thermiques pour les équipements de bâtiments et les installations
industrielles - Détermination de la résistance thermique par la méthode de la plaque
chaude gardée - Partie 1: Mesurages à haute témperature entre 100 °C et 850 °C
Ta slovenski standard je istoveten z: CEN/TS 15548-1:2014
ICS:
91.100.60 0DWHULDOL]DWRSORWQRLQ Thermal and sound insulating
]YRþQRL]RODFLMR materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL SPECIFICATION
CEN/TS 15548-1
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
August 2014
ICS 91.100.60 Supersedes CEN/TS 15548-1:2011
English Version
Thermal insulation products for building equipment and industrial
installations - Determination of thermal resistance by means of
the guarded hot plate method - Part 1: Measurements at
elevated temperatures from 100 °C to 850 °C
Produits isolants thermiques pour les équipements de Wärmedämmstoffe für die Haustechnik und für
bâtiments et les installations industrielles - Détermination de betriebstechnische Anlagen - Bestimmung des
la résistance thermique par la méthode de la plaque chaude Wärmedurchlasswiderstandes nach dem Verfahren mit dem
gardée - Partie 1: Mesurages à haute témperature entre Plattengerät - Teil 1: Messungen bei erhöhten
100 °C et 850 °C Temperaturen von 100 °C bis 850 °C
This Technical Specification (CEN/TS) was approved by CEN on 28 June 2014 for provisional application.

The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.

CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available
promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the CEN/TS)
until the final decision about the possible conversion of the CEN/TS into an EN is reached.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2014 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 15548-1:2014 E
worldwide for CEN national Members.

Contents Page
Foreword .3
Introduction .4
1 Scope .5
2 Normative references .5
3 Terms and definitions, symbols and units .5
3.1 Terms and definitions .5
3.2 Symbols and units .5
4 Principle .6
4.1 Apparatus .6
4.2 Measuring the density of heat flow rate .6
4.3 Measuring the temperature difference .6
4.4 Deriving the thermal resistance or transfer factor .6
4.5 Computing thermal conductivity or thermal transmissivity .6
4.6 Apparatus limits .7
4.7 Specimen limits.7
5 Apparatus description and design requirement .7
5.1 General .7
5.2 Two specimen apparatus .8
5.3 Single specimen apparatus .8
5.4 Plates .8
5.5 Main heating unit . 10
5.6 Edge insulation and auxiliary guards . 11
5.7 Cold plates . 11
5.8 Thickness measurement system . 11
5.9 Accuracy and repeatability . 11
5.10 Uncertainty analysis and equipment performance checks . 11
6 Test specimen . 12
6.1 General . 12
6.2 Selection and size . 12
6.3 Specimen preparation . 12
7 Testing procedure. 13
7.1 General . 13
7.2 Conditioning . 13
7.3 Measurements . 13
8 Calculations and test report . 15
8.1 Density and mass changes . 15
8.2 Heat transfer properties . 16
9 Test report . 17
Annex A (normative) Limits for equipment performance and test conditions . 19
A.1 General . 19
A.2 Accuracy and repeatability, stability, uniformity . 19
A.3 Suggested apparatus sizes . 20
A.4 Equipment design requirements . 20
A.5 Acceptable specimen characteristics . 21
A.6 Acceptable testing conditions . 22
Foreword
This document (CEN/TS 15548-1:2014) has been prepared by Technical Committee CEN/TC 89 “Thermal
performance of buildings and building components”, the secretariat of which is held by SIS.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes CEN/TS 15548-1:2011.
Significant changes between this and the previous edition are:
— In clause 5.4.3, modifications of Figure 1 and Figure 2; now denoted Figure 1a and Figure 1b
— In A.4, for clause 2.1.4.1.2, the value for minimum numbers of sensors is changed to 10√A or 2
— In A.6, for clause 1.7.3, the values are changed to 20 K and 50 K respectively.
— In A.6, for clause 3.3.3, the lower and upper limits of temperature differences across the specimen have
been changed to 30 K and 70 K respectively.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to announce this Technical Specification: Austria, Belgium, Bulgaria, Croatia, Cyprus,
Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany,
Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Introduction
This Technical Specification is an interim solution to the need for a standard to complement EN 12667:2001 in
the approximate temperature range 100 °C to 850 °C.
The Technical Specification is chosen to publish the knowledge gained in the field of measuring thermal
conductivity at elevated temperature now, as the finalisation of a standard is a complex matter requiring
further investigations.
Among existing apparatus for steady state thermal testing, the guarded hot plate can be operated at selected
mean temperatures over the temperature range -100 °C to 850 °C. In general these apparatus exist in three
forms covering roughly the following temperature ranges -100 °C to ambient, ambient to 100 °C and above
100 °C. However it has been found that it is not possible to achieve the uncertainties of ± 2 % claimed as
achievable for the low and ambient temperature forms when using the high temperature version in accordance
with ISO 8302. More realistic figures adopting the method and procedures detailed in this document are ± 5 %
up to 450 °C and ± 7 % at temperatures above 450 °C.
Many issues are more difficult at high temperatures. There are design issues due to apparatus material
stability, the level of temperature measurement uncertainty is higher than at ambient temperatures and there
is also greater degradation in the performance of temperature sensors when operated at high temperatures,
requiring calibration checks to be more frequent. At high temperature it is more likely to get hot spots on a
plate due to non uniformity of a heater; these could be near temperature sensors and give false readings. Any
air gaps will have greater heat flow across them due to radiation heat exchange and finally provisions for
specimen expansion or shrinkage are needed.
Due to the above considerations the following clauses of EN 12667:2001 have been expanded and detailed:
5 Apparatus
5.1 General
5.2.4 Heating Unit
5.2.5 Metering Area
5.2.6 Edge insulation and auxiliary guards
5.2.7 Cooling units
5.3.5 Accuracy and repeatability
6 Test specimens
6.2 Selection and size
7 Testing procedure
7.3.8 Settling time and measurement interval
Annex A
Annex B.2
1 Scope
This Technical Specification provides the additional information to that given in EN 12667, EN 12664,
EN 12939 and ISO 8302 on the design of apparatus and operational procedures required to determine the
thermal resistance of thermal insulation products in the temperature range 100 °C to 850 °C using the
guarded hot plate method.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 1946-2, Thermal performance of building products and components - Specific criteria for the assessment
of laboratories measuring heat transfer properties - Part 2: Measurements by guarded hot plate method
EN 12664, Thermal performance of building materials and products - Determination of thermal resistance by
means of guarded hot plate and heat flow meter methods - Dry and moist products of medium and low
thermal resistance
EN 12667:2001, Thermal performance of building materials and products - Determination of thermal
resistance by means of guarded hot plate and heat flow meter methods - Products of high and medium
thermal resistance
EN 12939, Thermal performance of building materials and products - Determination of thermal resistance by
means of guarded hot plate and heat flow meter methods - Thick products of high and medium thermal
resistance
EN ISO 7345, Thermal insulation - Physical quantities and definitions (ISO 7345)
EN ISO 9288, Thermal insulation - Heat transfer by radiation - Physical quantities and definitions (ISO 9288)
ISO 8302:1991, Thermal insulation - Determination of steady-state thermal resistance and related properties -
Guarded hot plate apparatus
3 Terms and definitions, symbols and units
3.1 Terms and definitions
For the purposes of this document the terms and definitions given in EN ISO 7345 and EN ISO 9288 apply.
3.2 Symbols and units
Symbol Quantity Unit
A metering area measured on a selected isothermal surface m
d thickness; average thickness of specimen m
e edge number ratio -
m mass ( of the specimen ) kg
Δm mass change kg
q density of heat flow rate W/m
R thermal resistance m²·K/W
ΔR increment of thermal resistance m²·K/W
r thermal resistivity m·K/W
T temperature of the warm surface of the specimen K
T temperature of the cold surface of the specimen K
T specimen edge temperature K
T mean test temperature (usually (T + T )/2) K
m 1 2
ΔT temperature difference (usually T - T ) K
1 2
Δt time interval s
T transfer factor W/(m·K)
V volume m
Φ heat flow rate W
λ thermal conductivity W/(m·K)
λ thermal transmissivity W/(m·K)
t
ρ density kg/m
4 Principle
4.1 Apparatus
The principle of the guarded hot plate method is as described in subclause 1.6 of ISO 8302:1991.The guarded
hot plate apparatus is intended to establish a unidirectional constant and uniform density of heat flow rate
within homogeneous specimens, in the form of slabs with flat parallel faces. The part of the apparatus where
this takes place with acceptable accuracy is around its centre; the apparatus is therefore divided in a central
metering section in which measurements are taken, and a surrounding guard section.
NOTE Specimen homogeneity is discussed in A.3.2 of EN 12667:2001.
4.2 Measuring the density of heat flow rate
Following the establishment of steady state in the metering section, the density of heat flow rate, q, is
determined from measurement of the heat flow rate, Φ, and the metering area, A, that the heat flow crosses.
4.3 Measuring the temperature difference
The temperature difference across the specimens, ΔT, is measured by temperature sensors fixed on or in the
surfaces of the plates in contact with the specimens and/or those fixed on/or in the surfaces of the specimens
themselves, where appropriate.
4.4 Deriving the thermal resistance or transfer factor
The thermal resistance, R, is calculated from q, A and ΔT. From the additional knowledge of the thickness, d,
of the specimen, the transfer factor, T, is computed; see A.2.8 of EN 12667:2001.
4.5 Computing thermal conductivity or thermal transmissivity
The mean thermal conductivity, λ or thermal transmissivity λ , of the specimen may also be computed if the
t
appropriate conditions to identify them and those given in A.4.3 of EN 12667:2001 are realised.
4.6 Apparatus limits
The application of the method is limited by the capability of the apparatus to maintain an unidirectional,
constant and uniform density of heat flow rate in the specimen, coupled with the ability to measure power,
temperature and dimensions to the limit of accuracy required, see Annex A.
4.7 Specimen limits
The application of the method is also limited by the shape of the specimen(s) and the degree to which they
are identical in thickness and uniformity of structure (in the case of two specimen apparatus) and whether their
surfaces are flat or parallel, see Annex A.
5 Apparatus description and design requirement
5.1 General
A guarded hot plate apparatus used for measurements according to this document shall comply with the limits
on equipment performance and test conditions given in Annex A and shall conform with the requirements
concerning the assessment of equipment accuracy given in EN 1946-2; this requires that the equipment
design, error analysis and performance checks are according to Section 2 in ISO 8302.
A guarded hot plate design for high temperature measurement needs detailed modelling of heater plates, gap,
imbalance sensors, guard plates, edge insulation and auxiliary guards and requires much more careful design
than its ambient temperature counterpart for the following reasons:
— The heater plate material needs to retain its mechanical properties to the higher operating temperatures.
Suitable materials with the higher strength requirements usually have a lower thermal conductivity than
pure copper and aluminium alloys that are normally used at ambient temperatures. This can mean that
the heater plates have to be thicker to ensure uniform temperature distribution across the plate, which in
turn can lead to higher heat losses or gains from the edges of the plate.
— Extra precautions have to be taken to electrically insulate heater wires and temperature sensors from the
heater plate. One solution is to use sheathed wires but this raises the problem of accurately locating the
voltage probes on the heater wire in the centre of the guard centre gap.
— The use of sheathed temperature sensors to limit the degradation of temperature sensors due to
oxidation can also create additional problems because of the increased area of metal that crosses the
guard centre gap compared to a 0,2 mm diameter thermocouple.
— Despite the use of materials with high strength at high temperatures there could still be problems with
plate distortion at higher temperatures due to residual stresses introduced by machining. This could result
in non parallelism and unacceptable air gaps between the specimen and the heater plates.
In a guarded hot plate apparatus the heat flow rate is obtained from the measurement of the electrical power
input to the heating unit in the metering section. The general features of the apparatus with specimens
installed are shown in Figure 1. The apparatus can have an enclosure to exclude air exchange from enclosure
to ambient and be provided with additional edge guard heaters or a temperature controlled environment
around the specimen assembly.
There exist two types of guarded hot plate apparatus, which conform to the basic principle outlined in
Clause 4:
a) with two specimens (and a central heating unit);
b) with a single specimen.
5.2 Two specimen apparatus
In the two specimen apparatus, (see Figure 1a), a central round or square flat plate assembly, consisting of a
heater and surface plates, called the heating unit, is sandwiched between two nearly identical specimens. The
heat flow rate is transferred through the specimens to separate round or square isothermal flat assemblies,
which may consist of either a heated “cold plate” with additional cooling plates separated by insulation slabs or
separate cooling units.
5.3 Single specimen apparatus
In the single specimen apparatus (see Figure 1b), one of the specimens and its cold plate is replaced by a
combination of a piece of insulation and a guard plate. Zero temperature difference is then established across
this combination. Providing all other applicable requirements of this document are fulfilled, accurate
measurements and reporting according to this method can be achieved with this type of apparatus, but the
test report shall state that a single specimen apparatus was used.
5.4 Plates
5.4.1 General
A guarded hot plate designed for high temperature measurements uses heated plates for both faces of the
specimen, the “cold” plates may also be equipped for cooling or the cooling can be established by other
means, e.g. separate cooling plates.
5.4.2 Plate material
The materials used in the construction of the heating unit shall be chosen carefully to ensure adequate
performance at the temperatures at which the heating unit is to be operated. At high temperatures the chosen
material shall be
— resistant to further oxidation once an initial thin oxidation film has formed;
— able to withstand repeated cycling from room temperature to the highest design temperature without
distorting beyond the flatness requirements;
— of sufficiently high thermal conductivity in relation to the plate thickness and the separation of the wires or
strips forming the heating element to ensure that uniform temperatures can be maintained across the
working surfaces.
Suitable materials might be nickel alloy, pure aluminium, silver, tungsten or aluminium nitride.
5.4.3 Plate geometry
Plates are either square or circular.
Round plates are simpler to model and design although greater care is required both in the assembly and to
ensure uniform heating per area.
Square plates offer a simpler design but for high temperature operation additional heaters with control may be
required in the corners of the guard area in order to maintain a uniform temperature across the plates.
The surface departure from plane shall not exceed 0,025 % as specified in A.4.
Heating unit Heating unit Heating unit
guard section metering section guard section

a) Two specimen apparatus
Heating unit Heating unit Heating unit
guard section metering section guard section

b) Single specimen apparatus
Key
A Metering section heater G Heating unit surface thermocouples
B Metering section surface plates H Cooling unit surface thermocouples
C Guard section heater I Test specimen
D Guard section surface plates L Guard plate heater
E Cooling unit surface plate M Guard plate insulation
F Differential thermocouples N Guard plate differential thermocouples
The gap is the separation between metering section (see A and B) and the guard section (see
C and D)
Figure 1 – General features of the two specimen and single specimen guarded hot plate apparatus
5.4.4 Plate emissivity
The total hemispherical emissivity of the surfaces of the heater plates in contact with the specimen/s shall be
greater than 0,8. As radiative heat transfer through the specimen can be very significant at high temperatures
the actual total hemispherical emissivity shall be determined over the temperature range of the apparatus.
NOTE Details of how to measure the plate emissivity is given in Annex A of EN 1946-2:1999.
5.4.5 Plate temperature uniformity
The heater and cold plates shall be designed carefully to ensure that the temperature uniformity across the
plates is better than 2 % of the temperature drop across the specimens for mean specimen temperatures
below and 450 °C and 3 % for temperatures above 450 °C.
5.4.6 Heating elements, principle and electrical insulation
The electrical insulation of the heater resistance wire shall provide an electrical resistance between the heater
windings and the heater plate greater than 100 MΩ over the whole temperature range of the apparatus.
Suitably insulated potential leads shall be attached to the heater wires at the midpoint of the guard–centre gap
to determine the power delivered to the metering area, or a correction factor shall be determined by
measurement and/or calculation to account for the power loss outside the mid-point of the guard-centre gap.
5.4.7 Plate temperature sensors
Great care shall be taken in choosing a temperature measurement system that does not deteriorate or
degrade with prolonged exposure to high temperatures. A solution to reduce degradation is to use sheathed
temperature sensors but this gives added heat exchange across the gap between the guard and metering
area. If sheathed temperature sensors are used then the outer diameter of the sheath material shall not
exceed 2 mm.
5.5 Main heating unit
5.5.1 General
The heating unit consists of a separate central metering section surrounded by a guard section with minimal
direct contact between the two and separated by a narrow gap. The heating units are applied to establish a
unidirectional, constant and uniform density of heat flow rate within the specimens to be measured.
5.5.2 Metering area and guard to metering area gap
The metering area is the central area of the specimen delimited by the centre line of the gap of the heating
unit. When relevant this area shall be corrected for plate expansion.
This definition, which applies in principle to thick specimens only, has been retained for all the specimens to
be tested according to this document. Due to this approximation, the thickness of the specimen shall be at
least ten times the width of the gap.
5.5.3 Imbalance across gap and position of imbalance sensors
The imbalance sensors, e.g. thermocouples connected as a thermopile or resistance thermometers, shall be
of cross-section as small as possible in order to reduce heat transfer across the gap. Where possible the wire
shall be covered to avoid excessive exposure to air at high temperatures which causes oxidation and
degradation of performance and ultimate breakage of the wire. See ISO 8302:1991 for guidance on placement
and number of sensors.
If the apparatus is designed to operate at temperatures above 450 °C then in order to reduce radiation
exchange across the gap at high temperatures the guard-centre gap shall be filled with a material that is
opaque to thermal radiation and has a thermal conductivity less than 0,1 W/(m·K).
5.6 Edge insulation and auxiliary guards
If the apparatus is not surrounded by an enclosure that is controlled at a temperature that minimises edge
heat transfer then additional edge insulation and/or auxiliary guard sections are required to ensure that the
environment adjacent to the specimen stack is maintained at a uniform temperature close to the mean
specimen temperature. Measurements on edge guard(s) shall be made at minimum four evenly spaced
positions for circular plates, or at mid side positions for square plates to determine temperature uniformity
around the specimen stack. This shall be carried out for at least three temperatures including the minimum,
mid-point and maximum temperatures of the stated temperature range for the apparatus.
The specimen edge temperature shall be monitored and used in the relationship (T – T )/ΔT < 0,2, where
3 m
0,2 is applicable to a mean specimen temperature up to 450 °C and for higher mean temperatures it shall be
less than 0,1.
5.7 Cold plates
The cooling units or heated cold plates shall have dimensions at least as large as those of the heating unit,
including the guard heater(s). They shall consist of plates made from materials with high thermal conductivity
and maintained at a constant and uniform temperature.
5.8 Thickness measurement system
For compressible specimens the thickness shall be determined either by spacers or devices monitoring the
plate positions at all test temperatures. Corrections due to expansion or contraction of spacers shall be
applied. When spacers are used it shall be checked at the end of the test that specimens are in full contact
with plates, if not the test is not valid.
In case of incompressible specimens that expand or contract, plate positions are given by constant plate load
and the thickness can be determined by device(s) monitoring the plate position, or by operator adjustment of
plate positions according to pre-calculated thickness based on the thermal expansion behaviour of the
product.
...