ASTM E377-08(2020)

Standard Practice for Internal Temperature Measurements in Low-Conductivity Materials

SIGNIFICANCE AND USE
2.1 Internal temperature measurements are made on both in-flight vehicles and on-ground test specimens; and, because of the importance of the temperature measurements to the design of various missile and spacecraft heat shields, it is essential that care be taken to minimize the sources of error in obtaining these measurements.  
2.2 Over the past several years, the problems of using thermocouples to obtain accurate temperature measurements in low-conductivity specimens have been studied by various people to isolate the sources of error and to establish improved temperature measurement techniques. The major sources of error are listed in this document and recommended solutions to the problems are given.
SCOPE
1.1 This practice covers methods for instrumenting low-conductivity specimens for testing in an environment subject to rapid thermal changes such as produced by rocket motors, atmospheric re-entry, electric-arc plasma heaters, and so forth. Specifically, practices for bare-wire thermocouple instrumentation applicable to sheath-type thermocouples are discussed.  
1.2 The values stated in inch-pound units are to be regarded as the standard. The metric equivalents of inch-pound units may be approximate.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2020
• ICS: 49.025.40 - Rubber and plastics
• Technical Committee: E21 - Space Simulation and Applications of Space Technology
• Drafting Committee: E21.08 - Thermal Protection

Overview

ASTM E377-08(2020), Standard Practice for Internal Temperature Measurements in Low-Conductivity Materials, establishes standardized methods for accurately measuring internal temperatures of low-conductivity materials. These measurements are critical in high-performance environments such as aerospace, where materials are exposed to rapid thermal changes from rocket motors, atmospheric re-entry, or electric-arc plasma heaters. This practice focuses on instrumenting specimens using thermocouples-specifically, bare-wire types and their sheath-type equivalents.

The accuracy of internal temperature data plays a vital role in the design and validation of heat shields for missiles and spacecraft, as well as in on-ground specimen testing. By identifying and minimizing sources of measurement error, this standard ensures that temperature readings reflect actual material behavior and support informed engineering decisions.

Key Topics

• Instrumentation Techniques
  Methods for positioning and securing thermocouples in low-conductivity materials to minimize measurement errors.

• Error Sources and Mitigation
  Details common sources of error, such as thermal disturbance from the sensor, electrical shorting of leads, and inaccuracies in sensor placement. Presents recommended solutions for each situation.

• Thermocouple Configuration
  Best practices regarding junction bead diameter, thermocouple wire length and size, and appropriate insulation approaches.

• Verification Procedures
  Emphasizes the importance of accurate thermocouple placement, including the use of X-ray examination to ensure precise location and avoid gas pockets or misalignment.

• Safety, Health, and Environmental Considerations
  Highlights the need for users to implement safety and regulatory practices tailored to their applications and locations.

Practical Applications

The ASTM E377-08(2020) standard is highly relevant in industries requiring precise internal temperature measurements of low-conductivity materials under extreme thermal conditions:

• Aerospace
  Used for the instrumentation of spacecraft and missile heat shields to record internal temperatures during simulated or actual flight conditions.

• Material Testing Laboratories
  Applies during the evaluation of new ablative and insulating materials exposed to sudden temperature changes, such as those from plasma arcs or re-entry simulation.

• Thermal Protection System Design
  Temperature measurement data gathered according to this standard is crucial for validating computational models, determining minimum material thickness, and overall thermal protection system design.

• Industrial Furnace and Kiln Testing
  Relevant for monitoring temperature profiles within low-conductivity refractory linings, where thermal gradients can significantly affect performance and safety.

Related Standards

Adhering to ASTM E377-08(2020) complements using other key standards and references in temperature measurement:

• ASTM MNL12 - Manual on the Use of Thermocouples in Temperature Measurement
• ASTM STP 492 - The Theory and Properties of Thermocouple Elements
• ANSI MC96.1 - Temperature Measurement Thermocouples
• Other ASTM E21 Series Standards - Pertaining to space technology and thermal protection

Professionals using this practice should ensure compatibility and compliance with the above standards for reliable, repeatable, and internationally recognized results.

Keywords: internal temperature measurement, low-conductivity materials, thermocouples, thermal protection, aerospace, ASTM E377, spacecraft heat shields, measurement error minimization, bare-wire thermocouples, high-temperature testing.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E377 − 08 (Reapproved 2020)
Standard Practice for
Internal Temperature Measurements in Low-Conductivity
Materials
This standard is issued under the fixed designation E377; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope error are listed in this document and recommended solutions to
the problems are given.
1.1 This practice covers methods for instrumenting low-
conductivityspecimensfortestinginanenvironmentsubjectto
3. General
rapid thermal changes such as produced by rocket motors,
3.1 Before proceeding to the major sources of error, it is
atmospheric re-entry, electric-arc plasma heaters, and so forth.
assumed that the reader is familiar with basic methods of
Specifically, practices for bare-wire thermocouple instrumen-
forming and using thermocouples , that is (1) electric welding
tation applicable to sheath-type thermocouples are discussed.
to form junctions, (2) maintaining cleanliness of junction area
1.2 The values stated in inch-pound units are to be regarded
and lead wires, (3) proper selection of thermocouple type and
as the standard. The metric equivalents of inch-pound units
size, corresponding to both the temperature range to be
may be approximate.
measured and the chemical compatibility with the
1.3 This standard does not purport to address all of the
environment, and (4) proper use of instrumentation for readout
safety concerns, if any, associated with its use. It is the
of thermocouple emf.
responsibility of the user of this standard to establish appro-
NOTE 1—Reader is referred toASTM MNL12 (1), and STP492 (2), as
priate safety, health, and environmental practices and deter-
well as Kinzie, P.A., Thermocouple Temperature Measurement (3), for
mine the applicability of regulatory limitations prior to use.
needed information.
1.4 This international standard was developed in accor-
3.2 The most important sources of error beyond the above
dance with internationally recognized principles on standard-
basic areas are the following:
ization established in the Decision on Principles for the
3.2.1 The thermal disturbance produced in the low-
Development of International Standards, Guides and Recom-
conductivitymaterialatthevicinityofthethermocouplesensor
mendations issued by the World Trade Organization Technical
hot junction due to the sensor size, configuration, and instal-
Barriers to Trade (TBT) Committee.
lation method.
3.2.2 Electrical shorting of lead wires due to the electrical
2. Significance and Use
conductivity of the virgin or charred ablation material, and
2.1 Internal temperature measurements are made on both
3.2.3 Thermocouple sensor hot junction location accuracy.
in-flight vehicles and on-ground test specimens; and, because
4. Thermal Disturbance at Vicinity of Thermocouple
of the importance of the temperature measurements to the
Sensor Hot Junction
design of various missile and spacecraft heat shields, it is
essential that care be taken to minimize the sources of error in
4.1 General—Ideally, to measure the true internal tempera-
obtaining these measurements.
ture of a solid body, it would be desirable not to have any
foreign substance present that would create a disturbance
2.2 Over the past several years, the problems of using
affecting the natural flow of heat in the body. Since it is
thermocouplestoobtainaccuratetemperaturemeasurementsin
physically impossible to exclude the temperature sensor from
low-conductivity specimens have been studied by various
theinternalconfinesofthebody,itisnecessarythatthethermal
people to isolate the sources of error and to establish improved
disturbanceintroducedbythesensorbeminimizedforaccurate
temperature measurement techniques. The major sources of
temperature measurements (See Refs (4-10)).
4.2 Thermocouple Junction Bead Diameter:
1 4.2.1 General—Excessively large junction beads result in
This practice is under the jurisdiction of ASTM Committee E21 on Space
Simulation andApplications of Space Technology and is the direct responsibility of lower than true temperature measurements in low-conductivity
Subcommittee E21.08 on Thermal Protection.
Current edition approved Nov. 1, 2020. Published December 2020. Originally
approvedin1968.Lastpreviouseditionapprovedin2015asE377 – 08(2015).DOI: ANSI MC96.1-1975. Temperature Measurement Thermocouples (Sponsor
10.1520/E0377-08R20. ISA).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E377 − 08 (2020)
materials (conductivity of material less than conductivity of AWG gage (0.127-mm or 0.005-in.) wire should be used for
thermocouple wire) because of the heat sink effect of the bead. the thermocouple wire from the junction and along the isother-
4.2.2 Recommendations—To minimize this effect, the junc- mal surface which includes the junction. Holes drilled for
tion bead diameter should be no larger than 1.5 wire diameters placementofthermocouplewiresshouldbe3wirediametersor
for butt-welded junctions and 2 wire diameters for other types smaller. It is recommended also that the difference in thermal
of welds. conductivity between thermocouple assembly and the sur-
rounding material be minimized by: (1) avoiding the use of
4.3 Thermocouple Wire in Isothermal Surface of Hot Junc-
relatively conductive (thermal) insulation (such as ceramic and
tion:
fiberglass types) around the portion of wire that is located in
4.3.1 General—Because many materials have low thermal
the isothermal surface that includes the thermocouple junction,
conductivity compared with those of thermocouple assemblies,
and (2) maintaining good thermal contact with the low-
it has been found that certain methods of installing sensors can
conductivity material by bonding the thermocouple to the
produce significant errors in internal temperature measurement
3 specimen (thus eliminating air pockets) with the same or
(1-4). Errors of several hundred degrees are possible unless
similar compound (such as an epoxy plastic) as that used to
heat conduction away from the sensor hot junction, by the
make the specimen.
sensor materials, is minimized. Test results show that a
thermocouple having a sufficient length of bare wire in the
5. Electrical Shorting by Conductive Char Layers
isothermal surface that includes the junction will minimize
these errors.
5.1 General—The char layer formed by most organic ma-
4.3.2 Recommendations—It is therefore recommended that
terials becomes highly conductive (electrically) as pyrolysis
the configuration of the thermocouple sensor be such that the
progresses. Care should be taken to avoid the possibility of
leads perpendicular to the heat flow have a length equivalent to
...