ASTM E344-23

Terminology Relating to Thermometry and Hydrometry

SCOPE
1.1 This terminology is a compilation of definitions of terms used by ASTM Committee E20 on Temperature Measurement.  
1.2 Terms with definitions generally applicable to the fields of thermometry and hydrometry are listed in 3.1.  
1.3 Terms with definitions applicable only to the indicated standards in which they appear are listed in 3.2.  
1.4 Information about the International Temperature Scale of 1990 is given in Appendix X1.  
1.5 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: 30-Nov-2023
• ICS: 01.040.17 - Metrology and measurement. Physical phenomena (Vocabularies)
• ICS: 17.200.20 - Temperature-measuring instruments
• Technical Committee: E20 - Temperature Measurement
• Drafting Committee: E20.91 - Editorial and Terminology

Relations

• Replaces: ASTM E344-20 - Terminology Relating to Thermometry and Hydrometry
• Effective Date: 01-Dec-2023
• Refers: ASTM E230/E230M-23a - Standard Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 01-Nov-2023
• Refers: ASTM E230/E230M-23 - Standard Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 01-May-2023
• Refers: ASTM E230/E230M-17 - Standard Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 01-Nov-2017
• Referred By: ASTM E574-23 - Standard Specification for Duplex, Base Metal Thermocouple Wire With Glass Fiber or Silica Fiber Insulation
• Effective Date: 01-Dec-2023
• Referred By: ASTM E601-20 - Standard Guide for Measuring Electromotive Force (EMF) Stability of Base-Metal Thermoelement Materials With Time in Air
• Effective Date: 01-Dec-2023
• Referred By: ASTM E2995-15a(2020) - Standard Specification for ASTM Thermohydrometers with Integral Low-Hazard Thermometers
• Effective Date: 01-Dec-2023
• Referred By: ASTM E1104-98(2023) - Standard Specification for Clinical Thermometer Probe Covers and Sheaths
• Effective Date: 01-Dec-2023
• Referred By: ASTM E2593-17(2023) - Standard Guide for Accuracy Verification of Industrial Platinum Resistance Thermometers
• Effective Date: 01-Dec-2023
• Referred By: ASTM D7583-16(2023) - Standard Test Method for John Deere Coolant Cavitation Test
• Effective Date: 01-Dec-2023
• Referred By: ASTM E825-98(2023) - Standard Specification for Phase Change-Type Disposable Fever Thermometer for Intermittent Determination of Human Temperature
• Effective Date: 01-Dec-2023
• Referred By: ASTM E879-20 - Standard Specification for Thermistor Sensors for General Purpose and Laboratory Temperature Measurements
• Effective Date: 01-Dec-2023
• Referred By: ASTM E77-14(2021) - Standard Test Method for Inspection and Verification of Thermometers
• Effective Date: 01-Dec-2023
• Referred By: ASTM E1750-23 - Standard Guide for Use of Water Triple Point Cells
• Effective Date: 01-Dec-2023
• Referred By: ASTM E1480-92(2022) - Standard Terminology of Facility Management (Building-Related)
• Effective Date: 01-Dec-2023

Overview

ASTM E344-23, Terminology Relating to Thermometry and Hydrometry, is an international standard developed by ASTM Committee E20 on Temperature Measurement. This standard provides a comprehensive compilation of definitions and terminology widely used in the fields of thermometry and hydrometry. It serves as the foundational reference for clear communication, quality assurance, and consistency amongst professionals, standard developers, laboratories, and industries that require precise temperature and hydrometric measurements.

The terminology outlined in this standard applies generally to temperature and hydrometric measurement, with some terms specifically referenced within individual standards. Additionally, ASTM E344-23 includes important references to the International Temperature Scale of 1990 (ITS-90) and acknowledges its development in line with the globally recognized principles on standardization by the WTO Technical Barriers to Trade (TBT) Committee.

Key Topics

• Definitions for Thermometry and Hydrometry: Includes core terms such as accuracy, calibration, calibration point, reference junction, repeatability, reproducibility, traceability, thermocouple, resistance thermometer, and more.
• Types of Temperature Sensors: Explains the distinctions among thermocouples (base metal, noble metal, refractory metal), platinum resistance thermometers (SPRTs, IPRTs, secondary reference PRTs), thermistors, and hydrometers.
• Measurement and Calibration Concepts: Clarifies concepts such as temperature scales (Celsius, Fahrenheit, Kelvin), fixed points (triple point, freezing point, melting point), error, uncertainty, precision, bias, and tolerance.
• Components and Assemblies: Defines items like connection heads, probe covers, protecting tubes, thermowells, styles of measuring junctions, and cable types.
• International Standards Alignment: Includes terminology and references in line with ITS-90 and other major international guides (ISO, IEC, NIST, ANSI).

Applications

ASTM E344-23 is essential across a range of practical and industrial contexts, including:

• Calibration Laboratories: Facilitates consistent documentation and reporting of thermometer and hydrometer calibrations by ensuring the proper use of standard terms.
• Manufacturing and Quality Control: Supports process consistency and compliance when measuring and controlling temperature and density in manufacturing environments, from chemical processing to food production.
• Healthcare and Clinical Labs: Ensures uniform understanding in the design, use, and calibration of clinical thermometers and hydrometers for diagnostics and laboratory studies.
• Research and Development: Provides those involved in temperature-related research with a common language for describing measurement principles, results, and uncertainties.
• Instrument Design and Maintenance: Enables manufacturers and field service providers to describe instrument components, sensor types, and operational characteristics with precision.
• International Trade and Regulatory Compliance: Supports the clear communication required for conformity assessment, accreditation, and standardization in the global marketplace.

Related Standards

ASTM E344-23 draws upon and supports the use of a variety of ASTM and internationally recognized standards, including:

• ASTM E1 - Specification for ASTM Liquid-in-Glass Thermometers
• ASTM E100 - Specification for ASTM Hydrometers
• ASTM E220 - Calibration of Thermocouples by Comparison Techniques
• ASTM E1137/E1137M - Specification for Industrial Platinum Resistance Thermometers
• ASTM E1594 - Guide for Expression of Temperature
• ISO/IEC 17025 - Competence of Testing and Calibration Laboratories
• IEC 61298-1 - Process Measurement and Control Devices
• NIST Monographs and Technical Notes - Calibration and uncertainty evaluation guidance
• JCGM 100:2008 - Guide to the expression of uncertainty in measurement
• ANSI/NCSL Z540 - Guide to the expression of uncertainty in measurement

For those involved in temperature and hydrometric measurement, ASTM E344-23 provides the essential terminology and conceptual clarity needed for standardization, regulatory compliance, and accuracy across scientific and industrial domains.

Keywords: ASTM E344-23, thermometry terminology, hydrometry definitions, temperature measurement, calibration standards, ITS-90, ASTM standards, international temperature scale.

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: E344 − 23
Terminology Relating to
Thermometry and Hydrometry
This standard is issued under the fixed designation E344; 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 E574 Specification for Duplex, Base Metal Thermocouple
Wire With Glass Fiber or Silica Fiber Insulation
1.1 This terminology is a compilation of definitions of terms
E585/E585M Specification for Compacted Mineral-
used by ASTM Committee E20 on Temperature Measurement.
Insulated, Metal-Sheathed, Base Metal Thermocouple
1.2 Terms with definitions generally applicable to the fields
Cable
of thermometry and hydrometry are listed in 3.1.
E601 Guide for Measuring Electromotive Force (EMF) Sta-
1.3 Terms with definitions applicable only to the indicated bility of Base-Metal Thermoelement Materials With Time
in Air
standards in which they appear are listed in 3.2.
E608/E608M Specification for Mineral-Insulated, Metal-
1.4 Information about the International Temperature Scale
Sheathed Base Metal Thermocouples
of 1990 is given in Appendix X1.
E644 Test Methods for Testing Industrial Resistance Ther-
1.5 This international standard was developed in accor-
mometers
dance with internationally recognized principles on standard-
E667 Specification for Mercury-in-Glass, Maximum Self-
ization established in the Decision on Principles for the 3
Registering Clinical Thermometers (Withdrawn 2022)
Development of International Standards, Guides and Recom-
E696 Specification for Tungsten-Rhenium Alloy Thermo-
mendations issued by the World Trade Organization Technical
couple Wire
Barriers to Trade (TBT) Committee.
E710 Test Method for Comparing EMF Stabilities of Base-
Metal Thermoelements in Air Using Dual, Simultaneous,
2. Referenced Documents
Thermal-EMF Indicators (Withdrawn 2006)
2.1 ASTM Standards:
E780 Test Method for Measuring the Insulation Resistance
E1 Specification for ASTM Liquid-in-Glass Thermometers
of Mineral-Insulated, Metal-Sheathed Thermocouples and
E77 Test Method for Inspection and Verification of Ther-
Mineral-Insulated, Metal-Sheathed Cable at Room Tem-
mometers
perature
E100 Specification for ASTM Hydrometers
E825 Specification for Phase Change-Type Disposable Fe-
E126 Test Method for Inspection, Calibration, and Verifica-
ver Thermometer for Intermittent Determination of Hu-
tion of ASTM Hydrometers
man Temperature
E207 Test Method for Thermal EMF Test of Single Thermo-
E839 Test Methods for Sheathed Thermocouples and
element Materials by Comparison With Reference Ther-
Sheathed Thermocouple Cable
moelement of Similar EMF-Temperature Properties
E879 Specification for Thermistor Sensors for General Pur-
E220 Test Method for Calibration of Thermocouples By
pose and Laboratory Temperature Measurements
Comparison Techniques
E1061 Specification for Direct-Reading Liquid Crystal Fore-
E230/E230M Specification for Temperature-Electromotive
head Thermometers
Force (emf) Tables for Standardized Thermocouples
E1104 Specification for Clinical Thermometer Probe Covers
E452 Test Method for Calibration of Refractory Metal Ther-
and Sheaths
mocouples Using a Radiation Thermometer
E1112 Specification for Electronic Thermometer for Inter-
mittent Determination of Patient Temperature
E1129/E1129M Specification for Thermocouple Connectors
This terminology is under the jurisdiction of ASTM Committee E20 on
Temperature Measurement and is the direct responsibility of Subcommittee E20.91 E1137/E1137M Specification for Industrial Platinum Resis-
on Editorial and Terminology.
tance Thermometers
Current edition approved Dec. 1, 2023. Published December 2023. Originally
E1159 Specification for Thermocouple Materials, Platinum-
approved in 1968. Last previous edition approved in 2020 as E344 – 20. DOI:
Rhodium Alloys, and Platinum
10.1520/E0344-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E344 − 23
E1256 Test Methods for Radiation Thermometers (Single NIST Monograph 175 Temperature-Electromotive Force
Waveband Type) Reference Functions and Tables for the Letter-Designated
E1299 Specification for Reusable Phase-Change-Type Fever Thermocouple Types Based on the ITS-90
Thermometer for Intermittent Determination of Human NIST SP 250-22 Platinum Resistance Thermometer Calibra-
Temperature tions
E1350 Guide for Testing Sheathed Thermocouples, Thermo- NIST SP 250-23 Liquid-in-Glass Thermometer Calibration
couple Assemblies, and Connecting Wires Prior to, and Service
After Installation or Service NIST Technical Note 1297 Guidelines for Evaluating and
E1502 Guide for Use of Fixed-Point Cells for Reference Expressing the Uncertainty of NIST Measurement
Temperatures Results, 1994 Edition
E1594 Guide for Expression of Temperature 2.2.2 ANSI Documents
E1684/E1684M Specification for Miniature Thermocouple ANSI/NCSL Z540.2-1997 (R2012) U.S. Guide to the Ex-
Connectors pression of Uncertainty in Measurement
E1750 Guide for Use of Water Triple Point Cells ANSI/NCSL Z540.3-2006 American National Standard for
E1751/E1751M Guide for Temperature Electromotive Force Calibration—Calibration Laboratories and Measuring and
(emf) Tables for Non-Letter Designated Thermocouple Test Equipment—General Requirements
Combinations 2.2.3 IEC Documents
E1965 Specification for Infrared Thermometers for Intermit- IEC 61298-1 Process Measurement and Control Devices—
tent Determination of Patient Temperature General Methods and Procedures for Evaluating
E2181/E2181M Specification for Compacted Mineral- Performance—Part 1: General Considerations
Insulated, Metal-Sheathed, Noble Metal Thermocouples IEC TS 62492-1 Industrial Process Control Devices—
and Thermocouple Cable Radiation Thermometers—Part 1: Technical Data for
E2251 Specification for Liquid-in-Glass ASTM Thermom- Radiation Thermometers
eters with Low-Hazard Precision Liquids 2.2.4 BIPM Documents
E2488 Guide for the Preparation and Evaluation of Liquid JCGM 100:2008 Evaluation of measurement data—Guide to
Baths Used for Temperature Calibration by Comparison the expression of uncertainty in measurement
E2593 Guide for Accuracy Verification of Industrial Plati- JCGM 200:2012 International Vocabulary of Metrology—
num Resistance Thermometers Basic and General Concepts and Associated Terms (VIM)
E2623 Practice for Reporting Thermometer Calibrations 2.2.5 ISO Documents
E2730 Guide for Calibration and Use of Thermocouple ISO/IEC 17025:2017 General Requirements for the Compe-
Reference Junction Probes in Evaluation of Electronic tence of Testing and Calibration Laboratories
Reference Junction Compensation Circuits ISO/IEC Guide 98-3 Uncertainty of Measurement—Part 3:
E2758 Guide for Selection and Use of Infrared Thermom- Guide to the Expression of Uncertainty in Measurement
eters (GUM:1995)
E2820 Test Method for Evaluating Thermal EMF Properties ISO 1768:1975 Glass Hydrometers—Conventional Value
of Base-Metal Thermocouple Connectors for the Thermal Cubic Expansion Coefficient (for Use in
E2821 Specification for Compacted Mineral-Insulated, the Preparation of Measurement Tables for Liquids)
Metal-Sheathed Cable Used in Industrial Resistance Ther- 2.2.6 Other documents
mometers UKAS M3003 The Expression of Uncertainty and Confi-
E2846 Guide for Thermocouple Verification dence in Measurement, Edition 4
E2847 Test Method for Calibration and Accuracy Veri-
3. Terminology
fication of Wideband Infrared Thermometers
E2877 Guide for Digital Contact Thermometers
3.1 Definitions:
E2995 Specification for ASTM Thermohydrometers with
accuracy, n—of a temperature measurement, closeness of
Integral Low-Hazard Thermometers
agreement between the result of a temperature measurement
E3186 Guide for Use and Testing of Dry-Block Temperature
and a true value of the temperature.
Calibrators
DISCUSSION—Accuracy is a qualitative concept.
2.2 Other Standards, Supplementary Vocabularies, and
Sources:
2.2.1 NIST Documents
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org.
ITS-90 The International Temperature Scale of 1990
Available from International Electrotechnical Commission (IEC), 3, rue de
NIST Monograph 126 Platinum Resistance Thermometry
Varembé, 1st floor, P.O. Box 131, CH-1211, Geneva 20, Switzerland, https://
NIST Monograph 150 Liquid-in-Glass Thermometry
www.iec.ch.
Available from International Bureau of Weights and Measures (BIPM),
Pavillon de Breteuil, F-92312 Sèvres Cedex, Paris, France, http://www.bipm.org.
4 9
Available from National Institute of Standards and Technology (NIST), 100 Available from International Organization for Standardization (ISO), ISO
Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov. Central Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Preston-Thomas, H., METROLOGIA, Vol. 27, 1990, pp 3-10 and 107 (errata). Switzerland, https://www.iso.org.
Mangum, B. W., JOURNAL OF RESEARCH, National Institute of Standards and United Kingdom Accreditation Service 2 Pine Trees, Chertsey Lane, Staines-
Technology, Vol 95, 1990, p. 69. upon-Thames, TW18 3HR, https://www.ukas.com.
E344 − 23
base metal thermocouple, n—thermocouple whose thermo- form with the wire being electrically insulated from the tube
elements are composed primarily of base metals and their except at the measuring junction.
alloys. (See also noble metal thermocouple; refractory
compensating extension wires, n—those extension wires
metal; thermocouple.)
fabricated from materials basically different in composition
DISCUSSION—Base metals used in thermoelements include nickel,
from the thermocouple.
iron, chromium, copper, and aluminum. Letter-designated types E, J, K,
DISCUSSION—They have similar thermoelectric properties and within
T, and N are considered base metal thermocouples.
a stated temperature range effectively transfer the reference junction to
the other end of the wires.
bias, n—the scatter between the mean values of subsets of data,
from each other or from the accepted value.
complete immersion thermometer, n—a liquid-in-glass ther-
mometer designed to indicate temperatures correctly when
blackbody, n—the perfect or ideal source of thermal radiant
the entire thermometer is exposed to the temperature being
power having a spectral distribution described by the Planck
measured. (Compare total immersion thermometer and
equation.
partial immersion thermometer.)
DISCUSSION—The term blackbody is often used to describe a furnace
or other source of radiant power which approximates the ideal.
connection head, n—a housing enclosing a terminal block for
an electrical temperature-sensing device and usually pro-
bulb, n—of a liquid-in-glass thermometer, reservoir for the
vided with threaded openings for attachment to a protecting
thermometric liquid.
tube and for attachment of conduit.
calibration, n—of a thermometer or thermometric system, the
defining fixed point, n—thermometric fixed point of an
set of operations that establishes the relationship between the
idealized system, to which a numerical value has been
indications of a thermometer or thermometric system and the
assigned, used in defining a temperature scale.
corresponding reference standard at discrete temperature
values; the operations are performed under specified condi-
degree Celsius, °C, n—derived unit of temperature in the
tions; the calibration results are often used to establish this
International System of Units (SI). (See kelvin.)
relationship at other temperature values; the communicated
DISCUSSION—At any temperature, an interval of one degree Celsius is
results shall include a statement of the measurement uncer-
the same as an interval of one kelvin, by definition. (For information
tainty for each measurement result.
about the relation between units and values of temperature expressed in
different units, see Guide E1594.)
DISCUSSION—(1) The result of a calibration permits either the
assignment of values of temperature to indicated values of thermomet-
degree centigrade, n—obsolete term; use degree Celsius.
ric quantity, or the determination of additive or multiplicative correc-
tions with respect to indications, or both. (2) A calibration may also
degree Fahrenheit, °F, n—non-SI unit of temperature com-
determine other metrological properties such as the effect of influence
monly used in the United States of America.
quantities. (3) The result of a calibration may be communicated in a
DISCUSSION—At any temperature, an interval of one degree Fahren-
document such as a calibration certificate, calibration report, calibration
heit is the same as an interval of 5/9 kelvin (or 5/9 degree Celsius). (For
function, calibration diagram, calibration curve, or calibration table. (4)
information about the relation between units and values of temperature
The term calibration has also been used in standards under E20
expressed in different units, see Guide E1594.)
jurisdiction to refer to the result of the operations, to representations of
the result, and to the actual relationship between values of the
electromotive force (emf), n—the electrical potential differ-
thermometric quantity and temperature.
ence which produces or tends to produce an electric current.
calibration point, n—a specific value, established by a
error, n—of a temperature measurement, result of a tempera-
reference, at which the indication or output of a measuring
ture measurement minus a true value of temperature.
device is determined.
extension wires, n—those having temperature-emf character-
Celsius, adj—pertaining to or denoting something related to
istics that when connected to a thermocouple effectively
the expression of temperature in degrees Celsius.
transfer the reference junction to the other end of the wires.
DISCUSSION—For example, “A Celsius thermometer has a scale
(Compare compensating extension wires.)
marked in degrees Celsius.”
extrapolation, n—the estimation of a value of a measurement
center wavelength, n—a wavelength, usually near the middle
beyond the values already measured by the extension of a
of the band of radiant power over which a radiation
curve based on the measured values.
thermometer responds, that is used to characterize its per-
formance. Fahrenheit, adj—pertaining to or denoting something related
DISCUSSION—The value of the center wavelength is usually specified to the expression of temperature in degrees Fahrenheit.
by the manufacturer of the instrument.
DISCUSSION—For example, “A Fahrenheit thermometer has a scale
marked in degrees Fahrenheit.”
clinical thermometer, n—thermometer of any type designed to
fixed point, n—in thermometry, reproducible temperature of
measure human body temperature.
equilibrium of a system of two or more phases under
DISCUSSION—Some clinical thermometers may be designed to mea-
sure the body temperature of animals. specified conditions.
coaxial thermocouple, n—a thermocouple consisting of a freezing point, n—fixed point of a single component system in
thermoelement in wire form within a thermoelement in tube which liquid and solid phases are in equilibrium at a
E344 − 23
specified pressure, usually 101 325 Pa, and the system is maximum permissible errors, n—of a thermometer or ther-
losing heat slowly. (Compare melting point.) mometric system, extreme values permitted by regulation or
specification of the difference between the indication of a
grounded junction, n—a measuring junction of a thermo-
thermometer or thermometeric system and the true value of
couple assembly that is electrically and physically connected
temperature.
to its sheath. (See also Style G.)
DISCUSSION—The term tolerance is sometimes used in ASTM stan-
DISCUSSION—The term “grounded” has been historically accepted in
dards to represent this concept.
the field of thermometry to indicate the electrical connectivity of a
thermocouple’s measuring junction to its sheath; the term does not maximum self-registering clinical thermometer, n—clinical
indicate whether or not the measuring junction is electrically connected
thermometer designed to retain the indication of its maxi-
to earth or circuit ground.
mum measured temperature until reset.
hysteresis, n—the property of a device or instrument whereby
measuring junction, n—that junction of a thermocouple
it gives different output values in relation to its input values
which is subjected to the temperature to be measured.
depending upon the directional sequence in which the input
melting point, n—fixed point of a single component system in
values have been applied. IEC 61298-1
which liquid and solid phases are in equilibrium at a
ice point, n—thermometric fixed point of ice and water
specified pressure, usually 101 325 Pa, and the system is
saturated with air at a pressure of 101 325 Pa. gaining heat slowly. (Compare freezing point.)
industrial platinum resistance thermometer (IPRT), n—a mineral insulated metal-sheathed (MIMS) cable, n—a bend-
able cable consisting of one or more conductors embedded in
rugged platinum resistance thermometer suitable for tem-
a metal protecting sheath, insulated from each other and
perature measurements in harsh industrial environments
from the sheath by a compacted mineral material.
over all or part of the temperature range –200 to 650 °C.
DISCUSSION—(1) The sensing element is made from platinum wire or
noble metal thermocouple, n—thermocouple whose thermo-
film and packaged in a rugged housing to withstand harsh operating
elements are composed primarily of noble metals and their
conditions. The sheath material is usually stainless steel or Inconel;
alloys. (See also base metal thermocouple; refractory
however, other materials may be used for special applications. (2) The
resistance-temperature relationship is usually defined by a specified metal thermocouple.)
nominal equation and interchangeability tolerances over a specified DISCUSSION—Noble metals used in thermoelements include platinum,
temperature range. (3) IPRTs have ice-point resistance values of at least rhodium, gold, palladium, and iridium. Letter designated types B, R,
100 ohm, and are available with two-wire, three-wire or four-wire and S are considered noble metal thermocouples.
terminations. (4) IPRTs are the most rugged and lowest cost platinum
partial immersion thermometer, n—a liquid-in-glass ther-
resistance thermometers.
mometer designed to indicate temperatures correctly when
International Practical Temperature Scale (IPTS-48),
the bulb and a specified part of the stem are exposed to the
n—the temperature scale adopted by the 11th General
temperatures being measured. (Compare complete immer-
Conference on Weights and Measures in 1960 and replaced
sion thermometer and total immersion thermometer.)
in 1968 by the International Practical Temperature Scale of
Peltier coefficient, n—the reversible heat which is absorbed or
1968.
evolved at a thermocouple junction when unit current passes
International Practical Temperature Scale of 1968 (IPTS- in unit time.
68), n—the temperature scale adopted by the 13th General
platinum 27 (Pt-27), n—the platinum standard to which the
Conference on Weights and Measures in 1968.
National Bureau of Standards referred thermoelectric mea-
DISCUSSION—The IPTS-68 was superseded in 1990 by the Interna-
surements prior to 1973.
tional Temperature Scale of 1990.
platinum 67 (Pt-67), n—the platinum standard used by the
International Temperature Scale of 1990 (ITS-90), n—the
National Bureau of Standards after 1972 as the reference to
temperature scale prepared in accordance with instructions
which thermoelectric measurements are referred.
of the 18th General Conference on Weights and Measures,
platinum resistance thermometer (PRT), n—a resistance
and adopted on January 1, 1990.
thermometer with the resistance element constructed from
interpolation, n—the estimation of a value of a measurement
platinum or platinum alloy.
between the values already measured by the estimation of a
DISCUSSION—Platinum resistance thermometers are available in a
curve based on the measured values.
variety of designs for use over the general temperature range of –259
to 962 °C or portions thereof. The construction details of each PRT
kelvin, K, n—base unit of temperature in the International
design (type of element, connecting wire construction, insulation,
System of Units (SI).
sealing, and mounting) are tailored to maximize the performance of the
thermometer for the intended application and temperature range. (See
liquid-in-glass thermometer, n—a temperature-measuring in-
also Standard Platinum Resistance Thermometer (SPRT); Indus-
strument whose indications are based on the temperature
trial Platinum Resistance Thermometer (IPRT); Secondary Refer-
coefficient of expansion of a liquid relative to that of its
ence PRT Thermometer.)
containing glass bulb.
precision, n—the scatter between individual values of test data
lower range value, n—the lowest quantity that an instrument within the subset, normally computed with respect to the
is adjusted to measure. mean of the subset. (See bias.)
E344 − 23
probe cover and sheath, n—a device provided for the purpose repeatability, n—of results of temperature measurements,
of preventing biological contact between the patient and the closeness of agreement between the results of successive
probe or thermometer. measurements of the same temperature carried out under the
same conditions of measurement.
protecting tube, n—a tube designed to enclose a temperature-
DISCUSSION—(1) Repeatability conditions include the same measure-
sensing device and protect it from the deleterious effects of
ment procedure; the same observer; the same thermometer or thermom-
the environment.
eteric system, used under the same conditions; the same location; and
DISCUSSION—It may provide for attachment to a connection head but repetition over a short interval of time. (2) Repeatability may be
is not primarily designed for pressure-tight attachment to a vessel. (See expressed quantitatively in terms of the dispersion characteristics of the
also thermowell.) results such as the mean value and standard deviation.
radiation thermometer, n—a radiometer calibrated to indicate
reproducibility, n—of results of temperature measurements,
the temperature of a blackbody. closeness of agreement between the results of measurements
of the same temperature carried out under changed condi-
radiometer, n—a device for measuring radiant power that has
tions of measurement.
an output proportional to the intensity of the input power.
DISCUSSION—(1) A valid statement of reproducibility requires speci-
fication of the conditions changed. (2) The changed conditions may
range, n—of a thermometer of thermometric system, a set of
include principle of measurement, method of measurement, observer,
temperatures within specified lower and upper tempurature
thermometer or thermometric system, reference standard(s), location,
limits.
conditions of use, and time. For ASTM standard test methods, the
DISCUSSION—The “operating range,” “measuring range,” “working
method is not changed. (3) Reproducibility may be expressed quanti-
range,” or “scale range” is the set of exposure temperatures for the
tatively in terms of the dispersion characteristics of the results such as
sensing portion of a thermometer or thermometric system that permits
the mean value and standard deviation. (4) Results are here usually
temperature measurements to be made with specified uncertainty. With
understood to be corrected results.
certain liquid-in-glass thermometers, an auxiliary scale or reference
scale is provided. The “range” of such liquid-in-glass thermometers resistance thermometer, n—a temperature-measuring device
includes only the “working range” or “measuring range” and does not
comprised of a resistance thermometer element, internal
include the auxiliary scale or reference scale (when applicable).
connecting wires, a protective shell with or without means
for mounting, a connection head, or connecting wire or other
DISCUSSION—The “storage temperature range” or “non-operating
fittings, or both.
temperature range” is set of exposure temperatures that the thermom-
eter or thermometric system can endure without adversely affecting the
resistance thermometer element, n—the temperature-
ability to make temperature measurements with specified uncertainty
when subsequently placed into service. Some specifications provide for sensitive portion of the thermometer composed of resistance
a maximum increase in specified uncertainty after exposure to the
wire, film or semiconductor material, its supporting
storage temperature range for a specified period of time.
structure, and means for attaching connecting wires.
DISCUSSION—The “ambient temperature range” is the set of exposure
secondary reference PRT thermometers, n—a general pur-
temperatures that the indication or display portion of the thermometer
pose laboratory reference thermometer (also referred to as
or thermometric system can endure during the measurement process
“Secondary SPRT” and “Secondary Reference PRT”) de-
without adversely affecting the ability to make temperature measure-
signed to be a suitable standard for routine temperature
ments.
measurement over all or part of the range –200 to 650 °C.
DISCUSSION—See also span.
DISCUSSION—(1) Secondary reference PRT thermometers have a
sensing element made from strain-free platinum wire such that the
reference junction, n—that junction of a thermocouple which
finished thermometer meets the specified stability and repeatability
is at a known temperature.
requirements but not necessarily the acceptance criteria defined by the
ITS-90. (2) Secondary reference PRT thermometers are typically
reference temperature, n—that temperature, however
configured with a long-stem metal sheath, have nominal ice-point
determined, whose value and accompanying uncertainty, are
resistance values between 25 and 100 ohm, and feature four-wire
taken to be known in the calibration of thermometers or for
terminations. (3) The resistance-temperature relationship is usually
other purposes.
defined by a thermometer-specific calibration and uncertainty appli-
DISCUSSION—This temperature can be determined through measure- cable over a specified temperature range. (4) Secondary reference PRT
ment using a calibrated thermometer such as a Standard Platinum thermometers have greater uncertainty than SPRTs but are generally
Resistance Thermometer (SPRT), or through the realization of a more rugged and less costly.
thermometric fixed point cell with an assigned value. Examples of fixed
secondary standard thermocouple, n—a thermocouple that
point cells include the triple point of water cell and the freezing point
of zinc cell, among others. has had its temperature-emf relationship determined by
reference to a primary standard of temperature.
refractory metal thermocouple, n—(1) one whose thermoele-
ments have melting points above 1935 °C (3515 °F). (2)
Seebeck coefficient, n—the change in thermoelectric emf per
thermocouple whose thermoelements are composed primar-
unit change of temperature at a given temperature for a
ily of refractory metals and their alloys. (See also base metal
thermoelement exposed to a thermal gradient.
thermocouple; noble metal thermocouple.)
DISCUSSION—The units of the Seebeck coefficient are volts per kelvin
DISCUSSION—Refractory metals used in thermoelements include (V/K), although it is often expressed as microvolts per kelvin (μV/K).
tungsten, rhenium, and molybdenum. (See also thermoelectric power.)
E344 − 23
Seebeck effect, n—a phenomenon in which a temperature- Style IU, n—designation for an isolated ungrounded measuring
dependent electromotive force is generated between two junction in a thermocouple assembly.
points of a thermoelement that are at different temperatures;
Style U, n—designation for an ungrounded measuring junction
the Seebeck effect provides the physical basis for thermo-
in a thermocouple assembly.
couples.
target plane, n—the plane, perpendicular to the line of sight of
Seebeck emf, n—an electrical potential difference between two
a radiation thermometer, that is in focus for that instrument.
points in a region of electrically conducting material that
exists solely because of temperature gradients between those
temperature coefficient of resistance, α, n—the ratio of the
two points in the material.
fractional change in electrical resistance of a substance to a
sensor, n—of a thermometer or thermometric system, element corresponding change in temperature of that substance.
of the thermometer or thermometric system that is directly
DISCUSSION—(1) The temperature coefficient of resistance is given by
α (T) = (1/R) (dR/dT), where α is the symbol representing the
affected by the temperature to be measured.
temperature coefficient of resistance, R is the resistance of the ther-
sheath-enclosed-scale thermometer, n—the cylindrical glass
mometer resistor at temperature T, and (dR/dT) is the first derivative of
envelope which encloses the scale and capillary tube. R with respect to T. (2) The dimension of α is reciprocal temperature.
In general, α = α (T) is a function of temperature. (3) For platinum
sheathed thermocouple, n—a thermocouple having its
resistance thermometers, over the temperature interval 0 to 100 °C, the
thermoelements, and sometimes its measuring junction,
platinum resistor has been characterized historically by an average
temperature coefficient of resistance using α = (R − R )/100R ,
embedded in ceramic insulation compacted within a metal
100 0 0
where R is the resistance at 0 °C and R is the resistance at 100 °C.
protecting tube. 0 100
The value of α for industrial platinum resistance thermometers speci-
fied in Specification E1137/E1137M can be derived from the coeffi-
sheathed thermocouple wire, n—one or more pairs of ther-
cients A and B given in that standard using α = A + 100B.
moelements (without measuring junction(s)) embedded in
ceramic insulation compacted within a metal protecting tube.
test thermoelement, n—a thermoelement that is to be cali-
brated with reference to platinum 67 (Pt-67) by comparing
sheathed thermoelement, n—a thermoelement embedded in
its thermal emf with that of a standard thermoelement.
ceramic insulation compacted within a metal protecting tube.
span, n—of a thermometer or thermometric system, the abso- thermal electromotive force (thermal emf), n—the net emf
lute value of the difference between the specified lower and set up in a thermocouple under conditions of zero current.
upper temperature limits within a range. (Same as Seebeck emf.)
standard platinum resistance thermometer (SPRT), n—a
thermistor, n—a temperature sensor employing a semiconduc-
precision laboratory reference thermometer and defining
tor that exhibits a continuous change in electrical resistance
interpolating instrument on the ITS-90 from approximately
with a change in sensor temperature (that is, a semiconductor
–259 to 962 °C or portions thereof.
for which the temperature coefficient of resistance over a
DISCUSSION—(1) Standard platinum resistance thermometers have a
specified temperature range is either negative or positive and
sensing element made from strain-free platinum wire with sufficient
exhibits no discontinuities).
purity such that the finished thermometer meets the acceptance criteria
DISCUSSION—(1) A negative temperature coefficient thermistor (NTC)
defined by the ITS-90. (2) Common SPRT configurations include the
is a ceramic semiconductor that exhibits a monotonic decrease in
Capsule type (CSPRT), the Long-stem type (LSPRT), and the High
electrical resistance with an increase in sensor temperatures and
Temperature type (HTSPRT). These configurations have nominal
exhibits no changes in sign. (2) A positive temperature coefficient
icepoint resistance values between 0.25 and 25 ohm, four-wire
thermistor (PTC) is a semiconductor that exhibits an increase in
terminations, and are optimized to cover portions of the temperature
electrical resistance with an increase in sensor temperature when used
range above. (3) The resistance-temperature relationship is defined by
within its normal operating range. One type of PTC thermistor exhibits
a thermometer-specific calibration and uncertainty applicable over a
a monotonic increase in electrical resistance with increasing tempera-
specified temperature range. (4) SPRTs are capable of achieving the
ture and exhibits no changes in sign. Another type of PTC thermistor
lowest calibration uncertainty of any reference thermometer, but are
has a transition or switching temperature that is determined by its
relatively delicate and require careful handling to avoid damage caused
physical composition. The temperature coefficient of resistance for this
by mechanical shock.
switching type device exhibits a slight negative value at temperatures
standard thermoelement, n—a thermoelement that has been below the transition temperature, becomes zero in the region of the
transition temperature and then exhibits a large positive value at
calibrated with reference to platinum 67 (Pt-67).
temperatures above the transition temperature. The electrical resistance
of these switching PTC devices is a relatively low value at low body
stem, n—of a liquid-in-glass thermometer, capillary tube
temperatures, decreases to a minimum value in the region of the
through which the meniscus of the thermometric liquid
transition temperature and then rapidly increases to an extremely high
moves with change of temperature.
value as the device is heated above the transition temperature.
Style CU, n—designation for a common ungrounded measur-
thermocouple, n—in thermometry, the sensor of a thermoelec-
ing junction in a thermocouple assembly.
tric thermometer, consisting of electrically conducting cir-
Style G, n—designation for a grounded measuring junction in cuit elements of two different thermoelectric characteristics
a thermocouple assembly. joined at a junction.
E344 − 23
accuracy of the nominal value. Tolerance can be symmetrical or
thermocouple assembly, n—an assembly consisting of two
asymmetrical. When the term is used in quality control, it refers to the
thermocouple elements and one or more associated parts
limiting values between which measurements must lie if an article is to
such as terminal block, connection head, and protecting tube.
be acceptable, as distinct from confidence limits. The term “tolerance”
should not be used to designate “maximum permissible error.”
thermocouple calibration, n—the process of determining the
emf developed by a thermocouple with respect to tempera-
total immersion thermometer, n—a liquid-in-glass thermom-
ture established by a standard.
eter designed to indicate temperatures correctly when just
that portion of the thermometer containing the liquid is
thermocouple electromotive force (emf), n—the electrical
exposed to the temperature being measured. (Compare
potential difference between the open ends of the thermo-
complete immersion thermometer and partial immersion
couple’s positive and negative thermoelements at the refer-
thermometer.)
ence junction.
DISCUSSION—Thermocouple emf is dependent on the temperature
traceability, n—of a temperature measurement, the ability to
difference between the thermocouple’s measuring junction and refer-
relate, with scientific credibility, the result of a temperature
ence junction.
measurement and its associated uncertainty to a stated
thermocouple inhomogeneity, n—the variation of the thermo- temperature scale through a sequence of comparisons with
electric properties of a thermocouple’s thermoelements references, usually national or international standards,
along their length. whose values have been determined on the scale with stated
DISCUSSION—This variation may exist in a new thermocouple, but it uncertainty.
also may be due to the exposure of certain segments of the thermo-
triple point, n—fixed point of a system in which three phases
couple to hot temperatures or harsh chemical environments. Inhomo-
are in equilibrium.
geneity results in the deviation of a thermocouple’s Seebeck coefficient
at a given temperature from its normal Seebeck coefficient at that
triple point of water, n—triple point of the liquid, solid, and
temperature. Thermocouple inhomogeneity is often reported as a
vapor phases of water.
fractional variation in the Seebeck coefficient.
DISCUSSION—The idealized triple point of water, to which a value of
thermoelectric power, n—(See Seebeck coefficient.) 273.16 K (0.01 °C) is assigned, is a defining fixed point for both the
Kelvin Thermodynamic Temperature Scale (KTTS) and the Interna-
thermoelectric properties, n—electrical properties of a ma-
tional Temperature Scale of 1990 (ITS-90).
terial related to the electric potential gradient generated in
true value, n—of a temperature, value attributed to a particular
the material by a temperature gradient in the material.
temperature and accepted, sometimes by convention, as
thermoelectric thermometer, n—thermometer for which the
having an uncertainty appropriate for a given purpose.
thermometric quantity is an emf produced by the Seebeck DISCUSSION—(1) For example, in a given situation, the value assigned
to a temperature determined by measurement with a reference standard
effect.
thermometer may be taken as a true value. (2) This concept is often
thermoelement, n—in thermometry, each of the materially designated by the term conventional true value.
dissimilar electrical conductors or circuit elements that
uncertainty, n—of a temperature measurement, parameter,
comprise a thermocouple.
derived from an analysis of a measurement and its result,
that characterizes the range in which the true value of
thermometric fixed point, n—fixed point useful in the prac-
temperature is estimated to lie, generally with a given
tice of thermometry.
confidence.
thermopile, n—a number of similar thermocouples connected
DISCUSSION—The parameter may be, for example, a standard devia-
in series, arranged so that alternate junctions are at the
tion (or a multiple of it), or the half-width of an interval having a stated
reference temperature and at the measured temperature, to level of confidence.
increase the output for a given temperature difference
DISCUSSION—The parameter has many components. Some compo-
between reference and measuring junctions.
nents may be evaluated by statistical methods; others may be based on
experience, using assumed probability distributions.
thermowell, n—a closed-end reentrant tube designed for the
insertion of a temperature-sensing element, and provided ungrounded junction, n—measuring junction within a ther-
mocouple assembly that is electrically isolated from its
with means for pressure-tight attachment to a vessel. (See
also protecting tube.) sheath. (See also Style U.)
upper range-value, n—the highest quantity that an instrument
tolerance, n—the defined limits of allowable deviation from a
is adjusted to measure.
standard in a measured quantity or other value such as
temperature, relative humidity, resistance, and so forth;
when the term is used for a measurement instrument or
system, it refers to the permitted variation of a measured
3.2 Definitions of Terms Specific to Standards in Which
value from the correct value. (See also error; maximum
They Appear:
permissible error.)
absolute zero, n—a temperature of 0 K (–273.15 °C). E2758
DISCUSSION—The tolerance may be specified as a factor or percentage
accuracy, n—ability of an infrared thermometer to give a
of the nominal value; a maximum deviation from a nominal value; an
explicit range of allowed values; or, be implied by the numeric reading close to the true temperature. E1965
E344 − 23
accuracy class, n—class of an item that meets certain metro- attenuating medium, n—a semi-transparent solid, liquid or
logical requirements intended to keep errors within specified gas, such as a window, filter, external optics, or an atmo-
limits. sphere that reduces thermal radiation, or combinations
thereof. E2758
DISCUSSION—This document describes accuracy classes for digital
thermometers. E2877 axial temperature uniformity, n—temperature differences
along the immersed length of the thermometer boring under
adjacent thermoelement configuration, n—thermoelement
test.
configuration within a multi-pair thermocouple or cable
DISCUSSION—Axial temperature uniformity is sometimes referred to
where two or more positive thermoelements are immediately
as axial temperature homogeneity. E3186
adjacent to one another around the circular pattern and two
or more negative thermoelements are also immediately
axillary temperature, t , n—temperature at the apex of either
ba
adjacent to one another around the circular pattern as shown
axilla (armpit) as measured by a contact thermometer. E1965
in Fig. 1 (compare with alternating thermoelement configu-
background radiation—see reflected radiation. E2758
ration in Fig. 2 and 3.2.2).
band width or span (Δ), n—the temperature difference defined
DISCUSSION—By default, a multi-pair thermocouple or cable with a
by the equation:
thermoelement in the center shall be considered an adjacent
configuration. E2181/E2181M Δ 5 SB 2 SR (2)
E1061
adjusted mode, n—output of an IR thermometer that gives
band width or span (Δ), n—the temperature difference defined
temperature measured and calculated from a subject or
by the following equation:
object, by correcting such temperature for variations in
ambient temperature, subject’s temperature, emissivity, body
Δ 5 T°470 2 T°650 (3)
site (that is, oral, or rectal), etc. E1965
E1061
adjusting device, n—a section of the instrument used to adjust bath gradient error, n—the error caused by temperature
differences within the working space of the bath. E2488
the amount of mercury in the bulb and main capillary to that
needed for the intended temperature interval. E1
bath gradient error, n—the error caused by temperature
differences in the working space of the bath; the bath or
alpha (α), n—the temperature coefficient of resistance of a
temperature equalizing blocks should be explored to deter-
PRT over the range 0 to 100 °C. E1137/E1137M
mine the work areas in which the temperature gradients are
alternating thermoelement configuration, n—thermoelement
insignificant. E644
configuration within a multi-pair thermocouple or cable
battery charger, n—an electrical circuit designed to restore the
where positive thermoelements and negative thermoele-
electrical potential of a battery. E1112
ments alternate around the circular pattern as shown in Fig.
2 (compare with adjacent thermoelement configuration in blackbody, n—the perfect or ideal source of thermal radiant
Fig. 1 and 3.2.1). power having a spectral distribution described by Planck’s
Law. E2758
DISCUSSION—In an alternating thermoelements pattern, there are
never two or more positive thermoelements nor two or more negative blackbody, n—a reference source of infrared radiation made in
thermoelements immediately adjacent to one another.
the shape of a cavity and characterized by precisely known
E2181/E2181M
temperature of the cavity walls and having effective emis-
sivity at the cavity opening arbitrarily considered equal to
amorphous silica fiber, n—a continuous filament of heat
unity. E1965
insulating material whose principal constituent is amorphous
silica. E574 blackbody simulator, n—a device with an emissivity close to
unity that can be heated or cooled to a stable temperature.
annealing, v—a heat treating process intended to stabilize
E2758
resistance thermometers prior to calibration and use. E2593
blackbody temperature, t , n—temperature of blackbody
BB
API gravity, n—the gravity obtained from the following
cavity walls as measured by an imbedded or immersed
relationship:
contact th
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E344 − 20 E344 − 23
Terminology Relating to
Thermometry and Hydrometry
This standard is issued under the fixed designation E344; 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
1.1 This terminology is a compilation of definitions of terms used by ASTM Committee E20 on Temperature Measurement.
1.2 Terms with definitions generally applicable to the fields of thermometry and hydrometry are listed in 3.1.
1.3 Terms with definitions applicable only to the indicated standards in which they appear are listed in 3.2.
1.4 Information about the International Temperature Scale of 1990 is given in Appendix X1.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
E1 Specification for ASTM Liquid-in-Glass Thermometers
E77 Test Method for Inspection and Verification of Thermometers
E100 Specification for ASTM Hydrometers
E126 Test Method for Inspection, Calibration, and Verification of ASTM Hydrometers
E207 Test Method for Thermal EMF Test of Single Thermoelement Materials by Comparison With Reference Thermoelement
of Similar EMF-Temperature Properties
E220 Test Method for Calibration of Thermocouples By Comparison Techniques
E230/E230M Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
E452 Test Method for Calibration of Refractory Metal Thermocouples Using a Radiation Thermometer
E574 Specification for Duplex, Base Metal Thermocouple Wire With Glass Fiber or Silica Fiber Insulation
E585/E585M Specification for Compacted Mineral-Insulated, Metal-Sheathed, Base Metal Thermocouple Cable
E601 Guide for Measuring Electromotive Force (EMF) Stability of Base-Metal Thermoelement Materials With Time in Air
E608/E608M Specification for Mineral-Insulated, Metal-Sheathed Base Metal Thermocouples
E644 Test Methods for Testing Industrial Resistance Thermometers
E667 Specification for Mercury-in-Glass, Maximum Self-Registering Clinical Thermometers (Withdrawn 2022)
This terminology is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.91 on Editorial
and Terminology.
Current edition approved Nov. 1, 2020Dec. 1, 2023. Published November 2020December 2023. Originally approved in 1968. Last previous edition approved in 20192020
ε1
as E344 – 19E344 – 20. . DOI: 10.1520/E0344-20.10.1520/E0344-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E344 − 23
E696 Specification for Tungsten-Rhenium Alloy Thermocouple Wire
E710 Test Method for Comparing EMF Stabilities of Base-Metal Thermoelements in Air Using Dual, Simultaneous,
Thermal-EMF Indicators (Withdrawn 2006)
E780 Test Method for Measuring the Insulation Resistance of Mineral-Insulated, Metal-Sheathed Thermocouples and
Mineral-Insulated, Metal-Sheathed Cable at Room Temperature
E825 Specification for Phase Change-Type Disposable Fever Thermometer for Intermittent Determination of Human
Temperature
E839 Test Methods for Sheathed Thermocouples and Sheathed Thermocouple Cable
E879 Specification for Thermistor Sensors for General Purpose and Laboratory Temperature Measurements
E1061 Specification for Direct-Reading Liquid Crystal Forehead Thermometers
E1104 Specification for Clinical Thermometer Probe Covers and Sheaths
E1112 Specification for Electronic Thermometer for Intermittent Determination of Patient Temperature
E1129/E1129M Specification for Thermocouple Connectors
E1137/E1137M Specification for Industrial Platinum Resistance Thermometers
E1159 Specification for Thermocouple Materials, Platinum-Rhodium Alloys, and Platinum
E1256 Test Methods for Radiation Thermometers (Single Waveband Type)
E1299 Specification for Reusable Phase-Change-Type Fever Thermometer for Intermittent Determination of Human Tempera-
ture
E1350 Guide for Testing Sheathed Thermocouples, Thermocouple Assemblies, and Connecting Wires Prior to, and After
Installation or Service
E1502 Guide for Use of Fixed-Point Cells for Reference Temperatures
E1594 Guide for Expression of Temperature
E1684/E1684M Specification for Miniature Thermocouple Connectors
E1750 Guide for Use of Water Triple Point Cells
E1751/E1751M Guide for Temperature Electromotive Force (emf) Tables for Non-Letter Designated Thermocouple Combina-
tions
E1965 Specification for Infrared Thermometers for Intermittent Determination of Patient Temperature
E2181/E2181M Specification for Compacted Mineral-Insulated, Metal-Sheathed, Noble Metal Thermocouples and Thermo-
couple Cable
E2251 Specification for Liquid-in-Glass ASTM Thermometers with Low-Hazard Precision Liquids
E2488 Guide for the Preparation and Evaluation of Liquid Baths Used for Temperature Calibration by Comparison
E2593 Guide for Accuracy Verification of Industrial Platinum Resistance Thermometers
E2623 Practice for Reporting Thermometer Calibrations
E2730 Guide for Calibration and Use of Thermocouple Reference Junction Probes in Evaluation of Electronic Reference
Junction Compensation Circuits
E2758 Guide for Selection and Use of Infrared Thermometers
E2820 Test Method for Evaluating Thermal EMF Properties of Base-Metal Thermocouple Connectors
E2821 Specification for Compacted Mineral-Insulated, Metal-Sheathed Cable Used in Industrial Resistance Thermometers
E2846 Guide for Thermocouple Verification
E2847 Test Method for Calibration and Accuracy Verification of Wideband Infrared Thermometers
E2877 Guide for Digital Contact Thermometers
E2995 Specification for ASTM Thermohydrometers with Integral Low-Hazard Thermometers
E3186 Guide for Use and Testing of Dry-Block Temperature Calibrators
2.2 Other Standards, Supplementary Vocabularies, and Sources:
2.2.1 NIST Documents
ITS-90 International Vocabulary of Basic and General Terms in Metrology (VIM), 1993The International Temperature Scale of
NIST Monograph 126 Platinum Resistance Thermometry
NIST Monograph 150 Liquid-in-Glass Thermometry
NIST Monograph 175 Temperature-Electromotive Force Reference Functions and Tables for the Letter-Designated Thermo-
couple Types Based on the ITS-90
NIST SP 250-22 Platinum Resistance Thermometer Calibrations
NIST SP 250-23 Liquid-in-Glass Thermometer Calibration Service
Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Switzerland, http://www.iso.org.National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
Preston-Thomas, H., METROLOGIA, Vol. 27, 1990, pp 3-10 and 107 (errata). Mangum, B. W., JOURNAL OF RESEARCH, National Institute of Standards and
Technology, Vol 95, 1990, p. 69.
E344 − 23
NIST Technical Note 1297 Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results, 1994
Edition
2.2.2 ANSI Documents
ANSI/NCSL Z540.2-1997 (R2012) U.S. Guide to the Expression of Uncertainty in Measurement (GUM), 1995
ANSI/NCSL Z540.3-2006 American National Standard for Calibration—Calibration Laboratories and Measuring and Test
Equipment—General Requirements
2.2.3 IEC Documents
IEC 61298-1 Process Measurement and Control Devices General Devices—General Methods and Procedures for Evaluating
Performance Part Performance—Part 1: General Considerations
IEC TS 62492-1 Industrial Process Control Devices—Radiation Thermometers—Part 1: Technical Data for Radiation
Thermometers
2.2.4 BIPM Documents
JCGM 100:2008 Evaluation of measurement data—Guide to the expression of uncertainty in measurement
JCGM 200:2012 International Vocabulary of Metrology—Basic and General Concepts and Associated Terms (VIM)
2.2.5 ISO Documents
ISO/IEC 17025:2017 General Requirements for the Competence of Testing and Calibration Laboratories
ISO/IEC Guide 98-3 Uncertainty of Measurement—Part 3: Guide to the Expression of Uncertainty in Measurement
(GUM:1995)
ISO 1768:1975 Glass Hydrometers—Conventional Value for the Thermal Cubic Expansion Coefficient (for Use in the
Preparation of Measurement Tables for Liquids)
2.2.6 Other documents
UKAS M3003 The Expression of Uncertainty and Confidence in Measurement, Edition 4
3. Terminology
3.1 Definitions:
accuracy, n—of a temperature measurement, closeness of agreement between the result of a temperature measurement and a true
value of the temperature.
DISCUSSION—
Accuracy is a qualitative concept.
base metal thermocouple, n—thermocouple whose thermoelements are composed primarily of base metals and their alloys.
(See also noble metal thermocouple; refractory metal; thermocouple.)
DISCUSSION—
Base metals used in thermoelements include nickel, iron, chromium, copper, and aluminum. Letter-designated types E, J, K, T, and N are considered
base metal thermocouples.
bias, n—the scatter between the mean values of subsets of data, from each other or from the accepted value.
blackbody, n—the perfect or ideal source of thermal radiant power having a spectral distribution described by the Planck
equation.
DISCUSSION—
The term blackbody is often used to describe a furnace or other source of radiant power which approximates the ideal.
bulb, n—of a liquid-in-glass thermometer, reservoir for the thermometric liquid.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from International Electrotechnical Commission (IEC), 3, rue de Varembé, 1st floor, P.O. Box 131, CH-1211, Geneva 20, Switzerland, https://www.iec.ch.
Available from International Bureau of Weights and Measures (BIPM), Pavillon de Breteuil, F-92312 Sèvres Cedex, Paris, France, http://www.bipm.org.
Available from International Organization for Standardization (ISO), ISO Central Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva, Switzerland,
https://www.iso.org.
United Kingdom Accreditation Service 2 Pine Trees, Chertsey Lane, Staines-upon-Thames, TW18 3HR, https://www.ukas.com.
E344 − 23
calibration, n—of a thermometer or thermometric system, the set of operations that establishes the relationship between the
indications of a thermometer or thermometric system and the corresponding reference standard at discrete temperature values;
the operations are performed under specified conditions; the calibration results are often used to establish this relationship at
other temperature values; the communicated results shall include a statement of the measurement uncertainty for each
measurement result.
DISCUSSION—
(1) The result of a calibration permits either the assignment of values of temperature to indicated values of thermometric quantity, or the determination
of additive or multiplicative corrections with respect to indications, or both. (2) A calibration may also determine other metrological properties such
as the effect of influence quantities. (3) The result of a calibration may be communicated in a document such as a calibration certificate, calibration
report, calibration function, calibration diagram, calibration curve, or calibration table. (4) The term calibration has also been used in standards under
E20 jurisdiction to refer to the result of the operations, to representations of the result, and to the actual relationship between values of the thermometric
quantity and temperature.
calibration point, n—a specific value, established by a reference, at which the indication or output of a measuring device is
determined.
Celsius, adj—pertaining to or denoting something related to the expression of temperature in degrees Celsius.
DISCUSSION—
For example, “A Celsius thermometer has a scale marked in degrees Celsius.”
center wavelength, n—a wavelength, usually near the middle of the band of radiant power over which a radiation thermometer
responds, that is used to characterize its performance.
DISCUSSION—
The value of the center wavelength is usually specified by the manufacturer of the instrument.
clinical thermometer, n—thermometer of any type designed to measure human body temperature.
DISCUSSION—
Some clinical thermometers may be designed to measure the body temperature of animals.
coaxial thermocouple, n—a thermocouple consisting of a thermoelement in wire form within a thermoelement in tube form with
the wire being electrically insulated from the tube except at the measuring junction.
compensating extension wires, n—those extension wires fabricated from materials basically different in composition from the
thermocouple.
DISCUSSION—
They have similar thermoelectric properties and within a stated temperature range effectively transfer the reference junction to the other end of the
wires.
complete immersion thermometer, n—a liquid-in-glass thermometer designed to indicate temperatures correctly when the
entire thermometer is exposed to the temperature being measured. (Compare total immersion thermometer and partial
immersion thermometer.)
connection head, n—a housing enclosing a terminal block for an electrical temperature-sensing device and usually provided
with threaded openings for attachment to a protecting tube and for attachment of conduit.
defining fixed point, n—thermometric fixed point of an idealized system, to which a numerical value has been assigned, used
in defining a temperature scale.
degree Celsius, °C, n—derived unit of temperature in the International System of Units (SI). (See kelvin.)
DISCUSSION—
At any temperature, an interval of one degree Celsius is the same as an interval of one kelvin, by definition. (For information about the relation between
units and values of temperature expressed in different units, see Guide E1594.)
degree centigrade, n—obsolete term; use degree Celsius.
E344 − 23
degree Fahrenheit, °F, n—non-SI unit of temperature commonly used in the United States of America.
DISCUSSION—
At any temperature, an interval of one degree Fahrenheit is the same as an interval of 5/9 kelvin (or 5/9 degree Celsius). (For information about the
relation between units and values of temperature expressed in different units, see Guide E1594.)
electromotive force (emf), n—the electrical potential difference which produces or tends to produce an electric current.
error, n—of a temperature measurement, result of a temperature measurement minus a true value of temperature.
extension wires, n—those having temperature-emf characteristics that when connected to a thermocouple effectively transfer the
reference junction to the other end of the wires. (Compare compensating extension wires.)
extrapolation, n—the estimation of a value of a measurement beyond the values already measured by the extension of a curve
based on the measured values.
Fahrenheit, adj—pertaining to or denoting something related to the expression of temperature in degrees Fahrenheit.
DISCUSSION—
For example, “A Fahrenheit thermometer has a scale marked in degrees Fahrenheit.”
fixed point, n—in thermometry, reproducible temperature of equilibrium of a system of two or more phases under specified
conditions.
freezing point, n—fixed point of a single component system in which liquid and solid phases are in equilibrium at a specified
pressure, usually 101 325 Pa, and the system is losing heat slowly. (Compare melting point.)
grounded junction, n—a measuring junction of a thermocouple assembly that is electrically and physically connected to its
sheath. (See also Style G.)
DISCUSSION—
The term “grounded” has been historically accepted in the field of thermometry to indicate the electrical connectivity of a thermocouple’s measuring
junction to its sheath; the term does not indicate whether or not the measuring junction is electrically connected to earth or circuit ground.
hysteresis, n—the property of a device or instrument whereby it gives different output values in relation to its input values
depending upon the directional sequence in which the input values have been applied. IEC 61298-1
ice point, n—thermometric fixed point of ice and water saturated with air at a pressure of 101 325 Pa.
industrial platinum resistance thermometer (IPRT), n—a rugged platinum resistance thermometer suitable for temperature
measurements in harsh industrial environments over all or part of the temperature range –200 to 650 °C.
DISCUSSION—
(1) The sensing element is made from platinum wire or film and packaged in a rugged housing to withstand harsh operating conditions. The sheath
material is usually stainless steel or Inconel; however, other materials may be used for special applications. (2) The resistance-temperature relationship
is usually defined by a specified nominal equation and interchangeability tolerances over a specified temperature range. (3) IPRTs have ice-point
resistance values of at least 100 ohm, and are available with two-wire, three-wire or four-wire terminations. (4) IPRTs are the most rugged and lowest
cost platinum resistance thermometers.
International Practical Temperature Scale (IPTS-48), n—the temperature scale adopted by the 11th General Conference on
Weights and Measures in 1960 and replaced in 1968 by the International Practical Temperature Scale of 1968.
International Practical Temperature Scale of 1968 (IPTS-68), n—the temperature scale adopted by the 13th General
Conference on Weights and Measures in 1968.
DISCUSSION—
The IPTS-68 was superseded in 1990 by the International Temperature Scale of 1990.
E344 − 23
International Temperature Scale of 1990 (ITS-90), n—the temperature scale prepared in accordance with instructions of the
18th General Conference on Weights and Measures, and adopted on January 1, 1990.
interpolation, n—the estimation of a value of a measurement between the values already measured by the estimation of a curve
based on the measured values.
kelvin, K, n—base unit of temperature in the International System of Units (SI).
liquid-in-glass thermometer, n—a temperature-measuring instrument whose indications are based on the temperature
coefficient of expansion of a liquid relative to that of its containing glass bulb.
lower range value, n—the lowest quantity that an instrument is adjusted to measure.
maximum permissible errors, n—of a thermometer or thermometric system, extreme values permitted by regulation or
specification of the difference between the indication of a thermometer or thermometeric system and the true value of
temperature.
DISCUSSION—
The term tolerance is sometimes used in ASTM standards to represent this concept.
maximum self-registering clinical thermometer, n—clinical thermometer designed to retain the indication of its maximum
measured temperature until reset.
measuring junction, n—that junction of a thermocouple which is subjected to the temperature to be measured.
melting point, n—fixed point of a single component system in which liquid and solid phases are in equilibrium at a specified
pressure, usually 101 325 Pa, and the system is gaining heat slowly. (Compare freezing point.)
mineral insulated metal-sheathed (MIMS) cable, n—a bendable cable consisting of one or more conductors embedded in a
metal protecting sheath, insulated from each other and from the sheath by a compacted mineral material.
noble metal thermocouple, n—thermocouple whose thermoelements are composed primarily of noble metals and their alloys.
(See also base metal thermocouple; refractory metal thermocouple.)
DISCUSSION—
Noble metals used in thermoelements include platinum, rhodium, gold, palladium, and iridium. Letter designated types B, R, and S are considered
noble metal thermocouples.
partial immersion thermometer, n—a liquid-in-glass thermometer designed to indicate temperatures correctly when the bulb
and a specified part of the stem are exposed to the temperatures being measured. (Compare complete immersion thermometer
and total immersion thermometer.)
Peltier coefficient, n—the reversible heat which is absorbed or evolved at a thermocouple junction when unit current passes in
unit time.
platinum 27 (Pt-27), n—the platinum standard to which the National Bureau of Standards referred thermoelectric measurements
prior to 1973.
platinum 67 (Pt-67), n—the platinum standard used by the National Bureau of Standards after 1972 as the reference to which
thermoelectric measurements are referred.
E344 − 23
platinum resistance thermometer (PRT), n—a resistance thermometer with the resistance element constructed from platinum
or platinum alloy.
DISCUSSION—
Platinum resistance thermometers are available in a variety of designs for use over the general temperature range of –259 to 962 °C or portions thereof.
The construction details of each PRT design (type of element, connecting wire construction, insulation, sealing, and mounting) are tailored to maximize
the performance of the thermometer for the intended application and temperature range. (See also Standard Platinum Resistance Thermometer
(SPRT); Industrial Platinum Resistance Thermometer (IPRT); Secondary Reference PRT Thermometer.)
precision, n—the scatter between individual values of test data within the subset, normally computed with respect to the mean
of the subset. (See bias.)
probe cover and sheath, n—a device provided for the purpose of preventing biological contact between the patient and the
probe or thermometer.
protecting tube, n—a tube designed to enclose a temperature-sensing device and protect it from the deleterious effects of the
environment.
DISCUSSION—
It may provide for attachment to a connection head but is not primarily designed for pressure-tight attachment to a vessel. (See also thermowell.)
radiation thermometer, n—a radiometer calibrated to indicate the temperature of a blackbody.
radiometer, n—a device for measuring radiant power that has an output proportional to the intensity of the input power.
range, n—of a thermometer of thermometric system, a set of temperatures within specified lower and upper tempurature limits.
DISCUSSION—
The “operating range,” “measuring range,” “working range,” or “scale range” is the set of exposure temperatures for the sensing portion of a
thermometer or thermometric system that permits temperature measurements to be made with specified uncertainty. With certain liquid-in-glass
thermometers, an auxiliary scale or reference scale is provided. The “range” of such liquid-in-glass thermometers includes only the “working range”
or “measuring range” and does not include the auxiliary scale or reference scale (when applicable).
DISCUSSION—
The “storage temperature range” or “non-operating temperature range” is set of exposerexposure temperatures that the thermometer or thermometric
system can endure without adversely affecting the ability to make temperature measurements with specified uncertainty when subsequently placed into
service. Some specifications provide for a maximum increase in specified uncertainty after exposerexposure to the storage temperature range for a
specified period of time.
DISCUSSION—
The “ambient temperature range” is the set of exposure temperatures that the indication or display portion of the thermometer or thermometric system
can endure during the measurement process without adversely affecting the ability to make temperature measurements.
DISCUSSION—
See also span.
reference junction, n—that junction of a thermocouple which is at a known temperature.
reference temperature, n—that temperature, however determined, whose value and accompanying uncertainty, are taken to
be known in the calibration of thermometers or for other purposes.
DISCUSSION—
This temperature can be determined through measurement using a calibrated thermometer such as a Standard Platinum Resistance Thermometer
(SPRT), or through the realization of a thermometric fixed point cell with an assigned value. Examples of fixed point cells include the triple point of
water cell and the freezing point of zinc cell, among others.
refractory metal thermocouple, n—(1) one whose thermoelements have melting points above 1935 °C (3515 °F). (2)
thermocouple whose thermoelements are composed primarily of refractory metals and their alloys. (See also base metal
thermocouple; noble metal thermocouple.)
DISCUSSION—
Refractory metals used in thermoelements include tungsten, rhenium, and molybdenum.
E344 − 23
repeatability, n—of results of temperature measurements, closeness of agreement between the results of successive
measurements of the same temperature carried out under the same conditions of measurement.
DISCUSSION—
(1) Repeatability conditions include the same measurement procedure; the same observer; the same thermometer or thermometeric system, used under
the same conditions; the same location; and repetition over a short interval of time. (2) Repeatability may be expressed quantitatively in terms of the
dispersion characteristics of the results such as the mean value and standard deviation.
reproducibility, n—of results of temperature measurements, closeness of agreement between the results of measurements of the
same temperature carried out under changed conditions of measurement.
DISCUSSION—
(1) A valid statement of reproducibility requires specification of the conditions changed. (2) The changed conditions may include principle of
measurement, method of measurement, observer, thermometer or thermometric system, reference standard(s), location, conditions of use, and time. For
ASTM standard test methods, the method is not changed. (3) Reproducibility may be expressed quantitatively in terms of the dispersion characteristics
of the results such as the mean value and standard deviation. (4) Results are here usually understood to be corrected results.
resistance thermometer, n—a temperature-measuring device comprised of a resistance thermometer element, internal
connecting wires, a protective shell with or without means for mounting, a connection head, or connecting wire or other fittings,
or both.
resistance thermometer element, n—the temperature-sensitive portion of the thermometer composed of resistance wire, film
or semiconductor material, its supporting structure, and means for attaching connecting wires.
secondary reference PRT thermometers, n—a general purpose laboratory reference thermometer (also referred to as
“Secondary SPRT” and “Secondary Reference PRT”) designed to be a suitable standard for routine temperature measurement
over all or part of the range –200 to 650 °C.
DISCUSSION—
(1) Secondary reference PRT thermometers have a sensing element made from strain-free platinum wire such that the finished thermometer meets the
specified stability and repeatability requirements but not necessarily the acceptance criteria defined by the ITS-90. (2) Secondary reference PRT
thermometers are typically configured with a long-stem metal sheath, have nominal ice-point resistance values between 25 and 100 ohm, and feature
four-wire terminations. (3) The resistance-temperature relationship is usually defined by a thermometer-specific calibration and uncertainty applicable
over a specified temperature range. (4) Secondary reference PRT thermometers have greater uncertainty than SPRTs but are generally more rugged and
less costlycostly.
secondary standard thermocouple, n—a thermocouple that has had its temperature-emf relationship determined by reference
to a primary standard of temperature.
Seebeck coefficient, n—the change in thermoelectric emf per unit change of temperature at a given temperature for a
thermoelement exposed to a thermal gradient.
DISCUSSION—
The units of the Seebeck coefficentcoefficient are volts per kelvin (V/K), although it is often expressed as microvolts per kelvin (μV/K). (See also
thermoelectric power.)
Seebeck effect, n—a phenomenon in which a temperature-dependent electromotive force is generated between two points of
a thermoelement that are at different temperatures; the Seebeck effect provides the physical basis for thermocouples.
Seebeck emf, n—an electrical potential difference between two points in a region of electrically conducting material that exists
solely because of temperature gradients between those two points in the material.
sensor, n—of a thermometer or thermometric system, element of the thermometer or thermometric system that is directly
affected by the temperature to be measured.
sheath-enclosed-scale thermometer, n—the cylindrical glass envelope which encloses the scale and capillary tube.
E344 − 23
sheathed thermocouple, n—a thermocouple having its thermoelements, and sometimes its measuring junction, embedded in
ceramic insulation compacted within a metal protecting tube.
sheathed thermocouple wire, n—one or more pairs of thermoelements (without measuring junction(s)) embedded in ceramic
insulation compacted within a metal protecting tube.
sheathed thermoelement, n—a thermoelement embedded in ceramic insulation compacted within a metal protecting tube.
span, n—of a thermometer or thermometric system, the absolute value of the difference between the specified lower and upper
temperature limits within a range.
standard platinum resistance thermometer (SPRT), n—a precision laboratory reference thermometer and defining
interpolating instrument on the ITS-90 from approximately –259 to 962 °C or portions thereof.
DISCUSSION—
(1) Standard platinum resistance thermometers have a sensing element made from strain-free platinum wire with sufficient purity such that the finished
thermometer meets the acceptance criteria defined by the ITS-90. (2) Common SPRT configurations include the Capsule type (CSPRT), the Long-stem
type (LSPRT), and the High Temperature type (HTSPRT). These configurations have nominal icepoint resistance values between 0.25 and 25 ohm,
four-wire terminations, and are optimized to cover portions of the temperature range above. (3) The resistance-temperature relationship is defined by
a thermometer-specific calibration and uncertainty applicable over a specified temperature range. (4) SPRTs are capable of achieving the lowest
calibration uncertainty of any reference thermometer, but are relatively delicate and require careful handling to avoid damage caused by mechanical
shock.
standard thermoelement, n—a thermoelement that has been calibrated with reference to platinum 67 (Pt-67).
stem, n—of a liquid-in-glass thermometer, capillary tube through which the meniscus of the thermometric liquid moves with
change of temperature.
Style CU, n—designation for a common ungrounded measuring junction in a thermocouple assembly.
Style G, n—designation for a grounded measuring junction in a thermocouple assembly.
Style IU, n—designation for an isolated ungrounded measuring junction in a thermocouple assembly.
Style U, n—designation for an ungrounded measuring junction in a thermocouple assembly.
target plane, n—the plane, perpendicular to the line of sight of a radiation thermometer, that is in focus for that instrument.
temperature coefficient of resistance, α, n—the ratio of the fractional change in electrical resistance of a substance to a
corresponding change in temperature of that substance.
DISCUSSION—
(1) The temperature coefficient of resistance is given by α (T) = (1/R) (dR/dT), where α is the symbol representing the temperature coefficient of
resistance, R is the resistance of the thermometer resistor at temperature T, and (dR/dT) is the first derivative of R with respect to T. (2) The dimension
of α is reciprocal temperature. In general, α = α (T) is a function of temperature. (3) For platinum resistance thermometers, over the temperature interval
0 to 100 °C, the platinum resistor has been characterized historically by an average temperature coefficient of resistance using α = (R − R )/100R ,
100 0 0
where R is the resistance at 0 °C and R is the resistance at 100 °C. The value of α for industrial platinum resistance thermometers specified in
0 100
Specification E1137/E1137M can be derived from the coefficients A and B given in that standard using α = A + 100B.
test thermoelement, n—a thermoelement that is to be calibrated with reference to platinum 67 (Pt-67) by comparing its thermal
emf with that of a standard thermoelement.
E344 − 23
thermal electromotive force (thermal emf), n—the net emf set up in a thermocouple under conditions of zero current. (Same
as Seebeck emf.)
thermistor, n—a temperature sensor employing a semiconductor that exhibits a continuous change in electrical resistance with
a change in sensor temperature (that is, a semiconductor for which the temperature coefficient of resistance over a specified
temperature range is either negative or positive and exhibits no discontinuities).
DISCUSSION—
(1) A negative temperature coefficient thermistor (NTC) is a ceramic semiconductor that exhibits a monotonic decrease in electrical resistance with
an increase in sensor temperatures and exhibits no changes in sign. (2) A positive temperature coefficient thermistor (PTC) is a semiconductor that
exhibits an increase in electrical resistance with an increase in sensor temperature when used within its normal operating range. One type of PTC
thermistor exhibits a monotonic increase in electrical resistance with increasing temperature and exhibits no changes in sign. Another type of PTC
thermistor has a transition or switching temperature that is determined by its physical composition. The temperature coefficient of resistance for this
switching type device exhibits a slight negative value at temperatures below the transition temperature, becomes zero in the region of the transition
temperature and then exhibits a large positive value at temperatures above the transition temperature. The electrical resistance of these switching PTC
devices is a relatively low value at low body temperatures, decreases to a minimum value in the region of the transition temperature and then rapidly
increases to an extremely high value as the device is heated above the transition temperature.
thermocouple, n—in thermometry, the sensor of a thermoelectric thermometer, consisting of electrically conducting circuit
elements of two different thermoelectric characteristics joined at a junction.
thermocouple assembly, n—an assembly consisting of two thermocouple elements and one or more associated parts such as
terminal block, connection head, and protecting tube.
thermocouple calibration, n—the process of determining the emf developed by a thermocouple with respect to temperature
established by a standard.
thermocouple electromotive force (emf), n—the electrical potential difference between the open ends of the thermocouple’s
positive and negative thermoelements at the reference junction.
DISCUSSION—
Thermocouple emf is dependent on the temperature difference between the thermocouple’s measuring junction and reference junction.
thermocouple inhomogeneity, n—the variation of the thermoelectric properties of a thermocouple’s thermoelements along their
length.
DISCUSSION—
This variation may exist in a new thermocouple, but it also may be due to the exposure of certain segments of the thermocouple to hot temperatures
or harsh chemical environments. Inhomogeneity results in the deviation of a thermocouple’s Seebeck coefficient at a given temperature from its normal
Seebeck coefficient at that temperature. Thermocouple inhomogeneity is often reported as a fractional variation in the Seebeck coefficient.
thermoelectric power, n—(See Seebeck coefficient.)
thermoelectric properties, n—electrical properties of a material related to the electric potential gradient generated in the
material by a temperature gradient in the material.
thermoelectric thermometer, n—thermometer for which the thermometric quantity is an emf produced by the Seebeck effect.
thermoelement, n—in thermometry, each of the materially dissimilar electrical conductors or circuit elements that comprise a
thermocouple.
thermometric fixed point, n—fixed point useful in the practice of thermometry.
thermopile, n—a number of similar thermocouples connected in series, arranged so that alternate junctions are at the reference
temperature and at the measured temperature, to increase the output for a given temperature difference between reference and
measuring junctions.
E344 − 23
thermowell, n—a closed-end reentrant tube designed for the insertion of a temperature-sensing element, and provided with
means for pressure-tight attachment to a vessel. (See also protecting tube.)
tolerance, n—the defined limits of allowable deviation from a standard in a measured quantity or other value such as
temperature, relative humidity, resistance, and so forth; when the term is used for a measurement instrument or system, it refers
to the permitted variation of a measured value from the correct value. (See also error;maximum permissible error.)
DISCUSSION—
The tolerance may be specified as a factor or percentage of the nominal value; a maximum deviation from a nominal value; an explicit range of allowed
values; or, be implied by the numeric accuracy of the nominal value. Tolerance can be symmetrical or asymmetrical. When the term is used in quality
control, it refers to the limiting values between which measurements must lie if an article is to be acceptable, as distinct from confidence limits. The
term “tolerance” should not be used to designate “maximum permissible error.”
total immersion thermometer, n—a liquid-in-glass thermometer designed to indicate temperatures correctly when just that
portion of the thermometer containing the liquid is exposed to the temperature being measured. (Compare complete immersion
thermometer and partial immersion thermometer.)
traceability, n—of a temperature measurement, the ability to relate, with scientific credibility, the result of a temperature
measurement and its associated uncertainty to a stated temperature scale through a sequence of comparisons with references,
usually national or international standards, whose values have been determined on the scale with stated uncertainty.
triple point, n—fixed point of a system in which three phases are in equilibrium.
triple point of water, n—triple point of the liquid, solid, and vapor phases of water.
DISCUSSION—
The idealized triple point of water, to which a value of 273.16 K (0.01 °C) is assigned, is a defining fixed point for both the Kelvin Thermodynamic
Temperature Scale (KTTS) and the International Temperature Scale of 1990 (ITS-90).
true value, n—of a temperature, value attributed to a particular temperature and accepted, sometimes by convention, as having
an uncertainty appropriate for a given purpose.
DISCUSSION—
(1) For example, in a given situation, the value assigned to a temperature determined by measurement with a reference standard thermometer may be
taken as a true value. (2) This concept is often designated by the term conventional true value.
uncertainty, n—of a temperature measurement, parameter, derived from an analysis of a measurement and its result, that
characterizes the range in which the true value of temperature is estimated to lie, generally with a given confidence.
DISCUSSION—
The parameter may be, for example, a standard deviation (or a multiple of it), or the half-width of an interval having a stated level of confidence.
DISCUSSION—
The parameter has many components. Some components may be evaluated by statistical methods; others may be based on experience, using assumed
probability distributions.
ungrounded junction, n—measuring junction within a thermocouple assembly that is electrically isolated from its sheath. (See
also Style U.)
upper range-value, n—the highest quantity that an instrument is adjusted to measure.
3.2 Definitions of Terms Specific to Standards in Which They Appear:
absolute zero, n—a temperature of 0 K (–273.15 °C). E2758
accuracy, n—ability of an infrared thermometer to give a reading close to the true temperature. E1965
E344 − 23
accuracy class, n—class of an item that meets certain metrological requirements intended to keep errors within specified limits.
DISCUSSION—
This document describes accuracy classes for digital thermometers. E2877
adjacent thermoelement configuration, n—thermoelement configuration within a multi-pair thermocouple or cable where two
or more positive thermoelements are immediately adjacent to one another around the circular pattern and two or more negative
thermoelements are also immediately adjacent to one another around the circular pattern as shown in Fig. 1 (compare with
alternating thermoelement configuration in Fig. 2 and 3.2.2).
DISCUSSION—
By default, a multi-pair thermocouple or cable with a thermoelement in the center shall be considered an adjacent configuration. E2181/E2181M
adjusted mode, n—output of an IR thermometer that gives temperature measured and calculated from a subject or object, by
correcting such temperature for variations in ambient temperature, subject’s temperature, emissivity, body site (that is, oral, or
rectal), etc. E1965
adjusting device, n—a section of the instrument used to adjust the amount of mercury in the bulb and main capillary to that
needed for the intended temperature interval. E1
alpha (α), n—the temperature coefficient of resistance of a PRT over the range 0 to 100 °C. E1137/E1137M
alternating thermoelement configuration, n—thermoelement configuration within a multi-pair thermocouple or cable where
positive thermoelements and negative thermoelements alternate around the circular pattern as shown in Fig. 2 (compare with
adjacent thermoelement configuration in Fig. 1 and 3.2.1).
DISCUSSION—
In an alternating thermoelements pattern, there are never two or more positive thermoelements nor two or more negative thermoelements immediately
adjacent to one another.
E2181/E2181M
amorphous silica fiber, n—a continuous filament of heat insulating material whose principal constituent is amorphous silica.
E574
annealing, v—a heat treating process intended to stabilize resistance thermometers prior to calibration and use. E2593
API gravity, n—the gravity obtained from the following relationship:
API Gravity,deg 5 141.5/~sp gr 60/60 °F!2 131.5 (1)
E126
atmospheric attenuation, n—a ratio showing how much thermal radiation in a given spectral range is absorbed or scattered in
air over a given distance. E2758
atmospheric transmission, n—a ratio showing how well thermal radiation in a given spectral range at a given distance travels
through a certain distance of air. E2758
attenuating medium, n—a semi-transparent solid, liquid or gas, such as a window, filter, external optics, or an atmosphere that
reduces thermal radiation, or combinations thereof. E2758
axial temperature uniformity, n—temperature differences along the immersed length of the thermometer boring under test.
DISCUSSION—
Axial temperature uniformity is sometimes referred to as axial temperature homogeneity. E3186
E344 − 23
axillary temperature, t , n—temperature at the apex of either axilla (armpit) as measured by a contact thermometer. E1965
ba
background radiation—see reflected radiation. E2758
band width or span (Δ), n—the temperature difference defined by the equation:
Δ5 SB 2 SR (2)
E1061
band width or span (Δ), n—the temperature difference defined by the following equation:
Δ5 T°470 2 T°650 (3)
E1061
bath gradie
...