Standard Test Method for Measuring Electromotive Force (emf) Stability of Base-Metal Thermoelement Materials with Time in Air

SIGNIFICANCE AND USE
This test method is important because the accuracy of a temperature measurement by a thermocouple is directly related to the emf stability of the thermoelements.
This test method is used to verify that the tested thermoelements meet the intended requirements.
This test method is useful in comparing the emf stability of two base metal thermoelements under the same conditions. The test and reference emf may be measured either simultaneously or alternately.
The relative stabilities of base metal thermoelements determined by this test method are valid only under the specified test conditions. Results would be affected by changes in the following conditions: (1) temperature profile or gradient along the length of the thermoelements; (2) abundance, velocity and composition of the air surrounding the test pieces; (3) thermoelectric inhomogeneity of the test thermoelements; (4) stability of the platinum thermoelement.
The test method does not address the determination of base metal thermoelement stabilities over a series of temperature changes.
The reliability of this test method depends on the emf stability of the reference platinum thermoelement. For testing the relative emf stability of base-metal thermoelements, a reference element of platinum that has sufficient thermoelectric stability to determine any significant change in emf of base-metal thermoelements shall be used. To ascertain that the experimental method protects the platinum sufficiently from degradation, the method shall be validated by performing the procedure described in Appendix X1 prior to the actual test.
The test result does not apply to applications in which the temperature distribution, for a given measuring junction temperature, changes with time.
SCOPE
1.1 This test method measures emf stability of base-metal thermoelement materials in air referenced to platinum at specified constant elevated temperatures using dual, simultaneous, emf indicators, or using a single emf indicator, with the test and reference emf measured alternately. This test is conducted over a period of weeks.
1.2 A calibrated platinum-rhodium/platinum thermocouple is used as a reference standard to establish the test temperature.
1.3 The useful life of a thermocouple depends on the stability of the emf generated at given temperatures for a required time interval. This method provides a quantitative measure of the stability of individual thermoelements. By combining the results of the positive (P) and negative (N) thermoelements, the stability of a thermocouple comprised of both P and N thermoelements may be obtained. The emf of an individual thermoelement is measured against platinum, which may be the platinum leg of the platinum-rhodium/platinum reference thermocouple, or an additional platinum reference.Note 1
Some thermoelements may show insignificant emf drift while undergoing relatively rapid oxidation. In these cases, failure of the thermoelement may be indicated only by a large rise in the electrical resistance of the thermocouple, as measured between the reference junctions.Note 2
See ASTM MNL 12 for recommended upper temperature limits in air.Note 3
This test method is only applicable for initially new thermoelements. Base-metal thermoelements exposed to temperatures above 200 C become thermoelectrically inhomogeneous, and stability testing of inhomogeneous thermoelements will give ambiguous results.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

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Historical
Publication Date
30-Apr-2007
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ASTM E601-07e1 - Standard Test Method for Measuring Electromotive Force (emf) Stability of Base-Metal Thermoelement Materials with Time in Air
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
e1
Designation: E 601 – 07
Standard Test Method for
Measuring Electromotive Force (emf) Stability of Base-Metal
1
Thermoelement Materials with Time in Air
This standard is issued under the fixed designation E 601; 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 (e) indicates an editorial change since the last revision or reapproval.
1
e NOTE—Editorial changes were made throughout in July 2007.
1. Scope priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 This test method measures emf stability of base-metal
thermoelement materials in air referenced to platinum at
2. Referenced Documents
specified constant elevated temperatures using dual, simulta-
3
2.1 ASTM Standards:
neous, emf indicators, or using a single emf indicator, with the
E 220 Test Method for Calibration of Thermocouples By
test and reference emf measured alternately. This test is
Comparison Techniques
conducted over a period of weeks.
E 230 Specification and Temperature-Electromotive Force
1.2 A calibrated platinum-rhodium/platinum thermocouple
(EMF) Tables for Standardized Thermocouples
is used as a reference standard to establish the test temperature.
E 344 Terminology Relating to Thermometry and Hydrom-
1.3 The useful life of a thermocouple depends on the
etry
stability of the emf generated at given temperatures for a
E 563 Practice for Preparation and Use of an Ice-Point Bath
required time interval. This method provides a quantitative
as a Reference Temperature
measure of the stability of individual thermoelements. By
E 1159 Specification for Thermocouple Materials,
combining the results of the positive (P) and negative (N)
Platinum-Rhodium Alloys, and Platinum
thermoelements, the stability of a thermocouple comprised of
both P and N thermoelements may be obtained. The emf of an
3. Terminology
individual thermoelement is measured against platinum, which
3.1 Definitions—The definitions given in Terminology
may be the platinum leg of the platinum-rhodium/platinum
E 344 shall apply to this test method.
reference thermocouple, or an additional platinum reference.
3.2 Definitions of Terms Specific to This Standard:
NOTE 1—Some thermoelements may show insignificant emf drift while
3.2.1 emf indicator, n—aninstrumentthatmeasurestheemf
undergoing relatively rapid oxidation. In these cases, failure of the
and displays the value, for example, a digital voltmeter
thermoelement may be indicated only by a large rise in the electrical
(DVM).
resistance of the thermocouple, as measured between the reference
3.2.2 emf stability, n—change in emf (or in equivalent
junctions.
temperature) with time, with the thermocouple junctions held
NOTE 2—See ASTM MNL 12 for recommended upper temperature
2
limits in air. at fixed temperatures and with the thermal profile along the
NOTE 3—This test method is only applicable for initially new thermo-
thermoelements held constant.
elements. Base-metal thermoelements exposed to temperatures above 200
3.2.3 immersion depth, n—the distance between the tip of
°C become thermoelectrically inhomogeneous, and stability testing of
the temperature sensor and the position along the length of the
inhomogeneous thermoelements will give ambiguous results.
sensor leads or sheath where the temperature equals the
1.4 This standard does not purport to address all of the
average of the calibration-point and ambient temperatures.
safety concerns, if any, associated with its use. It is the
3.2.4 gradient zone, n—thesectionofathermocouplethatis
responsibility of the user of this standard to establish appro-
exposed during a measurement to temperatures in the range
from t + 0.1(t –t )tot + 0.9(t –t ), where t
amb m amb amb m amb amb
is ambient temperature and t is the temperature of the
m
1
This test method is under the jurisdiction of ASTM Committee E20 on
measuring junction.
Temperature Measurement and is the direct responsibility of Subcommittee E20.04
on Thermocouples.
Current edition approved May 1, 2007. Published June 2007. Originally
approved in 1977. Last previous edition approved in 1997 as E 601 – 81 (1997)
3
which was withdrawn in January 2006 and reinstated in May 2007. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
2
Manual on the Use of Thermocouples in Temperature Measurement: Fourth contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Edition, Available from ASTM Headquarters, 100 Barr Harbor Drive, West Standards volume information, refer to the standard’s Document Summary page on
Conshohocken, PA 19428, www.astm.org. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box
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