ASTM E601-07a(2013)
(Test Method)Standard Test Method for Measuring Electromotive Force (emf) Stability of Base-Metal Thermoelement Materials with Time in Air
Standard Test Method for Measuring Electromotive Force (emf) Stability of Base-Metal Thermoelement Materials with Time in Air
SIGNIFICANCE AND USE
5.1 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.
5.2 This test method is used to verify that the tested thermoelements meet the intended requirements.
5.3 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.
5.4 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.
5.5 The test method does not address the determination of base metal thermoelement stabilities over a series of temperature changes.
5.6 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.
5.7 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 between joined thermoelements, as measured at the reference junctions. Note 2—See ASTM MNL 12 for recommended upper temperature limits in air.2Note 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.
1.4 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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Designation: E601 − 07a(Reapproved 2013)
Standard Test Method for
Measuring Electromotive Force (emf) Stability of Base-Metal
Thermoelement Materials with Time in Air
This standard is issued under the fixed designation E601; 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 2. Referenced Documents
1.1 This test method measures emf stability of base-metal 2.1 ASTM Standards:
thermoelement materials in air referenced to platinum at E220 Test Method for Calibration of Thermocouples By
specified constant elevated temperatures using dual, Comparison Techniques
simultaneous, emf indicators, or using a single emf indicator, E230 Specification and Temperature-Electromotive Force
with the test and reference emf measured alternately. This test (EMF) Tables for Standardized Thermocouples
is conducted over a period of weeks. E344 Terminology Relating to Thermometry and Hydrom-
etry
1.2 A calibrated platinum-rhodium/platinum thermocouple
E563 Practice for Preparation and Use of an Ice-Point Bath
is used as a reference standard to establish the test temperature.
as a Reference Temperature
1.3 The useful life of a thermocouple depends on the
E1159 Specification for Thermocouple Materials, Platinum-
stability of the emf generated at given temperatures for a
Rhodium Alloys, and Platinum
required time interval. This method provides a quantitative
measure of the stability of individual thermoelements. By
3. Terminology
combining the results of the positive (P) and negative (N)
3.1 Definitions—The definitions given inTerminologyE344
thermoelements, the stability of a thermocouple comprised of
shall apply to this test method.
both P and N thermoelements may be obtained. The emf of an
3.2 Definitions of Terms Specific to This Standard:
individual thermoelement is measured against platinum, which
3.2.1 emf indicator, n—an instrument that measures the emf
may be the platinum leg of the platinum-rhodium/platinum
and displays the value, for example, a digital voltmeter
reference thermocouple, or an additional platinum reference.
(DVM).
NOTE 1—Some thermoelements may show insignificant emf drift while
undergoing relatively rapid oxidation. In these cases, failure of the
3.2.2 emf stability, n—change in emf (or in equivalent
thermoelement may be indicated only by a large rise in the electrical
temperature) with time, with the thermocouple junctions held
resistance between joined thermoelements, as measured at the reference
at fixed temperatures and with the thermal profile along the
junctions.
NOTE 2—See ASTM MNL 12 for recommended upper temperature
thermoelements held constant.
limits in air.
3.2.3 half-maximum heated length, n—the distance between
NOTE 3—This test method is only applicable for initially new thermo-
the tip of the temperature sensor and the position along the
elements. Base-metal thermoelements exposed to temperatures above 200
°C become thermoelectrically inhomogeneous, and stability testing of length of the sensor leads or sheath where the temperature
inhomogeneous thermoelements will give ambiguous results.
equals the average of the calibration-point and ambient tem-
1.4 This standard does not purport to address all of the peratures.
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
priate safety and health practices and determine the applica-
from t + 0.1(t – t )to t + 0.9(t – t ), where t
amb m amb amb m amb amb
bility of regulatory limitations prior to use.
is ambient temperature and t is the temperature of the
m
measuring junction.
This test method is under the jurisdiction of ASTM Committee E20 on
3.2.5 reference thermocouple, n—calibrated Type S or Type
Temperature Measurement and is the direct responsibility of Subcommittee E20.04
R thermocouple.
on Thermocouples.
Current edition approved May 1, 2013. Published May 2013. Originally
approved in 1977. Last previous edition approved in 2007 as E601 – 07a. DOI:
10.1520/E0601-07AR13. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
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 C700, West Conshohocken, PA 19428-2959. United States
E601 − 07a (2013)
3.2.6 test thermocouple, n—thermocouple composed of the stability to determine any significant change in emf of base-
thermoelement being tested and the platinum reference ther- metal thermoelements shall be used. To ascertain that the
moelement. experimental method protects the platinum sufficiently from
degradation, the method shall be validated by performing the
3.2.7 normalize, v—to mathematically adjust experimental
procedure described in Appendix X1 prior to the actual test.
emf data acquired at a set of temperatures to values corre-
sponding to a common reference temperature. 5.7 The test result does not apply to applications in which
the temperature distribution, for a given measuring junction
4. Summary of Test Method
temperature, changes with time.
4.1 In this test method, the emf of a test thermocouple,
6. Apparatus
comprised of a base-metal thermoelement relative to a plati-
6.1 Thermocouple Used to Measure the Test
num reference thermoelement, is determined as a function of
Temperature—A reference Type S or Type R thermocouple
time for a specified test temperature and thermal profile. If care
with 0.50 mm diameter (24 AWG) thermoelements or larger
is taken to maintain the chemical purity and annealed metal-
shall be used to measure the test temperature. The reference
lurgical state of the platinum thermoelement, the platinum will
thermocouple shall consist of either standard tolerance or
be thermoelectrically stable. In that case, variation in this emf
specialtolerancewireasperTable 1inSpecificationE230.The
value is attributed to instability of the base-metal thermoele-
choice of tolerance will not affect the determination of ther-
ment. The emf of the reference thermocouple (E ) is used to
ref
moelement drift. This thermocouple shall be of sufficient
measure the test temperature, and the emf (E ) of the test
test
length to minimize the effect of heat conduction along the
thermocouple is measured either simultaneously or alternately
lengths of the wires upon the measuring junction temperature.
with E . The test method consists of the measurement of E
ref test
(Note:platinumisabetterheatconductorthanmostbasemetal
at specified time intervals and at a specified constant value of
thermocouple wires.) Length shall be sufficient to enable the
E which corresponds to a specified, constant temperature,
ref
reference thermocouple’s measuring junction to be located
until the required time of the test is exceeded or until an open
within the test furnace’s zone of nearly uniform temperature
circuit in the base-metal thermoelement results.
(refer to 6.5.2).
4.2 This test method is based on Method A of Test
6.2 Platinum Reference Thermoelement —The emf of the
MethodE220, where the reference thermocouple of Test
test thermoelements shall be measured relative to a 0.50 mm
Method E220 becomes the reference thermocouple used to
diameter (24 AWG) platinum wire. This wire may be the
measure the test temperature and one specified constant tem-
platinum wire of the Type S or R reference thermocouple or a
perature replaces the series of measured temperatures of Test
second0.50mmdiameter(24AWG)platinumwire.Thelength
Method E220.
of this wire shall exceed that of the test specimen to minimize
the transfer of heat from the measuring junction to the
5. Significance and Use
reference junction during testing (see 6.3). For more informa-
5.1 This test method is important because the accuracy of a
tion concerning a platinum reference thermoelement, Specifi-
temperature measurement by a thermocouple is directly related
cation E1159 may be consulted.
to the emf stability of the thermoelements.
6.3 Test Specimens— The test specimens shall be lengths of
5.2 This test method is used to verify that the tested
wires, rods, ribbons, or strips of the coils or spools of the
thermoelements meet the intended requirements.
base-metal thermoelements to be evaluated.Their lengths shall
be adequate to minimize the transfer of heat from the measur-
5.3 This test method is useful in comparing the emf stability
ing junctions to the reference junctions during the period of
of two base metal thermoelements under the same conditions.
test. The lengths shall be at least 0.8 m (30 in.) depending on
The test and reference emf may be measured either simultane-
the length of the testing medium and the transverse sizes of the
ously or alternately.
thermoelements. The specimens shall be free of kinks or other
5.4 The relative stabilities of base metal thermoelements
defectsduetomechanicaldeformation,andshallbecontinuous
determined by this test method are valid only under the
withoutsplicesbetweenthemeasuringandreferencejunctions.
specified test conditions. Results would be affected by changes
6.4 Reference Junction Temperature —The reference junc-
in the following conditions: (1) temperature profile or gradient
tion ends of the test specimens, of the platinum reference
along the length of the thermoelements; (2) abundance, veloc-
element, if used, and of the reference thermocouple must be
ity and composition of the air surrounding the test pieces; (3)
maintained at a known constant temperature during a measure-
thermoelectric inhomogeneity of the test thermoelements; (4)
ment cycle. The uncertainty attributable to the reference
stability of the platinum thermoelement.
junction temperature shall be less than 60.1 °C. Ice point
5.5 The test method does not address the determination of
reference junction baths provide a relatively simple and reli-
base metal thermoelement stabilities over a series of tempera-
able means for maintaining the reference junction at 0 °C (32
ture changes.
°F)whenproperprecautionsareexercisedintheiruse.Practice
5.6 The reliability of this test method depends on the emf E563 provides an acceptable method for utilizing the ice point
stability of the reference platinum thermoelement. For testing as a reference junction bath. Section 7.3 of Test Method E220
the relative emf stability of base-metal thermoelements, a may be consulted for alternative methods of providing a
referenceelementofplatinumthathassufficientthermoelectric reference junction temperature.
E601 − 07a (2013)
TABLE 1 Approximate Thermal Conductivities of Thermoelement
6.5 Tube Furnace— The test shall be conducted in an
Materials at 200 ° C
electrically heated tube furnace such as described in Section
Thermoelement Type k (W/(m · K))
7.2.3 of E220. The furnace employed shall have the following
Pt 72
capabilities: The furnace tube shall be long enough to permit a
EP, KP 21
depth of immersion of the thermocouple measuring junctions
EN, JN, TN 31
JP 62
thatissufficienttoassurethatthetemperatureofthemeasuring
KN 32
junctions is not affected by heat conduction along the thermo-
NP 19
elements. NN 31
TP 380
6.5.1 Means shall be provided to control the temperature of
the furnace to within 610 °C (618 °F) of a nominal tempera-
ture during the performance of the test.
6.5.2 The test shall be conducted in a uniformly heated
furnace providing a nearly isothermal work zone sufficiently
from Section 6.5.3 between the measuring junction location
large to maintain all junctions at the same temperature.
and a distance L away from the measuring junction.
max
6.5.3 To determine the uncertainty resulting from tempera-
6.5.3.3 Alternative methods may be used to determine the
ture non-uniformities in the work zone, measure the tempera-
standard uncertainty due to thermal non-uniformity, such as
ture profile along the thermocouple axis in the vicinity of the
comparison of results in the test furnace with results obtained
work zone, using a platinum-rhodium alloy thermocouple or a
either in fixed-point cells or in a stirred liquid bath of high
platinum resistance thermometer prior to commencement of
temperature uniformity; or numerical heat-transfer calcula-
the test. If the furnace temperature is not sufficiently stable to
tions.
obtain a temperature profile with a single thermometer, it may
6.6 Electromotive Force Indicator —The emf measuring
be useful to place one thermometer at a fixed half-maximum
instrumentation shall have a measurement uncertainty of not
heated length, and to move a second thermometer along the
more than 1 µV at 1 000 µV and 12 µV at 50 000 µV for this
furnace-tube axis. Adjust the readings of the moveable ther-
test. The emf indicators may be potentiometers or digital
mometerbyaddingthecorrection–(t (time)–t (initial)),
fixed fixed
voltmeters. Sections 6.2 and 7.4 of Test Method E220 may be
where t is the temperature indication of the thermometer at
fixed
consulted for further discussions of thermal emf indicators and
fixed half-maximum heated length.
methods of emf measurement.
6.5.3.1 Athermoelement extending from ambient tempera-
ture into an isothermal zone of a furnace will come to 6.7 Connecting Wires— Connecting wires from the refer-
equilibrium with the temperature of the isothermal zone
ence junctions to the emf indicator or indicators shall be
through radiative, convective, and conductive heat transfer electrically insulated copper. If the test is sensitive to electro-
between the thermoelement and the surrounding furnace envi-
static interference, the wires shall be electrically shielded. If
ronment. The distance of immersion into the isothermal zone electromagnetic interference is present, the conductors shall be
neededtoachievethermalequilibriumdependssignificantlyon
twisted to minimize this effect.
both the thermoelement diameter and its thermal conductivity.
6.8 Selector Switches—When more than one thermoelement
The characteristic length for a wire to achieve thermal equi-
is to be tested, a selector switch is introduced into the copper
librium with its surroundings is given by the approximate
part of the circuit between the reference junctions and the
correlation:
thermal-emfindicators
...
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