ASTM E780-92(1998)
(Test Method)Standard Test Method for Measuring the Insulation Resistance of Sheathed Thermocouple Material at Room Temperature
Standard Test Method for Measuring the Insulation Resistance of Sheathed Thermocouple Material at Room Temperature
SCOPE
1.1 This test method covers the techniques and requirements for measuring the electrical insulation resistance at room temperature between the thermoelements and between each of the thermoelements and the metal sheath of compacted ceramic-insulated, sheathed thermocouple material. It may be used to measure the insulation resistance of bulk lengths of sheathed thermocouple material environmentally sealed at the time of manufacture. It may also be used for testing sheathed thermocouples with a Type U junction. This test method cannot be used for sheathed thermocouples with a Type G junction unless the junction is removed, prior to testing.
1.2 This test method applies to the testing of sheathed thermocouple materials that are suitable for use in air. It is also applicable for sheathed thermocouple materials whose sheath or thermoelements are composed of refractory metals and are tested in a dry and nonreactive environment.
1.3 This test method may be used for sheathed thermocouple material having an outside diameter of 1.0 mm or larger.
1.4 Since the insulation resistance at room temperature of sheathed thermocouple materials may change during shipment, storage and use, the results obtained by this test method may not be the same as insulation resistance values determined at some later time.
1.5 This standard does not purport to address all of the safety problems, 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:E780–92 (Reapproved 1998)
Standard Test Method for
Measuring the Insulation Resistance of Sheathed
Thermocouple Material at Room Temperature
This standard is issued under the fixed designation E 780; 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. Scope E 344 Terminology Relating to Thermometry and Hydrom-
etry
1.1 Thistestmethodcoversthetechniquesandrequirements
E 585 Specification for Sheathed Base-Metal Thermo-
for measuring the electrical insulation resistance at room
couple Materials
temperature between the thermoelements and between each of
E 608 Specification for Metal-Sheathed Base-Metal Ther-
the thermoelements and the metal sheath of compacted
mocouples
ceramic-insulated, sheathed thermocouple material. It may be
used to measure the insulation resistance of bulk lengths of
3. Terminology
sheathed thermocouple material environmentally sealed at the
3.1 Definitions—The definitions given in Terminology
time of manufacture. It may also be used for testing sheathed
E 344 shall apply to the terms used in this test method.
thermocoupleswithaTypeUjunction.Thistestmethodcannot
3.2 Definitions of Terms Specific to This Standard:
be used for sheathed thermocouples with a Type G junction
3.2.1 bulk material length (BML), n—a single length of
unless the junction is removed, prior to testing.
thermocouple material (produced from the same raw material
1.2 This test method applies to the testing of sheathed
lot) after completion of fabrication resulting in sheathed
thermocouple materials that are suitable for use in air. It is also
thermocouple material.
applicable for sheathed thermocouple materials whose sheath
3.2.2 dry, adj—a condition which does not exceed the
or thermoelements are composed of refractory metals and are
equivalent of 50 % relative humidity at 22°C.
tested in a dry and nonreactive environment.
3.2.3 nonreactive, adj—a condition which will not produce
1.3 This test method may be used for sheathed thermo-
a chemical transformation or change.
couplematerialhavinganoutsidediameterof1.0mmorlarger.
3.2.4 test specimen, n—ashortlength,atleast300mmlong,
1.4 Since the insulation resistance at room temperature of
cut from the bulk material length.
sheathed thermocouple materials may change during shipment,
storage and use, the results obtained by this test method may
4. Summary of Test Method
not be the same as insulation resistance values determined at
4.1 This test method involves measuring the d-c electrical
some later time.
resistance at normal room temperatures (22 6 5°C) between
1.5 This standard does not purport to address all of the
the thermoelements and between each of the thermoelements
safety concerns, if any, associated with its use. It is the
and the metal sheath of a length of sheathed thermocouple
responsibility of the user of this standard to establish appro-
material. The resistance measurements are made with an
priate safety and health practices and determine the applica-
instrument such as a megohm bridge or megohmeter. The
bility of regulatory limitations prior to use.
instrument must be capable of determining values of resistance
4 12
from 5 3 10 V to 1 3 10 V with an uncertainty of not more
2. Referenced Documents
than 610 %. The applied voltage for the resistance measure-
2.1 ASTM Standards:
ment is 500 V d-c for sheathed thermocouple material having
E 235 Specification for Thermocouples, Sheathed, Type K,
an outside diameter larger than 1.5 mm, and an applied voltage
for Nuclear or for Other High-Reliability Applications
of 50 V d-c is recommended for smaller diameter sheathed
thermocouple materials.
4.2 Special precautions must be exercised when preparing
This test method is under the jurisdiction of ASTM Committee E-20 on
the sheathed thermocouple material for the resistance measure-
Temperature Measurement and is the direct responsibility of Subcommittee E20.04
ments to prevent the intrusion of moisture and other contami-
on Thermocouples.
nants that might alter the insulation resistance. The repeatabil-
Current edition approved Oct. 15, 1992. Published December 1992.
Annual Book of ASTM Standards, Vol 14.03. ity of the test method depends primarily upon how well this is
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E780
NOTE 1—Caution: All tools that are used must be clean and must not
achieved. Preparation of the sheathed thermocouple material
introduce oil or other contaminants into the insulation.
involves removing 5 to 30 mm of the metal sheath from the
ends of the sheathed thermocouple material, heating the sheath
7. Test Specimen
adjacent to the open ends, and sealing the ends with epoxy
7.1 Conduct the test by using an entire bulk length of
resin.
sheathed thermocouple material or a test specimen removed
5. Significance and Use
from it. Determine the test specimen length by the distance
from one end of the compacted ceramic insulation to the other.
5.1 Thermocouples fabricated from sheathed thermocouple
7.2 In cases where a test specimen is removed for testing,
material that has been contaminated by moisture, or by certain
take the test specimen from any location along the bulk
otherimpurities,mayundergolargecalibrationchangesormay
material length, provided the ends of the bulk material length
failcatastrophicallywhentheyareheatedtohightemperatures.
were sealed at the time of manufacture. If the ends were
Since such contamination usually substantially lowers the
unsealed and exposed to ambient surroundings for more than 1
electrical resistance between the thermoelements and the
min at any time since manufacture, take the test specimen from
sheath, a measurement of the insulation resistance can provide
a location that is at least 300 mm from the ends. This also
a valuable check on insulation quality and cleanliness, and it
applies when the integrity of the end seals is in doubt or when
can serve as a basis for rejection of unsuitable material.
the history of the bulk material length is not known.
5.2 This test method is primarily intended for use by the
manufacturers and users of sheathed thermocouple materials to
8. Procedure
verify that the measured values of insulation resistance meet or
exceed specified values, such as those listed in Specifications
8.1 Preparation of Sheathed Thermocouple Material for
E 235, E 585, and E 608. Both manufacturers and users should
Test:
be aware, however, that when the insulation resistance is high,
8.1.1 Bulk Material Length—Complete the procedures de-
above 1 3 10 V, disagreement by an order of magnitude in
scribed in 8.1.1.1, 8.1.1.2, and 8.1.1.3 within 1 min and
results obtained by using this method is not unusual. In
perform in a location where the moisture content of the
addition, users should be aware that the insulation resistance at
ambient atmosphere (air) does not exceed the equivalent of
room temperature of sheathed thermocouple materials and of
50 % relative humidity at 22°C.
finished sheathed thermocouples may change during shipment,
8.1.1.1 Remove the seal anda5to30mm length of the
storage, and use, particularly if the end seals are damaged or
metal sheath from one end of the bulk material length. Use of
defective. Consequently, values of insulation resistance deter-
a metal-sheathed cable stripper (commercially available) is
mined by this test method may not necessarily apply at a later
recommended for removing the sheath.
time.
NOTE 2—Other sheath removal methods will be permitted provided a
cleansheathremovalismade,onethatdoesnotcontaminatetheinsulation
6. Apparatus
nor reduce the effective cross-sectional insulation spacing dimensions.
6.1 Megohmeter or Megohm Bridge, with ranges from
4 12
8.1.1.2 Remove the exposed compacted ceramic insulation
5 3 10 Vto1 3 10 Vwithanaccuracyofbetterthan 610 %
surrounding the thermoelements.
of the measured resistance and test voltage of 50 or 500 V d-c,
8.1.1.3 Separate (or spread apart) the thermoelements so
depending upon the outside diameter of the sheathed thermo-
that they are not in contact with each other or with the sheath.
coupl
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