Standard Test Method for Measuring the Insulation Resistance of Mineral-Insulated, Metal-Sheathed Thermocouples and Thermocouple Cable at Room Temperature

SIGNIFICANCE AND USE
Thermocouples fabricated from thermocouple cable that has been contaminated by moisture or by other impurities may undergo large changes in thermoelectric properties or may fail catastrophically when exposed to high temperatures. Since such contamination usually lowers the electrical resistance between the thermoelements and the sheath substantially, measurement of the insulation resistance can provide a valuable check of insulation quality and cleanliness, and can serve as a basis for rejection of unsuitable material and unreliable components. For manufacturers in particular, low electrical insulation resistance can also be indicative of displaced thermoelements or defects in the metal sheath which will require further investigation, but all users should be aware of these potential defects when faced with an unacceptable insulation resistance measurement.
This test method is primarily intended for use by manufacturers and users of mineral-insulated, metal-sheathed thermocouples or thermocouple cables to verify that measured values of insulation resistance exceed specified minimum values, such as those listed in Specifications E 235, E 585/E 585M, E 608/E 608M, and E 2181/E 2181M. Manufacturers and users should be aware, however, that when the insulation resistance is greater than 1 × 108 Ω, disagreement by an order of magnitude in the results obtained with this test method is not unusual. In addition, users of this test method should appreciate that the room temperature insulation resistance of both thermocouple cables and of finished thermocouples may change during shipment, storage, and use, particularly if the end seals are damaged or defective. Consequently, values of insulation resistance determined by this test method may not necessarily be repeatable.
SCOPE
1.1 This test method provides the procedures for measuring the room temperature electrical insulation resistance between the thermoelements, and between the thermoelements and the sheath, of a mineral-insulated, metal-sheathed thermocouple or thermocouple cable. It may be used to measure the insulation resistance of bulk lengths of thermocouple cable previously sealed against moisture intrusion or to test a thermocouple having an ungrounded class 2 junction. This method cannot be used to test a thermocouple having a grounded class 1 junction unless the junction is removed prior to testing, after which the thermocouple may be dealt with in the same manner as a thermocouple cable.
1.2 This test method applies primarily to thermocouple cables conforming to Specifications E 585/E 585M and E 2181/E 2181M and to thermocouples conforming to Specifications E 608/E 608M and E 2181/E 2181M, but may also be applied to thermocouples or thermocouple cables that are suitable for use in air, whose sheath or thermoelements are comprised of refractory metals, that are tested in a dry and chemically inert environment, and that may employ compacted ceramic insulating materials other than magnesia (MgO) or alumina (Al2O3). Users of this test method should note that specifications dealing with compacted ceramic insulating materials other than magnesia or alumina, which are described in Specification E 1652, are not currently available. As a result, acceptance criteria must be agreed upon between the customer and supplier at the time of purchase, or alternatively, judgment and experience must be applied in establishing test voltage levels and acceptable insulation resistance values for these types of thermocouples and thermocouple cables.
1.3 This test method may be used for thermocouples or thermocouple cables having an outside diameter of 0.5 mm (0.020 in) or larger.
1.4 Users of this test method should be aware that the room temperature insulation resistance of a mineral-insulated, metal-sheathed thermocouple or thermocouple cable may change during shipment, storage, or use.
1.5 The values stated in SI units are to be regarded as standard. The...

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ASTM E780-06 - Standard Test Method for Measuring the Insulation Resistance of Mineral-Insulated, Metal-Sheathed Thermocouples and Thermocouple Cable at Room Temperature
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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
Designation: E780 – 06
Standard Test Method for
Measuring the Insulation Resistance of Mineral-Insulated,
Metal-Sheathed Thermocouples and Thermocouple Cable at
1
Room Temperature
This standard is issued under the fixed designation E780; 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 1.4 Users of this test method should be aware that the room
temperature insulation resistance of a mineral-insulated, metal-
1.1 This test method provides the procedures for measuring
sheathed thermocouple or thermocouple cable may change
the room temperature electrical insulation resistance between
during shipment, storage, or use.
the thermoelements, and between the thermoelements and the
1.5 The values stated in SI units are to be regarded as
sheath, of a mineral-insulated, metal-sheathed thermocouple or
standard. The values given in parentheses are for information
thermocouple cable. It may be used to measure the insulation
only.
resistance of bulk lengths of thermocouple cable previously
1.6 This standard does not purport to address all of the
sealed against moisture intrusion or to test a thermocouple
safety concerns, if any, associated with its use. It is the
having an ungrounded class 2 junction. This method cannot be
responsibility of the user of this standard to establish appro-
used to test a thermocouple having a grounded class 1 junction
priate safety and health practices and determine the applica-
unless the junction is removed prior to testing, after which the
bility of regulatory limitations prior to use.
thermocouple may be dealt with in the same manner as a
thermocouple cable.
2. Referenced Documents
1.2 This test method applies primarily to thermocouple
2
2.1 ASTM Standards:
cables conforming to Specifications E585/E585M and E2181/
E235 Specification for Thermocouples, Sheathed, Type K
E2181M and to thermocouples conforming to Specifications
and Type N, for Nuclear or for Other High-Reliability
E608/E608M and E2181/E2181M, but may also be applied to
Applications
thermocouples or thermocouple cables that are suitable for use
E344 Terminology Relating to Thermometry and Hydrom-
in air, whose sheath or thermoelements are comprised of
etry
refractory metals, that are tested in a dry and chemically inert
E585/E585M Specification for Compacted Mineral-
environment, and that may employ compacted ceramic insu-
Insulated, Metal-Sheathed, Base Metal Thermocouple
lating materials other than magnesia (MgO) or alumina
Cable
(Al O ). Users of this test method should note that specifica-
2 3
E608/E608M Specification for Mineral-Insulated, Metal-
tions dealing with compacted ceramic insulating materials
Sheathed Base Metal Thermocouples
other than magnesia or alumina, which are described in
E1652 Specification for Magnesium Oxide and Aluminum
Specification E1652, are not currently available. As a result,
Oxide Powder and Crushable Insulators Used in the
acceptance criteria must be agreed upon between the customer
Manufacture of Metal-Sheathed Platinum ResistanceTher-
and supplier at the time of purchase, or alternatively, judgment
mometers, Base Metal Thermocouples, and Noble Metal
and experience must be applied in establishing test voltage
Thermocouples
levels and acceptable insulation resistance values for these
E2181/E2181M Specification for Compacted Mineral-
types of thermocouples and thermocouple cables.
Insulated, Metal-Sheathed, Noble Metal Thermocouples
1.3 This test method may be used for thermocouples or
and Thermocouple Cable
thermocouple cables having an outside diameter of 0.5 mm
(0.020 in) or larger.
1
This test method is under the jurisdiction of ASTM Committee E20 on
Temperature Measurement and is the direct responsibility of Subcommittee E20.04
2
on Thermocouples. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2006. Published May 2006. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1992. Last previous edition approved in 1998 as E780 – 92 (1998). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E0780-06. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1

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E780 – 06
3. Terminology catastrophically when exposed to high temperatures. Since
such contamination usually lowers the electrical resistance
3.1 Definitions—The definitions given inTerminology E344
between the thermoelements and the sheath substantially,
sha
...

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