ASTM E1350-97

Standard Test Methods for Testing Sheathed Thermocouples Prior to, During, and After Installation

SCOPE
1.1 This guide covers methods for users to test metal sheathed thermocouple assemblies, including the extension wires, just prior to, during, and after installation.
1.2 The tests are intended to ensure that the thermocouple assemblies have not been damaged during storage or installation, to ensure that the extension wires have been attached to connectors and terminals with the correct polarity, and to provide benchmark data for later reference when testing to assess possible damage of the thermocouple assembly after operation. They are not, generally, applicable to thermocouples that have been exposed to temperatures higher than the recommended limits for the particular type.
1.3 The tests described herein include methods to measure the following variables of installed sheathed thermocouple assemblies and to provide benchmark data for determining if the thermocouple assembly is subsequently damaged in operation:
1.3.1 Loop Resistance:
1.3.1.1 Thermoelements,
1.3.1.2 Combined extension wires and the thermoelements,
1.3.2 Insulation Resistance:
1.3.2.1 Insulation, thermocouple assembly,
1.3.2.2 Insulation, thermocouple assembly and extension wires.
1.3.3 Seebeck Voltage:
1.3.3.1 Thermoelements,
1.3.3.2 Combined extension wires and thermocouple assembly.
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.

General Information

• Status: Historical
• Publication Date: 09-Apr-1997
• Technical Committee: E20 - Temperature Measurement

Relations

• Replaced By: ASTM E1350-97(2001) - Standard Guide for Testing Sheathed Thermocouples Prior to, During, and After Installation
• Effective Date: 10-Apr-1997
• Referred By: ASTM E344-20 - Terminology Relating to Thermometry and Hydrometry
• Effective Date: 10-Apr-1997
• Referred By: ASTM E839-11(2016)e1 - Standard Test Methods for Sheathed Thermocouples and Sheathed Thermocouple Cable
• Effective Date: 10-Apr-1997
• Referred By: ASTM E2846-20 - Standard Guide for Thermocouple Verification
• Effective Date: 10-Apr-1997

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 1350 – 97
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Guide for
Testing Sheathed Thermocouples Prior to, During, and After
Installation
This standard is issued under the fixed designation E 1350; 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.
INTRODUCTION
Thermocouples are widely used in industry and provide reliable service when used within their
specified temperature range. However, if thermocouples fail in service the consequences can range
from negligible to life-threatening. Often, an expensive loss of equipment, product, or operating time
will result. The user should weigh the potential consequences of thermocouple failure when
considering what tests should be performed either prior to, during, or after installation.
This standard is a guide for the field testing of thermocouples to ensure that they were not damaged
during storage, installation, or use rather than being a guide for acceptance testing of thermocouples
as delivered from the vendor. The test methods range from the most basic tests to assure the
thermocouple was properly installed to simple tests necessary for failure analysis. Thermocouple tests
such as homogeneity, capacitance, and loop-current step-response require elaborate equipment and
sophisticated analysis and are not included in this guide.
Faulty installation practices and in-service operation beyond prescribed limits are frequently the
cause of failure in properly made sheathed thermocouples. Many of the most common forms of these
conditions may be detected through use of the test methods described in this document. For further
information, the reader is directed to MNL 12, Manual on the Use of Thermocouples in Temperature
Measurement, which is an excellent reference document on metal sheathed thermocouples.
The user should always remember that a voltage (not a temperature) is measured when a
thermocouple is used. Any extraneous voltages that are introduced in the thermocouple circuit will be
interpreted as a temperature, resulting in an error in the indicated temperature. Although the extension
wires are not usually a part of the sheathed thermocouple, they are a portion of the measuring system
and, if the extension wires are improperly installed with incorrectly matched material or polarity, the
extension wires can produce voltages that will introduce substantial errors into the temperature
measurements. When high accuracy measurements are made with calibrated thermocouples, it is
especially important that the extension wires have thermoelectric properties closely matched to those
of the thermocouple over the temperature range to which the extension wires are exposed.
1. Scope assess possible damage of the thermocouple assembly after
operation. They are not, generally, applicable to thermocouples
1.1 This guide covers methods for users to test metal
that have been exposed to temperatures higher than the
sheathed thermocouple assemblies, including the extension
recommended limits for the particular type.
wires, just prior to, during, and after installation.
1.3 The tests described herein include methods to measure
1.2 The tests are intended to ensure that the thermocouple
the following variables of installed sheathed thermocouple
assemblies have not been damaged during storage or installa-
assemblies and to provide benchmark data for determining if
tion, to ensure that the extension wires have been attached to
the thermocouple assembly is subsequently damaged in opera-
connectors and terminals with the correct polarity, and to
tion:
provide benchmark data for later reference when testing to
1.3.1 Loop Resistance:
1.3.1.1 Thermoelements,
This guide is under the jurisdiction of ASTM Committee E-20 on Temperature
1.3.1.2 Combined extension wires and the thermoelements,
Measurement and is the direct responsibility of Subcommittee E20.04 on Thermo-
1.3.2 Insulation Resistance:
couples.
Current edition approved April 10, 1997. Published April 1998. Originally
1.3.2.1 Insulation, thermocouple assembly
e1
published as E 1350 – 91. Last previous edition E 1350 – 91 .
1.3.2.2 Insulation, thermocouple assembly and extension
Manual on the Use of Thermocouples in Temperature Measurement, MNL 12,
wires.
ASTM. Available from ASTM Headquarters.
E 1350
1.3.3 Seebeck Voltage: 3.2.6.1 Discussion—The temperature-emf characteristics of
1.3.3.1 Thermoelements the connector parts will match the extension wires or the
1.3.3.2 Combined extension wires and thermocouple assem- thermoelements only over a specified temperature range. Ther-
bly. mocouple connectors are described in Specifications E 1129/
1.4 This standard does not purport to address all of the E 1129M and E 1684.
safety concerns, if any, associated with its use. It is the
4. Summary of Tests
responsibility of the user of this standard to establish appro-
4.1 Loop Resistance Measurements:
priate safety and health practices and determine the applica-
4.1.1 Thermocouple—The electrical loop resistance is com-
bility of regulatory limitations prior to use.
pared to the resistance measured before installation to ensure
2. Referenced Documents that the thermoelements have not been broken or shorted to
each other (for example, at the thermocouple connector) during
2.1 ASTM Standards:
the installation process.
E 344 Terminology Relating to Thermometry and Hydrom-
3 4.1.2 Sensing Circuit—The measurements are to establish
etry
the loop resistance of the combined thermocouple assembly
E 780 Test Method for Measuring the Insulation Resistance
3 and extension wires and to ensure that the extension wires are
of Sheathed Thermocouple Material at Room Temperature
not shorted and that connections are secure. The resistance of
E 839 Test Methods of Testing Sheated Thermocouples and
3 the extension wires should be determined before they are
Sheathed Thermocouple Material
joined to the thermocouple assembly.
E 1129/E 1129M Specification for Thermocouple Connec-
3 4.2 Insulation Resistance Measurements:
tors
4.2.1 Thermocouple Assembly—The room temperature in-
E 1684 Specification for Miniature Thermocouple Connec-
3 sulation resistance of the installed Class 2 thermocouple
tors
assembly is compared to the resistance measured before
3. Terminology installation to ensure that the sheath and moisture seal has not
been damaged or that the thermoelements are not shorted to the
3.1 Definitions—The definitions given in Terminology
sheath during installation.
E 344 shall apply to this guide.
3.2 Definitions of Terms Specific to This Standard:
NOTE 1—This test applies only to thermocouple assemblies with Class
3.2.1 extension wires, n—pair of wires having temperature- 2 thermocouple junctions. Thermocouples with junctions attached to the
sheath cannot be tested in this manner.
emf characteristics that match the thermocouple temperature-
emf characteristics over a specified temperature range.
4.2.2 Sensing Circuit—The measurement is to establish that
3.2.2 junction class, n—class 2 junctions are electrically
the electrical isolation of the thermocouples with class 2
isolated from conductive sheaths and from reference ground
junctions is not degraded by the extension circuit.
and class 1 junctions are electrically connected to conductive
4.2.3 Extension Wires—The measurement is to establish
sheaths.
that the extension wires are continuous and not shorted to each
3.2.3 sensing circuit, n—the combination of the thermoele-
other, or to any other component, including earth ground. This
ments and extension wires, but excluding active signal condi-
is a necessary measurement when Class 1 thermocouples are
tioning components such as reference junction compensators,
used.
amplifiers, and transmitters.
4.3 Seebeck Voltage Measurements:
3.2.4 sheathed-thermocouple assembly, n—an assembly
4.3.1 Thermocouple Assembly—The measurement, depen-
consisting of two thermoelements in ceramic insulation within
dent on a temperature difference between the measuring
a metal protecting tube, electrically joined at a junction to form
junction and the terminal block, is to establish that the
a thermocouple, with its associated parts.
thermocouple connector is mated to the thermoelements with
3.2.4.1 Discussion—An assembly may include associated
the proper polarity.
parts such as a terminal block and a connection head. The metal
4.3.2 Sensing Circuit—The measurement, dependent on a
protecting tube, or sheath, has a moisture seal at the reference
temperature difference between the measuring junction and the
junction end. Usually the metal sheath is welded closed at the
terminating hardware, is to establish that the correct polarity
measuring end. If, however, the thermocouple has an exposed
has been maintained in connecting the extension wires to the
junction, it must have an effective moisture seal at the
thermocouple.
measuring end as well as at the reference junction end.
5. Significance and Use
3.2.5 terminal block, n—a terminal device for mechanical
5.1 These test procedures ensure and document that the
connection of thermoelements and extension wires or for the
thermocouple assembly was not damaged prior to or during the
connection of extension wires to each other or to instruments.
installation process and that the extension wires are properly
3.2.6 thermocouple connector, n—a quick-connect plug and
connected.
jack in which the electrically connecting components have
5.2 The test procedures should be used when thermocouple
temperature-emf characteristics matching the extension wires
assemblies are first installed in their working environment.
or thermoelements they are intended to connect.
5.3 In the event of subsequent thermocouple failure, these
procedures will provide benchmark data to verify failure and to
Annual Book of ASTM Standards, Vol 14.03. help evaluate the cause of failure.
E 1350
NOTE 3—The installed thermocouples will often be at a different
5.4 The usefulness and purpose of the applicable tests will
temperature than when they were measured before installation. The
be found within each category.
different temperature will produce a different loop resistance which should
5.5 These tests are not meant to ensure that the thermo-
not be interpreted as a thermocouple defect.
couple assembly will indicate temperatures accurately. Such
7.1.2 If several thermocouples of the same type are installed
assurance derives from proper thermocouple and instrumenta-
in the same location and in the same thermal environment,
tion selection and proper placement in the location where the
compare the resistance per unit length, for the group before and
temperature is to be measured. For further information, the
after installation. See Note 3. Suspect damage has occurred in
reader is directed to MNL 12, Manual on the Use of the
a given thermocouple if the measured before-and-after differ-
Thermocouples in Temperature Measurement which is an
ence of resistance per unit length is significantly (>10 %)
excellent reference document on metal sheathed thermo-
different than the before-and-after difference of resistance per
couples.
unit length of its companion thermocouples.
6. General Requirements
NOTE 4—If the loop resistance is greatly different after the thermo-
6.1 These test procedures presume that the loop resistance
couple assembly has been installed (that is, particularly if the resistance
and the room temperature insulation resistance of the delivered
shows open circuit or near zero), then the thermocouple must be replaced
or repaired. If, for example, the thermocouple connector was rotated in
thermocouples was already found to be appropriate by Test
relation to the sheath during installation, the thermoelements could have
Method E 839 before installation.
been broken or shorted at the connector and might be repairable.
6.2 All thermocouple assemblies tested should be identified
by a serial number or by some other type of unique identifier 7.1.3 An alternative method to determine the loop resistance
traceable to preinstallation tests and to a manufacturer’s of a thermocouple at elevated temperatures is to shunt the
production run. thermocouple at the connector prongs with a switchable
6.3 The procedures require that the circuit have electrical variable resistor. Measure the open-switch thermocouple See-
continuity. beck voltage between the connector prongs with a high
impedance voltmeter capable of measuring in the microvolt
7. Procedure: Loop Resistance Measurements
range (see Fig. 1). The measuring junction must be at constant
7.1 Thermocouple Loop Resistance—With the thermo-
temperature and the connector prongs must remain at the same
couple disconnected from the extensions and temperature
terminal temperature during this test. Close the switch and
measuring instruments, measure the loop resistance at the plug
adjust the resistance of the variable resistor until the closed-
connector pins or at the terminal block. The most basic
switch measured voltage is ⁄2 that of the open-switch Seebeck
measurement is simply to establish circuit continuity. For
voltage (at which time the variable resistor has the same
accurate loop resistance measurements to establish benchmark
resistance as the thermocouple loop). The variable resistor is
data and to assure that the thermoelements are not shorted to
then removed from the circuit and its resistance measured
each other (for example at the thermocouple connector assem-
directly with an ohmmeter. This method avoids the complica-
bly) an ohmmeter capable of measuring the indicated resis-
tion of the Seebeck voltage that is referred to in Note 2.
tance to at least 0.1 V must be used. Because any Seebeck
NOTE 5—At elevated (>800°C) temperatures the insulation resistance
voltage from the thermocouple will affect the measured resis-
of a thermocouple with a class 2 junction may be so low that significant
tance, two resistance measurements must be made, with the
electrical shunting may occur either between the thermoelements or the
second measurement at reversed polarity from the first mea-
thermoelement and the sheath. In that case neither of the loop resistance
surement. The average of the two measurements is the ther-
measurements nor the temperature measurements will produce an accurate
result. The insulation resistance of a thermocouple with a class 2 junction
mocouple loop resistance.
at elevated temper
...