1、Designation: E 1350 07Standard Guide forTesting Sheathed Thermocouples, ThermocouplesAssemblies, and Connecting Wires Prior to, and AfterInstallation or Service1This standard is issued under the fixed designation E 1350; the number immediately following the designation indicates the year oforiginal
2、adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThermocouples are widely used in industry and provide reliable serv
3、ice when used within theirspecified temperature range. However, if thermocouples fail in service the consequences can rangefrom negligible to life-threatening. Often, an expensive loss of equipment, product, or operating timewill result. The user should weigh the potential consequences of thermocoup
4、le failure whenconsidering what tests should be performed either prior to, during, or after installation.This standard is a guide for the field testing of thermocouples, thermocouple assemblies, and theirconnecting wires to ensure that they were not damaged during storage, installation, or use rathe
5、r thanbeing a guide for acceptance testing of thermocouples as delivered from the vendor. The test methodsrange from the most basic tests to assure the thermocouple was properly installed to simple testsnecessary for failure analysis. Thermocouple tests such as homogeneity, capacitance, and loop-cur
6、rentstep-response require elaborate equipment and sophisticated analysis and are not included in thisguide.Faulty installation practices and in-service operation beyond prescribed limits are frequently thecause of failure in properly made sheathed thermocouples. Many of the most common forms of thes
7、econditions may be detected through use of the test methods described in this document. For furtherinformation, the reader is directed to MNL 12, Manual on the Use of Thermocouples in TemperatureMeasurement,2which is an excellent reference document on metal sheathed thermocouples.1. Scope1.1 This gu
8、ide covers methods for users to test metalsheathed thermocouple assemblies, including the extensionwires, just prior to, and after installation or some period ofservice.1.2 The tests are intended to ensure that the thermocoupleassemblies have not been damaged during storage or installa-tion, to ensu
9、re that the extension wires have been attached toconnectors and terminals with the correct polarity, and toprovide benchmark data for later reference when testing toassess possible damage of the thermocouple assembly afteroperation. Some of these tests may not be appropriate forthermocouples that ha
10、ve been exposed to temperatures higherthan the recommended limits for the particular type.1.3 The tests described herein include methods to measurethe following variables of installed sheathed thermocoupleassemblies and to provide benchmark data for determining ifthe thermocouple assembly is subsequ
11、ently damaged in opera-tion: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 extensionwires.1.3.3 Seebeck Voltage:1.3.3.1 Thermoelem
12、ents,1.3.3.2 Combined extension wires and thermocouple assem-bly.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the appl
13、ica-bility of regulatory limitations prior to use.1This guide is under the jurisdiction of ASTM Committee E20 on TemperatureMeasurement and is the direct responsibility of Subcommittee E20.04 on Thermo-couples.Current edition approved May 1, 2007. Published June 2007. Originallyapproved in 1991. Las
14、t previous edition approved in 2001 as E 1350 97 (2001).2Manual on the Use of Thermocouples in Temperature Measurement, MNL 12,ASTM. Available from ASTM International, www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2. R
15、eferenced Documents2.1 ASTM Standards:3E 230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE 344 Terminology Relating to Thermometry and Hydrom-etryE 780 Test Method for Measuring the Insulation Resistanceof Mineral-Insulated, Metal-Sheathed Thermocouple
16、s andThermocouple Cable at Room TemperatureE 839 Test Methods for Sheathed Thermocouples andSheathed Thermocouple MaterialE 1129/E 1129M Specification for Thermocouple Connec-torsE 1684 Specification for Miniature Thermocouple Connec-tors3. Terminology3.1 DefinitionsThe definitions given in Terminol
17、ogyE 344 shall apply to this guide.3.2 Definitions of Terms Specific to This Standard:3.2.1 extension wires, npair of wires having temperature-emf characteristics that match the thermocouple temperature-emf characteristics over a specified temperature range.3.2.2 junction class, nStyle U junctions a
18、re electricallyisolated from conductive sheaths and from reference groundand Style G junctions are electrically connected to conductivesheaths.43.2.3 sensing circuit, nthe combination of the thermoele-ments and extension wires, but excluding active signal condi-tioning components such as reference j
19、unction compensators,amplifiers, and transmitters.3.2.4 sheathed-thermocouple assembly, nan assemblyconsisting of two thermoelements in ceramic insulation withina metal protecting tube, electrically joined at a junction to forma thermocouple, with its associated parts.3.2.4.1 DiscussionAn assembly m
20、ay include associatedparts such as a terminal block and a connection head. The metalprotecting tube, or sheath, has a moisture seal at the referencejunction end. Usually the metal sheath is welded closed at themeasuring end. If, however, the thermocouple has an exposedjunction, it must have an effec
21、tive moisture seal at themeasuring end as well as at the reference junction end.3.2.5 terminal block, na terminal device for mechanicalconnection of thermoelements and extension wires or for theconnection of extension wires to each other or to instruments.3.2.6 thermocouple connector, na quick-conne
22、ct plug andjack in which the electrically connecting components havetemperature-emf characteristics matching the extension wiresor thermoelements they are intended to connect.3.2.6.1 DiscussionThe temperature-emf characteristics ofthe connector parts will match the extension wires or thethermoelemen
23、ts only over a specified temperature range. Ther-mocouple connectors are described in Specifications E 1129/E 1129M and E 1684.4. Summary of Tests4.1 Loop Resistance Measurements:4.1.1 ThermocoupleThe electrical loop resistance is com-pared to the resistance measured before installation to ensuretha
24、t the thermoelements have not been broken or shorted toeach other (for example, at the thermocouple connector) duringthe installation process.4.1.2 Sensing CircuitThe measurements are to establishthe loop resistance of the combined thermocouple assemblyand extension wires and to ensure that the exte
25、nsion wires arenot shorted and that connections are secure. The resistance ofthe extension wires should be determined before they arejoined to the thermocouple assembly.4.2 Insulation Resistance Measurements:4.2.1 Thermocouple AssemblyThe room temperature in-sulation resistance of the installed Styl
26、e U thermocoupleassembly is compared to the resistance measured beforeinstallation to ensure that the sheath and moisture seal has notbeen damaged or that the thermoelements are not shorted to thesheath during installation.NOTE 1This test applies only to thermocouple assemblies with StyleU thermocou
27、ple junctions. Thermocouples with junctions attached to thesheath cannot be tested in this manner.4.2.2 Sensing CircuitThe measurement is to establish thatthe electrical isolation Style U thermocouples is not degradedby the extension circuit.4.2.3 Extension WiresThe measurement is to establishthat t
28、he extension wires are continuous and not shorted to eachother, or to any other component, including earth ground. Thisis a necessary measurement when Style G thermocouples areused.4.3 Seebeck Voltage Measurements:4.3.1 Thermocouple AssemblyThe measurement, depen-dent on a temperature difference bet
29、ween the measuringjunction and the terminal block, is to establish that thethermocouple connector is mated to the thermoelements withthe proper polarity.4.3.2 Sensing CircuitThe measurement, dependent on atemperature difference between the measuring junction and theterminating hardware, is to establ
30、ish that the correct polarityhas been maintained in connecting the extension wires to thethermocouple.5. Significance and Use5.1 These test procedures ensure and document that thethermocouple assembly was not damaged prior to or during theinstallation process and that the extension wires are properl
31、yconnected.5.2 The test procedures should be used when thermocoupleassemblies are first installed in their working environment.5.3 In the event of subsequent thermocouple failure, theseprocedures will provide benchmark data to verify failure and tohelp evaluate the cause of failure.5.4 The usefulnes
32、s and purpose of the applicable tests willbe found within each category.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe AS
33、TM website.4Historically reffered to as class 1 and class 2 junctions.E13500725.5 These tests are not meant to ensure that the thermo-couple assembly will indicate temperatures accurately. Suchassurance derives from proper thermocouple and instrumenta-tion selection and proper placement in the locat
34、ion where thetemperature is to be measured. For further information, thereader is directed to MNL 12, Manual on the Use of theThermocouples in Temperature Measurement2which is anexcellent reference document on metal sheathed thermo-couples.6. Apparatus6.1 Resistance Measuring Digital Meter or Multi-
35、meter,adigital direct current resistance measurement device having arange from 0 Ohms to 1 megohms and a resolution of betterthan 1KV.6.2 Megohmeter or Megohm B Ridge, with ranges from 5 3104V to 1012V with an accuracy of better than 610.0 % of themeasured test resistance and a test voltage of 50 to
36、 500 VDCdepending on the outside diameter of the sheathed thermo-couple material.6.3 Heat Source, for example, a small propane type torch oran electric heat gun.7. General Requirements7.1 These test procedures presume that the loop resistanceand the room temperature insulation resistance of the deli
37、veredthermocouples was already found to be appropriate by TestMethod E 839 before installation.7.2 All thermocouple assemblies tested should be identifiedby a serial number or by some other type of unique identifiertraceable to pre-installation tests and to a manufacturersproduction run.7.3 The proc
38、edures require that the circuit have electricalcontinuity.7.4 For all connections the color codes and material com-position of the extension wires should be appropriate for theparticular thermocouple type being used. See SpecificationE 230 for standard thermocouple type color coding.8. Procedure: Lo
39、op Resistance Measurements8.1 Thermocouple Loop ResistanceWith the thermo-couple disconnected from the extensions and temperaturemeasuring instruments, measure the loop resistance at the plugconnector pins or at the terminal block. The most basicmeasurement is simply to establish circuit continuity.
40、 Foraccurate loop resistance measurements to establish benchmarkdata and to assure that the thermoelements are not shorted toeach other (for example at the thermocouple connector assem-bly) an ohmmeter capable of measuring the indicated resis-tance to at least 0.1 V must be used. Because any Seebeck
41、voltage from the thermocouple will affect the measured resis-tance, two resistance measurements must be made, with thesecond measurement at reversed polarity from the first mea-surement. The average of the two measurements is the ther-mocouple loop resistance. WarningOhmmeters operate bymeasuring a
42、voltage produced by passing a current through themeasured resistance. If the thermocouple is in a temperaturegradient so that the measuring and reference junctions are atdifferent temperatures, the Seebeck voltage from the thermo-couple will add to or subtract from the voltage measured by theohmmete
43、r. The purpose of averaging loop resistance measure-ments in forward and reverse directions is to eliminate theeffect of the Seebeck voltage on the resistance measurements.If, however, a thermocouple with a low loop resistance ismeasured while it is installed in a high temperature zone, theSeebeck v
44、oltage from the thermocouple may then be greaterthan the voltage produced by the ohmmeter, resulting in ameasured negative voltage at the ohmmeter (see 8.1.3). Somedigital multi-metres do not indicate a negative resistance andthus averaging both forward and reverse resistances as positivewill result
45、 in an erroneous resistance measurement.8.1.1 If accurate resistance measurements are to be made,measure the ohmmeter lead resistance. If the ohmmeter leadresistance is significant (0.1 %), compared to the thermo-couple loop resistance, subtract the ohmmeter lead resistancefrom all subsequent measur
46、ements of the thermocouple loopresistance.NOTE 2The installed thermocouples will often be at a differenttemperature than when they were measured before installation. Thedifferent temperature will produce a different loop resistance that shouldnot be interpreted as a thermocouple defect.8.1.2 If seve
47、ral thermocouples of the same type are installedin the same location and in the same thermal environment,compare the resistance per unit length, for the group before andafter installation. See Note 2. Suspect damage has occurred ina given thermocouple if the measured before-and-after differ-ence of
48、resistance per unit length is significantly (10 %)different than the before-and-after difference of resistance perunit length of its companion thermocouples.NOTE 3If the loop resistance is greatly different after the thermo-couple assembly has been installed (that is, particularly if the resistances
49、hows open circuit or near zero), then the thermocouple must be replacedor repaired. If, for example, the thermocouple connector was rotated inrelation to the sheath during installation, the thermoelements could havebeen broken or shorted at the connector and might be repairable.8.1.3 An alternative method to determine the loop resistanceof a thermocouple at elevated temperatures is to shunt thethermocouple at the connector prongs with a variable resistor.Measure the open-switch thermocouple Seebeck voltage be-tween the connector prongs with a high impedance voltm
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