ASTM E1350-2018 Standard Guide for Testing Sheathed Thermocouples Thermocouple Assemblies and Connecting Wires Prior to and After Installation or Service.pdf

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1、Designation: E1350 18Standard Guide forTesting Sheathed Thermocouples, ThermocoupleAssemblies, and Connecting Wires Prior to, and AfterInstallation or Service1This standard is issued under the fixed designation E1350; the number immediately following the designation indicates the year oforiginal ado

2、ption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONThermocouples are widely used in industry and provide reliable service

3、when used within theirspecified temperature range. However, if thermocouples fail in service the consequences can rangefrom insignificant to life-threatening. Often, a costly loss of equipment, product, or operating time willresult. The user should weigh the potential consequences of thermocouple fa

4、ilure when consideringwhich 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 rather th

5、anbeing a guide for acceptance testing of thermocouples as delivered from the vendor. The test methodsrange from basic tests to verify that the thermocouple was properly installed to tests necessary forfailure analysis. Thermocouple tests such as homogeneity, capacitance, and loop-current step-respo

6、nserequire elaborate equipment and sophisticated analysis and are not included in this guide.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 types of theseapplication e

7、rrors may be identified through use of the test methods described in this document. Forfurther information, the reader is directed to MNL 12, Manual on the Use of Thermocouples inTemperature Measurement,2which is an excellent reference document on metal sheathed thermo-couples.1. Scope1.1 This guide

8、 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 orinstallation, to ensure that

9、 the extension wires have beenattached to connectors and terminals with the correct polarity,and to provide benchmark data for later reference when testingto assess possible damage of the thermocouple assembly afteroperation. Some of these tests may not be appropriate forthermocouples that have been

10、 exposed to temperatures higherthan the recommended limits for the particular type.1.3 The tests described herein include methods to measurethe following characteristics of installed sheathed thermo-couple assemblies and to provide benchmark data for deter-mining if the thermocouple assembly has bee

11、n subsequentlydamaged in operation:1.3.1 Loop Resistance:1.3.1.1 Thermoelements,1.3.1.2 Combined extension wires and 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 Thermoe

12、lements,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 the1This guide is under the jurisdiction of ASTM Committee E20 on TemperatureMeasurement and is the direct responsibilit

13、y of Subcommittee E20.14 on Thermo-couples - Testing.Current edition approved May 1, 2018. Published May 2018. Originallyapproved in 1991. Last previous edition approved in 2013 as E1350 13. DOI:10.1520/E1350-18.2Manual on the Use of Thermocouples in Temperature Measurement, MNL 12,ASTM. Available f

14、rom ASTM International, www.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on P

15、rinciples for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1responsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the

16、 applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issue

17、d by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3E230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE344 Terminology Relating to Thermometry and Hydrom-etryE780 Test Method for Measur

18、ing the Insulation Resistanceof Mineral-Insulated, Metal-Sheathed Thermocouples andMineral-Insulated, Metal-Sheathed Cable at Room Tem-peratureE839 Test Methods for Sheathed Thermocouples andSheathed Thermocouple CableE1129/E1129M Specification for Thermocouple ConnectorsE608/E608M Specification for

19、 Mineral-Insulated, Metal-Sheathed Base Metal ThermocouplesE1684 Specification for Miniature Thermocouple Connec-torsE2181/E2181M Specification for Compacted Mineral-Insulated, Metal-Sheathed, Noble Metal Thermocouplesand Thermocouple CableMNL 12 Manual on the Use of Thermocouples in Tempera-ture Me

20、asurement3. Terminology3.1 DefinitionsThe definitions given in Terminology E344shall 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

21、specified temperature range.3.2.2 junction class, nStyle U junctions are 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, bu

22、t excluding active signal condi-tioning components such as reference junction compensators,amplifiers, and transmitters.3.2.4 sheathed-thermocouple assembly, nan assemblyconsisting of one or more pairs of thermoelements withinceramic insulation contained within a metal protective sheath(also referre

23、d to as MIMS), having a junction, or junctions,electrically joined to form a thermocouple, or thermocouples,with its associated parts.3.2.4.1 DiscussionAn assembly may include associatedparts such as a terminal block and a connection head.The metalprotecting tube, or sheath, has a moisture seal at t

24、he referencejunction end. Usually the metal sheath is welded closed at themeasuring end. However, if the thermocouple has an exposedjunction, it must have an effective moisture seal at themeasuring end as well as at the reference junction end.3.2.5 terminal block, na terminal device for mechanicalco

25、nnection of thermoelements and extension wires or for theconnection of extension wires to each other or to instruments.3.2.6 thermocouple connector, na quick-connect plug andjack in which the electrically connecting components havetemperature-emf characteristics matching the extension wiresor thermo

26、elements they are intended to connect.3.2.6.1 DiscussionThe temperature-emf characteristics ofthe connector parts will match the extension wires or thethermoelements only over a specified temperature range. Ther-mocouple connectors are described in Specifications E1129/E1129M and E1684.4. Summary of

27、 Tests4.1 Loop Resistance Measurements:4.1.1 ThermocoupleThe electrical loop resistance is com-pared to the resistance measured before installation to ensurethat the thermoelements have not been broken or been shortcircuited (for example, at the thermocouple connector) duringthe installation process

28、.4.1.2 Sensing CircuitThe measurements may be used toestablish the loop resistance of the combined thermocoupleassembly and extension wires and to ensure that the extensionwires are not shorted and that all connections are secure. Theresistance of the extension wires should be measured sepa-rately b

29、efore they are connected to the thermocouple assembly.4.2 Insulation Resistance Measurements:4.2.1 Thermocouple AssemblyThe room temperature in-sulation resistance of the installed Style U thermocoupleassembly is compared to the resistance measured beforeinstallation to ensure that the sheath and mo

30、isture seal have notbeen damaged and that the thermoelements were not shorted tothe sheath during installation.NOTE 1This test applies only to thermocouple assemblies with StyleU thermocouple junctions or exposed junction thermocouples with aneffective moisture seal at the junction. Thermocouples ha

31、ving Style Gjunctions cannot be tested in this manner.4.2.2 Sensing CircuitThe measurement is to establish thatthe electrical isolation of the Style U thermocouples has notbeen degraded by the extension circuit.4.2.3 Extension WiresThe measurement is to establish thatthe extension wires are continuo

32、us and not shorted to eachother, or to any other component, including earth ground. Thisis a necessary measurement when Style G thermocouples aretested.4.3 Seebeck Voltage Measurements:4.3.1 Thermocouple AssemblyThe measurement, depen-dent on a temperature difference between the measuring3For refere

33、nced 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 ASTM website.4Historically referred to as class 1 and class 2 junctions.E1350 182junc

34、tion and the terminal block, is to verify that the thermo-couple connector is mated to the thermocouple with properpolarity.4.3.2 Sensing CircuitThe measurement, dependent on atemperature difference between the measuring junction and theterminating hardware, is to verify that correct polarity has be

35、enmaintained in connecting the extension wires to the thermo-couple.5. Significance and Use5.1 These test procedures confirm and document that thethermocouple assembly was not damaged prior to or during theinstallation process and that the extension wires are properlyconnected.5.2 The test procedure

36、s 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 andmay help to identify the cause of failure.5.4 The usefulness and purpose of the applicab

37、le tests willbe found within each category.5.5 These tests are not meant to ensure that the thermo-couple assembly will measure temperatures accurately. Suchassurance is derived from proper thermocouple and instrumen-tation selection and proper placement in the location at whichthe temperature is to

38、 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 thermocoupleuses.6. Apparatus6.1 Digital Ohm-meter or Multi-meter, a direct currentresistance measurement

39、 instrument having a measuring rangefrom zero ohms to at least 1 megohm with a resolution of10 milliohms or better. If a digital multimeter is used, readingsrequire the capability to indicate a negative resistance.6.2 Megohmeter or Megohm Bridge, with ranges from 5 104ohm to 1012ohm with an accuracy

40、 of better than 610.0 %of the measured resistance and a test voltage selectablebetween 10 and 500 dc volts (VDC).6.3 Heat Source or Cold Source, a small propane type torchor an electric heat gun as a heat source. Freeze spray can beused as a cold source.7. General Requirements7.1 The following test

41、procedures assume that the loopresistance and room temperature insulation resistance of thedelivered thermocouple were already found to be acceptable byTest Method E839 prior to installation.7.2 All thermocouple assemblies to be tested should beidentified by a serial number or by some other type of

42、uniqueidentifier traceable to pre-installation tests and to a manufac-turers production run.7.3 These procedures require that all circuits have electricalcontinuity.7.4 For all connections the color codes and material com-position of the extension wires should be appropriate for theparticular thermo

43、couple type being tested. See SpecificationE230 for standard thermocouple type color codes.8. Procedure: Loop Resistance Measurements8.1 Thermocouple Loop ResistanceWith the thermo-couple disconnected from its extension wires and temperaturemeasuring instrument, measure the loop resistance at the pl

44、ugconnector pins or at the terminal block. The basic measurementis simply to establish circuit continuity. For accurate loopresistance measurements to establish benchmark data and toensure that the thermoelements are not shorted to each other(for example, at the thermocouple connector) use a digital

45、ohmmeter able to measure resistance with a resolution less than0.01 ohm. Because any Seebeck voltage generated by thethermocouple will affect the resistance value measured, tworesistance measurements shall be made, with the secondmeasurement taken with reversed polarity from the first. Theaverage of

46、 the two measurements is the thermocouples trueloop resistance. WarningOhm-meters function by measur-ing the voltage produced by passing a small DC currentthrough the unknown resistance. If the thermocouple is in atemperature gradient zone such that the measuring and refer-ence junctions are at diff

47、erent temperatures, the thermocouplesSeebeck voltage will add to or subtract from the voltagemeasured by the ohm-meter. The objective of averaging theloop resistance measurements in forward and reverse polaritiesis to eliminate the effect of the thermocouples Seebeckvoltage. However, if a thermocoup

48、le with low loop resistanceis tested while it is installed in a high temperature zone, theSeebeck voltage may be greater than the voltage produced bythe ohm-meter, resulting in a negative voltage at the ohm-meters terminals (see 8.1.3). Some digital multimeters maynot indicate negative resistance an

49、d thus averaging the forwardand reverse polarity measurements will result in an erroneousloop resistance measurement.8.1.1 If very accurate resistance measurements are required,measure the ohm-meters test lead resistance. If the ohm-meters lead resistance is significant (0.1 % compared to thethermocouples loop resistance), subtract the ohm-meters testlead resistance from all subsequent measurements of thethermocouples loop resistance.NOTE 2An installed thermocouple will often be at a differenttemperature than when it was tested before installation. The