1、Designation: E1350 13Standard Guide forTesting Sheathed Thermocouples, ThermocouplesAssemblies, 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 ad
2、option 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 f
4、ailure 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 t
5、hanbeing 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-resp
6、onserequire 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
7、errors 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 guid
8、e 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 tha
9、t 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 bee
10、n 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 be
11、en 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 Thermo
12、elements,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 responsibili
13、ty of Subcommittee E20.04 on Thermo-couples.Current edition approved June 1, 2013. Published July 2013. Originally approvedin 1991. Last previous edition approved in 2007 as E1350 07. DOI: 10.1520/E1350-13.2Manual on the Use of Thermocouples in Temperature Measurement, MNL 12,ASTM. Available from AS
14、TM International, www.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1responsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitation
15、s prior to use.2. Referenced Documents2.1 ASTM Standards:3E230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE344 Terminology Relating to Thermometry and Hydrom-etryE608/E608M Specification for Mineral-Insulated, Metal-Sheathed Base Metal ThermocouplesE7
16、80 Test Method for Measuring the Insulation Resistanceof Mineral-Insulated, Metal-Sheathed Thermocouples andThermocouple Cable at Room TemperatureE839 Test Methods for Sheathed Thermocouples andSheathed Thermocouple CableE1129/E1129M Specification for Thermocouple ConnectorsE1684 Specification for M
17、iniature 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 Measurement3. Terminology3.1 DefinitionsThe definitions given in Terminology E344shall
18、 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 are electricall
19、yisolated 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 junction compen
20、sators,amplifiers, and transmitters.3.2.4 sheathed-thermocouple assembly, nan assemblyconsisting of two thermoelements within ceramic insulationcontained within a metal protective sheath, electrically joinedat a junction to form a thermocouple, with its associated parts.3.2.4.1 DiscussionAn assembly
21、 may 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. However, if the thermocouple has an exposedjunction, it must have an effec
22、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
23、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
24、ts only over a specified temperature range. Ther-mocouple connectors are described in Specifications E1129/E1129M and E1684.4. Summary of Tests4.1 Loop Resistance Measurements:4.1.1 ThermocoupleThe electrical loop resistance is com-pared to the resistance measured before installation to ensurethat t
25、he thermoelements have not been broken or been shortcircuited (for example, at the thermocouple connector) duringthe installation process.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
26、extensionwires are not shorted and that all connections are secure. Theresistance of the extension wires should be measured sepa-rately before they are connected to the thermocouple assembly.4.2 Insulation Resistance Measurements:4.2.1 Thermocouple AssemblyThe room temperature in-sulation resistance
27、 of the installed Style U thermocoupleassembly is compared to the resistance measured beforeinstallation to ensure that the sheath and moisture seal have notbeen damaged and that the thermoelements were not shorted tothe sheath during installation.NOTE 1This test applies only to thermocouple assembl
28、ies with StyleU thermocouple junctions. Thermocouples having Style G junctionscannot 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 measurem
29、ent is to establish thatthe 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 aretested.4.3 Seebeck Voltage Measurements:4.3.1 Thermocouple AssemblyThe measurement, depen-dent on a
30、 temperature difference between the measuringjunction 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 ha
31、rdware, is to verify that correct polarity has beenmaintained in connecting the extension wires to the thermo-couple.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
32、 the standards Document Summary page onthe ASTM website.4Historically referred to as class 1 and class 2 junctions.E1350 1325. 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 exte
33、nsion wires are properlyconnected.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 andmay help to identify the cause o
34、f failure.5.4 The usefulness and purpose of the applicable 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
35、 placement in the location at whichthe temperature 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 thermocoupleuses.6. Apparatus6.1 Digital Ohm-mete
36、r or Multi-meter, a direct currentresistance measurement instrument having a measuring rangefrom zero ohms to at least 1 megohm with a resolution lessthan 1kilohm.6.2 Megohmeter or Megohm Bridge, with ranges from 5 104ohm to 1012ohm with an accuracy of better than 610.0 %of the measured resistance a
37、nd a test voltage selectablebetween 50 and 500 dc volts (VDC).6.3 Heat Source, for example, a small propane type torch oran electric heat gun.7. General Requirements7.1 The following test procedures assume that the loopresistance and room temperature insulation resistance of thedelivered thermocoupl
38、e 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 uniqueidentifier traceable to pre-installation tests and to a manufac-turers production run.7.3 These procedures
39、 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 thermocouple type being tested. See SpecificationE230 for standard thermocouple type color codes.8. Procedure: Loop Re
40、sistance Measurements8.1 Thermocouple Loop ResistanceWith the thermo-couple disconnected from its extension wires and temperaturemeasuring instrument, measure the loop resistance at the plugconnector pins or at the terminal block. The basic measurementis simply to establish circuit continuity. For a
41、ccurate 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 digitalohmmeter able to measure resistance with a resolution smallerthan 0.1 ohm. Because any Seebeck voltage generated
42、 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 the two measurements is the thermocouples trueloop resistance. WarningOhm-meters function by measur-ing the v
43、oltage 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 different temperatures, the thermocouplesSeebeck voltage will add to or subtract from the voltagemeasured by the o
44、hm-meter. The objective of averaging theloop resistance measurements in forward and reverse polaritiesis to eliminate the effect of the thermocouples Seebeckvoltage. However, if a thermocouple with low loop resistanceis tested while it is installed in a high temperature zone, theSeebeck voltage may
45、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 and thus averaging the forwardand reverse polarity measurements will result in an erroneousloop resistance measu
46、rement.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 %), of the thermo-couples loop resistance), subtract the ohm-meters test leadresistance from all subsequent measurements of the thermo
47、-couples loop resistance.NOTE 2An installed thermocouple will often be at a differenttemperature than when it was tested before installation. The differenttemperature will result in a different loop resistance that should not beinterpreted as a thermocouple defect.8.1.2 If several thermocouples of t
48、he same type are installednear the same location and in the same thermal environment,compare the resistance per unit length, for all thermocouples inthe group before and after installation. Damage may besuspected in a given thermocouple if its resistance per unitlength is significantly (10 %) differ
49、ent from the before andafter installation readings of resistance per unit length of itscompanion thermocouples in the group.NOTE 3A loop resistance measurement, taken after the thermocoupleassembly has been installed, which differs significantly from the initialloop resistance measurement will require replacement or repair of thethermocouple. If, for example, the thermocouple connector was rotated inrelation to the sheath during installation, the thermoelements might havebeen broken or shorted at the connector and may be repairable.8.1.3 An alternativ
