ASTM E644-2008 952 Standard Test Methods for Testing Industrial Resistance Thermometers.pdf

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1、Designation: E 644 08Standard Test Methods forTesting Industrial Resistance Thermometers1This standard is issued under the fixed designation E 644; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number

2、 in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover the principles, apparatus, andprocedures for calibration and testing of industrial resistancethermometers.1.2 These

3、test methods cover the tests for insulation resis-tance, calibration, immersion error, pressure effects, thermalresponse time, vibration effect, mechanical shock, self-heatingeffect, stability, thermoelectric effect, humidity, thermal hys-teresis, thermal shock, and end seal integrity.1.3 These test

4、 methods are not necessarily intended for,recommended to be performed on, or appropriate for everytype of thermometer. The expected repeatability and reproduc-ibility of the results are tabulated in Appendix X4.1.4 These test methods, when specified in a procurementdocument, shall govern the method

5、of testing the resistancethermometer.1.5 Thermometer performance specifications, acceptancelimits, and sampling methods are not covered in these testmethods; they should be specified separately in the procure-ment document.1.6 This standard does not purport to address all of thesafety concerns, if a

6、ny, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific precau-tionary statements are given in 6.3.2, 6.3.5, and 8.1.2. Referenced Documen

7、ts2.1 ASTM Standards:2E1 Specification for ASTM Liquid-in-Glass ThermometersE77 Test Method for Inspection and Verification of Ther-mometersE 230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE 344 Terminology Relating to Thermometry and Hydrom-etryE 563

8、 Practice for Preparation and Use of an Ice-Point Bathas a Reference TemperatureE 1137/E 1137M Specification for Industrial Platinum Re-sistance ThermometersE 1502 Guide for Use of Freezing-Point Cells for ReferenceTemperaturesE 1750 Guide for Use of Water Triple Point CellsE 1751 Guide for Temperat

9、ure Electromotive Force (EMF)Tables for Non-Letter Designated Thermocouple Combi-nationsE 2251 Specification for Liquid-in-Glass ASTM Thermom-eters with Low-Hazard Precision Liquids2.2 Military Standard:3MIL-STD-202 Test Methods for Electronic and ElectricalComponent Parts3. Terminology3.1 Definitio

10、ns of Terms Specific to This Standard:3.1.1 The definitions given in Terminology E 344 shallapply to these test methods.3.1.2 bath gradient error, nthe error caused by tempera-ture differences in the working space of the bath. (The bath ortemperature equalizing blocks should be explored to determine

11、the work areas in which the temperature gradients are insig-nificant.)3.1.3 calibration, nthe determination of the indications ofa thermometer with respect to temperatures established by astandard resulting in scale corrections to be applied whenmaximum accuracy is required.3.1.4 connecting wire err

12、or, nthe error caused by uncom-pensated connecting wire resistance. (Although the connectingwire is part of the measurement circuit, most of it is not at thetemperature that is being determined. Thermometers are avail-able in two-, three-, and four-wire configurations. There is nosatisfactory way to

13、 compensate for the wire resistance in themeasurement with a two-wire thermometer although the wireresistance can be compensated for in three and four-wirethermometers.)1These test methods are under the jurisdiction of ASTM Committee E20 onTemperature Measurement and are the direct responsibility of

14、 Subcommittee E20.03on Resistance Thermometers.Current edition approved May 1, 2008. Published June 2008. Originallyapproved in 1978. Last previous edition approved in 2006 as E 644 06.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceast

15、m.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from Superintendent of Documents, U.S. Government PrintingOffice, Washington, DC 20234.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consho

16、hocken, PA 19428-2959, United States.3.1.5 immersion error, nan error caused by the heatconduction or radiation, or both, between the resistance ther-mometer element and the environment external to the measure-ment system, because of insufficient immersion length andthermal contact of the thermomete

17、r with the medium undermeasurement.3.1.6 interchangeability, nthe extent to which the ther-mometer matches a resistance-temperature relationship. (Theverification of interchangeability can be accomplished only bycalibration. The deviations at the temperature limits and themaximum deviation from the

18、established resistance-temperature relationship shall be specified.)3.1.7 self-heating, nthe increase in the temperature of thethermometer element caused by the electric power dissipated inthe element, the magnitude depending upon the thermometercurrent and heat conduction from the thermometer eleme

19、nt tothe surrounding medium.3.1.8 self-heating error, nthe error caused by variationsfrom the calibration conditions in the self-heating of thethermometer element at a given current, arising from thevariations in the heat conduction from the thermometer to thesurrounding medium.3.1.9 thermoelectric

20、effect error, nthe error caused by athermal emf in the measurement circuit as a result of dissimilarmetals and temperature gradients in the circuit.4. Significance and Use4.1 These test methods provide uniform methods for testingindustrial resistance thermometers so that a given tester mayexpect to

21、obtain the same value of a test result from makingsuccessive measurements on the same test article within thelimits of repeatability given in Appendix X4. Independenttesters may also expect to obtain the same result from thetesting of the same article within the limits of reproducibilitygiven in App

22、endix X4.4.2 These tests may be used to qualify platinum resistancethermometers for use in specific applications to meet a particu-lar specification such as Specification E 1137/E 1137M,ortoevaluate relative merits of equivalent test articles supplied byone or more manufacturers, or to determine the

23、 limits of theapplication of a particular design of thermometer.4.3 The expected repeatability and reproducibility of se-lected test methods are included in Appendix X4.4.4 Some non-destructive tests described in these test meth-ods may be applied to thermometers that can be subsequentlysold or used

24、; other destructive tests may preclude the sale oruse of the test article because of damage that the test mayproduce.PROCEDURES5. Insulation Resistance Test5.1 ScopeThe insulation resistance between the thermom-eter element with its connecting wires and its external shield,case or means for mounting

25、, should be sufficient to preventsignificant electrical shunting or ground loop current in themeasurement circuit, or any circuit failure if the excitationsource is grounded. This test assumes that the thermometer hasa metallic or other electrically conductive sheath or housing.The most probable fac

26、tors that contribute to insulation failureare contamination, typically from moisture, and mechanicalbreakdown due to physical damage to the device. Most ceramicoxide insulation absorbs moisture. This moisture is expected tomigrate inside the thermometer, depending upon the tempera-ture condition of

27、use, and to cause variations in the insulationresistance. Test conditions for insulation resistance shouldtherefore approximate the most severe conditions of probableuse and shall be specified as a minimum at a specifictemperature, humidity, pressure and test voltage. It is recom-mended that insulat

28、ion resistance be measured using forwardand reversed polarity on applied dc voltages. The test methodscustomarily applied with the test article at room temperaturemay also be employed to determine the insulation resistance attemperatures up to the rated application temperature for theresistance ther

29、mometer. This is intended to be a non-destructive test.5.1.1 The insulation resistance, as measured between thelead wires and case, does not represent the shunt resistance inparallel with the sensing element. Therefore, this test shouldnot be used to estimate temperature measurement errors causedby

30、inadequate insulation resistance across the sensing element.5.2 Apparatus:5.2.1 Because the insulation resistance is to be measured inconjunction with other tests, the thermometer shall be mountedas required for these tests.5.2.2 Any equipment made for the purpose of insulationresistance testing sha

31、ll be capable of measuring a resistance ofat least 10 gigohms (1010V) at the specified test voltage.(WarningSome instruments designed for insulation resis-tance testing are capable of producing lethal voltages (100 V orgreater) at their measuring terminals. Such instruments shouldhave warning labels

32、 and used only by supervised and welltrained personnel.)5.3 Measurement Procedure:5.3.1 Make check measurements on a reference resistor of10 gigohms (1010V). Check the measurement instrument to65 % at the required minimum insulation resistance using acertified reference resistor. These results shoul

33、d accompany thetest report on the platinum resistance thermometer (PRT). Forexample: When testing a PRT with a specified 100 megohm(108V) minimum insulation resistance, the meter should betested with a resistor that has a certified resistance of 100megohms 65%.5.3.2 Make insulation resistance measur

34、ements between theconnecting wires and the shield or case, (1) before thethermometer is subjected to the conditions of any concurrenttest (calibration, pressure, vibration), (2) during the test, and(3) immediately after the thermometer has returned to ambientconditions. All measured values of insula

35、tion resistance foreach test condition shall exceed the minimum specified value.5.3.3 Apply the specified measuring voltage between thejoined connecting wires and the thermometer sheath or be-tween circuits that are intended to be isolated. Take measure-ments with normal and reversed polarity and re

36、cord the lowerreading. Take the reading within 10 s of voltage application.Since only minimum values of insulation resistance are ofconcern, measurement accuracy need only be sufficient toE644082ensure that the minimum requirement is met. Insulation resis-tance measurements made during vibration req

37、uire a highspeed indicating device, such as an oscilloscope, to detect rapidtransient changes in resistance.5.4 The repeatability of the measurements value is ex-pected to be 65 % and the reproducibility 610 %. SeeAppendix X4 for the results of round robin testing used todetermine the repeatability

38、and reproducibility of this test.6. Thermometer Calibration6.1 ScopeThis test method covers recommended ways ofcalibrating industrial resistance thermometers. Methods com-mon to most calibrations will be described, but the testmethods presented do not usually test the thermometer underthe actual con

39、ditions of use. The heat transfer conditions canvary widely, depending upon the medium, immersion length,rate of flow of the medium, etc. These and other conditionsshould be carefully evaluated before installing a thermometerfor calibration or for temperature measurement. A resistancethermometer can

40、 be calibrated by using the comparison methodor the fixed-point method, or both. The calibration results maybe used to assess interchangeability, to establish a uniqueresistance-temperature relationship for the thermometer undertest, or to verify conformance to a standard. In calibration tests,care

41、should be taken to minimize thermal shock to thethermometer when inserting it into a heated or cooled environ-ment, or when withdrawing it from a furnace or heated bath.Transitions should be made slowly, preheating or pre-coolingthe thermometer when possible. This test is intended to be anon-destruc

42、tive test. However, calibration of a thermometer toa higher temperature than it has previously experienced maychange its calibration at lower temperatures. Resistances takenat ascending temperatures should be compared with thosetaken at descending temperatures to detect any change in thethermometers

43、 characteristics (see Section 16, Thermal Hys-teresis).6.2 Calibration Methods:6.2.1 Comparison MethodThis method consists of mea-suring the resistance of the test thermometer in an isothermalmedium, the temperature of which is determined by a cali-brated reference thermometer. The reference thermom

44、eter maybe a thermocouple, a liquid-in-glass thermometer, a resistancethermometer, or another thermometer of sufficient accuracythat has been calibrated by an approved method.6.2.2 Fixed-Point MethodThis method consists of mea-suring the resistance of the thermometer at the temperaturedefined by the

45、 equilibrium state between different phases of apure substance or a mixture of pure substances. Each fixedpoint provides a calibration of the test thermometer at only onetemperature defined by suitable equilibrium phases. The tem-perature is an intrinsic property of a properly specified equi-librium

46、 state of a substance, such as the freezing point at 1 atm.The temperature of some fixed-point devices can be repeated to60.1 mC or better.6.3 Apparatus and Procedure:6.3.1 Ice-Point Bath The most widely used and simplestfixed point is the ice-point. The ice point (0 C) may berealized with an error

47、of less than 0.01 C if properly preparedand used. Significantly greater errors may be realized if certainconditions exist. Users of this test method are referred toPractice E 563 which contains a more detailed discussion as tothe proper preparation and use of ice point baths.6.3.2 Freezing Points In

48、 addition to the ice-point bath, thefreezing-point temperature of various substances can be usedas fixed points. The metal freezing point materials identified inGuide E 1502 are those most commonly employed.6.3.3 Triple Point of WaterThe triple point of water is acommonly used thermometric fixed poi

49、nt used for calibratingthermometers. To accurately realize the triple point of water, atriple point of water cell is used. This cell must be prepared andhandled in a specific manner. The user is directed to GuideE 1750 for the preparation and use of water triple point cells.6.3.4 Fluid Baths Control the temperature of fluid bathsby adjusting the amount of heating or cooling while agitatingthe bath fluid. Determine the amount of heating or cooling bythe indication of a sensitive thermometer in the bath. Table 1lists some of the common bath media and their useful