ASTM E2593-17 Standard Guide for Accuracy Verification of Industrial Platinum Resistance Thermometers.pdf

1、Designation: E2593 17Standard Guide forAccuracy Verification of Industrial Platinum ResistanceThermometers1This standard is issued under the fixed designation E2593; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last

2、revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide describes the techniques and apparatus re-quired for the accuracy verification of industrial platinumresistance

3、thermometers constructed in accordance with Speci-fication E1137/E1137M and the evaluation of calibrationuncertainties. The procedures described apply over the range of-200 C to 650 C.1.2 This guide does not intend to describe proceduresnecessary for the calibration of platinum resistance thermom-et

4、ers used as calibration standards or Standard PlatinumResistance Thermometers. Consequently, calibration of thesetypes of instruments is outside the scope of this guide.1.3 Industrial platinum resistance thermometers are avail-able in many styles and configurations. This guide does notpurport to det

5、ermine the suitability of any particular design,style, or configuration for calibration over a desired tempera-ture range.1.4 The evaluation of uncertainties is based upon currentinternational practices as described in JCGM 100:2008 “Evalu-ation of measurement dataGuide to the expression of uncer-ta

6、inty in measurement” and ANSI/NCSL Z540.2-1997 “U.S.Guide to the Expression of Uncertainty in Measurement.”1.5 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,

7、health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of Inte

8、rnational Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E344 Terminology Relating to Thermometry and Hydrom-etryE563 Practice for Preparation and Use of an Ice-Point Bathas a Referen

9、ce TemperatureE644 Test Methods for Testing Industrial Resistance Ther-mometersE1137/E1137M Specification for Industrial Platinum Resis-tance ThermometersE1502 Guide for Use of Fixed-Point Cells for ReferenceTemperaturesE1750 Guide for Use of Water Triple Point CellsE2623 Practice for Reporting Ther

10、mometer CalibrationsE2488 Guide for the Preparation and Evaluation of LiquidBaths Used for Temperature Calibration by Comparison2.2 ANSI Publications:3ANSI/NCSL Z540.2-1997 U.S. Guide to the Expression ofUncertainty in MeasurementANSI/NCSL Z540.3-2006 Requirements for the Calibra-tions of Measuring

11、and Test Equipment2.3 Other Publication:4JCGM 100:2008 Evaluation of measurement dataGuide tothe expression of uncertainty in measurement3. Terminology3.1 DefinitionsThe definitions given in Terminology E344shall be considered as applying to the terms used in this guide.3.2 Definitions of Terms Spec

12、ific to This Standard:3.2.1 annealing, va heat treating process intended tostabilize resistance thermometers prior to calibration and use.1This guide is under the jurisdiction of ASTM Committee E20 on TemperatureMeasurement and is the direct responsibility of Subcommittee E20.03 on ResistanceThermom

13、eters.Current edition approved Nov. 1, 2017. Published November 2017. Originallyapproved in 2007. Last previous edition approved in 2012 as E2593 12. DOI:10.1520/E2593-17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Ann

14、ual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4JCGM 100:2008, Evaluation of measurement dataGuide to the expr

15、ession ofuncertainty in measurement. Available from the BIPM, Sevres, France, http:/www.bipm.org/en/publications/guides/gum.html.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance wi

16、th internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.2 check standard, na thermometer sim

17、ilar in design tothe unit under test, but of superior stability, which is includedin the calibration process for the purpose of quantifying theprocess variability.3.2.3 coverage factor, nnumerical factor used as a multi-plier of the combined standard uncertainty in order to obtain anexpanded uncerta

18、inty.3.2.4 dielectric absorption, nan effect in an insulatorcaused by the polarization of positive and negative chargeswithin the insulator which manifests itself as an in-phasecurrent when the voltage is removed and the charges recom-bine.3.2.5 expanded uncertainty, U, nquantity defining aninterval

19、 about the result of a measurement that may beexpected to encompass a large fraction of the distribution ofvalues that could reasonably be attributed to the measurand.3.2.5.1 DiscussionTypically, U is given at a coveragefactor of 2, approximating to a 95.45 % confidence interval fora normal distribu

20、tion.3.2.6 hysteresis, nproperty associated with the resistanceof a thermometer whereby the value of resistance at a tempera-ture is dependent upon previous exposure to different tempera-tures.3.2.7 normal distribution, na frequency distribution char-acterized by a bell-shaped curve and defined by t

21、wo param-eters: mean and standard deviation.3.2.8 platinum resistance thermometer (PRT), na resis-tance thermometer with the resistance element constructedfrom platinum or platinum alloy.3.2.9 rectangular distribution, na frequency distributioncharacterized by a rectangular-shaped curve and defined

22、bytwo parameters: mean and magnitude (semi-range).3.2.10 standard deviation of the mean, nan estimate of thestandard deviation of the sampling distribution of means, basedon the data from one or more random samples.3.2.10.1 DiscussionNumerically, it is equal to the stan-dard deviation obtained (s) w

23、hen divided by the square root ofthe size of the sample (n).Standard Deviation of the Mean 5s=n(1)3.2.11 standard platinum resistance thermometer (SPRT),na specialized platinum resistance thermometer constructedin such a way that it fulfills the requirements of the ITS-90.53.2.12 standard uncertaint

24、y, nuncertainty of the result ofa measurement expressed as a standard deviation, designatedas S.3.2.13 Type A evaluation (of uncertainty), nmethod ofevaluation of uncertainty by the statistical analysis of a seriesof observations.43.2.14 Type B evaluation (of uncertainty), nmethod ofevaluation of un

25、certainty by means other than statisticalanalysis of a series of observations.43.2.15 test uncertainty ratio (TUR), nthe ratio of thetolerance of the unit under test to the expanded calibrationuncertainty.3.2.16 uncertainty budget, nan analysis tool used forassembling and combining component uncerta

26、inties expectedin a measurement process into an overall expected uncertainty.3.2.17 unit under test (UUT), nthe platinum resistancethermometer to be calibrated.4. Summary of Guide4.1 The UUT is calibrated by determining the electricalresistance of its sensing element at one or more knowntemperatures

27、 covering the temperature range of interest. Theknown temperatures may be established by means of fixed-point systems or by using a reference thermometer. Either anSPRT or a PRT is recommended for use as the referencethermometer. However, a liquid in glass (LIG) thermometer,thermistor, or thermocoup

28、le may be acceptable, dependingupon the temperature of calibration, required accuracy, or otherconsiderations.4.2 The success of the calibration depends largely upon theability of the UUT to come to thermal equilibrium with thecalibration temperature of interest (fixed point cell or compari-son syst

29、em) and upon accurate measurement of the sensingelement resistance at that time. Instructions are included toguide the user in achieving thermal equilibrium and properresistance measurement, including descriptions of apparatusand instrumentation.4.3 Industrial platinum resistance thermometers are av

30、ail-able in many styles and configurations. This guide includeslimited instructions pertaining to the preparation of the UUTinto a configuration that facilitates proper calibration.4.4 Proper evaluation of calibration uncertainties is criticalfor the result of a calibration to be useful. Therefore,

31、aconsiderable portion of this guide is devoted to uncertaintybudgets and the evaluation of uncertainties.5. Significance and Use5.1 This guide is intended to be used for verifying theresistance-temperature relationship of industrial platinum re-sistance thermometers that are intended to satisfy the

32、require-ments of Specification E1137/E1137M. It is intended to pro-vide a consistent method for calibration and uncertaintyevaluation while still allowing the user some flexibility in thechoice of apparatus and instrumentation. It is understood thatthe limits of uncertainty obtained depend in large

33、part upon theapparatus and instrumentation used. Therefore, since this guideis not prescriptive in approach, it provides detailed instructionin uncertainty evaluation to accommodate the variety ofapparatus and instrumentation that may be employed.5.2 This guide is intended primarily to satisfy appli

34、cationsrequiring compliance to Specification E1137/E1137M.However, the techniques described may be appropriate forapplications where more accurate calibrations are needed.5Mangum, B. W., NIST Technical Note 1265, Guidelines for Realizing theInternational Temperature Scale of 1990 (ITS-90).E2593 1725

35、.3 Many applications require tolerances to be verifiedusing a minimum test uncertainty ratio (TUR). This standardprovides guidelines for evaluating uncertainties used to supportTUR calculations.6. Sources of Error6.1 Uncertainties are present in all calibrations. Errors arisewhen the effects of unce

36、rtainties are underestimated or omitted.The predominant sources of uncertainty are described inSection 12 and listed in Table 2.7. Apparatus7.1 Resistance Measuring InstrumentsThe choice of aspecific instrument to use for measuring the UUTand referencethermometer resistance will depend upon several

37、factors. Someof these factors are ease of use, compatibility with computer-ized data acquisition systems, method of balancing, computa-tion ability, and so forth. All of the instruments listed arecommercially available in high precision designs and aresuitable for use. They require periodic linearit

38、y checks orperiodic calibration. (Refer to Appendix X2 for detaileddescriptions and schematics.) The uncertainty of the resistancemeasurements directly impacts the uncertainty of the tempera-ture measurement as shown in Eq 2.Uncertaintyt5UncertaintySensitivity(2)where:.Uncertaintyt= equivalent tempe

39、rature uncertainty at tem-perature (t), C,Uncertainty= resistance uncertainty at temperature (t), ,andSensitivity = sensitivity at temperature (t), C-17.1.1 BridgePrecision bridges with linearity specificationsranging from 10 ppm of range to 0.01 ppm of range and with612 to 912 digit resolution are

40、available. These instruments areavailable in models using either alternating current (AC) ordirect current (DC) excitation. The linearity is typically basedupon resistive or inductive dividers and is generally quitestable over time. Modern bridges are convenient automaticbalancing instruments but ma

41、nual balancing types are alsosuitable. These instruments typically require external referenceresistors and do not perform temperature calculations.7.1.2 Digital Thermometer ReadoutDigital instrumentsdesigned specifically to measure resistance thermometers areavailable. Modern versions function essen

42、tially as automaticpotentiometers and reverse the current to minimize DC offseterrors caused by thermal emf and residual voltages inherent tothe electronic components and related circuitry. Precisioninstruments with linearity specifications ranging from 20 ppmof indication to 1 ppm of indication and

43、 with 612 to 812 digitresolution are commercially available. Some models haveextensive internal computation capability, performing bothtemperature and statistical calculations. Periodic calibration isrequired.7.1.3 Digital Multimeter (DMM)Digital multimeters areconvenient direct indication instrumen

44、ts typically able toindicate in resistance or voltage. Some models have extensiveinternal computation ability, performing both temperature andstatistical calculations. The use of DC offset compensation isrecommended. Caution must be exercised to ensure that theexcitation current is appropriate for t

45、he UUT and referencethermometer to avoid excessive self-heating. Periodic calibra-tion is required.7.1.4 Reference ResistorReference resistors are speciallydesigned and manufactured to be stable over long periods oftime. Typically, they have significant temperature coefficientsof resistance and requ

46、ire maintenance in a temperature-enclosed air or oil bath. Some have inductive and capacitivecharacteristics that limit their suitability for use with ACbridges. Periodic (yearly or semi-yearly) calibration is re-quired. Resistors (AC or DC) are required to match the type ofmeasurement (AC or DC) sy

47、stem in use.7.2 Reference ThermometersThe choice of a specific in-strument to use as the reference thermometer will depend uponseveral factors, including the uncertainty desired, temperaturerange of interest, compatibility with existing instrumentationand apparatus, expertise of staff, cost limitati

48、ons, and so forth.All of the instruments listed are commercially available invarious levels of precision and stability and may be suitable foruse. They all require calibration. The frequency of calibrationdepends a great deal upon the manner in which they are usedand the uncertainty required in use.

49、7.2.1 SPRTSPRTs are the most accurate reference ther-mometers available and are used in defining the ITS-90 fromapproximately -260 C to 962 C. The SPRT sensing elementis made from nominally pure platinum and is supportedessentially strain-free. These instruments are extremely deli-cate and are easily damaged by mechanical shock. They areavailable sheathed in glass or metal and in long-stem andcapsule configurations. The design and materials of construc-tion limit the temperature range of a specific instrument type.Some sheath