1、Designation: E2593 11Standard 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.1NOTEEditorial changes were made throughout in March 2008.1. Scope1.1 This guide describes the techniques and apparatus re-quired for t
3、he accuracy verification of industrial platinumresistance thermometers constructed in accordance with Speci-fication E1137/E1137M and the evaluation of calibrationuncertainties. The procedures described apply over the range of200C to 650C.1.2 This guide does not intend to describe proceduresnecessar
4、y for the calibration of platinum resistance thermom-eters 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 style
5、s and configurations. This guide does notpurport to determine 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 ISO/TAG 4/WG 3“Guide to th
6、e Evaluation of Uncertainty in Measurement” andANSI/NCSL Z540-2-1997 “U.S. Guide to the Expression ofUncertainty 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
7、 appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.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 Reference TemperatureE64
8、4 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 Cells2.2 ANSI Publication:ANSI/NCSL Z540-2-1997 U.S. Gu
9、ide to the Expression ofUncertainty in Measurement32.3 Other Publication:ISO/TAG 4/WG 3 Guide to the Evaluation of Uncertainty inMeasurement3. Terminology3.1 DefinitionsThe definitions given in TerminologyE344 shall be considered as applying to the terms used in thisguide.3.2 Definitions of Terms Sp
10、ecific to This Standard:3.2.1 annealing, va heat treating process intended tostabilize resistance thermometers prior to calibration and use.3.2.2 check standard, na thermometer similar in design tothe unit under test, but of superior stability, which is includedin the calibration process for the pur
11、pose of quantifying theprocess variability.3.2.3 coverage factor, nnumerical factor used as a mul-tiplier of the combined standard uncertainty in order to obtainan expanded uncertainty.3.2.4 dielectric absorption, nan effect in an insulatorcaused by the polarization of positive and negative chargesw
12、ithin the insulator which manifests itself as an in-phasecurrent when the voltage is removed and the charges recom-bine.1This guide is under the jurisdiction of ASTM Committee E20 on TemperatureMeasurement and is the direct responsibility of Subcommittee E20.03 on ResistanceThermometers.Current edit
13、ion approved May 1, 2011. Published June 2011. Originallyapproved in 2007. Last previous edition approved in 2007 as D545607E01. DOI:10.1520/E2593-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStand
14、ards 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken
15、, PA 19428-2959, United States.3.2.5 expanded uncertainty, U, nquantity defining aninterval 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 DiscussionNormally, U is given at
16、a coveragefactor of 2, approximating to a 95 % confidence interval.3.2.6 hysteresis, nproperty associated with the resistanceof a thermometer whereby the value of resistance at a tempera-ture is dependant upon previous exposure to different tempera-tures.3.2.7 normal distribution, na frequency distr
17、ibution char-acterized by a bell shaped curve and defined by two 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 distri
18、butioncharacterized by a rectangular shaped curve and defined by twoparameters: 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 DiscussionNume
19、rically, it is equal to the stan-dard deviation obtained (s) when divided by the square root ofthe size of the sample (n).Standard Deviation of the Mean 5s=n(1)3.2.10.2 standard platinum resistance thermometer (SPRT),na specialized platinum resistance thermometer constructedin such a way that it ful
20、fills the requirements of the ITS-90.43.2.10.3 standard uncertainty, nuncertainty of the resultof a measurement expressed as a standard deviation, desig-nated as S.3.2.10.4 Type A evaluation (of uncertainty), nmethod ofevaluation of uncertainty by the statistical analysis of a seriesof observations.
21、3.2.10.5 Type B evaluation (of uncertainty), nmethod ofevaluation of uncertainty by means other than statisticalanalysis of a series of observations.3.2.10.6 test uncertainty ratio (TUR), nthe ratio of thetolerance of the unit under test to the expanded calibrationuncertainty.3.2.10.7 uncertainty bu
22、dget, nan analysis tool used forassembling and combining component uncertainties expectedin a measurement process into an overall expected uncertainty.3.2.10.8 unit under test (UUT), nthe platinum resistancethermometer to be calibrated.4. Summary of Guide4.1 The UUT is calibrated by determining the
23、electricalresistance of its sensing element at one or more knowntemperatures 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 referencethermom
24、eter. However a liquid in glass (LIG) thermometer,thermistor, or thermocouple 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 th
25、ecalibration temperature of interest (fixed point cell or compari-son system) 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 apparatus
26、and instrumentation.4.3 Industrial platinum resistance thermometers are avail-able in many styles and configurations. This guide includeslimited instructions pertaining to preparation of the UUT into aconfiguration that facilitates proper calibration.4.4 Proper evaluation of calibration uncertaintie
27、s is criticalfor the result of a calibration to be useful. Therefore, aconsiderable portion of this guide is devoted to uncertaintybudgets and the evaluation of uncertainties.5. Significance and Use5.1 This guide is used for verifying the resistance-temperature characteristics of industrial platinum
28、 resistancethermometers that are intended to satisfy the requirements ofSpecification E1137/E1137M. It is intended to provide aconsistent method for calibration and uncertainty evaluationwhile still allowing the user some flexibility in choice ofapparatus and instrumentation. It is understood that t
29、he limitsof uncertainty obtained depend in a large 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.
30、2 This guide is intended primarily to satisfy applicationsrequiring compliance to Specification E1137/E1137M. How-ever, the techniques described may be appropriate for applica-tions where higher accuracy calibrations are needed.5.3 Many applications require tolerances to be verifiedusing a minimum t
31、est 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 uncertainties are underestimated or omitted.The predominant sources of unce
32、rtainty are described inSection 12 and listed in Table 2.7. Apparatus7.1 Resistance Measuring InstrumentsThe choice of aspecific instrument to use for measuring the UUT and referencethermometer resistance will depend upon several factors. Someof these factors are ease of use, compatibility with comp
33、uter-ized data acquisition systems, method of balancing, computa-tion ability, etc. All of the instruments listed are commerciallyavailable in high precision designs and are suitable for use.4Mangum, B. W., NIST Technical Note 1265, Guidelines for Realizing theInternational Temperature Scale of 1990
34、 (ITS-90).E2593 112They require periodic linearity checks or periodic calibration.(Refer to Appendix X2 for detailed descriptions and schemat-ics.) The accuracy of the resistance measurements directlyimpacts the accuracy of the temperature measurement asshown in Eq 2.Accuracyt5AccuracyVSensitivity(2
35、)where:Accuracyt= temperature accuracy at temperature (t), C,AccuracyV= resistance accuracy at temperature (t), V, andSensitivity = sensitivity at temperature (t), V C-17.1.1 BridgePrecision bridges are available with linearityspecifications ranging from 10 ppm of range to 0.01 ppm ofrange and with
36、612 to 912 digit resolution. These instrumentsare available in models using either AC or DC excitation. Thelinearity is typically based upon resistive or inductive dividersand is generally quite stable over time. Modern bridges areconvenient automatic balancing instruments but manual bal-ancing type
37、s are also suitable. These instruments typicallyrequire external reference resistors and do not perform tem-perature calculations.7.1.2 Digital Thermometer ReadoutDigital instrumentsdesigned specifically to measure resistance thermometers areavailable. Modern versions function essentially as automat
38、icpotentiometers and reverse the current to eliminate spuriousthermal emf. Precision instruments with linearity specificationsranging from 20 ppm of indication to 1 ppm of indication andwith 612 to 812 digit resolution are commercially available.Some models have extensive internal computation capabi
39、lity,performing both temperature and statistical calculations. Peri-odic calibration is required.7.1.3 Digital Multimeter (DMM)Digital multimeters areconvenient direct indication instruments typically able toindicate in resistance or voltage. Some models have extensiveinternal computation ability, p
40、erforming both temperature andstatistical calculations. The use of DC offset compensation isrecommended. Caution must be exercised to ensure that theexcitation current is appropriate for the UUT and referencethermometer to avoid excessive self-heating. Periodic calibra-tion is required.7.1.4 Referen
41、ce ResistorReference resistors are speciallymanufactured resistors designed to be stable over long periodsof time. Typically, they have significant temperature coeffi-cients of resistance and require maintenance in a temperatureenclosed air or oil bath. Some have inductive and capacitivecharacterist
42、ics that limit their suitability for use with ACbridges. Periodic calibration (yearly or semi yearly) is required.Resistors (AC or DC) are required to match the type ofmeasurement (AC or DC) system in use.7.2 Reference ThermometersThe choice of a specificinstrument to use as the reference thermomete
43、r will dependupon several factors, including the uncertainty desired, tem-perature range of interest, compatibility with existing instru-mentation and apparatus, expertise of staff, cost limitations,etc. All of the instruments listed are commercially available invarious levels of precision and stabi
44、lity and may be suitable foruse. They all require calibration. The frequency of calibrationdepends a great deal upon the manner (care) in which they areused and the uncertainty required in use.7.2.1 SPRTSPRTs are the most accurate reference ther-mometers available and are used in defining the ITS-90
45、 fromapproximately 260C to 962C. The SPRT sensing element ismade from nominally pure platinum and is supported essen-tially strain-free. These instruments are extremely delicate andare easily damaged by mechanical shock. They are availablesheathed in glass or metal and in long stem and capsuleconfig
46、urations. The design and materials of construction limitthe temperature range of a specific instrument type. Somesheath materials can be damaged by use at high temperatures inmetal blocks or molten salt baths. Calibration on the ITS-90 isrequired.7.2.2 Secondary Reference PRTSecondary ReferencePRTs
47、are specially manufactured PRTs designed to be suitablecalibration standards. These instruments are typically lessdelicate than SPRTs but have higher measurement uncertaintiesand narrower usage ranges. They are typically sheathed inmetal to allow immersion directly into metal furnaces ormolten salt
48、baths. Calibration on the ITS-90 is required.7.3 Fixed Point SystemsFixed point systems are requiredin the ITS-90 calibration of SPRTs. Very low uncertainties areattainable with these systems, but their complex proceduresand design criteria may limit their application to other types ofthermometers.
49、However, certain adaptations are suitable for thecalibration of industrial platinum resistance thermometers.7.3.1 TPW Cell and ApparatusThe triple point of watercell is a critical thermometric fixed point for calibration andcontrol of SPRTs. These devices can be useful in the calibrationof industrial resistance thermometers but typically are not usedbecause of limited throughput capabilities. For further infor-mation refer to Guide E1750.7.3.2 Freeze-Point Cell and FurnaceMetal freeze pointcells are used in the calibration of SPRTs and th
