1、Designation: E 2593 07e1Standard Guide forAccuracy Verification of Industrial Platinum ResistanceThermometers1This standard is issued under the fixed designation E 2593; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEEditorial changes were made throughout in March 2008.1. Scope1.1 This guide describes the techniques and apparatus re-quired
3、 for the accuracy verification of industrial platinumresistance thermometers constructed in accordance with Speci-fication E 1137/E 1137M and the evaluation of calibrationuncertainties. The procedures described apply over the range of200 C to 650 C.1.2 This guide is not intended to describe the proc
4、eduresnecessary for the calibration of platinum resistance thermom-eters intended to be used as calibration standards or StandardPlatinum Resistance Thermometers. Consequently, calibrationof these types of instruments is outside the scope of this guide.1.3 Industrial platinum resistance thermometers
5、 are avail-able in many styles 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
6、in ISO/TAG 4/WG 3“Guide to the 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
7、of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 344 Terminology Relating to Thermometry and Hydrom-etryE 563 Practice for Preparation and Use of an Ice-Point Ba
8、thas a Reference TemperatureE 644 Test Methods for Testing Industrial Resistance Ther-mometersE 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 Cells2.2 ANSI Pu
9、blication:ANSI/NCSL Z540-2-1997 U.S. Guide 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 TerminologyE 344 shall be considered as applying to the terms used
10、in thisguide.3.2 Definitions of Terms Specific 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 of similar designbut superior stability than the UUTs which is included in thecalib
11、ration process for the purpose of quantifying the processvariability.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 posi
12、tive 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 about the result of a measurement that may beexpected to encompass a large fraction of the di
13、stribution ofvalues that could reasonably be attributed to the measurand.1This guide is under the jurisdiction of ASTM Committee E20 on TemperatureMeasurement and is the direct responsibility of Subcommittee E20.03 on ResistanceThermometers.Current edition approved Dec. 1, 2007. Published January 20
14、08.2For 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 the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANS
15、I), 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, PA 19428-2959, United States.3.2.5.1 DiscussionNormally, U is given at a coveragefactor of 2, approximating to a 95 % confidence interval.3.2.6 h
16、ysteresis, 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 distribution char-acterized by a bell shaped curve and defined by two param-ete
17、rs: 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 by twoparame
18、ters: 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) when divided
19、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 fulfills the requirements of the ITS-90.43.2.10.3 standard uncertainty, nunce
20、rtainty 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.3.2.10.5 Type B evaluation (of uncertainty), nmethod ofevaluation of uncer
21、tainty 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 budget, nan analysis tool used forassembling and combining component uncerta
22、inties 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 electricalresistance of its sensing element at one or more knowntemperatur
23、es 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 thermocou
24、ple 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
25、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
26、ail-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 uncertainties is criticalfor the result of a calibration to be useful. Therefore, acon
27、siderable 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 by laboratoriesinterested in the calibration of industrial platinum resistancethermometers that are intended to satisfy the requirements o
28、fSpecification E 1137/E 1137M. 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 the limitsof uncertainty obtained depend in a large part upon theappar
29、atus 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 applicationsrequiring c
30、ompliance to Specification E 1137/E 1137M. How-ever, the techniques described may be appropriate for applica-tions where higher accuracy calibrations are needed.6. Sources of Error6.1 Uncertainties are present in all calibrations. Errors arisewhen the effects of uncertainties are underestimated or o
31、mitted.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 UUT and referencethermometer resistance will depend upon several factors. Someof these factors ar
32、e ease of use, compatibility with computer-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.They require periodic linearity checks or periodic calibration.(Refer t
33、o 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)where:4Mangum, B. W., NIST Technical Note 1265, Guidelines for Realizing theInternational
34、 Temperature Scale of 1990 (ITS-90).E259307e12Accuracyt= 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
35、 of range to 0.01 ppm ofrange and with 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
36、 instruments but manual bal-ancing types 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 v
37、ersions function essentially as automaticpotentiometers 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 hav
38、e extensive internal computation capability,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 e
39、xtensiveinternal 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 the UUT and referencethermometer to avoid excessive self-heating. Periodic
40、 calibra-tion is required.7.1.4 Reference 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 ha
41、ve inductive and capacitivecharacteristics 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 specificinstru
42、ment to use as the reference thermometer 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
43、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 (care) in which they areused and the uncertainty required in use.7.2.1 SPRTSPRTs are the most accurate reference ther-mometers availa
44、ble 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
45、 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 materials can be damaged by use at hightemperatures in metal blocks or molten salt baths. Calibrationon the ITS-90 is required.7.2.2 Seco
46、ndary Reference PRTSecondary ReferencePRTs 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
47、directly into metal furnaces ormolten salt 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
48、application to other types ofthermometers. 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 c
49、an be useful in the calibrationof industrial resistance thermometers but typically are not usedbecause of limited throughput capabilities. For further infor-mation refer to Guide E 1750.7.3.2 Freeze-Point Cell and FurnaceMetal freeze pointcells are used in the calibration of SPRTs and thermocouples.These devices can be useful in the calibration of industrialplatinum resistance thermometers but typically are not usedbecause of limited throughput capabilities. For further infor-mation refer to Guide E 1502.7.3.3 Ice-Point BathThe ice point is
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