1、Designation: E2593 111 E2593 12Standard 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 yea
2、r 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.1 NOTEThe previous epsilon note was removed in July 2011.1. Scope1.1 This guide describes the techniques and apparatus requir
3、ed for the accuracy verification of industrial platinum resistancethermometers constructed in accordance with Specification E1137/E1137M and the evaluation of calibration uncertainties. Theprocedures described apply over the range of 200C to 650C.1.2 This guide does not intend to describe procedures
4、 necessary for the calibration of platinum resistance thermometers usedas calibration standards or Standard Platinum Resistance Thermometers. Consequently, calibration of these types of instrumentsis outside the scope of this guide.1.3 Industrial platinum resistance thermometers are available in man
5、y styles and configurations. This guide does not purport todetermine the suitability of any particular design, style, or configuration for calibration over a desired temperature range.1.4 The evaluation of uncertainties is based upon current international practices as described in ISO/TAG 4/WG 3 “Gu
6、ide tothe Evaluation of Uncertainty in Measurement” and ANSI/NCSL Z540-2-1997 “U.S. Guide to the Expression of Uncertainty inMeasurement.”1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to
7、 establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E344 Terminology Relating to Thermometry and HydrometryE563 Practice for Preparation and Use of an Ice-Point Bath as a Reference Tempera
8、tureE644 Test Methods for Testing Industrial Resistance ThermometersE1137/E1137M Specification for Industrial Platinum Resistance ThermometersE1502 Guide for Use of Fixed-Point Cells for Reference TemperaturesE1750 Guide for Use of Water Triple Point Cells2.2 ANSI Publication:ANSI/NCSL Z540-2-1997 U
9、.S. Guide to the Expression of Uncertainty in Measurement32.3 Other Publication:ISO/TAG 4/WG 3 Guide to the Evaluation of Uncertainty in Measurement3. Terminology3.1 DefinitionsThe definitions given in Terminology E344 shall be considered as applying to the terms used in this guide.3.2 Definitions o
10、f Terms Specific to This Standard:3.2.1 annealing, va heat treating process intended to stabilize resistance thermometers prior to calibration and use.1 This guide is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.03 on Re
11、sistanceThermometers.Current edition approved May 1, 2011Nov. 1, 2012. Published June 2011December 2012. Originally approved in 2007. Last previous edition approved in 20072011 asD545607E01.11E01. DOI: 10.1520/E2593-11E01.10.1520/E2593-12.2 For referenced ASTM standards, visit the ASTM website, www.
12、astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www
13、.ansi.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult
14、 prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.2 check standard, na thermometer s
15、imilar in design to the unit under test, but of superior stability, which is included inthe calibration process for the purpose of quantifying the process variability.3.2.3 coverage factor, nnumerical factor used as a multiplier of the combined standard uncertainty in order to obtain anexpanded unce
16、rtainty.3.2.4 dielectric absorption, nan effect in an insulator caused by the polarization of positive and negative charges within theinsulator which manifests itself as an in-phase current when the voltage is removed and the charges recombine.3.2.5 expanded uncertainty, U, nquantity defining an int
17、erval about the result of a measurement that may be expected toencompass a large fraction of the distribution of values that could reasonably be attributed to the measurand.3.2.5.1 DiscussionNormally, U is given at a coverage factor of 2, approximating to a 95 % confidence interval.3.2.6 hysteresis,
18、 nproperty associated with the resistance of a thermometer whereby the value of resistance at a temperatureis dependant upon previous exposure to different temperatures.3.2.7 normal distribution, na frequency distribution characterized by a bell shaped curve and defined by two parameters: meanand st
19、andard deviation.3.2.8 platinum resistance thermometer (PRT), na resistance thermometer with the resistance element constructed fromplatinum or platinum alloy.3.2.9 rectangular distribution, na frequency distribution characterized by a rectangular shaped curve and defined by twoparameters: mean and
20、magnitude (semi-range).3.2.10 standard deviation of the mean, nan estimate of the standard 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 standard deviation obtained (s) when divided by the square r
21、oot of the size of the sample (n).Standard Deviation of the Mean5 s=n(1)3.2.11 standard platinum resistance thermometer (SPRT), na specialized platinum resistance thermometer constructed in sucha way that it fulfills the requirements of the ITS-90.43.2.12 standard uncertainty, nuncertainty of the re
22、sult of a measurement expressed as a standard deviation, designated as S.3.2.13 Type A evaluation (of uncertainty), nmethod of evaluation of uncertainty by the statistical analysis of a series ofobservations.3.2.14 Type B evaluation (of uncertainty), nmethod of evaluation of uncertainty by means oth
23、er than statistical analysis of aseries of observations.3.2.15 test uncertainty ratio (TUR), nthe ratio of the tolerance of the unit under test to the expanded calibration uncertainty.3.2.16 uncertainty budget, nan analysis tool used for assembling and combining component uncertainties expected in a
24、measurement process into an overall expected uncertainty.3.2.17 unit under test (UUT), nthe platinum resistance thermometer to be calibrated.4. Summary of Guide4.1 The UUT is calibrated by determining the electrical resistance of its sensing element at one or more known temperaturescovering the temp
25、erature range of interest. The known temperatures may be established by means of fixed-point systems or byusing a reference thermometer. Either an SPRT or a PRT is recommended for use as the reference thermometer. However a liquidin glass (LIG) thermometer, thermistor, or thermocouple may be accepta
26、ble depending upon the temperature of calibration,required accuracy, or other considerations.4.2 The success of the calibration depends largely upon the ability of the UUT to come to thermal equilibrium with thecalibration temperature of interest (fixed point cell or comparison system) and upon accu
27、rate measurement of the sensing elementresistance at that time. Instructions are included to guide the user in achieving thermal equilibrium and proper resistancemeasurement, including descriptions of apparatus and instrumentation.4 Mangum, B. W., NIST Technical Note 1265, Guidelines for Realizing t
28、he International Temperature Scale of 1990 (ITS-90).E2593 1224.3 Industrial platinum resistance thermometers are available in many styles and configurations. This guide includes limitedinstructions pertaining to the preparation of the UUT into a configuration that facilitates proper calibration.4.4
29、Proper evaluation of calibration uncertainties is critical for the result of a calibration to be useful. Therefore, a considerableportion of this guide is devoted to uncertainty budgets and the evaluation of uncertainties.5. Significance and Use5.1 This guide is intended to be used for verifying the
30、 resistance-temperature characteristicsrelationship of industrial platinumresistance thermometers that are intended to satisfy the requirements of Specification E1137/E1137M. It is intended to provide aconsistent method for calibration and uncertainty evaluation while still allowing the user some fl
31、exibility in the choice of apparatusand instrumentation. It is understood that the limits of uncertainty obtained depend in a large part upon the apparatus andinstrumentation used. Therefore, since this guide is not prescriptive in approach, it provides detailed instruction in uncertaintyevaluation
32、to accommodate the variety of apparatus and instrumentation that may be employed.5.2 This guide is intended primarily to satisfy applications requiring compliance to Specification E1137/E1137M. However, thetechniques described may be appropriate for applications where higher accuracy calibrations ar
33、e needed.5.3 Many applications require tolerances to be verified using a minimum test uncertainty ratio (TUR). This standard providesguidelines for evaluating uncertainties used to support TUR calculations.6. Sources of Error6.1 Uncertainties are present in all calibrations. Errors arise when the ef
34、fects of uncertainties are underestimated or omitted. Thepredominant sources of uncertainty are described in Section 12 and listed in Table 2.7. Apparatus7.1 Resistance Measuring InstrumentsThe choice of a specific instrument to use for measuring the UUT and referencethermometer resistance will depe
35、nd upon several factors. Some of these factors are ease of use, compatibility with computerizeddata acquisition systems, method of balancing, computation ability, etc. All of the instruments listed are commercially availablein high precision designs and are suitable for use. They require periodic li
36、nearity checks or periodic calibration. (Refer to AppendixX2 for detailed descriptions and schematics.) The accuracy of the resistance measurements directly impacts the accuracy of thetemperature measurement as shown in Eq 2.Accuracyt 5 AccuracySensitivity (2)where:Accuracyt = temperature accuracy a
37、t temperature (t), C,Accuracy = resistance accuracy at temperature (t), , andSensitivity = sensitivity at temperature (t), C-17.1.1 BridgePrecision bridges are available with linearity specifications ranging from 10 ppm of range to 0.01 ppm of rangeand with 612 to 912 digit resolution. resolution ar
38、e available. These instruments are available in models using either AC or DCexcitation. The linearity is typically based upon resistive or inductive dividers and is generally quite stable over time. Modernbridges are convenient automatic balancing instruments but manual balancing types are also suit
39、able. These instruments typicallyrequire external reference resistors and do not perform temperature calculations.7.1.2 Digital Thermometer ReadoutDigital instruments designed specifically to measure resistance thermometers areavailable. Modern versions function essentially as automatic potentiomete
40、rs and reverse the current to eliminate spurious thermalemf. Precision instruments with linearity specifications ranging from 20 ppm of indication to 1 ppm of indication and with 612 to812 digit resolution are commercially available. Some models have extensive internal computation capability, perfor
41、ming bothtemperature and statistical calculations. Periodic calibration is required.7.1.3 Digital Multimeter (DMM)Digital multimeters are convenient direct indication instruments typically able to indicate inresistance or voltage. Some models have extensive internal computation ability, performing b
42、oth temperature and statisticalcalculations. The use of DC offset compensation is recommended. Caution must be exercised to ensure that the excitation currentis appropriate for the UUT and reference thermometer to avoid excessive self-heating. Periodic calibration is required.7.1.4 Reference Resisto
43、rReference resistors are specially manufactured resistors designeddesigned and manufactured to bestable over long periods of time. Typically, they have significant temperature coefficients of resistance and require maintenance ina temperature enclosed air or oil bath. Some have inductive and capacit
44、ive characteristics that limit their suitability for use withAC bridges. Periodic calibration (yearly or semi yearly)semi-yearly) calibration is required. Resistors (AC or DC) are required tomatch the type of measurement (AC or DC) system in use.7.2 Reference ThermometersThe choice of a specific ins
45、trument to use as the reference thermometer will depend upon severalfactors, including the uncertainty desired, temperature range of interest, compatibility with existing instrumentation and apparatus,expertise of staff, cost limitations, etc. All of the instruments listed are commercially available
46、 in various levels of precision andE2593 123stability and may be suitable for use. They all require calibration. The frequency of calibration depends a great deal upon themanner (care) in which they are used and the uncertainty required in use.7.2.1 SPRTSPRTs are the most accurate reference thermome
47、ters available and are used in defining the ITS-90 fromapproximately 260C to 962C. The SPRT sensing element is made from nominally pure platinum and is supported essentiallystrain-free. These instruments are extremely delicate and are easily damaged by mechanical shock. They are available sheathed i
48、nglass or metal and in long stem and capsule configurations. The design and materials of construction limit the temperature rangeof a specific instrument type. Some sheath materials can be damaged by use at high temperatures in metal blocks or molten saltbaths. Calibration on the ITS-90 is required.
49、7.2.2 Secondary Reference PRTSecondary Reference PRTs are specially manufactured PRTs designed to be suitablecalibration standards. These instruments are typically less delicate than SPRTs but have higher measurement uncertainties andnarrower usage ranges. They are typically sheathed in metal to allow immersion directly into metal furnaces or molten salt baths.Calibration on the ITS-90 is required.7.3 Fixed Point SystemsFixed point systems are required in the ITS-90 calibration of SPRTs. Very low uncertainties areattainable with
