Asme ptc 19 3 1974 (2004) scan (american society of mechanical engineers)

FOR CURRENT COMMITTEE PERSONNEL PLEASE E-MAIL CS@asme.org Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontr REAFFIRMED 2004 Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontroll I AND APPARATUS Temperature Measurement INSTRUMENTS PART of Congress Catalog No 74-76612 No part of this document may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher Copyright, Q 1974, by The American Society of Mechanical ‘ Engineers Rinted in the United States of America Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrol Library The Scope of the work of Technical Committee No 19 on Instruments andApparatus is to describe the various types of instruments and methods of measurement likely to be prescribed in any of the ASUE Performance Test Codes Such details as the limits and sources of error, method of calibration, precautions, etc., as will determine their range of application are given Only the methods of measurement and instruments, including instructions for their use, specified in the individual test codes are mandatory Other methods of measurement and instruments, that may be treated in the Supplements on Instruments and Apparatus, shall not be used unless agreeable to all the parties to the test This Supplement on Instruments and Apparatus, Part on Temperature Measurement, replaces an older one published during the period from 19521961 Since that time the technology of temperature measurement has so changed and broadened that the earlier material has become obsolete This necessitated a complete revision on the Supplement resulting in the currently expanded and more comprehensive document In accordance with the established policy of the American Society of Mechanical Engineers concerning the inclusion of metric (SI or International System) units in all ASME publications, this document includes an Appendix of appropriate conversion factors which will enable the user to utilize both systems These conversions are listed in the Appendix as they first appear throughout the Supplement Extensive use was made of the “ASME Orientation and Guide forUseof Metric Units, Third Edition” and The ASTM Metric Practice Guide E380-92.” These two publications should be consulted for additional material concerning conversions from the US system to SI units This Edition was approved by the Performance Test Codes Committee on July 12, 19’73 It was approved and adopted by the Council of the Society by action of the Board on Codes and Standards on May 29, !974 111 Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontroll FOREWORD Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontroll This page intentionally left blank ON INSTRUMENTS AND APPARATUS R F Abrahamsen, Chairmm K W Woodfield, Secretary Il F Abrahamsen, oratory, Manager, Technical and Administrative Services, Kreisinger Research Engineering Inc., 1000 Prospect Hill Road, Windsor, Ct 06095 Combustion R P- Benedict, Fellow Engineer, STDE, 9175, Philadelphia, Pa 19113 J T Callahan, Research sion, Applied G Nutter, Mechanical Physics Assistant Engineer, Department, Director, Professor Avenue, Flint, Naval Philadelphia, Instrumentation son, 1500 Johnson Drive, Madison, K W Woodfield, Westinghouse of Mechanical Electric Corp., Lester Ship Engineering Lab- Branch Post Office Center, Philadelphia Divi- Pa 19112 Systems Center, University of Wisconsin - Madi- Wi 53706 Engineering, Mi 48502 V General Moton Institute, 1700 West Third Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolle PERSONNEL OF PERFORMANCE TEST CODES COMMITTEE NO 19.3 of Performance K C Cotton, J H Fernandes, Test Codes Committee Chairman Vice Chairman Hilke Knoedler Leung Light L C Neate C A Dewey J L E L Paul F H V F Estcourt S W Lovejoy C B Scharp A S Grimes W G McLean J F Sebald K G Grothues S L Morse J C Westcott R P Benedict W A Crandall R C Dannettel J W Murdock vi W C Osborne W A Pollock J H Potter Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolle Personnel Performance Supplement Instruments and Part Temperature Test Codes on Apparatus Measurement TABLE OFCONTENTS Chapter Pages GENERAL 12 RADIATION THERMOMETERS 17 THERMOCOUPLE THERMOMETERS Section A, Thermocouples 17 Section B, Instrumentation 27 36 RESISTANCE THERMOMETERS 44 LIQUID-IN-GLASS THERMOMETERS FILLED SYSTEM THERMOMETERS 55 70 OPTICAL PYROMETERS 86 BIMETALLIC THERMOMETERS 91 CALIBRATION OF INSTRUMENTS APPENDIX 134 CHAPTER 1, ,GENERAL CONTENTS GENERAL Par GENERAL: scope Introduction TEMPERATURE SCALES INSTRUMENTS ACCESSORIES: Wells Other Accessories INSTALLATION SOURCES OF ERROR: Introduction Conduction Error Radiation Error Heat Transfer at Low Velocity Aerodynamic Heating Effect Heat Transfer at High Velocity Gradient Error Dynamic Error CONCLUSIONS REFERENCES Scope The purpose of this chapter is to present a summary discussion of temperature measurement as related to Performance Test Code work with particular emphasis on basic sources of error and means for 20 21 coping with them 25 Introduction :8 28 29 31 34 36 38 39 Measurement of temperature is generally considered to be one of the simplest and most accurate measurements performed in engineering cidedly a misconception measurement Accurate under some conditions with our present knowledge This is de- temperature is impossible Under many of the con- Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolle ASME ditions met in Performance sired accuracy Test cautions in the selection, measuring of suitable installation instruments; pre and use of available (o) Radiation temperature measurements encountered in installation centrate a definite accurate Specific directions system, of the body They conused to intercept from a body whose temperature is being measured; a temperature sensitive usually element, force measuring and pre- lb) are given in A Thermocouple temperature measuring Thermometer (Chapter 3) is a system comprising converting scales electrical (centi- the boiling and freezing ard atmospheric the interval scale, and electrical point is formulas: Thermometers (Chapter 4) are temin which the electri- is used as a means of temperature conductors for operatively connecting with the bulb and a portion of the stem filled expansive C t 32 C = 5/9 (F - 32) where F = reading in deg Fahrenheit C = reading in deg Celsius for converting (e) Filled temperature with an liquid System Thermometers (Chapter 6) are measuring instruments in which the change in volume of a liquid, a change in pressure of a gas, or the change in vapor pressure of a volatile liquid is used as a means of temperature meas- FACTORS temperature the ferential expansion of a liquid in a closed glass systern is used as a means of temperature measurement They consist of a thin-walled glass bulb attached to a glass capillary stem closed at the opposite end, temperature on one scale may be converted to the corresponding reading on the other scale by use Tables and ass Thermometers (Chapter 5) are (d) Liquid&G1 temperature measuring instruments in which the dif- scales is called a degree The reading for a given CONVERSION units, connecting the two marked 100, and the freezing point is marked Each of the 180 or 100 divisions in the respective F = 9/5 temperature measurement They consist of a sensing element called a resistor, a resistance measuring instrument, between the same fixed points is di- of the following for 3.1A.l Resistance cal resistance point is marked 212, and the vided into 100 equal parts; the boiling emf to equivalent perature measuring instruments into 180 equal point is marked 32 In the Celsius the interval (c) between points of water at stand- pressure is divided parts; the boiling freezing scale, which a printed scale for conductors for operatively two (See Fig grade) temperature scales A detailed discussion of these and other scales is given in Chapter In the Fahrenheit a tempera- force (emf), a device sensing emf which includes and the Celsius instru- ture sensing element called a thermocouple SCALES There are in general use two temperature device, ment produces an electromotive known as the Fahrenheit a thermo- and a measuring such as an electromotive subsequent chapters for each of the various types of temperature measuring instruments TEMPERATURE and con- portion of the energy radiated couple or a thermopile; is 2) are tem- in which the intensity emitted from a body is used as a sist of an optical or use of the temperature in usage of the instruments Measurement measure of the temperature tempera- with such instruments are availabIe The chapter Thermometers (Chapter perature measuring instruments for tempera- in obtaining conditions tus, Part 3, Temperature ture to a closer degree of accuracy than is required in some of the tests considered in the Performance Test Codes The difficulty types of instruments numbers refer to chapters in the ASME Performance Test Codes, Supplement on Instruments and Appara- and in the proper are capable of indicating instruments following of the radiation Some of the instruments cautions The for use under appropriate under such conditions measuring CODES INSTRUMENTS of temperature interpretation of the results obtained with them In some cases an arbitrarily standardized method is prescribed in the Performance Test Codes which is to be followed in making temperature measurements ture measurement TEST Code work, the de- in the measurement can be obtained only by observance temperature PERFORMANCE readings urement They consist from of an all metal assembly comprised of a bulb, capillary tube and Bourdon tube, provided with a temperature responsive fill one scale to another are given in the Appendix.* *Whenever U.S Customary units are used in this suppliment the SI equivalent may be calculated by using the conversion factors listed in the Appendix (f) Optical Pyrometers (Chapter 7) are temperature measuring instruments in which the brightness Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolle ASME of radiation AND APPARATUS ACCESSORIES in a very narrow band of wavelengths emitted by a source, the temperature of which is to be measured photometrically matched against the brightness of a calibrated source, Wells* is used as a Introduction means of temperature measurement They consist of a telescope, a calibrated lamp, a filter to provide for viewing nearly monochromatic readout device, and usually radiation, an absorption a glass instruments differential of two metals expansion means of temperature in which the is used as a measurement They consist of Thermometer wells an indicating or recording device, a sensing element called a bimetallic thermometer bulb, and a means temperature for operatively ties of 300 fps or less, connecting are used in measuring of a moving fluid in a conduit, the stream exerts an appreciable the two the where force For veloci- tapered thermometer wells of the design shown in Fig given in Table The above instruments are those which are recommended for ASME Performance Test Code work for the measurement of temperature under appropriate conditions ele- a well may be used, which by definition is a pressure tight receptacle adapted to receive a temperature sensing element and provided with external threads or other means for tight pressure attachment to a vessel [l].** Bimetallic Thermometers(Chapter 8) are (g) measurements temperature Test Code work the sensitive ment cannot be placed directly into the medium whose temperature is to be measured In such cases filter temperature measuring In many in Performance 1.1, and of dimensions 1.3, shall be used For velocities in excess of 300 fps, a fixed beam type thermometer well is recommended [7] when used The recommended ranges of use for these temperature measuring instruments when properly installed are indicated in Table 1.1: TABLE l.lRECOMMENDEDTEMPERATURE I Tee (a) Radiation thermometers RANGES I Chtz+er Ran e of Use, Beg F Ambient and above -300 to t4500 450 to t1950 (b) Thermocouple (c) Resistance (d) Liquid-in-Glass thermometers -328 to t1110 (e) Filled System thermometers 400 to t1200 (f) Optical pyrometers (g) Bimetallic thermometers thermometers thermometers Above 1300 -200 to t 800 FIG 1.1 PERFORMANCE TEST CODE THERMOMETER WELLS 10 Attachment *At the time of the current revision, ASME Ad Hoc &;;rittee PR 51 is writing a new standard for thermo- l *N;mbers iu b a kets designate References to the vessel may be made in any manner approved by the ASME Boiler and Pressure Vessel or Piping Codes Any material approved by these Codes for the intended service may be used Where materials are specified for the purposes of at end of chapter, thus [Ij Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontroll INSTRUMENTS AND APPARATUS TABLE 9.11 AVERAGE THERMAL* EMF/DEG F OF PLATINUM AGAINST OTHER THERMOCOUPLE MATERIALS Some of the precautions tain accurate results paragraphs that must be observed to ob are discussed in the following 129 Platinum The thermal emf of thermocouple platinum against the standard Pt 27 is usually less than 20 /.LV at 2192oF and in testing one sample of Matsri al platinum against another it is not necessary ure the temperature of the hot junction Platinum-10 percent rhodium 1832 6.4 Platinum-13 percent rhodium 1832 7.3 Chrome1 1652 Alumel 1652 4.8 1112 6.4 Constantan 1112 26.0 Constantan 212 20.8 Copper 212 5.2 The reference-junction curately controlled accurate measurement of temperature, avoided when the measurements a working standard of material ing platinumqhodium tested, temperature 130 In many laboratories the platinum standard and the platinum element of the couple used to measure the temperature are one and the same The sample or wire being tested is then welded to the junction of the couple and the emf of the couple and that between the two platinum simultaneously to that being wires are measured with two potentiometers or alter nately with one instrument Simultaneous readings of these electromotive forces should not be made is small even for large changes in with a millivoltmeter or with a current flowing in either circuit, because one wire is common to both In the latter method, the accurate but merely shifted to the laboratory Meas- about 1112 and 2192oF, the temperature however, is measurement of temperature is not entirely The wires and protected are sufficient to develop the emf at any temperature as the emf is small and practically proportional to for this since in this case the emf developed and changes very little thermocouples insulated urements at two temperatures, are made by using similar standard (i.e., atures by any of the methods described for calibrat- * Complete tables giving the average thermal emf of platinum-10 percent rhodium, and platinum-13 percent are aiven in NBS Circular 561 rhodium aaainst DhinUm The averaie theimal emf of chrome1 and of alumel against plitinum are given in NBS Research Paper 767, cower and constantan aaainst platinum in NBS Research Paper RP 1080, of iron and constantan against platinum in NBS Research Paper 2415 The necessity temperature need not be acThe platinum the wire previously compared with the standard Pt 27) is welded to the wire being tested to form a couple and the emf measured at one or more temper should be carefully perature of the junctions to closer than 9OoF to obtain a comparison accurate to /LV 17.5 Iroll to meas- avoided, circuits that determines and in this case the potential difference the thermal emf of the working standards against the measured by one instrument standard Pt 27 current flowing in the other circuit However, this objection is not encountered in the method described I27 The small thermal emf of a platinum standard against working as accurately as the emf can 131 be measured These standards are subject to change during use but, if properly used and occasionally checked, can be relied upon to about PV at 1832°F The thermal emf of working standards rials is determined and certified Platinum-Rhodium platinum-rhodium platinum Alloy The testing of thermocouple wire directly is exactly against the same as the calibration of platinum-rhodium thermocouples Platinum against platinum-10 percent rhodium develops 6.5 pV/deg F of other mate- at the National Bureau of Standards to the equivalent by the above in which the platinum standard is not the same wire as the platinum of the thermocouple the standard Pt 27 at any tempera- ture can be determined is influenced and platinum of +2 deg F at against platinum-13 develops about 7.3 pV/deg percent rhodium F at 1832oF Therefore, high temperatures order to determine the thermal emf of a sample of In any event the testing of a thermocouple material is essentially the determination of the emf necessary platinum-rhodium 128 of a thermocouple in which the material against platinum to 220 /LV, it is to measure the temperature to +2.7 deg F Such an accuracy in temperature measurements being tested is obtained only with a very homogeneous and ac- is one element and a working standard the other 121 in Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolle INSTRUMENTS curately furnace, calibrated couple in a uniformly heated but if the emf of one sample of wire is known with this accuracy, measuring into a hole drilled it may be used to deter the temperature CODES welding in the junction the material the junctions mine the emf of other samples without the necessity of accurately TEST formed by to platinum This brings to the same temperature In the use of platinum or platinum-rhodium for testing thermocouple materials, the wires are For ex- ample, the thermal emf per degree of any sample of used a large number of times before checking platinum-10 or scrapping percent rhodium against any other sample rarely exceeds 0.03 pV/deg I832oF) Therefore, F (5OpV at Base-metal used for testing if the thermal emf of one similar thermocouple materials wires should not be used more than once if the highest accuracy sample against platinum is known to +2OgV at 1832cF, th e emf of other samples against the same required, change in platinum ture and if they are used repeatedly, can be determined these materials to about the same ac- curacy by comparing the samples of platinumrhodium and measuring junction of the hot to select for The working standard used to determine of platinum-rhodium, measuring the 13 percent rhodium develops or either element about 0.89 pV/deg homogeneous accurately standard, F as necessary by comparison the coil against for most purposes similar standard and the material of some materials Moteriols dardized, base-metal thermocouple materials (alumel, chromel, constantan, copper, and iron) the procedure is very much the same as in calibrating thermocouples Although measurements are ultimately it is not necessary rectly temperature In case are small enough that of 90 deg F is sufficient if ever, should it be necessary Seldom, to measure the closer than 18 deg F base-metal such thermal-emf Annealed electrolytic (b) At LOW Temperatures copper is very uniform in its thermoelectric referred to platinum, to measure each sample di- against platinum between the being tested that have been well stan- the differences an accuracy The accuracy must be measured depends upon the difference In testing Any sample from materials with which the temperature A number of wires can be welded together At High Temperatures from this coil may then be used as a working stan- and tested by any of these methods (a) samples the standard Pt 27 will apply for the remainder of the coil with sufficient accuracy dard for testing Thermocouple as with a the emf of which is known, against thermal emf of the few selected is known to 2% gV at 211 deg F Basa4otal as found one or more samples may be the standard Pt 27 The average value for the 1832oF, the thermal emf of the other against the 134 and samples taken from it and the thermal emf determined same platinum can be determined to 230 PV by comparing the two and measuring the temperature to I33 from different the emf between the various from such tests, at 183201;’ so that if the thermal emf of one of these against platinum samples If the coil is sufficiently may be a sample of the thermocouple used in measuring the temperature Platinum-10 percent rhodium against platinum- materials a coil of wire and test if for homoge- parts of the coil, welding them all together, thermal emf of the platinum-rhodium of platinum, the wires The procedure then is neity by taking several percent rhodium is when heated to a high tempera- become heterogeneous to 18 or 36 deg F The same applies platinum-I3 132 the temperature because there is a slight properties When the measurements and is often used as a standard for thermoelectric testing at temperatures below are made against platinum (and this must frequently be done), the platinum wire should be 572oF The th ermal emf of other materials sealed through the end of a glazed porcelain termined very accurately by using a stirred liquid bath or fixed points The steam point is an excellent one for this purpose protecting tube with Pyrex glass, leaving cm of the wire exposed for welding base-metal tainty wire or wires in the measurements certainty The largest arises in the determination ture of the junction platinumrhodium about to the uncer- Table from the un- either copper or platinum 9.12 specifies nealed electrolytic of the tempera- The junction thermocouple against may be de- the’ thermal emf of ancopper against National Bureau of Standards standard Pt 27 and may be of a standard used to convert values of the thermal emf of any material against one of these standard materials may be inserted 122 Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontroll ASME PERFORMANCE AND APPARATUS TABLE 9.12 THERMAL EMF OF ANNEALED ELECTROLYTIC COPPER AGAINST NBS PLATINUM STANDARD PT 27 Temperature oF’ r Emf, PV ence-junction various temperature thermocouple and, therefore, in determining materials corrections must be applied TempeJ~ture~ Emf, thermocouples under the testing The average temperature-emf -328 -194 212 766 -238 -354 302 1265 tions for the various thermocouple -148 -367 392 1831 platinum -58 -242 482 2459 used for making reference-junction 572 3145 t340 662 3885 t122 136 are specified necessary against in Table against 9.13 and may be corrections at high temperatures, junctions ther- it is not to measure or control accurately perature of the reference the other standard material of rela- materials In comparing two samples of a similar mocouple material to values of emf of the same material to ar- rive at values for a common reference junction temperature The method of applying these corrections is the same as that discussed 32 the emf of against platinum the tem- The emf devel- oped by two samples of platinum-rhodium, even the 10 against the 13 percent rhodium alloy, is prac135 Reference-Junction convenient TABLE 9.13 It is not Corrections for everyone tically independent of the temperature of the reference junctions between -4 and +122qF In all other to obtain the same refer- AVERAGE TEMPERATURE.EMF RELATIONSHIPS OF VARIOUS AGAINST PLATINUM FOR APPLYING REFERENCE-JUNCTION Electromotive Temperature, OF Platinum Versus PlatinumRhodium* mV Chrome1 Versus THERMOCOUPLE CORRECTIONS MATERIALS Force Platinum Alumel Versus Platinum Constanton Versus Platinum Iron Versus Platinum C opper Versus Platinum mV mV mV mV mV -4 -0.103 -0.50 0.27 0.64 -0.36 -0.109 t5 -0.079 -0.38 0.20 0.48 -0.27 -0.084 14 -0.054 -0.25 0.14 0.32 -0.18 -0.057 23 -0.027 -0.13 0.07 0.16 -0.09 -0.029 0.00 0.00 32 0.000 0.00 0.000 t 0.030 t 0.13 -0.07 -0.16 t 0.09 50 0.056 0.26 -0.14 -0.33 0.18 0.060 59 0.084 0.40 -0.20 -0.49 0.27 0.091 68 0.113 0.52 -0.28 -0.66 0.36 0.124 77 0.143 0.66 -0.34 -0.83 0.45 0.158 86 0.173 0.79 -0.41 -1.00 0.54 0.193 95 0.204 0.93 -0.47 -1.17 0.63 0.229 104 0.235 1.07 -0.54 -1.34 0.72 0.265 113 0.266 1.21 -0.60 -1.51 0.81 0.302 122 0.299 1.35 -0.67 -1.69 0.90 0.340 41 +0.028 0.00 * These values apply for either 10 or 13 percent rhodium 123 Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontroll INSTRUMENTS Type of Thermocouple s rhodium versus platinum iG 6~%nk?rhSodium* versus platinum SUMMARY OF METHODS Methods of Cali brotion International temperature scale (fixed points) Fixed P 9.14 points NBS Standard fixed points 1166.9 to 1945.4 Comparison with standard thermocouple 9, OBTAINABLE at Coli bration Points Freezing points Sb, Ag, and Au of Freezing point of Zn, Sb, Ag, and Au 32 to 2642 0.36 Equation: 0.36 Difference reference 0.36 About every 200 deg F 0.54 About 0.54 1100 and 2000°F (or more points) 32 to 2012 About every 200 deg F 0.9 L.inear 32 to 2012 Abouh 900, 1500 and 2000 F(or more points) 0.9 Difference reference Comparison with standard resistance thermometer** or at fixed points 32 to 662 About resistance Comparison thermometer** with standard 32 to -310 About every thermocouple**with standard Comparison 32 to 1400 About every 200 deg F 0.9 Linear , 32 to 1400 About 209, 600, and 1400 F 0.9 Difference reference 32 to 662 About every 200 deg F 32 to -310 About every thermocouple* with standard Comparison Type K Chromel-Alumel Type S THER M Int Observed Points, Dsg F 32 to 2642 32 to 2642 IN CALIBRATING Accuracy Temperature Range, OF 32 to 2642 samples, AND ACCURAClES Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolle TABLE resistance Comparison thermometer** with standard every 200 deg F 100degF 900, 0.18 0.18 0.18 Iron-constantan or at fixed points Comparison with starldard resistance thermometer** 100 deg F 0.18 9.14 Continued Type of Thermocouple h ‘e T Copper-constantan Accuracy at Observed Points, Deg F Methods of Calibration Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolle TABLE In Comparison with standard resistance thermometer** or at fixed points 32 to 572 About every 200 deg F 0.18 Equation: or differenc reference Compaiison with standard resistance thermometer** 32 to 212 About 0.09 E uation: dijference reference Fixed 32 to 212 Boiling 0.09 Equation: points 122, and 212’F point of water + Comparison with standard resistance thermometer** 32 to -310 About every 100 deg F 0.18 F.quation: or differenc erence tab Fixed to -310 Sublimation point of CO, and boiling point of 0, 0.18 Difference ence table *Either 10 or 13 percent ** In stirred liquid bath points rhodium cases, with the possible exception mav be taken as proportional of iron, the emf to the difference of the two junctions, when the emf is small, the corrections for the tem- perature changes of the reference junctions and of the reference junctions are protected stirred than by comparison that the emf (320 ,V) developed by two samples of iron when one junction was at 1112oF and the other 137 container of the calibrating nitrogen The accuracies in calibrating These accuracies homogeneous may be obtained thermocouples the is exercised in the test procedure curate results can be obtained In the case of chromel-alumel conplrs at low temperatures, fied in Table interpolated be greatly 9.14 are limited values couples at more points with copper-constantan is usually limited in junction I39 143 ards General obtained I44 and in General according by em- cases, indications standardization are I45 Platinum, thermometers nickel, are usually specified THERMOMETERS ways Platinum Immersion Thermom- in manufacturers’ is usually catalogs are normally of the temper- with the of Special Use Partial Immersion the emergent mercury column or stem may be specified temperatures Cognizance may be exercised One method involves comparison will calibrated by comparison shall then be measured thermometer, rections of those in various of the therimmersion The number of degrees of scale, and copper resistance 126 tem- In such carried out for the prevailing mometers at total immersion with total Thermometer with a standard platinum resistance Partiol equipment being employed In the Case standards 140 stand- and Pars of the thermometers st&d.ardization temperatures Resistonce Purpose to their own specifications, Thermometers, With Stondord as secondary 14 to 24, inclusive emergent column temperature encountered Comporison thermom- thermometers atures of the emergent column for the various and leads or thermocouple, leads, and indicator as a unit by any of the methods described in the pre- RESISTANCE resistance bought and sold without specification (multiple- difficulties Thermom- by comparing their readings as commonly listed eters, to test a thermocouple no additional THERMOMETERS Purpose Liquid-in-Gloss Refer to Pars perature ceding paragraphs, of the 35 to 38 inclusive couples) When it is desired in Par 47 the resistance which have been standardized at low temperatures a number of couples in series air or liquid eters or general purpose liquid-in-glass the emf of the suc!~ cases the accuracy may be improved ploying bridge as described with those of standard platinum can by the emf measurements is cooled with liquid Refer to Pars 44 to 46, inclusive eters are calibrated speci- this uncertainty The accuracy lower Generol by the uncertainty couples For still care by the same methods reduced by observing liquid in a may be used in which the LIQUID-IN-GLASS and iron-constantan However, resistance standard bulb More or less ac- the accuracies a cryostat with when reasonable of below the ice point, should be used in measuring various tvpes of thermocouples by different methods and the uncertainty in the interpolated values by various methods are specified in Table 9.14 138 of the the limits may be immersed in alcohol A Mueller 142 Obtoinoble obtained in a thoroughly The temperature surrounded with dry ice temperatures, junctions Accuracies winding at temperatures the thermometers and 0.78pV for each degree change in the temperature reference for test by immersing a suitably with the standard platinum thermometer changed by 0.06 FV for each degree change of the hot junction thermometer water or oil bath with- error of the calibration, may be measured by means of a standard platinum resistance thermometer For changing that of the hot junction by the same For example it was observed (in one case) in the temperature which is satisfactory is obtained bath, which should be constant within amount at 77% A calibration 141 code purposes In comparing two samples of iron, the negligible emf developed is changed more by changing the temperature CODES though the ice point value can be determined out the use of a standard thermometer be- tween the temperatures TEST which be in the emergent column when in actual use, From these data the car- under the specified emergent column tem- Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrol ASME PERFORMANCE peratures may then be calculated organic liquid-filled expansion periment In the case of thermometers the coefficient of the liquid should be obtained or from the manufacturer these computations to drive the liquid into the expansion by ex- overheat in order to perform the accuracy testing, thermometers of constructions differing comparison similar but an auxiliary cause the separated ice point scale For separations VISUAL 146 General INSPECTION Thermometers bulb itself tected and are more likely during service will entirely to occur in shipment than that prevent such displacement If bubbles are observed I49 of the gas mometer other convenient spected into the bulb Gentle while held upright will the surface cooled in this process the liquid, is drawn tapping of the thermometer below the freezing point of during the melting no solidification occurs in the stem; otherwise bulb may burst or the capillary cause of the expansion split process forces generated should always described above in the bulb 150 Organic liquids contrast to mercury, should always particularly the be allowed and slowly heating for drainage It is frequently in time to occur, such thera good prac- tice to immerse only the bulb of the thermometer appreciably with an ex- retarded because drainage if the capillary is is also cooled can be joined 151 the bulb until the Globules separated portion is driven into the expansion from mechanical chamber When the column itself by heating flows into the of Liquid separation in the stem which result can normally the bulb until the liquid chamber, the separated portion usually will join with the main column A slight tapping of the ther- with the globules mometer against the palm of the hand will facilitate Th is method should not be employed this joining dicative for high-temperature mometer should be rejected thermometers Sufficient when using or standardizing until drainage has taken place, at the top of the chamber, the liquid usually to the as used in thermometers, wet the glass tion of the liquid has separated by carefully If the thermom- of the chamber to drive the columns, depending on the construction of the thermometer and the type of separation If a small por- pansion be in- which can be repaired mometers below 32°F is provided of the the be- I48 If gas bubbles are observed in the stem, several different ways are suggested for joining column and the thermometer distilla- condensation liquid into the bore whence it can be rejoined main body as described above so that internally Such thermometers for these separations very careful heating to warm the stem sufficiently thermometers eter has an expansion chamber that is observed to be filled with liquid, the’column can be reunited by that, if the bulb is care should be exercised should emerge parent liquid in the upper part of the ther- by the procedures cause the bubbles to rise to It is very important Then the bulb should be al- In organic-liquid-filled ally be removed by cooling the bulb with dry ice or into the to bring the liquid tion may occur, with subsequent colorless it on a pad or against is possible in the bulb in the bulb, they can gener- coolant until all the liquid By softly tapping The liquid lowed to warm up slowly into the bore with no separation de- No method has been discovered to join to join, to cool the bulb in dry ice to a the hand it usually together Gas bubbles are readily usually of the liquid point low enough to bring all of the liquid should be inspected faults Gas Bubbles portions which are more difficult may be necessary for gas bubbles in the bulb or liquid column, globules of liquid in the stem, foreign matter, and glass 147 chamber beto develop tapping the bulb on a pad of paper will below the immersion point to the extent of including are likely cooling the thermometer so that the separated portion as well as the main column both stand in the chamber Tapping the tube against the hand, or of the point, graduation the ac- the bulb separations either in the chamber or above it It is frequently possible to join such separations by in all details above the immersion that have a contraction low the lowest of measurement involves with standards of the pressure of the gas or destroy Thermometers being test- A second method, which is the one best suited to large-quantity result chamber, may the glass and either break the bulb as a curacy of the thermometer by expanding to have than the thermometer ed, thus increasing because the heating of the bulb, which is necessary of This method has the advan- tage that the standard may be selected greater sensitivity AND APPARATUS If such globules and then reappear upon cooling of oxidation of obstructions (above 500°F), 127 be rejoined column merges appear to unite the bulb, this is in- of the mercury, or the presence in the bore, and therefore, the ther- Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontroll INSTRUMENTS 152 Foreign detected in the bore can sometimes Matter TEST be pearance convenient to use a magnifying of low power for this examination of the tested and untested the scale portion with the unaided eye, but it is desirable and generally CODES chalking glass sections Burning out, loosening, of or of the pigment shall be cause for re- jection The most com- mon types of foreign matter which should be cause for rejection are glass chips, particles of dirt or lint, oxide of mercury either red, yellow, or black, products of glass weathering deposit, Test 156 commonly called white and stones or iron spots traceable treatment glass fabrication I53 as filling above the liquid, may be treated example specifications thermometers, by accident thermometer these conditions crystals 157 be perature tions, 900°F column in Fig 9.1 by the production quality of may be of various types the glass as observed with a polarized gage near enlargements are detrimental severe that fire cracks may later occur near the bulb are indicative and are particularly thermometers for use above 320°F permanency of range will normally high range thermometers most significant 158 General (a) Test Conriderbtions ings at fixed points, glass comparison in selected The test for The test for permanency to determine the ability (a) Pigment of pigment such as the ice point, with secondary of the pigment the exposure in use without graduation and exactly con- will being oblit- observing may be eliminated the thermometer to be tested of the line of sight so that the of the scale nearest the meniscus hides its own image; the line of sight then be normal to the stem at that point one must realize that the scale lines are of appreciable and compensate in an oven of the type shown in Fig 9.1 Heat for hr at approximately 500°F Allow it to cool slowly perature Inspect parts for differences by in a assure that the reflection When reading thermometers, portion of the scale sec- the thermometer in Reading Thermometers to Avoid Parallax (2) by adjusting erated tion of the thermometer discussed the scale can be seen in the mercury thread and material other markings to withstand (b) Place any convenient readand by standard thermometers in accord with the criteria manner which will is designed graduations encountered by observing Pars 35 to 38, inclusive is used to fill the thermometer ditions Liquid-in-glass The error due to parallax of to of range serve to reject in which this defect for Permanency standard- the prescribed shall be considered may be calibrated (1) carefully 155 is within the thermometer thermometers Strains objectionable the thermom- Calibration if so of incomplete stabilization is a measure of If upon subsequent the thermometer light strain in the stem or bore, or at the top of the thermometer, of specifica- accorded have passed the test for permanency stones or striae that distort the bore or its appearance is sufficient cause for rejection Strains in Heat for the ice point in ice point readings of the heat treatment tolerances, Any 9.2 bulb at least at the tem- or, in the absence eter in manufacture ization Faults specified, in Fig to of range com- to not over ‘700’F for normal glass bulbs or for borosilicate bulbs Allow it to cool slow- The difference of red oxide of mercury after being heated Glass it in a permanency ly, and after 72 hr again determine Under 10 to 12 hr 154 bulb will under the ice point of the thermometer 24 hr with the thermometer portion of the of the liquid Determine parator of the type illustrated of the of the mercury will occur and will normally be evidenced stabilized at higher temperatures be tested and place of 650 to ‘7OOoF, using the same oxidation heat bulb during manu- with time which may be significant, particularly in of air can readily the gas filled type of equipment as illustrated An inadequately go shrinkage which may have and a short section to a temperature of nitrogen or in violation The presence by heating the adequacy of the stabilizing The most common is in the use of air instead mercury-in-glass to be used any other gas present as foreign matter been introduced detected gas is specified of range is designed accorded the thermometer facture Where a specific of Range The test for permanency to determine to faulty for Permanency position in ap- 128 for this in arriving The best practice width at the tem- is to consider of the lines as defined the by their middle Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontroll ASME PERFORMANCE AND APPARATUS lb) Depth of Immersion for Total Immersion TherAlthough mometers sion thermometers immersed, by definition should have the entire index inconvenient to so portion of the index is exposed, mercury column correction No correction error; otherwise should be applied mersion thermometers ditions of complete is standardized described mometer of the standard- 162 the thermometer under the same conditions previous as of in- mometers Thermometers standardized Immersion Ther- corresponding readings to a at all other tem- will be correspondingly increased If the method involving the taking of the after heating or de- to a specified is used, a note should appear in the for the thermometer, as follows: NOTE:The tabulated corrections apply for the condition of immersion indicated, provided the ice point reading taken after heating to for not less than is using the If the thermometer are found to be creased table of corrections by one of the methods described comparators the ther- peratures temperature of this type shall be in Pars 38 (b) and 38 (c) inclusive, appropriate standardization, ice point immediately of the bulb Dept of immersion for Partial raising and compare with pre- If the readings higher or lower than the reading creased gas pressure above the column produc(c) may then be made as however, Record the readings vious readings A significant This is due to the effect ing a distortion Observations above without, total im- may be used under conunless of the which is thus kept well below the general level of the ice if it is the proper correction error may be introduced those in use meniscus should be deter- immersion some of the ice may be heaped row channel formed to permit observations the emergent In some instances Alternatively, around the stem above the ice point and a deep nar- If any need be applied found to be less than one-fifth ization I61 both in use and in standardization, it is frequently mined ings taken at least apart should agree within one-tenth of a division, total immer- is of the general purpose type, it should be standardized by immersion to the specified the readings ary depth and 163 compared with those of the second- If the ice point reading (taken in not less than and not more than after removal of the thermometer from the heated bath) is found to be standard higher (or lower) than stated, 159 Calibration of ice, preferably Discard ice with distilled made from relatively direct Fill precooled packing is not included, included, the Dewar in fractional Massachusetts point, is such that the ice point may be made to the publica- Institute the triple of Technology point of benzoic fur point are particularly worthy of mention graduated should be 165 Calibration at Temperatures Other it is specified ondary standard and the thermometer that the ice point be taken immedito a specified temperature For Points described Determine in Par 127 thermometers graduated in single degrees or large of the liquid-in-glass subdivisions, this waiting room temperature period may be omitted termination, 160 Raise the thermometer gently, termined a few millimeters after at least have elapsed, and observe the reading The steam acid, and the sul- Fixed after heating For descripbest suited to Bureau of Standards and the held at room temperature for at least 72 hr, unless ately If the Points it may be used to advantage tions of the National the ice gently about the stem, degrees the thermometer Fixed but one of the other fixed points is the purpose, reference Insert the For thermometers at Other tion of the equipment and techniques dis- to a depth sufficient to cover the 32? graduation As the ice melts, drain off some of the water and add more crushed ice Calibration range of the thermometer water to form a slush, but not enough to float the ice thermometer, 164 Rinse the with the crushed ice and add sufficient and preferably will pure water contact with the hands unclean objects all other readings be higher (or lower) to the same extent clear pieces water and shave or crush into avoiding or any chemically tilled Select Point any cloudy or unsound portions small pieces, vessel at Ice Successive 129 standard is type, it should be held at the ice point was originally after heating de- to a specified The thermometer to be tested be treated in similar manner read- to be tested as If the secondary for at least 72 hr before this de- unless immediately temperature tap the stem Than the ice point of the sec- should Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrol INSTRUMENTS Insert the thermometer 166 secondary standard in the thermometer adjust the temperature approximately perature Checking for Chonges nificant graduated though the thermometer exposed portion of the stem will have attained or aged thermal equilibrium a result the thermometer When the proper rate of temperature 167 been established, lowing read the thermometers order at equal time intervals: mometer or thermometers thermometers ard are taken rise has in the fol- standard, to be tested, to be tested in reverse standard, the standard should agree with the second parison of differences also indicate in successive mometers the average readings Apply the appropriate reading of the standard to be applied For purposes of checking I69 with specifications, ally sufficient For purposes check determinations 173 minus one-tenth I70 Unless are first received, rection for each thermometer from a table are plotted I74 Where corrections 175 tests should be jarred, as by tapping, tem- the thermometer described is 176 in with thermometers having a capillary diameter to ensure that all portions of any temperature made with a standardized thermometer, applying all corrections, is termed in degrees” of the thermomete:‘ FILLED 177 of the thermom- Filled SYSTEM THERMOMETERS system thermometers may be cali- brated by any of the methods described 130 by stated to.” of the to ad- vantage in the rising temperature method of test as well Sufficient time should elapse before taking readings measured and is generally “corrections The limit of reliability after carefully the “accuracy shall be tables or charts shall of the thermometer by the phrase, measurement order to overcome any sticking of the mercury to the glass Such tapping is particularly important order of 0.1 mm or less and may be employed to which the correc- shall be reported is a measure of the sensitivity does not vary more than the before taking a reading to which correction for in Chapter temperatures be made, or to which any temperature perature in preference to the use of slowly rising temperatures Such a procedure is satisfactory if of reading and if the thermometer read- are to be calculated The limit of precision recorded, precision In such a curve the cor- emergent columns, the method described 5, Par 37 shall be used plus or apart throughout the range of the thermometer the bath temperature a corthan ings The results may be made at constant at tem- against the temperature made not less than 40 nor more than 100 divisions Comparisons standardized is to be used frequently tions at the standardization 171 prepare a table other than those of standardization, interpolation of standardization, specified, at the ice point and the temperatures, curve will be found more convenient rections is usu- of Data From the corrections peratures of a division otherwise When make a monthly if the changes are found to be If the thermometer for compliance of at least three series should agree within than it did originally read lower after use than originally of corrections to the under test should be made, and as in service Treatment for all ther- one series of readings slowly, will read higher after it the bulb expands and the thermom- frequently will the corrections to the thermometers even annealed Less may be lengthened insignificant of rise has corrections Calculate degreees, has been placed other standardization Calculate in fractional has been carefully check of the ice point: later these time intervals been uniform I68 sig- short range A com- readings if the rate of temperature is especially the bulb contracts the thermometers order, stand- The average of the first and third readings Usually eter will ther- This for large bulb and relatively thermometers point in Bulb Volume Small changes in volume of the thermometer 172 bulb may occur during use at a will ensure that any before readings is remote from room temperatures The rate should not exceed one scale of this requirement This at test temperatures tem- Apply suf- slowly in to 10 at the standardization Fulfillment thermal equilibrium important errors of the detected heat to raise the temperature uniform rate particularly to use two stand- since observational standard may then be readily CODES eter have attained and of the comparator to a value It may be advantageous division holder, 10 deg F below the standardization ard thermometers, ficient to be tested and the TEST under Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolle ASME PERFORMANCE “Liquid-in-Class specified 178 Thermometers,” in some particular unless temperature the average service and in a descending From these data a correction should be deter average service by steps in an Considerations, sume that the error between cording to a straight-line in a separable Figs be necessary necessary [29] If the bulb is used it should be calibrated socket to install If properly filled, 182 ac- Errors may be introduced temperature law Any great variations or V filled with the temperature the result of indications ascending of (a) not allowing check point for establishment librium, of the capillary by variations tubing of Classes system thermometers, II, III or V filled is of temperature (c) excessive hysteresis or (d) excessive and the chart friction If excessive system thermometers I, The magniin the follow- ing manner 183 While holding the bulb temperature in a suitable in the Bourdon bath, the capillary entire instrument between the pen before final in of Classes equi- environmental lost motion or friction is found it should be corrected in the I, III or by variations tude of these errors can be determined time at any (b) loose fits in the mechanism of the in- strument, spring, obtained and descending sufficient in the it is un- the bulb in the same position the case (Bourdon spring) temperature 179 I in- to the as when calibrated to as- check points varies pressure socket, same separable order, successively It will During calibration, strument should be as close as possible curve, such as shown in I & A, Part on General and 4, should be drawn temperature the pressure of the air surrounding the Class points on its scale while the of the bulb is varied ascending otherwise code The errors of the instrument mined at successive AND APPARATUS should be placed test chamber by the tubing and/or calibra- mined together tion and use constant tubing and/or the in a suitable The error introduced instrument or separately can then be deter- at various ambient temperatures 180 The pen movement of a recording should be further checked by bringing such a position curved radial instruments temperature because the temperature 184 The failure son of the optical to the of a pen to travel to it indicates platinum-rhodium in the multiplying pyrometer reading thermocouple the comparison perature indicates temperature eccentricity conditions before final can be corrected one not having The 185 exist, calibration they bulb and the indicating instruments of this type, the or recording in the manner de- To carry out the former method, the thermo- of smoke and incandescent Chart only by substituting this fault In calibrating pyrometer couple is heated in a closed furnace which is free of the thermo- couple tube immediately the measuring “peep part of the in- gases and at such a point in the furnace that that section junction 181 taken with a poten- by revolv- when the bulb is at a constant If such faulty with the simul- should be made against the reading scribed later should be eliminated and compari- tiometer If points above 27504: are to be checked, sys- loose fits in the mechanism checking by direct of the emf of a standard platinum- of a standard optical chart should be checked for concentricity be,low 2750%, may be accomplished tem or a bent pen arm The failure of the pen to trace the same curve with rising and falling tem- ing it upon its spindle PYROMETERS At temperatures calibration taneous reading along the curved line or parallel either a lack of adjustment instrument it may vary with them OPTICAL of the bulb should be varied so that the pen travels limit of the chart and/or at the commonly used bulb The others should move While holding the chart in this position, of the capillary On multi-pen no more than one pen can be adjusted to a time line stationary The magnitude error should be checked that the pen lies on one of the time lines of the chart to move along a time line parallel instrument the chart to surrounding of the thermocouple hole.” is visible through a If the test is made in a laboratory, tubular type electric strument should be at the same relative elevations as when in use The bulbs of Class I and III Ther dimensions mometers should be immersed couple in this case is inserted at one end of the furnace tube to such a depth as will bring the end of the thermocouple tube to the middle of the fur- the capillary tubing of the thermometers at a temperature should be which is as close as possible are not less than 24 in long and not more than 1% in in diameter to the same depth and to 131 a furnace should be used whose The standard thermo- Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontroll INSTRUMENTS nace, the other end of the furnace being left open so that the end of the couple is in sight I86 After heating perature, the furnace to the desired optical and with the optical pyrometer between thermocouple and the optical sighted to read black-body 190 As the tungsten be a considerable overlap there will, device with resultant is blackening in general, so that the reading may be applied to each scale and a check secured upon the accuracy of the range shifting filament pyrometer lamps operated at filament temper- due to evaporation increase of the tungsten of filament of the bulb resistance and Lamps which have had years of service in industrial plants have shown no appreciable change in calibration Lamp life is usua!ly limited only by mechanical defects in the Occasional checking is debase or by breakage between the two or several the overlap, the pyrometer un- in the same terms- atures higher than 2700%‘, they undergo practically In such a case, it is well to check at a point lying within The calibrated OrigidlY temperatures, are never intentionally is estab- When, as is usual, a range shifting depart from the true temby the same amount der check will be calibrated no deterioration a part of the optical pyrometer ranges of both will