1、 PART 8 I INSTRUMENTS Temperature AND Measurement APPARATUS Library 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 Socie
2、ty of Mechanical Engineers Rinted in the United States of America FOREWORD 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. Suc
3、h details as the limits and sources of error, method of calibra- tion, precautions, etc., as will determine their range of application are given. Only the methods of measurement and instruments, including instructions for their use, spec- ified in the individual test codes are mandatory. Other metho
4、ds 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 3 on Temperature Measurement, replaces an older one published during the perio
5、d from 19521961. Since that time the technology of tem- perature 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
6、 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 conversio
7、ns are listed in the Appendix as they first appear through- out 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 c
8、onversions from the US system to SI units. This Edition was approved by the Performance Test Codes Committee on July 12, 1973. 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 PERSONNEL OF PERFORMANCE TEST CODES COMMIT
9、TEE NO. 19.3 ON INSTRUMENTS AND APPARATUS R. F. Abrahamsen, Chairmm K. W. Woodfield, Secretary Il. F. Abrahamsen, Manager, Technical and Administrative Services, Kreisinger Research Lab- oratory, Combustion Engineering Inc., 1000 Prospect Hill Road, Windsor, Ct. 06095 R. P- Benedict, Fellow Engineer
10、, STDE, Westinghouse Electric Corp., Lester Branch Post Office 9175, Philadelphia, Pa. 19113 J. T. Callahan, Research Mechanical Engineer, Naval Ship Engineering Center, Philadelphia Divi- sion, Applied Physics Department, Philadelphia, Pa. 19112 G. 0. Nutter, Assistant Director, Instrumentation Sys
11、tems Center, University of Wisconsin - Madi- son, 1500 Johnson Drive, Madison, Wi. 53706 K. W. Woodfield, Professor of Mechanical Engineering, General Moton Institute, 1700 West Third Avenue, Flint, Mi. 48502 V R. P. Benedict W. A. Crandall R. C. Dannettel C. A. Dewey V. F. Estcourt A. S. Grimes K.
12、G. Grothues Personnel of Performance Test Codes Committee K. C. Cotton, Chairman J. H. Fernandes, Vice Chairman J. L. Hilke E. L. Knoedler Paul Leung F. H. Light S. W. Lovejoy W. G. McLean S. L. Morse J. W. Murdock L. C. Neate W. C. Osborne W. A. Pollock J. H. Potter C. B. Scharp J. F. Sebald J. C.
13、Westcott vi ASME Performance Test Codes Supplement on Instruments and Apparatus Part 3 Temperature Measurement TABLE OFCONTENTS Chapter 1 2 3 Pages GENERAL 1 RADIATION THERMOMETERS 12 THERMOCOUPLE THERMOMETERS 17 Section A, Thermocouples 17 Section B, Instrumentation 27 RESISTANCE THERMOMETERS 36 LI
14、QUID-IN-GLASS THERMOMETERS 44 FILLED SYSTEM THERMOMETERS 55 OPTICAL PYROMETERS 70 BIMETALLIC THERMOMETERS 86 CALIBRATION OF INSTRUMENTS 91 APPENDIX . 134 CHAPTER 1, ,GENERAL CONTENTS GENERAL GENERAL: scope . Introduction . TEMPERATURE SCALES . INSTRUMENTS . ACCESSORIES: Wells Other Accessories . INS
15、TALLATION . 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 . Par. 8 20 21 25 :8 28 29 31 34 36 38 39 Scope 1 The purpose of thi
16、s chapter is to present a sum- mary discussion of temperature measurement as re- lated to Performance Test Code work with particular emphasis on basic sources of error and means for coping with them. Introduction 2 Measurement of temperature is generally con- sidered to be one of the simplest and mo
17、st accurate measurements performed in engineering. This is de- cidedly a misconception. Accurate temperature measurement under some conditions is impossible with our present knowledge. Under many of the con- 1 ASME PERFORMANCE TEST CODES ditions met in Performance Test Code work, the de- sired accur
18、acy in the measurement of temperature can be obtained only by observance of suitable pre cautions in the selection, installation and use of temperature measuring instruments; and in the proper interpretation of the results obtained with them. In some cases an arbitrarily standardized method is presc
19、ribed in the Performance Test Codes which is to be followed in making temperature measurements under such conditions. 3 Some of the instruments available for tempera- ture measurement are capable of indicating tempera- ture to a closer degree of accuracy than is required in some of the tests conside
20、red in the Performance Test Codes. The difficulty in obtaining accurate temperature measurements with such instruments is encountered in installation or use of the temperature measuring instruments. Specific directions and pre- cautions in usage of the instruments are given in subsequent chapters fo
21、r each of the various types of temperature measuring instruments. TEMPERATURE SCALES 4 There are in general use two temperature scales known as the Fahrenheit and the Celsius (centi- grade) temperature scales. A detailed discussion of these and other scales is given in Chapter 9. In the Fahrenheit s
22、cale, the interval between the boiling and freezing points of water at stand- ard atmospheric pressure is divided into 180 equal parts; the boiling point is marked 212, and the freezing point is marked 32. In the Celsius scale, the interval between the same fixed points is di- vided into 100 equal p
23、arts; the boiling point is marked 100, and the freezing point is marked 0. Each of the 180 or 100 divisions in the respective scales is called a degree. The reading for a given temperature on one scale may be converted to the corresponding reading on the other scale by use of the following formulas:
24、 F = 9/5 C t 32 C = 5/9 (F - 32) where F = reading in deg Fahrenheit C = reading in deg Celsius. CONVERSION FACTORS Tables for converting temperature readings from one scale to another are given in the Appendix.* *Whenever U.S. Customary units are used in this sup- pliment the SI equivalent may be c
25、alculated by using the conversion factors listed in the Appendix. INSTRUMENTS 5 The following types of instruments are availabIe for use under appropriate conditions. The chapter numbers refer to chapters in the ASME Performance Test Codes, Supplement on Instruments and Appara- tus, Part 3, Temperat
26、ure Measurement. (o) Radiation Thermometers (Chapter 2) are tem- perature measuring instruments in which the intensity of the radiation emitted from a body is used as a measure of the temperature of the body. They con- sist of an optical system, used to intercept and con- centrate a definite portion
27、 of the energy radiated from a body whose temperature is being measured; a temperature sensitive element, usually a thermo- couple or a thermopile; and a measuring device, such as an electromotive force measuring instru- ment. lb) A Thermocouple Thermometer (Chapter 3) is a temperature measuring sys
28、tem comprising a tempera- ture sensing element called a thermocouple which produces an electromotive force (emf), a device for sensing emf which includes a printed scale for converting emf to equivalent temperature units, and electrical conductors for operatively connecting the two. (See Fig. 3.1A.l
29、 (c) Resistance Thermometers (Chapter 4) are tem- perature measuring instruments in which the electri- cal resistance is used as a means of temperature measurement. They consist of a sensing element called a resistor, a resistance measuring instrument, and electrical conductors for operatively conne
30、cting the two. (d) Liquid;rittee PR 51 is writing a new standard for thermo- l *N;mbers iu b a kets designate References at end of chapter, thus Ij. ACCESSORIES Wells* 8 Introduction. In many temperature measurements in Performance Test Code work the sensitive ele- ment cannot be placed directly int
31、o the medium whose temperature is to be measured. In such cases a well may be used, which by definition is a pres- sure tight receptacle adapted to receive a tempera- ture sensing element and provided with external threads or other means for tight pressure attachment to a vessel l.* 9 Thermometer we
32、lls are used in measuring the temperature of a moving fluid in a conduit, where the stream exerts an appreciable force. For veloci- ties of 300 fps or less, tapered thermometer wells of the design shown in Fig. 1.1, and of dimensions given in Table 1.3, shall be used. For velocities in excess of 300
33、 fps, a fixed beam type thermometer well is recommended 7. FIG. 1.1 PERFORMANCE TEST CODE THERMOMETER WELLS 10 Attachment 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
34、. Where materials are specified for the purposes of 3 ASME PERFORMANCE TEST CODES illustrating the example, no inference is intended that these materials are preferred. 11 For the experimental and theoretical bases of the design procedure set forth herein, Ref. 2 should be consulted. I2 Strength Ver
35、sus Measurement. Those factors required to produce adequate well strength tend to reduce the accuracy and response of the temperature measurement, as shown in Table 1.2 below. I3 Table 1.2 is not all inclusive, but indicates that thermometer.well design methods must care- fully balance these factors
36、 so that accuracy is com- promised a minimum when using a well of adequate strength. 14 Design Procedure. The purpose of this design procedure is to enable the user to determine if a well selected for thermometry considerations is strong enough to withstand specific application con- ditions of tempe
37、rature, pressure, velocity and vibra- tion. Well failures are caused by forces imposed bv static pressure, steady state flow, and vibration. Separate evaluations of each of the above effects should be made in order to determine the limiting condition. This design procedure does not allow for effects
38、 due to corrosion or erosion. 15 The natural frequency of a well desieed in accordance with Fig. 1.1 and of the dimensions given in Table 1.3 is given by the following equa- tion: where f - n - natural frequency of the well at use tem- perature, cycles per set L = length of well as given in Fig. 1.1
39、, in. E = modulus of elasticity of well material at use temperature, psi y = specific weight of well material at use temperature, lb per cu in. A, = a constant obtained from Table 1.4 The wake or Strouhal frequency is given by: where f, = 2.64; (2) f, = wake frequency, cycles per set V = fluid veloc
40、ity, fps B = diameter at tip (Fig. l.l), in. The ratio of wake to natural frequency (f /f ) shall not exceed 0.8, and when this conditYonis met, the Magnification Factor, relationship of dy- namic to static amplitude is given by: FMz i=mm)2=iJ2 For r 5 0.8 where FM = magnification factor, dimensionl
41、ess r = frequency ratio, (f,Jf,), dimensionless 16 Stress Analysis. The maximum pressure that a thermometer well can withstand for a given mate- rial at a given temperature shall be computed from TABLE 1.2 FACTORS THAT INFLUENCE STRENGTH AND MEASUREMENT Factor Length Thickness Mass Velocity Ideal fo
42、r Measurement Long Conductivity errors reduced. Active por- tion of thermometer must be in flow stream. Thin Reduced conductivity loss. Faster response. High Increased heat transfer. Faster response. Ideal for Strength Short Impingement force reduced. Higher natural frequency. Thick Greater moment o
43、f inertia, less stress. Higher natural frequency. Low Reduces impingement forces. Lower Karman trail vortex frequency. 4 INSTRUIIENTS AND APPARATUS the following: P =K,S (4) P = maximum allowable static gage pressure, psi S = allowable stress for material at operating temperature as given in the ASM
44、E Boiler and Pressure Vessel or Piping Codes, psi K, = a stress constant obtained from Table 1.5. TABLE 1.3 WELL DIMENSIONS, IN IN. Nominol Size of Sensing Element Dimension l/4 3/8 9/16 1 l/16 7/a A (minimum) 13/16 15/16 l-1/8 l-1/4 l-7/16 B (minimum) 5/8 3/4 15/16 l-1/16 l-1/4 d (minimum) 0.254 0.
45、379 0.566 0.691 0.879 d (maximum) 0.262 0.387 0.575 0.700 0.888 TABLE 1.4 VALUES OF Kf we! Llengrh , n. 2-l/2 4-l/2 7-l/2 10-l/2 16 24 Nominal Size of Sensing Element l/4 3/8 9/16 1 l/16 7/8 2.06 2.42 2.97 3.32 3.84 2.07 2.45 3.01 3.39 3.96 2.08 2.46 3.05 3.44 4.03 2.09 2.47 3.06 3.46 4.06 2.09 2.47
46、 3.07 3.47 4.08 2.09 2.47 3.07 3.48 4.09 17 The maximum length that a thermometer well can be made for a given service is dependent upon both vibratory and steady state stress. The neces- sity for keeping the frequency ratio at 0.8 or less imposes one limitation on maximum length. The Solution: Step
47、 l-Obtain the necessary data as follows: TABLE 1.5 VALUES OF STRESS CONSTANTS Nominal Size of Sensing Element Stress Constant l/4 3/8 9/16 11/16 7/8 Kl 0.412 0.334 0.223 0.202 0.155 K2 37.5 42.3 46.8 48.7 50.1 KS 0.116 0.205 0.389 0.548 0.864 other limitation is one of steady state stress con- sider
48、ations, as given by the following equation: L _1 (8) Heat Transfer at Low Velocity 28 Consider the case of a temperature sensor exposed to a low velocity (i.e., no aerodynamic heating) gas stream with the sensor experiencing both radiation and conduction effects. For the steady-state condition betwe
49、en the flowing gas and the sensor, heat transfer by convection must equal the rate of heat transfer by radiation and conduction. This equilibrium condition may be written as follows: hA, (T, - Ti) = 0.1714 es A, It can be seen from the above expression that as the radiation and conduction effects are reduced, the temperature of the sensor, Ti, will approach the static temperature of the gas, T,. Means of reduc- ing the radiation effect are described in Par. 20. There is alsb a more complete discussion of radia- tion and related factors in C
