1、AMERICAN NATIONAL STANDARD Temperature and Humidity tnvironment tor Dimensional Measurement ANSI 989.6.2 - 1973 REAFFIRMED 1995 FOR CURRENT COMMITEE PERSONNEL PLEASE SEE ASME MANUAL AS-1 1 SECRETARIAT THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS PUBLISHED BY THE AMERICAN SOCIETY OF MECHANICAL ENGINE
2、ERS United Engineering Center 345 East 47th Street New York, N. Y. 1001 7 No part of this document may be reproduced in any form, in an electronic retrieval system or orherwise, wirhour the prior written permission of rhe publisher. Copyright 0 1974 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS Pr
3、inted in U.S.A. FOREWORD American National Standards Committee B89 on Dimensional Metrology, organized under the procedures of the American National Standards Institute, was formed to develop certain minimum stand- ards for the various parameters in metrology and represents the consensus of United S
4、tates industry. The various subcommittees of Committee B89 deal with the different parameters, i.e., environment, angle, length, geometry, etc. Subcommittee B89.6 is assigned the task of developing standards in physical environ- ment and the effects of this environment and other extraneous influence
5、s on accuracy and precision of hensional measurements. This standard for temperature and humidity is the work of the ANSI B89.6.2 Working Group. The results of its cooperative efforts are expressed in this document. The effect of heat flow and resulting temperature gradients, differences and variati
6、on from measure- ment to measurement can result in errors of dimensional measurement because of the thermal expansion properties of materials. By international agreement the true size and shape of an object is that which exists at a uniform temperature of 68“ F (20“ C). The purpose of this standard
7、is to provide American industry with practical requirements, procedures, and methods by whch the intent of the international agreement can be satisfied without compromise to economical operation. In discharging its responsibilities, the Working Group has recognized two basic needs of industry. First
8、, it recognizes the need for standard approaches to the buying and selling of artificially controlled en- vironments. Second, it recognizes the need for the qualification of individual measurements regarding errors induced by non-ideal temperature conditions. Standard specifications for artificially
9、 controlled environments, in terms of the quality of temperature control, are especially necessary as a means of communicating metrological requirements to construction agencies such as heating and air-conditioning contractors. In specific instances, sufficient experience has been obtained such that
10、 required dimensional accuracies can be translated directly into temperature control specifications. However, the Working Group has concluded that no general set of temperature control specifications can be stated that will simultaneously assure levels of measurement accuracy and avoid the risk of o
11、verdesign or underdesign. Indeed, no recommendation can be made on which type of artificial en- vironment, or even whether one is necessary or not, that would represent the most satisfactory engineering for every application. Consequently, the Working Group has chosen to list those properties of an
12、artificially controlled environment that must be specified for an adequate description, to specify standard procedures for the administration of the required specifications, and to provide advisory information in the form of guidelines that the users of this standard may find helpful in the developm
13、ent of specifications adapted to individual needs. The metrologist, his management, or a potential customer of a metrological service has, each for his own purpose, a need and a right to know the magnitude of measurement errors induced by the thermal en- vironment. Therefore, this standard includes
14、a description of procedures for the estimation of the error con- tributions caused by various defects of the thermal environment. Further, there is a need for a convenient means of communication between these parties. For this purpose, the Working Group has provided a stand- ard figure of merit, the
15、 Thermal Error Index. Because this document, for the first time, presents the Thermal Error Index for use by industry at large, the methods for its determination and use are carefully developed in an appendix. Recommendations for the control of humidity in metrological environments are included in t
16、his document, because it is often directly affected by and related to the control of temperature, especially in the design of room enclosures. ard was approved by ANSI as a National Standard on October 30, 1973. After approval by the B89 National Standards Committee and submittal to public review th
17、e Stand- iii AMERICAN NATIONAL STANDARDS COMMITTEE 889 DIMENSIONAL METROLOGY (The following is the roster of the Committee at the time of approval of this Stmdatd) OFFICERS E. C. Loewen, Choirmon 1. K. Emery, 1st Vice-Choirmon J. C. Moody, 2nd Vice-Choirman Mary Horkins,: Executive Secretory AEROSPA
18、CE INDUSTRIES ASSOCIATION OF AMERICA, INC. M. J. Lcight, Metrology Section, Primary Standards Laboratories, Hughes Aircraft Company, Culver City, California AMERICAN ORDNANCE ASSOCIATION J, C. Moody, Sandia Corporation, Albuquerque, New Mexico AMERICAN SOCIETY FOR QUALITY CONTROL John Novotny, Sperr
19、y Gyroscope, Great Neck, New York AMERICAN SOCIETY FOR TESTING AND MATERIALS H. J. Strembo, Associate Director, Technical Operations, AST (b) The estimate may be based on the dispersion found among-published data. Of the two possibilities given above, (a) is the Because the effects of inaccuracy of
20、the estimate of the uncertainty are of second order, it is con- sidered sufficient that good judgment be used. 3.28 Uncertainty of Nominal Differential Expansion The sum of Uncertainties of Nominal Expansion of the part and master is called the Uncertainty of Nominal Differential Expansion. recommen
21、ded procedure. UNDE = (Uwpalt + (uw-*er (6) 3.29 Uncertainty of Nominal Expansion The maximum difference between the true thermal expansion and the nominal expansion is called the Un- certainty of Nominal Expansion. It is determined from UNE = KL (t - 68) (A) % *. (7) *See Equation 23, Paragraph 20.
22、2 for possible revision. ANSI 889.6.2-1973 4. GENERAL REQUIREMENTS 4.1 The methods of describing and testing tempera- turecontrolled environments shall be in accordance with Section 5. 4.2 A calibration, part manufacture, or part ac- ceptance procedure complies with this standard if it is carried ou
23、t with all pertinent components of the measurement system at 68 F; or if it can be shown that the Thermal Error Index (as defined in Section 6) is a reasonable and acceptable percentage of the working tolerance. 5. DESCRIPTION AND TESTING OF ENVIRONMENT In this section an environment is to be unders
24、tood as a room, box or other enclosure through which a temperaturecontrolled fluid (liquid or gaseous) is circulated and which is intended to contain dimen- sional measurement apparatus. 5.1 Description of Environment In the following paragraphs the essential properties of an environment are listed.
25、 These characteristics must be unequivocally specified. 5.1.1 Thermal Specifications. The following prop- erties of a controlled environment must be specified. 5.1.1.1 Cooling Medium. The type of cooling medium is to be described in terms of its chemical composition and physical properties of viscos
26、ity, den- sity, specific heat and thermal conductivity. When common substances such as ambient air or water are to be used, unless otherwise specified, their properties are to be assumed those given in standard tables. Commercial fluids such as oils may be specified by manufacturer and type. 5.1.1.2
27、 Flow Rate and Velocity. The flow rate of the cooling medium shall be specified in units of weight per unit time, volume per unit time, or changes per unit time. Velocity shall be specified in feet per unit time. 5.1.1.3 Ranges of Frequencies of Temperarure Variation and Limit from Mean Temperature.
28、 These two properties are interrelated and cannot be specified separately. For example, in general, the higher the frequency the wider the permissible temperature ex- cursions from the mean temperature in the cooling medium (see Section 10). Frequencies are to be specified in cycles per unit time, a
29、nd limits from mean temperature in plus or minus (*) units Fahrenheit (units Celsius). Separate limit specifications may be applied to a number of frequency ranges. 4 AMERICAN NATIONAL STANDARD TEMPERATURE AND HUMIDITY ENVIRONMENT FOR DIMENSIONAL MEASUREMENT ANSI 089.6.2-1973 5.1.1.4 Mean Temperatur
30、e. The mean temperature shall be the time average temperature at a specified point (or time average of the average of temperatures at more than one specified point) within the bounda- ries of the environment. A period of time over which the time average is to be computed shall be specified. 5.1.1.5
31、Gradients. Within the working volume of the environment, maximum steady-state temperature differences are to be specified. The specification can take one or both of two forms: (a) “Worst case”maximum temperature difference in the cooling medium between any two points within the specified boundaries
32、of the environment; (b) Maximum rate of change of temperature along one or more specified directions within the specified boundaries. Skcifications can be applied to sub-boundaries, or Each such specification should be qualified as to the conditions of acceptance testing, e.g., whether or not equipm
33、ent and/or personpel are to be within the boundaries during the testing. 5.1.2 Humidity. Requirements for humidity con- trol arise from desires to provide human comfort, to prevent deleterious effects of moisture such as corro- sion of workpieces and measurement apparatus, and to maintain measuremen
34、t accuracy of workpieces that are dimensionally sensitive to moisture (for example, certain hygroscopic materials). Specifications for humidity control shall be consistent with the practices established by the American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE). 5.1.3
35、Maintainability. Requirements shall be speci- fied governing the maintenance of performance in ac- cordance with the above requirements in order that deterioration of the environment with time, due to the reduction of control efficiency, can be held within acceptable limits by implementation of esta
36、blished operating and maintenance procedures. volumes within volumes. 5.2 Testing of Environments 5.2.1 Thermal Specifications 5.2.1.1 Cooling Medium. When a cooling medium other than air or water is to be supplied as a part of the environment, its thermal properties must be qualified. The standard
37、test methods listed here may be used to determine the required properties. The list is not intended to be exhaustive, but is only representative of the many standard procedures available. 5.2. I. 1. I Viscosity ASTM D44565 - Viscosity of Transparent and ASTM D1545-63 - Viscosity of Transparent Liq-
38、5.2.1.1.2 Density (Specific Gravity) ASTM D941-55 (Reapproved 1968)-Density and Specific Gravity of Liquids by Lipkin Bicapillary Pycnometer ASTM Dl 298-67 - Density, Specific Gravity or API Gravity of Crude Petro- leum and Liquid Petroleum Products by Hydrometer Meth- od Opaque Liquids uids by Bubb
39、le Time Method 5.2.1.1.3 Thermal Conductivity ASTM D2717-68T-Thermal Conductivity of Liq- uids 5.2.1.2 Flow Rate and Velocity 5.2.1.2.1 Flow Rate ASTM D2458-69 - Flow Measurement of Water by the Venturi Meter Tube IS0 R541-1967 - Measurement of Fluid Flow by Means of Orifice Plates and Nozzles 5.2,
40、I. 2.2 Velocity ASHRAE Handbook lists several accepted test methods. 5.2.1.3 Ranges of Frequencies of Temperature Variatior; and Limits from Mean Temperature. Limits of variation from mean temperature in the cooling medium at any specified point or points within the specified boundaries is to be det
41、ermined by use of a sensitive recording thermometer. The time constant of this instrument is to be no more than one-fifth (1/5) of the period of the shortest cycle period (highest frequency) of interest; and its resolution is to be at least one-tenth (1/10) of the smallest amplitude of specified tem
42、perature variation. The temperature recording duration shall be a mini- mum of 24 hours and should be as long as the representative work cycle (e.g., a week). The test should be performed under worst-case conditions (Le., hottest day of year and coldest day of year). The maximum peak-to-valley tempe
43、rature varia- tion is to be determined from the recorded data for every discernible frequency component. Isolated dis- turbances, i.e., single “spikes”, are to be regarded as a component of the appropriate frequency. 5 AMERICAN NATIONAL STANDARD TEMPERATURE AND HUMIDITY ENVIRONMENT - - . . - . . . .
44、 - FOR DIMENSIONAL MEASUREMENT ANSI 689.6.2-1973 Limits from mean for each frequency component are to be calculated as one-half (%) of the observed peak-to-valley excursion. 5.2.1.4 Mean Temperatures. A thermometer that has been calibrated by comparison with a standard platinum-resistance thermomete
45、r in the specified cool- ing medium is to be used to determine mean tempera- ture. A recording thermometer whose output is averaged over the test period is preferred. However, a thermometer with a large time constant can be used if it is read at a frequency corresponding to one-half (X) of its time
46、constant over the test period and all such readings averaged. The resolution of the test thermometer shall be one-tenth (l/lO) of the specified tolerance for the . . mean temperature. Also, the test thermometer should be standardized or calibrated so that in use it would indicate temperatures with a
47、n inaccuracy no worse than one-fourth (%) of the specified tolerance for the mean temperature. 5.2.1.5 Gradients. If a “worst case“ specification is to be administered, the locations of the temperature sensors are to be clearly specified. If a maximum rate of change of temperature per unit length in
48、 a given direction or directions is to be administered, a grid pattern shall be established to define the locations of temperature sensors. In the case of room, box, and tank enclosures, that fraction of the total volume immediately adjacent to the en- closure walls is to be excluded from the grid p
49、attern. Unless otherwise specified, for an enclosure that is empty, does not contain furniture, personnel, and equipment other than that used in the performance of the test, the excepted volumes shall be those obtained by reducing each dimension by 10 percent. For example, a 10 x 10 x 10 room shall be reduced to 9 x 9 x 9, the excluded volume being that contained within 6“ from the walls, ceiling, and floor. If the specification calls for testing with equipment or personnel in the enclosure, the specification shall include a description of excluded areas or volumes ad- jacent to s
