-6-2_R2003_E1973.pdf

A M E R I C A N N A T I O N A L S T A N D A R D 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 T H E A M E R I C A N S O C I E T Y O F M E C H A N I C A L E N G I N E E R S United Engineering Center 345 East 47th Street New York,N.Y.1001 7 Copyrighted material licensed to Stanford University by Thomson Scientific(),downloaded on Oct-05-2010 by Stanford University User.No further reproduction or distribution is permitted.Uncontrolled when printed.REAFFIRMED 2003FOR CURRENT COMMITTEE PERSONNELPLEASE E-MAIL CSasme.orgNo part of this document may be reproduced in any form,in an electronic retrieval system or orherwise,wirhour the prior written permission o f rhe publisher.Copyright 0 1974 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS Printed in U.S.A.Copyrighted material licensed to Stanford University by Thomson Scientific(),downloaded on Oct-05-2010 by Stanford University User.No further reproduction or distribution is permitted.Uncontrolled when printed.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 States 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 influences 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 variation 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 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,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 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 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 overdesign 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 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 development 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 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 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 this document,because it is ofte