ASTM_C_1426_-_14.pdf

Designation:C142614Standard Practices forVerification and Calibration of Polarimeters1This standard is issued under the fixed designation C1426;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 Polarimeters and polariscopes used for measuring stressin glass are described in Test Methods F218,C148,and C978.These instruments include a light source and several opticalelements(polarizers,optical retarders,filters,and so forth)thatrequire occasional cleaning,realigning,and calibration.Theobjective of these practices is to describe the calibration andverification procedures required to maintain these instrumentsin calibration and ensure that the optical setup is withinspecification for satisfactory measurements.1.2 It is mandatory throughout these practices that bothverification and calibration are carried out by qualified person-nel who fully understand the concepts used in measurements ofstress retardation and are experienced in the practices ofmeasuring procedures described in Test Methods F218,C148,and C978.1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.2.Referenced Documents2.1 ASTM Standards:2C148 Test Methods for Polariscopic Examination of GlassContainersC162 Terminology of Glass and Glass ProductsC770 Test Method for Measurement of Glass StressOptical CoefficientC978 Test Method for Photoelastic Determination of Re-sidual Stress in a Transparent Glass Matrix Using aPolarizing Microscope and Optical Retardation Compen-sation ProceduresF218 Test Method for Measuring Optical Retardation andAnalyzing Stress in Glass3.Terminology3.1 For definitions of terms used in these practices,seeTerminology C162.4.Principles of Verification and Calibration Procedures4.1 Verification and calibration of polarimeters are accom-plished using the following procedures:4.1.1 Procedure A:(Verification)Measure individual com-ponents and their orientation to ensure that the requirements ofTest Methods F218,C148,and C978 are satisfied.4.1.2 Procedure B:(Calibration)Determine the accuracyof the polarimeter using a calibrated gage or retarder.5.Auxiliary Component Requirements5.1 The following are required to verify and calibrate apolarimeter:5.1.1 Verification of Components(Procedure A):5.1.1.1 Verification of Polarization Effciency,a light-intensity meter,linear over the range of measured values.5.1.1.2 Verification of Quarter-Wave Plate,a Babinet com-pensator equipped polarimeter,with a monochromatic lightsource of traceable wavelength.5.1.1.3 Reference Polarizer with Known Axis.5.1.2 Calibration of Polarimeter(Procedure B):5.1.2.1 Procedure B requires a gage with a calibrated,known retardation.The calibrated gage must have sufficientretardation to calibrate the instrument within its intended userange.For example,a polariscope/polarimeter used in TestMethods C148 should be calibrated using a gage exhibiting aretardation range of from 0 to 227 nm(0 to 10 temper grade).5.1.2.2 Alternately,a rectangular cross-section specimenprepared from an SRM glass having a known stress-opticalconstant,subjected to uniaxial compression in a calibratedtesting machine,may be used instead of a calibrated gage withknown retardation.6.Verification and Calibration Procedures6.1 Procedure AVerification and Aligning of Components:6.1.1 Verification of Polarization EffciencyUsing a light-intensity meter,measure the light intensity,with polarizerscrossed,Ic(dark field)and then with polarizers parallel,Ip.Calculate the polarization efficiency,E,as follows:E 5Ip2 Ic!Ip(1)1These practices are under the jurisdiction of ASTM Committee C14 on Glassand Glass Productsand are the direct responsibility of Subcommittee C14.04 onPhysical and Mechanical Properties.Current edition approved May 1,2014.Published May 2014.Originallyapproved in 1999.Last previous addition approved in 2009 as C142609.DOI:10.1520/C1426-14.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 The efficiency must satisfy the requirements of the testmethod for which the polarimeter is used.6.1.2 Verification of Position of AxesUsing a referencepolarizer,verify that the polarizer,P,is oriented at 45 6 1 tothe instrument reference axis.Rotate the analyzer to attain themaximum dark field,and record the analyzer reading to thenearest degree or 0.05 fringe.Repeat this measurement fivetimes and compute the average.This“zero”reading to thenearest degree or 0.05 fringe must be algebraically appli