ASTM_D_637_-_90_scan.pdf

4ITb Designation:D 637-90 AMERICAN SOCIETY FOR TESTINO AND MATERIALS 1018 Rico S I.Philidriphii.PI.19105 Roprmlod Ifom lho AnnuJ Book o(M M SlJndrrdr.CopyfigM m u I!n hied in lha curion4 combined i-.wiu rpprir m)u M u I I odWn.Standard Test Method for Surface Irregularities of Flat Transparent Plastic Sheets This standard is issued under the fixed designation D 637;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon(E)indicates an editorial change since the last revision or reapproval.This standard has been approvedjor use by agencies o f the Deparlment o f Definse Consult the DoD Index o f Spec$cations and Siandards fir the speci/ic year o f issue which has been adopted by the Deparlment o f Definse.1.Scope 1.1 This test method covers the measurement of the surface irregularities of flat transparent plasfic sheets that are ordinarily used to cover openings through which visual and instrumental observations are made.1.2 This test method measures the distortion and the deviation of line of sight through flat sheets of transparent plastics.The test method makes use of the prismatic or optical wedge deflection of a beam of light as it passes through a distortion spot or wave in the body of or on the surface of the material being inspected,1.3 The values stated in SI units are to be regarde.d as the standard.1.4 This standard does not purport to address the safity problems associated with its use,It is the responsibility o f the user o f this standard to establish appropriate safity and health practices and determine the applicability o f regulatory limitations prior to use.2.Referenced Document _-2.1 ASTM Standard:D 6 18 Methods of Conditioning Plastics and Electrical D 883 Definitions of Terms Relating to Plastics2.Insulating Materials for Testing I-3.Terminology 3.1 Description o f Terms SpeciJic to This Standard:.3.1.1 displacement factor-displacement factor is the maximum movement(in inches)of the image of the cross,divided by the distance(in feet)from the projector to the screen,multiplied by 1000.3.1.2 frequency o f image movement-frequency of image movement shali be described as(I)irregular or wavy,(2)frequent,or(3)single shift.3.1.3 pattern distance-pattern distance is the maximum distance(in integer multiples of 127 mm(5 in,)from the screen at which the specimen can be held without producing a sharply defined pattern of its minor surface irregularities.3.1.4 General-Definitions of terms applying to this test method appear in Definitions D 883.I This test method is under the jurisdiction of ASTM Committee D2O on Plastics and is the direct responsibility of Subcommittee D20.40 on Optical Propcrlics.Curant cdiiion approvcd October 26,1990.Publishcd Dcccmber 1990.Onginally published as D 637-41 T.Last previous edition D 637-86.Anniial Book ofASTM Standards,Vol 08.01.4.Significance and Use 4.1 This test method profides empirical results useful for control purposes and for correlation with service applica-tions.The accuracy is much greater than required for most applications,but it is not expected to measure microscopic defects or the optical perfection of surfaces in terms of wave length of light.5.Apparatus 5.1 Projector-A good quality lantern slide projector or similar assembly of light source and lenses that is capable of producing a sharply defined image on a screen at a distance of 7.62 m(25 f i).The objective lens of this system shall have an aperture approximately 50.8 mm(2 in.)in diameter and a focal length of approximately 12 in.5.2 Slide-A transparent slide on which have been ruled two very fine black lines crossing at right angles at the center of the slide.This slide may be prepared by photographing a drawing-or by directly ruling fine lines on some suitable transparent medium.5.3 Screen-A square white screen measuring about 1.5 m(5 ft)on a side.This screen shali have a symmetrical cross ruled on it consisting of seven horizontai parallel fine lines spaced 12.7 mm(0.5 in.)apart and seven vertical parallel fine lines spaced 12.7 mm(0.5 i n.)apart,These lines shall be as fine as it is possible to make them and still have them distinctly visible at a distance of 7.62 m(25 ft).A width of about 1.6 mm(/I6 in.)is suggested,NOTE 1-An alternative form of target may be preferred,consisting of concentric circles having radii increasing by 25.4 mm(I in.)from a 25.4-mm(I-in.)radius for the innermost circle,ruled in the center of a piece of white cardboard 0.3 m(1 fi)square.It is suggested that the first circle be ruled with a line thickness of 3.2 mm(y8 in.),the second with a line thickness of 1.6 mm(Ih6 in.),the third with a line thickness of 3.2 mm(%in.),and so on.5.4 Supports-A suitable means of rigidly supporting the projector and the screen,5.5 Dark Room-A slightly darkened or dark room of sufficient Ingth to accommodate the test